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Sample records for characterizing mode-i fatigue

  1. X-ray fractography of fatigue fracture surface under mode I and mode III loading

    International Nuclear Information System (INIS)

    Akiniwa, Yoshiaki; Tanaka, Keisuke; Tsumura, Tsuyoshi

    2001-01-01

    The propagation behavior of a circumferential fatigue crack in cylindrical bars of a carbon steel (JIS SGV410) and a stainless steel (JIS SUS316NG) was investigated under cyclic axial and torsional loadings. The J-integral range was used as a fracture mechanics parameter. When compared at the same J-integral range, the crack propagation rate under mode III was smaller than that under mode I. Parallel markings perpendicular to the crack propagation direction were observed on the fatigue fracture surface obtained under mode III loading. The residual stresses in the radial direction, σ r , and in the tangential direction, σ θ , were measured for both mode I and mode III fatigue fracture surfaces. For mode I fracture surface, σ r was tension, and was almost constant irrespective of the applied J-integral range. σ θ was close to zero for both materials. On the other hand, for mode III, σ r and σ θ were compression. For SUS316NG steel, the compressive stress of σ θ increased with the J-integral range. For SGV410 steel, the change of σ θ with the J-integral range was small. The breadth of diffraction profiles increased with J-integral range for both mode I and III. The breadth was found to be a good parameter to evaluate the applied J-integral range. (author)

  2. Effect of Compressive Mode I on the Mixed Mode I/II Fatigue Crack Growth Rate of 42CrMo4

    Science.gov (United States)

    Heirani, Hasan; Farhangdoost, Khalil

    2018-01-01

    Subsurface cracks in mechanical contact loading components are subjected to mixed mode I/II, so it is necessary to evaluate the fatigue behavior of materials under mixed mode loading. For this purpose, fatigue crack propagation tests are performed with compact tension shear specimens for several stress intensity factor (SIF) ratios of mode I and mode II. The effect of compressive mode I loading on mixed mode I/II crack growth rate and fracture surface is investigated. Tests are carried out for the pure mode I, pure mode II, and two different mixed mode loading angles. On the basis of the experimental results, mixed mode crack growth rate parameters are proposed according to Tanaka and Richard with Paris' law. Results show neither Richard's nor Tanaka's equivalent SIFs are very useful because these SIFs depend strongly on the loading angle, but Richard's equivalent SIF formula is more suitable than Tanaka's formula. The compressive mode I causes the crack closure, and the friction force between the crack surfaces resists against the crack growth. In compressive loading with 45° angle, d a/d N increases as K eq decreases.

  3. Influence of Mixed Mode I-Mode II Loading on Fatigue Delamination Growth Characteristics of a Graphite Epoxy Tape Laminate

    Science.gov (United States)

    Ratcliffe, James G.; Johnston, William M., Jr.

    2014-01-01

    Mixed mode I-mode II interlaminar tests were conducted on IM7/8552 tape laminates using the mixed-mode bending test. Three mixed mode ratios, G(sub II)/G(sub T) = 0.2, 0.5, and 0.8, were considered. Tests were performed at all three mixed-mode ratios under quasi-static and cyclic loading conditions, where the former static tests were used to determine initial loading levels for the latter fatigue tests. Fatigue tests at each mixed-mode ratio were performed at four loading levels, Gmax, equal to 0.5G(sub c), 0.4G(sub c), 0.3G(sub c), and 0.2G(sub c), where G(sub c) is the interlaminar fracture toughness of the corresponding mixed-mode ratio at which a test was performed. All fatigue tests were performed using constant-amplitude load control and delamination growth was automatically documented using compliance solutions obtained from the corresponding quasi-static tests. Static fracture toughness data yielded a mixed-mode delamination criterion that exhibited monotonic increase in Gc with mixed-mode ratio, G(sub II)/G(sub T). Fatigue delamination onset parameters varied monotonically with G(sub II)/G(sub T), which was expected based on the fracture toughness data. Analysis of non-normalized data yielded a monotonic change in Paris law exponent with mode ratio. This was not the case when normalized data were analyzed. Fatigue data normalized by the static R-curve were most affected in specimens tested at G(sub II)/G(sub T)=0.2 (this process has little influence on the other data). In this case, the normalized data yielded a higher delamination growth rate compared to the raw data for a given loading level. Overall, fiber bridging appeared to be the dominant mechanism, affecting delamination growth rates in specimens tested at different load levels and differing mixed-mode ratios.

  4. Fatigue crack growth in mixed mode I+III+III non proportional loading conditions in a 316 stainless steel, experimental analysis and modelization of the effects of crack tip plasticity

    International Nuclear Information System (INIS)

    Fremy, F.

    2012-01-01

    This thesis deals with fatigue crack growth in non-proportional variable amplitude mixed mode I + II + III loading conditions and analyses the effects of internal stresses stemming from the confinement of the plastic zone in small scale yielding conditions. The tests showed that there are antagonistic long-distance and short-distance effects of the loading history on fatigue crack growth. The shape of loading path, and not only the maximum and minimum values in this path, is crucial and, by comparison, the effects of contact and friction are of lesser importance. Internal stresses play a major role on the fatigue crack growth rate and on the crack path. An approach was developed to analyze the elastic-plastic behavior of a representative section of the crack front using the FEA. A model reduction technic is used to extract the relevant information from the FE results. To do so, the velocity field is partitioned into mode I, II, III elastic and plastic components, each component being characterized by an intensity factor and a fixed spatial distribution. The calculations were used to select seven loading paths in I + II and I + II + III mixed mode conditions, which all have the same amplitudes for each mode, the same maximum, minimum and average values. These paths are supposed to be equivalent in the sense of common failure criteria, but differ significantly when the elastic-plastic behavior of the material is accounted for. The results of finite element simulations and of simulations using a simplified model proposed in this thesis are both in agreement with experimental results. The approach was also used to discuss the role of mode III loading steps. Since the material behavior is nonlinear, the nominal loading direction does not coincide with the plastic flow direction. Adding a mode III loading step in a mode I+II fatigue cycle, may, in some cases, significantly modify the behaviour of the crack (crack growth rate, crack path and plastic flow). (author)

  5. Characterization of Mode I and Mode II delamination growth and thresholds in AS4/PEEK composites

    Science.gov (United States)

    Martin, Roderick H.; Murri, Gretchen Bostaph

    1990-01-01

    Composite materials often fail by delamination. The onset and growth of delamination in AS4/PEEK, a tough thermoplastic matrix composite, was characterized for mode 1 and mode 2 loadings, using the Double Cantilever Beam (DCB) and the End Notched Flexure (ENF) test specimens. Delamination growth per fatigue cycle, da/dN, was related to strain energy release rate, G, by means of a power law. However, the exponents of these power laws were too large for them to be adequately used as a life prediction tool. A small error in the estimated applied loads could lead to large errors in the delamination growth rates. Hence strain energy release rate thresholds, G sub th, below which no delamination would occur were also measured. Mode 1 and 2 threshold G values for no delamination growth were found by monitoring the number of cycles to delamination onset in the DCB and ENF specimens. The maximum applied G for which no delamination growth had occurred until at least 1,000,000 cycles was considered the threshold strain energy release rate. Comments are given on how testing effects, facial interference or delamination front damage, may invalidate the experimental determination of the constants in the expression.

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

    International Nuclear Information System (INIS)

    Lim, Yee Yan; Soh, Chee Kiong

    2011-01-01

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

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

    Science.gov (United States)

    Lim, Yee Yan; Kiong Soh, Chee

    2011-12-01

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

  8. Mode I Cohesive Law Characterization of Through-Crack Propagation in a Multidirectional Laminate

    Science.gov (United States)

    Bergan, Andrew C.; Davila, Carlos G.; Leone, Frank A.; Awerbuch, Jonathan; Tan, Tein-Min

    2014-01-01

    A method is proposed and assessed for the experimental characterization of through-the-thickness crack propagation in multidirectional composite laminates with a cohesive law. The fracture toughness and crack opening displacement are measured and used to determine a cohesive law. Two methods of computing fracture toughness are assessed and compared. While previously proposed cohesive characterizations based on the R-curve exhibit size effects, the proposed approach results in a cohesive law that is a material property. The compact tension specimen configuration is used to propagate damage while load and full-field displacements are recorded. These measurements are used to compute the fracture toughness and crack opening displacement from which the cohesive law is characterized. The experimental results show that a steady-state fracture toughness is not reached. However, the proposed method extrapolates to steady-state and is demonstrated capable of predicting the structural behavior of geometrically-scaled specimens.

  9. Fatigue Characterization of Functionally Graded Metallic Alloys

    International Nuclear Information System (INIS)

    Silva, F. S.

    2008-01-01

    Functionally graded components exhibit spatial variations of mechanical properties in contrast with, and as an alternative to, purely homogeneous components. A large class of graded materials, however, are in fact mostly homogeneous materials with property variations (chemical or mechanical) restricted to a specific area or layer produced by applying for example a coating or by introducing sub-surface residual stresses. However, it is also possible to obtain graded materials with a smooth transition of mechanical properties along the entire component, for example in a 40 mm component. This is possible, for example, by using centrifugal casting technique or incremental melting and solidification technique. In this paper we will study fully metallic functionally graded components with a smooth gradient, focusing on fatigue crack propagation. Fatigue propagation will be assessed in the direction parallel to the gradation (in different homogeneous layers of the functionally graded component) to assess what would be fatigue crack propagation on the direction perpendicular to the gradation. Fatigue crack growth rate (standard mode I fatigue crack growth) will be correlated to the mode I stress intensity factor range. Other mechanical properties of different layers of the component (Young's modulus) will also be considered in this analysis. The effect of residual stresses along the component gradation on crack propagation will also be taken into account. A qualitative analysis of the effects of some important features, present in functionally graded materials, will be made based on the obtained results

  10. 3D atomistic studies of fatigue behaviour of edge crack (0 0 1) in bcc iron loaded in mode i and II

    Czech Academy of Sciences Publication Activity Database

    Machová, Anna; Pokluda, J.; Uhnáková, Alena; Hora, Petr

    2014-01-01

    Roč. 66, September (2014), s. 11-19 ISSN 0142-1123 R&D Projects: GA ČR(CZ) GAP108/10/0698 Institutional support: RVO:61388998 Keywords : fatigue crack growth * bcc iron * 3D atomistic simulations * molecular dynamics Subject RIV: JQ - Machines ; Tools Impact factor: 2.275, year: 2014 www.elsevier.com/locate/ijfatigue

  11. Mode I and mixed I/III crack initiation and propagation behavior of V-4Cr-4Ti alloy at 25{degrees}C

    Energy Technology Data Exchange (ETDEWEB)

    Li, H.X.; Kurtz, R.J.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States)

    1997-04-01

    The mode I and mixed-mode I/III fracture behavior of the production-scale heat (No. 832665) of V-4Cr-4Ti has been investigated at 25{degrees}C using compact tension (CT) specimens for a mode I crack and modified CT specimens for a mixed-mode I/III crack. The mode III to mode I load ratio was 0.47. Test specimens were vacuum annealed at 1000{degrees}C for 1 h after final machining. Both mode I and mixed-mode I/III specimens were fatigue cracked prior to J-integral testing. It was noticed that the mixed-mode I/III crack angle decreased from an initial 25 degrees to approximately 23 degrees due to crack plane rotation during fatigue cracking. No crack plane rotation occurred in the mode I specimen. The crack initiation and propagation behavior was evaluated by generating J-R curves. Due to the high ductility of this alloy and the limited specimen thickness (6.35 mm), plane strain requirements were not met so valid critical J-integral values were not obtained. However, it was found that the crack initiation and propagation behavior was significantly different between the mode I and the mixed-mode I/III specimens. In the mode I specimen crack initiation did not occur, only extensive crack tip blunting due to plastic deformation. During J-integral testing the mixed-mode crack rotated to an increased crack angle (in contrast to fatigue precracking) by crack blunting. When the crack initiated, the crack angle was about 30 degrees. After crack initiation the crack plane remained at 30 degrees until the test was completed. Mixed-mode crack initiation was difficult, but propagation was easy. The fracture surface of the mixed-mode specimen was characterized by microvoid coalescence.

  12. Energy based study of quasi-static delamination as a low cycle fatigue process

    NARCIS (Netherlands)

    Amaral, L.; Yao, L.; Alderliesten, R.C.; Benedictus, R.

    2015-01-01

    This work proposes to treat quasi-static mode I delamination growth of CFRP as a low-cycle fatigue process. To this end, mode I quasi-static and fatigue delamination tests were performed. An average physical Strain Energy Release Rate (SERR), derived from an energy balance, is used to characterize

  13. Fatigue life characterization for piezoelectric macrofiber composites

    International Nuclear Information System (INIS)

    A Henslee, Isaac; Miller, David A; Tempero, Tyler

    2012-01-01

    In an effort to aid the investigation into lightweight and reliable materials for actuator design, a study was developed to characterize the temperature-dependent lifetime performance of a piezoelectric macrofiber composite (MFC). MFCs are thin rectangular patches of polyimide film, epoxy and a single layer of rectangular lead zirconium titanate (PZT) fibers. In this study, the useful life of the MFC is characterized to determine the effect of temperature on the performance of the composite as it is fatigued by cyclic piezoelectric excitation. The test specimen consists of the MFC laminated to a cantilevered stainless steel beam. Beam strain and tip displacement measurements are used as a basis for determining the performance of the MFC as it is cyclically actuated under various operating temperatures. The temperature of the beam laminate is held constant and then cycled to failure, or 250 million cycles, in order to determine the useful life of the MFC over a temperature range from − 15 to 145 °C. The results of the experiments show a strong temperature dependence of the operational life for the MFC. Damage inside the composite was identified through in situ visual inspection and during post-test microstructural observation; however, no degradation in operational performance was identified as it was cyclically actuated up to the point of failure, regardless of temperature or actuation cycle number. (paper)

  14. Fatigue life characterization for piezoelectric macrofiber composites

    Science.gov (United States)

    Henslee, Isaac A.; Miller, David A.; Tempero, Tyler

    2012-10-01

    In an effort to aid the investigation into lightweight and reliable materials for actuator design, a study was developed to characterize the temperature-dependent lifetime performance of a piezoelectric macrofiber composite (MFC). MFCs are thin rectangular patches of polyimide film, epoxy and a single layer of rectangular lead zirconium titanate (PZT) fibers. In this study, the useful life of the MFC is characterized to determine the effect of temperature on the performance of the composite as it is fatigued by cyclic piezoelectric excitation. The test specimen consists of the MFC laminated to a cantilevered stainless steel beam. Beam strain and tip displacement measurements are used as a basis for determining the performance of the MFC as it is cyclically actuated under various operating temperatures. The temperature of the beam laminate is held constant and then cycled to failure, or 250 million cycles, in order to determine the useful life of the MFC over a temperature range from - 15 to 145 °C. The results of the experiments show a strong temperature dependence of the operational life for the MFC. Damage inside the composite was identified through in situ visual inspection and during post-test microstructural observation; however, no degradation in operational performance was identified as it was cyclically actuated up to the point of failure, regardless of temperature or actuation cycle number.

  15. Multi-parametric characterization of mode I fracture toughness of asphalt concrete: Influence of void and RA contents, binder and aggregate types

    Directory of Open Access Journals (Sweden)

    Saannibe Ciryle Somé

    2018-05-01

    Full Text Available This study aims to evaluate the fracture toughness (KIc in mode I cracking using semi-circular bending test (SCB. Experiment has been performed to investigate the influence of bitumen grade (using P15/25 and P50/70 bitumens, reclaimed asphalt (RA content (using 0%, 20% and 40% RA contents and temperature (using −20 °C, −5 °C, 10 °C test temperatures, through ANOVA. Additional investigations have been performed: (i to evaluate the effect of the use of polymer modified bitumen (PMB, (ii to evaluate the effect compactness using 5% and 8% air void contents, (iii to evaluate the effect of aggregate type using siliceous-limestone and porphyry aggregates. The results show an important decrease in KIc when temperature increases from −5 °C to 10 °C and a slight decrease between −20 °C and −5 °C. The results also show that increasing RA content increases slightly the KIc. It was found from the ANOVA that the influent parameters can be ranked as follows: temperature, RA content and binder grade. The investigations show that PMB increases the KIc value than pure bitumens. Porphyry aggregates increase the KIc by about 16% than silica-limestone aggregates at low temperatures between −20 °C and −5 °C. However, this ranking is slightly inverted at 10 °C. In addition, KIc decreases by about 12% at 10 °C with an increase in air voids (by 5% to 8%. Void content effect is more significant at −5 °C and 10 °C, and negligible at −20 °C. Keywords: Fracture toughness, SCB, Bituminous mixture, Reclaimed asphalt

  16. Fatigue characterization of mechanical components in service

    Directory of Open Access Journals (Sweden)

    G. Fargione

    2013-10-01

    Full Text Available The quickly identify of fatigue limit of a mechanical component with good approximation is currently a significant practical problem not yet resolved in a satisfactory way. Generally, for a mechanical component, the fatigue strength reduction factor (i is difficult to evaluate especially when it is in service.In this paper, the procedures for crack paths individuation and consequently damage evaluation (adopted in laboratory for stressed specimens with planned load histories are applied to mechanical components, already failed during service. The energy parameters, proposed by the authors for the evaluation of the fatigue behavior of the materials [1-5], are defined on specimens derived from a flange bolts. The flange connecting pipes at high temperature and pressure. Due to the loss of the seal, the bolts have been subjected to a hot flow steam addition to the normal stress.The numerical analysis coupled experimental analysis (measurement of surface temperature during static and dynamic tests of specimens taken from damaged tie rods, has helped to determine the causes of failure of the tie rods.The determination of an energy parameter for the evaluation of the damage showed that factors related to the heat release of the material (loaded may also help to understand the causes of failure of mechanical components.

  17. Fatigue Characterization of Fire Resistant Syntactic Foam Core Material

    Science.gov (United States)

    Hossain, Mohammad Mynul

    Eco-Core is a fire resistant material for sandwich structural application; it was developed at NC A&T State University. The Eco-Core is made of very small amount of phenolic resin and large volume of flyash by a syntactic process. The process development, static mechanical and fracture, fire and toxicity safety and water absorption properties and the design of sandwich structural panels with Eco-Core material was established and published in the literature. One of the important properties that is needed for application in transportation vehicles is the fatigue performance under different stress states. Fatigue data are not available even for general syntactic foams. The objective of this research is to investigate the fatigue performance of Eco-Core under three types of stress states, namely, cyclic compression, shear and flexure, then document failure modes, and develop empherical equations for predicting fatigue life of Eco-Core under three stress states. Compression-Compression fatigue was performed directly on Eco-Core cylindrical specimen, whereas shear and flexure fatigue tests were performed using sandwich beam made of E glass-Vinyl Ester face sheet and Eco-Core material. Compression-compression fatigue test study was conducted at two values of stress ratios (R=10 and 5), for the maximum compression stress (sigmamin) range of 60% to 90% of compression strength (sigmac = 19.6 +/- 0.25 MPa) for R=10 and 95% to 80% of compression strength for R=5. The failure modes were characterized by the material compliance change: On-set (2% compliance change), propagation (5%) and ultimate failure (7%). The number of load cycles correspond to each of these three damages were characterized as on-set, propagation and total lives. A similar approach was used in shear and flexure fatigue tests with stress ratio of R=0.1. The fatigue stress-number of load cycles data followed the standard power law equation for all three stress states. The constant of the equation were

  18. Fatigue

    Science.gov (United States)

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

  19. Characterization of the Effects of Fatigue on the Central Nervous System (CNS) and Drug Therapies

    National Research Council Canada - National Science Library

    Mery, Laura

    2007-01-01

    .... The modified flower pot method of sleep disruption was used to induce fatigue. This study utilized hippocampal dependant tasks, the radial arm maze and the Barnes maze, to characterize the effects of sleep disruption fatigue...

  20. Graphite nodules in fatigue-tested cast iron characterized in 2D and 3D

    DEFF Research Database (Denmark)

    Mukherjee, Krishnendu; Fæster, Søren; Hansen, Niels

    2017-01-01

    Thick-walled ductile iron casts have been studied by applying (i) cooling rate calculations by FVM, (ii) microstructural characterization by 2D SEM and 3D X-ray tomography techniques and (iii) fatigue testing of samples drawn from components cast in sand molds and metal molds. An analysis has shown...... correlations between cooling rate, structure and fatigue strengths demonstrating the benefit of 3D structural characterization to identify possible causes of premature fatigue failure of ductile cast iron....

  1. Fatigue

    Science.gov (United States)

    ... sleep. Fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of not caring ... Call your provider right away if you have any of the following: Confusion or dizziness Blurred vision Little or no urine, or recent ...

  2. Development and characterization of fatigue resistant Aramid reinforced aluminium laminates (ARALL) for fatigue Critical aircraft components

    Science.gov (United States)

    Qaiser, M. H.; Umar, S.; Nauman, S.

    2014-06-01

    The structural weight of an aircraft has always been a controlling parameter that governs its fuel efficiency and transport capacity. In pursuit of achieving light-weight aircraft structures, high design stress levels have to be adopted and materials with high specific strength such as Aluminum etc. are to be deployed. However, an extensive spectrum of fatigue load exists at the aircraft wings and other aerodynamic components that may cause initiation and propagation of fatigue cracks and concludes in a catastrophic rupture. Fatigue is therefore the limiting design parameter in such cases and materials with high fatigue resistance are then required. A major improvement in the fatigue behavior was observed by laminating Kevlar fibers with Aluminum using epoxy. ARALL (Aramid Reinforced ALuminum Laminates) is a fatigue resistant hybrid composite that consists of layers of thin high strength aluminum alloy sheets surface bonded with aramid fibers. The intact aramid fibers tie up the fatigue cracks, thus reducing the stress intensity factor at the crack tip as a result of which the fatigue properties of can be enhanced with orders of magnitude as compared to monolithic high strength Aluminum alloy sheets. Significant amount of weight savings can be achieved in fatigue critical components in comparison with the traditional materials used in aircraft.

  3. Development and characterization of fatigue resistant Aramid reinforced aluminium laminates (ARALL) for fatigue Critical aircraft components

    International Nuclear Information System (INIS)

    Qaiser, M H; Umar, S; Nauman, S

    2014-01-01

    The structural weight of an aircraft has always been a controlling parameter that governs its fuel efficiency and transport capacity. In pursuit of achieving light-weight aircraft structures, high design stress levels have to be adopted and materials with high specific strength such as Aluminum etc. are to be deployed. However, an extensive spectrum of fatigue load exists at the aircraft wings and other aerodynamic components that may cause initiation and propagation of fatigue cracks and concludes in a catastrophic rupture. Fatigue is therefore the limiting design parameter in such cases and materials with high fatigue resistance are then required. A major improvement in the fatigue behavior was observed by laminating Kevlar fibers with Aluminum using epoxy. ARALL (Aramid Reinforced ALuminum Laminates) is a fatigue resistant hybrid composite that consists of layers of thin high strength aluminum alloy sheets surface bonded with aramid fibers. The intact aramid fibers tie up the fatigue cracks, thus reducing the stress intensity factor at the crack tip as a result of which the fatigue properties of can be enhanced with orders of magnitude as compared to monolithic high strength Aluminum alloy sheets. Significant amount of weight savings can be achieved in fatigue critical components in comparison with the traditional materials used in aircraft

  4. Development and characterization of fatigue resistant aramid reinforced aluminium laminates (ARALL) for fatigue critical aircraft components

    International Nuclear Information System (INIS)

    Qaiser, M. H.; Umar, S.; Nauman, S.

    2013-01-01

    The structural weight of an aircraft has always been a controlling parameter that governs its fuel efficiency and transport capacity. In pursuit of achieving light-weight aircraft structures, high design stress levels have to be adopted and materials with high specific strength such as Aluminum etc. are to be deployed. However, an extensive spectrum of fatigue load exists at the aircraft wings and other aerodynamic components that may cause initiation and propagation of fatigue cracks and concludes in a catastrophic rupture. Fatigue is therefore the limiting design parameter in such cases and materials with high fatigue resistance are then required. A major improvement in the fatigue behavior was observed by laminating Kevlar fibers with Aluminum using epoxy. ARALL (Aramid Reinforced Aluminum Laminates) is a fatigue resistant hybrid composite that consists of layers of thin high strength aluminum alloy sheets surface bonded with aramid fibers. The intact aramid fibers tie up the fatigue cracks, thus reducing the stress intensity factor at the crack tip as a result of which the fatigue properties of can be enhanced with orders of magnitude as compared to monolithic high strength Aluminum alloy sheets. Significant amount of weight savings can be achieved in fatigue critical components in comparison with the traditional materials used in aircraft. (author)

  5. Using endogenous saccades to characterize fatigue in multiple sclerosis.

    Science.gov (United States)

    Ferreira, Marisa; Pereira, Paulo A; Parreira, Marta; Sousa, Inês; Figueiredo, José; Cerqueira, João J; Macedo, Antonio F

    2017-05-01

    Multiple Sclerosis (MS) is likely to cause dysfunction of neural circuits between brain regions increasing brain working load or a subjective overestimation of such working load leading to fatigue symptoms. The aim of this study was to investigate if saccades can reveal the effect of fatigue in patients with MS. Patients diagnosed with MS (EDSSendogenous generated saccade paradigm (valid and invalid trials). The fatigue severity scale (FSS) was used to assess the severity of fatigue. FSS scores were used to define two subgroups, the MS fatigue group (score above normal range) and the MS non-fatigue. Differences between groups were tested using linear mixed models. Thirty-one MS patients and equal number of controls participated in this study. FSS scores were above the normal range in 11 patients. Differences in saccade latency were found according to group (p<0.001) and trial validity (p=0.023). Differences were 16.9ms, between MS fatigue and MS non-fatigue, 15.5ms between MS fatigue and control. The mean difference between valid and invalid trials was 7.5ms. Differences in saccade peak velocity were found according to group (p<0.001), the difference between MS fatigue and control was 22.3°/s and between MS fatigue and non-fatigue was 12.3°/s. Group was a statistically significant predictor for amplitude (p<0.001). FSS scores were correlated with peak velocity (p=0.028) and amplitude (p=0.019). Consistent with the initial hypothesis, our study revealed altered saccade latency, peak velocity and amplitude in patients with fatigue symptoms. Eye movement testing can complement the standard inventories when investigating fatigue because they do not share similar limitations. Our findings contribute to the understanding of functional changes induced by MS and might be useful for clinical trials and treatment decisions. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Fractografia de compósito estrutural aeronáutico submetido à caracterização de tenacidade à fratura interlaminar em modo I Fractography of aeronautical composite structures submitted to mode I interlaminar fracture toughness characterization

    Directory of Open Access Journals (Sweden)

    Geraldo Maurício Cândido

    2012-01-01

    used method to determine the Mode I fracture toughness of structural composites. In this work samples prepared from a plain weave fabric laminate were submitted to Mode I delamination under static load at room temperature. The analysis of the delaminated surfaces was performed with scanning electron microscopy (SEM. The results show that the fracture process initiates at the resin pockets after a Teflon® insert and propagates along the resin rich areas at the crossing of weft and warp tows. The main fractographical aspects revealed are identified, reported and discussed.

  7. Matrix resin effects in composite delamination - Mode I fracture aspects

    Science.gov (United States)

    Hunston, Donald L.; Moulton, Richard J.; Johnston, Norman J.; Bascom, Willard D.

    1987-01-01

    A number of thermoset, toughened thermoset, and thermoplastic resin matrix systems were characterized for Mode I critical strain energy release rates, and their composites were tested for interlaminar critical strain energy release rates using the double cantilever beam method. A clear correlation is found between the two sets of data. With brittle resins, the interlaminar critical strain energy release rates are somewhat larger than the neat resin values due to a full transfer of the neat resin toughness to the composite and toughening mechanisms associated with crack growth. With tougher matrices, the higher critical strain energy release rates are only partially transferred to the composites, presumably because the fibers restrict the crack-tip deformation zones.

  8. Structural characterization and magnetic properties of steels subjected to fatigue

    International Nuclear Information System (INIS)

    Lo, C.C.H.; Tang, F.; Biner, S.B.; Jiles, D.C.

    2000-01-01

    Studies have been made on the effects of residual stress and microstructure on the variations of magnetic properties of steels during fatigue. Strain-controlled fatigue tests have been conducted on 0.2wt% C steel samples which were (1) cold-worked (2) cold-worked and annealed at 500 deg. C to relieve residual stress, and (3) annealed at 905 deg. C to produce a ferrite/pearlite structure. The changes of surface microstructure were studied by SEM replica technique. The dislocation structures of samples fatigued for different numbers of cycle were studied by TEM. In the initial stage of fatigue coercivity was found to behave differently for samples which have different residual stress levels. In the intermediate stage the magnetic hysteresis parameters became stable as the dislocation cell structure developed in the samples. In the final stage the magnetic parameters decreased dramatically. The decrease rate is related to the propagation rate of fatigue cracks observed in the SEM study, which was found to be dependent on the sample microstructure. The present results indicate that the magnetic inspection technique is able to differentiate the residual stress effects from the fatigue damage induced by cyclic loading, and therefore it is possible to detect the onset of fatigue failure in steel components via measurements of the changes in magnetic properties.--This work was sponsored by the National Science Foundation, under grant number CMS-9532056

  9. Fatigue Characterization of Fabricated Ship Details for Design.

    Science.gov (United States)

    1982-08-01

    than the ques- tion of brittle fracture. Such cracking has been found in the forepeak region, bottom amidships, at the bulwark at both ends of the...results of the laboratory studies are presented in the Appendices. 1.3 References 1.1 Vedeler, G. "To What Extent Do Brittle Fracture and Fatigue...Civil Engineering. Appre- ciation is extended to Mr. John R. Williams who prepared the weldments, to Mr. Glen Lafenhagen who assisted in the fatigue

  10. Magnetic characterization of creep-fatigue damage for energy structural materials

    International Nuclear Information System (INIS)

    Suzuki, Takayuki; Hashidate, Ryuta; Harada, Yoshihisa

    2012-01-01

    Magnetic characterization of creep-fatigue damage for welded specimens of austenitic stainless steel (SUS316FR) and high-chromium steel (Mod.9Cr-1Mo) steel was performed using magnetic force microscope and Hall sensor. In SUS316FR volume fraction of δ-ferrite at weld metal region decreased by creep or creep-fatigue and the remanent magnetic flux density at weld metal region also decreased. In Mod.9Cr-1Mo steel magnetic characteristics at weld metal region were different from those at base metal initially, however, during creep or creep fatigue the difference of magnetic characteristics between welded metal and base metal became small. It was found that the degradation mechanism for these energy structural materials during creep or creep fatigue could be clarified by magnetic characterization techniques. (author)

  11. Characterization of the Effects of Fatigue on the Central Nervous System (CNS) and Drug Therapies

    National Research Council Canada - National Science Library

    Mery, Laura

    2007-01-01

    .... The model focused on central fatigue. Central fatigue associated with sleep disruption may precede peripheral fatigue, and therefore may predict impaired performance earlier than peripheral fatigue...

  12. Quantitative Acoustic Emission Fatigue Crack Characterization in Structural Steel and Weld

    Directory of Open Access Journals (Sweden)

    Adutwum Marfo

    2013-01-01

    Full Text Available The fatigue crack growth characteristics of structural steel and weld connections are analyzed using quantitative acoustic emission (AE technique. This was experimentally investigated by three-point bending testing of specimens under low cycle constant amplitude loading using the wavelet packet analysis. The crack growth sequence, that is, initiation, crack propagation, and fracture, is extracted from their corresponding frequency feature bands, respectively. The results obtained proved to be superior to qualitative AE analysis and the traditional linear elastic fracture mechanics for fatigue crack characterization in structural steel and welds.

  13. Microstructural characterization of EUROFER 97 during low-cycle fatigue

    Energy Technology Data Exchange (ETDEWEB)

    Giordana, M.F., E-mail: giordana@ifir-conicet.gov.ar [Instituto de Fisica Rosario, CONICET-UNR, Bv. 27 de Febrero 210 bis, 2000 Rosario (Argentina); Alvarez-Armas, I., E-mail: alvarez@ifir-conicet.gov.ar [Instituto de Fisica Rosario, CONICET-UNR, Bv. 27 de Febrero 210 bis, 2000 Rosario (Argentina); Armas, A., E-mail: armas@ifir-conicet.gov.ar [Instituto de Fisica Rosario, CONICET-UNR, Bv. 27 de Febrero 210 bis, 2000 Rosario (Argentina)

    2012-05-15

    The quenched and tempered reduced-activation ferritic/martensitic steel EUROFER 97 is one of the candidates for structural components of Generation IV nuclear power plants. The cyclic behaviour of this steel during isothermal plastic strain-controlled tests was investigated at room temperature and at 550 Degree-Sign C. Under low-cycle fatigue test this steel shows, after the first few cycles, a pronounced cyclic softening accompanied by microstructural changes such as the decrease of the free dislocation density inside the subgrain. The rate of softening increases with temperature being very pronounced at temperatures above 500 Degree-Sign C. The evolution of the flow stress during cycling was studied by analyzing the so-called 'back' and 'friction' stresses obtained from the hysteresis loops measured along the entire test. From the analysis of the hysteresis loops and corroborated by electron microscopy observations, it can be concluded that the strong cyclic softening observed is produced by the decrease exhibited by the friction stress. The Taylor coefficient was calculated measuring the evolution of the free dislocation density.

  14. Microstructural characterization of EUROFER 97 during low-cycle fatigue

    International Nuclear Information System (INIS)

    Giordana, M.F.; Alvarez-Armas, I.; Armas, A.

    2012-01-01

    The quenched and tempered reduced-activation ferritic/martensitic steel EUROFER 97 is one of the candidates for structural components of Generation IV nuclear power plants. The cyclic behaviour of this steel during isothermal plastic strain-controlled tests was investigated at room temperature and at 550 °C. Under low-cycle fatigue test this steel shows, after the first few cycles, a pronounced cyclic softening accompanied by microstructural changes such as the decrease of the free dislocation density inside the subgrain. The rate of softening increases with temperature being very pronounced at temperatures above 500 °C. The evolution of the flow stress during cycling was studied by analyzing the so-called “back” and “friction” stresses obtained from the hysteresis loops measured along the entire test. From the analysis of the hysteresis loops and corroborated by electron microscopy observations, it can be concluded that the strong cyclic softening observed is produced by the decrease exhibited by the friction stress. The Taylor coefficient was calculated measuring the evolution of the free dislocation density.

  15. Friction stress effects on mode I crack growth predictions

    NARCIS (Netherlands)

    Chen, Q.; Deshpande, V.S.; Giessen, E. van der; Needleman, A.

    2003-01-01

    The effect of a lattice friction stress on the monotonic growth of a plane strain mode I crack under small-scale yielding conditions is analyzed using discrete dislocation plasticity. When the friction stress is increased from zero to half the dislocation nucleation stress, the crack tip stress

  16. Observations on Mode I ductile tearing in sheet metals

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah; Nielsen, Kim Lau

    2013-01-01

    Cracked ductile sheet metals, subject to Mode I tearing, have been observed to display a variety of fracture surface morphologies depending on the material properties, and a range of studies on the fracture surface appearance have been published in the literature. Whereas classical fractures...

  17. Assisted crack tip flipping under Mode I thin sheet tearing

    DEFF Research Database (Denmark)

    Felter, Christian Lotz; Nielsen, Kim Lau

    2017-01-01

    Crack tip flipping, where the fracture surface alternates from side to side in roughly 45° shear bands, seems to be an overlooked propagation mode in Mode I thin sheet tearing. In fact, observations of crack tip flipping is rarely found in the literature. Unlike the already established modes...

  18. Crack Tip Flipping Under Mode I/III Tearing

    DEFF Research Database (Denmark)

    Felter, Christian Lotz; Specht Jensen, Lasse; Nielsen, Kim Lau

    Crack tip flipping, where the fracture surface alternates from side to side in 45° shear bands, seems to be an overlooked propagation mode in Mode I sheet tearing often disregarded as  “transitional” or tied to randomness in the material. In fact, such observations rarely make it to the literature...

  19. Noncontact measurement of guided ultrasonic wave scattering for fatigue crack characterization

    Science.gov (United States)

    Fromme, P.

    2013-04-01

    Fatigue cracks can develop in aerospace structures at locations of stress concentration such as fasteners. For the safe operation of the aircraft fatigue cracks need to be detected before reaching a critical length. Guided ultrasonic waves offer an efficient method for the detection and characterization of fatigue cracks in large aerospace structures. Noncontact excitation of guided waves was achieved using electromagnetic acoustic transducers (EMAT). The transducers were developed for the specific excitation of the A0 Lamb mode. Based on the induced eddy currents in the plate a simple theoretical model was developed and reasonably good agreement with the measurements was achieved. However, the detection sensitivity for fatigue cracks depends on the location and orientation of the crack relative to the measurement locations. Crack-like defects have a directionality pattern of the scattered field depending on the angle of the incident wave relative to the defect orientation and on the ratio of the characteristic defect size to wavelength. The detailed angular dependency of the guided wave field scattered at crack-like defects in plate structures has been measured using a noncontact laser interferometer. Good agreement with 3D Finite Element simulation predictions was achieved for machined part-through and through-thickness notches. The amplitude of the scattered wave was quantified for a variation of angle of the incident wave relative to the defect orientation and the defect depth. These results provide the basis for the defect characterization in aerospace structures using guided wave sensors.

  20. Material Characterization of Fatigue Specimens made from Meta-stable Austenitic Stainless Steel

    Energy Technology Data Exchange (ETDEWEB)

    Niffenegger, M.; Grosse, M.; Kalkhof, D.; Leber, H. [Paul Scherrer Institut Villigen (Switzerland); Vincent, A.; Pasco, L.; Morin, M. [Insa de Lyon (France)

    2003-07-01

    The main objective of the EU-project CRETE (Contract No.: FIS5-1999-00280) was to assess the capability and the reliability of innovative NDT-inspection techniques for the detection of material degradation, induced by thermal fatigue and neutron irradiation, of metastable austenitic and ferritic low-alloy steel. Several project partners tested aged or irradiated samples, using various techniques (acoustic, magnetic and thermoelectric). However, these indirect methods require a careful interpretation of the measured signal in terms of micro-structural evolutions due to ageing of the material. Therefore the material had to be characterized in its undamaged, as well as in its damaged state. The present report summarises only the material characterization of the fatigue specimens. It is issued simultaneously as an PSI Bericht and the CRETE work package 3 (WP3) report. Each partner according to their own specifications purchased three materials under investigation, namely AISI 347, AISI 321 and AISI 304L. After sending the material to PSI, all fatigue specimens were manufactured by the same Swiss company. Each partner was responsible for his fatigue tests which are documented in the report WP1, written by FANP. In order to characterize the material in its unfatigued as well as in its fatigued state and to consider microstructural changes related to fatigue damage the methods listed below were employed either by PSI or by INSA de Lyon: (1) Inductive Coupled Plasma Emission Photometry (ICP-OES) was applied to determine the chemical composition, (2) Scanning electron microscopy (SEM) for observing cracks, slip bands between grain and twin boundaries, - Ferromaster for measuring the magnetic permeability, (3) Physical Properties Measuring System (PPMS) for measuring magnetization characteristics, (4) Neutron- and advanced X-ray diffraction methods for the quantitative determination of martensite, - Transmission electron microscopy (TEM) for the observation of crystalline

  1. A Practical Test Method for Mode I Fracture Toughness of Adhesive Joints with Dissimilar Substrates

    Energy Technology Data Exchange (ETDEWEB)

    Boeman, R.G.; Erdman, D.L.; Klett, L.B.; Lomax, R.D.

    1999-09-27

    A practical test method for determining the mode I fracture toughness of adhesive joints with dissimilar substrates will be discussed. The test method is based on the familiar Double Cantilever Beam (DCB) specimen geometry, but overcomes limitations in existing techniques that preclude their use when testing joints with dissimilar substrates. The test method is applicable to adhesive joints where the two bonded substrates have different flexural rigidities due to geometric and/or material considerations. Two specific features discussed are the use of backing beams to prevent substrate damage and a compliance matching scheme to achieve symmetric loading conditions. The procedure is demonstrated on a modified DCB specimen comprised of SRIM composite and thin-section, e-coat steel substrates bonded with an epoxy adhesive. Results indicate that the test method provides a practical means of characterizing the mode I fracture toughness of joints with dissimilar substrates.

  2. Functional characterization of muscle fibres from patients with chronic fatigue syndrome: case-control study.

    Science.gov (United States)

    Pietrangelo, T; Toniolo, L; Paoli, A; Fulle, S; Puglielli, C; Fanò, G; Reggiani, C

    2009-01-01

    Chronic fatigue syndrome (CFS) is a disabling condition characterized by unexplained chronic fatigue that impairs normal activities. Although immunological and psychological aspects are present, symptoms related to skeletal muscles, such as muscle soreness, fatigability and increased lactate accumulation, are prominent in CFS patients. In this case-control study, the phenotype of the same biopsy samples was analyzed by determining i) fibre-type proportion using myosin isoforms as fibre type molecular marker and gel electrophoresis as a tool to separate and quantify myosin isoforms, and ii) contractile properties of manually dissected, chemically made permeable and calcium-activated single muscle fibres. The results showed that fibre-type proportion was significantly altered in CSF samples, which showed a shift from the slow- to the fast-twitch phenotype. Cross sectional area, force, maximum shortening velocity and calcium sensitivity were not significantly changed in single muscle fibres from CSF samples. Thus, the contractile properties of muscle fibres were preserved but their proportion was changed, with an increase in the more fatigue-prone, energetically expensive fast fibre type. Taken together, these results support the view that muscle tissue is directly involved in the pathogenesis of CSF and it might contribute to the early onset of fatigue typical of the skeletal muscles of CFS patients.

  3. Mode II Interlaminar Fracture Toughness and Fatigue Characterization of a Graphite Epoxy Composite Material

    Science.gov (United States)

    O'Brien, T. Kevin; Johnston, William M.; Toland, Gregory J.

    2010-01-01

    Mode II interlaminar fracture toughness and delamination onset and growth characterization data were generated for IM7/8552 graphite epoxy composite materials from two suppliers for use in fracture mechanics analyses. Both the fracture toughness testing and the fatigue testing were conducted using the End-notched Flexure (ENF) test. The ENF test for mode II fracture toughness is currently under review by ASTM as a potential standard test method. This current draft ASTM protocol was used as a guide to conduct the tests on the IM7/8552 material. This report summarizes the test approach, methods, procedures and results of this characterization effort.

  4. The concept of fatigue fracture toughness in fatigue delamination growth behavior

    NARCIS (Netherlands)

    Yao, L.; Alderliesten, R.C.; Benedictus, R.

    2015-01-01

    This paper provides a study on mode I fatigue delamination growth in composite laminates using energy principles. Experimental data has been obtained from fatigue tests conducted on Double Cantilever Beam (DCB) specimens at various stress ratios. A concept of fatigue fracture toughness is proposed

  5. Development, Characterization and Piezoelectric Fatigue Behavior of Lead-Free Perovskite Piezoelectric Ceramics

    Science.gov (United States)

    Patterson, Eric Andrew

    Much recent research has focused on the development lead-free perovskite piezoelectrics as environmentally compatible alternatives to lead zirconate titanate (PZT). Two main categories of lead free perovskite piezoelectric ceramic systems were investigated as potential replacements to lead zirconate titanate (PZT) for actuator devices. First, solid solutions based on Li, Ta, and Sb modified (K0.5Na0.5)NbO3 (KNN) lead-free perovskite systems were created using standard solid state methods. Secondly, Bi-based materials a variety of compositions were explored for (1-x)(Bi 0.5Na0.5)TiO3-xBi(Zn0.5Ti0.5)O 3 (BNT-BZT) and Bi(Zn0.5Ti0.5)O3-(Bi 0.5K0.5)TiO3-(Bi0.5Na0.5)TiO 3 (BZT-BKT-BNT). It was shown that when BNT-BKT is combined with increasing concentrations of Bi(Zn1/2i1/2)O3 (BZT), a transition from normal ferroelectric behavior to a material with large electric field induced strains was observed. The higher BZT containing compositions are characterized by large hysteretic strains(> 0.3%) with no negative strains that might indicate domain switching. This work summarizes and analyzes the fatigue behavior of the new generation of Pb-free piezoelectric materials. In piezoelectric materials, fatigue is observed as a degradation in the electromechanical properties under the application of a bipolar or unipolar cyclic electrical load. In Pb-based materials such as lead zirconate titanate (PZT), fatigue has been studied in great depth for both bulk and thin film applications. In PZT, fatigue can result from microcracking or electrode effects (especially in thin films). Ultimately, however, it is electronic and ionic point defects that are the most influential mechanism. Therefore, this work also analyzes the fatigue characteristics of bulk polycrystalline ceramics of the modified-KNN and BNT-BKT-BZT compositions developed. The defect chemistry that underpins the fatigue behavior will be examined and the results will be compared to the existing body of work on PZT. It will

  6. Characterization of the temperature evolution during high-cycle fatigue of the ULTIMET superalloy: Experiment and theoretical modeling

    Science.gov (United States)

    Jiang, L.; Wang, H.; Liaw, P. K.; Brooks, C. R.; Klarstrom, D. L.

    2001-09-01

    High-speed, high-resolution infrared thermography, as a noncontact, full-field, and nondestructive technique, was used to study the temperature variations of a cobalt-based ULTIMET alloy subjected to high-cycle fatigue. During each fatigue cycle, the temperature oscillations, which were due to the thermal-elastic-plastic effects, were observed and related to stress-strain analyses. A constitutive model was developed for predicting the thermal and mechanical responses of the ULTIMET alloy subjected to cyclic deformation. The model was constructed in light of internal-state variables, which were developed to characterize the inelastic strain of the material during cyclic loading. The predicted stress-strain and temperature responses were found to be in good agreement with the experimental results. In addition, the change of temperature during fatigue was employed to reveal the accumulation of fatigue damage, and the measured temperature was utilized as an index for fatigue-life prediction.

  7. Determination of mode-I cohesive strength for interfaces

    DEFF Research Database (Denmark)

    Jørgensen, J. B.; Thouless, M. D.; Sørensen, Bent F.

    2016-01-01

    The cohesive strength is one of the governing parameters controlling crack deflection at interfaces, but measuring its magnitude is challenging. In this paper, we demonstrate a novel approach to determine the mode-I cohesive strength of an interface by using a 4-point single-edge-notch beam...... in response to this stress, before the main crack starts to grow. Observations using 2D digital-image correlation showed that an ''apparent" strain across the interface initially increases linearly with the applied load, but becomes nonlinear upon the initiation of the interface crack. The cohesive strength...

  8. Mode I fatigue delamination growth in composite laminates with fibre bridging

    NARCIS (Netherlands)

    Yao, L.

    2015-01-01

    Advanced composite materials have been commonly used in aerospace engineering, because of their good mechanical properties and attractive potential for creating lightweight structures. Susceptibility to delamination is one of the most important issues in the applications of these materials. This

  9. Mode I Failure of Armor Ceramics: Experiments and Modeling

    Science.gov (United States)

    Meredith, Christopher; Leavy, Brian

    2017-06-01

    The pre-notched edge on impact (EOI) experiment is a technique for benchmarking the damage and fracture of ceramics subjected to projectile impact. A cylindrical projectile impacts the edge of a thin rectangular plate with a pre-notch on the opposite edge. Tension is generated at the notch tip resulting in the initiation and propagation of a mode I crack back toward the impact edge. The crack can be quantitatively measured using an optical method called Digital Gradient Sensing, which measures the crack-tip deformation by simultaneously quantifying two orthogonal surface slopes via measuring small deflections of light rays from a specularly reflective surface around the crack. The deflections in ceramics are small so the high speed camera needs to have a very high pixel count. This work reports on the results from pre-crack EOI experiments of SiC and B4 C plates. The experimental data are quantitatively compared to impact simulations using an advanced continuum damage model. The Kayenta ceramic model in Alegra will be used to compare fracture propagation speeds, bifurcations and inhomogeneous initiation of failure will be compared. This will provide insight into the driving mechanisms required for the macroscale failure modeling of ceramics.

  10. Fatigue tests and characterization of resulting microstructure by transmission electron microscope on zircaloy 4

    International Nuclear Information System (INIS)

    Di Toma, S.; Bertolino, G.; Tolley, A.

    2012-01-01

    This work reports the results of load controlled tension-tension fatigue tests on Zircaloy 4 (Zy-4). The resulting microstructure, particularly the kind and density of dislocations was characterized using a Transmission Electron Microscope (TEM). Specimens were cut from a rolled plate, with tensile axis parallel and perpendicular to the rolling direction. The results show a significant anisotropy of the mechanical properties due to the strong texture developed during rolling. Mainly type dislocations were observed, only in a longitudinal tensile axis specimen, dislocations were observed with a much lower density. The Schmid factors corresponding to the different glide systems were determined for specific grains in both tensile directions (author)

  11. Mechanical characterization of W-armoured plasma-facing components after thermal fatigue

    International Nuclear Information System (INIS)

    Serret, D; Richou, M; Missirlian, M; Loarer, T

    2011-01-01

    The future fusion device ITER is aimed at demonstrating the scientific and technical feasibility of fusion power. Tens of thousands of W-armoured plasma-facing components (PFCs) will be installed in the vertical targets of the ITER divertor and subjected to a high heat flux. The purpose of this paper is to present the results of mechanical and microstructural characterization of tungsten PFCs after thermal fatigue tests. On each component, Vickers hardness measurements are made. In parallel, the mean grain diameter in the corresponding zone of tungsten material is determined. The empirical Hall-Petch relation was adapted to experimental data. However, due to the plateau effect on recrystallization hardness, this relation does not seem to be relevant once recrystallization is complete: a new approach is proposed for predicting the margin to the tungsten melting onset.

  12. Stress intensity factors of eccentric cracks in bi-materials plate under mode I loading

    Energy Technology Data Exchange (ETDEWEB)

    Ismail, A. E. [Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor (Malaysia)

    2015-05-15

    Bi-material plates were generally used to joint electronic devices or mechanical components requiring dissimilar materials to be attached. During services, mechanical failure can be occurred due to the formation of cracks at the interfacial joint or away from the centre. Generally, linear elastic fracture mechanics approach is used to characterize these cracks based on stress intensity factors (SIF). Based on the literature survey, the SIFs for the central cracks were easily available. However, the SIFs for eccentric cracks were difficult to obtain. Therefore, this paper presented the SIFs for eccentric cracks subjected to mode I tension loading. Three important parameters were used such as relative crack depth, a/L, relative offset distance, b/L and elastic mismatch, E{sub 1}/E{sub 2} or α. It was found that such parameters significantly affected the characteristic of SIFs and it was depend on the location of cracks.

  13. Comparison of Intralaminar and Interlaminar Mode-I Fracture Toughness of Unidirectional IM7/8552 Graphite/Epoxy Composite

    Science.gov (United States)

    Czabaj, Michael W.; Ratcliffe, James

    2012-01-01

    The intralaminar and interlaminar mode-I fracture-toughness of a unidirectional IM7/8552 graphite/epoxy composite were measured using compact tension (CT) and double cantilever beam (DCB) test specimens, respectively. Two starter crack geometries were considered for both the CT and DCB specimen configurations. In the first case, starter cracks were produced by 12.5 micron thick, Teflon film inserts. In the second case, considerably sharper starter cracks were produced by fatigue precracking. For each specimen configuration, use of the Teflon film starter cracks resulted in initially unstable crack growth and artificially high initiation fracture-toughness values. Conversely, specimens with fatigue precracks exhibited stable growth onset and lower initiation fracture toughness. For CT and DCB specimens with fatigue precracks, the intralaminar and interlaminar initiation fracture toughnesses were approximately equal. However, during propagation, the CT specimens exhibited more extensive fiber bridging, and rapidly increasing R-curve behavior as compared to the DCB specimens. Observations of initiation and propagation of intralaminar and interlaminar fracture, and the measurements of fracture toughness, were supported by fractographic analysis using scanning electron microscopy.

  14. Effect of Grinding and Resintering on the Fatigue Limit and Surface Characterization of a Y-TZP Ceramic.

    Science.gov (United States)

    Polli, Gabriela Scatimburgo; Hatanaka, Gabriel Rodrigues; Abi-Rached, Filipe de Oliveira; Pinelli, Lígia Antunes Pereira; Góes, Márcio de Sousa; Cesar, Paulo Francisco; Reis, José Maurício Dos Santos Nunes

    2016-01-01

    This study evaluated the effect of grinding protocols and resintering on flexural fatigue limit and surface characterization of LavaTM Y-TZP. Bar-shaped specimens (20×4.0×1.2 mm, n=40; 20×4.0×1.5 mm, n=80) were obtained. Half of the thinner specimens (1.2 mm) constituted the as-sintered group (AS), while the thicker ones (1.5 mm) were ground with diamond burs under irrigation (WG) or not (G). The other half of thinner and half of ground specimens were resintered (1000 ºC, 30 min), forming the groups ASR, WGR and GR. Fatigue limit (500,000 cycles, 10 Hz) was evaluated by staircase method in a 4-point flexural fixture. Data were analyzed by 2-way ANOVA and Tukey's test (α=0.05). Surface topography (n=3) and fracture area (n=3) were evaluated by SEM. X-ray diffraction data (n=1) was analyzed by Rietveld refinement. ANOVA revealed significant differences (pgrinding protocol, resintering and their interaction. Grinding increased the fatigue limit of non-resintered groups. There was no significant difference among the resintered groups. Resintering significantly increased the fatigue limit of the AS group only. Both protocols created evident grooves on zirconia surface. The failures initiated at the tensile side of all specimens. The percentages (wt%) of monoclinic phase were AS (8.6), ASR (1.2), G (1.8), GR (0.0), WG (8.2), WGR (0.0) before, and AS (7.4), ASR (6.5), G (3.2), GR (0.2), WG (4.6), WGR (1.1) after cyclic loading. Grinding increased the fatigue limit of non-resintered Y-TZP and formed evident grooves on its surface. Resintering provided significant increase in the fatigue limit of as-sintered specimens. In general, grinding and resintering decreased or zeroed the monoclinic phase.

  15. Characterization of fatigue-corrosion phenomena for Zircaloy in iodine environment

    International Nuclear Information System (INIS)

    Schuster-Magallon, Isabelle

    1986-01-01

    In this research thesis, the acquisition of data related to crack propagation rates and to smooth specimen lifetime in corrosion-fatigue of zircaloy allowed the quantification of the influence of iodine with respect to material, to loading direction and to test frequency. A systematic fractographic examination of propagation and fatigue strength specimens allowed the fatigue-corrosion fracture scenario to be described. This scenario comprises pitting for a stress higher than a threshold stress, the development of an intergranular corrosion area limited by a threshold stress intensity factor overrun, and the propagation by fatigue-corrosion in steady regime. This propagation is an association of a quasi-cleavage which is typical of stress corrosion cracking, and a plastic deformation under fatigue. This combination leads to the sudden disappearance of cleavage, and to a ductile fracture [fr

  16. Microstructural Characterization Of Laser Heat Treated AISI 4140 Steel With Improved Fatigue Behavior

    Directory of Open Access Journals (Sweden)

    Oh M.C.

    2015-06-01

    Full Text Available The influence of surface heat treatment using laser radiation on the fatigue strength and corresponding microstructural evolution of AISI 4140 alloy steel was investigated in this research. The AISI 4140 alloy steel was radiated by a diode laser to give surface temperatures in the range between 600 and 800°C, and subsequently underwent vibration peening. The fatigue behavior of surface-treated specimens was examined using a giga-cycle ultrasonic fatigue test, and it was compared with that of non-treated and only-peened specimens. Fatigue fractured surfaces and microstructural evolution with respect to the laser treatment temperatures were investigated using an optical microscope. Hardness distribution was measured using Vickers micro-hardness. Higher laser temperature resulted in higher fatigue strength, attributed to the phase transformation.

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

    Science.gov (United States)

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

    2014-01-01

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

  18. Characterization of Residual Stress Effects on Fatigue Crack Growth of a Friction Stir Welded Aluminum Alloy

    Science.gov (United States)

    Newman, John A.; Smith, Stephen W.; Seshadri, Banavara R.; James, Mark A.; Brazill, Richard L.; Schultz, Robert W.; Donald, J. Keith; Blair, Amy

    2015-01-01

    An on-line compliance-based method to account for residual stress effects in stress-intensity factor and fatigue crack growth property determinations has been evaluated. Residual stress intensity factor results determined from specimens containing friction stir weld induced residual stresses are presented, and the on-line method results were found to be in excellent agreement with residual stress-intensity factor data obtained using the cut compliance method. Variable stress-intensity factor tests were designed to demonstrate that a simple superposition model, summing the applied stress-intensity factor with the residual stress-intensity factor, can be used to determine the total crack-tip stress-intensity factor. Finite element, VCCT (virtual crack closure technique), and J-integral analysis methods have been used to characterize weld-induced residual stress using thermal expansion/contraction in the form of an equivalent delta T (change in local temperature during welding) to simulate the welding process. This equivalent delta T was established and applied to analyze different specimen configurations to predict residual stress distributions and associated residual stress-intensity factor values. The predictions were found to agree well with experimental results obtained using the crack- and cut-compliance methods.

  19. Characterization of high cycle fatigue behavior of a new generation aluminum lithium alloy

    International Nuclear Information System (INIS)

    De, P.S.; Mishra, R.S.; Baumann, J.A.

    2011-01-01

    Highlights: → Effect of microstructure on fatigue fracture of an advanced Al-Li alloy was studied in detail. → Preferential crack propagation in T3 state at specific orientations was analyzed. → Fatigue crack propagation difference between T3 and T8 tempers and friction stir welded condition was rationalized. → The effect of grain size on fatigue life for T3 and T8 tempers was justified based on current theories. → Delamination in T3 and T8 tempers was rationalized using microstructural analysis and FEA simulation. - Abstract: The high cycle fatigue life characteristics of an Al-Li alloy were studied as a function of microstructure. While for the parent microstructure fatigue life decreased as grain size increased, no such effect was noted at high stresses. This decrease in fatigue life was correlated with lower crack initiation life due to small crack effect. Under multiaxial stress conditions, the alloy exhibited intergranular cracking. The cross-linking of intergranular cracks (in the T8 condition) caused a further deterioration in fatigue life. Additionally, planar slip movements (in the T3 condition) in stage I crack propagation were observed. Slip planarity depended on both the sample texture and the nature of the precipitates. Fractographic and textural evidence is presented.

  20. Characterization of high cycle fatigue behavior of a new generation aluminum lithium alloy

    Energy Technology Data Exchange (ETDEWEB)

    De, P.S. [Center for Friction Stir Processing, Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO 65409 (United States); Mishra, R.S., E-mail: rsmishra@mst.edu [Center for Friction Stir Processing, Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO 65409 (United States); Baumann, J.A. [Boeing Company, St. Louis, MO 631666 (United States)

    2011-09-15

    Highlights: {yields} Effect of microstructure on fatigue fracture of an advanced Al-Li alloy was studied in detail. {yields} Preferential crack propagation in T3 state at specific orientations was analyzed. {yields} Fatigue crack propagation difference between T3 and T8 tempers and friction stir welded condition was rationalized. {yields} The effect of grain size on fatigue life for T3 and T8 tempers was justified based on current theories. {yields} Delamination in T3 and T8 tempers was rationalized using microstructural analysis and FEA simulation. - Abstract: The high cycle fatigue life characteristics of an Al-Li alloy were studied as a function of microstructure. While for the parent microstructure fatigue life decreased as grain size increased, no such effect was noted at high stresses. This decrease in fatigue life was correlated with lower crack initiation life due to small crack effect. Under multiaxial stress conditions, the alloy exhibited intergranular cracking. The cross-linking of intergranular cracks (in the T8 condition) caused a further deterioration in fatigue life. Additionally, planar slip movements (in the T3 condition) in stage I crack propagation were observed. Slip planarity depended on both the sample texture and the nature of the precipitates. Fractographic and textural evidence is presented.

  1. Characterization of uniaxial fatigue behavior of precipitate strengthened Cu-Ni-Si alloy (SICLANIC(TM

    Directory of Open Access Journals (Sweden)

    B. Saadouki

    2018-01-01

    Full Text Available Fatigue tests were conducted on cylindrical bars specimens to understand the fatigue behavior of SICLANIC. Although it displays good resistance in monotonic tension, this material weakens and shows a softening in repeated solicitation. This has been verified through a SEM observation, the Cu-Ni-Si alloy presents transgranular failure by cleavage. The MansonCoffin diagram exhibited the plastic deformation accommodation. The plastic deformation becomes periodic and decreases progressively as the cycle number increases. The approximations of Manson Coffin give fatigue parameters values which are in good agreement with the experience

  2. Fatigue and Fracture Characterization of Aircraft Aluminum Alloys Damaged by Prior Corrosion

    National Research Council Canada - National Science Library

    Baldwin, J

    2002-01-01

    At the time of the initiation of this project, there was no comprehensive data describing corrosion's effect on the fatigue and fracture behavior of aluminum alloys typically found in aging aircraft...

  3. Tensile and superelastic fatigue characterization of NiTi shape memory cables

    Science.gov (United States)

    Sherif, Muhammad M.; Ozbulut, Osman E.

    2018-01-01

    This paper discusses the tensile response and functional fatigue characteristics of a NiTi shape memory alloy (SMA) cable with an outer diameter of 5.5 mm. The cable composed of multiple strands arranged as one inner core and two outer layers. The results of the tensile tests revealed that the SMA cable exhibits good superelastic behavior up to 10% strain. Fatigue characteristics were investigated under strain amplitudes ranging from 3% to 7% and a minimum of 2500 loading cycles. The evolutions of maximum tensile stress, residual strains, energy dissipation, and equivalent viscous damping under a number of loading cycles were analyzed. The fracture surface of a specimen subjected to 5000 loading cycles and 7% strain was discussed. Functional fatigue test results indicated a very high superelastic fatigue life cycle for the tested NiTi SMA cable.

  4. Effect of residual stress induced by cold expansion on fatigue crack ...

    African Journals Online (AJOL)

    Fatigue life and fatigue crack growth rate are controlled by stress ratio, stress level, orientation of crack, temper-ature, residual stress, corrosion, etc. The effects of residual stress on fatigue crack growth in aluminium (Al) alloy 2024-T351 by Mode I crack were investigated by applying constant amplitude cycles based on ...

  5. Mode I and Mode II Interlaminar Crack Growth Resistances of Ceramic Matrix Composites at Ambient Temperature

    National Research Council Canada - National Science Library

    Choi, Sung R; Kowalik, Robert W; Alexander, Donald J

    2007-01-01

    ...) including three gas-turbine grade melt-infiltrated SiC/SiC composites. Modes I and II crack growth resistances, GI and GII, were evaluated at ambient temperature using double cantilever beam and end notched flexure methods, respectively...

  6. A boundary integral method for a dynamic, transient mode I crack problem with viscoelastic cohesive zone

    KAUST Repository

    Leise, Tanya L.; Walton, Jay R.; Gorb, Yuliya

    2009-01-01

    interpenetration, in contrast to the usual mode I boundary conditions that assume all unloaded crack faces are stress-free. The nonlinear viscoelastic cohesive zone behavior is motivated by dynamic fracture in brittle polymers in which crack propagation

  7. Characterization of fatigue resistance in photochromic composite materials for 3D rewritable optical memory applications

    International Nuclear Information System (INIS)

    Samoylova, Elena; Dallari, William; Allione, Marco; Pignatelli, Francesca; Marini, Lara; Cingolani, Roberto; Diaspro, Alberto; Athanassiou, Athanassia

    2013-01-01

    Highlights: • Fatigue resistance of diarylethene–polymer composites was tested with optical absorption and fluorescence methods upon repetitive UV–VIS irradiation. • Significant differences in fatigue were found in different polymeric matrices and in one-photon and two-photon excitation experiments. • Several explanations for fatigue resistance of the composites are proposed based on the physico-chemical properties of the diarylethenes and polymeric matrices. -- Abstract: Fatigue resistance of the photochromic diarylethene molecules 1,2-bis[2-methylbenzo[b]thyophen-3-yl] -3,3,4,4,5,5-hexafluoro-1-cyclopentene embedded in three different acrylic polymers is studied upon multiple coloration–decoloration cycles. The resistance to photofatigue is found to be different in the three polymeric materials when one-photon excitation was used for the reversible photoconversion experiment. In particular, the photochromic molecules lose their photoisomerization ability faster if they are embedded in poly(methyl methacrylate) (PMMA) with respect to poly(ethyl methacrylate-co-methyl acrylate) (PEMMA) and poly(ethyl methacrylate) (PEMA). We propose several explanations based on the physico-chemical properties of the matrix and of the photochromic molecules. In the case of two-photon excitation, which is necessary for 3D optical writing, the fatigue resistance is found to be poorer than in the one-photon case. The accelerated photodegradation can be assigned to the non-linear nature of interaction between the polymeric composite material and light

  8. Characterization of fatigue resistance in photochromic composite materials for 3D rewritable optical memory applications

    Energy Technology Data Exchange (ETDEWEB)

    Samoylova, Elena, E-mail: Elena.Samoylova@physik.uni-muenchen.de [Nanophysics, Istituto Italiano di Tecnologia, via Morego 30, 16163 Genova (Italy); Dallari, William; Allione, Marco; Pignatelli, Francesca; Marini, Lara; Cingolani, Roberto; Diaspro, Alberto [Nanophysics, Istituto Italiano di Tecnologia, via Morego 30, 16163 Genova (Italy); Athanassiou, Athanassia, E-mail: athanassia.athanassiou@iit.it [Nanophysics, Istituto Italiano di Tecnologia, via Morego 30, 16163 Genova (Italy); Center for Biomolecular Nanotechnologies-Unile, Istituto Italiano di Tecnologia, via Barsanti, 73010 Arnesano, Lecce (Italy)

    2013-06-01

    Highlights: • Fatigue resistance of diarylethene–polymer composites was tested with optical absorption and fluorescence methods upon repetitive UV–VIS irradiation. • Significant differences in fatigue were found in different polymeric matrices and in one-photon and two-photon excitation experiments. • Several explanations for fatigue resistance of the composites are proposed based on the physico-chemical properties of the diarylethenes and polymeric matrices. -- Abstract: Fatigue resistance of the photochromic diarylethene molecules 1,2-bis[2-methylbenzo[b]thyophen-3-yl] -3,3,4,4,5,5-hexafluoro-1-cyclopentene embedded in three different acrylic polymers is studied upon multiple coloration–decoloration cycles. The resistance to photofatigue is found to be different in the three polymeric materials when one-photon excitation was used for the reversible photoconversion experiment. In particular, the photochromic molecules lose their photoisomerization ability faster if they are embedded in poly(methyl methacrylate) (PMMA) with respect to poly(ethyl methacrylate-co-methyl acrylate) (PEMMA) and poly(ethyl methacrylate) (PEMA). We propose several explanations based on the physico-chemical properties of the matrix and of the photochromic molecules. In the case of two-photon excitation, which is necessary for 3D optical writing, the fatigue resistance is found to be poorer than in the one-photon case. The accelerated photodegradation can be assigned to the non-linear nature of interaction between the polymeric composite material and light.

  9. Metallurgical characterization of M-Wire nickel-titanium shape memory alloy used for endodontic rotary instruments during low-cycle fatigue.

    Science.gov (United States)

    Ye, Jia; Gao, Yong

    2012-01-01

    Rotary instruments made of a new nickel-titanium (NiTi) alloy (M-Wire) have shown improved cyclic fatigue resistance and mechanical properties compared with those made of conventional superelastic NiTi wires. The objective of this study was to characterize microstructural changes of M-Wire throughout the cyclic fatigue process under controlled strain amplitude. The average fatigue life was calculated from 30 M-Wire samples that were subjected to a strain-controlled (≈ 4%) rotating bend fatigue test at room temperature and rotational speed of 300 rpm. Microstructural evolution of M-Wire has been investigated by different metallurgical characterization techniques, including differential scanning calorimetry, Vickers microhardness, and transmission electron microscopy at 4 different stages (as-received state, 30%, 60%, and 90% of average fatigue life). During rotating bend fatigue test, no statistically significant difference (P > .05) was found on austenite finish temperatures between as-received M-Wire and fatigued samples. However, significant differences (P Wire are expected to have higher strength and wear resistance than similar instruments made of conventional superelastic NiTi wires because of its unique nano-crystalline martensitic microstructure. Copyright © 2012 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  10. Face/core debond fatigue crack growth characterization using the sandwich mixed mode bending specimen

    DEFF Research Database (Denmark)

    Manca, Marcello; Quispitupa, Amilcar; Berggreen, Christian

    2012-01-01

    Face/core fatigue crack growth in foam-cored sandwich composites is examined using the mixed mode bending (MMB) test method. The mixed mode loading at the debond crack tip is controlled by changing the load application point in the MMB test fixture. Sandwich specimens were manufactured using H45...... and H100 PVC foam cores and E-glass/polyester face sheets. All specimens were pre-cracked in order to define a sharp crack front. The static debond fracture toughness for each material configuration was measured at different mode-mixity phase angles. Fatigue tests were performed at 80% of the static...

  11. Fatigue damage characterization in plain-wave carbon-carbon fabric reinforced plastic composites

    International Nuclear Information System (INIS)

    Khan, Z.; Al-sulaiman, F.S.; Farooqi, J.K.

    1997-01-01

    In this paper fatigue damage mechanisms in 8 ply Carbon-Carbon Fabric reinforced Plastic Laminates obtained from polyester resin-prepreg plain weave carbon-carbon fabric layers have been investigated. Enhanced dye penetrant, X-ray radiography, optical microscopy, edge replication, and scanning electron fractography have been employed to examine the fatigue damage in three classes of laminates having the unidirectional (O)/sub delta/, the angle-plied (0,0,45,-45)/sub s/ fiber orientations. It is shown the laminates that have off axis plies, i.e.,0,0,45,-45), and (45,-45,0,0) /sub s/, the fatigue damage is initiated through matrix cracking. This matrix cracking induces fiber fracture in adjacent plies near the matrix crack tip. This event is followed by the man damage event of delamination of the stacked plies. It is shown that the delamination was the major damage mode, which caused the eventual fatigue failure in the angle-plied composites. The unidirectional composite (O)/sub delta/ laminates failed predominantly by lateral fracture instead of delamination. Fiber fracture was observed in the prime damage mode in unidirectional (O)/sub delta/ composite laminates. (author)

  12. Nano-Impact (Fatigue Characterization of As-Deposited Amorphous Nitinol Thin Film

    Directory of Open Access Journals (Sweden)

    Rehan Ahmed

    2012-08-01

    Full Text Available This paper presents nano-impact (low cycle fatigue behavior of as-deposited amorphous nitinol (TiNi thin film deposited on Si wafer. The nitinol film was 3.5 µm thick and was deposited by the sputtering process. Nano-impact tests were conducted to comprehend the localized fatigue performance and failure modes of thin film using a calibrated nano-indenter NanoTest™, equipped with standard diamond Berkovich and conical indenter in the load range of 0.5 mN to 100 mN. Each nano-impact test was conducted for a total of 1000 fatigue cycles. Depth sensing approach was adapted to understand the mechanisms of film failure. Based on the depth-time data and surface observations of films using atomic force microscope, it is concluded that the shape of the indenter test probe is critical in inducing the localized indentation stress and film failure. The measurement technique proposed in this paper can be used to optimize the design of nitinol thin films.

  13. Characterization of pituitary function with emphasis on GH secretion in the chronic fatigue syndrome.

    Science.gov (United States)

    Moorkens, G; Berwaerts, J; Wynants, H; Abs, R

    2000-07-01

    Previous studies have revealed that hormonal disturbances may accompany the chronic fatigue syndrome (CFS). Changes in the secretion of the pituitary-adrenal axis have been demonstrated, as well as abnormalities in the GH-IGF-I axis. However, data have not always been well characterized and were sometimes conflicting. The small number of CFS patients investigated in earlier studies may have played a role in the interpretation of the results. Hormonal testing was performed in 73 nonobese CFS patients and nonobese 21 age-and gender-matched healthy controls. We investigated GH, ACTH and cortisol responses to insulin-induced hypoglycaemia. In a subgroup of patients arginine and clonidine stimulation for GH was also performed. Nocturnal secretion of GH, ACTH and cortisol were determined. Serum levels of IGF-I, prolactin, TSH, and free thyroxine were also measured. Visceral fat mass was assessed by CT scanning. GH response to insulin induced hypoglycaemia assessed by peak value (17.0 +/- 13.1 microg/l vs. 22. 1 +/- 9.8 microg/l; P = 0.01) and by AUC (450.0 +/- 361.3 microg/l vs. 672.3 +/- 393.0 microg/l; P = 0.002) was significantly decreased in CFS patients vs. controls. Nocturnal GH secretion assessed by GH peak value (5.4 +/- 3.7 vs. 9.0 +/- 5.1 microg/l; P = 0.44) and by AUC (34.4 +/- 20.2 vs. 67.4 +/- 43.1; P = 0.045) was also significantly impaired in CFS patients. Arginine and clonidine administration showed no differences in GH secretion between CFS patients and controls. In the CFS group, GH peak values were significantly higher after ITT than after arginine (P = 0.017) or clonidine (P = 0.001). No differences in serum IGF-I levels were found between CFS patients and controls. Except for a significantly lower nocturnal cortisol peak value, no differences were found in ACTH and cortisol secretion between CFS patients and controls. Significantly higher serum prolactin levels (7.4 +/- 4.7 microg/l vs. 4.4 +/- 1.3 microg/l; P = 0.004) and significantly higher serum

  14. Effects of Forming Process on Composite mode I Interlaminar Fracture Toughness

    Directory of Open Access Journals (Sweden)

    CHEN Xingyi

    2016-10-01

    Full Text Available In order to compare and analyse the effect of two different kinds of forming process on composite mode I interlaminar fracture toughness, the DCB specimens were tested by using hypothesis inspeetion method.A finite element model was also used to simulate the crack propagation process.The results demonstrate that the average of mode I interlaminar fracture toughness from silicon rubber flexible mold forming is a bit higher than that from metal rigid mold forming.Howevers the variance of mode I interlaminar fracture toughness from the two groups shows no significant difference.The crack propagation process of the two forming process is similar. The established finite element model, which is identical to the test results, can predict the process of the crack expansion effectively.

  15. Dynamic fracture initiation in brittle materials under combined mode I/II loading

    International Nuclear Information System (INIS)

    Nakano, M.; Kishida, K.; Yamauchi, Y.; Sogabe, Y.

    1994-01-01

    A new test method has been developed to measure the resistance of dynamic fracture initiation in brittle materials under combined mode I/II loadings. The Brazilian disks with center-cracks have been fractured under oblique impact loadings in diametral-compression. The dynamic stress intensity factors of mode I and II are evaluated from the superposition integrals of the step response functions for the cracked disk. The experimental results are presented to elucidate the influence of loading rate on the combined mode fracture toughness for ceramics and glasses. (orig.)

  16. Post Stroke Fatigue; Point Prevalence, Characterization, Associations and Radiological Correlation in a Rehabilitation Hospital

    LENUS (Irish Health Repository)

    Khan, A

    2017-11-01

    Post stroke fatigue (PSF) is a frequently reported symptom by stroke survivors undergoing rehabilitation. This cross sectional observational study was undertaken in a rehabilitation facility to look at its prevalence and relationship with various variables like personal factors, type of stroke, social context, hemispheric involvement on CT scan and mobility status. The results showed that PSF was present in 83% (25 out of 30) of the patients included in the study. No clear association could be established between PSF, social, radiological and functional characteristics.

  17. A two-dimensional problem of a mode-I crack in a rotating fibre ...

    Indian Academy of Sciences (India)

    AHMED E ABOUELREGAL

    2018-02-07

    Feb 7, 2018 ... Fibre-reinforced; mode-I crack; dual-phase-lag theory; rotation; normal mode analysis. 1. Introduction ... acki [2, 3] rests upon the hypothesis of the Fourier law of .... forcement and rotation on the variations of different field quantities inside ... The principle of balance of linear momentum leads to the following ...

  18. Rock Fracture Toughness Study Under Mixed Mode I/III Loading

    Science.gov (United States)

    Aliha, M. R. M.; Bahmani, A.

    2017-07-01

    Fracture growth in underground rock structures occurs under complex stress states, which typically include the in- and out-of-plane sliding deformation of jointed rock masses before catastrophic failure. However, the lack of a comprehensive theoretical and experimental fracture toughness study for rocks under contributions of out-of plane deformations (i.e. mode III) is one of the shortcomings of this field. Therefore, in this research the mixed mode I/III fracture toughness of a typical rock material is investigated experimentally by means of a novel cracked disc specimen subjected to bend loading. It was shown that the specimen can provide full combinations of modes I and III and consequently a complete set of mixed mode I/III fracture toughness data were determined for the tested marble rock. By moving from pure mode I towards pure mode III, fracture load was increased; however, the corresponding fracture toughness value became smaller. The obtained experimental fracture toughness results were finally predicted using theoretical and empirical fracture models.

  19. SCC and Corrosion Fatigue characterization of a Ti-6Al-4V alloy in a corrosive environment – experiments and numerical models

    Directory of Open Access Journals (Sweden)

    S. Baragetti

    2014-10-01

    Full Text Available In the present article, a review of the complete characterization in different aggressive media of a Ti-6Al-4V titanium alloy, performed by the Structural Mechanics Laboratory of the University of Bergamo, is presented. The light alloy has been investigated in terms of corrosion fatigue, by axial fatigue testing (R = 0.1 of smooth and notched flat dogbone specimens in laboratory air, 3.5% wt. NaCl–water mixture and methanol–water mixture at different concentrations. The first corrosive medium reproduced a marine environment, while the latter was used as a reference aggressive environment. Results showed that a certain corrosion fatigue resistance is found in a salt water medium, while the methanol environment caused a significant drop – from 23% to 55% in terms of limiting stress reduction – of the fatigue resistance of the Ti-6Al-4V alloy, even for a solution containing 5% of methanol. A Stress Corrosion Cracking (SCC experimental campaign at different methanol concentrations has been conducted over slightly notched dog-bone specimens (Kt = 1.18, to characterize the corrosion resistance of the alloy under quasi-static load conditions. Finally, crack propagation models have been implemented to predict the crack propagation rates for smooth specimens, by using Paris, Walker and Kato-Deng-Inoue-Takatsu propagation formulae. The different outcomes from the forecasting numerical models were compared with experimental results, proposing modeling procedures for the numerical simulation of fatigue behavior of a Ti-6Al-4V alloy.

  20. Characterization of coatings and the low cycle fatigue behaviour of 316L

    International Nuclear Information System (INIS)

    Groot, P.; Horsten, M.G.; Tjoa, G.L.

    1993-03-01

    In the framework of the European Fusion Technology Programme ECN participates in a NET task PSM-8 'Coatings and Surface Effects on Stainless Steel 316L'. High emissivity coatings were developed for enhanced heat transfer from graphite tiles to a Stainless Steel First Wall. Four candidate materials, Cr 2 O 3 , Black Cr, Al 2 O 3 /TiO 2 and TiC were tested as candidate high emissivity coatings. These coatings were manufactured by atmospheric and vacuum plasma spraying technique and the Black Chromium coatings were manufactured by a galvanic coating technique. The tests included total emissivity measurements and Low Cycle Fatigue (LCF) experiments. The total emissivity of two TiC coatings at 525 K appeared to be 0.62 and 0.64. The total emissivity of the TiC and 5 wt% TiO 2 /Al 2 O 3 coating was about 0.7. (orig.)

  1. A review on mode-I interlaminar fracture toughness of fibre reinforced composites

    Science.gov (United States)

    Nasuha, N.; Azmi, A. I.; Tan, C. L.

    2017-10-01

    Composite material has been growing rapidly throughout the year for its unique properties in comparisons with metal. Recently, there has been a growth on studying the way to reduce the delamination failure, which is the primary challenge on laminated fibre composite. This failure can degrade the strength of composite materials, hence loses its function. In this review, database search was performed using the keywords search on “interlaminar fracture toughness”, “double cantilever beam”, “delamination resistance” and “Mode-I GIC”. The searches were performed on Google Scholar, Scopus and Web of Science with further cross-referencing with other databases. Most relevant studies were selected for review and referencing by the author. This review paper gives a brief explanation on Mode-I interlaminar fracture toughness of composite material. This fracture mode is the most common modes on studying the delamination failure.

  2. A boundary integral method for a dynamic, transient mode I crack problem with viscoelastic cohesive zone

    KAUST Repository

    Leise, Tanya L.

    2009-08-19

    We consider the problem of the dynamic, transient propagation of a semi-infinite, mode I crack in an infinite elastic body with a nonlinear, viscoelastic cohesize zone. Our problem formulation includes boundary conditions that preclude crack face interpenetration, in contrast to the usual mode I boundary conditions that assume all unloaded crack faces are stress-free. The nonlinear viscoelastic cohesive zone behavior is motivated by dynamic fracture in brittle polymers in which crack propagation is preceeded by significant crazing in a thin region surrounding the crack tip. We present a combined analytical/numerical solution method that involves reducing the problem to a Dirichlet-to-Neumann map along the crack face plane, resulting in a differo-integral equation relating the displacement and stress along the crack faces and within the cohesive zone. © 2009 Springer Science+Business Media B.V.

  3. Crack Tip Flipping under Mode I Tearing: Investigated by X-Ray Tomography

    DEFF Research Database (Denmark)

    Nielsen, Kim Lau; Gundlach, Carsten

    2017-01-01

    The fracture surface morphology that results from mode I tearing of ductile plate metals depends heavily on both the elastic-plastic material properties and the microstructure. Severe tunneling of the advancing crack tip (resulting in cup-cup, or bath-tub like fracture surfaces) can take place...... in a range of materials, often of low strength, while tearing of high strength metals typically progress by the shear band failure mechanism (slanting). In reality, however, most fracture surfaces display a mixture of morphologies. For example, slant crack propagation can be accompanied by large shear lips...... near the outer free plate surface or a complete shear band switch - seemingly distributed randomly on the fracture surface. The occasionally observed shear band switch of mode I slant cracks, related to ductile plate tearing, is far from random as the crack can flip systematically from one side...

  4. Mode I and mixed mode crack-tip fields in strain gradient plasticity

    DEFF Research Database (Denmark)

    Goutianos, Stergios

    2011-01-01

    Strain gradients develop near the crack-tip of Mode I or mixed mode cracks. A finite strain version of the phenomenological strain gradient plasticity theory of Fleck–Hutchinson (2001) is used here to quantify the effect of the material length scales on the crack-tip stress field for a sharp...... stationary crack under Mode I and mixed mode loading. It is found that for material length scales much smaller than the scale of the deformation gradients, the predictions converge to conventional elastic–plastic solutions. For length scales sufficiently large, the predictions converge to elastic solutions....... Thus, the range of length scales over which a strain gradient plasticity model is necessary is identified. The role of each of the three material length scales, incorporated in the multiple length scale theory, in altering the near-tip stress field is systematically studied in order to quantify...

  5. Acoustic emission studies for characterization of fatigue crack growth behavior in HSLA steel

    Science.gov (United States)

    Kumar, Jalaj; Ahmad, S.; Mukhopadhyay, C. K.; Jayakumar, T.; Kumar, Vikas

    2016-01-01

    High strength low alloy (HSLA) steels are a group of low carbon steels and used in oil and gas pipelines, automotive components, offshore structures and shipbuilding. Fatigue crack growth (FCG) characteristics of a HSLA steel have been studied at two different stress ratios (R = 0.3 and 0.5). Acoustic emission (AE) signals generated during the FCG tests have been used to understand the FCG processes. The AE signals were captured by mounting two piezoelectric sensors on compact tension specimens in liner location configuration. The AE generated in stage II of the linear Paris region of FCG has been attributed to the presence of two sub-stages with two different slopes. The AE generated at higher values of stress intensity factor is found to be useful to identify the transition from stage II to stage III of the FCG. AE location analysis has provided support for increased damage at the crack tip for higher stress ratio. The peak stress intensity (Kmax) values at the crack tip have shown good correlation with the transitions from stage IIa to stage IIb and stage II to stage III of the FCG for the two stress ratios.

  6. Mixed-mode I/III fracture toughness of a ferritic/martensitic stainless steel

    International Nuclear Information System (INIS)

    Li, Huaxin; Jones, R.H.; Gelles, D.S.; Hirth, J.P.

    1993-10-01

    The critical J-integrals of mode I (J IC ), mixed-mode I/III (J MC ), and mode III (J IIIC ) were examined for a ferritic stainless steel (F-82H) at ambient temperature. A determination of J MC was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 55 degrees from the load line. Results showed that J MC and tearing modulus (T M ) values varied with the crack angles and were lower than their mode I and mode III counterparts. Both the minimum J MC and T M values occurred at a crack angle between 40 and 50 degrees, where the load ratio of σ i /σ iii was 1.2 to 0.84. The J min was 240 Kj/M 2 , and ratios of J IC /J min and J IIIC /J min were 2.1 and 1.9, respectively. The morphology of fracture surfaces was consistent with the change of J MC and T M values. While the upper shelf-fracture toughness of F-82H depends on loading mode, the J min remains very high. Other important considerations include the effect of mixed-mode loading on the DBT temperature, and effects of hydrogen and irradiation on J min

  7. Characterization of a 14Cr ODS steel by means of small punch and uniaxial testing with regard to creep and fatigue at elevated temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Bruchhausen, M., E-mail: matthias.bruchhausen@ec.europa.eu [European Commission, Joint Research Centre, Institute for Energy and Transport, P.O. Box 2, 1755 ZG Petten (Netherlands); Turba, K. [European Commission, Joint Research Centre, Institute for Energy and Transport, P.O. Box 2, 1755 ZG Petten (Netherlands); Lund University, Division of Materials Engineering, P.O. Box 118, SE-221 00 Lund (Sweden); Haan, F. de; Hähner, P.; Austin, T. [European Commission, Joint Research Centre, Institute for Energy and Transport, P.O. Box 2, 1755 ZG Petten (Netherlands); Carlan, Y. de [CEA, DEN, Service de Recherches Métallurgiques Appliquées, 91191 Gif-sur-Yvette (France)

    2014-01-15

    A 14Cr ODS steel was characterized at elevated temperatures with regard to its behavior in small punch and uniaxial creep tests and in low cycle fatigue tests. A comparison of small punch and uniaxial creep tests at 650 °C revealed a strong anisotropy of the material when strained parallel and perpendicular to the extrusion direction with rupture times being several orders of magnitude lower for the perpendicular direction. The stress-rupture and Larson–Miller plots show a very large scatter of the creep data. This scatter is strongly reduced when rupture time is plotted against minimum deflection rate or minimum creep rate (Monkman–Grant plot). Fatigue tests have been carried out at 650 °C and 750 °C. The alloy is cyclically very stable with practically no hardening/softening. Results from the tests at both temperatures can be described by a common power law. An increase in the test temperature has little influence on the fatigue ductility exponent. For a given total strain level, the fatigue life of the alloy is reduced with increasing temperature.

  8. Fatigue Behavior of Inconel 718 TIG Welds

    Science.gov (United States)

    Alexopoulos, Nikolaos D.; Argyriou, Nikolaos; Stergiou, Vasillis; Kourkoulis, Stavros K.

    2014-08-01

    Mechanical behavior of reference and TIG-welded Inconel 718 specimens was examined in the present work. Tensile, constant amplitude fatigue, and fracture toughness tests were performed in ambient temperature for both, reference and welded specimens. Microstructure revealed the presence of coarse and fine-grained heat-affected zones. It has been shown that without any post-weld heat treatment, welded specimens maintained their tensile strength properties while their ductility decreased by more than 40%. It was found that the welded specimens had lower fatigue life and this decrease was a function of the applied fatigue maximum stress. A 30% fatigue life decrease was noticed in the high cycle fatigue regime for the welded specimens while this decrease exceeded 50% in the low cycle fatigue regime. Cyclic stress-strain curves showed that Inconel 718 experiences a short period of hardening followed by softening for all fatigue lives. Cyclic fatigue response of welded specimens' exhibited cyclically stable behavior. Finally, a marginal decrease was noticed in the Mode I fracture toughness of the welded specimens.

  9. Adrenal Fatigue

    Science.gov (United States)

    ... Search Featured Resource New Mobile App DOWNLOAD Adrenal Fatigue October 2017 Download PDFs English Editors Irina Bancos, MD Additional Resources Mayo Clinic What is adrenal fatigue? The term “adrenal fatigue” has been used to ...

  10. Combined mode I-mode II fracture of 12-mol%-ceria-doped tetragonal zirconia polycrystalline ceramic

    International Nuclear Information System (INIS)

    Tikare, V.; Choi, S.R.

    1997-01-01

    The mode I, mode II, and combined mode I-mode II fracture behavior of ceria-doped tetragonal zirconia polycrystalline (Ce-TZP) ceramic was studied. The single-edge-precracked-beam (SEPB) samples were fractured using the asymmetric four-point-bend geometry. The ratio of mode I to mode II loading was varied by varying the degree of asymmetry in the four-point-bend geometry. The minimum strain energy density theory best described the mixed-mode fracture behavior of Ce-TZP with the mode I fracture toughness, K IC = 8.2 ± 0.6 MPa·m 1/2 , and the mode II fracture toughness, K IIC = 8.6 ± 1.3 MPa·m 1/2

  11. 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.

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

    International Nuclear Information System (INIS)

    Wilhelm, Paul; Rudolph, Juergen; Steinmann, Paul

    2015-01-01

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

  13. Steady-state crack growth in single crystals under Mode I loading

    DEFF Research Database (Denmark)

    Juul, Kristian Jørgensen; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2017-01-01

    The active plastic zone that surrounds the tip of a sharp crack growing under plane strain Mode I loading conditions at a constant velocity in a single crystal is studied. Both the characteristics of the plastic zone and its effect on the macroscopic toughness is investigated in terms of crack tip...... that the largest shielding effect develops in HCP crystals, while the lowest shielding exists for FCC crystals. Rate-sensitivity is found to affect the plastic zone size, but the characteristics overall remain similar for each individual crystal structure. An increasing rate-sensitivity at low crack velocities...... shielding due to plasticity (quantified by employing the Suo, Shih, and Varias set-up). Three single crystals (FCC, BCC, HCP) are modelled in a steady-state elastic visco-plastic framework, with emphasis on the influence of rate-sensitivity and crystal structures. Distinct velocity discontinuities...

  14. Reconsidering the boundary conditions for a dynamic, transient mode I crack problem

    KAUST Repository

    Leise, Tanya

    2008-11-01

    A careful examination of a dynamic mode I crack problem leads to the conclusion that the commonly used boundary conditions do not always hold in the case of an applied crack face loading, so that a modification is required to satisfy the equations. In particular, a transient compressive stress wave travels along the crack faces, moving outward from the loading region on the crack face. This does not occur in the quasistatic or steady state problems, and is a special feature of the transient dynamic problem that is important during the time interval immediately following the application of crack face loading. We demonstrate why the usual boundary conditions lead to a prediction of crack face interpenetration, and then examine how to modify the boundary condition for a semi-infinite crack with a cohesive zone. Numerical simulations illustrate the resulting approach.

  15. Mode I type delamination fracture toughness of YBCO coated conductor with additional Cu layer

    International Nuclear Information System (INIS)

    Miyazato, T.; Hojo, M.; Sugano, M.; Adachi, T.; Inoue, Y.; Shikimachi, K.; Hirano, N.; Nagaya, S.

    2011-01-01

    A fracture toughness test method was developed for a YBCO coated conductor with an additional Cu layer. Mode I type tests were carried out using double cantilever beam (DCB) specimens. Delamination propagated into the YBCO layer, and sometimes reached the Ag/YBCO interface. The fracture toughness for YBCO was about 10 J/m 2 . That for Ag/YBCO interface was about 100 J/m 2 . Although interlaminar fracture at a YBa 2 Cu 3 O 7-δ (YBCO)/CeO 2 interface was reported for YBCO coated conductors, this has not yet been investigated by a fracture mechanical approach. In the present study, we developed a mode I type fracture toughness test method for a YBCO coated conductor with an additional Cu layer using double cantilever beam (DCB) specimens. Fracture mechanism was investigated by microscopic observation by a scanning electron microscope (SEM), together with composition analysis by an energy dispersive X-ray spectroscope (EDS). A pre-crack introduced at the YBCO/CeO 2 interface deviated from the interface, and propagated into the YBCO layer, and sometimes reached the Ag/YBCO interface. The fracture toughness, G R , for YBCO and the Ag/YBCO interface was evaluated to be 7-10 J/m 2 and 80-120 J/m 2 , respectively. The complex stress intensity factor ratio, K 2 /K 1 , at YBCO/CeO 2 interface was evaluated to be -0.19, and this ratio controlled the formation of microcracks in the YBCO layer. The main crack propagated into the YBCO layer accompanied with the formation of microcracks.

  16. Fracture under mixed-mode I+II of the austenitic stainless steel 316L

    International Nuclear Information System (INIS)

    Jeon, K.L.

    1993-08-01

    The stability of cracks under mixed-mode l+ll in an aged stainless steel type 316L is investigated using four-points bent specimens. The formulas of the bending moment, the shearing force, the mode mixity, the limit load and the J estimations are established and compared with the numerical results from elastoplastic finite element calculations. From the experimental and numerical tests results, the application and the validation of the R6 method and various local criteria (Beremin, McClintock, Guennouni-Francois and Lemaitre models) are carried out. For the R6 method, it is noted that the FAD (Failure Assessment Diagram) is nearly independent of the loading mode and the specimen geometry. The FAD of the option 1 is conservative for all the test results, but the option 3 seems to be non-conservative, especially in the cases near to the mode I. This apparent non-conservatism is probably due to the different definition of the crack initiation of the CT specimens and the 4-point bend specimens. According to the applied local criteria, the values of the damage variables at crack initiation are sufficiently stable, particularly for the Beremin model and the Guennouni-Francois model but not in the cases nearer to the mode I. The use of these local criteria is questionable in the case of axisymmetric notched specimens because of the influence of the fracture of transformed ferrite. A fractographic investigation is also discussed for different fracture modes. (author). 85 refs., 99 figs., 14 tabs

  17. The role of central and peripheral muscle fatigue in postcancer fatigue: a randomized controlled trial.

    Science.gov (United States)

    Prinsen, Hetty; van Dijk, Johannes P; Zwarts, Machiel J; Leer, Jan Willem H; Bleijenberg, Gijs; van Laarhoven, Hanneke W M

    2015-02-01

    Postcancer fatigue is a frequently occurring problem, impairing quality of life. Little is known about (neuro)physiological factors determining postcancer fatigue. It may be hypothesized that postcancer fatigue is characterized by low peripheral muscle fatigue and high central muscle fatigue. The aims of this study were to examine whether central and peripheral muscle fatigue differ between fatigued and non-fatigued cancer survivors and to examine the effect of cognitive behavioral therapy (CBT) on peripheral and central muscle fatigue of fatigued cancer survivors in a randomized controlled trial. Sixteen fatigued patients in the intervention group (CBT) and eight fatigued patients in the waiting list group were successfully assessed at baseline and six months later. Baseline measurements of 20 fatigued patients were compared with 20 non-fatigued patients. A twitch interpolation technique and surface electromyography were applied, respectively, during sustained contraction of the biceps brachii muscle. Muscle fiber conduction velocity (MFCV) and central activation failure (CAF) were not significantly different between fatigued and non-fatigued patients. Change scores of MFCV and CAF were not significantly different between patients in the CBT and waiting list groups. Patients in the CBT group reported a significantly larger decrease in fatigue scores than patients in the waiting list group. Postcancer fatigue is neither characterized by abnormally high central muscle fatigue nor by low peripheral muscle fatigue. These findings suggest a difference in the underlying physiological mechanism of postcancer fatigue vs. other fatigue syndromes. Copyright © 2015 American Academy of Hospice and Palliative Medicine. Published by Elsevier Inc. All rights reserved.

  18. Determining mode I cohesive law of Pinus pinaster by coupling double cantilever beam test with digital image correlation

    Directory of Open Access Journals (Sweden)

    J. Xavier

    2015-01-01

    Full Text Available The direct identification of the cohesive law in pure mode I of Pinus pinaster is addressed. The approach couples the double cantilever beam (DCB test with digital image correlation (DIC. Wooden beam specimens loaded in the radial-longitudinal (RL fracture propagation system are used. The strain energy release rate in mode I ( is uniquely determined from the load-displacement ( curve by means of the compliance-based beam method (CBBM. This method relies on the concept of equivalent elastic crack length ( and therefore does not require the monitoring of crack propagation during test. The crack tip opening displacement in mode I is determined from the displacement field at the initial crack tip. The cohesive law in mode I is then identified by numerical differentiation of the relationship. Moreover, the proposed procedure is validated by finite element analyses including cohesive zone modelling. It is concluded that the proposed data reduction scheme is adequate for assessing the cohesive law in pure mode I of P. pinaster

  19. Mode I fracture toughness analysis of a single-layer grapheme sheet

    Energy Technology Data Exchange (ETDEWEB)

    Ky, Minh Nguyen; Yum, Young Jin [University of Ulsan, Ulsan (Korea, Republic of)

    2014-09-15

    To predict the fracture toughness of a single-layer graphene sheet (SLGS), analytical formulations were devised for the hexagonal honeycomb lattice using a linkage equivalent discrete frame structure. Broken bonds were identified by a sharp increase in the position of the atoms. As crack propagation progressed, the crack tip position and crack path were updated from broken bonds in the molecular dynamics (MD) model. At each step in the simulation, the atomic model was centered on the crack tip to adaptively follow its path. A new formula was derived analytically from the deformation and bending mechanism of solid-state carbon-carbon bonds so as to describe the mode I fracture of SLGS. The fracture toughness of single-layer graphene is governed by a competition between bond breaking and bond rotation at a crack tip. K-field based displacements were applied on the boundary of the micromechanical model, and FEM results were obtained and compared with theoretical findings. The critical stress intensity factor for a graphene sheet was found to be K{sub IC} = 2.63 ∼ 3.2 MPa√m for the case of a zigzag crack.

  20. Investigation of Mode I fracture toughness of red Verona marble after thermal treatment

    Directory of Open Access Journals (Sweden)

    Daniela Scorza

    2015-10-01

    Full Text Available The present paper aims to assess the effect of freeze/thaw cycles on fracture behaviour of a natural stone: the red Verona marble. A wide variety of specimen types and methods to determine Mode I fracture toughness of natural stones are available in the literature and, in this context, the model originally proposed for plain concrete, i.e. the Two-Parameter Model (TPM, is adopted. Such a method is able to take into account the slow nonlinear crack growth occurring before the peak load, typical of quasi-brittle materials, with the advantage of easy specimen preparation and simple test configuration. In the present paper, the atmospheric ageing is simulated by means of thermal pre-treatments consisting of freeze/thaw cycles. Experimental tests are carried out using three-point bending Single-Edge Notched (SEN specimens, according to the TPM procedure. The effects of thermal treatment on both mechanical and fracture parameters are examined in terms of elastic modulus and fracture toughness, respectively

  1. Investigation of mixed mode - I/II fracture problems - Part 1: computational and experimental analyses

    Directory of Open Access Journals (Sweden)

    O. Demir

    2016-01-01

    Full Text Available In this study, to investigate and understand the nature of fracture behavior properly under in-plane mixed mode (Mode-I/II loading, three-dimensional fracture analyses and experiments of compact tension shear (CTS specimen are performed under different mixed mode loading conditions. Al 7075-T651 aluminum machined from rolled plates in the L-T rolling direction (crack plane is perpendicular to the rolling direction is used in this study. Results from finite element analyses and fracture loads, crack deflection angles obtained from the experiments are presented. To simulate the real conditions in the experiments, contacts are defined between the contact surfaces of the loading devices, specimen and loading pins. Modeling, meshing and the solution of the problem involving the whole assembly, i.e., loading devices, pins and the specimen, with contact mechanics are performed using ANSYSTM. Then, CTS specimen is analyzed separately using a submodeling approach, in which three-dimensional enriched finite elements are used in FRAC3D solver to calculate the resulting stress intensity factors along the crack front. Having performed the detailed computational and experimental studies on the CTS specimen, a new specimen type together with its loading device is also proposed that has smaller dimensions compared to the regular CTS specimen. Experimental results for the new specimen are also presented.

  2. Chronic Fatigue Syndrome: Review of the Literature

    OpenAIRE

    Turgeon, Sue A.

    1989-01-01

    Chronic fatigue syndrome, previously known as chronic mononucleosis or post-infectious fatigue, is a poorly understood illness characterized by chronic debilitating fatigue, recurrent flu-like symptoms, and few clinical or laboratory abnormalities. Attention was briefly focused on the Epstein-Barr virus (EBV) as a causal agent, but that hypothesis is now in serious doubt. While a significant incidence of psychiatric illness has been demonstrated among patients with the chronic fatigue syndrom...

  3. Thermal fatigue. Materials modelling

    International Nuclear Information System (INIS)

    Siegele, D.; Fingerhuth, J.; Mrovec, M.

    2012-01-01

    In the framework of the ongoing joint research project 'Thermal Fatigue - Basics of the system-, outflow- and material-characteristics of piping under thermal fatigue' funded by the German Federal Ministry of Education and Research (BMBF) fundamental numerical and experimental investigations on the material behavior under transient thermal-mechanical stress conditions (high cycle fatigue V HCF and low cycle fatigue - LCF) are carried out. The primary objective of the research is the further development of simulation methods applied in safety evaluations of nuclear power plant components. In this context the modeling of crack initiation and growth inside the material structure induced by varying thermal loads are of particular interest. Therefore, three scientific working groups organized in three sub-projects of the joint research project are dealing with numerical modeling and simulation at different levels ranging from atomistic to micromechanics and continuum mechanics, and in addition corresponding experimental data for the validation of the numerical results and identification of the parameters of the associated material models are provided. The present contribution is focused on the development and experimental validation of material models and methods to characterize the damage evolution and the life cycle assessment as a result of thermal cyclic loading. The individual purposes of the subprojects are as following: - Material characterization, Influence of temperature and surface roughness on fatigue endurances, biaxial thermo-mechanical behavior, experiments on structural behavior of cruciform specimens and scatter band analysis (IfW Darmstadt) - Life cycle assessment with micromechanical material models (MPA Stuttgart) - Life cycle assessment with atomistic and damage-mechanical material models associated with material tests under thermal fatigue (Fraunhofer IWM, Freiburg) - Simulation of fatigue crack growth, opening and closure of a short crack under

  4. Seafarer fatigue

    DEFF Research Database (Denmark)

    Jepsen, Jørgen Riis; Zhao, Zhiwei; van Leeuwen, Wessel M. A.

    2015-01-01

    Background: The consequences of fatigue for the health and safety of seafarers has caused concern in the industry and among academics, and indicates the importance of further research into risk factors and preventive interventions at sea. This review gives an overview of the key issues relating...... to seafarer fatigue. Materials and methods: A literature study was conducted aiming to collect publications that address risk factors for fatigue, short-term and long-term consequences for health and safety, and options for fatigue mitigation at sea. Due to the limited number of publications that deals...... with seafarers, experiences from other populations sharing the same exposures (e.g. shift work) were also included when appropriate. Results: Work at sea involves multiple risk factors for fatigue, which in addition to acute effects (e.g., impaired cognition, accidents) contributes through autonomic, immunologic...

  5. Mode I Stress Intensity Factors for triangular corner crack nearby intersecting of cylindrical holes

    Directory of Open Access Journals (Sweden)

    E. Salvati

    2013-10-01

    Full Text Available In this paper triangular flaws has been taken into account at the intersection of two holes inside a specified specimen. Influence of bore hole D1/D2 and angle between their axes α are examined. Numerical analysis are performed to determine Stress Intensity factors (SIF in many geometric configurations. Afterwards, fitting weight function’s parameters with FEM results, new SIF analytics expression are shown. Finally, the accuracy of weight functions in SIF predictions for different inner pressure, has been checked as well as the comparison between the SIF of a triangular crack and that of an actual crack shape obtained through a fatigue test.

  6. Mode I crack analysis in single crystals with anisotropic discrete dislocation plasticity : I. Formulation and crack growth

    NARCIS (Netherlands)

    Shishvan, Siamak Soleymani; Van der Giessen, Erik

    Analyses of monotonic loading of a plane-strain mode I crack in an fcc single crystal under small-scale yielding are carried out using discrete dislocation plasticity (DDP) incorporating anisotropic elasticity. Two crystallographically symmetric crack orientations are considered where plane-strain

  7. Three-dimensional deformation mapping of Mode I interlaminar crack extension in particle-toughened interlayers

    International Nuclear Information System (INIS)

    Borstnar, G.; Gillard, F.; Mavrogordato, M.N.; Sinclair, I.; Spearing, S.M.

    2016-01-01

    This paper presents the first use of Digital Volume Correlation (DVC) on Carbon Fibre Reinforced Plastics (CFRPs) to quantify the strain fields ahead of a Mode I delamination. DVC is a relatively novel tool that can be used to measure displacements and strains occurring inside materials under load. In conjunction with Computed Tomography (CT), the technique has been applied to porous materials, with results providing strain data for validation of Finite Element (FE) models. However, the application of the technique to laminated materials has been limited, with studies often requiring fiducial markings required for volume correlation. In this work, crack propagation steps were captured at a 325 nm voxel resolution using Synchrotron Radiation Computed Tomography (SRCT). The material systems investigated featured different crack bridging mechanisms such as; particle-bridges, resin ligaments, and fibre-bridges. An assessment of noise and sub-volume size on the strain measurement determined that the optimal sub-volume size was 150 voxels with 50% overlap. This provided a spatial resolution of 48.8 μm for strain and a corresponding strain resolution ranging between 220 and 690 με for the repeated reference scans. A rigid body translation study confirmed that specimen movements perpendicular to the fibre orientation support the ‘real’ physical displacements. However, along the fibre direction, the correlation was poor, with correct displacements being detected only within the particle-toughened interlayers. The study demonstrates that strain measurements can be made perpendicular to the fibre direction across the interlayer, which could be used to validate future FE models of these poorly understood particle-toughened interlayers.

  8. A Mixed-Mode (I-II) Fracture Criterion for AS4/8552 Carbon/Epoxy Composite Laminate

    Science.gov (United States)

    Karnati, Sidharth Reddy

    A majority of aerospace structures are subjected to bending and stretching loads that introduce peel and shear stresses between the plies of a composite laminate. These two stress components cause a combination of mode I and II fracture modes in the matrix layer of the composite laminate. The most common failure mode in laminated composites is delamination that affects the structural integrity of composite structures. Damage tolerant designs of structures require two types of materials data: mixed-mode (I-II) delamination fracture toughness that predicts failure and delamination growth rate that predicts the life of the structural component. This research focuses determining mixed-mode (I-II) fracture toughness under a combination of mode I and mode II stress states and then a fracture criterion for AS4/8552 composite laminate, which is widely used in general aviation. The AS4/8552 prepreg was supplied by Hexcel Corporation and autoclave fabricated into a 20-ply unidirectional laminate with an artificial delamination by a Fluorinated Ethylene Propylene (FEP) film at the mid-plane. Standard split beam specimens were prepared and tested in double cantilever beam (DCB) and end notched flexure modes to determine mode I (GIC) and II (GIIC) fracture toughnesses, respectively. The DCB specimens were also tested in a modified mixed-mode bending apparatus at GIIm /GT ratios of 0.18, 0.37, 0.57 and 0.78, where GT is total and GIIm is the mode II component of energy release rates. The measured fracture toughness, GC, was found to follow the locus a power law equation. The equation was validated for the present and literature experimental data.

  9. A Comparison of Fatigue Crack Growth in Human Enamel and Hydroxyapatite

    OpenAIRE

    Bajaj, Devendra; Nazari, Ahmad; Eidelman, Naomi; Arola, Dwayne

    2008-01-01

    Cracks and craze lines are often observed in the enamel of human teeth, but they rarely cause tooth fracture. The present study evaluates fatigue crack growth in human enamel, and compares that to the fatigue response of sintered hydroxyapatite (HAp) with similar crystallinity, chemistry and density. Miniature inset compact tension (CT) specimens were prepared that embodied a small piece of enamel (N=8) or HAp (N=6). The specimens were subjected to mode I cyclic loads and the steady state cra...

  10. Fatigue (PDQ)

    Science.gov (United States)

    ... Data Conducting Clinical Trials Statistical Tools and Data Terminology Resources NCI Data Catalog Cryo-EM NCI's Role ... Problems getting enough sleep. Being less active. Other medical conditions. Fatigue is common in people with advanced ...

  11. Analysis of Mode I and Mode II Crack Growth Arrest Mechanism with Z-Fibre Pins in Composite Laminated Joint

    Science.gov (United States)

    Jeevan Kumar, N.; Ramesh Babu, P.

    2018-04-01

    This paper presents the numerical study of the mode I and mode II interlaminar crack growth arrest in hybrid laminated curved composite stiffened joint with Z-fibre reinforcement. A FE model of hybrid laminated skin-stiffener joint reinforced with Z-pins is developed to investigate the effect of Z- fibre pins on mode I and mode II crack growth where the delamination is embedded inbetween the skin and stiffener interface. A finite element model was developed using S4R element of a 4-node doubly curved thick shell elements to model the composite laminates and non linear interface elements to simulate the reinforcements. The numerical analyses revealed that Z-fibre pinning were effective in suppressing the delamination growth when propagated due to applied loads. Therefore, the Z-fibre technique effectively improves the crack growth resistance and hence arrests or delays crack growth extension.

  12. Rate-dependent mode I interlaminar crack growth mechanisms in graphite/epoxy and graphite/PEEK

    Science.gov (United States)

    Gillespie, J. W., Jr.; Carlsson, L. A.; Smiley, A. J.

    1987-01-01

    In this paper the mode I fracture behavior of graphite/epoxy and graphite/PEEK composites is examined over four decades of crosshead rates (0.25-250 mm/min). Straight-sided double-cantilever-beam specimens consisting of unidirectional laminates were tested at room temperature. For graphite/epoxy the load-deflection response was linear to fracture, and stable slow crack growth initiating at the highest load level was observed for all rates tested. In contrast, mode I crack growth in the graphite/PEEK material was often unstable and showed stick-slip behavior. Subcritical crack growth occurring prior to the onset of fracture was observed at intermediate displacement rates. A mechanism for the fracture behavior of the graphite/PEEK material (based on viscoelastic, plastic, and microcrack coalescence in the process zone) is proposed and related to the observed rate-dependent phenomena.

  13. Finite element reliability analysis of fatigue life

    International Nuclear Information System (INIS)

    Harkness, H.H.; Belytschko, T.; Liu, W.K.

    1992-01-01

    Fatigue reliability is addressed by the first-order reliability method combined with a finite element method. Two-dimensional finite element models of components with cracks in mode I are considered with crack growth treated by the Paris law. Probability density functions of the variables affecting fatigue are proposed to reflect a setting where nondestructive evaluation is used, and the Rosenblatt transformation is employed to treat non-Gaussian random variables. Comparisons of the first-order reliability results and Monte Carlo simulations suggest that the accuracy of the first-order reliability method is quite good in this setting. Results show that the upper portion of the initial crack length probability density function is crucial to reliability, which suggests that if nondestructive evaluation is used, the probability of detection curve plays a key role in reliability. (orig.)

  14. 3D characterization and modeling of low cycle fatigue damage mechanisms at high temperature in a cast aluminum alloy

    International Nuclear Information System (INIS)

    Dezecot, Sebastien; Maurel, Vincent; Buffiere, Jean-Yves; Szmytka, Fabien; Koster, Alain

    2017-01-01

    Synchrotron X-ray tomography was used to monitor damage evolution in three dimensions during in situ Low Cycle Fatigue (LCF) tests at high temperature (250 °C) for an industrial material. The studied material is an AlSi7Cu3Mg aluminum alloy (close to ASTM A319) produced by Lost Foam Casting (LFC), a process which generates coarse microstructures but is nevertheless used for engine parts by the automotive industry. The volume analysis (3D images) has shown that cracks are extremely sensitive to microstructural features: coarse pores and hard particles of the eutectic regions are critical regarding respectively the main crack initiation and the crack growth. Finite Elements (FE) simulations, performed on meshes directly generated from 3D volumes and containing only pores, have revealed that mechanical fields also play a major role on the crack behavior. Initiation sites corresponded to areas of maximum inelastic strain while the crack path was globally correlated to high stress triaxiality and inelastic strain fields.

  15. Fatigue: Is it all neurochemistry?

    Science.gov (United States)

    Meeusen, Romain; Roelands, Bart

    2018-02-01

    Fatigue during exercise can be approached from different angles. Peripheral fatigue is usually described as an impairment located in the muscle and characterized by a metabolic end point, while central fatigue is defined as a failure of the central nervous system to adequately drive the muscle. The aim of the present narrative review paper is to look at the mechanisms involved in the occurrence of fatigue during prolonged exercise, predominantly from a brain neurochemical point of view. From studies in rodents it is clear that exercise increases the release of several neurotransmitters in different brain regions, and that the onset of fatigue can be manipulated when dopaminergic influx in the preoptic and anterior hypothalamus is increased, interfering with thermoregulation. This is however not as straightforward in humans, in which most studies manipulating brain neurotransmission failed to change the onset of fatigue in normal ambient temperatures. When the ambient temperature was increased, dopaminergic and combined dopaminergic and noradrenergic reuptake inhibition appeared to override a safety switch, allowing subjects to push harder and become much warmer, without changing their perception. In general, we can conclude that brain neurochemistry is clearly involved in the complex regulation of fatigue, but many other mediators also play a role.

  16. Characterization of a protein-bound polysaccharide from Herba Epimedii and its metabolic mechanism in chronic fatigue syndrome.

    Science.gov (United States)

    Chi, Aiping; Shen, Zhimei; Zhu, Wenfei; Sun, Yuliang; Kang, Yijiang; Guo, Fei

    2017-05-05

    Herba Epimedii is one of the famous Traditional Chinese Medicines used to treat the chronic fatigue syndrome (CFS). The polysaccharides are the main active components in H. epimedii. The aim of this study is to discover the therapeutic effect and metabolic mechanism of H. epimedii polysaccharides against CFS. The polysaccharide conjugates named HEP2-a were isolated from the leaves of H. epimedii using a water extraction method, and the general physicochemical properties of HEP2-a were analysed. In addition, a CFS rat model was established, and then, urinary metabonomic studies were performed using gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) in combination with multivariate statistical analysis. The physicochemical properties revealed that HEP2-a had an average molecular weight of 13.6×10 4 Da and consisted of mannose (4.41%), rhamnose (5.43%), glucose (31.26%), galactose (27.07%), arabinose (23.43%), and galacturonic acid (8.40%). The amino acids in HEP2-a include glutamate, cysteine, leucine, tyrosine, lysine, and histidine. Molecular morphology studies revealed many highly curled spherical particles with diameters of 5-10µm in solids and 100-200nm for particles in water. Five metabolites in the HEP2-a group were oppositely and significantly changed compared to the CFS model group. Two metabolic pathways were identified as significant metabolic pathways involved with HEP2-a. The therapeutic effects of HEP2-a on CFS were partially due to the restoration of these disturbed pathways. Copyright © 2017 Elsevier Ireland Ltd. All rights reserved.

  17. A Novel Procedure for Prediction of Mixed Mode I/II in Fracture Toughness of Laminate Composites

    Directory of Open Access Journals (Sweden)

    M. Mahmood Shokrieh

    2014-06-01

    Full Text Available Delamination is one of the important modes of failure in laminated composite materials. In this respect, the mixed mode I/II fracture is the most major mode of delamination incidence in laminated composite. In the present research, a relation between the fracture toughness of double cantilever beam (DCB and asymmetric double cantilever beam (ADCB specimens is presented. The DCB and ADCB samples are used for measuring the mode I and mixed mode I/II fracture toughness (G of laminated composite materials, respectively. By considering the diversity of the stacking sequence of lay-ups, the test performance on all different types of lay-ups in order to measure the fracture toughness of laminated composites is a tedious, costly and time consuming task. The purpose of deriving this relation is to estimate the value of the strain energy release rate of laminated composite ADCB specimens by testing a unidirectional DCB. To develop this relationship, the geometry of DCB and ADCB specimens are considered to obtain fracture toughness of multi-directional laminate composites of ADCB samples with arbitrary ply sequence which may be used for design purposes. The procedure presented here reduces the calculation costs of the finite element modeling and its corresponding test significantly. The results obtained by this method are compared with those of experimental and numerical methods. It is shown that the fracture toughness of multi-directional lay-ups can be predicted by measuring the unidirectional ply with an error less than 10% demonstrating the accuracy of the procedure developed in the present research.

  18. Fatigue crack growth and life prediction under mixed-mode loading

    Science.gov (United States)

    Sajith, S.; Murthy, K. S. R. K.; Robi, P. S.

    2018-04-01

    Fatigue crack growth life as a function of crack length is essential for the prevention of catastrophic failures from damage tolerance perspective. In damage tolerance design approach, principles of fracture mechanics are usually applied to predict the fatigue life of structural components. Numerical prediction of crack growth versus number of cycles is essential in damage tolerance design. For cracks under mixed mode I/II loading, modified Paris law (d/a d N =C (ΔKe q ) m ) along with different equivalent stress intensity factor (ΔKeq) model is used for fatigue crack growth rate prediction. There are a large number of ΔKeq models available for the mixed mode I/II loading, the selection of proper ΔKeq model has significant impact on fatigue life prediction. In the present investigation, the performance of ΔKeq models in fatigue life prediction is compared with respect to the experimental findings as there are no guidelines/suggestions available on the selection of these models for accurate and/or conservative predictions of fatigue life. Within the limitations of availability of experimental data and currently available numerical simulation techniques, the results of present study attempt to outline models that would provide accurate and conservative life predictions. Such a study aid the numerical analysts or engineers in the proper selection of the model for numerical simulation of the fatigue life. Moreover, the present investigation also suggests a procedure to enhance the accuracy of life prediction using Paris law.

  19. An overview of fatigue

    International Nuclear Information System (INIS)

    Mc Evily, A.J.

    1987-01-01

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

  20. Side Effects: Fatigue

    Science.gov (United States)

    Fatigue is a common side effect of many cancer treatments such as chemotherapy, radiation therapy, immunotherapy, and surgery. Anemia and pain can also cause fatigue. Learn about symptoms and way to manage fatigue.

  1. Predicting the mixed-mode I/II spatial damage propagation along 3D-printed soft interfacial layer via a hyperelastic softening model

    Science.gov (United States)

    Liu, Lei; Li, Yaning

    2018-07-01

    A methodology was developed to use a hyperelastic softening model to predict the constitutive behavior and the spatial damage propagation of nonlinear materials with damage-induced softening under mixed-mode loading. A user subroutine (ABAQUS/VUMAT) was developed for numerical implementation of the model. 3D-printed wavy soft rubbery interfacial layer was used as a material system to verify and validate the methodology. The Arruda - Boyce hyperelastic model is incorporated with the softening model to capture the nonlinear pre-and post- damage behavior of the interfacial layer under mixed Mode I/II loads. To characterize model parameters of the 3D-printed rubbery interfacial layer, a series of scarf-joint specimens were designed, which enabled systematic variation of stress triaxiality via a single geometric parameter, the slant angle. It was found that the important model parameter m is exponentially related to the stress triaxiality. Compact tension specimens of the sinusoidal wavy interfacial layer with different waviness were designed and fabricated via multi-material 3D printing. Finite element (FE) simulations were conducted to predict the spatial damage propagation of the material within the wavy interfacial layer. Compact tension experiments were performed to verify the model prediction. The results show that the model developed is able to accurately predict the damage propagation of the 3D-printed rubbery interfacial layer under complicated stress-state without pre-defined failure criteria.

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

    Science.gov (United States)

    Gupta, Vipul K.

    crystallographic {111} slip-plane cracking typical of the Stage I crack growth mode observed in single crystals and high purity polycrystals of face centered cubic metals, and which has presently been assumed for the present materials within fatigue crack initiation models. Rather, the facets tend to have near-Mode I spatial orientation, which is another indicator of the importance of environmentally affected fatigue damage. The results provide a physical basis to develop microstructurally-based next generation multi-stage fatigue (MSF) models that should include a new crack decohesion criteria based upon environmental fatigue cracking mechanisms. EBSD study of small-cracks in alloy 7050-T7451, stressed in warm-humid environment, showed that crack-path orientation changes and crack-branching occurred at both low/high-angle grain and subgrain boundaries. Single surface trace analysis suggests that the crack-path differs substantially from crystallographic slip-planes. EBSD-based observations of small-crack propagation through subgrain structure, either formed by cyclic plastic strain accumulation or pre-existing (typical of unrecrystallized grain structure in the present materials), suggest that subgrain structure plays a crucial role in small fatigue crack propagation. As mentioned earlier, local fluctuations in small-crack growth rates appear to be caused by frequent interaction with subgrain boundaries, and multiple occurrences of crack-branching and crack-path orientation changes at low/high-angle grain and subgrain boundaries. The aforementioned deviation from low-index {001}/{101}-planes and the occurrence of high-index cracking planes observed by EBSD/Stereology, in this study and others, are interpreted as trans-subgranular decohesion or inter-subgranular cracking, due to trapped hydrogen. In summary, the results provide a firmer experimental foundation for, and clearer understanding of, the mechanisms of environmental fatigue cracking of aluminum alloys, especially the

  3. Fatigue limits of titanium-bar joints made with the laser and the electric resistance welding techniques: microstructural characterization and hardness properties.

    Science.gov (United States)

    Degidi, Marco; Nardi, Diego; Morri, Alessandro; Sighinolfi, Gianluca; Tebbel, Florian; Marchetti, Claudio

    2017-09-01

    Fatigue behavior of the titanium bars is of utmost importance for the safe and reliable operation of dental implants and prosthetic constructions based on these implants. To date, however, only few data are available on the fatigue strength of dental prostheses made with electric resistance welding and laser welding techniques. This in-vitro study highlighted that although the joints made with the laser welding approach are credited of a superior tensile strength, joints made with electric resistance welding exhibited double the minimum fatigue strength with respect to the joints made with laser welding (120 vs 60 N).

  4. Synthesis and characterization of a family of structurally characterized dysprosium alkoxides for improved fatigue-resistance characteristics of PDyZT thin films.

    Science.gov (United States)

    Boyle, Timothy J; Bunge, Scott D; Clem, Paul G; Richardson, Jacob; Dawley, Jeffrey T; Ottley, Leigh Anna M; Rodriguez, Mark A; Tuttle, Bruce A; Avilucea, Gabriel R; Tissot, Ralph G

    2005-03-07

    Using either an ammoniacal route, the reaction between DyCl3, Na0, and HOR in liquid ammonia, or preferentially reacting Dy(N(SiMe3)2)3 with HOR in a solvent, we isolated a family of dysprosium alkoxides as [Dy(mu-ONep)2(ONep)]4 (1), (ONep)2Dy[(mu3-ONep)(mu-ONep)Dy(ONep)(THF)]2(mu-ONep) (2), (ONep)2Dy[(mu3-ONep)(mu-ONep)Dy(ONep)(py)]2(mu-ONep) (3), [Dy3(mu3-OBut)2(mu-OBut3(OBut)4(HOBut)2] (4), [Dy3(mu3-OBut)2(mu-OBut)3(OBut)4(THF)2] (5), [Dy3(mu3-OBut)2(mu-OBut)3(OBut)4(py)2] (6), (DMP)Dy(mu-DMP)4[Dy(DMP)2(NH3)]2 (7), [Dy(eta6-DMP)(DMP)2]2 (8), Dy(DMP)3(THF)3 (9), Dy(DMP)3(py)3 (10), Dy(DIP)3(NH3)2 (11), [Dy(eta6-DIP)(DIP)2]2 (12), Dy(DIP)3(THF)2 (13), Dy(DIP)3(py)3 (14), Dy(DBP)3(NH3) (15), Dy(DBP)3 (16), Dy(DBP)3(THF) (17), Dy(DBP)3(py)2 (18), [Dy(mu-TPS)(TPS2]2 (19), Dy(TPS)3(THF)3 (20), and Dy(TPS)3(py)3 (21), where ONep = OCH2CMe3, OBut) = OCMe3, DMP = OC6H3(Me)(2)-2,6, DIP = OC6H3(CHMe2)(2)-2,6, DBP = OC6H3(CMe3)(2)-2,6, TPS = OSi(C6H5)3, tol = toluene, THF = tetrahydrofuran, and py = pyridine. We were not able to obtain X-ray quality crystals of compounds 2, 8, and 9. The structures observed and data collected for the Dy compounds are consistent with those reported for its other congeners. A number of these precursors were used as Dy dopants in Pb(Zr0.3Ti0.7)O3 (PZT 30/70) thin films, with compound 12 yielding the highest-quality films. The resulting Pb0.94Dy0.04(Zr0.3Ti0.7)O3 [PDyZT (4/30/70)] had similar properties to PZT (30/70), but showed substantial resistance to polarization reversal fatigue.

  5. Random accumulated damage evaluation under multiaxial fatigue loading conditions

    Directory of Open Access Journals (Sweden)

    V. Anes

    2015-07-01

    Full Text Available Multiaxial fatigue is a very important physical phenomenon to take into account in several mechanical components; its study is of utmost importance to avoid unexpected failure of equipment, vehicles or structures. Among several fatigue characterization tools, a correct definition of a damage parameter and a load cycle counting method under multiaxial loading conditions show to be crucial to estimate multiaxial fatigue life. In this paper, the SSF equivalent stress and the virtual cycle counting method are presented and discussed, regarding their physical foundations and their capability to characterize multiaxial fatigue damage under complex loading blocks. Moreover, it is presented their applicability to evaluate random fatigue damage.

  6. Characterization of high temperature tensile and creep–fatigue properties of Alloy 800H for intermediate heat exchanger components of (V)HTRs

    Energy Technology Data Exchange (ETDEWEB)

    Kolluri, M., E-mail: kolluri@nrg.eu; Pierick, P. ten, E-mail: tenpierick@nrg.eu; Bakker, T., E-mail: t.bakker@nrg.eu

    2015-04-01

    Highlights: • High temperature tensile, creep–fatigue (C–F) properties of Alloy 800H are studied. • Strength and uniform elongation properties at 800 °C are much lower than RT values. • Strong influence of hold time and Δε{sub tot} on low cycle fatigue life was observed. • The total allowable C–F damage (D) at 800 °C decreases with the decreasing Δε{sub tot}. • Synergetic effect of C–F interactions showed stronger effect at lower Δε{sub tot} values. - Abstract: Alloy 800H is considered as a candidate material for intermediate heat exchanger (IHX) components of (very) high temperature reactors (V)HTRs. Qualification of the this alloy for the aforementioned nuclear applications requires understanding of its high temperature tensile, low-cycle fatigue behavior and creep–fatigue interactions because the IHX components suffer from combined creep–fatigue loadings resulting from thermally induced strain cycles associated with start-up and shutdown cycles. To this end, in this paper, the tensile properties of the Alloy 800H base and tungsten inert gas (TIG) welded materials are studied at three different temperatures, room temperature 21, 700 and 800 °C. Low cycle fatigue (LCF) behavior of the base material is investigated at 800 °C with no-hold time (no-HT) and hold time (HT) to study creep–fatigue interactions. The tensile test results showed substantial differences between the strength and ductility properties of the base and weld materials at all 3 temperatures, however, the trends in temperature dependence of tensile properties are similar for both base and weld materials. LCF studies with no-HT and HT showed a strong influence of HT on the low cycle fatigue life of this alloy illustrating the substantial influence of creep mechanisms at 800 °C. Finally, cumulative values of creep versus fatigue damage fractions are plotted in a creep–fatigue interaction diagram and these results are discussed with respect to the existing bi

  7. Asphalt Mixture Fatigue Testing : Influence of Test Type and Specimen Size

    NARCIS (Netherlands)

    Li, N.

    2013-01-01

    Fatigue characterization of an asphalt mixture is commonly estimated by laboratory fatigue tests. Based on the classical fatigue analysis, fatigue lives obtained from different test devices are not comparable even when they are performed at the same test conditions. It is believed that there are two

  8. 3D atomistic simulation of fatigue behavior of a ductile crack in bcc iron

    Czech Academy of Sciences Publication Activity Database

    Uhnáková, Alena; Machová, Anna; Hora, Petr

    2011-01-01

    Roč. 33, č. 9 (2011), s. 1182-1188 ISSN 0142-1123 R&D Projects: GA ČR(CZ) GAP108/10/0698 Institutional research plan: CEZ:AV0Z20760514 Keywords : 3D molecular dynamics * fatigue * bcc iron * mode I Subject RIV: JG - Metallurgy Impact factor: 1.546, year: 2011 http://www.sciencedirect.com/science/article/pii/S0142112311000600

  9. Cumulative fatigue and creep-fatigue damage at 3500C on recrystallized zircaloy 4

    International Nuclear Information System (INIS)

    Brun, G.; Pelchat, J.; Floze, J.C.; Galimberti, M.

    1985-06-01

    An experimental programme undertaken by C.E.A., E.D.F. and FRAGEMA with the aim of characterizing the fatigue and creep fatigue behaviour of zircaloy-4 following annealing treatments (recrystallized, stress-delived) is in progress. The results given below concern only recrystallized material. Cyclic properties, low-cycle fatigue curves and creep behaviour laws under stresses have been established. Sequential tests of pure fatigue and creep-fatigue were performed. The cumulative life fractions at fracture depend on the sequence of leading, stress history and number of cycles of prestressing. The MINER's rule appears to be conservative with regard to a low-high loading sequence whereas it is not for the reverse high-low loading sequences. Fatigue and creep damage are not interchangeable. Pre-creep improves the fatigue resistance. Pre-fatigue improves the creep strength as long as the beneficial effect of cyclic hardening overcomes the damaging effect of surface cracking. The introduction of a tension hold time into the fatigue cycle slightly increases cyclic hardening and reduces the number of cycles to failure. For hold times of less than one hour, the sum of fatigue and creep life fractions is closed to one

  10. Effect of nanoparticles and nanofibers on Mode I fracture toughness of fiber glass reinforced polymeric matrix composites

    International Nuclear Information System (INIS)

    Kelkar, Ajit D.; Mohan, Ram; Bolick, Ronnie; Shendokar, Sachin

    2010-01-01

    Graphical abstract: Use of alumina nanoparticles and TEOS electrospun nanofibers at the interfaces of glass fiber plies to develop delamination resistant epoxy polymeric composites and compare their Mode I fracture toughness characteristics. - Abstract: In the recent past, the research involving the fabrication and processing of reinforced polymer nanocomposites has increased significantly. These new materials are enabling in the discovery, development and incorporation of improved nanocomposite materials with effective manufacturing methodologies for several defense and industrial applications. These materials eventually will allow the full utilization of nanocomposites in not only reinforcing applications but also in multifunctional applications where sensing and the unique optical, thermal, electrical and magnetic properties of nanoparticles can be combined with mechanical reinforcement to offer the greatest opportunities for significant advances in material design and function. This paper presents two methods and material systems for processing and integration of the nanomaterial constituents, namely: (a) dispersing alumina nanoparticles using high energy mixing (using ultrasonication, high shear mixing and pulverization) and (b) electrospinning technique to manufacture nanofibers. These reinforced polymer nanocomposites and the processing methodologies are likely to provide effective means of improving the interlaminar properties of woven fiber glass composites compared to the traditional methods such as stitching and Z-pinning. The electrospinning technology relies on the creation of nanofibers with improved molecular orientation with reduced concentration of fiber imperfections and crystal defects. Electrospinning process utilizes surface tension effects created by electrostatic forces acting on liquid droplets, creating numerous nanofibers. These nanofibers thus have potential to serve as through-the-thickness reinforcing agents in woven composites. While

  11. An investigation on a two-dimensional problem of Mode-I crack in a thermoelastic medium

    Science.gov (United States)

    Kant, Shashi; Gupta, Manushi; Shivay, Om Namha; Mukhopadhyay, Santwana

    2018-04-01

    In this work, we consider a two-dimensional dynamical problem of an infinite space with finite linear Mode-I crack and employ a recently proposed heat conduction model: an exact heat conduction with a single delay term. The thermoelastic medium is taken to be homogeneous and isotropic. However, the boundary of the crack is subjected to a prescribed temperature and stress distributions. The Fourier and Laplace transform techniques are used to solve the problem. Mathematical modeling of the present problem reduces the solution of the problem into the solution of a system of four dual integral equations. The solution of these equations is equivalent to the solution of the Fredholm's integral equation of the first kind which has been solved by using the regularization method. Inverse Laplace transform is carried out by using the Bellman method, and we obtain the numerical solution for all the physical field variables in the physical domain. Results are shown graphically, and we highlight the effects of the presence of crack in the behavior of thermoelastic interactions inside the medium in the present context, and its results are compared with the results of the thermoelasticity of type-III.

  12. Fatigue impact on Mod-1 wind turbine design

    Science.gov (United States)

    Stahle, C. V., Jr.

    1978-01-01

    Fatigue is a key consideration in the design of a long-life Wind Turbine Generator (WTG) system. This paper discusses the fatigue aspects of the large Mod-1 horizontal-axis WTG design starting with the characterization of the environment and proceeding through the design. Major sources of fatigue loading are discussed and methods of limiting fatigue loading are described. NASTRAN finite element models are used to determine dynamic loading and internal cyclic stresses. Recent developments in determining the allowable fatigue stress consistent with present construction codes are discussed relative to their application to WTG structural design.

  13. The anti-fatigue action of cocaine and habituation to coca in Peru

    OpenAIRE

    Cabieses Molina, Fernando

    2014-01-01

    The concept of fatigue, stressing that this is a likely to be broken down into a series of links, the main process is first established in broad terms: fatigue of central synapses, fatigue neuromuscular plate and fatigue of the muscle fiber. The central synapses fatigue related to movement, is explained by the breakdown of some of the chemical equilibrium states that characterize the function of the neuron. It is located in the synapse and its essence is the inability to transmit nerve impuls...

  14. Fatigue with HIV/AIDS

    Science.gov (United States)

    ... 21, 2014 Select a Language: Fact Sheet 551 Fatigue WHAT IS FATIGUE? IS FATIGUE IMPORTANT? HOW DO ... It can be physical or psychological. With physical fatigue , your muscles cannot do things as easily as ...

  15. Prediction of fretting fatigue behavior under elastic-plastic conditions

    International Nuclear Information System (INIS)

    Shin, Ki Su

    2009-01-01

    Fretting fatigue generally leads to the degradation of the fatigue strength of a material due to cyclic micro-slip between two contacting materials. Fretting fatigue is regarded as an important issue in designing aerospace structures. While many studies have evaluated fretting fatigue behavior under elastic deformation conditions, few have focused on fretting fatigue behavior under elastic-plastic deformation conditions, especially the crack orientation and fatigue life prediction for Ti-6Al-4V. The primary goal of this study was to characterize the fretting fatigue crack initiation behavior in the presence of plasticity. Experimental tests were performed using pad configurations involving elastic-plastic deformations. To calculate stress distributions under elastic-plastic fretting fatigue conditions, FEA was also performed. Several parametric approaches were used to predict fretting fatigue life along with stress distribution resulting from FEA. However, those parameters using surface stresses were unable to establish an equivalence between elastic fretting fatigue data and elastic-plastic fretting fatigue data. Based on this observation, the critical distance methods, which are commonly used in notch analysis, were applied to the fretting fatigue problem. In conclusion, the effective strain range method when used in conjunction with the SMSSR parameter showed a good correlation of data points between the pad configurations involving elastic and elastic plastic deformations

  16. Statistical analysis of fatigue crack propagation data of materials from ancient portuguese metallic bridges

    Directory of Open Access Journals (Sweden)

    J A F O. Correia

    2017-10-01

    Full Text Available In Portugal there is a number of old metallic riveted railway and highway bridges that were erected by the end of the 19th century and beginning of the 20th century, and are still in operation, requiring inspections and remediation measures to overcome fatigue damage. Residual fatigue life predictions should be based on actual fatigue data from bridge materials which is scarce due to the material specificities. Fatigue crack propagation data of materials from representative Portuguese riveted bridges, namely the Pinh�o and Luiz I road bridges, the Viana road/railway bridge, the F�o road bridge and the Trez�i railway bridge were considered in this study. The fatigue crack growth rates were correlated using the Pariss law. Also, a statistical analysis of the pure mode I fatigue crack growth (FCG data available for the materials from the ancient riveted metallic bridges is presented. Based on this analysis, design FCG curves are proposed and compared with BS7910 standard proposal, for the Paris region, which is one important fatigue regime concerning the application of the Fracture Mechanics approaches, to predict the remnant fatigue life of structural details

  17. 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...

  18. Gut inflammation in chronic fatigue syndrome

    OpenAIRE

    Lakhan, Shaheen E; Kirchgessner, Annette

    2010-01-01

    Abstract Chronic fatigue syndrome (CFS) is a debilitating disease characterized by unexplained disabling fatigue and a combination of accompanying symptoms the pathology of which is incompletely understood. Many CFS patients complain of gut dysfunction. In fact, patients with CFS are more likely to report a previous diagnosis of irritable bowel syndrome (IBS), a common functional disorder of the gut, and experience IBS-related symptoms. Recently, evidence for interactions between the intestin...

  19. Determinants of seafarers’ fatigue

    DEFF Research Database (Denmark)

    Bøggild Dohrmann, Solveig; Leppin, Anja

    2017-01-01

    in the review. The main reason for exclusion was fatigue not being the outcome variable. Results: Most evidence was available for work time-related factors suggesting that working nights was most fatiguing, that fatigue levels were higher toward the end of watch or shift, and that the 6-h on–6-h off watch...

  20. Chronic post-inflammatory fatigue in sarcoidosis : from cytokines to behavior

    NARCIS (Netherlands)

    Korenromp, I.H.E.

    2011-01-01

    Sarcoidosis is a systemic inflammatory disorder that is characterized by granuloma formation in different organs. Sarcoidosis patients frequently report fatigue. Even when the clinical symptoms of the inflammatory disease sarcoidosis have resolved, chronic fatigue may persist. In this study 75

  1. In situ 3D characterization of high temperature fatigue damage mechanisms in a cast aluminum alloy using synchrotron X-ray tomography

    International Nuclear Information System (INIS)

    Dezecot, Sebastien; Buffiere, Jean-Yves; Koster, Alain; Maurel, Vincent; Szmytka, Fabien; Charkaluk, Eric; Dahdah, Nora; El Bartali, Ahmed; Limodin, Nathalie; Witz, Jean-Francois

    2016-01-01

    Fatigue tests were performed at 250 °C on a cast AlSi7Cu3Mg aluminum alloy and monitored with Synchrotron in situ X-ray tomography in order to understand the micro-mechanisms of crack initiation and propagation. The analysis of the 3D images reveals that internal shrinkage pores are responsible for the main crack initiation. Crack propagation is mainly due to the complex and highly interconnected network of hard particles of the eutectic regions.

  2. Fatigue Damage in Wood

    DEFF Research Database (Denmark)

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

    1996-01-01

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

  3. Cancer-related fatigue: Mechanisms, risk factors, and treatments

    Science.gov (United States)

    Bower, Julienne E.

    2015-01-01

    Fatigue is one of the most common and distressing side effects of cancer and its treatment, and may persist for years after treatment completion in otherwise healthy survivors. Cancer-related fatigue causes disruption in all aspects of quality of life and may be a risk factor for reduced survival. The prevalence and course of fatigue in cancer patients has been well characterized, and there is growing understanding of underlying biological mechanisms. Inflammation has emerged as a key biological pathway for cancer-related fatigue, with studies documenting links between markers of inflammation and fatigue before, during, and particularly after treatment. There is considerable variability in the experience of cancer-related fatigue that is not explained by disease- or treatment-related characteristics, suggesting that host factors may play an important role in the development and persistence of this symptom. Indeed, longitudinal studies have begun to identify genetic, biological, psychosocial, and behavioral risk factors for cancer-related fatigue. Given the multi-factorial nature of cancer-related fatigue, a variety of intervention approaches have been examined in randomized controlled trials, including physical activity, psychosocial, mind-body, and pharmacological treatments. Although there is currently no gold standard for treating fatigue, several of these approaches have shown beneficial effects and can be recommended to patients. This report provides a state of the science review of mechanisms, risk factors, and interventions for cancer-related fatigue, with a focus on recent longitudinal studies and randomized trials that have targeted fatigued patients. PMID:25113839

  4. Identification of distinct fatigue trajectories in patients with breast cancer undergoing adjuvant chemotherapy.

    Science.gov (United States)

    Junghaenel, Doerte U; Cohen, Jules; Schneider, Stefan; Neerukonda, Anu R; Broderick, Joan E

    2015-09-01

    The goal of this study was to characterize changes in daily fatigue in women undergoing chemotherapy for breast cancer. We examined whether there are subgroups of patients with distinct fatigue trajectories and explored potential psychosocial and biomedical predictors of these subgroups. Participants were 77 women with breast cancer receiving adjuvant chemotherapy with AC-T (2-week cycle) and TC or TCH (3-week cycle) regimens. They completed 28 daily ratings online using an adapted version of the Patient-Reported Outcomes Measurement Information System (PROMIS®) fatigue instrument. Both regimens followed an "inverted-U-shaped" fatigue pattern over approximately 2 weeks. Growth mixture modeling identified three patient subgroups with distinct trajectories. Fatigue scores in the "low fatigue" group (23 %) increased following the infusion and quickly abated. The "transient fatigue" (27 %) group had a very pronounced increase. Patients in the "high fatigue" (50 %) group reported consistently elevated fatigue with a relatively small increase. Demographic and medical variables were not associated with fatigue trajectory. Patients in the "high fatigue" group reported significantly poorer physical, emotional, and social functioning, poorer general health, and more depressed mood than patients in the "low fatigue" group. The "transient fatigue" group reported significantly better physical and social functioning than the "high fatigue" group, but emotional distress and depression similar to the "high fatigue" group. The identification of patient subgroups with distinct fatigue trajectories during chemotherapy is an essential step for developing preventative strategies and tailored interventions. Our results suggest that different trajectories are associated with patients' psychosocial and general health.

  5. Fatigue crack layer propagation in silicon-iron

    Science.gov (United States)

    Birol, Y.; Welsch, G.; Chudnovsky, A.

    1986-01-01

    Fatigue crack propagation in metal is almost always accompanied by plastic deformation unless conditions strongly favor brittle fracture. The analysis of the plastic zone is crucial to the understanding of crack propagation behavior as it governs the crack growth kinetics. This research was undertaken to study the fatigue crack propagation in a silicon iron alloy. Kinetic and plasticity aspects of fatigue crack propagation in the alloy were obtained, including the characterization of damage evolution.

  6. The effect of manufacturing conditions on discontinuity population and fatigue fracture behavior in carbon/epoxy composites

    Science.gov (United States)

    Hakim, Issa; Laquai, Rene; Walter, David; Mueller, Bernd; Graja, Paul; Meyendorf, Norbert; Donaldson, Steven

    2017-02-01

    Carbon fiber composites have been increasingly used in aerospace, military, sports, automotive and other fields due to their excellent properties, including high specific strength, high specific modulus, corrosion resistance, fatigue resistance, and low thermal expansion coefficient. Interlaminar fracture is a serious failure mode leading to a loss in composite stiffness and strength. Discontinuities formed during manufacturing process degrade the fatigue life and interlaminar fracture resistance of the composite. In his study, three approaches were implemented and their results were correlated to quantify discontinuities effecting static and fatigue interlaminar fracture behavior of carbon fiber composites. Samples were fabricated by hand layup vacuum bagging manufacturing process under three different vacuum levels, indicated High (-686 mmHg), Moderate (-330 mmHg) and Poor (0 mmHg). Discontinuity content was quantified through-thickness by destructive and nondestructive techniques. Eight different NDE methods were conducted including imaging NDE methods: X-Ray laminography, ultrasonic, high frequency eddy current, pulse thermography, pulse phase thermography and lock-in-thermography, and averaging NDE techniques: X-Ray refraction and thermal conductivity measurements. Samples were subsequently destructively serial sectioned through-thickness into several layers. Both static and fatigue interlaminar fracture behavior under Mode I were conducted. The results of several imaging NDE methods revealed the trend in percentages of discontinuity. However, the results of averaging NDE methods showed a clear correlation since they gave specific values of discontinuity through-thickness. Serial sectioning exposed the composite's internal structure and provided a very clear idea about the type, shape, size, distribution and location of most discontinuities included. The results of mechanical testing showed that discontinuities lead to a decrease in Mode I static interlaminar

  7. Low cycle fatigue: high cycle fatigue damage accumulation in a 304L austenitic stainless steel

    International Nuclear Information System (INIS)

    Lehericy, Y.

    2007-05-01

    The aim of this study was to evaluate the consequences of a Low Cycle Fatigue pre-damage on the subsequent fatigue limit of a 304L stainless steel. The effects of hardening and severe roughness (grinding) have also been investigated. In a first set of tests, the evolution of the surface damage induced by the different LCF pre-cycling was characterized. This has permitted to identify mechanisms and kinetics of damage in the plastic domain for different surface conditions. Then, pre-damaged samples were tested in the High Cycle Fatigue domain in order to establish the fatigue limits associated with each level of pre-damage. Results evidence that, in the case of polished samples, an important number of cycles is required to initiate surface cracks ant then to affect the fatigue limit of the material but, in the case of ground samples, a few number of cycles is sufficient to initiate cracks and to critically decrease the fatigue limit. The fatigue limit of pre-damaged samples can be estimated using the stress intensity factor threshold. Moreover, this detrimental effect of severe surface conditions is enhanced when fatigue tests are performed under a positive mean stress (author)

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

    Science.gov (United States)

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

    2018-02-01

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

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

    Science.gov (United States)

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

    2018-03-01

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

  10. Clinical neurophysiology of fatigue.

    Science.gov (United States)

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

    2008-01-01

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

  11. Miniature specimen technology for postirradiation fatigue crack growth testing

    International Nuclear Information System (INIS)

    Mervyn, D.A.; Ermi, A.M.

    1979-01-01

    Current magnetic fusion reactor design concepts require that the fatigue behavior of candidate first wall materials be characterized. Fatigue crack growth may, in fact, be the design limiting factor in these cyclic reactor concepts given the inevitable presence of crack-like flaws in fabricated sheet structures. Miniature specimen technology has been developed to provide the large data base necessary to characterize irradiation effects on the fatigue crack growth behavior. An electrical potential method of measuring crack growth rates is employed on miniature center-cracked-tension specimens (1.27 cm x 2.54 cm x 0.061 cm). Results of a baseline study on 20% cold-worked 316 stainless steel, which was tested in an in-cell prototypic fatigue machine, are presented. The miniature fatigue machine is designed for low cost, on-line, real time testing of irradiated fusion candidate alloys. It will enable large scale characterization and development of candidate first wall alloys

  12. The Identification of Fatigue Resistant and Fatigue Susceptible Individuals

    National Research Council Canada - National Science Library

    Harrison, Richard; Chaiken, Scott; Harville, Donald; Fischer, Joseph; Fisher, Dion; Whitmore, Jeff

    2008-01-01

    The present study was designed to target two specific areas regarding fatigue. The primary purpose was to begin investigations into possible genetic markers linked to fatigue resistance and fatigue susceptibility...

  13. Fatigue Debond Growth in Sandwich Structures Loaded in Mixed Mode Bending (MMB)

    DEFF Research Database (Denmark)

    Quispitupa, Amilcar; Berggreen, Christian; Carlsson, Leif A.

    2008-01-01

    Static and cyclic debond growth in sandwich specimens loaded in mixed mode bending (MMB) is examined. The MMB sandwich specimens were manufactured using H100 PVC foam core and E-glass/polyester non-crimp quadro-axial [0/45/90/-45]s DBLT-850 face sheets. Static test were performed to determine...... the fracture toughness of the debonded sandwich specimens at different mixed mode loadings. The mixed mode ratio (mode I to mode II) was controlled by changing the lever arm distance of the MMB test rig. Compliance technique and visual inspection was employed to measure the crack length during fatigue. Fatigue...... tests were performed at 90% of the static fracture toughness at a loading ratio of R=0.1. Fatigue results revealed higher debond crack growth rates when the lever arm distance was increased. For some specimens, the crack propagated just below the face/core interface in the foam core and for others...

  14. Fatigue Crack Topography.

    Science.gov (United States)

    1984-01-01

    alloys (2). [--I Fig. 6. Fatigue fracture in Nitrile- butadien rubber ( NBR ). Fig. 7. The characteristic features of fatigue fracture in press moulded...in plastics and even in rubber . It follows therefore, that fatigue fractures must also occur in the mineral layers of our earth or in the rock on...effective until the weakest point yields and forms a crack. To get a feeling for this process, you can imagine that the stressed article is made of rubber

  15. Fatigue 󈨛. Volume 2,

    Science.gov (United States)

    1987-06-01

    ROLAND STICKLER Absolute Fatigue Thresholds in Metallic 801 Materials - J.A. LEWIS Thermometrical Investigations on the Near 809 Threshold Fatigue...impurities reported by Semi- Alloys Inc. totaled less than 0.1%. Specimens were cast in a flat open aluminum mold. Each specimen was 6 mm thick and 12...and 2024-T351 Aluminum Alloy", in "Fatigue Crack Growth Threshold Concepts", D.L. Davidson, S. Suresh, editors, TMS-AIME. 1984, pp. 63-82. (2) Bailon

  16. Analysis of bearing steel exposed to rolling contact fatigue

    DEFF Research Database (Denmark)

    Hansen, K. T.; Fæster, Søren; Natarajan, Anand

    2017-01-01

    The objective of this work is to characterize fatigue damage in roller bearings under conditions of high load and slippage. A test rig constructed for rolling contact fatigue tests of rings is described, and test results are presented for rings taken from two spherical roller bearings. The prepar...

  17. Optimal Fatigue Testing

    DEFF Research Database (Denmark)

    Faber, Michael Havbro; Sørensen, John Dalsgaard; Kroon, I. B.

    1993-01-01

    life experiments for the same purpose. The methodology is basedon modern probabilistic concepts amd classical decision theory. The special case where the fatigue life experiments are given in terms of SN curves is considered in Particular. The proposed techniques are illustrated by an example.......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...

  18. Fatigue-Arrestor Bolts

    Science.gov (United States)

    Onstott, Joseph W.; Gilster, Mark; Rodriguez, Sergio; Larson, John E.; Wickham, Mark D.; Schoonover, Kevin E.

    1995-01-01

    Bolts that arrest (or, more precisely, retard) onset of fatigue cracking caused by inelastic strains developed. Specifically developed to be installed in flange holes of unrestrained rocket engine nozzle. Fanges sometimes used to bolt nozzle to test stand; however, when rocket engine operated without this restraint, region around bolt holes experience severe inelastic strains causing fatigue cracking. Interference fits introduce compressive preloads that retard fatigue by reducing ranges of strains. Principle of these fatigue-arrestor bolts also applicable to holes in plates made of other materials and/or used for different purposes.

  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...

  20. Fitting fatigue test data with a novel S-N curve using frequentist and Bayesian inference

    NARCIS (Netherlands)

    Leonetti, D.; Maljaars, J.; Snijder, H.H.B.

    2017-01-01

    In design against fatigue, a lower bound stress range vs. endurance curve (S-N curve) is employed to characterize fatigue resistance of plain material and structural details. With respect to the inherent variability of the fatigue life, the S-N curve is related to a certain probability of

  1. Chronic fatigue syndrome after infectious mononucleosis in adolescents.

    Science.gov (United States)

    Katz, Ben Z; Shiraishi, Yukiko; Mears, Cynthia J; Binns, Helen J; Taylor, Renee

    2009-07-01

    The goal was to characterize prospectively the course and outcome of chronic fatigue syndrome in adolescents during a 2-year period after infectious mononucleosis. A total of 301 adolescents (12-18 years of age) with infectious mononucleosis were identified and screened for nonrecovery 6 months after infectious mononucleosis by using a telephone screening interview. Nonrecovered adolescents underwent a medical evaluation, with follow-up screening 12 and 24 months after infectious mononucleosis. After blind review, final diagnoses of chronic fatigue syndrome at 6, 12, and 24 months were made by using established pediatric criteria. Six, 12, and 24 months after infectious mononucleosis, 13%, 7%, and 4% of adolescents, respectively, met the criteria for chronic fatigue syndrome. Most individuals recovered with time; only 2 adolescents with chronic fatigue syndrome at 24 months seemed to have recovered or had an explanation for chronic fatigue at 12 months but then were reclassified as having chronic fatigue syndrome at 24 months. All 13 adolescents with chronic fatigue syndrome 24 months after infectious mononucleosis were female and, on average, they reported greater fatigue severity at 12 months. Reported use of steroid therapy during the acute phase of infectious mononucleosis did not increase the risk of developing chronic fatigue syndrome. Infectious mononucleosis may be a risk factor for chronic fatigue syndrome in adolescents. Female gender and greater fatigue severity, but not reported steroid use during the acute illness, were associated with the development of chronic fatigue syndrome in adolescents. Additional research is needed to determine other predictors of persistent fatigue after infectious mononucleosis.

  2. Fatigue Evaluation Algorithms: Review

    DEFF Research Database (Denmark)

    Passipoularidis, Vaggelis; Brøndsted, Povl

    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...

  3. Clinical neurophysiology of fatigue.

    NARCIS (Netherlands)

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

    2008-01-01

    Fatigue is a multidimensional concept covering both physiological and psychological aspects. Chronic fatigue is a typical symptom of diseases such as cancer, multiple sclerosis (MS), Parkinson's disease (PD) and cerebrovascular disorders but is also presented by people in whom no defined somatic

  4. Corrosion fatigue of steels

    International Nuclear Information System (INIS)

    Spaehn, H.; Wagner, G.H.

    1976-01-01

    Corrosion fatigue phenomena can be classified into two main groups according to the electrochemical state of the metal surface in the presence of electrolytes: the active and the passive state with an important sub-group of corrosion fatigue in the unstable passive state. The allowable stress for structures exposed to the conjoint action of corrosion and fatigue is influenced by many factors: kind of media, number of cycles, frequency, mean stress, size, notches, loading mode, alloy composition and mechanical strength. A critical literature review shows contradictory results if a classification by the electrochemical surface state is not applied. Case histories and counter measures illustrate the practical importance of corrosion fatigue in many branches of industry as well as the urgent need for a better knowledge about the mutual influence of the phenomena to get rules by which the engineer can appraise the risk of corrosion fatigue. (orig.) [de

  5. 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...

  6. Multi-Axial Damage Index and Accumulation Model for Predicting Fatigue Life of CMC Materials, Phase I

    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...

  7. 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)

  8. 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

  9. Cancer-related fatigue--mechanisms, risk factors, and treatments.

    Science.gov (United States)

    Bower, Julienne E

    2014-10-01

    Fatigue is one of the most common adverse effects of cancer that might persist for years after treatment completion in otherwise healthy survivors. Cancer-related fatigue causes disruption in all aspects of quality of life and might be a risk factor of reduced survival. The prevalence and course of fatigue in patients with cancer have been well characterized and there is growing understanding of the underlying biological mechanisms. Inflammation seems to have a key role in fatigue before, during, and after cancer-treatment. However, there is a considerable variability in the presentation of cancer-related fatigue, much of which is not explained by disease-related or treatment-related characteristics, suggesting that host factors might be important in the development and persistence of this symptom. Indeed, longitudinal studies have identified genetic, biological, psychosocial, and behavioural risk factors associated with cancer-related fatigue. Although no current gold-standard treatment for fatigue is available, a variety of intervention approaches have shown beneficial effects in randomized controlled trials, including physical activity, psychosocial, mind-body, and pharmacological treatments. This Review describes the mechanisms, risk factors, and possible interventions for cancer-related fatigue, focusing on recent longitudinal studies and randomized trials that have targeted fatigued patients.

  10. Dependence of the specific essential work of fracture in mode I in commercially pure copper with thickener

    International Nuclear Information System (INIS)

    Ochoa M, Herman; Monsalve G, Alberto

    2004-01-01

    Due to the great ductility of DHP copper, the classic characterization of the fracture's lineal mechanics with the critical intensity factor of K 10 tensions fails because of the increased amount of plastic deformation that the material displays before fracturing. For this reason other parameters such as the integral J are also not able to characterize the fracture phenomenon. Therefore there is a need to define a more appropriate parameter, that is able to describe the breakage phenomenon in this type of material: the specific essential work of fracture that includes the large amount of plastic deformation that can absorb materials with definite ductile behavior. Tests with DENT (Double Edge Notched Tension) pieces were carried out for the calculation of the specific essential fracture work, according to the pre-standard ESIS 1995. These tests have been carried out with pieces of different ligament lengths, so that the specific fracture energy (W sf ) correlates with the ligament length, allowing the value of the specific essential fracture work (W sf ) to be calculated. Tests have been made using pieces of different thicknesses to establish the relationship between specific essential fracture work and the thickness of the material, finding that the value of W sf increases with the increased thickness of the material (CW)

  11. A fiber bridging model for fatigue delamination in composite materials

    International Nuclear Information System (INIS)

    Gregory, Jeremy R.; Spearing, S. Mark

    2004-01-01

    A fiber bridging model has been created to examine the effects of bridging on Mode I delamination fatigue fracture in a carbon fiber polymer-matrix composite. The model uses a cohesive zone law that is derived from quasi-static R-curves to determine the bridging energy applied in the bridged region. Timoshenko beam theory and an iterative self-consistent scheme are used to calculate the bridging tractions and displacements. After applying the bridging model to crack propagation data the scatter in the data was significantly reduced and clear trends were observed as a function of temperature that were not apparent previously. This indicated that the model appropriately accounted for the bridging in the experiments. Scanning electron microscopy crack opening displacement measurements were performed to validate the model's predictions. The measurements showed that the predictions were close to the actual bridging levels in the specimen

  12. Fatigue behavior of ULTIMETRTM alloy: Experiment and theoretical modeling

    Science.gov (United States)

    Jiang, Liang

    ULTIMETRTM alloy is a commercial Co-26Cr-9Ni (weight percent) superalloy, which possesses excellent resistance to both wear and corrosion. In order to extend the structural applications of this alloy and improve the fundamental understanding of the fatigue damage mechanisms, stress- and strain-controlled fatigue tests were performed at various temperatures and in different environments. The stress- and strain-life data were developed for the structural design and engineering applications of this material. Fractographic studies characterized the crack-initiation and propagation behavior of the alloy. Microstructure evolution during fatigue was revealed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Specifically, it was found that the metastable face-centered-cubic structure of this alloy in the as-received condition could be transformed into a hexagonal-close-packed structure either under the action of plastic deformation at room temperature, or due to the aging and cyclic deformation at intermediate temperatures. This interesting observation constructed a sound basis for the alloy development. The dominant mechanisms, which control the fatigue behavior of ULTIMET alloy, were characterized. High-speed, high-resolution infrared (IR) thermography, as a non-contact, full-field, and nondestructive technique, was used to characterize the damage during fatigue. The temperature variations during each fatigue cycle, which were due to the thermal-elastic-plastic effect, were observed and related to stress-strain analyses. The temperature evolution during fatigue manifested the cumulative fatigue damage process. A constitutive model was developed to predict thermal and mechanical responses of ULTIMET alloy subjected to cyclic deformation. The predicted cyclic stress-strain responses and temperature variations were found to be in good agreement with the experimental results. In addition, a fatigue life prediction model was developed

  13. Insomnia and Fatigue

    Science.gov (United States)

    ... week at work or a busy day of hiking or chasing a toddler. Fatigue related to cancer ... Coworkers About Your Diagnosis Work Accommodations and Disability Benefits Offsetting the “Hidden Costs” of Breast Cancer Getting ...

  14. Brain Tumors and Fatigue

    Science.gov (United States)

    ... Subscribe for e-updates Please leave this field empty Fatigue SHARE Home > Treatment and Care > Side Effects ... take-out food tends to be high in calories, fat and sodium and low in energy-boosting ...

  15. Hyperthermia and fatigue

    DEFF Research Database (Denmark)

    Nybo, Lars

    2008-01-01

    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 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...... in the heat, because increased oxygen extraction compensates for the reduction in systemic blood flow. The decrease in endurance seems to involve changes in the function of the central nervous system (CNS) that lead to fatigue. The CNS fatigue appears to be influenced by neurotransmitter activity...

  16. 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...

  17. 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...

  18. Fatigue in Parkinson's disease: concepts and clinical approach.

    Science.gov (United States)

    Nassif, Daniel V; Pereira, João S

    2018-03-01

    Parkinson's disease (PD) is a progressive neurological disorder characterized by a large number of motor and non-motor features. Fatigue is one of the most common and most disabling symptoms among patients with PD, and it has a significant impact on their quality of life. Although fatigue has been recognized for a long time, its pathophysiology remains poorly understood, and there is no evidence to support any therapeutic approach in PD patients. Expert consensus on case definition and diagnostic criteria for PD-related fatigue have been recently published, and although they still need to be adequately validated, they provide a great step forward in the study of fatigue. The goal of this article is to provide relevant information for the identification and management of patients with fatigue. © 2018 Japanese Psychogeriatric Society.

  19. Experiences of Fatigue at Sea

    DEFF Research Database (Denmark)

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

    2016-01-01

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

  20. Thermomechanical fatigue life prediction for several solders

    Science.gov (United States)

    Wen, Shengmin

    Since solder connections operate at high homologous temperature, solders are high temperature materials. This feature makes their mechanical behavior and fatigue phenomena unique. Based on experimental findings, a physical damage mechanism is introduced for solders. The mechanism views the damage process as a series of independent local damage events characterized by the failure of individual grains, while the structural damage is the eventual percolation result of such local events. Fine's dislocation energy density concept and Mura's microcrack initiation theory are adopted to derive the fatigue formula for an individual grain. A physical damage metric is introduced to describe the material with damage. A unified creep and plasticity constitutive model is adopted to simulate the mechanical behavior of solders. The model is cast into a continuum damage mechanics framework to simulate material with damage. The model gives good agreement with the experimental results of 96.5Pb-3.5Sn and 96.5Sn-3.5Ag solders under uniaxial strain-controlled cyclic loading. The model is convenient for implementation into commercial computational packages. Also presented is a fatigue theory with its failure criterion for solders based on physical damage mechanism. By introducing grain orientation into the fatigue formula, an m-N curve (m is Schmid factor) at constant loading condition is suggested for fatigue of grains with different orientations. A solder structure is defined as fatigued when the damage metric reaches a critical threshold, since at this threshold the failed grains may form a cluster and percolate through the structure according to percolation theory. Fatigue data of 96.5Pb-3.5Sn solder bulk specimens under various uniaxial tension tests were analyzed. Results show that the theory gives consistent predictions under broad conditions, while inelastic strain theory does not. The theory is anisotropic with no size limitation to its application, which could be suitable for

  1. Investigations of mode I crack propagation in fibre-reinforced plastics with real time X-ray tests and simultaneous sound emission analysis

    International Nuclear Information System (INIS)

    Brunner, A.; Nordstrom, R.; Flueeler, P.

    1992-01-01

    The described investigation of crack formation and crack propagation in mode I (tensile stress) in fibre-reinforced plastic samples, especially uni-directional carbon fibre reinforced polyether-ether ketone (PEEK) has several aims. On the one hand, the phenomena of crack formation and crack propagation in these materials are to be studied, and on the other hand, the draft standards for these tests are to be checked. It was found that the combination of real time X-ray tests and simultaneous sound emission analysis is excellently suited for the basic examination of crack formation and crack propagation in DCB samples. With the aid of picture processing and analysis of the video representation, consistent crack lengths and resulting G IC values can be determined. (orig./RHM) [de

  2. Fatigue crack growth prediction in 2xxx AA with friction stir weld HAZ properties

    Directory of Open Access Journals (Sweden)

    A. Tzamtzis

    2016-02-01

    Full Text Available An analytical model is developed to predict fatigue crack propagation rate under mode I loading in 2024 aluminum alloy with FSW HAZ material characteristics. Simulation of the HAZ local properties in parent 2024 AA was performed with overaging using specific heat treatment conditions. The model considers local cyclic hardening behavior in the HAZ to analyze crack growth. For the evaluation of the model, the analytical results have been compared with experimental fatigue crack growth on overaged 2024 alloy simulating material behavior at different positions within the HAZ. The analytical results showed that cyclic hardening at the crack tip can be used successfully with the model to predict FCG in a material at overaged condition associated with a location in the FSW HAZ.

  3. Thermal fatigue of beryllium

    International Nuclear Information System (INIS)

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

    1995-01-01

    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 2 to 5 MW/m 2 and under pulsed heat fluxes (10-20 MW/m 2 ) for which the time averaged heat flux is 5 MW/m 2 . These tests were carried out in the JET neutral beam test facility A test sequence with peak surface temperatures ≤ 600 degrees C produced no visible fatigue cracks. In the second series of tests, with T max ≤ 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 Φ = 25 MW/m 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. Modafinil May Alleviate Poststroke Fatigue

    DEFF Research Database (Denmark)

    Poulsen, Mai Bang; Damgaard, Bodil; Zerahn, Bo

    2015-01-01

    was randomized, double-blinded, and placebo-controlled. Patients were treated with 400-mg modafinil or placebo for 90 days. Assessments were done at inclusion, 30, 90, and 180 days. The primary end point was fatigue at 90 days measured by the Multidimensional Fatigue Inventory-20 general fatigue domain......BACKGROUND AND PURPOSE: Poststroke fatigue is common and reduces quality of life. Current evidence for intervention is limited, and this is the first placebo-controlled trial to investigate treatment of poststroke fatigue with the wakefulness promoting drug modafinil. METHODS: The trial....... Secondary end points included the Fatigue Severity Scale, the Montreal Cognitive Assessment, the modified Rankin Scale and the Stroke-specific quality of Life questionnaire. Adult patients with a recent stroke achieving a score of ≥12 on the Multidimensional Fatigue Inventory-20 general fatigue domain were...

  5. 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.)

  6. Near threshold fatigue testing

    Science.gov (United States)

    Freeman, D. C.; Strum, M. J.

    1993-01-01

    Measurement of the near-threshold fatigue crack growth rate (FCGR) behavior provides a basis for the design and evaluation of components subjected to high cycle fatigue. Typically, the near-threshold fatigue regime describes crack growth rates below approximately 10(exp -5) mm/cycle (4 x 10(exp -7) inch/cycle). One such evaluation was recently performed for the binary alloy U-6Nb. The procedures developed for this evaluation are described in detail to provide a general test method for near-threshold FCGR testing. In particular, techniques for high-resolution measurements of crack length performed in-situ through a direct current, potential drop (DCPD) apparatus, and a method which eliminates crack closure effects through the use of loading cycles with constant maximum stress intensity are described.

  7. Fatigue Strength of Weathering Steel

    Czech Academy of Sciences Publication Activity Database

    Kunz, Ludvík; Lukáš, Petr; Klusák, Jan

    2012-01-01

    Roč. 18, č. 1 (2012), s. 18-22 ISSN 1392-1320 Grant - others:GA MPO(CZ) FT/TA5/076 Institutional support: RVO:68081723 Keywords : fatigue of weathering steel * corrosion pits * fatigue notch factor Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 0.522, year: 2012

  8. Fatigue data compilation and evaluation of fatigue on design

    International Nuclear Information System (INIS)

    Nyilas, A.

    1985-05-01

    The aim of this report is a review of the available fatigue data of various materials necessary for the design of large superconducting magnets for fusion. One of the primary objectives of this work is to present a broad outline of the low temperature fatigue data of relevant materials within the scope of available data. Besides the classical fatigue data of materials the fatigue crack propagation measurements are outlined widely. The existing recommendations for the design of cryogenic structures are described. A brief introduction of fracture mechanics as well as a historical background of the development of our present day understanding of fatigue has been done. (orig.) [de

  9. Residual Fatigue Properties of Asphalt Pavement after Long-Term Field Service

    Directory of Open Access Journals (Sweden)

    Peide Cui

    2018-05-01

    Full Text Available Asphalt pavement is widely used for expressways due to its advantages of flexibility, low cost, and easy maintenance. However, pavement failures, including cracking, raveling, and potholes, will appear after long-term service. This research evaluated the residual fatigue properties of asphalt pavement after long-term field service. Fatigue behavior of specimens with different pavement failure types, traffic load, service time, and layers were collected and characterized. Results indicate that after long-term field service, surface layer has a longer fatigue life under small stress levels, but shorter fatigue life under large stress levels. Longer service time results in greater sensitivity to loading stress, while heavier traffic results in shorter fatigue life. Surface and underneath layers present very close fatigue trend lines in some areas, indicating that the fatigue behavior of asphalt mixture in surface and underneath layers are aged to the same extent after eight to ten years of field service.

  10. Fatigue and thermal fatigue of Pb-Sn solder joints

    International Nuclear Information System (INIS)

    Frear, D.; Grivas, D.; McCormack, M.; Tribula, D.; Morris, J.W. Jr.

    1987-01-01

    This paper presents a fundamental investigation of the fatigue and thermal fatigue characteristics, with an emphasis on the microstructural development during fatigue, of Sn-Pb solder joints. Fatigue tests were performed in simple shear on both 60Sn-40Pb and 5Sn-95Pb solder joints. Isothermal fatigue tests show increasing fatigue life of 60Sn-40Pb solder joints with decreasing strain and temperature. In contrast, such behavior was not observed in the isothermal fatigue of 5Sn-95Pb solder joints. Thermal fatigue results on 60Sn-40Pb solder cycled between -55 0 C and 125 0 C show that a coarsened region develops in the center of the joint. Both Pb-rich and Sn-rich phases coarsen, and cracks form within these coarsened regions. The failure mode 60Sn-40Pb solder joints in thermal and isothermal fatigue is similar: cracks form intergranularly through the Sn-rich phase or along Sn/Pb interphase boundaries. Extensive cracking is found throughout the 5Sn-95Pb joint for both thermal and isothermal fatigue. In thermal fatigue the 5Sn-95Pb solder joints failed after fewer cycles than 60Sn-40Pb

  11. The Nature of Fatigue in Chronic Fatigue Syndrome.

    Science.gov (United States)

    Olson, Karin; Zimka, Oksana; Stein, Eleanor

    2015-10-01

    In this article, we report the findings of our study on the nature of fatigue in patients diagnosed with chronic fatigue syndrome. Using ethnoscience as a design, we conducted a series of unstructured interviews and card sorts to learn more about how people with chronic fatigue syndrome describe fatigue. Participants (N = 14) described three distinct domains: tiredness, fatigue, and exhaustion. Most participants experienced tiredness prior to diagnosis, fatigue during daily life, and exhaustion after overexertion. We also discuss participants' ability to adapt to a variety of stressors and prevent shifts to exhaustion, and relate our findings to stress theory and other current research. Primary strategies that promoted adaptation to stressors included pacing and extended rest periods. These findings can aid health care professionals in detecting impending shifts between tiredness, fatigue, and exhaustion and in improving adaptive strategies, thereby improving quality of life. © The Author(s) 2015.

  12. 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.

  13. 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

  14. Chronic fatigue syndrome.

    NARCIS (Netherlands)

    Prins, J.B.; Meer, J.W.M. van der; Bleijenberg, G.

    2006-01-01

    During the past two decades, there has been heated debate about chronic fatigue syndrome (CFS) among researchers, practitioners, and patients. Few illnesses have been discussed so extensively. The existence of the disorder has been questioned, its underlying pathophysiology debated, and an effective

  15. 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…

  16. Are nurses able to assess fatigue, exertion fatigue and types of fatigue in residential home patients?

    NARCIS (Netherlands)

    Tiesinga, L.J.; Dijkstra, Ate; Dassen, T.W.N.; Halfens, R.J.G.; van den Heuvel, W.J.A.

    Although fatigue is recognized as a subjective, generalized, extensive and disabling health care problem with a relatively high prevalence among the chronically ill, there have been no studies to show whether nurses caring for fatigued subjects are able to accurately assess the level of fatigue that

  17. Muscle Deoxygenation Causes Muscle Fatigue

    Science.gov (United States)

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

    1999-01-01

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

  18. Designing Fatigue Warning Systems: The perspective of professional drivers.

    Science.gov (United States)

    Meng, Fanxing; Li, Shuling; Cao, Lingzhi; Peng, Qijia; Li, Musen; Wang, Chunhui; Zhang, Wei

    2016-03-01

    Professional drivers have been characterized as experiencing heavy fatigue resulting from long driving time in their daily work. This study aimed to explore the potential demand of Fatigue Warning Systems (FWSs) among professional drivers as a means of reducing the danger of fatigue driving and to examine their opinions regarding the design of FWSs. Six focus groups with 35 participants and a questionnaire survey with 600 respondents were conducted among Chinese truck and taxi drivers to collect qualitative and quantitative data concerning the current situation of fatigue driving and opinions regarding the design of FWSs. The results revealed that both truck and taxi drivers had a positive attitude toward FWSs, and they hoped this system could not only monitor and warn them regarding their fatigue but also somewhat relieve their fatigue before they could stop and rest. As for warning signals, participants preferred auditory warnings, as opposed to visual, vibrotactile or electric stimuli. Interestingly, it was proposed that verbal warnings involving the information regarding consequences of fatigue driving or the wishes of drivers' family members would be more effective. Additionally, different warning patterns, including graded, single and continuous warnings, were discussed in the focus group. Finally, the participants proposed many other suggestions, as well as their concerns regarding FWSs, which will provide valuable information for companies who wish to develop FWSs for professional drivers. Copyright © 2015. Published by Elsevier Ltd.

  19. Fatigue failure analysis of V-4Ti-4Cr alloy

    International Nuclear Information System (INIS)

    Aglan, H.; Gan, Y.X.; Grossbeck, M.

    1999-01-01

    In the present work, the fatigue fracture and failure behavior of a V-4Ti-4Cr has been studied. Static tests were conducted to study the overloading behavior and to select the magnitude of the stress level for the fatigue studies. Fatigue tests were performed using single edge notched (SEN) specimens under tension-tension load control conditions. Fatigue crack propagation (FCP) data such as the crack length, number of cycles, and hysteresis loops were recorded to calculate the crack speed, the energy release rate, and the change in work expended on damage formation and dissipative processes within the material. Parameters characterizing the fatigue fracture resistance of V-4Ti-4Cr alloy, namely the specific energy of damage (γ'), and the dissipative coefficient (β'), were determined from the fatigue data using the modified crack layer (MCL) theory. Fracture surface examination using scanning electron microscopy (SEM) revealed ductile failure mechanisms under tensile overloading conditions. The fatigue fracture surface of the V-4Ti-4Cr consists of three distinct regions, corresponding to the threshold, stable and unstable crack propagation stages. (orig.)

  20. Syndrome de fatigue chronique: Revue de la littérature

    OpenAIRE

    Turgeon, Sue A.

    1991-01-01

    Chronic fatigue syndrome, previously known as chronic mononucleosis or post-infectious faligue, is a poorly understood illness characterized by chronic debilitating fatigue, recurrent flu-like symptoms, and few clinical or laboratory abnormalities. While a significant incidence of psychiatric illness has been demonstrated among patients with the chronic fatigue syndrome, there is also evidence of subtle immune system abnormalities, leading some researchers to postulate a multi-fatorial psycho...

  1. Fractal cluster modeling of the fatigue behavior of lead zirconate titanate

    OpenAIRE

    Priya, Shashank; Kim, Hyeoung Woo; Ryu, Jungho; Uchino, Kenji; Viehland, Dwight D.

    2002-01-01

    The fatigue behavior of lead zirconate titanate ceramics (PZT) has been studied under electrical and mechanical drives. Piezoelectric fatigue was studied using a mechanical method. Under ac mechanical drive, hard and soft PZTs showed an increase in the longitudinal piezoelectric constant at short times, reaching a maximum at intermediate times. Systematic investigations were performed to characterize the electrical fatigue behavior. A decrease in the magnitude of the remanent polarization was...

  2. Fatigue crack propagation in additively manufactured porous biomaterials.

    Science.gov (United States)

    Hedayati, R; Amin Yavari, S; Zadpoor, A A

    2017-07-01

    Additively manufactured porous titanium implants, in addition to preserving the excellent biocompatible properties of titanium, have very small stiffness values comparable to those of natural bones. Although usually loaded in compression, biomedical implants can also be under tensional, shear, and bending loads which leads to crack initiation and propagation in their critical points. In this study, the static and fatigue crack propagation in additively manufactured porous biomaterials with porosities between 66% and 84% is investigated using compact-tension (CT) samples. The samples were made using selective laser melting from Ti-6Al-4V and were loaded in tension (in static study) and tension-tension (in fatigue study) loadings. The results showed that displacement accumulation diagram obtained for different CT samples under cyclic loading had several similarities with the corresponding diagrams obtained for cylindrical samples under compression-compression cyclic loadings (in particular, it showed a two-stage behavior). For a load level equaling 50% of the yield load, both the CT specimens studied here and the cylindrical samples we had tested under compression-compression cyclic loading elsewhere exhibited similar fatigue lives of around 10 4 cycles. The test results also showed that for the same load level of 0.5F y , the lower density porous structures demonstrate relatively longer lives than the higher-density ones. This is because the high bending stresses in high-density porous structures gives rise to local Mode-I crack opening in the rough external surface of the struts which leads to quicker formation and propagation of the cracks. Under both the static and cyclic loading, all the samples showed crack pathways which were not parallel to but made 45 ° angles with respect to the notch direction. This is due to the fact that in the rhombic dodecahedron unit cell, the weakest struts are located in 45 ° direction with respect to the notch direction

  3. Deformation Parameters and Fatigue of the Recycled Asphalt Mixtures

    Directory of Open Access Journals (Sweden)

    Šrámek Juraj

    2015-12-01

    Full Text Available The deformational properties of asphalt mixtures measured by dynamic methods and fatigue allow a design the road to suit the expected traffic load. Quality of mixtures is also expressed by the resistance to permanent deformation. Complex modulus of stiffness and fatigue can reliably characterize the proposed mixture of asphalt pavement. The complex modulus (E* measurement of asphalt mixtures are carried out in laboratory of Department of Construction Management at University of Žilina by two-point bending test method on trapezoid-shaped samples. Today, the fatigue is verified on trapezoid-shaped samples and is assessed by proportional strain at 1 million cycles (ε6. The test equipment and software is used to evaluate fatigue and deformation characteristics.

  4. Fatigue Experiences Among OCD Outpatients.

    Science.gov (United States)

    Pasquini, Massimo; Piacentino, Daria; Berardelli, Isabella; Roselli, Valentina; Maraone, Annalisa; Tarsitani, Lorenzo; Biondi, Massimo

    2015-12-01

    Patients with OCD are impaired in multiple domains of functioning and quality of life. While associated psychopathology complaints and neuropsychological deficits were reported, the subjective experience of general fatigue and mental fatigue was scarcely investigated. In this single-center case-control study we compared 50 non-depressed OCD outpatients consecutively recruited and 50 panic disorder (PD) outpatients, to determine whether they experienced fatigue differently. Assessment consisted of structured clinical interview for DSM-IV criteria by using the SCID-I and the SCID-II. Symptom severity was assessed using the Yale-Brown Obsessive-Compulsive Scale, the Hamilton Anxiety Rating Scale, the Hamilton Depression Rating Scale, the Clinical Global Impressions Scale, severity and the Global Assessment of Functioning Scale. Fatigue was assessed by using the Multidimensional Fatigue Inventory (MFI). Regarding MFI physical fatigue, an OR of 0.196 (95 % CI 0.080-0.478) was found, suggesting that its presence is associated with lower odds of OCD compared to PD. The same can be said for MFI mental fatigue, as an OR of 0.138 (95 % CI 0.049-0.326) was found, suggesting that its presence is associated with lower odds of OCD. Notably, OCD patients with OCDP co-morbidity reported higher scores of mental fatigue. In this study fatigue, including mental fatigue, seems not to be a prominent experience among adult non-depressed OCD patients.

  5. Caffeine, fatigue, and cognition.

    Science.gov (United States)

    Lorist, Monicque M; Tops, Mattie

    2003-10-01

    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 the general belief that caffeine acts as a stimulant. Studies using ERP measures indicate that caffeine has an effect on attention, which is independent of specific stimulus characteristics. Behavioural effects on response related processes turned out to be mainly related to more peripheral motor processes. Recent insights in adenosine and dopamine physiology and functionality and their relationships with fatigue point to a possible modulation by caffeine of mechanisms involved in the regulation of behavioural energy expenditure.

  6. Fatigue 󈨛. Volume 1,

    Science.gov (United States)

    1987-06-01

    277 FATIGUE 87 da/dn (m/ ciclo ) 10 - 07 10 - 08 10 - 0 9 R=0.5 S* • -Long Crack 10-10 e Smax = 195 MPa *Smax = 205 MPa 1Smax = 225 MPa 0.5 1 5 10 AK...MPa/m) Figure 1 Crack growth rate vs stress intensity factor range 10 . da/dn (m/ ciclo ) i0 - ° 09 i0-o -Long crack 10 . ° Smax = 10 Pa 10 Smax...120 NPa Smax = 145 NlPa 0.5 I 10 AKN~~)50 Figure 2 Crack growth rate vs stress intensity factor range 278 FATIGUE 87 da/dn (m/ ciclo ) 10- 10- 0 7 % 10

  7. Effects of fretting fatigue on the residual stress of shot peened Ti-6Al-4V samples

    International Nuclear Information System (INIS)

    Martinez, S.A.; Sathish, S.; Blodgett, M.P.; Mall, S.; Namjoshi, S.

    2005-01-01

    X-ray diffraction residual stress measurement has been utilized as nondestructive tool for the characterization of fretting fatigue damage in shot peened samples of Ti-6Al-4V. Prior to fretting fatigue damage, compressive residual stresses were found to be uniform over the entire face of the sample and independent of the measurement direction. After fretting fatigue, inside and in the vicinity of the fretting damage zone large relaxation of compressive residual stress was observed. An anisotropic residual stress distribution has been observed in the fretting fatigue damaged region. Residual stress measurements in interrupted fretting fatigue experiments showed that the relaxation of residual stress increases as the number of fretting fatigue cycles increase. The results are discussed in the light of their importance in establishing X-ray diffraction residual stress measurement technique as a nondestructive tool to characterize fretting fatigue damage

  8. Recovery from Fatigue

    Science.gov (United States)

    1973-06-30

    functioning to replace sleep or recover from fatigue. Possibly the hypnagogic period of descending Stage I, apparently perceived differently S-1 of...partly to quality of mentation during the Stage I hypnagogic period. It may well be that nappers belong to the group described by Foulkes, Spear, and...Symonds (1966) who engage in hypnagogic mentation, and this is clearly perceived by them as different from sleep. The present study suggests that napping

  9. 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.

  10. Deformation Properties and Fatigue of Bituminous Mixtures

    Directory of Open Access Journals (Sweden)

    Frantisek Schlosser

    2013-01-01

    Full Text Available Deformation properties and fatigue performance are important characteristics of asphalt bound materials which are used for construction of pavement layers. Viscoelastic asphalt mixtures are better characterized via dynamic tests. This type of tests allows us to collate materials with regard to axle vibrations which lie usually in the range of 6 Hz–25 Hz for standard conditions. Asphalt modified for heat sensitivity in the range from −20°C to +60°C has significant impact on the overall characteristics of the mixture. Deformation properties are used as inputs for empirical mixture design, and fatigue performance of asphalt mixtures reflects the parameters of functional tests. Master curves convey properties of asphalt mixtures for various conditions and allow us to evaluate them without the need of time expensive testing.

  11. Probabilistic Fatigue Damage Program (FATIG)

    Science.gov (United States)

    Michalopoulos, Constantine

    2012-01-01

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

  12. Increase in Prefrontal Cortical Volume following Cognitive Behavioural Therapy in Patients with Chronic Fatigue Syndrome

    Science.gov (United States)

    de Lange, Floris P.; Koers, Anda; Kalkman, Joke S.; Bleijenberg, Gijs; Hagoort, Peter; van der Meer, Jos W. M.; Toni, Ivan

    2008-01-01

    Chronic fatigue syndrome (CFS) is a disabling disorder, characterized by persistent or relapsing fatigue. Recent studies have detected a decrease in cortical grey matter volume in patients with CFS, but it is unclear whether this cerebral atrophy constitutes a cause or a consequence of the disease. Cognitive behavioural therapy (CBT) is an…

  13. Effect of temperature upon the fatigue-crack propagation behavior of Inconel X-750

    International Nuclear Information System (INIS)

    James, L.A.

    1976-05-01

    The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of precipitation heat-treated Inconel X-750 in an air environment over the range 75-1200 0 F. In general, fatigue-crack growth rates increased with increasing test temperature

  14. The creep-fatigue crack growth behaviour of a 1CrMoV rotor steel

    International Nuclear Information System (INIS)

    Priest, R.H.; Miller, D.A.; Gladwin, D.N.; Maguire, J.

    1989-01-01

    Crack growth rates under simultaneous creep-fatigue conditions have been quantified for a 1CrMoV rotor steel. Measured growth rates were partitioned into cyclic and hold period contributions and these characterized by the relevant fracture mechanics parameters K and C. Cyclic growth rates measured in the creep-fatigue tests were enhanced compared with pure fatigue rates. This observation is compared with the behaviour of other steels and explained by quantitative metallography. The resulting crack growth equation can be used during integrity assessments for plant components containing cracks which are subject to thermal fatigue

  15. Surface crack nucleation and propagation in electrodeposited nanocrystalline Ni-P alloy during high cycle fatigue

    Energy Technology Data Exchange (ETDEWEB)

    Kobayashi, Shigeaki; Kamata, Akiyuki [Department of Mechanical Engineering, Faculty of Engineering, Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558 (Japan); Watanabe, Tadao, E-mail: skoba@ashitech.ac.j [Key Laboratory for Anisotropy and Texture of Materials, Northeastern University, Shenyang, 110004 (China)

    2010-07-01

    The morphology of specimen surface after fatigue fracture was evaluated in connection with grain orientation distribution and grain boundary microstructure to reveal a mechanism of fatigue fracture in nanocrystalline materials. The electrodeposited and sharply {l_brace}001{r_brace} textured Ni -2.0 mass% P alloy with the average grain size of ca. 45 nm and high fractions of low-angle and {Sigma}3 boundaries showed 2 times higher fatigue limit than electrodeposited microcrystalline Ni polycrystal. The surface features of fatigued specimen were classified into two different types of morphologies characterized as brittle fracture at the central area and as ductile fracture at the surrounding area.

  16. A sociological stance on fatigue and tiredness: Social inequalities, norms and representations.

    Science.gov (United States)

    Loriol, Marc

    2017-04-01

    Fatigue is complex, representing simultaneously a physiological, psychological and social phenomenon. The sociological approach attempts to understand the experience of fatigue and its characterization at diverse periods and in various social contexts. After giving a sociological history of different forms of fatigue through the ages (acedia, melancholy, neurasthenia, chronic fatigue syndrome, etc.), this article proposes a social epidemiology of fatigue in the current period. Objectification of working and living conditions allows us to illustrate social inequalities in fatigue and exhaustion, but seems to contradict dominant social representations of fatigue today. It invites a critical discussion of contemporary theories of fatigue (such those of Alain Ehrenberg or Byung-Chul Han), which consider that fatigue is a condition of modern man, overwhelmed by his freedom. More modestly, analysis of the fatigue presented here rests on the capacity to be able to find a good balance between too much investment in work or life (which is exhausting) and not enough investment (which leads to boredom and lack of self-fulfillment). This balance depends on fragile and specific social norms in different professional or social circles and cannot be defined a priori. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  17. Research on Fatigue Damage of Compressor Blade Steel KMN-I Using Nonlinear Ultrasonic Testing

    Directory of Open Access Journals (Sweden)

    Pengfei Wang

    2017-01-01

    Full Text Available The fatigue damage of compressor blade steel KMN-I was investigated using nonlinear ultrasonic testing and the relation curve between the material nonlinearity parameter β and the fatigue life was obtained. The results showed that the nonlinearity parameter increased first and then decreased with the increase of the fatigue cycles. The microstructures were observed by scanning electron microscopy (SEM. It was found that some small defects like holes and pits appeared in the material matrix with the increase of the fatigue cycles, and the nonlinearity parameter increased correspondingly. The nonlinearity parameter reached the peak value when the microcracks initiated, and the nonlinearity parameter began to decrease when the microcracks further propagated to macrocracks. Therefore, it is proved that the nonlinearity parameter can be used to characterize the initiation of microcracks at the early stage of fatigue, and a method of evaluating the fatigue life of materials by nonlinear ultrasonic testing is proposed.

  18. Mechanism of fatigue crack initiation in austenitic stainless steels in light water reactor environments

    International Nuclear Information System (INIS)

    Chopra, O.K.; Shack, W.J.; Muscara, J.

    2003-01-01

    This paper examines the mechanism of fatigue crack initiation in austenitic stainless steels (SSs) in light water reactor (LWR) coolant environments. The effects of key material and loading variables on the fatigue lives of wrought and cast austenitic SSs in air and LWR environments have been evaluated. The influence of reactor coolant environments on the formation and growth of fatigue cracks in polished smooth SS specimens is discussed. The results indicate that the fatigue lives of these steels are decreased primarily by the effects of the environment on the growth of cracks <200 μm and, to a lesser extent, on enhanced growth rates of longer cracks. The fracture morphology in the specimens has been characterized. Exploratory fatigue tests were conducted to study the effects of surface micropits or minor differences in the surface oxide on fatigue crack initiation. (author)

  19. Translating Fatigue to Human Performance

    Science.gov (United States)

    Enoka, Roger M.; Duchateau, Jacques

    2016-01-01

    Despite flourishing interest in the topic of fatigue—as indicated by the many presentations on fatigue at the 2015 annual meeting of the American College of Sports Medicine—surprisingly little is known about its impact on human performance. There are two main reasons for this dilemma: (1) the inability of current terminology to accommodate the scope of the conditions ascribed to fatigue, and (2) a paucity of validated experimental models. In contrast to current practice, a case is made for a unified definition of fatigue to facilitate its management in health and disease. Based on the classic two-domain concept of Mosso, fatigue is defined as a disabling symptom in which physical and cognitive function is limited by interactions between performance fatigability and perceived fatigability. As a symptom, fatigue can only be measured by self-report, quantified as either a trait characteristic or a state variable. One consequence of such a definition is that the word fatigue should not be preceded by an adjective (e.g., central, mental, muscle, peripheral, and supraspinal) to suggest the locus of the changes responsible for an observed level of fatigue. Rather, mechanistic studies should be performed with validated experimental models to identify the changes responsible for the reported fatigue. As indicated by three examples (walking endurance in old adults, time trials by endurance athletes, and fatigue in persons with multiple sclerosis) discussed in the review, however, it has proven challenging to develop valid experimental models of fatigue. The proposed framework provides a foundation to address the many gaps in knowledge of how laboratory measures of fatigue and fatigability impact real-world performance. PMID:27015386

  20. Ultrathin flexible piezoelectric sensors for monitoring eye fatigue

    Science.gov (United States)

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

    2018-02-01

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

  1. Fatigue and fracture: Overview

    Science.gov (United States)

    Halford, G. R.

    1984-01-01

    A brief overview of the status of the fatigue and fracture programs is given. The programs involve the development of appropriate analytic material behavior models for cyclic stress-strain-temperature-time/cyclic crack initiation, and cyclic crack propagation. The underlying thrust of these programs is the development and verification of workable engineering methods for the calculation, in advance of service, of the local cyclic stress-strain response at the critical life governing location in hot section compounds, and the resultant crack initiation and crack growth lifetimes.

  2. Multidimensional fatigue and its correlates in hospitalised advanced cancer patients.

    NARCIS (Netherlands)

    Echteld, M.A.; Passchier, J.; Teunissen, S.; Claessen, S.; Wit, R. de; Rijt, C.C.D. van der

    2007-01-01

    Although fatigue is a multidimensional concept, multidimensional fatigue is rarely investigated in hospitalised cancer patients. We determined the levels and correlates of multidimensional fatigue in 100 advanced cancer patients admitted for symptom control. Fatigue dimensions were general fatigue

  3. Mode-I Fracture Toughness Testing and Coupled Cohesive Zone Modeling at In Situ P, T, and Chemical (H2O-CO2-NaCl) Conditions

    Science.gov (United States)

    Dewers, T. A.; Choens, R. C., II; Regueiro, R. A.; Eichhubl, P.; Bryan, C. R.; Rinehart, A. J.; Su, J. C.; Heath, J. E.

    2017-12-01

    Propagation of mode I cracks is fundamental to subsurface engineering endeavors, but the majority of fracture toughness measurements are performed at ambient conditions. A novel testing apparatus was used to quantify the relationship between supercritical carbon dioxide (scCO2), water vapor, and fracture toughness in analogs for reservoir rock and caprock lithologies at temperature and pressure conditions relevant to geologic carbon storage. Samples of Boise Sandstone and Marcellus Shale were subject to fracture propagation via a novel short rod fracture toughness tester composed of titanium and Hastelloy® and designed to fit inside a pressure vessel. The tester is controlled by a hydraulically-driven ram and instrumented with a LVDT to monitor displacement. We measure fracture toughness under conditions of dry supercritical CO2 (scCO2), scCO2-saturated brine, and scCO2 with varying water content ( 25%, 90%, and 100% humidity) at 13.8 MPa and 70oC. Water film development as a function of humidity is determined in situ during the experiments with a quartz crystal microbalance. Two orientations of the Marcellus are included in the testing matrix. Dry CO2 has a negligible to slightly strengthening effect compared to a control, however hydrous scCO2 can decrease the fracture toughness, and the effect increases with increasing humidity, which likely is due to capillary condensation of reactive water films at nascent crack tips and associated subcritical weakening. A 2D poromechanical finite element model with cohesive surface elements (CSEs) and a chemo-plasticity phenomenology is being used to describe the chemical weakening/softening effects observed in the testing. The reductions in fracture toughness seen in this study could be important in considerations of borehole stability, in situ stress measurements, changes in fracture gradient, and reservoir caprock integrity during CO2 injection and storage. Sandia National Laboratories is a multimission laboratory managed

  4. Neuromuscular Fatigue During 200 M Breaststroke

    Directory of Open Access Journals (Sweden)

    Ana Conceição

    2014-03-01

    Full Text Available The aims of this study were: i to analyze activation patterns of four upper limb muscles (duration of the active and non-active phase in each lap of 200m breaststroke, ii quantify neuromuscular fatigue, with kinematics and physiologic assessment. Surface electromyogram was collected for the biceps brachii, deltoid anterior, pectoralis major and triceps brachii of nine male swimmers performing a maximal 200m breaststroke trial. Swimming speed, SL, SR, SI decreased from the 1st to the 3rd lap. SR increased on the 4th lap (35.91 ± 2.99 stroke·min-1. Peak blood lactate was 13.02 ± 1.72 mmol·l-1 three minutes after the maximal trial. The EMG average rectified value (ARV increased at the end of the race for all selected muscles, but the deltoid anterior and pectoralis major in the 1st lap and for biceps brachii, deltoid anterior and triceps brachii in the 4th lap. The mean frequency of the power spectral density (MNF decreased at the 4th lap for all muscles. These findings suggest the occurrence of fatigue at the beginning of the 2nd lap in the 200m breaststroke trial, characterized by changes in kinematic parameters and selective changes in upper limb muscle action. There was a trend towards a non-linear fatigue state.

  5. Fatigue of Concrete Armour Units

    DEFF Research Database (Denmark)

    Sørensen, N. B.; Burcharth, H. F.; Liu, Z.

    1995-01-01

    In the present article fatigue as a possible reason for failure of Dolosse armour units made of plain concrete is discussed.......In the present article fatigue as a possible reason for failure of Dolosse armour units made of plain concrete is discussed....

  6. Fatigue test on aluminium bridges

    NARCIS (Netherlands)

    Maljaars, J.; Soetens, F.; Straalen, van IJ.J.

    2005-01-01

    Traffic bridges are subjected to variable loads and should therefore be checked on fatigue. Especially low weight materials, like aluminium, are sensitive to fatigue, because the variable load is a substantial part of the total load. This paper shows the structural design of an aluminium bridge

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

    International Nuclear Information System (INIS)

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

    2013-01-01

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

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

    International Nuclear Information System (INIS)

    Heinz, Benedikt; Bergholz, Steffen; Rudolph, Juergen

    2011-01-01

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

  9. Research on driver fatigue detection

    Science.gov (United States)

    Zhang, Ting; Chen, Zhong; Ouyang, Chao

    2018-03-01

    Driver fatigue is one of the main causes of frequent traffic accidents. In this case, driver fatigue detection system has very important significance in avoiding traffic accidents. This paper presents a real-time method based on fusion of multiple facial features, including eye closure, yawn and head movement. The eye state is classified as being open or closed by a linear SVM classifier trained using HOG features of the detected eye. The mouth state is determined according to the width-height ratio of the mouth. The head movement is detected by head pitch angle calculated by facial landmark. The driver's fatigue state can be reasoned by the model trained by above features. According to experimental results, drive fatigue detection obtains an excellent performance. It indicates that the developed method is valuable for the application of avoiding traffic accidents caused by driver's fatigue.

  10. Roughness Effects on Fretting Fatigue

    Science.gov (United States)

    Yue, Tongyan; Abdel Wahab, Magd

    2017-05-01

    Fretting is a small oscillatory relative motion between two normal loaded contact surfaces. It may cause fretting fatigue, fretting wear and/or fretting corrosion damage depending on various fretting couples and working conditions. Fretting fatigue usually occurs at partial slip condition, and results in catastrophic failure at the stress levels below the fatigue limit of the material. Many parameters may affect fretting behaviour, including the applied normal load and displacement, material properties, roughness of the contact surfaces, frequency, etc. Since fretting damage is undesirable due to contacting, the effect of rough contact surfaces on fretting damage has been studied by many researchers. Experimental method on this topic is usually focusing on rough surface effects by finishing treatment and random rough surface effects in order to increase fretting fatigue life. However, most of numerical models on roughness are based on random surface. This paper reviewed both experimental and numerical methodology on the rough surface effects on fretting fatigue.

  11. Daily cytokine fluctuations, driven by leptin, are associated with fatigue severity in chronic fatigue syndrome: evidence of inflammatory pathology.

    Science.gov (United States)

    Stringer, Elizabeth Ann; Baker, Katharine Susanne; Carroll, Ian R; Montoya, Jose G; Chu, Lily; Maecker, Holden T; Younger, Jarred W

    2013-04-09

    Chronic fatigue syndrome (CFS) is a debilitating disorder characterized by persistent fatigue that is not alleviated by rest. The lack of a clearly identified underlying mechanism has hindered the development of effective treatments. Studies have demonstrated elevated levels of inflammatory factors in patients with CFS, but findings are contradictory across studies and no biomarkers have been consistently supported. Single time-point approaches potentially overlook important features of CFS, such as fluctuations in fatigue severity. We have observed that individuals with CFS demonstrate significant day-to-day variability in their fatigue severity. Therefore, to complement previous studies, we implemented a novel longitudinal study design to investigate the role of cytokines in CFS pathophysiology. Ten women meeting the Fukuda diagnostic criteria for CFS and ten healthy age- and body mass index (BMI)-matched women underwent 25 consecutive days of blood draws and self-reporting of symptom severity. A 51-plex cytokine panel via Luminex was performed for each of the 500 serum samples collected. Our primary hypothesis was that daily fatigue severity would be significantly correlated with the inflammatory adipokine leptin, in the women with CFS and not in the healthy control women. As a post-hoc analysis, a machine learning algorithm using all 51 cytokines was implemented to determine whether immune factors could distinguish high from low fatigue days. Self-reported fatigue severity was significantly correlated with leptin levels in six of the participants with CFS and one healthy control, supporting our primary hypothesis. The machine learning algorithm distinguished high from low fatigue days in the CFS group with 78.3% accuracy. Our results support the role of cytokines in the pathophysiology of CFS.

  12. Simplified elastoplastic fatigue analysis

    International Nuclear Information System (INIS)

    Autrusson, B.; Acker, D.; Hoffmann, A.

    1987-01-01

    Oligocyclic fatigue behaviour is a function of the local strain range. The design codes ASME section III, RCC-M, Code Case N47, RCC-MR, and the Guide issued by PNC propose simplified methods to evaluate the local strain range. After having briefly described these simplified methods, we tested them by comparing the results of experimental strains with those predicted by these rules. The experiments conducted for this study involved perforated plates under tensile stress, notched or reinforced beams under four-point bending stress, grooved specimens under tensile-compressive stress, and embedded grooved beams under bending stress. They display a relative conservatism depending on each case. The evaluation of the strains of rather inaccurate and sometimes lacks conservatism. So far, the proposal is to use the finite element codes with a simple model. The isotropic model with the cyclic consolidation curve offers a good representation of the real equivalent strain. There is obviously no question of representing the cycles and the entire loading history, but merely of calculating the maximum variation in elastoplastic equivalent deformations with a constant-rate loading. The results presented testify to the good prediction of the strains with this model. The maximum equivalent strain will be employed to evaluate fatigue damage

  13. Understanding postoperative fatigue.

    Science.gov (United States)

    Rose, E A; King, T C

    1978-07-01

    Performance characteristics of the central nervous, cardiovascular, respiratory and muscular systems in man postoperatively have received little investigative attention, despite the well known syndrome of postoperative fatigue. The impairmen in perception and psychomotor skills that has been shown to result from caloric restriction, bedrest, sedation and sleep deprivation suggests that a similar deficit may occur after surgical procedures. After a simple elective surgical procedure, maximal oxygen uptake decreases and the adaptability of heart rate to submaximal workloads is impaired. Similar deleterious effects on cardiorespiratory performance have been documented with starvation and bedrest; an understanding of cardiorespiratory performance postoperatively awaits further investigation. Maximal muscular force of contraction is also impaired by caloric restriction and bedrest, suggesting that similar effects may be seen in the postoperative state, although this has not been studied. A better understanding of the syndrome of postoperative fatigue could be achieved by a descriptive analysis of physiologic performance postoperatively. Such descriptive data could form the basis for objective evaluation of therapeutic measures intended to improve performance, such as nutritional supplementation and pharmacologic intervention. The observation that exercise with the patient in the supine position may decrease the impairment in maximal aerobic power otherwise expected in immobilized patients suggests that controlled exercise therapy may be of value in reducing physiologic impairment postoperatively.

  14. Diaphragmatic fatigue in man.

    Science.gov (United States)

    Roussos, C S; Macklem, P T

    1977-08-01

    The time required (tlim) to produce fatigue of the diaphragm was determined in three normal seated subjects, breathing through a variety of high alinear, inspiratory resistances. During each breath in all experimental runs the subject generated a transdiaphragmatic pressure (Pdi) which was a predetermined fraction of his maximum inspiratory Pdi (Pdimax) at functional residual capacity. The breathing test was performed until the subject was unable to generate this Pdi. The relationship between Pdi/Pdimax and tlim was curvilinear so that when Pdi/Pdimax was small tlim increased markedly for little changes in Pdi/Pdimax. The value of Pdi/Pdimax that could be generated indefinitely (Pdicrit) was around 0.4. Hypoxia appeared to have no influence on Pdicrit, but probably led to a reduction in tlim at Pdi greater than Pdicrit for equal rates of energy consumption. Insofar as the behavior of the diaphragm reflects that of other respiratory muscles it appears that quite high inspiratory loads can be tolerated indefinitely. However, when the energy consumption of the respiratory muscles exceeds a critical level, fatigue should develop. This may be a mechanism of respiratory failure in a variety in a variety of lung diseases.

  15. Estimation of fatigue life using electromechanical impedance technique

    Science.gov (United States)

    Lim, Yee Yan; Soh, Chee Kiong

    2010-04-01

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

  16. Fatigue and Damage Tolerance Analysis of a Hybrid Composite Tapered Flexbeam

    Science.gov (United States)

    Murri, Gretchen B.; Schaff, Jeffrey R.; Dobyns, Al

    2001-01-01

    region was predominantly mode I. The calculated peak G-values from either analysis predict delamination is most likely to occur along the same interface where it was observed in the test specimens. Calculated peak G values were used with material characterization data to calculate a curve relating the fatigue life of the specimens, N, to the applied transverse load, V, for a given constant axial load.

  17. Very High Cycle Fatigue Crack Initiation Mechanism in Nugget Zone of AA 7075 Friction Stir Welded Joint

    Directory of Open Access Journals (Sweden)

    Chao He

    2017-01-01

    Full Text Available Very high cycle fatigue behavior of nugget zone in AA 7075 friction stir welded joint was experimentally investigated using ultrasonic fatigue testing system (20 kHz to clarify the crack initiation mechanism. It was found that the fatigue strength of nugget zone decreased continuously even beyond 107 cycles with no traditional fatigue limits. Fatigue cracks initiated from the welding defects located at the bottom side of the friction stir weld. Moreover, a special semicircular zone could be characterized around the crack initiation site, of which the stress intensity factor approximately equaled the threshold of fatigue crack propagation rate. Finally, a simplified model was proposed to estimate the fatigue life by correlating the welding defect size and applied stress. The predicted results are in good agreement with the experimental results.

  18. Low cycle fatigue: high cycle fatigue damage accumulation in a 304L austenitic stainless steel; Endommagement et cumul de dommage en fatigue dans le domaine de l'endurance limitee d'un acier inoxydable austenitique 304L

    Energy Technology Data Exchange (ETDEWEB)

    Lehericy, Y

    2007-05-15

    The aim of this study was to evaluate the consequences of a Low Cycle Fatigue pre-damage on the subsequent fatigue limit of a 304L stainless steel. The effects of hardening and severe roughness (grinding) have also been investigated. In a first set of tests, the evolution of the surface damage induced by the different LCF pre-cycling was characterized. This has permitted to identify mechanisms and kinetics of damage in the plastic domain for different surface conditions. Then, pre-damaged samples were tested in the High Cycle Fatigue domain in order to establish the fatigue limits associated with each level of pre-damage. Results evidence that, in the case of polished samples, an important number of cycles is required to initiate surface cracks ant then to affect the fatigue limit of the material but, in the case of ground samples, a few number of cycles is sufficient to initiate cracks and to critically decrease the fatigue limit. The fatigue limit of pre-damaged samples can be estimated using the stress intensity factor threshold. Moreover, this detrimental effect of severe surface conditions is enhanced when fatigue tests are performed under a positive mean stress (author)

  19. Fatigue-crack propagation behavior of Inconel 600

    International Nuclear Information System (INIS)

    James, L.A.

    1976-05-01

    The techniques of linear-elastic fracture mechanics were employed to characterize the effects of several parameters upon the fatigue-crack propagation behavior of Inconel 600. The parameters studied included temperature, cyclic frequency, stress ratio, thermal aging, and a limited amount of testing in a liquid sodium environment

  20. Fatigue-crack propagation behavior of Inconel 718

    International Nuclear Information System (INIS)

    James, L.A.

    1975-09-01

    The techniques of linear-elastic fracture mechanics were used to characterize the effect of several variables (temperature, environment, cyclic frequency, stress ratio, and heat-treatment variations) upon the fatigue-crack growth behavior of Inconel 718 base metal and weldments. Relevant crack growth data on this alloy from other laboratories is also presented. (33 fig, 39 references)

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

    Science.gov (United States)

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

    2018-02-22

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

  2. Fracture mechanics and residual fatigue life analysis for complex stress fields. Technical report

    International Nuclear Information System (INIS)

    Besuner, P.M.

    1975-07-01

    This report reviews the development and application of an influence function method for calculating stress intensity factors and residual fatigue life for two- and three-dimensional structures with complex stress fields and geometries. Through elastic superposition, the method properly accounts for redistribution of stress as the crack grows through the structure. The analytical methods used and the computer programs necessary for computation and application of load independent influence functions are presented. A new exact solution is obtained for the buried elliptical crack, under an arbitrary Mode I stress field, for stress intensity factors at four positions around the crack front. The IF method is then applied to two fracture mechanics problems with complex stress fields and geometries. These problems are of current interest to the electric power generating industry and include (1) the fatigue analysis of a crack in a pipe weld under nominal and residual stresses and (2) fatigue analysis of a reactor pressure vessel nozzle corner crack under a complex bivariate stress field

  3. A comparison of fatigue crack growth in human enamel and hydroxyapatite.

    Science.gov (United States)

    Bajaj, Devendra; Nazari, Ahmad; Eidelman, Naomi; Arola, Dwayne D

    2008-12-01

    Cracks and craze lines are often observed in the enamel of human teeth, but they rarely cause tooth fracture. The present study evaluates fatigue crack growth in human enamel, and compares that to the fatigue response of sintered hydroxyapatite (HAp) with similar crystallinity, chemistry and density. Miniature inset compact tension (CT) specimens were prepared that embodied a small piece of enamel (N=8) or HAp (N=6). The specimens were subjected to mode I cyclic loads and the steady state crack growth responses were modeled using the Paris Law. Results showed that the fatigue crack growth exponent (m) for enamel (m=7.7+/-1.0) was similar to that for HAp (m=7.9+/-1.4), whereas the crack growth coefficient (C) for enamel (C=8.7 E-04 (mm/cycle)x(MPa m(0.5))(-m)) was significantly lower (pcrack growth in the enamel occurred primarily along the prism boundaries. In regions of decussation, the microstructure promoted microcracking, crack bridging, crack deflection and crack bifurcation. Working in concert, these mechanisms increased the crack growth resistance and resulted in a sensitivity to crack growth (m) similar to bone and lower than that of human dentin. These mechanisms of toughening were not observed in the crack growth response of the sintered HAp. While enamel is the most highly mineralized tissue of the human body, the microstructural arrangement of the prisms promotes exceptional resistance to crack growth.

  4. Fatigue testing of wood composites for aerogenerator blades. Pt. 11: Assessment of fatigue damage accumulation using a fatigue modulus approach

    Energy Technology Data Exchange (ETDEWEB)

    Hacker, C L; Ansell, M P [Bath Univ. (United Kingdom)

    1996-12-31

    Stress-strain hysteresis loops have been captured during fatigue tests performed at R=10 (compression-compression) and R=0.1 (tension-tension) on Khaya epoxy wood composites. A fatigue modulus approach, proposed by Hwang and Han in 1989, has been applied to the data and a relationship established between the initial change in fatigue modulus and fatigue life. By following changes in fatigue modulus during the first 100 test cycles it is possible to predict the life of the sample allowing rapid evaluation of the fatigue performance of wood composites. Fatigue modulus values have also been calculated for hysteresis loops captured during complex load - time history tests. Similar trends in change in fatigue modulus suggest that this approach could be used in complex loading conditions to evaluate fatigue damage accumulation and predict fatigue life. (Author)

  5. Very High Cycle Fatigue of Ni-Based Single-Crystal Superalloys at High Temperature

    Science.gov (United States)

    Cervellon, A.; Cormier, J.; Mauget, F.; Hervier, Z.; Nadot, Y.

    2018-05-01

    Very high cycle fatigue (VHCF) properties at high temperature of Ni-based single-crystal (SX) superalloys and of a directionally solidified (DS) superalloy have been investigated at 20 kHz and a temperature of 1000 °C. Under fully reversed conditions (R = - 1), no noticeable difference in VHCF lifetimes between all investigated alloys has been observed. Internal casting pores size is the main VHCF lifetime-controlling factor whatever the chemical composition of the alloys. Other types of microstructural defects (eutectics, carbides), if present, may act as stress concentration sites when the number of cycles exceed 109 cycles or when porosity is absent by applying a prior hot isostatic pressing treatment. For longer tests (> 30 hours), oxidation also controls the main crack initiation sites leading to a mode I crack initiation from oxidized layer. Under such conditions, alloy's resistance to oxidation has a prominent role in controlling the VHCF. When creep damage is present at high ratios (R ≥ 0.8), creep resistance of SX/DS alloys governs VHCF lifetime. Under such high mean stress conditions, SX alloys developed to retard the initiation and creep propagation of mode I micro-cracks from pores have better VHCF lifetimes.

  6. Mental Fatigue Affects Visual Selective Attention

    NARCIS (Netherlands)

    Faber, Leon G.; Maurits, Natasha M.; Lorist, Monicque M.

    2012-01-01

    Mental fatigue is a form of fatigue, induced by continuous task performance. Mentally fatigued people often report having a hard time keeping their attention focussed and being easily distracted. In this study, we examined the relation between mental fatigue, as induced by time on task, and

  7. Influence of Prior Fatigue Cycling on Creep Behavior of Reduced Activation Ferritic-Martensitic Steel

    Science.gov (United States)

    Sarkar, Aritra; Vijayanand, V. D.; Parameswaran, P.; Shankar, Vani; Sandhya, R.; Laha, K.; Mathew, M. D.; Jayakumar, T.; Rajendra Kumar, E.

    2014-06-01

    Creep tests were carried out at 823 K (550 °C) and 210 MPa on Reduced Activation Ferritic-Martensitic (RAFM) steel which was subjected to different extents of prior fatigue exposure at 823 K at a strain amplitude of ±0.6 pct to assess the effect of prior fatigue exposure on creep behavior. Extensive cyclic softening that characterized the fatigue damage was found to be immensely deleterious for creep strength of the tempered martensitic steel. Creep rupture life was reduced to 60 pct of that of the virgin steel when the steel was exposed to as low as 1 pct of fatigue life. However, creep life saturated after fatigue exposure of 40 pct. Increase in minimum creep rate and decrease in creep rupture ductility with a saturating trend were observed with prior fatigue exposures. To substantiate these findings, detailed transmission electron microscopy studies were carried out on the steel. With fatigue exposures, extensive recovery of martensitic-lath structure was distinctly observed which supported the cyclic softening behavior that was introduced due to prior fatigue. Consequently, prior fatigue exposures were considered responsible for decrease in creep ductility and associated reduction in the creep rupture strength.

  8. Fatigue Design and Prevention in Movable Scaffolding Systems

    Directory of Open Access Journals (Sweden)

    Coelho Hugo

    2017-06-01

    Full Text Available The Movable Scaffolding System (MSS is a heavy construction equipment used for casting situ of concrete bridge decks. In the past decades, MSSs have become increasingly complex and industrialized, enlarging its span ranges, incorporating auxiliary elevation machinery and increasing productivity. The tendency nowadays is for strong reutilization and the notion of MSS as a disposable or temporary structure is somehow reductive. The main structure of MSSs may be potentially exposed to fatigue, usually characterized by low number of cycles with significant stress amplitude. Fatigue may be prevented through adequate design; judicious selection of materials; demanding quality control and implementation of robust inspection and maintenance plans.

  9. Fatigue Design and Prevention in Movable Scaffolding Systems

    Science.gov (United States)

    Coelho, Hugo; Torres, Alberto; Pacheco, Pedro; Moreira, Cristiano; Silva, Rute; Soares, José M.; Pinto, Dânia

    2017-06-01

    The Movable Scaffolding System (MSS) is a heavy construction equipment used for casting situ of concrete bridge decks. In the past decades, MSSs have become increasingly complex and industrialized, enlarging its span ranges, incorporating auxiliary elevation machinery and increasing productivity. The tendency nowadays is for strong reutilization and the notion of MSS as a disposable or temporary structure is somehow reductive. The main structure of MSSs may be potentially exposed to fatigue, usually characterized by low number of cycles with significant stress amplitude. Fatigue may be prevented through adequate design; judicious selection of materials; demanding quality control and implementation of robust inspection and maintenance plans.

  10. Gray Matter Volumes in Patients with Chronic Fatigue Syndrome

    Directory of Open Access Journals (Sweden)

    Le-wei Tang

    2015-01-01

    Full Text Available Chronic fatigue syndrome (CFS is a debilitating and complex disorder characterized by profound fatigue with uncertain pathologic mechanism. Neuroimage may be an important key to unveil the central nervous system (CNS mechanism in CFS. Although most of the studies found gray matter (GM volumes reduced in some brain regions in CFS, there are many factors that could affect GM volumes in CFS, including chronic pain, stress, psychiatric disorder, physical activity, and insomnia, which may bias the results. In this paper, through reviewing recent literatures, we discussed these interferential factors, which overlap with the symptoms of CFS.

  11. Installation for fatigue testing of materials at cryogenic temperatures

    International Nuclear Information System (INIS)

    Abushenkov, I.D.; Chernetskij, V.K.; Il'ichev, V.Ya.

    1986-01-01

    A new installation for mechanical fatigue tests of structural material samples is described, in which the possibility to conduct tests in the range of lower temperatures (4.2-300 K) is ensured. The installation permits to carry out fatigue tests using the method of axial loading of annular (up to 6 mm in diameter) and plane (up to 12 mm wide) samples during symmetric, asymmetric and pulsing loading cycles. It is shown that the installation suggested has quite extended operation possibilities and, coincidentally, it is characterized by design simplicity, compactness, comparatively low metal consumption and maintenance convenience

  12. Fatigue-crack growth behavior in dissimilar metal weldments

    International Nuclear Information System (INIS)

    James, L.A.

    1977-03-01

    The techniques of linear-elastic fracture mechanics were used to characterize fatigue-crack propagation behavior in three dissimilar metal weldments at test temperatures of 800 0 F (427 0 C) and 1000 0 F (538 0 C). The weldments studied included Inconel 718/Type 316, all using Inconel 82 as the filler metal. In general, fatigue-crack growth rates in the weldments were equal to, or less than, those observed in the base metals. Crack deviation from the expected path perpendicular to the loading axis was noted in some cases, and is discussed

  13. Stress induced martensite at the crack tip in NiTi alloys during fatigue loading

    Directory of Open Access Journals (Sweden)

    E. Sgambitterra

    2014-10-01

    Full Text Available Crack tip stress-induced phase transformation mechanisms in nickel-titanium alloys (NiTi were analyzed by Digital Image Correlation (DIC, under fatigue loads. In particular, Single Edge Crack (SEC specimens, obtained from a commercial pseudoelastic NiTi sheet, and an ad-hoc experimental setup were used, for direct measurements of the near crack tip displacement field by the DIC technique. Furthermore, a fitting procedure was developed to calculate the mode I Stress Intensity Factor (SIF, starting from the measured displacement field. Finally, cyclic tensile tests were performed at different operating temperature, in the range 298-338 K, and the evolution of the SIF was studied, which revealed a marked temperature dependence.

  14. Joined application of a multiaxial critical plane criterion and a strain energy density criterion in low-cycle fatigue

    Directory of Open Access Journals (Sweden)

    Andrea Carpinteri

    2017-07-01

    Full Text Available In the present paper, the multiaxial fatigue life assessment of notched structural components is performed by employing a strain-based multiaxial fatigue criterion. Such a criterion, depending on the critical plane concept, is extended by implementing the control volume concept reated to the Strain Energy Density (SED approach: a material point located at a certain distance from the notch tip is assumed to be the verification point where to perform the above assessment. Such a distance, measured along the notch bisector, is a function of both the biaxiality ratio (defined as the ratio between the applied shear stress amplitude and the normal stress amplitude and the control volume radii under Mode I and Mode III. Once the position of the verification point is determined, the fatigue lifetime is assessed through an equivalent strain amplitude, acting on the critical plane, together with a unique material reference curve (i.e. the Manson-Coffin curve. Some uniaxial and multiaxial fatigue data related to V-notched round bars made of titanium grade 5 alloy (Ti-6Al-4V are examined to validate the present criterion.

  15. Influence of heat treatment on fatigue performances for self-piercing riveting similar and dissimilar titanium, aluminium and copper alloys

    OpenAIRE

    Zhang, Xianlian; He, Xiaocong; Xing, Baoying; Zhao, Lun; Lu, Yi; Gu, Fengshou; Ball, Andrew

    2016-01-01

    The fatigue performances of self-piercing riveting (SPR) joints connecting similar and dissimilar sheets of TA1 titanium alloy (TA1), Al5052 aluminium alloy (Al5052) and H62 copper alloy (H62) were studied in this paper. The specimens of similar TA1 sheets treated with stress relief annealing were prepared to investigate the influence of relief annealing on the mechanical properties of SPR joints. Fatigue tests were conducted to characterize the fatigue lives and failure modes of the joints. ...

  16. SI:FatiguePro 4 Advanced Approach for Fatigue Monitoring

    International Nuclear Information System (INIS)

    Evon, Keith; Gilman, Tim; Carney, Curt

    2012-01-01

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

  17. Fatigue Monitoring Tool for Airline Operators (FMT

    Directory of Open Access Journals (Sweden)

    Gislason Sigurdur Hrafn

    2017-12-01

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

  18. Fatigue Reliability of Offshore Wind Turbine Systems

    DEFF Research Database (Denmark)

    Marquez-Dominguez, Sergio; Sørensen, John Dalsgaard

    2012-01-01

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

  19. The effects of Nitinol phases on corrosion and fatigue behavior

    Science.gov (United States)

    Denton, Melissa

    The purpose of these studies was to provide a detailed understanding of Nitinol phases and their effects on corrosion and fatigue life. The two primary phases, austenite and martensite, were carefully evaluated with respect to material geometry, corrosion behavior, wear, and fatigue life. Material characterization was performed using several techniques that include metallography, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray photoelectron spectrum (XPS), and Auger electron spectroscopy (AES). Uniaxial tensile tests were conducted to determine the mechanical properties such as elongation, ultimate tensile strength, modulus, transformation strain, and plateau stress. In addition, accelerated wear testing and four point bend fatigue testing were completed to study the fatigue life and durability of the material. The corrosion of Nitinol was found to be dependent on various surface conditions. Electrochemical corrosion behavior of each phase was investigated using cyclic potentiodyamic polarization testing. The corrosion response of electropolished Nitinol was found to be acceptable, even after durability testing. Stress-induced martensite had a lower breakdown potential due to a rougher surface morphology, while thermally induced martensite and austenite performed similarly well. The surface conditioning also had a significant effect on Nitinol mechanical properties. Electropolishing provided a smooth mirror finish that reduced localized texture and enhanced the ductility of the material. Quasi-static mechanical properties can be good indicators of fatigue life, but further fatigue testing revealed that phase transformations had an important role as well. The governing mechanisms for the fatigue life of Nitinol were determined to be both martesitic phase transformations and surface defects. A new ultimate dislocation strain model was proposed based on specific accelerated step-strain testing.

  20. [Sleep patterns and fatigue of nursing students who work].

    Science.gov (United States)

    Ferreira, Luciane Ruiz Carmona; de Martino, Milva Maria Figueiredo

    2012-10-01

    It has been observed there is currently a growing interest in developing research regarding the sleep patterns of workers who must wake up very early or who work nights. Therefore, the objective of this study was to identify the levels of fatigue and the sleep patterns of nursing students who study during the day and work at night. Participants were thirty students who completed the Epworth Sleepiness Scale and Sleep Journal for thirty days. It was found that sleep duration was longer among men compared to women on days off work, and when on vacation from school compared to the regular school period. Participants showed high levels of fatigue and sleepiness, characterized by the incidence of excessive daytime sleepiness. In conclusion, night workers who endure sleep deprivation have additional wake hours due to studying, thus causing high levels of fatigue, which may harm their performance at school and at work.

  1. A cohesive zone framework for environmentally assisted fatigue

    DEFF Research Database (Denmark)

    del Busto, Susana; Betegón, Covadonga; Martínez Pañeda, Emilio

    2017-01-01

    We present a compelling finite element framework to model hydrogen assisted fatigue by means of a hydrogen- and cycle-dependent cohesive zone formulation. The model builds upon: (i) appropriate environmental boundary conditions, (ii) a coupled mechanical and hydrogen diffusion response, driven...... by chemical potential gradients, (iii) a mechanical behavior characterized by finite deformation J2 plasticity, (iv) a phenomenological trapping model, (v) an irreversible cohesive zone formulation for fatigue, grounded on continuum damage mechanics, and (vi) a traction-separation law dependent on hydrogen...... coverage calculated from first principles. The computations show that the present scheme appropriately captures the main experimental trends; namely, the sensitivity of fatigue crack growth rates to the loading frequency and the environment. The role of yield strength, work hardening, and constraint...

  2. Fatigue mechanisms in unidirectional glass-fibre-reinforced polypropylene

    DEFF Research Database (Denmark)

    Gamstedt, E.K.; Berglund, L.A.; Peijs, T.

    1999-01-01

    Polypropylene (PP) and polypropylene modified with maleic anhydride (MA-PP) reinforced by continuous longitudinal glass fibres have been investigated. The most prominent effect of the modification with maleic anhydride in the composite is a stronger fibre/matrix interface. The effects of interfac......Polypropylene (PP) and polypropylene modified with maleic anhydride (MA-PP) reinforced by continuous longitudinal glass fibres have been investigated. The most prominent effect of the modification with maleic anhydride in the composite is a stronger fibre/matrix interface. The effects...... of interfacial strength on fatigue performance and on the underlying micromechanisms have been studied for these composite systems. Tension-tension fatigue tests (R = 0.1) were carried out on 0 degrees glass-fibre/PP and glass-fibre/ MA-PP coupons. The macroscopic fatigue behaviour was characterized in terms...

  3. [Chronic fatigue syndrome--exercise and physical activity].

    Science.gov (United States)

    Greenberg, Shai; Frid, Mordechai

    2006-04-01

    One of the major symptoms of chronic fatigue syndrome (CFS) is reduced exercise and functional capacity and increased fatigue symptoms following physical effort. A review of the literature indicates that patients that suffer from CFS are characterized by: low aerobic capacity, higher heart rate during sub-maximal exercise, higher subjective effort prescription, reduced muscle strength, and prolonged recovery period. Although several symptoms are a result of lack of physical activity, several mechanisms were suggested to explain those symptoms: pathological heart rate control, reduced aerobic metabolic capacity, reduced blood supply to the working muscles and nerve system dysfunction. Participating in guided exercise programs was found to be the most effective treatment in improving exercise and functional capacity, reducing fatigue syndromes and improving patients' daily function.

  4. Consistent creep and rupture properties for creep-fatigue evaluation

    International Nuclear Information System (INIS)

    Schultz, C.C.

    1978-01-01

    The currently accepted practice of using inconsistent representations of creep and rupture behaviors in the prediction of creep-fatigue life is shown to introduce a factor of safety beyond that specified in current ASME Code design rules for 304 stainless steel Class 1 nuclear components. Accurate predictions of creep-fatigue life for uniaxial tests on a given heat of material are obtained by using creep and rupture properties for that same heat of material. The use of a consistent representation of creep and rupture properties for a mininum strength heat is also shown to provide adequate predictions. The viability of using consistent properties (either actual or those of a minimum heat) to predict creep-fatigue life thus identifies significant design uses for the results of characterization tests and improved creep and rupture correlations

  5. Consistent creep and rupture properties for creep-fatigue evaluation

    International Nuclear Information System (INIS)

    Schultz, C.C.

    1979-01-01

    The currently accepted practice of using inconsistent representations of creep and rupture behaviors in the prediction of creep-fatigue life is shown to introduce a factor of safety beyond that specified in current ASME Code design rules for 304 stainless steel Class 1 nuclear components. Accurate predictions of creep-fatigue life for uniaxial tests on a given heat of material are obtained by using creep and rupture properties for that same heat of material. The use of a consistent representation of creep and rupture properties for a minimum strength heat is also shown to provide reasonable predictions. The viability of using consistent properties (either actual or those of a minimum strength heat) to predict creep-fatigue life thus identifies significant design uses for the results of characterization tests and improved creep and rupture correlations. 12 refs

  6. Fibromyalgia and chronic fatigue syndrome in children.

    Science.gov (United States)

    Itoh, Yasuhiko; Shigemori, Tomoko; Igarashi, Tohru; Fukunaga, Yoshitaka

    2012-04-01

    Fibromyalgia (FM) is characterized by widespread persistent pain and the presence of multiple discrete tender points. Chronic fatigue syndrome (CFS) is a syndrome characterized by debilitating fatigue associated with a variable number of non-specific complaints. Because neither condition had necessarily been recognized in children until recently, those patients have been treated as having school refusal without being diagnosed as having either syndrome. There is a considerable overlap of clinical symptoms between these two syndromes. It is therefore controversial as to whether these syndromes have the same pathogenesis or not. The aim of the present study was to clarify the relationship between these syndromes in children. Fifteen patients with FM and 21 patients with CFS were investigated both clinically and immunologically. Immunological assessments included thorough analysis of autoantibodies using several techniques. Anti-nuclear antibody titers were higher and the prevalence of anti-Sa antibody was far more frequent in CFS patients than in FM patients. CFS and FM are different from each other at least in childhood, from an immunological aspect, although some patients could have both conditions. © 2011 The Authors. Pediatrics International © 2011 Japan Pediatric Society.

  7. Fatigue life prediction in composites

    CSIR Research Space (South Africa)

    Huston, RJ

    1994-01-01

    Full Text Available Because of the relatively large number of possible failure mechanisms in fibre reinforced composite materials, the prediction of fatigue life in a component is not a simple process. Several mathematical and statistical models have been proposed...

  8. Fatigue Fighters in Sjogren's Syndrome

    Science.gov (United States)

    ... your doctor to find a specific cause and treatment for your fatigue. The possibilities may include systemic inflammation, poor sleep, fibromyalgia, depression, hypothyroidism, muscle inflammation or side-effects of medications. Know ...

  9. Fatigue and Corrosion in Metals

    CERN Document Server

    Milella, Pietro Paolo

    2013-01-01

    This textbook, suitable for students, researchers and engineers, gathers the experience of more than 20 years of teaching fracture mechanics, fatigue and corrosion to professional engineers and running experimental tests and verifications to solve practical problems in engineering applications. As such, it is a comprehensive blend of fundamental knowledge and technical tools to address the issues of fatigue and corrosion. The book initiates with a systematic description of fatigue from a phenomenological point of view, since the early signs of submicroscopic damage in few surface grains and continues describing, step by step, how these precursors develop to become mechanically small cracks and, eventually, macrocracks whose growth is governed by fracture mechanics. But fracture mechanics is also introduced to analyze stress corrosion and corrosion assisted fatigue in a rather advanced fashion. The author dedicates a particular attention to corrosion starting with an electrochemical treatment that mechanical e...

  10. Coping with cancer -- managing fatigue

    Science.gov (United States)

    ... How severe your fatigue is depends on the type of cancer you have, the stage of cancer, and ... distressed. These emotions can drain your energy and motivation. Medicines. Many of the medicines for treating pain, depression, insomnia, and ...

  11. Fatigue of internal combustion engines

    Science.gov (United States)

    Dumanois, P

    1924-01-01

    The above conditions enable the employment of a criterion of general fatigue which simultaneously takes account of both mechanical and thermal conditions, for the sake of comparing any projected engine with engines of the same type already in use.

  12. Fatigue, burnout, and chronic fatigue syndrome among employees on sick leave: do attributions make the difference?

    NARCIS (Netherlands)

    Huibers, M.J.H.; Beurskens, A.J.H.M.; Prins, J.B.; Kant, I.J.; Bazelmans, H.M.; Schayck, C.P. van; Knottnerus, J.A.; Bleijenberg, G.

    2003-01-01

    BACKGROUND: Persistent fatigue among employees, burnout, and chronic fatigue syndrome (CFS) are three fatigue conditions that share some characteristics in theory. However, these conditions have not been compared in empirical research, despite conceptual similarities. METHODS: This cross sectional

  13. Are There Any Natural Remedies That Reduce Chronic Fatigue Associated with Chronic Fatigue Syndrome?

    Science.gov (United States)

    ... natural remedies that reduce chronic fatigue associated with chronic fatigue syndrome? Answers from Brent A. Bauer, M.D. Researchers ... a variety of natural products for effectiveness against chronic fatigue syndrome. Most results have been disappointing. A few remedies — ...

  14. Fatigue Perceived by Multiple Sclerosis Patients Is Associated With Muscle Fatigue

    NARCIS (Netherlands)

    Steens, Anneke; de Vries, Astrid; Hemmen, Jolien; Heersema, Thea; Heerings, Marco; Maurits, Natasha; Zijdewind, Inge

    Background. Fatigue is a debilitating symptom in multiple sclerosis (MS). Previous studies showed no association between fatigue as perceived by the patient and physiological measures of fatigability. Objective. The authors investigated associations between perceived fatigue and measures of

  15. Ultrasonic sizing of fatigue cracks

    International Nuclear Information System (INIS)

    Burns, D.J.

    1983-12-01

    Surface and buried fatigue cracks in steel plates have been sized using immersion probes as transmitters-receivers, angled to produce shear waves in the steel. Sizes have been estimated by identifying the ultrasonic waves diffracted from the crack tip and by measuring the time taken for a signal to travel to and from the crack tip. The effects of compression normal to a fatigue crack and of crack front curvature are discussed. Another diffraction technique, developed by UKAEA, Harwell, is reviewed

  16. Irradiation effect on fatigue behaviour of zircaloy-4 cladding tubes

    International Nuclear Information System (INIS)

    Soniak, A.; Lansiart, S.; Royer, J.; Waeckel, N.

    1993-01-01

    Since nuclear electricity has a predominant share in French generating capacity, PWR's are required to fit grid load following and frequency control operating conditions. Consequently cyclic stresses appear in the fuel element cladding. In order to characterize the possible resulting clad damage, fatigue tests were performed at 350 deg C on unirradiated material or irradiated stress relieved Zircaloy-4 tube portions, using a special device for tube fatigue by repeated pressurization. It appears that, for high stress levels, the material fatigue life is not affected by irradiation. But the endurance fatigue limit undergoes a decrease from the 350 MPa value for unirradiated material to the 210 MPa value for the material irradiated for four cycles in a PWR. However, this effect seems to saturate with irradiation dose: no difference could be detected between the two cycles results and the corresponding four cycles results. The corrosion effect and the load following influence were also investigated: they do not appear to modify the fatigue behaviour in our experimental conditions

  17. Development and initial validation of a cessation fatigue scale.

    Science.gov (United States)

    Mathew, Amanda R; Heckman, Bryan W; Meier, Ellen; Carpenter, Matthew J

    2017-07-01

    Smoking cessation fatigue, or tiredness of attempting to quit smoking, has been posited as a latent construct encompassing loss of motivation, loss of hope in cessation success, decreased self-efficacy, and exhaustion of self-control resources. Despite the potential clinical impact of characterizing cessation fatigue, there is currently no validated measure to assess it. Using a rational scale development approach, we developed a cessation fatigue measure and examined its reliability and construct validity in relation to a) smokers' experience of a recently failed quit attempt (QA) and b) readiness to engage in a subsequent QA. Data were drawn from an online cross-sectional survey of 484 smokers who relapsed from a QA within the past 30days. Exploratory factor analysis identified three factors within the 17-item Cessation Fatigue Scale (CFS), which we labeled: emotional exhaustion, pessimism, and devaluation. High internal consistency was observed for each factor and across the full scale. As expected, CFS overall was positively associated with withdrawal severity and difficulty quitting. CFS was negatively associated with previously validated measures of intention to quit, self-efficacy, and abstinence-related motivational engagement, even after adjusting for nicotine dependence. Findings provide initial validation for a new tool to assess cessation fatigue and contribute needed information on a theory-driven component of cessation-related motivation and relapse risk. Copyright © 2017. Published by Elsevier B.V.

  18. Accelerated fatigue of dentin with exposure to lactic acid.

    Science.gov (United States)

    Do, D; Orrego, S; Majd, H; Ryou, H; Mutluay, M M; Xu, Hockin H K; Arola, D

    2013-11-01

    Composite restorations accumulate more biofilm than other dental materials. This increases the likelihood for the hard tissues supporting a restoration (i.e. dentin and enamel) to be exposed to acidic conditions beyond that resulting from dietary variations. In this investigation the fatigue strength and fatigue crack growth resistance of human coronal dentin were characterized within a lactic acid solution (with pH = 5) and compared to that of controls evaluated in neutral conditions (pH = 7). A comparison of the fatigue life distributions showed that the lactic acid exposure resulted in a significant reduction in the fatigue strength (p ≤ 0.001), and nearly 30% reduction in the apparent endurance limit (from 44 MPa to 32 MPa). The reduction in pH also caused a significant decrease (p ≤ 0.05) in the threshold stress intensity range required for the initiation of cyclic crack growth, and significant increase in the incremental rate of crack extension. Exposure of tooth structure to lactic acid may cause demineralization, but it also increases the likelihood of restored tooth failures via fatigue, and after short time periods. © 2013 Elsevier Ltd. All rights reserved.

  19. Measurement of fatigue in industries.

    Science.gov (United States)

    Saito, K

    1999-04-01

    Fatigue of workers is a complex phenomenon resulting from various factors in technically innovated modern industries, and it appears as a feeling of exhaustion, lowering of physiological functions, breakdown of autonomic nervous balance, and decrease in work efficiency. On the other hand industrial fatigue is caused by excessive workload, remarkable alteration in working posture and diurnal and nocturnal rhythms in daily life. Working modes in modern industries have changed from work with the whole body into that with the hands, arms, legs and/or eyes which are parts of the body, and from physical work to mental work. Visual display terminal (VDT) work is one of the most characteristic jobs in the various kinds of workplaces. A large number of fatigue tests have already been adopted, but it is still hard to draw a generalized conclusion as to the method of selecting the most appropriate test battery for a given work load. As apparatus for fatigue measurement of VDT work we have developed VRT (Visual Reaction Test) and the Portable Fatigue Meter. Furthermore, we have presented immune parameters of peripheral blood and splenic T cells for physical fatigue.

  20. Probabilistic Meteorological Characterization for Turbine Loads

    DEFF Research Database (Denmark)

    Kelly, Mark C.; Larsen, Gunner Chr.; Dimitrov, Nikolay Krasimirov

    2014-01-01

    Beyond the existing, limited IEC prescription to describe fatigue loads on wind turbines, we look towards probabilistic characterization of the loads via analogous characterization of the atmospheric flow, particularly for today's "taller" turbines with rotors well above the atmospheric surface...

  1. Probabilistic modeling of fatigue crack growth in Ti-6Al-4V

    International Nuclear Information System (INIS)

    Soboyejo, W.O.; Shen, W.; Soboyejo, A.B.O.

    2001-01-01

    This paper presents the results of a combined experimental and analytical study of the probabilistic nature of fatigue crack growth in Ti-6Al-4V. A simple experimental fracture mechanics framework is presented for the determination of statistical fatigue crack growth parameters from two fatigue tests. The experimental studies show that the variabilities in long fatigue crack growth rate data and the Paris coefficient are well described by the log-normal distributions. The variabilities in the Paris exponent are also shown to be well characterized by a normal distribution. The measured statistical distributions are incorporated into a probabilistic fracture mechanics framework for the estimation of material reliability. The implications of the results are discussed for the probabilistic analysis of fatigue crack growth in engineering components and structures. (orig.)

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

    International Nuclear Information System (INIS)

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

    2004-01-01

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

  3. Protective effect of epigallocatechin gallate in murine water-immersion stress model of chronic fatigue syndrome.

    Science.gov (United States)

    Sachdeva, Anand Kamal; Kuhad, Anurag; Tiwari, Vinod; Arora, Vipin; Chopra, Kanwaljit

    2010-06-01

    Chronic fatigue syndrome (CFS) is a specific clinical condition that characterizes unexplained disabling fatigue. In the present study, chronic fatigue was produced in mice by subjecting them to forced swim inside a rectangular jar of specific dimensions for 6 min. daily for 15 days. Epigallocatechin gallate (EGCG; 25, 50 and 100 mg/kg, p.o.) was administered daily 30 min. before forced swim session. Immobility period and post-swim fatigue was assessed on alternate days. On the 16th day, after assessment of various behavioural parameters, mice were killed to harvest the brain, spleen and thymus. There was significant increase in oxidative-nitrosative stress and tumour necrosis factor-alpha levels in the brain of mice subjected to water-immersion stress as compared with naive group. These behavioural and biochemical alterations were restored after chronic treatment with EGCG. The present study points out that EGCG could be of therapeutic potential in the treatment of chronic fatigue.

  4. Probabilistic assessment of fatigue life including statistical uncertainties in the S-N curve

    International Nuclear Information System (INIS)

    Sudret, B.; Hornet, P.; Stephan, J.-M.; Guede, Z.; Lemaire, M.

    2003-01-01

    A probabilistic framework is set up to assess the fatigue life of components of nuclear power plants. It intends to incorporate all kinds of uncertainties such as those appearing in the specimen fatigue life, design sub-factor, mechanical model and applied loading. This paper details the first step, which corresponds to the statistical treatment of the fatigue specimen test data. The specimen fatigue life at stress amplitude S is represented by a lognormal random variable whose mean and standard deviation depend on S. This characterization is then used to compute the random fatigue life of a component submitted to a single kind of cycles. Precisely the mean and coefficient of variation of this quantity are studied, as well as the reliability associated with the (deterministic) design value. (author)

  5. 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.

  6. Biaxial fatigue of metals the present understanding

    CERN Document Server

    Schijve, Jaap

    2016-01-01

    Problems of fatigue under multiaxial fatigue loads have been addressed in a very large number of research publications. The present publication is primarily a survey of biaxial fatigue under constant amplitude loading on metal specimens. It starts with the physical understanding of the fatigue phenomenon under biaxial fatigue loads. Various types of proportional and non-proportional biaxial fatigue loads and biaxial stress distributions in a material are specified. Attention is paid to the fatigue limit, crack nucleation, initial micro crack growth and subsequent macro-crack in different modes of crack growth. The interference between the upper and lower surfaces of a fatigue crack is discussed. Possibilities for predictions of biaxial fatigue properties are analysed with reference to the similarity concept. The significance of the present understanding for structural design problems is considered. The book is completed with a summary of major observations.

  7. Fatigue after Stroke: The Patient's Perspective

    Directory of Open Access Journals (Sweden)

    Victoria Louise Barbour

    2012-01-01

    Full Text Available Background. Fatigue after stroke is common and distressing to patients. Aims. Our aims were to explore patients' perceptions of post-stroke fatigue, including the causes of fatigue and the factors that alleviate fatigue, in a mixed methods study. Results. We interviewed 15 patients who had had a stroke and were inpatients on stroke rehabilitation wards. A substantial proportion of patients reported that their fatigue started at the time of their stroke. Various different factors were reported to improve fatigue, including exercise, good sleep, rehabilitation and rest. Fatigue influences patients' sense of “control” after their stroke. Conclusion. Our results are consistent with the possibility that poststroke fatigue might be triggered by factors that occur at the time of the stroke (e.g., the stroke lesion itself, or admission to hospital and then exacerbated by poor sleep and boredom. These factors should be considered when developing complex interventions to improve post-stroke fatigue.

  8. Fatigue monitoring desktop guide

    International Nuclear Information System (INIS)

    Woods, K.; Thomas, K.

    2012-01-01

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

  9. Fatigue monitoring desktop guide

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-07-01

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

  10. Fatiguing exercise intensity influences the relationship between parameters reflecting neuromuscular function and postural control variables.

    Directory of Open Access Journals (Sweden)

    Sébastien Boyas

    Full Text Available The purpose of this study was to investigate the influence of fatiguing exercise intensity on the nature and extent of fatigue-induced changes in neuromuscular function and postural stability in quiet standing. We also explored the contribution of selected neuromuscular mechanisms involved in force production to postural stability impairment observed following fatigue using an approach based on multivariate regressions. Eighteen young subjects performed 30-s postural trials on one leg with their eyes closed. Postural trials were performed before and after fatiguing exercises of different intensities: 25, 50 and 75% of maximal isometric plantarflexor torque. Fatiguing exercises consisted of sustaining a plantarflexor isometric contraction at the target intensity until task failure. Maximal isometric plantarflexor torque, electromyographic activity of plantarflexor and dorsiflexor muscles, activation level (twitch interpolation technique and twitch contractile properties of plantarflexors were used to characterize neuromuscular function. The 25% exercise was associated with greater central fatigue whereas the 50 and 75% exercises involved mostly peripheral fatigue. However, all fatiguing exercises induced similar alterations in postural stability, which was unexpected considering previous literature. Stepwise multiple regression analyses showed that fatigue-related changes in selected parameters related to neuromuscular function could explain more than half (0.51≤R(2≤0.82 of the changes in postural variables for the 25% exercise. On the other hand, regression models were less predictive (0.17≤R(2≤0.73 for the 50 and 75% exercises. This study suggests that fatiguing exercise intensity does not influence the extent of postural stability impairment, but does influence the type of fatigue induced and the neuromuscular function predictors explaining changes in postural variables.

  11. The relationship between cell phone use and management of driver fatigue: It's complicated.

    Science.gov (United States)

    Saxby, Dyani Juanita; Matthews, Gerald; Neubauer, Catherine

    2017-06-01

    Voice communication may enhance performance during monotonous, potentially fatiguing driving conditions (Atchley & Chan, 2011); however, it is unclear whether safety benefits of conversation are outweighed by costs. The present study tested whether personalized conversations intended to simulate hands-free cell phone conversation may counter objective and subjective fatigue effects elicited by vehicle automation. A passive fatigue state (Desmond & Hancock, 2001), characterized by disengagement from the task, was induced using full vehicle automation prior to drivers resuming full control over the driving simulator. A conversation was initiated shortly after reversion to manual control. During the conversation an emergency event occurred. The fatigue manipulation produced greater task disengagement and slower response to the emergency event, relative to a control condition. Conversation did not mitigate passive fatigue effects; rather, it added worry about matters unrelated to the driving task. Conversation moderately improved vehicle control, as measured by SDLP, but it failed to counter fatigue-induced slowing of braking in response to an emergency event. Finally, conversation appeared to have a hidden danger in that it reduced drivers' insights into performance impairments when in a state of passive fatigue. Automation induced passive fatigue, indicated by loss of task engagement; yet, simulated cell phone conversation did not counter the subjective automation-induced fatigue. Conversation also failed to counter objective loss of performance (slower braking speed) resulting from automation. Cell phone conversation in passive fatigue states may impair drivers' awareness of their performance deficits. Practical applications: Results suggest that conversation, even using a hands-free device, may not be a safe way to reduce fatigue and increase alertness during transitions from automated to manual vehicle control. Copyright © 2017 Elsevier Ltd and National Safety

  12. The Longitudinal Course of Fatigue in Rheumatoid Arthritis: Results from the Norfolk Arthritis Register.

    Science.gov (United States)

    Druce, Katie L; Jones, Gareth T; Macfarlane, Gary J; Verstappen, Suzanne M M; Basu, Neil

    2015-11-01

    Fatigue is common and burdensome in rheumatoid arthritis (RA). Despite RA fatigue progression varying significantly between individuals in practice, existing longitudinal analyses only examine symptom advancement on a population level. This study aimed to determine fatigue trajectories at an individual level and to characterize those patients with the poorest prognosis, with a view to enabling earlier interventions. Patients with RA reporting clinically relevant baseline fatigue (≥ 20 mm on a 0-100 mm visual analog scale) were identified from a longterm inflammatory polyarthritis cohort (the Norfolk Arthritis Register). Fatigue changes from baseline to 1- and 4-year followups were calculated, and sex-stratified group-based trajectory modeling (GBTM) determined trajectories of the symptom between which baseline characteristics were compared. Among 338 patients, only minimal average changes were observed between recruitment to 1 year (6.0 mm, SD 26.9) and 4 years (5.5 mm, SD 29.3). This was despite 45.6% and 40.7% of participants reporting clinically significant improvements (≥ 10 mm) at these respective followups. GBTM revealed varied trajectories of fatigue, which for both sexes consisted of Improved (men, n = 48 and women, n = 81) or persistent Moderate-high paths (n = 54, n = 105), and further included a persistent High trajectory in women (n = 50). Participants who followed persistent trajectories were best distinguished from improvers by patient-reported rather than demographic or clinical variables. Among patients with RA presenting with clinically relevant fatigue, distinct longitudinal symptom trajectories were identified on an individual level despite nominal average changes in fatigue on a group level. It is possible to identify and characterize subgroups of participants who report persistent fatigue and should therefore be targeted to receive future fatigue-alleviating interventions.

  13. Fatigue and fatigue crack growth properties of 316LN and Incoloy 908 below 10 K

    International Nuclear Information System (INIS)

    Nyilas, A.; Zhang, J.; Obst, B.; Ulbricht, A.

    1992-01-01

    The cyclic loading characteristics of Tokamak type thermonuclear machines demand study of the fatigue response of the materials used in critical components. The large superconducting magnets and their superconductors will operate under cyclic mechanical stress conditions. The present paper is biased towards the current superconductor design of the NET (Next European Torus) model coil concept. The superconductor of this coil will be a cable-in-conduit Nb 3 Sn type with an enveloped stiff external jacket structure. The wall thickness of the jacket structure is within the range of 4-5 mm. The manufacturing of the jacket lengths for several hundred meters require an appropriate joining process due to the prefabricated section pieces available only in short lengths of 5-7 meters. The recently anticipated solution favors the flash butt welding technique. The performance of the superconductors jacket will depend on the material selection and the proper structural design according to the existing low temperature structural materials data base. The wind and react Nb 3 Sn-manufacturing process must also account the materials properties after ageing. A program was set up to elucidate the fatigue-life behavior and fatigue crack growth rate (FCGR) of the selected two candidate materials. These materials were the AISI 316LN with a specified low carbon content to avoid the embrittlement after the ageing process and the Incoloy 908. The 316LN material in the as received condition was tested with respect to its fatigue-life for specimens bearing predefined flaws and cracks. The propagation of surface cracks at 12 K and at 295 K was characterized with non standard specimens. The tests were performed in a cryogenic dynamic test facility under helium gas environment between 7 K and 20 K. Using the reference growth laws obtained from these measurements the total crack propagation starting with the initial crack length of the specimen could be predicted by numerical computation

  14. 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.

  15. Sleep complaints and fatigue of airline pilots.

    Science.gov (United States)

    Reis, Cátia; Mestre, Catarina; Canhão, Helena; Gradwell, David; Paiva, Teresa

    2016-01-01

    This work aimed to determine daytime sleepiness and sleep complaints prevalence and the corresponding influence on perceived fatigue and to evaluate the influence of sociodemographic parameters and labour variables on sleep complaints, sleepiness and fatigue. A questionnaire was developed including socio-economic and labour issues and instruments, focused in sleep and fatigue. The response rate was 32% and the final sample had 435 pilots. The prevalence of sleep complaints was 34.9%, daytime sleepiness 59.3% and fatigue 90.6%. The high prevalence of sleep complaints, sleepiness and fatigue was disclosed in pilots, with those who fly short/medium having an added risk of fatigue.

  16. Thermal-Acoustic Fatigue of a Multilayer Thermal Protection System in Combined Extreme Environments

    Directory of Open Access Journals (Sweden)

    Liu Liu

    2014-06-01

    Full Text Available In order to ensure integrity of thermal protection system (TPS structure for hypersonic vehicles exposed to severe operating environments, a study is undertaken to investigate the response and thermal-acoustic fatigue damage of a representative multilayer TPS structure under combined thermal and acoustic loads. An unsteady-state flight of a hypersonic vehicle is composed of a series of steady-state snapshots, and for each snapshot an acoustic load is imposed to a static steady-state TPS structure. A multistep thermal-acoustic fatigue damage intensity analysis procedure is given and consists of a heat transfer analysis, a nonlinear thermoelastic analysis, and a random response analysis under a combined loading environment and the fatigue damage intensity has been evaluated with two fatigue analysis techniques. The effects of thermally induced deterministic stress and nondeterministic dynamic stress due to the acoustic loading have been considered in the damage intensity estimation with a maximum stress fatigue model. The results show that the given thermal-acoustic fatigue intensity estimation procedure is a viable approach for life prediction of TPS structures under a typical mission cycle with combined loadings characterized by largely different time-scales. A discussion of the effects of the thermal load, the acoustic load, and fatigue analysis methodology on the fatigue damage intensity has been provided.

  17. Two different mechanisms of fatigue damage due to cyclic stress loading at 77 K for MOCVD-YBCO-coated conductors

    International Nuclear Information System (INIS)

    Sugano, M; Yoshida, Y; Hojo, M; Shikimachi, K; Hirano, N; Nagaya, S

    2008-01-01

    Tensile fatigue tests were carried out at 77 K for YBCO-coated conductors fabricated by metal-organic chemical vapor deposition (MOCVD). The S-N relationship, variation of critical current (I c ) during cyclic loading and microscopic fatigue damage were investigated. Fatigue strength at 10 6 cycles was evaluated to be σ max = 1300 MPa and 890 MPa under the stress ratios of 0.5 and 0.1. Two different mechanisms of fatigue damage, depending on the number of stress cycles to failure, were observed. In one of the fracture mechanisms, fatigue behavior is characterized by overall fracture which occurs at 10 4 -10 5 cycles. For these specimens, I c after unloading does not degrade before overall fracture. Although only shallow slip bands were found at the Ag surface, fatigue cracks were found on the Hastelloy C-276 surface of the fractured specimen. These results suggest that overall fracture due to cyclic stress was caused by fatigue of the Hastelloy substrate. In the other fracture mechanism, even though overall fracture did not occur at 10 6 cycles, a slight decrease of I c was detected after 10 5 cycles. No fatigue crack was found on the Hastelloy surface, while deep slip bands corresponding to the initial stage of fatigue crack were observed on the Ag surface. From these results, we concluded that I c degradation at a high cycle number is attributed to the fatigue of the Ag stabilizing layer

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

    Directory of Open Access Journals (Sweden)

    Adam Piesik

    2017-09-01

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

  19. Small fatigue cracks; Proceedings of the Second International Conference/Workshop, Santa Barbara, CA, Jan. 5-10, 1986

    Energy Technology Data Exchange (ETDEWEB)

    Ritchie, R.O.; Lankford, J.

    1986-01-01

    Topics discussed in this volume include crack initiation and stage I growth, microstructure effects, crack closure, environment effects, the role of notches, analytical modeling, fracture mechanics characterization, experimental techniques, and engineering applications. Papers are presented on fatigue crack initiation along slip bands, the effect of microplastic surface deformation on the growth of small cracks, short fatigue crack behavior in relation to three-dimensional aspects and the crack closure effect, the influence of crack depth on crack electrochemistry and fatigue crack growth, and nondamaging notches in fatigue. Consideration is also given to models of small fatigue cracks, short crack theory, assessment of the growth of small flaws from residual strength data, the relevance of short crack behavior to the integrity of major rotating aero engine components, and the relevance of short fatigue crack growth data to the durability and damage tolerance analyses of aircraft.

  20. High speed rails. Fatigue behaviour

    International Nuclear Information System (INIS)

    Duart, J. M.; Pero-Sanz, J. A.; Verdeja, J. I.

    2005-01-01

    In recent years, passenger train speed and freight train load have increased to enhance efficiency of rail road transportation. These trends have increased the severity of rail service conditions, calling for rails with greater wear resistance, strength and fatigue behaviour. In the United Stated and Europe, track site weld rails are made entirely by aluminothermic process. This work describes the results of experimental study conducted on bending fatigue strength of plain rails and aluminothermic welded rails with preheating procedures (oxipropane and air-induced propane) approved by railways authorities. Compliance with the required fatigue strength shall be ascertained by 4 point pulsating bending test in accordance with European standards by aluminothermic welding in rails. The locati method, based in the empirical Miner's law about the cumulative damage on a fatigue tested material, allows, once known the Wohler curve of the welding process in use to settle the fatigue tensile limit at 50% with only one test. The values obtained at 2.10''6 cycles for plain rails (S f =353 MPa), oxipropane preheated aluminothermic weld rails (S f =225 MPa), and propane-air induced aluminothermic weld rails (S f =210 MPa) are very similar to those resulting from test method stated in the European Standard. From our point of view and due to its ease, speediness and savings, this is the most suitable test to check the quality and compare the aluminothermic processes in use. (Author) 15 refs

  1. Fatigue of cord-rubber composites for tires

    Science.gov (United States)

    Song, Jaehoon

    Fatigue behaviors of cord-rubber composite materials forming the belt region of radial pneumatic tires have been characterized to assess their dependence on stress, strain and temperature history as well as materials composition and construction . Using actual tires, it was found that interply shear strain is one of the crucial parameters for damage assessment from the result that higher levels of interply shear strain of actual tires reduce the fatigue lifetime. Estimated at various levels of load amplitude were the fatigue life, the extent and rate of resultant strain increase ("dynamic creep"), cyclic strains at failure, and specimen temperature. The interply shear strain of 2-ply 'tire belt' composite laminate under circumferential tension was affected by twisting of specimen due to tension-bending coupling. However, a critical level of interply shear strain, which governs the gross failure of composite laminate due to the delamination, appeared to be independent of different lay-up of 2-ply vs. symmetric 4-ply configuration. Reflecting their matrix-dominated failure modes such as cord-matrix debonding and delamination, composite laminates with different cord reinforcements showed the same S-N relationship as long as they were constructed with the same rubber matrix, the same cord angle, similar cord volume, and the same ply lay-up. Because of much lower values of single cycle strength (in terms of gross fracture load per unit width), the composite laminates with larger cord angle and the 2-ply laminates exhibited exponentially shorter fatigue lifetime, at a given stress amplitude, than the composite laminates with smaller cord angle and 4-ply symmetric laminates, respectively. The increase of interply rubber thickness lengthens their fatigue lifetime at an intermediate level of stress amplitude. However, the increase in the fatigue lifetime of the composite laminate becomes less noticeable at very low stress amplitude. Even with small compressive cyclic

  2. Mean load effect on fatigue of welded joints using structural stress and fracture mechanics approach

    International Nuclear Information System (INIS)

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

    2006-01-01

    In order to ensure the structural integrity of nuclear welded structures during design life, the fatigue life has to be evaluated by fatigue analysis procedures presented in technical codes such as ASME B and PV Code Section III. However, existing fatigue analysis procedures do not explicitly consider the presence of welded joints. A new fatigue analysis procedure based on a structural stress/fracture mechanics approach has been recently developed in order to reduce conservatism by erasing uncertainty in the analysis procedure. A recent review of fatigue crack growth data under various mean loading conditions using the structural stress/fracture mechanics approach, does not consider the mean loading effect, revealed some significant discrepancies in fatigue crack growth curves according to the mean loading conditions. In this paper, we propose the use of the stress intensity factor range ΔK characterized with loading ratio R effects in terms of the structural stress. We demonstrate the effectiveness in characterizing fatigue crack growth and S-N behavior using the well-known data. It was identified that the S-N data under high mean loading could be consolidated in a master S-N curve for welded joints

  3. Very high cycle fatigue crack initiation in electroplated Ni films under extreme stress gradients

    International Nuclear Information System (INIS)

    Baumert, E.K.; Pierron, O.N.

    2012-01-01

    A characterization technique based on kilohertz micro-resonators is presented to investigate the very high cycle fatigue behavior of 20 μm thick electroplated Ni films with a columnar microstructure (grain diameter less than 2 μm). The films exhibit superior fatigue resistance due to the extreme stress gradients at the surface. The effects of stress amplitude and environment on the formation of fatigue extrusions and micro-cracks are discussed based on scanning electron microscopy and the tracking of the specimens’ resonant frequency.

  4. Probabilistic Modeling of the Fatigue Crack Growth Rate for Ni-base Alloy X-750

    International Nuclear Information System (INIS)

    Yoon, Jae Young; Nam, Hyo On; Hwang, Il Soon; Tae Hyun Lee

    2012-01-01

    The Bayesian inference was employed to reduce the uncertainties contained in EAC modeling parameters that have been established from experiments with Alloy X-750. Corrosion fatigue crack growth rate model(FCGR) was developed by fitting into Paris' Law of measured data from the several fatigue tests conducted either in constant load or constant ΔK mode. From fitting the data to Paris' Law, the parameters C and m of Paris' Law model were assumed to obey the Gaussian distribution. These parameters characterizing the corrosion fatigue crack growth behavior of X-750 were updated to reduce the uncertainty in the model by using the Bayesian inference method. (author)

  5. Fatigue assessment of a double submerged arc welded gas pipeline

    Energy Technology Data Exchange (ETDEWEB)

    Fazzini, Pablo; Otegui, Jose Luis [Universidad Nacional Mar del Plata, Mar del Plata (Argentina). Instituto de Ciencia y Tecnologia de Materiales (INTEMA); Teutonico, Mauricio; Manfredi, Carlos [GIE S.A., Mar del Plata (Argentina)

    2005-07-01

    An uncommon blowout in a 24'' diameter, 7 mm thick API 5L X52 gas pipeline was due to fracture at the longitudinal double submerged arc weld. Oddly enough for gas pipelines, it was found that fatigue cracks had propagated from a large embedded weld defect of lack of fusion resulting from severe geometrical mismatch between inner and outer weld passes. What makes this failure particularly interesting is that: previous in line inspections failed to detect any defect, no evidence of third party damage was found, and very few large pressure cycles had been recorded during the last 5 years of service, which were believed to be representative of the entire service life of the pipeline. Fatigue tests were carried out to characterize propagation of fatigue cracks in weld metal, it was found that a large Paris exponent made the few large amplitude cycles most contributing to crack propagation. Crack growth path and striation patterns were studied. Fatigue growth was modelled by integrating experimental results and by extrapolating striation spacing in the fracture surface of the failed pipe. Crack growth path and striation patterns were studied. It was found that microstructure discontinuities govern propagation at low {delta}K, but one striation per cycle was produced at large {delta}K, due to a mostly ductile propagation mode. Fatigue growth was modelled by integrating experimental results and by extrapolating striation spacing in the fracture surface of the failed pipe. It was found that in the early life of the line many more large pressure cycles than expected had occurred. Good correspondence between predicted and actual fatigue lives was in this way obtained (author)

  6. Fatigue assessment of a double submerged arc welded gas pipeline

    Energy Technology Data Exchange (ETDEWEB)

    Fazzini, Pablo; Otegui, Jose Luis [Universidad Nacional Mar del Plata, Mar del Plata (Argentina). Instituto de Ciencia y Tecnologia de Materiales (INTEMA); Teutonico, Mauricio; Manfredi, Carlos [GIE S.A., Mar del Plata (Argentina)

    2005-07-01

    An uncommon blowout in a 24'' diameter, 7 mm thick API 5L X52 gas pipeline was due to fracture at the longitudinal double submerged arc weld. Oddly enough for gas pipelines, it was found that fatigue cracks had propagated from a large embedded weld defect of lack of fusion resulting from severe geometrical mismatch between inner and outer weld passes. What makes this failure particularly interesting is that: previous in line inspections failed to detect any defect, no evidence of third party damage was found, and very few large pressure cycles had been recorded during the last 5 years of service, which were believed to be representative of the entire service life of the pipeline. Fatigue tests were carried out to characterize propagation of fatigue cracks in weld metal, it was found that a large Paris exponent made the few large amplitude cycles most contributing to crack propagation. Crack growth path and striation patterns were studied. Fatigue growth was modelled by integrating experimental results and by extrapolating striation spacing in the fracture surface of the failed pipe. Crack growth path and striation patterns were studied. It was found that microstructure discontinuities govern propagation at low {delta}K, but one striation per cycle was produced at large {delta}K, due to a mostly ductile propagation mode. Fatigue growth was modelled by integrating experimental results and by extrapolating striation spacing in the fracture surface of the failed pipe. It was found that in the early life of the line many more large pressure cycles than expected had occurred. Good correspondence between predicted and actual fatigue lives was in this way obtained (author)

  7. Perceived Fatigue Interference and Depressed Mood: Comparison of Chronic Fatigue Syndrome/Myalgic Encephalomyelitis Patients with Fatigued Breast Cancer Survivors.

    Science.gov (United States)

    Hall, Daniel L; Antoni, Michael H; Lattie, Emily G; Jutagir, Devika R; Czaja, Sara J; Perdomo, Dolores; Lechner, Suzanne C; Stagl, Jamie M; Bouchard, Laura C; Gudenkauf, Lisa M; Traeger, Lara; Fletcher, MaryAnn; Klimas, Nancy G

    Persistent fatigue and depressive symptoms are both highly prevalent among patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) as well as breast cancer survivors. This study aimed to assess and directly compare perceptions of fatigue as highly interfering in one's daily functioning in both patient populations to better understand their relationships with depressed mood. Participants were 95 female CFS/ME patients and 67 females who were approximately 5 years post-treatment for stage 0-III breast cancer presenting with clinically elevated fatigue severity. Self-report measures were obtained on participants' fatigue-related interference in daily functioning and fatigue severity as well as depressed mood. Hierarchical regression was used to test effects controlling for relevant demographic, psychosocial, and medical covariates. CFS/ME patients endorsed greater depressed mood and fatigue interference than did fatigued breast cancer survivors, p's fatigued breast cancer survivors (β=.18, p =.19). CFS/ME patients reported elevated fatigue symptoms and depression relative to fatigued breast cancer survivors. In the former group, greater depressed mood was highly and significantly associated with greater fatigue-related inference in daily activities. Potential targets for cognitive behavioral interventions are discussed.

  8. fatigue strength of reinforced concrete flexural members

    African Journals Online (AJOL)

    Dr Obe

    1980-03-01

    Mar 1, 1980 ... cyclic loads behave differently compared with static bending and can collapse due to the fatigue of concrete, reinforcement or both when maximum fatigue stresses of ... under low and medium load levels, than under high load ...

  9. Development of an in situ fatigue sensor.

    Science.gov (United States)

    2011-01-01

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

  10. Wake up to fatigue risk management

    CSIR Research Space (South Africa)

    Schutte, PC

    2009-06-01

    Full Text Available fatigue management programme should address the unique needs of the operation in which it will be implemented, it should be integrated into the normal operations, and it should encourage active participation from all stakeholders. A fatigue management...

  11. High temperature fatigue behaviour of intermetallics

    Indian Academy of Sciences (India)

    M. Senthilkumar (Newgen Imaging) 1461 1996 Oct 15 13:05:22

    The effect of processing route on strain-controlled low cycle fatigue (LCF) life of binary ..... the once regarding close control of composition, control and reproduction of ... inverse effect of temperature on fatigue life seen in tests conducted in air.

  12. Compassion Fatigue in Pediatric Nurses.

    Science.gov (United States)

    Berger, Jill; Polivka, Barbara; Smoot, Elizabeth Ann; Owens, Heather

    2015-01-01

    Compassion fatigue in nursing has been shown to impact the quality of patient care and employee satisfaction and engagement. The aims of this study were to determine the prevalence and severity of compassion fatigue among pediatric nurses and variations in prevalence based on respondent demographics using a cross-sectional survey design. Nurses under 40 years of age, with 6-10 years of experience and/or working in a medical-surgical unit had significantly lower compassion satisfaction and higher levels of burnout. Secondary traumatic stress from caring for children with severe illness or injury or end of life was a key contributor to compassion fatigue. Copyright © 2015 Elsevier Inc. All rights reserved.

  13. Advanced methods of fatigue assessment

    CERN Document Server

    Radaj, Dieter

    2013-01-01

    The book in hand presents advanced methods of brittle fracture and fatigue assessment. The Neuber concept of fictitious notch rounding is enhanced with regard to theory and application. The stress intensity factor concept for cracks is extended to pointed and rounded corner notches as well as to locally elastic-plastic material behaviour. The averaged strain energy density within a circular sector volume around the notch tip is shown to be suitable for strength-assessments. Finally, the various implications of cyclic plasticity on fatigue crack growth are explained with emphasis being laid on the DJ-integral approach.   This book continues the expositions of the authors’ well known reference work in German language ‘Ermüdungsfestigkeit – Grundlagen für Ingenieure’ (Fatigue strength – fundamentals for engineers).

  14. 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.

  15. Effect of temperature upon the fatigue-crack propagation behavior of Inconel 625

    International Nuclear Information System (INIS)

    James, L.A.

    1977-03-01

    The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of mill-annealed Inconel 625 in an air environment over the range 75 0 - 1200 0 F (24 0 - 649 0 C). In general, fatigue-crack growth rates increased with increasing test temperature. Two different specimen sizes were employed at each test temperature, and no effects of specimen size upon crack growth were noted

  16. Demographic and clinical aspects of an Italian patient population with chronic fatigue syndrome

    Directory of Open Access Journals (Sweden)

    N. Carlo-Stella

    2011-06-01

    Full Text Available Chronic Fatigue Syndrome (CFS is a debilitating syndrome characterized by fatigue which, by exclusion, cannot be ascribed to another illness. Because of the vagueness of the symptoms and signs in patients with CFS, various attempts have been made to define the syndrome and classification criteria have been developed (1- 3, of which the most well-known and used are those of Fukuda et al. (1 This classification includes two major criteria...

  17. Fatigue crack growth in fiber reinforced plastics

    Science.gov (United States)

    Mandell, J. F.

    1979-01-01

    Fatigue crack growth in fiber composites occurs by such complex modes as to frustrate efforts at developing comprehensive theories and models. Under certain loading conditions and with certain types of reinforcement, simpler modes of fatigue crack growth are observed. These modes are more amenable to modeling efforts, and the fatigue crack growth rate can be predicted in some cases. Thus, a formula for prediction of ligamented mode fatigue crack growth rate is available.

  18. Fatigue of vanadium--hydrogen alloys

    International Nuclear Information System (INIS)

    Lee, K.S.; Stoloff, N.S.

    1975-01-01

    Hydrogen contents near and above the room temperature solubility limit increase the high cycle fatigue life but decrease low cycle life of polycrystalline vanadium. Changes in endurance limit with hydrides may be a consequence of decreased cyclic strain hardening coefficient, n'. 132 ppM hydrogen in solution has only a slightly beneficial effect on stress controlled fatigue life and essentially no effect on low cycle fatigue life. Unalloyed vanadium exhibits profuse striations, while hydrides produce cleavage cracks in fatigued samples. 10 fig

  19. Multispecimen fatigue crack propagation testing

    International Nuclear Information System (INIS)

    Ermi, A.M.; Bauer, R.E.; Chin, B.A.; Straalsund, J.L.

    1981-01-01

    Chains of miniature center-cracked-tension specimens were tested on a conventional testing machine and on a prototypic in-reactor fatigue machine as part of the fusion reactor materials alloy development program. Annealed and 20 percent cold-worked 316 stainless steel specimens were cycled under various conditions of temperature, frequency, stress ratio and chain length. Crack growth rates determined from multispecimen visual measurements and from an electrical potential technique were consistent with those obtained by conventional test methods. Results demonstrate that multispecimen chain testing is a valid method of obtaining fatigue crack propagation information for alloy development. 8 refs

  20. Fatigue data bases in Europe

    International Nuclear Information System (INIS)

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

    1988-01-01

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

  1. Chronic fatigue syndrome: diagnosis and treatment | Revelas ...

    African Journals Online (AJOL)

    Chronic fatigue syndrome (CFS) refers to marked and prolonged fatigue, for which no indentifiable cause can be found. Despite the presence of extensive symptoms, diagnosis is made when there is profound fatigue, lasting for a duration of six months, or longer. CFS is frequently seen in association with psychiatric ...

  2. How do women with lupus manage fatigue?

    DEFF Research Database (Denmark)

    Kier, Anne Ørnholt; Midtgaard, Julie; Hougaard, Karin Sørig

    2016-01-01

    Objective: Half of patients with systemic lupus erythematosus (SLE) consider fatigue to be the most disabling disease symptom. To develop and promote strategies to prevent and control fatigue, this study aimed to describe how women with SLE manage the experience of fatigue. Methods: Four focus...

  3. [Epidemiology of fatigue in general practice].

    Science.gov (United States)

    Fuhrer, R

    1994-11-01

    The epidemiology of fatigue is not well known in France, and this study reports on factors associated with fatigue in a sample of 3,784 general practice patients. Prevalence rates according to several definitions of fatigue are presented and factors are examined that have been reported to be associated with fatigue. Although 41.2% of the sample report having experienced symptoms of fatigue for at least three days, only 7.6% declare fatigue as a reason for consulting a doctor. Women report more symptoms of fatigue, but they do not consult more often than men for this reason. Age is strongly correlated with fatigue, but this is found only for men. Socioprofessional category bears no relationship to fatigue as a reason for consultation, however, the diagnosis of fatigue is more often attributed to professionals and upper management than it is to office staff or skilled and unskilled workers. We do find a strong relationship between depressive symptomatology as measured by the Center for Epidemiologic Studies (CES-D) and fatigue; nonetheless, fatigue is neither sensitive nor specific to the diagnosis of depression.

  4. Fatigue modeling of materials with complex microstructures

    DEFF Research Database (Denmark)

    Qing, Hai; Mishnaevsky, Leon

    2011-01-01

    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...

  5. Influence of Lumbar Muscle Fatigue on Trunk Adaptations during Sudden External Perturbations

    Science.gov (United States)

    Abboud, Jacques; Nougarou, François; Lardon, Arnaud; Dugas, Claude; Descarreaux, Martin

    2016-01-01

    Introduction: When the spine is subjected to perturbations, neuromuscular responses such as reflex muscle contractions contribute to the overall balance control and spinal stabilization mechanisms. These responses are influenced by muscle fatigue, which has been shown to trigger changes in muscle recruitment patterns. Neuromuscular adaptations, e.g., attenuation of reflex activation and/or postural oscillations following repeated unexpected external perturbations, have also been described. However, the characterization of these adaptations still remains unclear. Using high-density electromyography (EMG) may help understand how the nervous system chooses to deal with an unknown perturbation in different physiological and/or mechanical perturbation environments. Aim: To characterize trunk neuromuscular adaptations following repeated sudden external perturbations after a back muscle fatigue task using high-density EMG. Methods: Twenty-five healthy participants experienced a series of 15 sudden external perturbations before and after back muscle fatigue. Erector spinae muscle activity was recorded using high-density EMG. Trunk kinematics during perturbation trials were collected using a 3-D motion analysis system. A two-way repeated measure ANOVA was conducted to assess: (1) the adaptation effect across trials; (2) the fatigue effect; and (3) the interaction effect (fatigue × adaptation) for the baseline activity, the reflex latency, the reflex peak and trunk kinematic variables (flexion angle, velocity and time to peak velocity). Muscle activity spatial distribution before and following the fatigue task was also compared using t-tests for dependent samples. Results: An attenuation of muscle reflex peak was observed across perturbation trials before the fatigue task, but not after. The spatial distribution of muscle activity was significantly higher before the fatigue task compared to post-fatigue trials. Baseline activity showed a trend to higher values after muscle

  6. Influence of lumbar muscle fatigue on trunk adaptations during sudden external perturbations

    Directory of Open Access Journals (Sweden)

    Jacques Abboud

    2016-11-01

    Full Text Available IntroductionWhen the spine is subjected to perturbations, neuromuscular responses such as reflex muscle contractions contribute to the overall balance control and spinal stabilization mechanisms. These responses are influenced by muscle fatigue, which has been shown to trigger changes in muscle recruitment patterns. Neuromuscular adaptations, e.g. attenuation of reflex activation and/or postural oscillations following repeated unexpected external perturbations, have also been described. However, the characterization of these adaptations still remains unclear. Using high-density electromyography (EMG may help understand how the nervous system chooses to deal with an unknown perturbation in different physiological and/or mechanical perturbation environments. AimTo characterize trunk neuromuscular adaptations following repeated sudden external perturbations after a back muscle fatigue task using high-density EMG.MethodsTwenty-five healthy participants experienced a series of 15 sudden external perturbations before and after back muscle fatigue. Erector spinae muscle activity was recorded using high-density EMG. Trunk kinematics during perturbation trials were collected using a 3-D motion analysis system. A two-way repeated measure ANOVA was conducted to assess 1 the adaptation effect across trials, 2 the fatigue effect, and 3 the interaction effect (fatigue x adaptation for the baseline activity, the reflex latency, the reflex peak and trunk kinematic variables (flexion angle, velocity and time to peak velocity. Muscle activity spatial distribution before and following the fatigue task was also compared using t-tests for dependent samples. ResultsAn attenuation of muscle reflex peak was observed across perturbation trials before the fatigue task, but not after. The spatial distribution of muscle activity was significantly higher before the fatigue task compared to post-fatigue trials. Baseline activity showed a trend to higher values after muscle

  7. Fatigue Life of Titanium Alloys Fabricated by Additive Layer Manufacturing Techniques for Dental Implants

    Science.gov (United States)

    Chan, Kwai S.; Koike, Marie; Mason, Robert L.; Okabe, Toru

    2013-02-01

    Additive layer deposition techniques such as electron beam melting (EBM) and laser beam melting (LBM) have been utilized to fabricate rectangular plates of Ti-6Al-4V with extra low interstitial (ELI) contents. The layer-by-layer deposition techniques resulted in plates that have different surface finishes which can impact significantly on the fatigue life by providing potential sites for fatigue cracks to initiate. The fatigue life of Ti-6Al-4V ELI alloys fabricated by EBM and LBM deposition techniques was investigated by three-point testing of rectangular beams of as-fabricated and electro-discharge machined surfaces under stress-controlled conditions at 10 Hz until complete fracture. Fatigue life tests were also performed on rolled plates of Ti-6Al-4V ELI, regular Ti-6Al-4V, and CP Ti as controls. Fatigue surfaces were characterized by scanning electron microscopy to identify the crack initiation site in the various types of specimen surfaces. The fatigue life data were analyzed statistically using both analysis of variance techniques and the Kaplan-Meier survival analysis method with the Gehan-Breslow test. The results indicate that the LBM Ti-6Al-4V ELI material exhibits a longer fatigue life than the EBM counterpart and CP Ti, but a shorter fatigue life compared to rolled Ti-6Al-4V ELI. The difference in the fatigue life behavior may be largely attributed to the presence of rough surface features that act as fatigue crack initiation sites in the EBM material.

  8. Perceived Fatigue Interference and Depressed Mood: Comparison of Chronic Fatigue Syndrome/Myalgic Encephalomyelitis Patients with Fatigued Breast Cancer Survivors

    Science.gov (United States)

    Hall, Daniel L.; Antoni, Michael H.; Lattie, Emily G.; Jutagir, Devika R.; Czaja, Sara J.; Perdomo, Dolores; Lechner, Suzanne C.; Stagl, Jamie M.; Bouchard, Laura C.; Gudenkauf, Lisa M.; Traeger, Lara; Fletcher, MaryAnn; Klimas, Nancy G.

    2015-01-01

    Objective Persistent fatigue and depressive symptoms are both highly prevalent among patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) as well as breast cancer survivors. This study aimed to assess and directly compare perceptions of fatigue as highly interfering in one’s daily functioning in both patient populations to better understand their relationships with depressed mood. Methods Participants were 95 female CFS/ME patients and 67 females who were approximately 5 years post-treatment for stage 0-III breast cancer presenting with clinically elevated fatigue severity. Self-report measures were obtained on participants’ fatigue-related interference in daily functioning and fatigue severity as well as depressed mood. Hierarchical regression was used to test effects controlling for relevant demographic, psychosocial, and medical covariates. Results CFS/ME patients endorsed greater depressed mood and fatigue interference than did fatigued breast cancer survivors, p’sfatigued breast cancer survivors (β=.18, p=.19). Conclusions CFS/ME patients reported elevated fatigue symptoms and depression relative to fatigued breast cancer survivors. In the former group, greater depressed mood was highly and significantly associated with greater fatigue-related inference in daily activities. Potential targets for cognitive behavioral interventions are discussed. PMID:26180660

  9. The potential significance of microalloying with niobium in governing very high cycle fatigue behavior of bainite/martensite multiphase steels

    International Nuclear Information System (INIS)

    Zhao, P.; Cheng, C.; Gao, G.; Hui, W.; Misra, R.D.K.; Bai, B.; Weng, Y.

    2016-01-01

    We elucidate here the effect of microalloying with niobium (Nb) on very high cycle fatigue (VHCF) behavior in high-strength C–Mn–Si–Cr bainite/martensite (B/M) multiphase steels studied through ultrasonic fatigue testing. The tensile strength (R_m) and fatigue limit strength after 10"9 cycles (σ_w_9) and in the non-failure condition of the steel microalloyed with Nb were 1640 MPa and 900 MPa, respectively. Thus, the value of σ_w_9/R_m exceeded in comparison to conventional steels and was approximate 0.55. Three types of failure modes were observed in Nb-bearing steels depending on the surface condition, inclusion, and the matrix microstructure, i.e., surface defect-induced failure mode (S-mode), inclusion-induced failure mode (I-mode), and non-inclusion induced failure mode (N-mode). Only two failure modes were observed in Nb-free steels, the S-mode and the N-mode. The study clearly suggests that Nb had a distinct effect on the VHCF properties of B/M steels. The VHCF limit of Nb-bearing steel was enhanced by 200 MPa because of refinement of the microstructure and pinning of dislocations by randomly distributed nanometer-sized Nb(C, N) precipitates. It is underscored that microalloying with Nb is a potential approach to enhance VHCF properties in advanced high-strength steels.

  10. Hormone levels in radiotherapy treatment related fatigue

    International Nuclear Information System (INIS)

    Biswal, B.M.; Mallik, G.S.

    2003-01-01

    Radiotherapy is known to cause debilitating treatment related fatigue. Fatigue in general is a conglomeration of psychological, physical, hematological and unknown factors influencing the internal milieu of the cancer patient. Radiotherapy can add stress at the cellular and somatic level to aggravate further fatigue in cancer patients undergoing radiotherapy. Stress related hormones might be mediating in the development of fatigue. This is an ongoing prospective study to evaluate if the hormonal profile related to stress is influenced by radiotherapy treatment related fatigue. The study was conducted from September 2002 onwards in the division of Radiotherapy and Oncology of our Medical School. Previously untreated patients with histopathology proof of malignancy requiring external beam radiotherapy were considered for this study. Selection criteria were applied to exclude other causes of fatigue. Initial fatigue score was obtained using Pipers Fatigue Score questionnaire containing 23 questions, subsequently final fatigue score was obtained at the end of radiotherapy. Blood samples were obtained to estimate the levels of ACTH, TSH, HGH, and cortisol on the final assessment. The hormone levels were compared with resultant post radiotherapy fatigue score. At the time of reporting 50 patients were evaluable for the study. The total significant fatigue score was observed among 12 (24%) patients. The individual debilitating fatigue score were behavioral severity 14 (28%), affective meaning 14(28%), Sensory 13 (26%) and cognitive mood 10 (20%) respectively. From the analysis of hormonal profile, growth hormone level > 1 ng/mL and TSH <0.03 appears to be associated with high fatigue score (though statistically not significant); whereas there was no correlation with ACTH and serum cortisol level. In our prospective study severe radiotherapy treatment related fatigue was found among our patient population. Low levels of TSH and high levels of GH appear to be associated

  11. Fatigue damage of nuclear facilities

    International Nuclear Information System (INIS)

    2001-01-01

    The conference on the fatigue damage of nuclear facilities, organized by the SFEN (french society of nuclear energy), took place at Paris the 23. of november 2000. Eleven papers were presented, showing the state of the art and the research programs in the domain of the sizing rules, safety, installations damage, examination and maintenance. (A.L.B.)

  12. Thermal fatigue behavior of valves

    International Nuclear Information System (INIS)

    Moinereau, D.; Scliffet, L.; Capion, J.C.; Genette, P.

    1991-01-01

    This paper reports that valves of pressurized water reactors are exposed to thermal shocks during transient operations. The numerous thermal shock tests performed on valves on the EDF test facilities have shown the sensibility of fillets and geometrical discontinuities to thermal fatigue: cracks can appear in those areas and grow through the valve body. Valves systems designated as level 1 must be designed to withstand fatigue up to the second isolation valve: the relevant rule is specified in the paragraph B 3500 of the French RCCM code. It is a simplified method which doesn't require finite element calculations. Many valve systems have been designed according to this rule and have been operated without accident. However, in one case, important cracks were found in the fillet of a check-valve after numerous thermal shocks. Calculation of the valve's behavior according to the RCCM code to estimate the fatigue damage resulting from thermal shocks led to a low damage factor, which doesn't agree with the experimental results. This was confirmed by new testings and showed the inadequacy of B 3500 rule for thermal transients. On this base a new rule is proposed to estimate fatigue damage resulting from thermal shocks. An experimental program has been realized to validate this rule. Axisymetrical analytical mock-ups with different geometries and one check-valve in austenitic stainless steel 316 L have been submitted to hot thermal shocks of 210 degrees C magnitude

  13. Fatigue Reliability under Random Loads

    DEFF Research Database (Denmark)

    Talreja, R.

    1979-01-01

    We consider the problem of estimating the probability of survival (non-failure) and the probability of safe operation (strength greater than a limiting value) of structures subjected to random loads. These probabilities are formulated in terms of the probability distributions of the loads...... propagation stage. The consequences of this behaviour on the fatigue reliability are discussed....

  14. Risk Based Optimal Fatigue Testing

    DEFF Research Database (Denmark)

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

    1992-01-01

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

  15. Fatigue of superalloys and intermetallics

    International Nuclear Information System (INIS)

    Stoloff, N.S.

    1993-01-01

    The fatigue behavior of intermetallic alloys and their composites is contrasted to that of nickel-base superalloys. The roles of microstructure and slip planarity are emphasized. Obstacles to use of intermetallics under cyclic loading conditions are described and future research directions are suggested

  16. Fatigue in the shipping industry

    NARCIS (Netherlands)

    Houtman, I.; Miedema, M.; Jettinghoff, K.; Starren, A.; Heinrich, J.; Gort, J.

    2005-01-01

    Fatigue is a 'reduction in physical and/or mental capacity as the result of physical, mental, or emotional exertion which may impair nearly all physical abilities including: strength, speed, reaction time, coordination, decision making or balance'. The literature is quite clear on the debilitating

  17. 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.

  18. Fatigue strength of a single lap joint SPR-bonded

    International Nuclear Information System (INIS)

    Di Franco, G.; Fratini, L.; Pasta, A.

    2011-01-01

    In the last years, hybrid joints, meaning with this the joints which consist in combining a traditional mechanical joint to a layer of adhesive, are gradually attracting the attention of various sectors of the construction of vehicles and transportation industries, for their better performance compared to just mechanical joints (self-piercing riveting SPR, riveting, and so on) or just to bonded joints.The paper investigates the fatigue behavior of a single lap joint self-piercing riveted (SPR) and bonded throughout fatigue tests. The considered geometric configuration allowed the use of two rivets placed longitudinally; an epoxy resin was used as adhesive. In the first part of the work static characterization of the joints was carried out through tensile tests. Then fatigue tests were made with the application of different levels of load. The fatigue curves were also obtained at the varying the distance between the two rivets in order to better assess the joint strength for a given length of overlap.

  19. Corrosion fatigue of zircalloy-4 in chloride medium

    International Nuclear Information System (INIS)

    Monnerat, C.S.S.

    1984-01-01

    The fatigue behaviour of zircalloy-4 in a 0,5 M NaCl aqueous solution was studied. The tests were performed under potenciostatic control at room temperature and mean frequency of 80 hz. The tests have shown that zircalloy-4 does not have its fatigue life decreased under cathodic potencials action. The application of anodic potentials, however, has markedly influenced the life of the material. This influence is characteristic for a certain range of applied potential and cyclic stress level. It was shown that, for a maximum stress higher than yield stress and potential values higher than + 120 mV sub(sce), the life of the material was drastically reduced due to pit formation and intergranular attack. This 'critical' potential is, however, lower than the pit potential (approx. + 180 mV sub(sce)) obtained by the usual electrochemical methods. For maximum cyclic stress lower than the yield stress, the material did not fail even at potential values higher than the critical + 120 mV sub(sce). The application of potential values lower than + 120 mV sub(sce) led to an increase in the fatigue properties of the material, that is characterized by an increase in fatigue life as compared to that observed in air. This behaviour is attributed to the high velocity of repassivation presented by zircalloy-4. (Author) [pt

  20. Fatigue and workload among Danish fishermen

    DEFF Research Database (Denmark)

    Remmen, Line Nørgaard; Herttua, Kimmo; Riss-Jepsen, Jørgen

    2017-01-01

    . Highest levels of fatigue were observed among fishermen at Danish seiners (mean 10.21), and fatigue scores decreased with more days at sea. However, none of these results were significant. Adjusted analyses showed that physical workload was significantly related to general fatigue (b = 0.20, 95% CI: 0...... was additionally significantly associated to the levels of physical and mental fatigue. Fishermen had a lower average score for all fatigue dimensions compared to those seen in general Danish working population. Prospective studies are required to assess whether the identified associations are causal....

  1. Fatigue and damage tolerance scatter models

    Science.gov (United States)

    Raikher, Veniamin L.

    1994-09-01

    Effective Total Fatigue Life and Crack Growth Scatter Models are proposed. The first of them is based on the power form of the Wohler curve, fatigue scatter dependence on mean life value, cycle stress ratio influence on fatigue scatter, and validated description of the mean stress influence on the mean fatigue life. The second uses in addition are fracture mechanics approach, assumption of initial damage existence, and Paris equation. Simple formulas are derived for configurations of models. A preliminary identification of the parameters of the models is fulfilled on the basis of experimental data. Some new and important results for fatigue and crack growth scatter characteristics are obtained.

  2. Variable amplitude fatigue, modelling and testing

    International Nuclear Information System (INIS)

    Svensson, Thomas.

    1993-01-01

    Problems related to metal fatigue modelling and testing are here treated in four different papers. In the first paper different views of the subject are summarised in a literature survey. In the second paper a new model for fatigue life is investigated. Experimental results are established which are promising for further development of the mode. In the third paper a method is presented that generates a stochastic process, suitable to fatigue testing. The process is designed in order to resemble certain fatigue related features in service life processes. In the fourth paper fatigue problems in transport vibrations are treated

  3. Visual perception of fatigued lifting actions.

    Science.gov (United States)

    Fischer, Steven L; Albert, Wayne J; McGarry, Tim

    2012-12-01

    Fatigue-related changes in lifting kinematics may expose workers to undue injury risks. Early detection of accumulating fatigue offers the prospect of intervention strategies to mitigate such fatigue-related risks. In a first step towards this objective, this study investigated whether fatigue detection was accessible to visual perception and, if so, what was the key visual information required for successful fatigue discrimination. Eighteen participants were tasked with identifying fatigued lifts when viewing 24 trials presented using both video and point-light representations. Each trial comprised a pair of lifting actions containing a fresh and a fatigued lift from the same individual presented in counter-balanced sequence. Confidence intervals demonstrated that the frequency of correct responses for both sexes exceeded chance expectations (50%) for both video (68%±12%) and point-light representations (67%±10%), demonstrating that fatigued lifting kinematics are open to visual perception. There were no significant differences between sexes or viewing condition, the latter result indicating kinematic dynamics as providing sufficient information for successful fatigue discrimination. Moreover, results from single viewer investigation reported fatigue detection (75%) from point-light information describing only the kinematics of the box lifted. These preliminary findings may have important workplace applications if fatigue discrimination rates can be improved upon through future research. Copyright © 2012 Elsevier B.V. All rights reserved.

  4. The numerical high cycle fatigue damage model of fillet weld joint under weld-induced residual stresses

    Science.gov (United States)

    Nguyen Van Do, Vuong

    2018-04-01

    In this study, a development of nonlinear continuum damage mechanics (CDM) model for multiaxial high cycle fatigue is proposed in which the cyclic plasticity constitutive model has been incorporated in the finite element (FE) framework. T-joint FE simulation of fillet welding is implemented to characterize sequentially coupled three-dimensional (3-D) of thermo-mechanical FE formulation and simulate the welding residual stresses. The high cycle fatigue damage model is then taken account into the fillet weld joints under the various cyclic fatigue load types to calculate the fatigue life considering the residual stresses. The fatigue crack initiation and the propagation in the present model estimated for the total fatigue is compared with the experimental results. The FE results illustrated that the proposed high cycle fatigue damage model in this study could become a powerful tool to effectively predict the fatigue life of the welds. Parametric studies in this work are also demonstrated that the welding residual stresses cannot be ignored in the computation of the fatigue life of welded structures.

  5. Microscopic local fatigue in PZT thin films

    International Nuclear Information System (INIS)

    Li, B S; Wu, A; Vilarinho, P M

    2007-01-01

    The reduction in switchable polarization during fatigue largely limits the application of PZT thin films in ferroelectric nonvolatile memories. So, it is very important to understand the fatigue mechanism in PZT films, especially at a nanoscale level. In this paper, nanoscale fatigue properties in PZT thin films have been studied by piezoresponse force microscopy and local piezoloops. It has been found that a piezoloop obtained on a fatigued point exhibits a much more pinched shape and a local imprint phenomenon is observed after severe fatigue. Furthermore, the domain structure evolves from a simple single-peak profile to a complex fluctuant one. However, there is only some shift of the piezoloop when a unipolar field with the same amplitude is applied on the film. The available experimental data show that there exist obvious domain wall pinning and injection of electrons into the film during fatigue. Finally, a schematic illustration is suggested to explain the possible fatigue mechanism

  6. Detection of thermal fatigue in composites by second harmonic Lamb waves

    International Nuclear Information System (INIS)

    Li, Weibin; Cho, Younho; Achenbach, Jan D

    2012-01-01

    Composite materials which are widely used in the aerospace industry, are usually subjected to frequent variation of temperature. Thermal cyclic loading may induce material degradation. Considering the long-term service of aircraft composites and the importance of safety in the aircraft industry, even a little damage that may be accumulative via thermal fatigue is often of great concern. Therefore, there is a demand to develop non-destructive approaches to evaluate thermal fatigue damage in an early stage. Due to the sensitivity of acoustic nonlinearity to micro-damage, the nonlinear ultrasonic technique has been explored as a promising tool for early detection of micro-damage. This paper investigates an experimental scheme for characterizing thermal fatigue damage in composite laminates using second harmonic Lamb waves. The present results show a monotonic increase of acoustic nonlinearity with respect to thermal fatigue cycles. The experimental observation of the correlation between the acoustic nonlinearity and thermal fatigue cycles in carbon/epoxy laminates verifies that nonlinear Lamb waves can be used to assess thermal fatigue damage rendering improved sensitivity over conventional linear feature based non-destructive evaluation techniques. Velocity and attenuation based ultrasonic studies are carried out for comparison with the nonlinear ultrasonic approach and it is found that nonlinear acoustic parameters are more promising indicators of thermal fatigue damage than linear ones. (paper)

  7. Fatigue damage mechanisms in short fiber reinforced PBT+PET GF30

    International Nuclear Information System (INIS)

    Klimkeit, B.; Castagnet, S.; Nadot, Y.; Habib, A. El; Benoit, G.; Bergamo, S.; Dumas, C.; Achard, S.

    2011-01-01

    Research highlights: → Final macroscopic cracking only affects the few last percent of the lifetime → Classical approach based on fracture surface observation is not sufficient to characterize micro-mechanisms → Different techniques (scanning electron microscopy, replica technique, infra-red imaging) are compared to the macroscopic mechanical behavior evolution (stiffness, viscous damping, ratcheting effect) → The influence of surrounding fibers on some observed damage processes is being evidenced for the first time. - Abstract: The fatigue damage of a glass-reinforced PolyButylene Terephthalate and PolyEthylene Terephthalate with the fiber volume fraction of 30% (PBT+PET GF30) is investigated by means of various techniques. Fatigue tests at R = 0.1 are carried out on dogbone specimens and tubular specimens with different fiber orientations. The macroscopic evolution of the material behavior is evaluated and fatigue damage mechanisms are observed with a replica technique, Infrared imaging and scanning electron microscopy. A fatigue damage scenario is finally proposed. It is shown that the propagation of a single macroscopic crack is not the major fatigue mechanism under fatigue loading. Damage is spatially distributed in the material and the classical circular crack at the end of the fiber is confirmed as the based fatigue mechanisms. It is also shown that the damage observed alongside the fibers is related to spatial distribution of fiber rather than stress distribution around one single fiber.

  8. Effect of surface integrity of hard turned AISI 52100 steel on fatigue performance

    International Nuclear Information System (INIS)

    Smith, Stephen; Melkote, Shreyes N.; Lara-Curzio, Edgar; Watkins, Thomas R.; Allard, Larry; Riester, Laura

    2007-01-01

    This paper addresses the relationship between surface integrity and fatigue life of hard turned AISI 52100 steel (60-62 HRC), with grinding as a benchmark. The impact of superfinishing on the fatigue performance of hard turned and ground surfaces is also discussed. Specifically, the surface integrity and fatigue life of the following five distinct surface conditions are examined: hard turned with continuous white layer, hard turned with no white layer, ground, and superfinished hard turned and ground specimens. Surface integrity of the specimens is characterized via surface topography measurement, metallography, residual stress measurements, transmission electron microscopy (TEM), and nano-indentation tests. High cycle tension-tension fatigue tests show that the presence of white layer does not adversely affect fatigue life and that, on average, the hard turned surface performs as well or better than the ground surface. The effect of superfinishing is to exaggerate these differences in performance. The results obtained from this study suggest that the effect of residual stress on fatigue life is more significant than the effect of white layer. For the hard turned surfaces, the fatigue life is found to be directly proportional to both the surface compressive residual stress and the maximum compressive residual stress. Possible explanations for the observed effects are discussed

  9. Application of viscoelastic continuum damage approach to predict fatigue performance of Binzhou perpetual pavements

    Directory of Open Access Journals (Sweden)

    Wei Cao

    2016-04-01

    Full Text Available For this study, the Binzhou perpetual pavement test sections constructed in Shandong Province, China, were simulated for long-term fatigue performance using the layered viscoelastic pavement analysis for critical distresses (LVECD finite element software package. In this framework, asphalt concrete was treated in the context of linear viscoelastic continuum damage theory. A recently developed unified fatigue failure criterion that defined the boundaries of the applicable region of the theory was also incorporated. The mechanistic modeling of the fatigue mechanisms was able to accommodate the complex temperature variations and loading conditions of the field pavements in a rigorous manner. All of the material models were conveniently characterized by dynamic modulus tests and direct tension cyclic fatigue tests in the laboratory using cylindrical specimens. By comparing the obtained damage characteristic curves and failure criteria, it is found that mixtures with small aggregate particle sizes, a dense gradation, and modified asphalt binder tended to exhibit the best fatigue resistance at the material level. The 15-year finite element structural simulation results for all the test sections indicate that fatigue performance has a strong dependence on the thickness of the asphalt pavements. Based on the predicted location and severity of the fatigue damage, it is recommended that Sections 1 and 3 of the Binzhou test sections be employed for perpetual pavement design.

  10. Effect of Applied Potential on Fatigue Life of Electropolished Nitinol Wires

    Science.gov (United States)

    Sivan, Shiril; Di Prima, Matthew; Weaver, Jason D.

    2017-09-01

    Nitinol is used as a metallic biomaterial in medical devices due to its shape memory and pseudoelastic properties. The clinical performance of nitinol depends on factors which include the surface finish, the local environment, and the mechanical loads to which the device is subjected. Preclinical evaluations of device durability are performed with fatigue tests while electrochemical characterization methods such as ASTM F2129 are employed to evaluate corrosion susceptibility by determining the rest potential and breakdown potential. However, it is well established that the rest potential of a metal surface can vary with the local environment. Very little is known regarding the influence of voltage on fatigue life of nitinol. In this study, we developed a fatigue testing method in which an electrochemical system was integrated with a rotary bend wire fatigue tester. Samples were fatigued at various strain levels at electropotentials anodic and cathodic to the rest potential to determine if it could influence fatigue life. Wires at potentials negative to the rest potential had a significantly higher number of cycles to fracture than wires held at potentials above the breakdown potential. For wires for which no potential was applied, they had fatigue life similar to wires at negative potentials.

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

    International Nuclear Information System (INIS)

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

    2007-01-01

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

  12. The nature of self-regulatory fatigue and “ego depletion”: Lessons from physical fatigue

    Science.gov (United States)

    Evans, Daniel R.; Boggero, Ian A.; Segerstrom, Suzanne C.

    2016-01-01

    Self-regulation requires overriding a dominant response, and leads to temporary self-regulatory fatigue. Existing theories of the nature and causes of self-regulatory fatigue highlight physiological substrates such as glucose or psychological processes such as motivation, but these explanations are incomplete on their own. Historically, theories of physical fatigue demonstrate a similar pattern of useful but incomplete explanations, as recent views of physical fatigue emphasize the roles of both physiological and psychological factors. In addition to accounting for multiple inputs, these newer views also explain how fatigue can occur even in the presence of sufficient resources. Examining these newer theories of physical fatigue can serve as a foundation on which to build a more comprehensive understanding of self-regulatory fatigue that integrates possible neurobiological underpinnings of physical and self-regulatory fatigue, and suggests the possible function of self-regulatory fatigue. PMID:26228914

  13. The Nature of Self-Regulatory Fatigue and "Ego Depletion": Lessons From Physical Fatigue.

    Science.gov (United States)

    Evans, Daniel R; Boggero, Ian A; Segerstrom, Suzanne C

    2015-07-30

    Self-regulation requires overriding a dominant response and leads to temporary self-regulatory fatigue. Existing theories of the nature and causes of self-regulatory fatigue highlight physiological substrates such as glucose, or psychological processes such as motivation, but these explanations are incomplete on their own. Historically, theories of physical fatigue demonstrate a similar pattern of useful but incomplete explanations, as recent views of physical fatigue emphasize the roles of both physiological and psychological factors. In addition to accounting for multiple inputs, these newer views also explain how fatigue can occur even in the presence of sufficient resources. Examining these newer theories of physical fatigue can serve as a foundation on which to build a more comprehensive understanding of self-regulatory fatigue that integrates possible neurobiological underpinnings of physical and self-regulatory fatigue, and suggests the possible function of self-regulatory fatigue. © 2015 by the Society for Personality and Social Psychology, Inc.

  14. EFFECT OF STRAIN HARDENING ON FATIGUE CRACK CLOSURE IN ALUMINUM ALLOY UNDER CONSTANT AMPLITUDE WITH SINGLE OVERLOAD

    Directory of Open Access Journals (Sweden)

    Nirpesh Vikram

    2015-12-01

    Full Text Available In this study effect of strain hardening on crack closure has been examined with the help of experiments and finite element method on the side edge notched specimen of five different Aluminum alloy (3003 Al, 5052 Al, 6061 T6, 6063 T6, 6351 in mode I under constant amplitude fatigue loading with single overload using Abaqus® 6.10 which is very well accepted FEM application in research. Extended Finite Element Method Module has been used to determine effective stress intensity factor at the crack tip while propagation takes place. FEM results have given good agreement with experimental results. Regression analysis has also been done with SPSS® 16 and dependency of strain hardening coefficient on crack closure has analyzed. A generalized empirical formula has been developed based on strain hardening to calculate effective stress intensity range ratio and a modified Paris law has also been formulated for these aluminum alloy.

  15. Fatigue processes in thermoplastic fibres; Les mecanismes de fatigue dans les fibres thermoplastiques

    Energy Technology Data Exchange (ETDEWEB)

    Herrera Ramirez, J.M.

    2004-09-15

    The present study examines and compares the behaviour of the two types of PA66 fibres and two types of PET fibres under fatigue loading up to failure, and the correlation between the fibres (nano)structures and their structural heterogeneities, with fatigue lifetimes. Several techniques have been used to analyze the materials, such as scanning electron microscopy (SEM), microanalysis (EDS), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and micro-Raman spectroscopy. A meticulous analysis by scanning electron microscopy of the fracture morphology of fibres broken in tension and in fatigue, as well as a study of the fatigue life, were undertaken. The fatigue process occurs when the cyclic load amplitude is sufficiently large, however a condition for fatigue failure is that the minimum load each cycle must be lower than a threshold stress level. Failure under fatigue conditions leads to distinctive fracture morphologies which are very different from those seen after tensile or creep failure and this allows easy identification of the fatigue process. The fibres have been analyzed in the as received state and after fatigue failure in order to observe the microstructural changes resulting from the fatigue loading. The results will be compared with those obtained for fibres loaded under conditions where the fatigue process was hindered. The role of the microstructure of the fibres in determining fatigue will be discussed in this work and the possibility of improving their resistance to fatigue or eliminating the fatigue process will be discussed. (author)

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

    Science.gov (United States)

    Rovigatti, Ugo

    2012-12-01

    In July 2010, at the Muscle Fatigue Meeting, I presented an overview of Chronic Fatigue Syndrome and Cancer Related Fatigue, emphasizing a critical interpretation of the potential association between Chronic Fatigue Syndrome and Cancer Related Fatigue and a newly discovered retrovirus: Xenotropic Murine Related Virus. Since this association was hotly debated at that time, I suggested at the Meeting that it was wrong and most likely due to the identification of the wrong virus culprit. Today, 20 months after the Meeting, the first part of our prediction has turned out to be correct, as Xenotropic Murine Related Virus was shown to be a laboratory-created artefact. Still, the potential association of fatigue-syndromes with an infection (most likely viral) is sustained by a plethora of evidence and this overview will initially summarize data suggesting prior viral infection(s). The principal hypothesized mechanisms for both peripheral and central Chronic Fatigue Syndrome/Cancer Related Fatigue will be then summarized, also indicating plausible associations and triggering factors. All evidence accrued so far suggests that further research work should be performed in this interesting area and in order to identify an infectious agent for Chronic Fatigue Syndrome/Cancer Related Fatigue. One candidate RNA virus, Micro-Foci inducing Virus, will be described in this overview. Copyright © 2012 Elsevier B.V. All rights reserved.

  17. Effect of tensile mean stress on fatigue behavior of single-crystal and directionally solidified superalloys

    Science.gov (United States)

    Kalluri, Sreeramesh; Mcgaw, Michael A.

    1990-01-01

    Two nickel base superalloys, single crystal PWA 1480 and directionally solidified MAR-M 246 + Hf, were studied in view of the potential usage of the former and usage of the latter as blade materials for the turbomachinery of the space shuttle main engine. The baseline zero mean stress (ZMS) fatigue life (FL) behavior of these superalloys was established, and then the effect of tensile mean stress (TMS) on their FL behavior was characterized. At room temperature these superalloys have lower ductilities and higher strengths than most polycrystalline engineering alloys. The cycle stress-strain response was thus nominally elastic in most of the fatigue tests. Therefore, a stress range based FL prediction approach was used to characterize both the ZMS and TMS fatigue data. In the past, several researchers have developed methods to account for the detrimental effect of tensile mean stress on the FL for polycrystalline engineering alloys. However, the applicability of these methods to single crystal and directionally solidified superalloys has not been established. In this study, these methods were applied to characterize the TMS fatigue data of single crystal PWA 1480 and directionally solidified MAR-M 246 + Hf and were found to be unsatisfactory. Therefore, a method of accounting for the TMS effect on FL, that is based on a technique proposed by Heidmann and Manson was developed to characterize the TMS fatigue data of these superalloys. Details of this method and its relationship to the conventionally used mean stress methods in FL prediction are discussed.

  18. Assessment of early onset of driver fatigue using multimodal fatigue measures in a static simulator.

    Science.gov (United States)

    Jagannath, M; Balasubramanian, Venkatesh

    2014-07-01

    Driver fatigue is an important contributor to road accidents. This paper reports a study that evaluated driver fatigue using multimodal fatigue measures, i.e., surface electromyography (sEMG), electroencephalography (EEG), seat interface pressure, blood pressure, heart rate and oxygen saturation level. Twenty male participants volunteered in this study by performing 60 min of driving on a static simulator. Results from sEMG showed significant physical fatiguefatigue. This will help us understand the influence of physical and mental fatigue on driver during monotonous driving. Copyright © 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.

  19. The reduction in fatigue crack growth resistance of dentin with depth.

    Science.gov (United States)

    Ivancik, J; Neerchal, N K; Romberg, E; Arola, D

    2011-08-01

    The fatigue crack growth resistance of dentin was characterized as a function of depth from the dentino-enamel junction. Compact tension (CT) specimens were prepared from the crowns of third molars in the deep, middle, and peripheral dentin. The microstructure was quantified in terms of the average tubule dimensions and density. Fatigue cracks were grown in-plane with the tubules and characterized in terms of the initiation and growth responses. Deep dentin exhibited the lowest resistance to the initiation of fatigue crack growth, as indicated by the stress intensity threshold (ΔK(th) ≈ 0.8 MPa•m(0.5)) and the highest incremental fatigue crack growth rate (over 1000 times that in peripheral dentin). Cracks in deep dentin underwent incremental extension under cyclic stresses that were 40% lower than those required in peripheral dentin. The average fatigue crack growth rates increased significantly with tubule density, indicating the importance of microstructure on the potential for tooth fracture. Molars with deep restorations are more likely to suffer from the cracked-tooth syndrome, because of the lower fatigue crack growth resistance of deep dentin.

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

    International Nuclear Information System (INIS)

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

    2001-01-01

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

  1. Enhancement of fatigue endurance in ferroelectric PZT ceramic by the addition of bismuth layered SBT

    Science.gov (United States)

    Namsar, O.; Pojprapai, S.; Watcharapasorn, A.; Jiansirisomboon, S.

    2014-10-01

    Electrical fatigue properties of (1-x)PZT-xSBT ceramics (x = 0-1.0 weight fraction) were characterized. It was found that pure PZT ceramic had severe polarization fatigue. This was mainly attributed to an occurrence of the macroscopic cracks at near-electrode regions. On the contrary, pure SBT ceramic exhibited excellent fatigue resistance, which was attributed primarily to weak domain wall pinning. As small amount of SBT (0.1 ≤ x ≤ 0.3) was added into PZT, a small reduction of remanent polarization after fatigue process was observed. This demonstrated that these ceramics had high stability during the repeated domain switching due to their low oxygen vacancy concentration. Therefore, these results suggested that this new ceramic PZT-SBT system seemed to be an alternative material for replacing pure PZT in ferroelectric memory applications.

  2. On the fatigue behavior of friction stir welded AlSi 10 Mg alloy

    International Nuclear Information System (INIS)

    Alburquerque, J. M.; Ramos, P. A.; Gomes, M. A.; Cruz, A. C.

    2005-01-01

    The high cycle fatigue behaviour of friction stir welded AISi 10 Mg samples was investigated for a stress ratio R=0.1, ranging from 0.5 to 0.9 of the yield strength, in addition to tensile tests. The welds were produced with different tool rotation and travel speeds, and these welding parameters were correlated to residual stresses, measured by X-ray diffraction (sen''2Ψ method). Moreover, the residual stresses were measured during the fatigue testing, at fixed cycle intervals, being reported. It was observed that the residual (compressive)stresses within the nugget were smaller than in the interface regions (between the thermo-mechanically affected zone and the base metal) and stabilized above 4 x 10''5 cycles. Fatigue crack morphology and microstructural changes were characterized by optical and electron microscopy and the observations are discussed along with the fatigue results. (Author) 14 refs

  3. Tension-Compression Fatigue Behavior of Plain Woven Kenaf/Kevlar Hybrid Composites

    Directory of Open Access Journals (Sweden)

    Suhad D. Salman

    2016-02-01

    Full Text Available The applications of hybrid natural/synthetic reinforced polymer composites have been rapidly gaining market share in structural applications due to their remarkable characteristics and the fact that most of the components made of these materials are subjected to cyclic loading. Their fatigue properties have received a lot of attention because predicting their behavior is a challenge due to the effects of the synergies between the fibers. The purpose of this work is to characterize the tension, compression, and tensile-compression fatigue behavior of six layers of Kevlar hybridized with one layer of woven kenaf reinforced epoxy, at a 35% weight fraction. Fatigue tests were carried out and loaded cyclically at 60%, 70%, 80%, and 90% of their ultimate compressive stress. The results give a complete description for tensile and compression properties and could be used to predict fatigue-induced failure mechanisms.

  4. High-temperature low cycle fatigue behavior of a gray cast iron

    Energy Technology Data Exchange (ETDEWEB)

    Fan, K.L., E-mail: 12klfan@tongji.edu.cn; He, G.Q.; She, M.; Liu, X.S.; Lu, Q.; Yang, Y.; Tian, D.D.; Shen, Y.

    2014-12-15

    The strain controlled low cycle fatigue properties of the studied gray cast iron for engine cylinder blocks were investigated. At the same total strain amplitude, the low cycle fatigue life of the studied material at 523 K was higher than that at 423 K. The fatigue behavior of the studied material was characterized as cyclic softening at any given total strain amplitude (0.12%–0.24%), which was attributed to fatigue crack initiation and propagation. Moreover, this material exhibited asymmetric hysteresis loops due to the presence of the graphite lamellas. Transmission electron microscopy analysis suggested that cyclic softening was also caused by the interactions of dislocations at 423 K, such as cell structure in ferrite, whereas cyclic softening was related to subgrain boundaries and dislocation climbing at 523 K. Micro-analysis of specimen fracture appearance was conducted in order to obtain the fracture characteristics and crack paths for different strain amplitudes. It showed that the higher the temperature, the rougher the crack face of the examined gray cast iron at the same total strain amplitude. Additionally, the microcracks were readily blunted during growth inside the pearlite matrix at 423 K, whereas the microcracks could easily pass through pearlite matrix along with deflection at 523 K. The results of fatigue experiments consistently showed that fatigue damage for the studied material at 423 K was lower than that at 523 K under any given total strain amplitude. - Highlights: • The low cycle fatigue behavior of the HT250 for engine cylinder blocks was investigated. • TEM investigations were conducted to explain the cyclic deformation response. • The low cycle fatigue cracks of HT250 GCI were studied by SEM. • The fatigue life of the examined material at 523 K is higher than that at 423 K.

  5. Fatigue properties of type 316LN stainless steel in air and mercury

    International Nuclear Information System (INIS)

    Strizak, J.P.; Tian, H.; Liaw, P.K.; Mansur, L.K.

    2005-01-01

    An extensive fatigue testing program on 316LN stainless steel was recently carried out to support the design of the mercury target container for the spallation neutron source (SNS) that is currently under construction at the Oak Ridge National Laboratory in the United States. The major objective was to determine the effects of mercury on fatigue behavior. The S-N fatigue behavior of 316LN stainless steel is characterized by a family of bilinear fatigue curves which are dependent on frequency, environment, mean stress and cold work. Generally, fatigue life increases with decreasing stress and levels off in the high cycle region to an endurance limit below which the material will not fail. For fully reversed loading as well as tensile mean stress loading conditions mercury had no effect on endurance limit. However, at higher stresses a synergistic relationship between mercury and cyclic loading frequency was observed at low frequencies. As expected, fatigue life decreased with decreasing frequency, but the response was more pronounced in mercury compared with air. As a result of liquid metal embrittlement (LME), fracture surfaces of specimens tested in mercury showed widespread brittle intergranular cracking as opposed to typical transgranular cracking for specimens tested in air. For fully reversed loading (zero mean stress) the effect of mercury disappeared as frequency increased to 10 Hz. For mean stress conditions with R-ratios of 0.1 and 0.3, LME was still evident at 10 Hz, but at 700 Hz the effect of mercury had disappeared (R 0.1). Further, for higher R-ratios (0.5 and 0.75) fatigue curves for 10 Hz showed no environmental effect. Finally, cold working (20%) increased tensile strength and hardness, and improved fatigue resistance. Fatigue behavior at 10 and 700 Hz was similar and no environmental effect was observed

  6. Fatigue properties of type 316LN stainless steel in air and mercury

    Science.gov (United States)

    Strizak, J. P.; Tian, H.; Liaw, P. K.; Mansur, L. K.

    2005-08-01

    An extensive fatigue testing program on 316LN stainless steel was recently carried out to support the design of the mercury target container for the spallation neutron source (SNS) that is currently under construction at the Oak Ridge National Laboratory in the United States. The major objective was to determine the effects of mercury on fatigue behavior. The S- N fatigue behavior of 316LN stainless steel is characterized by a family of bilinear fatigue curves which are dependent on frequency, environment, mean stress and cold work. Generally, fatigue life increases with decreasing stress and levels off in the high cycle region to an endurance limit below which the material will not fail. For fully reversed loading as well as tensile mean stress loading conditions mercury had no effect on endurance limit. However, at higher stresses a synergistic relationship between mercury and cyclic loading frequency was observed at low frequencies. As expected, fatigue life decreased with decreasing frequency, but the response was more pronounced in mercury compared with air. As a result of liquid metal embrittlement (LME), fracture surfaces of specimens tested in mercury showed widespread brittle intergranular cracking as opposed to typical transgranular cracking for specimens tested in air. For fully reversed loading (zero mean stress) the effect of mercury disappeared as frequency increased to 10 Hz. For mean stress conditions with R-ratios of 0.1 and 0.3, LME was still evident at 10 Hz, but at 700 Hz the effect of mercury had disappeared ( R = 0.1). Further, for higher R-ratios (0.5 and 0.75) fatigue curves for 10 Hz showed no environmental effect. Finally, cold working (20%) increased tensile strength and hardness, and improved fatigue resistance. Fatigue behavior at 10 and 700 Hz was similar and no environmental effect was observed.

  7. Fatigue Strength of Titanium Risers - Defect Sensitivity

    Energy Technology Data Exchange (ETDEWEB)

    Babalola, Olusegun Tunde

    2001-07-01

    This study is centred on assessment of the fatigue strength of titanium fusion welds for deep-water riser's applications. Deep-water risers are subjected to significant fatigue loading. Relevant fatigue data for titanium fusion welds are very scarce. Hence there is a need for fatigue data and life prediction models for such weldments. The study has covered three topics: Fatigue testing, Fractography and defect assessment, and Fracture Mechanics modelling of fatigue crack growth. Two series of welded grade of titanium consisting of 14 specimens in each series were fatigue tested under constant amplitude loading. Prior to fatigue testing, strain gauge measurements of some specimens was conducted to enable the definition of stress range in the fatigue assessment procedure. The results were compared with finite solid element analysis and related to fatigue stresses in a riser pipe wall. Distribution and geometry of internal and surface defects both in the as-welded and in the post-weld machined conditions were assessed using fractography. This served as a tool to determine the fatigue initiation point in the welds. Fracture mechanics was applied to model fatigue strength of titanium welds with initiation from weld defects. Two different stress intensity factor formulations for embedded eccentrically placed cracks were used for analysis of elliptical cracks with the major axis parallel and close to one of the free surfaces. The methods were combined to give a satisfactory model for crack growth analysis. The model analyses crack growth of elliptical and semi-elliptical cracks in two directions, with updating of the crack geometry. Fatigue strength assessment was conducted using two crack growth models, the Paris-Erdogan relation with no threshold and the Donahue et al. relation with an implied threshold. The model was validated against experimental data, with a discussion on the choice of crack growth model. (author)

  8. Fatigue in cancer: A review of literature

    Directory of Open Access Journals (Sweden)

    Vijayakumar Narayanan

    2009-01-01

    Full Text Available Fatigue is a common symptom of advanced cancer limiting one′s activity and affecting the quality of life. It is a multidimensional symptom complex with subjective and objective components. Hence, its definition and assessment seems arbitrary, incomplete, and elusive. Components of fatigue often merge with other ′disease states′ as anemia, depression and so on, compounding difficulty to assess it separately. Fatigue has a high prevalence rate, and lasts longer in chronic diseases like cancer. Its association with treatment modalities like chemotherapy, radiotherapy alongside the primary disease process makes it seemingly ubiquitous in many cases. Systemic manifestation of cancer causes excess demand on body resources on cell repair, uncontrolled growth with metabolite accumulation causing fatigue. Co-morbid conditions of organic and psychological nature causes fatigue. There are many assessment tools for fatigue with different uses and objectives, simple and reproducible tools like Brief Fatigue Inventory, Edmonton Symptom assessment scale seem feasible in everyday practice. Management of fatigue is not straightforward and rewarding. Although treatment of cause appears to be an attractive option, it is not possible in all cases. Therapeutic agents targeting cytokine load is in early stages of study and available results are not favorable. Specific measures aimed at pain relief, prevention/treatment of sepsis, management of depression, avoidance of drugs causing fatigue, restoring the metabolic profile are important. Methyl phenidate, megestrol, and modafinil are some drugs with promising effect to treat fatigue, though confirmatory studies are yet to be established. Non-pharmacological methods are also helpful. Forewarning patients on upcoming fatigue, active regular exercise, and stress management are some of them. Fatigue being a multidimensional entity, single mode of therapy is insufficient. Combined modality tailored to individual

  9. Mesoscopic scale thermal fatigue damage

    International Nuclear Information System (INIS)

    Robertson, C.; Fissolo, A.; Fivel, M.

    2001-01-01

    In an attempt to better understand damage accumulation mechanisms in thermal fatigue, dislocation substructures forming in 316L steel during one specific test were examined and simulated. Hence, thin foils taken out of massive, tested specimens were first observed in transmission electron microscopy (TEM). These observations help in determining one initial dislocation configuration to be implemented in a 3-D model combining 3D discrete dislocation dynamics simulation (DDD) and finite element method computations (FEM). It was found that the simulated mechanical behaviour of the DDD microstructure is compatible with FEM and experimental data. The numerically generated dislocation microstructure is similar to ladder-like dislocation arrangements as found in many fatigued f.c.c. materials. Distinct mechanical behaviour for the two active slip systems was shown and deformation mechanisms were proposed. (authors)

  10. Mesoscopic scale thermal fatigue damage

    Energy Technology Data Exchange (ETDEWEB)

    Robertson, C.; Fissolo, A. [CEA Saclay, Dept. des Materiaux pour le Nucleaire, DMN, 91 - Gif sur Yvette (France); Fivel, M. [Centre National de la Recherche Scientifique, CNRS-GPM2, 38 - Saint Martin d' Heres (France)

    2001-07-01

    In an attempt to better understand damage accumulation mechanisms in thermal fatigue, dislocation substructures forming in 316L steel during one specific test were examined and simulated. Hence, thin foils taken out of massive, tested specimens were first observed in transmission electron microscopy (TEM). These observations help in determining one initial dislocation configuration to be implemented in a 3-D model combining 3D discrete dislocation dynamics simulation (DDD) and finite element method computations (FEM). It was found that the simulated mechanical behaviour of the DDD microstructure is compatible with FEM and experimental data. The numerically generated dislocation microstructure is similar to ladder-like dislocation arrangements as found in many fatigued f.c.c. materials. Distinct mechanical behaviour for the two active slip systems was shown and deformation mechanisms were proposed. (authors)

  11. Creep-Fatigue Failure Diagnosis

    Science.gov (United States)

    Holdsworth, Stuart

    2015-01-01

    Failure diagnosis invariably involves consideration of both associated material condition and the results of a mechanical analysis of prior operating history. This Review focuses on these aspects with particular reference to creep-fatigue failure diagnosis. Creep-fatigue cracking can be due to a spectrum of loading conditions ranging from pure cyclic to mainly steady loading with infrequent off-load transients. These require a range of mechanical analysis approaches, a number of which are reviewed. The microstructural information revealing material condition can vary with alloy class. In practice, the detail of the consequent cracking mechanism(s) can be camouflaged by oxidation at high temperatures, although the presence of oxide on fracture surfaces can be used to date events leading to failure. Routine laboratory specimen post-test examination is strongly recommended to characterise the detail of deformation and damage accumulation under known and well-controlled loading conditions to improve the effectiveness and efficiency of failure diagnosis. PMID:28793676

  12. Identification and Validation of Clinically Relevant Clusters of Severe Fatigue in Rheumatoid Arthritis.

    Science.gov (United States)

    Basu, Neil; Jones, Gareth T; Macfarlane, Gary J; Druce, Katie L

    The considerable heterogeneity of rheumatoid arthritis (RA)-related fatigue is the greatest challenge to determining pathogenesis. The identification of homogenous subtypes of severe fatigue would inform the design and analysis of experiments seeking to characterize the likely numerous causal pathways that underpin the symptom. This study aimed to identify and validate such fatigue subtypes in patients with RA. Data were obtained from patients recruited to the British Society for Rheumatology Biologics register for RA, as either receiving traditional disease-modifying antirheumatic drugs (DMARD cohort, n = 522) or commencing anti-tumor necrosis factor therapy (anti-TNF cohort, n = 3909). In those reporting severe fatigue (Short-Form 36 vitality ≤ 12.5), this cross-sectional analysis applied hierarchical clustering with weighted-average linkage identified clusters of pain, fatigue, mental health (all Short-Form 36), disability (Health Assessment Questionnaire), and inflammation (erythrocyte sedimentation rate) in the DMARD cohort. K-means clustering sought to validate the solution in the anti-TNF cohort. Clusters were characterized using a priori generated symptom definitions and between-cluster comparisons. Four severe fatigue clusters, labeled as basic (46%), affective (40%), inflammatory (4.5%), and global (8.9%) were identified in the DMARD cohort. All clusters had severe levels of pain and disability and were distinguished by the presence/absence of poor mental health and high inflammation. The same symptom clusters were present in the anti-TNF cohort, although the proportion of participants in each cluster differed (basic = 28.7%; affective = 30.2%; global = 24.1%; inflammatory = 16.9%). Among RA patients with severe fatigue, recruited to two diverse RA cohorts, clinically relevant clusters were identified and validated. These may provide the basis for future mechanistic studies and ultimately support a stratified approach to fatigue management.

  13. Gut inflammation in chronic fatigue syndrome

    Directory of Open Access Journals (Sweden)

    Kirchgessner Annette

    2010-10-01

    Full Text Available Abstract Chronic fatigue syndrome (CFS is a debilitating disease characterized by unexplained disabling fatigue and a combination of accompanying symptoms the pathology of which is incompletely understood. Many CFS patients complain of gut dysfunction. In fact, patients with CFS are more likely to report a previous diagnosis of irritable bowel syndrome (IBS, a common functional disorder of the gut, and experience IBS-related symptoms. Recently, evidence for interactions between the intestinal microbiota, mucosal barrier function, and the immune system have been shown to play a role in the disorder's pathogenesis. Studies examining the microecology of the gastrointestinal (GI tract have identified specific microorganisms whose presence appears related to disease; in CFS, a role for altered intestinal microbiota in the pathogenesis of the disease has recently been suggested. Mucosal barrier dysfunction promoting bacterial translocation has also been observed. Finally, an altered mucosal immune system has been associated with the disease. In this article, we discuss the interplay between these factors in CFS and how they could play a significant role in GI dysfunction by modulating the activity of the enteric nervous system, the intrinsic innervation of the gut. If an altered intestinal microbiota, mucosal barrier dysfunction, and aberrant intestinal immunity contribute to the pathogenesis of CFS, therapeutic efforts to modify gut microbiota could be a means to modulate the development and/or progression of this disorder. For example, the administration of probiotics could alter the gut microbiota, improve mucosal barrier function, decrease pro-inflammatory cytokines, and have the potential to positively influence mood in patients where both emotional symptoms and inflammatory immune signals are elevated. Probiotics also have the potential to improve gut motility, which is dysfunctional in many CFS patients.

  14. Multiaxial creep-fatigue rules

    International Nuclear Information System (INIS)

    Spindler, M.W.; Hales, R.; Ainsworth, R.A.

    1997-01-01

    Within the UK, a comprehensive procedure, called R5, is used to assess the high temperature response of structures. One part of R5 deals with creep-fatigue initiation, and in this paper we describe developments in this part of R5 to cover multiaxial stress states. To assess creep-fatigue, damage is written as the linear sum of fatigue and creep components. Fatigue is assessed using Miner's law with the total endurance split into initiation and growth cycles. Initiation is assessed by entering the curve of initiation cycles vs strain range using a Tresca equivalent strain range. Growth is assessed by entering the curve of growth cycles vs strain range using a Rankine equivalent strain range. The number of allowable cycles is obtained by summing the initiation and growth cycles. In this way the problem of defining an equivalent strain range applicable over a range of endurance is avoided. Creep damage is calculated using ductility exhaustion methods. In this paper we address two aspects; first, the nature of stress relaxation and, hence, accumulated creep strain in multiaxial stress fields; secondly, the effect of multiaxial stress on creep ductility. The effect of multiaxial stress state on creep ductility has been examined using experimental data and mechanistic models. Good agreement is demonstrated between an empirical description of test data and a cavity growth model, provided a simple nucleation criterion is included. A simple scaling factor is applied to uniaxial creep ductility, defined as a function of stress state. The factor is independent of the cavity growth mechanisms and yields a value of equivalent strain which can be conveniently used in determining creep damage by ductility exhaustion. (author). 14 refs, 4 figs

  15. Fatigue Management in Spaceflight Operations

    Science.gov (United States)

    Whitmire, Alexandra

    2011-01-01

    Sleep loss and fatigue remain an issue for crewmembers working on the International Space Station, and the ground crews who support them. Schedule shifts on the ISS are required for conducting mission operations. These shifts lead to tasks being performed during the biological night, and sleep scheduled during the biological day, for flight crews and the ground teams who support them. Other stressors have been recognized as hindering sleep in space; these include workload, thinking about upcoming tasks, environmental factors, and inadequate day/night cues. It is unknown if and how other factors such as microgravity, carbon dioxide levels, or increased radiation, may also play a part. Efforts are underway to standardize and provide care for crewmembers, ground controllers and other support personnel. Through collaborations between research and operations, evidenced-based clinical practice guidelines are being developed to equip flight surgeons with the tools and processes needed for treating circadian desynchrony (and subsequent sleep loss) caused by jet lag and shift work. The proper implementation of countermeasures such as schedules, lighting protocols, and cognitive behavioral education can hasten phase shifting, enhance sleep and optimize performance. This panel will focus on Fatigue Management in Spaceflight Operations. Speakers will present on research-based recommendations and technologies aimed at mitigating sleep loss, circadian desynchronization and fatigue on-orbit. Gaps in current mitigations and future recommendations will also be discussed.

  16. Correlation between Fatigue Crack Growth Behavior and Fracture Surface Roughness on Cold-Rolled Austenitic Stainless Steels in Gaseous Hydrogen

    Directory of Open Access Journals (Sweden)

    Tai-Cheng Chen

    2018-03-01

    Full Text Available Austenitic stainless steels are often considered candidate materials for use in hydrogen-containing environments because of their low hydrogen embrittlement susceptibility. In this study, the fatigue crack growth behavior of the solution-annealed and cold-rolled 301, 304L, and 310S austenitic stainless steels was characterized in 0.2 MPa gaseous hydrogen to evaluate the hydrogen-assisted fatigue crack growth and correlate the fatigue crack growth rates with the fracture feature or fracture surface roughness. Regardless of the testing conditions, higher fracture surface roughness could be obtained in a higher stress intensity factor (∆K range and for the counterpart cold-rolled specimen in hydrogen. The accelerated fatigue crack growth of 301 and 304L in hydrogen was accompanied by high fracture surface roughness and was associated with strain-induced martensitic transformation in the plastic zone ahead of the fatigue crack tip.

  17. 2014 New Trends in Fatigue and Fracture Conference

    CERN Document Server

    Milovic, Ljubica

    2017-01-01

    This book is a compilation of selected papers from the 2014 New Trends in Fatigue and Fracture (NT2F14) Conference, which was held in Belgrade, Serbia. This prestigious conference brought together delegates from around the globe to discuss how to characterize, predict and analyze the fatigue and fracture of engineering materials, components, and structures using theoretical, experimental, numerical and practical approaches. It highlights some important new trends in fracture mechanics presented at the conference, such as: • two-parameter fracture mechanics, arising from the coupling of fracture toughness and stress constraints • high-performance steel for gas and oil transportation and production (pressure vessels and boilers) • safety and reliability of welded joints This book includes 12 contributions from well-known international scientists and a special tribute dedicated to the scientific contributions of Stojan Sedmark, who passed away in 2014.

  18. Fatigue evaluation of piping systems with limited vibration test data

    International Nuclear Information System (INIS)

    Huang, S.N.

    1990-11-01

    The safety-related piping in a nuclear power plant may be subjected to pump- or fluid-induced vibrations that, in general, affect only local areas of the piping systems. Pump- or fluid-induced vibrations typically are characterized by low levels of amplitudes and a high number of cycles over the lifetime of plant operation. Thus, the resulting fatigue damage to the piping systems could be an important safety concern. In general, tests and/or analyses are used to evaluate and qualify the piping systems. Test data, however, may be limited because of lack of instrumentation in critical piping locations and/or because of difficulty in obtaining data in inaccessible areas. This paper describes and summarizes a method to use limited pipe vibration test data, along with analytical harmonic response results from finite-element analyses, to assess the fatigue damage of nuclear power plant safety-related piping systems. 5 refs., 2 figs., 11 tabs

  19. Fatigue crack propagation: Probabilistic models and experimental evidence

    International Nuclear Information System (INIS)

    Lucia, A.C.; Jovanovic, A.

    1987-01-01

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

  20. Fatigue of LMFBR piping due to flow stratification

    Energy Technology Data Exchange (ETDEWEB)

    Woodward, W.S.

    1983-01-01

    Flow stratification due to reverse flow was simulated in a 1/5-scale water model of a LMFBR primary pipe loop. The stratified flow was observed to have a dynamic interface region which oscillated in a wave pattern. The behavior of the interface was characterized in terms of location, local temperature fluctuation and duration for various reverse flow conditions. A structural assessment was performed to determine the effects of stratified flow on the fatigue life of the pipe. Both the static and dynamic aspects of flow stratification were examined. The dynamic interface produces thermal striping on the inside of the pipe wall which is shown to have the most deleterious effect on the pipe wall and produce significant fatigue damage relative to a static interface.

  1. Fatigue of LMFBR piping due to flow stratification

    International Nuclear Information System (INIS)

    Woodward, W.S.

    1983-01-01

    Flow stratification due to reverse flow was simulated in a 1/5-scale water model of a LMFBR primary pipe loop. The stratified flow was observed to have a dynamic interface region which oscillated in a wave pattern. The behavior of the interface was characterized in terms of location, local temperature fluctuation and duration for various reverse flow conditions. A structural assessment was performed to determine the effects of stratified flow on the fatigue life of the pipe. Both the static and dynamic aspects of flow stratification were examined. The dynamic interface produces thermal striping on the inside of the pipe wall which is shown to have the most deleterious effect on the pipe wall and produce significant fatigue damage relative to a static interface

  2. Monitoring and Managing Fatigue in Basketball

    Directory of Open Access Journals (Sweden)

    Toby Edwards

    2018-02-01

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

  3. Fatigue in tension perpendicular to the grain

    DEFF Research Database (Denmark)

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

    1999-01-01

    Traditinally fatigue resistance is quantified as number of cycles to failure at a given stress level. A previous study by the authors showed that fatigue in compression parallel to the grain is governed partly by duration of load and partly by an effect of loading, i.e. a combination of a creep...... mechanism and a mechanism connected to damage introduce in the loading sequences. The purpose of the present study is to disentangle the effect of duration of load from the effect of load oscillation in fatigue in tension perpendicular to the grain. Fatigue experiments are made on small specimens...... and on dowel type joints with slotted in steel plates. In series of ten, the small specimens are taken to fatigue failure in uniform tension at square wave shaped load cycles at 0.01 Hz and 0.1 Hz. In order to test the predictive validity of the result from the small tension specimens, fatigue experiments...

  4. Fatigue In Tension Perpendicular to the Grain

    DEFF Research Database (Denmark)

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

    2004-01-01

    Traditionally fatigue resistance is quantified as number of cycles to failure at a given stress level. A previous study by the authors showed that fatigue in compression parallel to the grain is governed partly by duration of load and partly by an effect of loading, i.e. a combination of a creep...... mechanism and a mechanism connected to damage introduced in the loading sequences. The purpose of the present study is to disentangle the effect of duration of load from the effect of load oscillation in fatigue in tension perpendicular to the grain. Fatigue experiments are made on small specimens...... and on dowel type joints with slotted in steel plates. In series of ten, the small specimens are taken to fatigue failure in uniform tension at square wave shaped load cycles at 0.01 Hz and 0.1 Hz. In arder to test the predictive validity of the result from the small tension specimens, fatigue experiments...

  5. Noncontact fatigue crack evaluation using thermoelastic

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-12-15

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

  6. Adults living with heart failure and fatigue

    DEFF Research Database (Denmark)

    Schjødt, Inge; Sommer, Irene; Bjerrum, Merete

    studies have been performed to develop more coherent and effective interventions to support self-care among heart failure patients experiencing fatigue. The findings of qualitative research should be synthesised to optimise nurses' understanding of fatigue and develop recommendations for practice. Aim......Background Fatigue is one of the most common symptoms reported by patients with heart failure (HF). Fatigue negatively impacts on patients’ everyday life, prognosis and quality of life. No specific cure or effective interventions to alleviate fatigue are available. Over the past decade, qualitative...... To synthesise the best available evidence related to the lived experiences and management of fatigue in everyday life in adult patients with stable heart failure to develop effective interventions to support self-care. Specific questions on the patients’ lived experiences included: • How do patients with HF...

  7. Design fatigue curve for Hastelloy-X

    International Nuclear Information System (INIS)

    Nishiguchi, Isoharu; Muto, Yasushi; Tsuji, Hirokazu

    1983-12-01

    In the design of components intended for elevated temperature service as the experimental Very High-Temperature gas-cooled Reactor (VHTR), it is essential to prevent fatigue failure and creep-fatigue failure. The evaluation method which uses design fatigue curves is adopted in the design rules. This report discussed several aspects of these design fatigue curves for Hastelloy-X (-XR) which is considered for use as a heat-resistant alloy in the VHTR. Examination of fatigue data gathered by a literature search including unpublished data showed that Brinkman's equation is suitable for the design curve of Hastelloy-X (-XR), where total strain range Δ epsilon sub(t) is used as independent variable and fatigue life Nsub(f) is transformed into log(log Nsub(f)). (author)

  8. Fatigue assessments in operating nuclear power plants

    International Nuclear Information System (INIS)

    Gosselin, S.R.; Deardorff, A.F.; Peltola, D.W.

    1994-01-01

    In November 1991, the ASME Section XI Task Group on Operating Plant Fatigue Assessment was formed to develop criteria and evaluation methodology for evaluating the effects of cyclic operation in operating nuclear power plants. The objective was to develop guidelines for inclusion in Section XI that could be used by plant operators in evaluating fatigue concerns and their impact on serviceability. This paper discusses the work performed by the Task Group. It explores the concept of ''Fatigue Design Basis'' versus ''Fatigue Operating Basis'' by examining the roles of ASME Section III and ASME Section XI in the design and operation of the nuclear power plants. Guidelines are summarized that may help plant operators perform effective design transient cycle evaluations and optimize cycle counting and fatigue usage tracking. The alternative fatigue evaluation approach using flaw tolerance is also introduced

  9. Fatigue management considering LWR coolant environments

    International Nuclear Information System (INIS)

    Park, Heung Bae; Jin, Tae eun

    2000-01-01

    Design fatigue curve for structural material in the ASME Boiler and Pressure Vessel Code do not explicitly address the effects of reactor coolant environments on fatigue life. Environmentally assisted cracking (EAC) of low-alloy steels in light water reactor (LWR) coolant environments has been a concern ever since the early 1970's. And, recent fatigue test data indicate a significant decrease in fatigue lives of carbon steels, low-alloy steels and austenitic stainless steels in LWR coolant environments. For these reasons, fatigue of major components has been identified as a technical issue remaining to be resolved for life management and license renewal of nuclear power plants. In the present paper, results of recent investigations by many organizations are reviewed to provide technical justification to support the development of utility approach regarding the management of fatigue considering LWR coolant environments for the purpose of life management and license renewal of nuclear power plants. (author)

  10. Low cycle fatigue of irradiated LMFBR materials

    International Nuclear Information System (INIS)

    Blackburn, L.D.

    1976-01-01

    A review of low cycle fatigue data on irradiated LMFBR materials was conducted and extensive graphical representations of available data are presented. Representative postirradiation tensile properties of annealed 304 and 316 SS are selected and employed in several predictive methods to estimate irradiated material fatigue curves. Experimental fatigue data confirm the use of predictive methods for establishing conservative design curves over the range of service conditions relevant to such CRBRP components as core former, fixed radial shielding, core barrel, lower inlet module and upper internals structures. New experimental data on fatigue curves and creep-fatigue interaction in irradiated 20 percent cold worked (CW) 316 SS and Alloy 718 would support the design of removable radial shielding and upper internals in CRBRP. New experimental information on notched fatigue behavior and cyclic stress-strain curves of all these materials in the irradiated condition could provide significant design data

  11. IEA Joint Action. Wind turbine fatigue

    Energy Technology Data Exchange (ETDEWEB)

    Maribo Pedersen, B [ed.

    1996-09-01

    Fatigue research on wind turbine blade material has been an important issue over the years in many countries and in the E.U. As a result of the effort the knowledge on fatigue properties of fibre reinforced materials has been expanded enormously. Practical fatigue design properties are available for constant amplitude tests at ambient temperatures. A lack of knowledge can be shown in several other fields, such as variable amplitude and multi-axial testing and the influence of the environment and carbon fibres. Fatigue is seen as dominant for the blade design, improvements in both the load prediction and material fatigue properties should be strove for. In discussions with blade manufacturers and subsidy agencies (E.U. DGXII, NOVEM, ETSU, etc.) on the importance of continuous materials fatigue research the improvement in reliability should be stressed. (au)

  12. Fatigue mechanisms during physical exercise

    Directory of Open Access Journals (Sweden)

    Monique Gevaerd

    2006-03-01

    Full Text Available Fatigue can be defined as incapacity to maintain the required power output, with concomitant impairment of exercise performance, and it can be divided into chronic or acute. In acute fatigue a subdivision has been used to delimitate experimental studies. Thus, acute fatigue can be central or peripheral. We began the review process with a search on the Pubmed database, followed by selection of classical and more recent articles. As the fatigue mechanisms are linked to the predominant energy metabolism in the activity, the purpose of this paper was to review the main acute fatigue theories in activities with different metabolic demands. From this literature review, it was possible to infer that important metabolic alterations occurring during exercise, impair normal cellular activities,therefore, decreasing the speed of contraction and as well as energy replenishment. Many of those alterations give information to the central nervous system, limiting the time length of exercise. Theoretically, the elongation of exercise beyond biological limits can cause irreversible damages to the organism. RESUMO Fadiga pode ser definida como uma incapacidade na manutenção de uma determinada potência, com conseqüente redução no desempenho, podendo ser considerada como crônica ou aguda. Na fadiga aguda, uma subdivisão vem sendo utilizada para maior delimitação dos estudos experimentais. Nesse sentido, fadiga aguda pode ser descrita como central ou periférica. Nós iniciamos o processo de revisão sobre o assunto com uma busca no banco de dados Pubmed, seguido da seleção dos artigos clássicos e mais recentes. Como os mecanismos de fadiga estão intimamente ligados ao metabolismo energético predominante da atividade, a presente revisão destinou-se a levantar as principais teorias sobre fadiga aguda em atividades com diferentes exigências metabólicas. A partir desse apanhado bibliográfico podemos inferir que importantes alterações metab

  13. Assessing Fatigue in Late-Midlife

    DEFF Research Database (Denmark)

    Fieo, Robert A; Mortensen, Erik Lykke; Lund, Rikke

    2014-01-01

    Previous methods examining the Multiple Fatigue Inventory-20 (MFI-20) fatigue questionnaire have been limited to classical test theory, for example, factor analytic approaches. We employed modern test theory to further strengthen the construct validity of the MFI-20 fatigue in a sample of healthy...... the interpretive power of the MFI-20, allowing for the identification of the most optimal scales. Poorly performing items were more easily identified, and person ability was assessed more accurately....

  14. Fatigue Fracture Behaviors of Transparent Polycarbonate Materials

    OpenAIRE

    ZHANG Xiao-wen; WU Nan; ZHANG Xuan; MA Li-ting; LI Lei

    2017-01-01

    The effect of the different stress ratios (R) and annealing treatment on the fatigue properties of the transparent polycarbonate (PC) sheet and the mechanism behind were studied, the fatigue crack propagation (FCP) process and mechanism were analyzed. The results show that after annealing, the residual stress of the PC samples decreases obviously and the fatigue properties are greatly improved. This is because the machining process results in tensile stress in the PC samples, eliminating the ...

  15. Fatigue in Breakwater Concrete Armour Units

    OpenAIRE

    Burcharth, Hans F.

    1984-01-01

    The reliability of rubble mound breakwaters depends on the hydraulic stability and the mechanical strength of the armour units. The paper deals with the important aspect of fatigue related to the strength of concrete armour units. Results showing significant fatigue from impact tests with Dolosse made of unreinforced and steel fibre reinforced flyash concrete are presented. Moreover universal graphs for fatigue in armour units made of conventional unreinforced concrete exposed to impact load ...

  16. Fatigue lifetime estimation of railway axles

    Czech Academy of Sciences Publication Activity Database

    Náhlík, Luboš; Pokorný, Pavel; Ševčík, Martin; Fajkoš, R.; Matušek, P.; Hutař, Pavel

    2017-01-01

    Roč. 73, MAR (2017), s. 139-157 ISSN 1350-6307 R&D Projects: GA MŠk LM2015069; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : Residual fatigue lifetime * Railway axle * Variable amplitude loading * Fatigue crack propagation * Damage tolerance methodology Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis Impact factor: 1.676, year: 2016

  17. Random non-proportional fatigue tests with planar tri-axial fatigue testing machine

    OpenAIRE

    Inoue, T.; Nagao, R.; Takeda, N.

    2016-01-01

    Complex stresses, which occur on the mechanical surfaces of transport machinery in service, bring a drastic degradation in fatigue life. However, it is hard to reproduce such complex stress states for evaluating the fatigue life with conventional multiaxial fatigue machines. We have developed a fatigue testing machine that enables reproduction of such complex stresses. The testing machine can reproduce arbitrary in-plane stress states by applying three independent loads to the test specimen u...

  18. Mobile Technology Use by People Experiencing Multiple Sclerosis Fatigue: Survey Methodology.

    Science.gov (United States)

    Van Kessel, Kirsten; Babbage, Duncan R; Reay, Nicholas; Miner-Williams, Warren M; Kersten, Paula

    2017-02-28

    Fatigue is one of the most commonly reported symptoms of multiple sclerosis (MS). It has a profound impact on all spheres of life, for people with MS and their relatives. It is one of the key precipitants of early retirement. Individual, group, and Internet cognitive behavioral therapy-based approaches to supporting people with MS to manage their fatigue have been shown to be effective. The aim of this project was to (1) survey the types of mobile devices and level of Internet access people with MS use or would consider using for a health intervention and (2) characterize the levels of fatigue severity and their impact experienced by the people in our sample to provide an estimate of fatigue severity of people with MS in New Zealand. The ultimate goal of this work was to support the future development of a mobile intervention for the management of fatigue for people with MS. Survey methodology using an online questionnaire was used to assess people with MS. A total of 51 people with MS participated. The average age was 48.5 years, and the large majority of the sample (77%) was female. Participants reported significant levels of fatigue as measured with the summary score of the Neurological Fatigue Index (mean 31.4 [SD 5.3]). Most (84%) respondents scored on average more than 3 on the fatigue severity questions, reflecting significant fatigue. Mobile phone usage was high with 86% of respondents reporting having a mobile phone; apps were used by 75% of respondents. Most participants (92%) accessed the Internet from home. New Zealand respondents with MS experienced high levels of both fatigue severity and fatigue impact. The majority of participants have a mobile device and access to the Internet. These findings, along with limited access to face-to-face cognitive behavioral therapy-based interventions, create an opportunity to develop a mobile technology platform for delivering a cognitive behavioral therapy-based intervention to decrease the severity and impact of

  19. Fatigue behaviour of synthetic nodular cast irons

    Directory of Open Access Journals (Sweden)

    A. Vaško

    2015-01-01

    Full Text Available The paper shows the influence of charge composition on microstructure, fatigue properties and failure micromechanisms of nodular cast irons. The additive of metallurgical silicon carbide (SiC in analysed specimens increases the content of ferrite in the matrix, decreases the size of graphite and increases the average count of graphitic nodules per unit of area. Consequently, the mechanical and fatigue properties of nodular cast iron are improved. The best fatigue properties (fatigue strength were reached in the melt which was created by 60 % of steel scrap and 40 % of pig iron in the basic charge with SiC additive.

  20. 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

  1. Development of a fatigue analysis software system

    International Nuclear Information System (INIS)

    Choi, B. I.; Lee, H. J.; Han, S. W.; Kim, J. Y.; Hwang, K. H.; Kang, J. Y.

    2001-01-01

    A general purpose fatigue analysis software to predict fatigue lives of mechanical components and structures was developed. This software has some characteristic features including functions of searching weak regions on the free surface in order to reduce computing time significantly, a database of fatigue properties for various materials, and an expert system which can assist any users to get more proper results. This software can be used in the environment consists of commercial finite element packages. Using the software developed fatigue analyses for a SAE keyhole specimen and an automobile knuckle were carried out. It was observed that the results were agree well with those from commercial packages

  2. Fatigue and radiotherapy. A literature review

    International Nuclear Information System (INIS)

    Dilhuydy, J.M.; Ouhtatou, F.; Laporte, C.; Nguyen, T.V.F.; Vendrely, V.; Dilhuydy, J.M.; Dilhuydy, M.S.

    2001-01-01

    Fatigue is a common complaint for the cancer patient during and after radiotherapy, according to the published studies. Fatigue is a subjective symptom mostly underestimated by oncologists and other care givers. Etiology is complex, poorly understood in spite of obvious causes like insomnia, nausea, pain, depression, psychological distress, anemia, hypothyroidism, menopause disturbances, treatment adverse effects. Fatigue presents multi-factorial and multidimensional aspects. To evaluate it, many tools can be used as single-item, unidimensional and multidimensional instruments. Practically, the open discussion with the patient throughout radiotherapy is essential to define it. Taking charge fatigue requires its acknowledgement by radiotherapist, treatment of associated symptoms with a multidisciplinary approach. (authors)

  3. Fatigue in Breakwater Concrete Armour Units

    DEFF Research Database (Denmark)

    Burcharth, Hans F.

    1985-01-01

    The reliability of rubble mound breakwaters depends on the hydraulic stability and the mechanical strength of the armour units. The paper deals with the important aspect of fatigue related to the strength of concrete armour units. Results showing significant fatigue from impact tests with Dolosse...... made of unreinforced and steel fibre reinforced flyash concrete are presented. Moreover universal graphs for fatigue in armour units made of conventional unreinforced concrete exposed to impact load and pulsating load are presented. The effect of fibre reinforcement and the implementation of fatigue...

  4. Fatigue and creep-fatigue in sodium of 316 L stainless-steel

    International Nuclear Information System (INIS)

    Ardellier, A.

    1981-03-01

    The present paper describes test-facility developed to perform low-cycle fatigue and creep-fatigue interaction in sodium on stainless steel - 316 L . Fatigue life in sodium and in air are compared. A beneficial effect in sodium is noted

  5. Fatigue and fatigue-related symptoms in patients treated for different causes of hypothyroidism

    NARCIS (Netherlands)

    Louwerens, M.; Appelhof, B.C.; Verloop, H.; Medici, M.; Peeters, R.P.; Visser, T.J.; Boelen, A.; Fliers, E.; Smit, J.W.A.; Dekkers, O.M.

    2012-01-01

    OBJECTIVE: Research on determinants of well-being in patients on thyroid hormone replacement therapy is warranted, as persistent fatigue-related complaints are common in this population. In this study, we evaluated the impact of different states of hypothyroidism on fatigue and fatigue-related

  6. Fatigue and fatigue-related symptoms in patients treated for different causes of hypothyroidism

    NARCIS (Netherlands)

    Louwerens, Marloes; Appelhof, Bente C.; Verloop, Herman; Medici, Marco; Peeters, Robin P.; Visser, Theo J.; Boelen, Anita; Fliers, Eric; Smit, Johannes W. A.; Dekkers, Olaf M.

    2012-01-01

    Objective: Research on determinants of well-being in patients on thyroid hormone replacement therapy is warranted, as persistent fatigue-related complaints are common in this population. In this study, we evaluated the impact of different states of hypothyroidism on fatigue and fatigue-related

  7. [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.

  8. Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters

    Science.gov (United States)

    Liu, Yi; Dai, Feng; Dong, Lu; Xu, Nuwen; Feng, Peng

    2018-01-01

    Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.

  9. FATIGUE PROPERTIES OF MODIFIED 316LN STAINLESS STEEL AT 4 K FOR HIGH FIELD CABLE-IN-CONDUIT APPLICATIONS

    International Nuclear Information System (INIS)

    Toplosky, V. J.; Walsh, R. P.; Han, K.

    2010-01-01

    Cable-In-Conduit-Conductor (CICC) alloys, exposed to Nb 3 Sn reaction heat-treatments, such as modified 316LN require a design specific database. A lack of fatigue life data (S-n curves) that could be applied in the design of the ITER CS and the NHMFL Series Connected Hybrid magnets is the impetus for the research presented here. The modified 316LN is distinguished by a lower carbon content and higher nitrogen content when compared to conventional 316LN. Because the interstitial alloying elements affect the mechanical properties significantly, it is necessary to characterize this alloy in a systematic way. In conjunction, to ensure magnet reliability and performance, several criteria and expectations must be met, including: high fatigue life at the operating stresses, optimal stress management at cryogenic temperatures and thin walled conduit to reduce coil mass. Tension-tension load control axial fatigue tests have good applicability to CICC solenoid magnet design, thus a series of 4 K strength versus fatigue life curves have been generated. In-situ samples of 316LN base metal, seam welded, butt welded and seam plus butt welded are removed directly from the conduit in order to address base and weld material fatigue life variability. The more than 30 fatigue tests show good grouping on the fatigue life curve and allow discretionary 4 K fatigue life predictions for conduit made with modified 316LN.

  10. 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....

  11. High temperature creep-fatigue design

    International Nuclear Information System (INIS)

    Tavassoli, A. A. F.; Fournier, B.; Sauzay, M.

    2010-01-01

    Generation IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials performances are key to their success. This paper examines different types of high temperature creep-fatigue interactions and their implications on design rules for the structural materials retained in both programmes. More precisely, the paper examines current status of design rules for the stainless steel type 316L(N), the conventional Modified 9Cr-1Mo martensitic steel and the low activation Eurofer steel. Results obtained from extensive high temperature creep, fatigue and creep-fatigue tests performed on these materials and their welded joints are presented. These include sequential creep-fatigue and relaxation creep-fatigue tests with hold times in tension, in compression or in both. Effects of larger plastic deformations on fatigue properties are studied through cyclic creep tests or fatigue tests with extended hold time in creep. In most cases, mechanical test results are accompanied with microstructural and fractographic observations. In the case of martensitic steels, the effect of oxidation is examined by performing creep-fatigue tests on identical specimens in vacuum. Results obtained are analyzed and their implications on design allowable and creep-fatigue interaction diagrams are presented. While reasonable confidence is found in predicting creep-fatigue damage through existing code procedures for austenitic stainless steels, effects of cyclic softening and coarsening of microstructure of martensitic steels throughout the fatigue life on materials properties need to be taken into account for more precise damage calculations. In the long-term, development of ferritic/martensitic steels with stable microstructure, such as ODS steels, is proposed. (authors)

  12. High temperature creep-fatigue design

    Energy Technology Data Exchange (ETDEWEB)

    Tavassoli, A. A. F.; Fournier, B.; Sauzay, M. [CEA Saclay, DEN DMN, F-91191 Gif Sur Yvette (France)

    2010-07-01

    Generation IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials performances are key to their success. This paper examines different types of high temperature creep-fatigue interactions and their implications on design rules for the structural materials retained in both programmes. More precisely, the paper examines current status of design rules for the stainless steel type 316L(N), the conventional Modified 9Cr-1Mo martensitic steel and the low activation Eurofer steel. Results obtained from extensive high temperature creep, fatigue and creep-fatigue tests performed on these materials and their welded joints are presented. These include sequential creep-fatigue and relaxation creep-fatigue tests with hold times in tension, in compression or in both. Effects of larger plastic deformations on fatigue properties are studied through cyclic creep tests or fatigue tests with extended hold time in creep. In most cases, mechanical test results are accompanied with microstructural and fractographic observations. In the case of martensitic steels, the effect of oxidation is examined by performing creep-fatigue tests on identical specimens in vacuum. Results obtained are analyzed and their implications on design allowable and creep-fatigue interaction diagrams are presented. While reasonable confidence is found in predicting creep-fatigue damage through existing code procedures for austenitic stainless steels, effects of cyclic softening and coarsening of microstructure of martensitic steels throughout the fatigue life on materials properties need to be taken into account for more precise damage calculations. In the long-term, development of ferritic/martensitic steels with stable microstructure, such as ODS steels, is proposed. (authors)

  13. Fatigue Resistance of the Grain Size Transition Zone in a Dual Microstructure Superalloy Disk

    Science.gov (United States)

    Gabb, T. P.; Kantzos, P. T.; Telesman, J.; Gayda, J.; Sudbrack, C. K.; Palsa, B. S.

    2010-01-01

    Mechanical property requirements vary with location in nickel-based superalloy disks. To maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored microstructures. In this study, a specialized heat treatment method was applied to produce varying grain microstructures from the bore to the rim portions of a powder metallurgy processed nickel-based superalloy disk. The bore of the contoured disk consisted of fine grains to maximize strength and fatigue resistance at lower temperatures. The rim microstructure of the disk consisted of coarse grains for maximum resistance to creep and dwell crack growth at high temperatures up to 704 C. However, the fatigue resistance of the grain size transition zone was unclear, and needed to be evaluated. This zone was located as a band in the disk web between the bore and rim. Specimens were extracted parallel and transverse to the transition zone, and multiple fatigue tests were performed at 427 and 704 C. Mean fatigue lives were lower at 427 C than for 704 C. Specimen failures often initiated at relatively large grains, which failed on crystallographic facets. Grain size distributions were characterized in the specimens, and related to the grains initiating failures as well as location within the transition zone. Fatigue life decreased with increasing maximum grain size. Correspondingly, mean fatigue resistance of the transition zone was slightly higher than that of the rim, but lower than that of the bore. The scatter in limited tests of replicates was comparable for all transition zone locations examined.

  14. Three technical issues in fatigue damage assessment of nuclear power plant components

    International Nuclear Information System (INIS)

    Ware, A.G.; Shah, V.N.

    1991-01-01

    This paper addresses three technical issues that affect the fatigue damage assessment of nuclear power plant components: the effect of the environment on the fatigue life, the importance of the loading sequence in calculating the fatigue crack-initiation damage, and the adequacy of current inservice inspection requirements and methods to characterize fatigue cracks. The environmental parameters that affect the fatigue life of carbon and low alloy steel components are the sulphur content in the steel, the temperature, the amount of dissolved oxygen in the coolant, and the presence of oxidizing agents such as copper oxide. The occurrence of large-amplitude stress cycles early in a component's life followed by low-amplitude stress cycles may cause crack initiation at a cumulative usage factor less than 1.0. The current inservice inspection requirements include volumetric inspections of welds but not of some susceptible sites in the base metal. In addition, the conventional ultrasonic testing techniques need to be improved for reliable detection and accurate sizing of fatigue cracks. 28 refs., 4 figs., 1 tab

  15. Heterogeneity in chronic fatigue syndrome - empirically defined subgroups from the PACE trial.

    Science.gov (United States)

    Williams, T E; Chalder, T; Sharpe, M; White, P D

    2017-06-01

    Chronic fatigue syndrome is likely to be a heterogeneous condition. Previous studies have empirically defined subgroups using combinations of clinical and biological variables. We aimed to explore the heterogeneity of chronic fatigue syndrome. We used baseline data from the PACE trial, which included 640 participants with chronic fatigue syndrome. Variable reduction, using a combination of clinical knowledge and principal component analyses, produced a final dataset of 26 variables for 541 patients. Latent class analysis was then used to empirically define subgroups. The most statistically significant and clinically recognizable model comprised five subgroups. The largest, 'core' subgroup (33% of participants), had relatively low scores across all domains and good self-efficacy. A further three subgroups were defined by: the presence of mood disorders (21%); the presence of features of other functional somatic syndromes (such as fibromyalgia or irritable bowel syndrome) (21%); or by many symptoms - a group which combined features of both of the above (14%). The smallest 'avoidant-inactive' subgroup was characterized by physical inactivity, belief that symptoms were entirely physical in nature, and fear that they indicated harm (11%). Differences in the severity of fatigue and disability provided some discriminative validation of the subgroups. In addition to providing further evidence for the heterogeneity of chronic fatigue syndrome, the subgroups identified may aid future research into the important aetiological factors of specific subtypes of chronic fatigue syndrome and the development of more personalized treatment approaches.

  16. Fatigue Life Prediction of Self-Piercing Rivet Joints Between Magnesium and Aluminum Alloys

    Directory of Open Access Journals (Sweden)

    Kang Hong-Tae

    2018-01-01

    Full Text Available Various light materials including aluminum alloys and magnesium alloys are being used to reduce the weight of vehicle structures. Joining of dissimilar materials is always a challenging task to construct a solid structure. Self-piercing rivet (SPR joint is one of various joining methods for dissimilar materials. Front shock tower structures were constructed with magnesium alloy (AM60 joined to aluminum alloy (Al6082 by SPR joints. To evaluate the durability performance of the SPR joints in the structures, fatigue tests of the front shock tower structures were conducted with constant amplitude loadings. Furthermore, this study investigated fatigue life prediction method of SPR joints and compared the fatigue life prediction results with that of experimental results. For fatigue life prediction of the SPR joints in the front shock tower structures, lap-shear and cross-tension specimens of SPR joint were constructed and tested to characterize the fatigue properties of the SPR joint. Then, the SPR joint was represented with area contact method (ACM in finite element (FE models. The load-life curves of the lap-shear and cross-tension specimens were converted to a structural stress-life (S-N curve of the SPR joints. The S-N curve was used to predict fatigue life of SPR joints in the front shock tower structures. The test results and the prediction results were well correlated.

  17. Recommendations for joint fatigue coefficients for welded P91 junctions at 550 °C

    Energy Technology Data Exchange (ETDEWEB)

    Matheron, P., E-mail: philippe.matheron@cea.fr; Aiello, G.; Ancelet, O.; Forest, L.

    2016-04-15

    Modified 9Cr1Mo steels are potential candidates as structural materials of GEN-IV nuclear reactors. Since the design of structural components is influenced by the presence of the welds, their mechanical properties are also included in the design codes. In the European code RCC-MRx, a weld is considered as a homogeneous (base metal) component with a margin coefficient, called weld coefficient. Currently no values of joint fatigue coefficients for P91 junctions are given in RCC-MRx. After a recall of the weld design rules contained in the code, this work presents the experimental activities carried out to characterize the fatigue behaviour of TIG welded P91 junctions at high temperatures. Finite elements calculations were performed on the basis of the characterization of the base and weld metal. The results of the tests validate the numerical results. Values of the weld joint fatigue coefficients for P91 are proposed for possible inclusion in RCC-MRx.

  18. A Study on the Effects of Ball Defects on the Fatigue Life in Hybrid Bearings

    Science.gov (United States)

    Tang, Ching-Yao; Foerster, Chad E.; O'Brien, Michael J.; Hardy, Brian S.; Goyal, Vinay K.; Nelson, Benjamin A.; Robinson, Ernest Y.; Ward, Peter C.; Hilton, Michael R.

    2014-01-01

    Hybrid ball bearings using silicon nitride ceramic balls with steel rings are increasingly being used in space mechanism applications due to their high wear resistance and long rolling contact fatigue life. However, qualitative and quantitative reports of the effects of ball defects that cause early fatigue failure are rare. We report on our approach to study these effects. Our strategy includes characterization of defects encountered in use, generation of similar defects in a laboratory setting, execution of full-scale bearing tests to obtain lifetimes, post-test characterization, and related finite-element modeling to understand the stress concentration of these defects. We have confirmed that at least one type of defect of appropriate size can significantly reduce fatigue life. Our method can be used to evaluate other defects as they occur or are encountered.

  19. Coverage of multiaxial fatigue criteria in fatigue limit region

    Directory of Open Access Journals (Sweden)

    Papuga J.

    2007-11-01

    Full Text Available There is a power of methods aimed at calculation of equivalent fatigue limit for arbitrary multiaxial loading. Although there are so many ways of computation, their thorough mutual comparison in a larger scale is missing. The database project presented in this paper comprise of several databases crowned with the FatLim database, which comprise of a huge number of experimental results and of 18 computational method working in the category mentioned before. The great block of data was acquired using in-house fatigue software PragTic, which is offered as a freeware application. The FatLim database follows its philosophy of a simple and non-paid accessibility. Its query tool written in MySQL and PhP allows to users to evaluate a practical usability of tested methods on load cases, which the users define. All the issues covered within this paper are available on the website www.pragtic.com, structure of which is described here.

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

    OpenAIRE

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

    2016-01-01

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

  1. 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.

  2. Fatigue Life of Stainless Steel in PWR Environments with Strain Holding

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Taesoon; Kim, Kyuhyung [KHNP CRI, Daejeon (Korea, Republic of); Seo, Myeonggyu; Jang, Changheui [KAIST, Daejeon (Korea, Republic of)

    2016-10-15

    Many components and structures of nuclear power plants are exposed to the water chemistry conditions during the operation. Recently, as design life of nuclear power plant is expanded over 60 years, the environmentally assisted fatigue (EAF) due to these water chemistry conditions has been considered as one of the important damage mechanisms of the safety class 1 components. Therefore, many studies to evaluate the effect of light water reactor (LWR) coolant environments on fatigue life of materials have been conducted. Many EAF test results including Argonne National Laboratory’s consistently indicated the substantial reduction of fatigue life in the light water reactor environments. However, there is a discrepancy between laboratory test data and plant operating experience regarding the effects of environment on fatigue: while laboratory test data suggest huge accumulation of fatigue damage, very limited experience of cracking caused by the low cycle fatigue in light water reactor. These hold-time effect tests are preformed to characterize the effects of strain holding on the fatigue life of austenitic stainless steels in PWR environments in comparison with the existing fixed strain rate results. Low cycle fatigue life tests were conducted for the type 316 stainless steel in 310℃ air and PWR environments with triangular strain. In agreement with the previous reports, the LCF life was reduced in PWR environments. Also for the slower strain rate, the reduction of LCF life was greater than the faster strain rate. The LCF test conditions for the hold-time effects were determined by the references and consideration of actual plant transient. To simulate the heat-up and cooldown transient, sub-peak strain holding during the down-hill of strain amplitude was chosen instead of peak strain holding which used in the previous researches.

  3. Bioactivity-guided fractionation for anti-fatigue property of Acanthopanax senticosus.

    Science.gov (United States)

    Huang, Lin-Zhang; Huang, Bao-Kang; Ye, Qi; Qin, Lu-Ping

    2011-01-07

    The root of Acanthopanax senticosus (also called Eleutherococcus senticosus or Siberian ginseng) has been used extensively in China, Russia and Japan as an adaptogen to fight against stress and fatigue. The present study was designed to ascertain the anti-fatigue property of Acanthopanax senticosus by load-weighted swimming test, sleep deprivation test, also to isolate and characterize the active constituents. Animals were orally administered with the extract of Acanthopanax senticosus. The anti-fatigue effects of the four fractions with different polarities from the 80% ethanol extract, and the different eluates collected from D101 macroporous resin chromatography and eleutheroside E, were examined based on the weight-loaded swimming capacity (physical fatigue) and the change of biochemical parameters in ICR mice. Moreover, the active fraction was later submitted to sleep-deprived mice (mental fatigue). The results shown that the n-butanol fraction significant extends the swimming time of mice to exhaustion. Furthermore, the 60% ethanol-water eluate, more purified eleutherosides (including eleutheroside E, E(2) and derivatives), were the exactly active constituents. Two compounds were isolated, which were identified as eleutheroside E, E(2). The eleutherosides possess the potent abilities to alleviate fatigue both in physical and mental fatigue. Eleutheroside E may be responsible for the pharmacological effect of anti-fatigue. Furthermore, the possible mechanisms were reduced the level of TG by increasing fat utilization, delayed the accumulation of blood urea nitrogen (BUN), and increased the LDH to reduce the accumulation of lactic acid in muscle and then protect the muscle tissue. Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.

  4. Fatigue behavior and failure mechanisms of direct laser deposited Ti–6Al–4V

    Energy Technology Data Exchange (ETDEWEB)

    Sterling, Amanda J.; Torries, Brian [Department of Mechanical Engineering, Mississippi State University, Box 9552, Mississippi State, MS 39762 (United States); Shamsaei, Nima, E-mail: shamsaei@me.msstate.edu [Department of Mechanical Engineering, Mississippi State University, Box 9552, Mississippi State, MS 39762 (United States); Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Box 5405, , Mississippi State, MS 39762 (United States); Thompson, Scott M. [Department of Mechanical Engineering, Mississippi State University, Box 9552, Mississippi State, MS 39762 (United States); Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Box 5405, , Mississippi State, MS 39762 (United States); Seely, Denver W. [Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Box 5405, , Mississippi State, MS 39762 (United States)

    2016-02-08

    In order for additive-manufactured parts to become more widely utilized and trusted in application, it is important to have their mechanical properties well-characterized and certified. The fatigue behavior and failure mechanisms of Ti–6Al–4V specimens fabricated using Laser Engineered Net Shaping (LENS), a Direct Laser Deposition (DLD) additive manufacturing (AM) process, are investigated in this study. A series of fully-reversed strain-controlled fatigue tests is conducted on Ti–6Al–4V specimens manufactured via LENS in their as-built and heat-treated conditions. Scanning Electron Microscopy (SEM) is used to examine the fracture surfaces of fatigue specimens to qualify the failure mechanism, crack initiation sites, and defects such as porosity. Due to the relatively high localized heating and cooling rates experienced during DLD, fabricated parts are observed to possess anisotropic microstructures, and thus, different mechanical properties than those of their traditionally-manufactured wrought counterparts. The fatigue lives of the investigated LENS specimens were found to be shorter than those of wrought specimens, and porosity was found to be the primary contributor to these shorter fatigue lives, with the exception of the heat-treated LENS samples. The presence of pores promotes more unpredictable fatigue behavior, as evidenced by data scatter. Pore shape, size, location, and number were found to impact the fatigue behavior of the as-built and annealed DLD parts. As porosity seems to be the main contributor to the fatigue behavior of DLD parts, it is important to optimize the manufacturing process and design parameters to minimize and control pore generation during the build.

  5. Effect of mental fatigue caused by mobile 3D viewing on selective attention: an ERP study.

    Science.gov (United States)

    Mun, Sungchul; Kim, Eun-Soo; Park, Min-Chul

    2014-12-01

    This study investigated behavioral responses to and auditory event-related potential (ERP) correlates of mental fatigue caused by mobile three-dimensional (3D) viewing. Twenty-six participants (14 women) performed a selective attention task in which they were asked to respond to the sounds presented at the attended side while ignoring sounds at the ignored side before and after mobile 3D viewing. Considering different individual susceptibilities to 3D, participants' subjective fatigue data were used to categorize them into two groups: fatigued and unfatigued. The amplitudes of d-ERP components were defined as differences in amplitudes between time-locked brain oscillations of the attended and ignored sounds, and these values were used to calculate the degree to which spatial selective attention was impaired by 3D mental fatigue. The fatigued group showed significantly longer response times after mobile 3D viewing compared to before the viewing. However, response accuracy did not significantly change between the two conditions, implying that the participants used a behavioral strategy to cope with their performance accuracy decrement by increasing their response times. No significant differences were observed for the unfatigued group. Analysis of covariance revealed group differences with significant and trends toward significant decreases in the d-P200 and d-late positive potential (LPP) amplitudes at the occipital electrodes of the fatigued and unfatigued groups. Our findings indicate that mentally fatigued participants did not effectively block out distractors in their information processing mechanism, providing support for the hypothesis that 3D mental fatigue impairs spatial selective attention and is characterized by changes in d-P200 and d-LPP amplitudes. Copyright © 2014 Elsevier B.V. All rights reserved.

  6. Instantaneous quantification of skeletal muscle activation, power production, and fatigue during cycle ergometry.

    Science.gov (United States)

    Coelho, A C; Cannon, D T; Cao, R; Porszasz, J; Casaburi, R; Knorst, M M; Rossiter, H B

    2015-03-01

    A rapid switch from hyperbolic to isokinetic cycling allows the velocity-specific decline in maximal power to be measured, i.e., fatigue. We reasoned that, should the baseline relationship between isokinetic power (Piso) and electromyography (EMG) be reproducible, then contributions to fatigue may be isolated from 1) the decline in muscle activation (muscle activation fatigue); and 2) the decline in Piso at a given activation (muscle fatigue). We hypothesized that the EMG-Piso relationship is linear, velocity dependent, and reliable for instantaneous fatigue assessment at intolerance during and following whole body exercise. Healthy participants (n = 13) completed short (5 s) variable-effort isokinetic bouts at 50, 70, and 100 rpm to characterize baseline EMG-Piso. Repeated ramp incremental exercise tests were terminated with maximal isokinetic cycling (5 s) at 70 rpm. Individual baseline EMG-Piso relationships were linear (r(2) = 0.95 ± 0.04) and velocity dependent (analysis of covariance). Piso at intolerance (two legs, 335 ± 88 W) was ∼45% less than baseline [630 ± 156 W, confidence interval of the difference (CIDifference) 211, 380 W, P fatigue and muscle fatigue (one leg) were 97 ± 55 and 60 ± 50 W, respectively. Mean bias ± limits of agreement for reproducibility were as follows: baseline Piso 1 ± 30 W; Piso at 0-min recovery 3 ± 35 W; and EMG at Piso 3 ± 14%. EMG power is linear, velocity dependent, and reproducible. Deviation from this relationship at the limit of tolerance can quantify the "activation" and "muscle" related components of fatigue during cycling. Copyright © 2015 the American Physiological Society.

  7. Creep-fatigue of High Temperature Materials for VHTR: Effect of Cyclic Loading and Environment

    Energy Technology Data Exchange (ETDEWEB)

    Celine Cabet; L. Carroll; R. Wright; R. Madland

    2011-05-01

    Alloy 617 is the one of the leading candidate materials for Intermediate Heat eXchangers (IHX) of a Very High Temperature Reactor (VHTR). System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Furthermore, the anticipated IHX operating temperature, up to 950°C, is in the range of creep so that creep-fatigue interaction, which can significantly increase the fatigue crack growth, may be one of the primary IHX damage modes. To address the needs for Alloy 617 codification and licensing, a significant creep-fatigue testing program is underway at Idaho National Laboratory. Strain controlled LCF tests including hold times up to 1800s at maximum tensile strain were conducted at total strain range of 0.3% and 0.6% in air at 950°C. Creep-fatigue testing was also performed in a simulated VHTR impure helium coolant for selected experimental conditions. The creep-fatigue tests resulted in failure times up to 1000 hrs. Fatigue resistance was significantly decreased when a hold time was added at peak stress and when the total strain was increased. The fracture mode also changed from transgranular to intergranular with introduction of a tensile hold. Changes in the microstructure were methodically characterized. A combined effect of temperature, cyclic and static loading and environment was evidenced in the targeted operating conditions of the IHX. This paper This paper reviews the data previously published by Carroll and co-workers in references 10 and 11 focusing on the role of inelastic strain accumulation and of oxidation in the initiation and propagation of surface fatigue cracks.

  8. Neurodegenerative and Fatiguing Illnesses, Infections and Mitochondrial Dysfunction: Use of Natural Supplements to Improve Mitochondrial Function

    Directory of Open Access Journals (Sweden)

    Garth L. Nicolson

    2014-01-01

    Full Text Available Background: Many chronic diseases and illnesses are associated with one or more chronic infections, dysfunction of mitochondria and reduced production of ATP. This results in fatigue and other symptoms that occur in most if not all chronic conditions and diseases. Methods: This is a review of the published literature on chronic infections in neurodegenerative diseases and fatiguing illnesses that are also typified by mitochondrial dysfunction. This contribution also reviews the use of natural supplements to enhance mitochondrial function and reduce the effects of chronic infections to improve overall function in various chronic illnesses. Results: Mitochondrial function can be enhanced by the use of various natural supplements, notably Lipid Replacement Therapy (LRT using glyerolphospholipids and other mitochondrial supplements. In various chronic illnesses that are characterized by the presence of chronic infections, such as intracellular bacteria (Mycoplasma, Borrelia, Chlamydia and other infections and viruses, LRT has proven useful in multiple clinical trials. For example, in clinical studies on chronic fatigue syndrome, fibromyalgia syndrome and other chronic fatiguing illnesses where a large majority of patients have chronic infections, LRT significantly reduced fatigue by 35-43% in different clinical trials and increased mitochondrial function. In clinical trials on patients with multiple intracellular bacterial infections and intractable fatigue LRT plus other mitochondrial supplements significantly decreased fatigue and improved mood and cognition. Conclusions: LRT formulations designed to improve mitochondrial function appear to be useful as non-toxic dietary supplements for reducing fatigue and restoring mitochondrial and other cellular membrane functions in patients with chronic illnesses and multiple chronic infections.

  9. Optimal fatigue analysis of structures during complex loadings

    Directory of Open Access Journals (Sweden)

    Karaouni Habib

    2016-01-01

    Full Text Available A new framework for high cycle fatigue analysis of metallic structures under complex multi-parameter loadings was here developed. This allows to reduce the analysis on a 2-D window with a characterized one-parameter cyclic loading thanks to an equivalence rule relative to damage between any two loadings. The simplified inelastic analysis introduced by J. Zarka [J. Zarka et al. 1990. A new approach in inelastic analysis of structures. CADLM] was used to find the limit state of the structure. A new design rules for fatigue analysis by utilizing automatic learning systems was successfully performed. A database was built by coupling numerical simulations and experimental results on several welded specimens which are considered as a general structure in the proposed approach. This could be possible by the introduction of an intelligent description of a general fatigue case based on the actual theories and models. A software, FATPRO [M.I. Systems, FatPro, available at http://www.mzintsys.com/our_products_fatpro.html], based on this work has been developed at MZ Intelligent Systems.

  10. Hydrogen effect on the fatigue behavior of LBM Inconel 718

    Directory of Open Access Journals (Sweden)

    Puydebois Simon

    2018-01-01

    Full Text Available For several years, Inconel 718 made by Laser Beam Melting (LBM has been used for components of the Ariane propulsion systems manufactured by ArianeGroup. In the aerospace field, many components of space engines are used under hydrogen environment. The risk of hydrogen embrittlement (HE can be therefore a first order problem. Consequently, to improve the HE sensitivity of LBM Inconel 718, a systematic approach needs to be developed to characterize the microstructure at different scales and its interaction with hydrogen. This study addresses the impact of gaseous hydrogen on the material mechanical behavior under fatigue loadings. In a first step, the low cycle fatigue behavior under 300 bar of hydrogen gas has been evaluated with specimen loaded at a constant load ratio of R=0.1 and a frequency of 0.5 Hz. A reduction in the cycle number of fracture is shown. This reduction of fatigue life is a consequence of the impact of hydrogen damage processes. The impact of hydrogen is evaluated at the stages of crack initiation, crack propagation. These results are discussed in relation with the hydrogen embrittlement mechanisms and particularly in terms of hydrogen / plasticity interactions. To achieve this, the fracture surface morphology was first examined using scanning electron microscopy and second samples near the fracture surface were extracted using Focused-Ion Beam machining from regions containing striation. The main result observed is a reduction of the size of dislocation organization in relation with a decrease of the striation distance.

  11. Fatigue Reliability under Multiple-Amplitude Loads

    DEFF Research Database (Denmark)

    Talreja, R.

    1979-01-01

    for the initial tensile strength and the fatigue life, the probability distributions for the residual tensile strength in both the crack initiation and the crack propagation stages of fatigue are determined. The method is illustrated for two-amplitude loads by means of experimental results obtained by testing...

  12. 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.

  13. Fatigue of coated and laser hardened steels

    International Nuclear Information System (INIS)

    La Cruz, P. de.

    1990-01-01

    In the present work the effect of ion nitriding, laser hardening and hot dip galvanizing upon the fatigue limit and notch sensitivity of a B-Mn Swedish steel SS 2131 have been investigated. The fatigue tests were performed in plane reverse bending fatigue (R=1). The quenched and tempered condition was taken as the reference condition. The microstructure, microhardness, fracture surface and coating appearance of the fatigue surface treated specimens were studied. Residual stress and retained austenite measurements were also carried out. It was found that ion nitriding improves the fatigue limit by 53 % for smooth specimens and by 115 % for notched specimens. Laser hardening improves the fatigue limit by 18 % and 56 % for smooth and notched specimen respectively. Hot dip galvanizing gives a slight deterioration of the fatigue limit (9 % and 10 % for smooth and notched specimen respectively). Ion nitriding and laser hardening decrease the value of the notch sensitivity factor q by 78 % and 65 % respectively. Hot dip galvanizing does not modify it. A simple schematic model based on a residual stress distribution, has been used to explain the different effects. It seems that the presence of the higher compressive residual stresses and the higher uniformity of the microstructure may be the causes of the better fatigue performance of ion nitrided specimens. (119 refs.) (author)

  14. Fatigue strength of socket welded pipe joint

    International Nuclear Information System (INIS)

    Iida, K.; Matsuda, F.; Sato, M.; Higuchi, M.; Nakagawa, A.

    1994-01-01

    Fully reversed four point bending fatigue tests were carried out of small diameter socket welded joints made of carbon steels. Experimental parameters are pipe diameter, thickness of pipe and socket wall, throat depth and shape of fillet welds, slip-on and diametral gaps in the socket welding, lack of penetration at the root of fillet welds, and peening of fillet welds. In most cases a fatigue crack started from the root of the fillet, but in the case of higher stress amplitude, it tended to start from the toe of fillet. The standard socket welded joint of 50 mm diameter showed relatively low fatigue strength, 46 MPa in stress amplitude at the 10 7 cycles failure life. This value corresponds to about 1/5 of that of the smoothed base metal specimens in axial fatigue. The fatigue strength showed decrease with increasing pipe diameter, and increase with increasing the thickness of pipe and socket wall. The effects of throat depth and shape of fillet welds on fatigue strength were not significant. Contrary to the expectation, the fatigue strength of the socket welded joint without slip-on gap is higher than that of the joint with the normal gap. A lack of penetration at the root deleteriously reduced fatigue strength, showing 14 MPa in stress amplitude at the 10 7 cycles failure life for the 50 mm diameter socket joint. (orig.)

  15. Fatigue tests of dowel-socket systems

    International Nuclear Information System (INIS)

    Chiang, D.D.

    1976-01-01

    A test program was conducted to determine the fatigue behavior of LHTGR fuel element dowel/socket systems. Two dowel/socket systems, namely, a four-dowel system and a five-dowel system, were tested to failure under shear loads applied through a fatigue test apparatus to simulate repetitive loading during a seismic event

  16. Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Diagnosis

    Science.gov (United States)

    ... Controls Search Form Controls Cancel Submit Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Note: Javascript is disabled or is not supported ... Facebook Tweet Share Compartir To diagnose myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), a patient’s doctor or healthcare provider ...

  17. Chronic Fatigue Syndrome: How Vulnerable Are Athletes?

    Science.gov (United States)

    Eichner, Edward R.

    1989-01-01

    Discusses chronic fatigue syndrome as it affects elite athletes, noting that overtraining may mimic it. In some cases, athletes who have it perform exceedingly well in the face of debilitating fatigue. Among athletes and nonathletes, the cause and the mind-body connection are areas of controversy and research. (Author/SM)

  18. High-speed Stochastic Fatigue Testing

    DEFF Research Database (Denmark)

    Brincker, Rune; Sørensen, John Dalsgaard

    1990-01-01

    Good stochastic fatigue tests are difficult to perform. One of the major reasons is that ordinary servohydraulic loading systems realize the prescribed load history accurately at very low testing speeds only. If the speeds used for constant amplitude testing are applied to stochastic fatigue...

  19. Standard guide for fretting fatigue testing

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2010-01-01

    1.1 This guide defines terminology and covers general requirements for conducting fretting fatigue tests and reporting the results. It describes the general types of fretting fatigue tests and provides some suggestions on developing and conducting fretting fatigue test programs. 1.2 Fretting fatigue tests are designed to determine the effects of mechanical and environmental parameters on the fretting fatigue behavior of metallic materials. This guide is not intended to establish preference of one apparatus or specimen design over others, but will establish guidelines for adherence in the design, calibration, and use of fretting fatigue apparatus and recommend the means to collect, record, and reporting of the data. 1.3 The number of cycles to form a fretting fatigue crack is dependent on both the material of the fatigue specimen and fretting pad, the geometry of contact between the two, and the method by which the loading and displacement are imposed. Similar to wear behavior of materials, it is important t...

  20. 10 CFR 26.211 - Fatigue assessments.

    Science.gov (United States)

    2010-01-01

    ... licensee returns the individual to duty following a break of less than 10 hours in duration, the licensee... competently perform his or her duties for any part of a working tour because of fatigue, except if, following... 10 hours before the individual returns to duty; (3) Post-event. A fatigue assessment must be...

  1. Statistical treatment of fatigue test data

    International Nuclear Information System (INIS)

    Raske, D.T.

    1980-01-01

    This report discussed several aspects of fatigue data analysis in order to provide a basis for the development of statistically sound design curves. Included is a discussion on the choice of the dependent variable, the assumptions associated with least squares regression models, the variability of fatigue data, the treatment of data from suspended tests and outlying observations, and various strain-life relations

  2. Threshold Corrosion Fatigue of Welded Shipbuilding Steels.

    Science.gov (United States)

    1992-01-01

    8. J. C. Walter, E. Olbjorn, 0. Allstad and G. Elde, "Safety Against Corrosion Fatigue Offshore," Publication No. 94, Det Norske Ventas , Horik...Offshore. Publication No;. 94;, Det Norske Ventas , Horik, Norway, April 1976. 18. C. E. Jaske, D. Broek, J. E. Slater, W. E. Anderson. Corrosion Fatigue

  3. A critical evaluation on the fatigue problem

    International Nuclear Information System (INIS)

    Rosa, E. da; Costa Machado Leal, L. da

    1978-01-01

    A review of the different aspects of approaches to the fatigue problems since the Woehler curves till the crack propagation is presented. The interrelationship among each one of the aspects is then carried out as well as the relation of the aspects to the different fatigue phases, since the crack nucleation till the final rupture in an attempt to unify the design procedure. (Author)

  4. Fatigue and Depressive Symptoms in Older People

    DEFF Research Database (Denmark)

    Mänty, Minna; Rantanen, Taina; Era, Pertti

    2014-01-01

    Fatigue is considered an important indicator of aging-related declines in health and functional abilities. Previous studies have indicated strong associations between fatigue and depressive symptoms among younger populations and in patient groups with specific diseases. However, it is not known h...

  5. Work fatigue in urban bus drivers

    Directory of Open Access Journals (Sweden)

    Teresa Makowiec-Dąbrowska

    2015-10-01

    Full Text Available Background: Bus drivers are a special group of professional drivers who are at a very high risk of fatigue. The aim of the study was to examine whether the driver’s subjective assessment of fatigue allows for the determination of its level and identification of its causes. Material and Methods: The study group comprised 45 randomly selected bus drivers (mean age – 43.7±7.9 years, period of employment as drivers – 14.7±8.6 years. Examinations were performed in all subjects four times – before and after work on the “easy” route (outside the city center, small traffic intensity and before and after work on the “difficult” route (city center, heavy traffic. The fatigue test questionnaire, based on the list of symptoms of fatigue prepared by the Japan Research Committee of Fatigue, was used in the study. Results: The rating of fatigue after the work was significantly higher than that before the work. The profile of fatigue after work was not influenced by the type of route, but the assessment of most symptoms of fatigue reached a higher level after the “difficult” routes and the differences were statistically significant for 7 symptoms. Only the ratings of leg fatigue, feeling of heaviness, and the necessity to squint eyes and gaze with effort reached the higher levels after driving the “easy” routes. It has been found that the level of fatigue was significantly correlated with the job characteristics (driving time, the length of the route, number of stops, etc. and with the abundance of food ingested and type of beverage (coffee vs. others drunk prior to driving. Conclusions: The questionnaire used in our study to assess the subjective feeling of fatigue has proved to be a sensitive and useful tool for indicating the level and causes of fatigue. The relationship between the symptoms of fatigue and the characteristics of job and lifestyle shows that actions must be taken by both the employers and employees to prevent fatigue

  6. Environmental fatigue in aluminum-lithium alloys

    Science.gov (United States)

    Piascik, Robert S.

    1992-01-01

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

  7. Fatigue strength ofcomposite wind turbine blade structures

    DEFF Research Database (Denmark)

    Ardila, Oscar Gerardo Castro

    Wind turbines are normally designed to withstand 20-30 years of life. During this period, the blades, which are the main rotating structures of a wind turbine, are subjected to high fluctuating load conditions as a result of a combination of gravity, inertia, and aeroelastic forces. For this reason......, fatigue is one of the foremost concerns during the design of these structures. However, current standard fatigue methods used for designing wind turbine blades seem not to be completely appropriate for these structures because they are still based on methods developed for metals and not for composite...... materials from which the blades are made. In this sense, the aim of this work is to develop more accurate and reliable fatigue-life prediction models for composite wind turbine blades. In this project, two types of fatigue models are implemented: fatigue-life models and damage mechanics models. In the first...

  8. A Review on Fatigue Driving Detection

    Directory of Open Access Journals (Sweden)

    Shi Sheng-Yang

    2017-01-01

    Full Text Available The socialization of automobile development has brought great convenience to people’s travel. However, the rapid increase in the number of vehicles has also caused a series of problems. The increase in traffic accidents has brought great social casualties and economic losses. Fatigue driving, which is an important factor in the traffic accident, has aroused people’s attention. This paper reviews all kinds of fatigue driving detection methods at present; compares various fatigue driving detection methods in terms of accuracy, real-time and cost; analyses the advantages and disadvantages of various methods; introduces the application of fatigue detection system in automobile; summarizes the current deficiencies and future development trends in the field of fatigue driving detection. The future research of this field will be more to the data fusion, computer vision and deep learning.

  9. Fatigue in adults with traumatic brain injury

    DEFF Research Database (Denmark)

    Mollayeva, Tatyana; Kendzerska, Tetyana; Mollayeva, Shirin

    2013-01-01

    BACKGROUND: Despite strong indications that fatigue is the most common and debilitating symptom after traumatic brain injury, little is known about its frequency, natural history, or relation to other factors. The current protocol outlines a strategy for a systematic review that will identify......, assess, and critically appraise studies that assessed predictors for fatigue and the consequences of fatigue on at least two separate time points following traumatic brain injury. METHODS/DESIGN: MEDLINE, EMBASE, the Cochrane Database of Systematic Reviews, CINAHL, and PsycINFO will be systematically...... searched for relevant peer-reviewed studies. Reference lists of eligible papers will also be searched. All English language studies with a longitudinal design that focus on fatigue in adults with primary-impact traumatic brain injury will be included. Studies on fatigue following brain injury due...

  10. Interconnect fatigue design for terrestrial photovoltaic modules

    Science.gov (United States)

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

    1982-03-01

    The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable (1) the prediction of cumulative interconnect failures during the design life of an array field, and (2) the unambiguous--ie., quantitative--interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field.

  11. High cycle fatigue properties of inconel 690

    International Nuclear Information System (INIS)

    Lee, Young Ho; Lee, Byong Whi; Kim, In Sup; Park, Chi Yong

    1997-01-01

    Inconel 690 is presently used as sleeve material and a replacement alloy in degraded steam generators, as well as the material for new steam generators. But Inconel 690 has low thermal conductivity which are 3-8% less than that of Inconel 600 at operating temperature. For the same power output, conduction area must be increased. As a result, more fluid induced vibration can cause a fatigue damage of Inconel 690. High cycle fatigue ruptures occurred in the U-bend regions of North Anna Unit 1 and Mihama Unit 2 steam generators. At this study, the effect of temperature on fatigue crack growth rate in Inconel 690 steam generator tube was investigated at various temperature in air environment. With increasing temperature, fatigue crack growth rate increased and grain size effect decreased. Chromium carbides which have large size and semi-continuous distribution in the grain boundaries decreased fatigue crack growth rate

  12. Fatigue in Steel Structures under Random Loading

    DEFF Research Database (Denmark)

    Agerskov, Henning

    1999-01-01

    types of welded plate test specimens and full-scale offshore tubular joints. The materials that have been used are either conventional structural steel with a yield stress of ~ 360-410 MPa or high-strength steel with a yield stress of ~ 810-1010 MPa. The fatigue tests and the fracture mechanics analyses......Fatigue damage accumulation in steel structures under random loading is studied. The fatigue life of welded joints has been determined both experimentally and from a fracture mechanics analysis. In the experimental part of the investigation, fatigue test series have been carried through on various...... have been carried out using load histories, which are realistic in relation to the types of structures studied, i.e. primarily bridges, offshore structures and chimneys. In general, the test series carried through show a significant difference between constant amplitude and variable amplitude fatigue...

  13. Parallel monostrand stay cable bending fatigue

    DEFF Research Database (Denmark)

    Winkler, Jan Pawel

    This dissertation investigates the bending fatigue response of high-strength steel monostrands and multistrand stay cables to cyclic transverse deformations. Increasing bridge stock numbers and a push for longer cable-supported span lengths have led to an increased number of reported incidents...... of damage and replacement of bridge stay cables due to wind and traffic-induced fatigue. The understanding of fatigue mechanisms in most steel structures is well established. However, in the case of cables composed of steel strands, many important aspects related with bending fatigue remain to be clarified...... associated with variable loading, and different testing procedures. As most of the contemporary stay cables are comprised of a number of individual highstrength steel monostrands, the research study started with an extensive experimental work on the fatigue response of a single monostrand to cyclic flexural...

  14. Assessment of muscle fatigue using electromygraphm sensing

    Science.gov (United States)

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

    2017-08-01

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

  15. On the Fatigue Analysis of Wind Turbines

    Energy Technology Data Exchange (ETDEWEB)

    Sutherland, Herbert J.

    1999-06-01

    Modern wind turbines are fatigue critical machines that are typically used to produce electrical power from the wind. Operational experiences with these large rotating machines indicated that their components (primarily blades and blade joints) were failing at unexpectedly high rates, which led the wind turbine community to develop fatigue analysis capabilities for wind turbines. Our ability to analyze the fatigue behavior of wind turbine components has matured to the point that the prediction of service lifetime is becoming an essential part of the design process. In this review paper, I summarize the technology and describe the ''best practices'' for the fatigue analysis of a wind turbine component. The paper focuses on U.S. technology, but cites European references that provide important insights into the fatigue analysis of wind turbines.

  16. Shock Transmission and Fatigue in Human Running.

    Science.gov (United States)

    Verbitsky, Oleg; Mizrahi, Joseph; Voloshin, Arkady; Treiger, July; Isakov, Eli

    1998-08-01

    The goal of this research was to analyze the effects of fatigue on the shock waves generated by foot strike. Twenty-two subjects were instrumented with an externally attached, lightweight accelerometer placed over the tibial tuberosity. The subjects ran on a treadmill for 30 min at a speed near their anaerobic threshold. Fatigue was established when the end-tidal CO 2 pressure decreased. The results indicated that approximately half of the subjects reached the fatigue state toward the end of the test. Whenever fatigue occurred, the peak acceleration was found to increase. It was thus concluded that there is a clear association between fatigue and increased heel strike-induced shock waves. These results have a significant implication for the etiology of running injuries, since shock wave attenuation has been previously reported to play an important role in preventing such injuries.

  17. RMS fatigue curves for random vibrations

    International Nuclear Information System (INIS)

    Brenneman, B.; Talley, J.G.

    1984-01-01

    Fatigue usage factors for deterministic or constant amplitude vibration stresses may be calculated with well known procedures and fatigue curves given in the ASME Boiler and Pressure Vessel Code. However, some phenomena produce nondeterministic cyclic stresses which can only be described and analyzed with statistical concepts and methods. Such stresses may be caused by turbulent fluid flow over a structure. Previous methods for solving this statistical fatigue problem are often difficult to use and may yield inaccurate results. Two such methods examined herein are Crandall's method and the ''3sigma'' method. The objective of this paper is to provide a method for creating ''RMS fatigue curves'' which accurately incorporate the requisite statistical information. These curves are given and may be used by analysts with the same ease and in the same manner as the ASME fatigue curves

  18. On the transition of short cracks into long fatigue cracks in reactor pressure vessel steels

    Directory of Open Access Journals (Sweden)

    Singh Rajwinder

    2018-01-01

    Full Text Available Short fatigue cracks, having dimension less than 1 mm, propagate at much faster rates (da/dN even at lower stress intensity factor range (da/dN as compared to the threshold stress intensity factor range obtained from long fatigue crack growth studies. These short cracks originate at the sub-grain level and some of them ultimately transit into critical long cracks over time. Therefore, designing the components subjected to fatigue loading merely on the long crack growth data and neglecting the short crack growth behavior can overestimate the component’s life. This aspect of short fatigue cracks become even more critical for materials used for safety critical applications such as reactor pressure vessel (RPV steel in nuclear plants. In this work, the transition behaviour of short fatigue crack gowth into long fatigue crack is studied in SA508 Grade 3 Class I low alloy steel used in RPVs. In-situ characterization of initiation, propagation and transition of short fatigue cracks is performed using fatigue stage for Scanning Electron Microscope (SEM in addition to digital microscopes fitted over a servo-hydraulic fatigue machine and correlated with the microtructural information obtained using electron backscatter diffraction (EBSD. SA508 steel having an upper bainitic microstructure have several microstructural interfaces such as phase and grain boundaries that play a significant role in controlling the short fatigue crack propagation. Specially designed and prepared short fatigue specimens (eletro-polished with varying initial crack lengths of the order of tens of microns are used in this study. The transition of such short initial cracks into long cracks is then tracked to give detailed insight into the role of each phase and phase/grain boundary with an objective of establishing Kitagawa-Takahashi diagram for the given RPV steel. The behavior of the transited long cracks is then compared with the crack propagation behavior obtained using

  19. Flexural fatigue failures and lives of Eco-Core sandwich beams

    International Nuclear Information System (INIS)

    Hossain, Mohammad Mynul; Shivakumar, Kunigal

    2014-01-01

    Highlights: • Eco-Core sandwich beam is flexural fatigue tested to study its fatigue response. • The core showed three failure types: damage onset, progression and final failure. • These failures were found to be represented by 1%, 5% and 7% change in compliance. • The fatigue stress-life (S–N) relationship follows a power low, σ max /σ ct = A o N α . • The fatigue failure was by multiple vertical cracks followed by 45° shear failure. - Abstract: Eco-Core is a class of syntactic foam made from small volume of high char yield binder and large volume of a class of flyash for fire resistance application. Very little or no flexural fatigue data of this class of core material is reported in the open literature. This paper presents a flexural fatigue response of Eco-Core in a glass/vinyl ester composite face sheet sandwich beam. A four-point loaded flexural test specimen was designed and tested in static and fatigue loadings to cause tension failure in the core. The fatigue test was conducted at maximum cyclic stress (σ max ) ranged from 0.7σ ct to 0.9σ ct , where σ ct is the static flexural strength of the core. The sinusoidal loading frequency of 2 Hz with the stress ratio of 0.1 was used. Flexural fatigue failure modes of Eco-Core sandwich beam were classified: damage onset (single tension crack), damage progression (multiple tension cracks) and ultimate failure (a combination of tension and shear). These failures were characterized by 1%, 5% and 7% changes in compliance that corresponds to N 1% , N 5% and N 7% lives. The fatigue stress-life (S–N) relationship was found to follow the well-known power law equation, σ max /σ ct = A o N α . The constants A o and α were established for all three types of failures. The endurance limit was established based on 1 million cycles limit and it was found to be 0.65σ ct , 0.70σ ct and 0.71σ ct , respectively for the three modes of failure. Flexural fatigue and static failure modes of Eco-Core sandwich

  20. Fatigue cracking in road pavement

    Science.gov (United States)

    Mackiewicz, P.

    2018-05-01

    The article presents the problem of modelling fatigue phenomena occurring in the road pavement. The example of two selected pavements shows the changes occurring under the influence of the load in different places of the pavement layers. Attention is paid to various values of longitudinal and transverse strains generated at the moment of passing the wheel on the pavement. It was found that the key element in the crack propagation analysis is the method of transferring the load to the pavement by the tire and the strain distribution in the pavement. During the passage of the wheel in the lower layers of the pavement, a complex stress state arises. Then vertical, horizontal and tangent stresses with various values appear. The numerical analyses carried out with the use of finite element methods allowed to assess the strain and stress changes occurring in the process of cracking road pavement. It has been shown that low-thickness pavements are susceptible to fatigue cracks arising "bottom to top", while pavements thicker are susceptible to "top to bottom" cracks. The analysis of the type of stress allowed to determine the cracking mechanism.

  1. Mechanical characterization of composite repairs for fiberglass wind turbine blades

    Science.gov (United States)

    Chawla, Tanveer Singh

    affects the propagation fracture toughness values of the repair. Repairs conducted on surfaces with partially ground top plies possess higher fracture toughness values than those conducted on surfaces with complete top plies ground off. The three top repair resin candidates were then evaluated against the base repair resin under fatigue loading. The specimen configuration and testing method were chosen so as to be able to test hand layup repairs under tension -- tension cyclic loading. It was observed that all three new repair resins perform better than the base repair resin. The selection of the optimum repair resin was based on results from mode I and fatigue testing. Global manufacturing regulations and standards were also of prime concern. The final new repair resin is being used by the company in all of its plants over the globe. The balance of this work involves study of the effect of mixed mode I -- mode II loading on the strength of repairs conducted on fiber reinforced composite parts using hand lay-up technique. The specimens for this part were similar to those manufactured for mode I testing but with different dimensions and layup. They were made and tested in accordance with ASTM D 6671 (Standard Test Method for Mixed Mode I -- Mode II Interlaminar Fracture Toughness of Unidirectional Fiber Reinforced Polymer Matrix Composites). Comparison was made between the fracture toughness of the above chosen optimum repair resin and the base repair resin. At least two levels of mode mixture GII/G (Mode II fracture toughness / Mode I and II fracture toughness) were examined. Also, two levels of grinding were considered (complete ply vs. partial ply ground off) in order to establish the influence of varying top-ply grinding depths on the strength of hand layup repairs conducted on fiberglass composite structures. The results of this work have the potential to improve the repair process for current fiberglass wind turbine blades.

  2. Fatigue Characteristics of Selected Light Metal Alloys

    Directory of Open Access Journals (Sweden)

    Cieśla M.

    2016-03-01

    Full Text Available The paper addresses results of fatigue testing of light metal alloys used in the automotive as well as aerospace and aviation industries, among others. The material subject to testing comprised hot-worked rods made of the AZ31 alloy, the Ti-6Al-4V two-phase titanium alloy and the 2017A (T451 aluminium alloy. Both low- and high-cycle fatigue tests were conducted at room temperature on the cycle asymmetry ratio of R=-1. The low-cycle fatigue tests were performed using the MTS-810 machine on two levels of total strain, i.e.Δεc= 1.0% and 1.2%. The high-cycle fatigue tests, on the other hand, were performed using a machine from VEB Werkstoffprufmaschinen-Leipzig under conditions of rotary bending. Based on the results thus obtained, one could develop fatigue life characteristics of the materials examined (expressed as the number of cycles until failure of sample Nf as well as characteristics of cyclic material strain σa=f(N under the conditions of low-cycle fatigue testing. The Ti-6Al-4V titanium alloy was found to be characterised by the highest value of fatigue life Nf, both in lowand high-cycle tests. The lowest fatigue life, on the other hand, was established for the aluminium alloys examined. Under the high-cycle fatigue tests, the life of the 2017A aluminium and the AZ31 magnesium alloy studied was determined by the value of stress amplitude σa. With the stress exceeding 150 MPa, it was the aluminium alloy which displayed higher fatigue life, whereas the magnesium alloy proved better on lower stress.

  3. Temperament vs. chronic fatigue in police officers

    Directory of Open Access Journals (Sweden)

    Ewa Stępka

    2015-12-01

    Full Text Available Background: Chronic fatigue is a problem affecting a still growing number of people. Among them there are representatives of different professions who are forced to cope not only with occupational stress, but also with the problem of fatigue. The police is one of such occupational groups, in which exposure to stressful and often traumatic situations, contact with those who violate the law, shift work and contact with superiors can play a key role in the development of chronic fatigue. However, chronic fatigue, induced by the above mentioned factors, does not affect all police officers since its occurrence also depends on many personal traits, including temperament. Material and methods: We studied a group of 61 police officers of the Kuyavian-Pomeranian garrison. The study was conducted using the Buss and Plomin EAS (emotionality, activity, sociability Temperament Questionnaire, CIS-20R (community, innovation, survey Questionnaire, developed by Vercoulen et al. and a questionnaire on socio-demographic data. Results: The results indicated the relationship between chronic fatigue and emotionality. Statistical analyses showed a negative correlation between the nature of emotional components, distress, fear, anger, and the general rate of chronic fatigue. There was no statistically significant correlation between age, and service experience and the level of chronic fatigue. Conclusions: The results indicate that the officers of the study group show dramatically high levels of chronic fatigue. The results also revealed that temperament characteristics, such as sociability and activity, reported in the literature as factors reducing fatigue and stress, did not show relevance to chronic fatigue in the study group. Med Pr 2015;66(6:793–801

  4. Assessment of surgeon fatigue by surgical simulators

    Directory of Open Access Journals (Sweden)

    Tuwairqi K

    2015-04-01

    Full Text Available Khaled Tuwairqi,1 Jessica H Selter,2 Shameema Sikder3 1College of Medicine, University of Utah, Salt Lake City, UT, 2Johns Hopkins School of Medicine, 3Wilmer Eye Institute, Johns Hopkins University, Baltimore, MD, USA Background: The impact of fatigue on surgical performance and its implications for patient care is a growing concern. While investigators have employed a number of different tools to measure the effect of fatigue on surgical performance, the use of the surgical simulator has been increasingly implemented for this purpose. The goal of this paper is to review the published literature to achieve a better understanding of evaluation of fatigue on performance as studied with surgical simulators. Methods: A PubMed and Cochrane search was conducted using the search terms “simulator”, “surgery”, and “fatigue”. In total, 50 papers were evaluated, and 20 studies were selected after application of exclusion criteria. Articles were excluded if they did not use the simulator to assess the impact of fatigue on surgeon performance. Systematic reviews and case reports were also excluded. Results: Surgeon fatigue led to a consistent decline in cognitive function in six studies. Technical skills were evaluated in 18 studies, and a detrimental impact was reported in nine studies, while the remaining nine studies showed either no change or positive results with regard to surgical skills after experience of fatigue. Two pharmacological intervention studies reversed the detrimental impact of fatigue on cognitive function, but no change or a worsening effect was recognized for technical skills. Conclusion: Simulators are increasingly being used to evaluate the impact of fatigue on the surgeon's performance. With regard to the impact of fatigue in this regard, studies have demonstrated a consistent decline in cognitive function and mixed outcomes for technical skills. Larger studies that relate the simulator's results to real surgical

  5. Fatigue diminishes motoneuronal excitability during cycling exercise.

    Science.gov (United States)

    Weavil, Joshua C; Sidhu, Simranjit K; Mangum, Tyler S; Richardson, Russell S; Amann, Markus

    2016-10-01

    Exercise-induced fatigue influences the excitability of the motor pathway during single-joint isometric contractions. This study sought to investigate the influence of fatigue on corticospinal excitability during cycling exercise. Eight men performed fatiguing constant-load (80% W peak ; 241 ± 13 W) cycling to exhaustion during which the percent increase in quadriceps electromyography (ΔEMG; vastus lateralis and rectus femoris) was quantified. During a separate trial, subjects performed two brief (∼45 s) nonfatiguing cycling bouts (244 ± 15 and 331 ± 23W) individually chosen to match the ΔEMG across bouts to that observed during fatiguing cycling. Corticospinal excitability during exercise was quantified by transcranial magnetic, electric transmastoid, and femoral nerve stimulation to elicit motor-evoked potentials (MEP), cervicomedullary evoked potentials (CMEP), and M waves in the quadriceps. Peripheral and central fatigue were expressed as pre- to postexercise reductions in quadriceps twitch force (ΔQ tw ) and voluntary quadriceps activation (ΔVA). Whereas nonfatiguing cycling caused no measureable fatigue, fatiguing cycling resulted in significant peripheral (ΔQ tw : 42 ± 6%) and central (ΔVA: 4 ± 1%) fatigue. During nonfatiguing cycling, the area of MEPs and CMEPs, normalized to M waves, similarly increased in the quadriceps (∼40%; P fatiguing cycling. As a consequence, the ratio of MEP to CMEP was unchanged during both trials (P > 0.5). Therefore, although increases in muscle activation promote corticospinal excitability via motoneuronal facilitation during nonfatiguing cycling, this effect is abolished during fatigue. We conclude that the unaltered excitability of the corticospinal pathway from start of intense cycling exercise to exhaustion is, in part, determined by inhibitory influences on spinal motoneurons obscuring the facilitating effects of muscle activation.

  6. The hold-time effects on the low cycle fatigue behaviors of 316 SS in PWR primary environment

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Junho; Hong, Jong-Dae; Seo, Myung-Gyu; Jang, Changheui [KAIST, Daejeon (Korea, Republic of)

    2015-05-15

    The effects of the environments on fatigue life of the structural materials used in nuclear power plants (NPPs) were known to be significant according to the extensive test results. Accordingly, the fatigue analysis procedures and the design fatigue curves were proposed in the ASME Code. However, the implication that the existing ASME design fatigue curves did not sufficiently reflect the effect of the operation conditions of nuclear power plants emerged as an issue to be resolved. One of possible reasons to explain the discrepancy is that the laboratory test conditions do not represent the actual plant transients. Therefore, it is necessary to clarify the effects of light water environments on fatigue life while considering more plant-relevant transient conditions such as hold-time. For this reason, this study will focus on the fatigue life of type 316 stainless steel (SS) in the pressurized water reactor (PWR) environments while incorporating the hold-time during the low cycle fatigue (LCF) test in simulated PWR environments. The objective of this study is to characterize the effects of hold-time on the fatigue life of austenitic stainless steels in PWR environments in comparison with the existing fixed strain rate results. Low cycle fatigue life tests were conducted for the type 316 SS in 310 .deg. C air and simulated PWR environments. To simulate the heat-up and cool-down transient, sub-peak strain holding during the down-hill of strain amplitude was chosen. Currently, LCF tests with 60 seconds holding are in progress. The 0.4, 0.04%/s strain rate condition test results are presented in this study, which shows somewhat longer fatigue life.

  7. The hold-time effects on the low cycle fatigue behaviors of 316 SS in PWR primary environment

    International Nuclear Information System (INIS)

    Lee, Junho; Hong, Jong-Dae; Seo, Myung-Gyu; Jang, Changheui

    2015-01-01

    The effects of the environments on fatigue life of the structural materials used in nuclear power plants (NPPs) were known to be significant according to the extensive test results. Accordingly, the fatigue analysis procedures and the design fatigue curves were proposed in the ASME Code. However, the implication that the existing ASME design fatigue curves did not sufficiently reflect the effect of the operation conditions of nuclear power plants emerged as an issue to be resolved. One of possible reasons to explain the discrepancy is that the laboratory test conditions do not represent the actual plant transients. Therefore, it is necessary to clarify the effects of light water environments on fatigue life while considering more plant-relevant transient conditions such as hold-time. For this reason, this study will focus on the fatigue life of type 316 stainless steel (SS) in the pressurized water reactor (PWR) environments while incorporating the hold-time during the low cycle fatigue (LCF) test in simulated PWR environments. The objective of this study is to characterize the effects of hold-time on the fatigue life of austenitic stainless steels in PWR environments in comparison with the existing fixed strain rate results. Low cycle fatigue life tests were conducted for the type 316 SS in 310 .deg. C air and simulated PWR environments. To simulate the heat-up and cool-down transient, sub-peak strain holding during the down-hill of strain amplitude was chosen. Currently, LCF tests with 60 seconds holding are in progress. The 0.4, 0.04%/s strain rate condition test results are presented in this study, which shows somewhat longer fatigue life

  8. Fatigue crack propagation behavior under creep conditions

    International Nuclear Information System (INIS)

    Ohji, Kiyotsugu; Kubo, Shiro

    1991-01-01

    The crack propagation behavior of the SUS 304 stainless steel under creep-fatigue conditions was reviewed. Cracks propagated either in purely time-dependent mode or in purely cycle-dependent mode, depending on loading conditions. The time-dependent crack propagation rate was correlated with modified J-integral J * and the cycle-dependent crack propagation rate was correlated with J-integral range ΔJ f . Threshold was observed in the cycle-dependent crack propagation, and below this threshold the time-dependent crack propagation appeared. The crack propagation rates were uniquely characterized by taking the effective values of J * and ΔJ f , when crack closure was observed. Change in crack propagation mode occurred reversibly and was predicted by the competitive damage model. The threshold disappeared and the cycle-dependent crack propagation continued in a subthreshold region under variable amplitude conditions, where the threshold was interposed between the maximum and minimum ΔJ f . (orig.)

  9. Lifetime distribution in thermal fatigue - a stochastic geometry approach

    International Nuclear Information System (INIS)

    Kullig, E.; Michel, B.

    1996-02-01

    The present report describes the interpretation approach for crack patterns which are generated on the smooth surface of austenitic specimens under thermal fatigue loading. A framework for the fracture mechanics characterization of equibiaxially loaded branched surface cracks is developed which accounts also for crack interaction effects. Advanced methods for the statistical evaluation of crack patterns using suitable characteristic quantities are developed. An efficient simulation procedure allows to identify the impact of different variables of the stochastic crack growth model with respect to the generated crack patterns. (orig.) [de

  10. High cycle fatigue of Type 422 stainless steel

    International Nuclear Information System (INIS)

    Soo, P.; Chow, J.G.Y.; Sabatini, R.L.

    1978-01-01

    High cycle fatigue testing has been carried out on Type 422 stainless steel to determine the performance of cyclically stressed disks and blades in the main and auxiliary HTGR helium circulators. Tests were performed at 316, 482, and 538 0 C (600, 900, and 1000 0 F) in air for the fully reversible and mean load conditions. Goodman's analysis is shown to be valid in predicting failure at 316 0 C (600 0 F), marginally valid at 482 0 C (900 0 F), and probably invalid at 538 0 C (1000 0 F). Metallographic analyses were conducted to characterize the nature of failure for the temperatures and loading conditions investigated

  11. Fatigue damage sensor and substantitation of its application. Communication 2

    Energy Technology Data Exchange (ETDEWEB)

    Troshchenko, V T; Bojko, V I

    1985-01-01

    Block and random loading is studied for its effect on sensor readings. It is established that variation of electric sensor conductivity for these conditions does not depend on the loading prehistory and may be calculated according to the sensor test results at a regular loading. A general scheme of the sensor application is considered for determining residual part life with allowance for the factors. Effect on a part fatigue resistance when operating conditions of the loading are characterized by a stationary random process. Particular cases of the sensor application are considered coming out from a common scheme.

  12. Fatigue and functioning in rheumatic diseases: a biopsychological perspective

    OpenAIRE

    Overman, C.L.

    2015-01-01

    Rheumatic diseases are characterized by inflammation, damage and pain, mostly of the joints and connective tissues. They can have a profound negative impact on almost every aspect of a patient’s life as well as on the direct environment and society as a whole. Patients are hampered in their daily activities by pain, physical disability,and fatigue,and also psychological distress is more prevalent than in the general population. A patient’s health is determined by a complex interplay between p...

  13. Fatigue Crack and Delamination Growth in Fibre Metal Laminates under Variable Amplitude Loading

    NARCIS (Netherlands)

    Khan, S.

    2013-01-01

    This thesis presents the investigation into the fatigue propagation and delamination growth of Fibre Metal Laminates under variable amplitude loading. As explained in the first chapter, the motivation of the research is twofold: first, to obtain a clear understanding and detailed characterization of

  14. Effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280

    International Nuclear Information System (INIS)

    James, L.A.

    1976-05-01

    The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280 in an air environment. Also included in this study are survey tests to determine the effects of thermal aging and stress ratio upon crack growth behavior in this alloy

  15. Measuring School Functioning in Students with Chronic Fatigue Syndrome: A Systematic Review

    Science.gov (United States)

    Tollit, Michelle; Politis, Jennifer; Knight, Sarah

    2018-01-01

    Background: It is often surmised that school functioning is significantly impacted in chronic fatigue syndrome (CFS); however, how this phenomenon manifests itself has rarely been characterized. Methods: This systematic review synthesized and critically appraised methods, constructs, and instruments used to assess school functioning in students…

  16. Psychological treatment of patients with chronic toxic encephalopathy : Lessons from studies of chronic fatigue and whiplash

    NARCIS (Netherlands)

    van Hout, MSE; Wekking, EM; Berg, IJ; Deelman, BG

    2003-01-01

    Background. Chronic toxic encephalopathy (CTE), which can result from long-term exposure to organic solvents, is characterized by problems of attention and memory, fatigue and affective symptoms. There is little experience with (neuro)psychological treatment in this patient group. We reviewed

  17. Psychological treatment of patients with chronic toxic encephalopathy: lessons from studies of chronic fatigue and whiplash

    NARCIS (Netherlands)

    van Hout, Moniek S. E.; Wekking, Ellie M.; Berg, Ina J.; Deelman, Betto G.

    2003-01-01

    Chronic toxic encephalopathy (CTE), which can result from long-term exposure to organic solvents, is characterized by problems of attention and memory, fatigue and affective symptoms. There is little experience with (neuro)psychological treatment in this patient group. We reviewed treatment outcome

  18. Impact of operator fatigue on endoscopy performance: implications for procedure scheduling.

    LENUS (Irish Health Repository)

    Harewood, Gavin C

    2009-08-01

    With increasing volumes of endoscopic procedures, endoscopists\\' workload has had to increase to meet this escalating demand. The aim of this study was to characterize the impact of endoscopist fatigue on quality of endoscopy performance by comparing outcomes based on chronological procedure order.

  19. The fatigue and corrosion fatigue behavior of welded Inconel 625 alloy employed in off-shore platforms; Avaliacao do comportamento a fadiga e a corrosao-fadiga de juntas soldadas da liga Inconel 625 testada para uso em plaaformas off-shore

    Energy Technology Data Exchange (ETDEWEB)

    Pfingstag, M.E.; Schroeder, R.M.; Mueller, I.L. [Universidade Federal do Rio Grande do Sul (LAPEC/UFRGS), Porto Alegre, RS (Brazil). Dept. de Metalurgia. Lab. de Pesquisa em Corrosao], e-mail: maiquel10@walla.com

    2006-07-01

    The fatigue and corrosion fatigue behavior of welded Inconel 625 employed live like risers in off-shore platforms was studied. These risers may be employed integrally of this alloy, or combined with API 52 X60 steel in the form of 'Clads'. One of the most susceptible points in .these structures is the circumferential weld that joint the pipes together. In these regions, stresses and defects are generated by the welding process, and these material remind in contact with aggressive species like, chlorides and Co{sub 2} . Polarization curves, slow strain rate fatigue and corrosion fatigue tests were used to characterize the Inconel alloy behavior. In the welded deposit condition, this alloy shows an excellent resistance corrosion and a good fatigue and corrosion-fatigue behavior.(author)

  20. Random non-proportional fatigue tests with planar tri-axial fatigue testing machine

    Directory of Open Access Journals (Sweden)

    T. Inoue

    2016-10-01

    Full Text Available Complex stresses, which occur on the mechanical surfaces of transport machinery in service, bring a drastic degradation in fatigue life. However, it is hard to reproduce such complex stress states for evaluating the fatigue life with conventional multiaxial fatigue machines. We have developed a fatigue testing machine that enables reproduction of such complex stresses. The testing machine can reproduce arbitrary in-plane stress states by applying three independent loads to the test specimen using actuators which apply loads in the 0, 45, and 90 degree directions. The reproduction was tested with complex stress data obtained from the actual operation of transport machinery. As a result, it was found that the reproduced stress corresponded to the measured stress with an error range of less than 10 %. Then, we made a comparison between measured fatigue lives under random non-proportional loading conditions and predicted fatigue lives. It was found that predicted fatigue lives with cr, stress on critical plane, were over a factor of 10 against measured fatigue lives. On the other hand, predicted fatigue lives with ma, stress in consideration of a non-proportional level evaluated by using amplitude and direction of principal stress, were within a factor of 3 against measured fatigue lives

  1. Stress management skills, neuroimmune processes and fatigue levels in persons with chronic fatigue syndrome.

    Science.gov (United States)

    Lattie, Emily G; Antoni, Michael H; Fletcher, Mary Ann; Penedo, Frank; Czaja, Sara; Lopez, Corina; Perdomo, Dolores; Sala, Andreina; Nair, Sankaran; Fu, Shih Hua; Klimas, Nancy

    2012-08-01

    Stressors and emotional distress responses impact chronic fatigue syndrome (CFS) symptoms, including fatigue. Having better stress management skills might mitigate fatigue by decreasing emotional distress. Because CFS patients comprise a heterogeneous population, we hypothesized that the role of stress management skills in decreasing fatigue may be most pronounced in the subgroup manifesting the greatest neuroimmune dysfunction. In total, 117 individuals with CFS provided blood and saliva samples, and self-report measures of emotional distress, perceived stress management skills (PSMS), and fatigue. Plasma interleukin-1-beta (IL-1β, IL-2, IL-6, IL-10, and tumor necrosis factor-alpha (TNF-α), and diurnal salivary cortisol were analyzed. We examined relations among PSMS, emotional distress, and fatigue in CFS patients who did and did not evidence neuroimmune abnormalities. Having greater PSMS related to less fatigue (p=.019) and emotional distress (pfatigue levels most strongly in CFS patients in the top tercile of IL-6, and emotional distress mediated the relationship between PSMS and fatigue most strongly in patients with the greatest circulating levels of IL-6 and a greater inflammatory (IL-6):anti-inflammatory (IL-10) cytokine ratio. CFS patients having greater PSMS show less emotional distress and fatigue, and the influence of stress management skills on distress and fatigue appear greatest among patients who have elevated IL-6 levels. These findings support the need for research examining the impact of stress management interventions in subgroups of CFS patients showing neuroimmune dysfunction. Copyright © 2012 Elsevier Inc. All rights reserved.

  2. Mediators of the effects on fatigue of pragmatic rehabilitation for chronic fatigue syndrome.

    Science.gov (United States)

    Wearden, Alison J; Emsley, Richard

    2013-10-01

    To examine potential mediators of the effect of pragmatic rehabilitation on improvements in fatigue following a randomized controlled trial for patients with chronic fatigue syndrome (CFS/ME) in primary care (IRCTN 74156610). Patients fulfilled the Oxford criteria for CFS. Ninety-five patients were randomized to pragmatic rehabilitation and 100 to general practitioner (GP) treatment as usual. The outcome was the Chalder fatigue scale score (0123 scoring) at end of treatment (20 weeks) and 1-year follow up (70 weeks). First, the effect of treatment on potential mediators was assessed. Then fatigue was regressed on significant mediators, treatment allocation, and baseline measures of fatigue and significant mediators. Reduction in limiting activities at 20 weeks mediated the positive effect of pragmatic rehabilitation on fatigue at 70 weeks (mediated effect size = -2.64, SE = 0.81, p = .001, proportion of effect mediated = 82.0%). Reduction in catastrophizing at 20 weeks mediated the positive effect of pragmatic rehabilitation on fatigue at 70 weeks (mediated effect size = -1.39, SE = 0.61, p = .023, proportion of effect mediated = 43.2%). Reductions in 70-week measures of fear avoidance, embarrassment avoidance, limiting activities, and all-or-nothing behavior all mediated improvement in fatigue at 70 weeks, although the causal direction of these cross-sectional effects cannot be determined. There were no between-group differences on measures of exercise capacity (a timed step test). Improvements in fatigue following pragmatic rehabilitation are related to changes in behavioral responses to and beliefs about fatigue.

  3. 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

  4. A randomized controlled trial of qigong exercise on fatigue symptoms, functioning, and telomerase activity in persons with chronic fatigue or chronic fatigue syndrome.

    Science.gov (United States)

    Ho, Rainbow T H; Chan, Jessie S M; Wang, Chong-Wen; Lau, Benson W M; So, Kwok Fai; Yuen, Li Ping; Sham, Jonathan S T; Chan, Cecilia L W

    2012-10-01

    Chronic fatigue is common in the general population. Complementary therapies are often used by patients with chronic fatigue or chronic fatigue syndrome to manage their symptoms. This study aimed to assess the effect of a 4-month qigong intervention program among patients with chronic fatigue or chronic fatigue syndrome. Sixty-four participants were randomly assigned to either an intervention group or a wait list control group. Outcome measures included fatigue symptoms, physical functioning, mental functioning, and telomerase activity. Fatigue symptoms and mental functioning were significantly improved in the qigong group compared to controls. Telomerase activity increased in the qigong group from 0.102 to 0.178 arbitrary units (p chronic fatigue and chronic fatigue syndrome.

  5. Fatigue studies of superalloys in Japan

    International Nuclear Information System (INIS)

    Kitagawa, Masaki

    1985-01-01

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

  6. Creep fatigue assessment for EUROFER components

    Energy Technology Data Exchange (ETDEWEB)

    Özkan, Furkan, E-mail: oezkan.furkan@partner.kit.edu; Aktaa, Jarir

    2015-11-15

    Highlights: • Design rules for creep fatigue assessment are developed to EUROFER components. • Creep fatigue assessment tool is developed in FORTRAN code with coupling MAPDL. • Durability of the HCPB-TBM design is discussed under typical fusion reactor loads. - Abstract: Creep-fatigue of test blanket module (TBM) components built from EUROFER is evaluated based on the elastic analysis approach in ASME Boiler Pressure Vessel Code (BPVC). The required allowable number of cycles design fatigue curve and stress-to-rupture curve to estimate the creep-fatigue damage are used from the literature. Local stress, strain and temperature inputs for the analysis of creep-fatigue damage are delivered by the finite element code ANSYS utilizing the Mechanical ANSYS Parametric Design Language (MAPDL). A developed external FORTRAN code used as a post processor is coupled with MAPDL. Influences of different pulse durations (hold-times) and irradiation on creep-fatigue damage for the preliminary design of the Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) are discussed for the First Wall component of the TBM box.

  7. Effects of human fatigue on speech signals

    Science.gov (United States)

    Stamoulis, Catherine

    2004-05-01

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

  8. COGNITIVE FATIGUE FACILITATES PROCEDURAL SEQUENCE LEARNING

    Directory of Open Access Journals (Sweden)

    Guillermo eBorragán

    2016-03-01

    Full Text Available Enhanced procedural learning has been evidenced in conditions where cognitive control is diminished, including hypnosis, disruption of prefrontal activity and non-optimal time of the day. Another condition depleting the availability of controlled resources is cognitive fatigue. We tested the hypothesis that cognitive fatigue, eventually leading to diminished cognitive control, facilitates procedural sequence learning. In a two-day experiment, twenty-three young healthy adults were administered a serial reaction time task (SRTT following the induction of high or low levels of cognitive fatigue, in a counterbalanced order. Cognitive fatigue was induced using the Time load Dual-back (TloadDback paradigm, a dual working memory task that allows tailoring cognitive load levels to the individual's optimal performance capacity. In line with our hypothesis, reaction times in the SRTT were faster in the high- than in the low-level fatigue condition, and performance improvement showed more of a benefit from the sequential components than from motor. Altogether, our results suggest a paradoxical, facilitating impact of cognitive fatigue on procedural motor sequence learning. We propose that facilitated learning in the high-level fatigue condition stems from a reduction in the cognitive resources devoted to cognitive control processes that normally oppose automatic procedural acquisition mechanisms.

  9. Prevalence of fatigue in general practice.

    Science.gov (United States)

    Cullen, W; Kearney, Y; Bury, G

    2002-01-01

    Fatigue is an important symptom in general practice due to its association with physical, psychological and social problems. To determine the prevalence of fatigue as an unsolicited symptom during general practice consultations. A random sample of GPs practising in Ireland was invited to provide data on consultations held over one day. Data were recorded on the presence of fatigue as a main or supporting symptom, social and demographic characteristics. Data were recorded by 89 GPs on 1,428 consultations. The prevalence of fatigue was 25%. It was the main reason for attending the doctor in 6.5% and a secondary reason in 19%. Sixty-two per cent of patients were female and 48% were eligible for free GP services. The mean age was 47.1 years. The presence of fatigue was associated with: attending a female GP, being female, attending a GP who had been qualified for fewer years and attending the GP frequently. The prevalence of fatigue reported in this study is over three times higher than that reported in earlier work. Doctor characteristics appear to be as important as patient characteristics in determining fatigue.

  10. Chronic fatigue syndrome: aetiology, diagnosis and treatment

    Science.gov (United States)

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

    2009-01-01

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

  11. Fatigue in adults with post-infectious fatigue syndrome: a qualitative content analysis.

    Science.gov (United States)

    Stormorken, Eva; Jason, Leonard A; Kirkevold, Marit

    2015-01-01

    Fatigue is a major problem among individuals with post-infectious fatigue syndrome (PIFS), also known as chronic fatigue syndrome or myalgic encephalomyelitis. It is a complex phenomenon that varies across illnesses. From a nursing perspective, knowledge and understanding of fatigue in this illness is limited. Nurses lack confidence in caring for these patients and devalue their professional role. The aim of this study was to explore in-depth the experiences of fatigue among individuals with PIFS. A detailed description of the phenomenon of fatigue is presented. Increased knowledge would likely contribute to more confident nurses and improved nursing care. A qualitative study with open interviews was employed. In-depth interviews with patients were fully transcribed and underwent a qualitative content analysis. A maximum variation sample of 26 affected adults between 26-59 years old was recruited from a population diagnosed at a fatigue outpatient clinic. The fatigue was a post-exertional, multidimensional, fluctuating phenomenon with varying degrees of severity and several distinct characteristics and was accompanied by concomitant symptoms. Fatigue was perceived to be an all-pervasive complex experience that substantially reduced the ability to function personally or professionally. A range of trigger mechanisms evoked or worsened the fatigue, but the affected were not always aware of what triggered it. There was an excessive increase in fatigue in response to even minor activities. An increase in fatigue resulted in the exacerbation of other concomitant symptoms. The term fatigue does not capture the participants' experiences, which are accompanied by a considerable symptom burden that contributes to the illness experience and the severe disability. Although some aspects of the fatigue experience have been reported previously, more were added in our study, such as the dimension of awakening fatigue and the characteristic beyond time, when time passes unnoticed

  12. Muscle glycogen stores and fatigue

    DEFF Research Database (Denmark)

    Ørtenblad, Niels; Westerblad, Håkan; Nielsen, Joachim

    2013-01-01

      Studies performed at the beginning of the last century revealed the importance of carbohydrate as a fuel during exercise, and the importance of muscle glycogen on performance has subsequently been confirmed in numerous studies. However, the link between glycogen depletion and impaired muscle...... function during fatigue is not well understood and a direct cause-and-effect relationship between glycogen and muscle function remains to be established. The use of electron microscopy has revealed that glycogen is not homogeneously distributed in skeletal muscle fibres, but rather localized in distinct...... pools. Furthermore, each glycogen granule has its own metabolic machinery with glycolytic enzymes and regulating proteins. One pool of such glycogenolytic complexes is localized within the myofibrils in close contact with key proteins involved in the excitation-contraction coupling and Ca2+ release from...

  13. Fatigue aging of adhesive bonds

    International Nuclear Information System (INIS)

    DeLollis, N.J.

    1979-01-01

    A year long study has been made of the effect of fatigue on the bond between two epoxy encapsulant formulations and a fused alumina disc. The variables studied included isothermal aging at temperatures up to and including the cure temperature and cyclic thermal aging from +74 to -54 0 C. The encapsulants were glass microballoon filled epoxies differing only in curing agents. One was cured with an aromatic amine eutectic (Shell Curing Agent Z). The other was cured with diethanolamine. The Z cured encapsulant bond failed completely at the bond interface with little or no aging; infrared evidence indicated a soluble interlayer as a possible cause of failure. The diethanolamine cured encapsulant survived a year of isothermal aging with little or no evidence of bond degradation. Cyclic thermal aging resulted in gradual bond failure with time. An extrapolation of the cyclic aging data indicates that the stresses induced by thermal cycling would result in complete bond failure in about 1200 days

  14. Does Corruption Cause Aid Fatigue?

    DEFF Research Database (Denmark)

    Bauhr, Monika; Charron, Nicholas; Nasiritousi, Naghmeh

    2013-01-01

    Does perceived corruption in recipient countries reduce support for foreign aid in donor countries? This under-explored yet salient question is examined using the 2009 Eurobarometer survey for the 27 EU countries. We suggest that perceived corruption can cause aid fatigue but that this relationship...... is highly contextualized. The results show that perceptions about corruption in developing countries reduce overall support for aid among respondents in donor countries. However, this effect is mitigated by country and contextual-level effects and different understandings of what we call the “aid-corruption...... paradox,” namely that the need for foreign aid is often the greatest in corrupt environments. Three different dynamics of the aid-corruption paradox influence support for aid: moral, pragmatic, and strategic understandings. In EU-15 countries, the effect of perceived corruption in recipient states on aid...

  15. Model-experiment dialog in low cycle fatigue of stainless steels

    International Nuclear Information System (INIS)

    Aubin, Veronique

    2008-01-01

    In this HDR report (accreditation to supervise research), the author first proposes a synthesis of her research activities in the study of the mechanical behaviour in low cycle fatigue (cyclic hardening, plasticity surfaces), of modelling of the fatigue mechanical behaviour (phenomenological modelling, modelling with scale change), of progressive deformation (experimental analysis, analysis and simulation of plasticity at the microstructure scale). The second part addresses other activities in the field of research (behaviour and damage characterization of an austenitic-ferritic stainless steel), publication and education supervising, teaching

  16. Effects of an Exercise Intervention on Cancer-Related Fatigue and Its Relationship to Markers of Oxidative Stress.

    Science.gov (United States)

    Repka, Chris P; Hayward, Reid

    2018-06-01

    Although the underlying mechanisms of cancer-related fatigue (CRF) are not fully characterized, treatment-associated oxidative stress may play a role. The purpose of this study was to determine the effect of an exercise intervention on the relationship between CRF and oxidative stress. Upon cessation of radiation or chemotherapy, 8 cancer patients participated in a 10-week exercise intervention (EX), while 7 continued standard care (CON). Blood draws and fatigue questionnaires were administered to cancer patients before and after the intervention as well as to 7 age-matched individuals with no cancer history. Changes in plasma 8-hydroxy-deoxyguanosine (8-OHdG), protein carbonyls, antioxidant capacity, and fatigue were compared between groups. Correlations between CRF and oxidative stress were evaluated. Mean total fatigue scores decreased significantly (5.0 ± 2.2 to 2.6 ± 1.5, P fatigue ( r = -.58). Changes in total ( r = .46) and affective ( r = .47) fatigue exhibited significant correlations with changes in 8-OHdG over time, while behavioral ( r = .46) and sensory ( r = .47) fatigue changes were significantly correlated with protein carbonyls. Oxidative stress may be implicated in CRF, while improved antioxidant capacity following an exercise intervention may play a role in mitigating CRF in cancer survivors.

  17. Passive detection and localization of fatigue cracking in aluminum plates using Green's function reconstruction from ambient noise.

    Science.gov (United States)

    Yang, Yang; Xiao, Li; Qu, Wenzhong; Lu, Ye

    2017-11-01

    Recent theoretical and experimental studies have demonstrated that a local Green's function can be retrieved from the cross-correlation of ambient noise field. This technique can be used to detect fatigue cracking in metallic structures, owing to the fact that the presence of crack can lead to a change in Green's function. This paper presents a method of structural fatigue cracking characterization method by measuring Green's function reconstruction from noise excitation and verifies the feasibility of crack detection in poor noise source distribution. Fatigue cracks usually generate nonlinear effects, in which different wave amplitudes and frequency compositions can cause different nonlinear responses. This study also undertakes analysis of the capacity of the proposed approach to identify fatigue cracking under different noise amplitudes and frequency ranges. Experimental investigations of an aluminum plate are conducted to assess the cross-correlations of received noise between sensor pairs and finally to detect the introduced fatigue crack. A damage index is proposed according to the variation between cross-correlations obtained from the pristine crack closed state and the crack opening-closure state when sufficient noise amplitude is used to generate nonlinearity. A probability distribution map of damage is calculated based on damage indices. The fatigue crack introduced in the aluminum plate is successfully identified and oriented, verifying that a fatigue crack can be detected by reconstructing Green's functions from an imperfect diffuse field in which ambient noise sources exist locally. Copyright © 2017 Elsevier B.V. All rights reserved.

  18. Evaluation of Fatigue Behavior and Surface Characteristics of Aluminum Alloy 2024 T6 After Electric Discharge Machining

    Science.gov (United States)

    Mehmood, Shahid; Shah, Masood; Pasha, Riffat Asim; Sultan, Amir

    2017-10-01

    The effect of electric discharge machining (EDM) on surface quality and consequently on the fatigue performance of Al 2024 T6 is investigated. Five levels of discharge current are analyzed, while all other electrical and nonelectrical parameters are kept constant. At each discharge current level, dog-bone specimens are machined by generating a peripheral notch at the center. The fatigue tests are performed on four-point rotating bending machine at room temperature. For comparison purposes, fatigue tests are also performed on the conventionally machined specimens. Linearized SN curves for 95% failure probability and with four different confidence levels (75, 90, 95 and 99%) are plotted for each discharge current level as well as for conventionally machined specimens. These plots show that the electric discharge machined (EDMed) specimens give inferior fatigue behavior as compared to conventionally machined specimen. Moreover, discharge current inversely affects the fatigue life, and this influence is highly pronounced at lower stresses. The EDMed surfaces are characterized by surface properties that could be responsible for change in fatigue life such as surface morphology, surface roughness, white layer thickness, microhardness and residual stresses. It is found that all these surface properties are affected by changing discharge current level. However, change in fatigue life by discharge current could not be associated independently to any single surface property.

  19. Study on Standard Fatigue Vehicle Load Model

    Science.gov (United States)

    Huang, H. Y.; Zhang, J. P.; Li, Y. H.

    2018-02-01

    Based on the measured data of truck from three artery expressways in Guangdong Province, the statistical analysis of truck weight was conducted according to axle number. The standard fatigue vehicle model applied to industrial areas in the middle and late was obtained, which adopted equivalence damage principle, Miner linear accumulation law, water discharge method and damage ratio theory. Compared with the fatigue vehicle model Specified by the current bridge design code, the proposed model has better applicability. It is of certain reference value for the fatigue design of bridge in China.

  20. Corrosion Fatigue in District Heating Water Tanks

    DEFF Research Database (Denmark)

    Maahn, Ernst Emanuel

    1996-01-01

    Three candidate materials for construction of buffer tanks for district heating water have been tested for corrosion fatigue properties in a district heating water environment. The investigation included Slow Strain Rate Testing of plain tensile specimens, crack initiation testing by corrosion...... fatigue of plain tensile specimens and crack growth rate determination for Compact Tensile Specimens under corrosion fatigue conditions. The three materials are equal with respect to stress corrosion sensibility and crack initiation. Crack growth rate is increased with a factor of 4-6 relative to an inert...