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Sample records for mode ii fatigue

  1. Mode II fatigue crack propagation.

    NASA Technical Reports Server (NTRS)

    Roberts, R.; Kibler, J. J.

    1971-01-01

    Fatigue crack propagation rates were obtained for 2024-T3 bare aluminum plates subjected to in-plane, mode I, extensional loads and transverse, mode II, bending loads. These results were compared to the results of Iida and Kobayashi for in-plane mode I-mode II extensional loads. The engineering significance of mode I-mode II fatigue crack growth is considered in view of the present results. A fatigue crack growth equation for handling mode I-mode II fatigue crack growth rates from existing mode I data is also discussed.

  2. Comparison of Mode II and III Monotonic and Fatigue Delamination Onset Behavior for Carbon/Toughened Epoxy Composites

    NASA Technical Reports Server (NTRS)

    Li, Jian; OBrien, T. Kevin; Lee, Shaw Ming

    1997-01-01

    Monotonic and fatigue tests were performed to compare the Mode II and III interlaminar fracture toughness and fatigue delamination onset for Tenax-HTA/R6376 carbon/toughened epoxy composites. The Mode II interlaminar fracture toughness and fatigue delamination onset were characterized using the end-notched flexure (ENF) test while the Mode III interlaminar fracture toughness and fatigue delamination onset were characterized by using the edge crack torsion (ECT) test. Monotonic tests show that the Mode III fracture toughness is higher than the Mode II fracture toughness. Both Mode II and III cyclic loading greatly increases the tendency for a delamination to grow relative to a single monotonically increasing load. Under fatigue loading, the Mode III specimen also has a longer life than the Mode II specimen.

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

    NASA Technical Reports Server (NTRS)

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

    NASA Technical Reports Server (NTRS)

    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.

  5. Characterization of debond growth mechanism in adhesively bonded composites under mode II static and fatigue loadings

    NASA Technical Reports Server (NTRS)

    Mall, S.; Kochhar, N. K.

    1988-01-01

    An experimental investigation of adhesively bonded composite joint was conducted to characterize the debond growth mechanism under mode II static and fatigue loadings. For this purpose, end-notched flexure specimens of graphite/epoxy (T300/5208) adherends bonded with EC 3445 adhesive were tested. In all specimen tested, the fatigue failure occurred in the form of cyclic debonding. The present study confirmed the result of previous studies that total strain-energy-release rate is the driving parameter for cyclic debonding. Further, the debond growth resistance under cyclic loading with full shear reversal (i.e., stress ratio, R = -1) is drastically reduced in comparison to the case when subjected to cyclic shear loading with no shear reversal (i.e., R = 0.1).

  6. Development and Application of Benchmark Examples for Mode II Static Delamination Propagation and Fatigue Growth Predictions

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald

    2011-01-01

    The development of benchmark examples for static delamination propagation and cyclic delamination onset and growth prediction is presented and demonstrated for a commercial code. The example is based on a finite element model of an End-Notched Flexure (ENF) specimen. The example is independent of the analysis software used and allows the assessment of the automated delamination propagation, onset and growth prediction capabilities in commercial finite element codes based on the virtual crack closure technique (VCCT). First, static benchmark examples were created for the specimen. Second, based on the static results, benchmark examples for cyclic delamination growth were created. Third, the load-displacement relationship from a propagation analysis and the benchmark results were compared, and good agreement could be achieved by selecting the appropriate input parameters. Fourth, starting from an initially straight front, the delamination was allowed to grow under cyclic loading. The number of cycles to delamination onset and the number of cycles during delamination growth for each growth increment were obtained from the automated analysis and compared to the benchmark examples. Again, good agreement between the results obtained from the growth analysis and the benchmark results could be achieved by selecting the appropriate input parameters. The benchmarking procedure proved valuable by highlighting the issues associated with choosing the input parameters of the particular implementation. Selecting the appropriate input parameters, however, was not straightforward and often required an iterative procedure. Overall the results are encouraging, but further assessment for mixed-mode delamination is required.

  7. A la Mode II.

    ERIC Educational Resources Information Center

    Stowe, Richard A.

    This paper describes two modes of educational decision-making: Mode I, in which the instructor makes such decisions as what to teach, to whom, when, in what order, at what pace, and at what complexity level; and Mode II, in which the learner makes the decisions. While Mode I comprises most of what is regarded as formal education, the learner in…

  8. Mode and mechanism of fatigue fracture of a pearlitic steel in hydrogen

    NASA Technical Reports Server (NTRS)

    Lo, S. H.; Johnson, H. H.

    1986-01-01

    It is presently suggested that there are two mechanisms that cause fatigue crack initiation in a specimen subjected to a hydrogen environment: either a critical concentration of hydrogen is attained within the specimen, causing Mode I crack initiation, or the presence of some hydrogen (below critical concentration) promotes the early onset of plastic instability at the sites of maximum strain. It is further suggested that in the static loading condition, a high hydrogen concentration may be attained by way of mechanical factors, causing Mode I crack initiation. While cyclic fatigue specimens exhibited Mode II crack initiation in air, only Mode I crack initiation emerged in a hydrogen environment.

  9. Experimental compliance calibration of the NASA Lewis Research Center Mode 2 fatigue specimen

    NASA Technical Reports Server (NTRS)

    Buzzard, R. J.

    1985-01-01

    Calibration of the mode II aluminum fatigue specimen was performed experimentally to provide displacement and stress intensity coefficients over crack length to specimen width ratios (a/W) of 0.5 to 0.9. Displacements were measured both at the specimen notch mouth and at the intersection of the notch with the centerline of the loading pin holes.

  10. Combined mode I and mode II fracture of monolithic ceramics

    NASA Technical Reports Server (NTRS)

    Tikare, Veena; Choi, Sung R.

    1993-01-01

    The mode I, mode II, and combined mode I-mode II fracture behaviors of a coarse-grained silicon nitride, a fine-grained silicon nitride, and an alumina were investigated. These ceramics were fractured from two types of fracture initiating flaws: small surface flaws and large single edge precracks. The small surface flaws were introduced by Knoop indentation in flexural samples at various angles to the tensile stress direction and fractured in four-point bending. The samples with large precracks were fractured in the asymmetric four-point-bend geometry. The mixed-mode fracture toughness values obtained from the two flaw configurations were in good agreement with each other. All three ceramics displayed very similar mixed-mode fracture behavior, although their microstructures were not similar. Comparison of experimental data to mixed-mode fracture theories revealed that the minimum strain energy density theory best described the mixed-mode fracture behavior of all three ceramics.

  11. Crack path determination for non-proportional mixed-mode fatigue

    NASA Astrophysics Data System (ADS)

    Highsmith, Shelby, Jr.

    Turbine engine components such as fan and compressor blades experience complex combinations of steady and vibratory loads that lead to in-service cracking in directions that cannot be predicted by current fracture criteria. Accurate crack path predictions are required in order to characterize the risk and extent of damage resulting from liberation of a fractured ligament from rotating components. Under proportional in-phase mixed Mode I/Mode II loading conditions, crack growth direction has been observed in some materials to shift from tensile-dominated Mode I to shear-dominated Mode II or mixed-mode crack growth at higher proportions of initial Mode II loading, but non-proportional loads are not well-characterized. An extensive database of crack growth direction under non-proportional 2-D mixed-mode loading conditions is required to expand crack path prediction models, which are likely to vary between alloys. An approach based on linear elastic fracture mechanics (LEFM) is desired in order to implement the model in crack growth software such as the boundary element-based fracture analysis package FRANC3D. A novel specimen configuration has been designed and analyzed for generation of wide ranges of mixed-mode loading conditions in a single test. This specimen and a more conventional thin-walled tubular specimen have been used to test polycrystalline nickel-base superalloy Inconel 718 under proportional in-phase and 3 kinds of non-proportional fatigue loading. Stress intensity factors for the various configurations have been analyzed with FRANC3D. Modal transition from Mode I (tensile) to Mode II (shear) crack branching has been observed in several load cases. Qualitative microscopy of fracture surfaces was used to characterize the crack growth behavior. An LEFM approach based on an effective stress intensity factor range, which incorporates the maximum value and range of each appropriate stress intensity (Mode I or Mode II), has been used to successfully predict

  12. Effects of friction and high torque on fatigue crack propagation in Mode III

    NASA Astrophysics Data System (ADS)

    Nayeb-Hashemi, H.; McClintock, F. A.; Ritchie, R. O.

    1982-12-01

    Turbo-generator and automotive shafts are often subjected to complex histories of high torques. To provide a basis for fatigue life estimation in such components, a study of fatigue crack propagation in Mode III (anti-plane shear) for a mill-annealed AISI 4140 steel (RB88, 590 MN/m2 tensile strength) has been undertaken, using torsionally-loaded, circumferentially-notched cylindrical specimens. As demonstrated previously for higher strength AISI 4340 steel, Mode III cyclic crack growth rates (dc/dN) IIIcan be related to the alternating stress intensity factor ΔKIII for conditions of small-scale yielding. However, to describe crack propagation behavior over an extended range of crack growth rates (˜10-6 to 10-2 mm per cycle), where crack growth proceeds under elastic-plastic and full plastic conditions, no correlation between (dc/dN) III and ΔKIII is possible. Accordingly, a new parameter for torsional crack growth, termed the plastic strain intensity Γ III, is introduced and is shown to provide a unique description of Mode III crack growth behavior for a wide range of testing conditions, provided a mean load reduces friction, abrasion, and interlocking between mating fracture surfaces. The latter effect is found to be dependent upon the mode of applied loading (i.e., the presence of superimposed axial loads) and the crack length and torque level. Mechanistically, high-torque surfaces were transverse, macroscopically flat, and smeared. Lower torques showed additional axial cracks (longitudinal shear cracking) perpendicular to the main transverse surface. A micro-mechanical model for the main radi l Mode III growth, based on the premise that crack advance results from Mode II coalescence of microcracks initiated at inclusions ahead of the main crack front, is extended to high nominal stress levels, and predicts that Mode III fatigue crack propagation rates should be proportional to the range of plastic strain intensity (ΔΓIII if local Mode II growth rates are

  13. A combined mode fatigue model for glass reinforced nylon as applied to molded engine cooling fans

    SciTech Connect

    Smith, J.D.; Bennet, M.L.

    1985-01-01

    The use of glass reinforced nylon in fatigue inducing environments calls for a new method of stress analysis. With an engine cooling fan, both mean and vibratory stresses need to be examined. Speed cycling can cause tensile fatigue, while vibration can cause flexural fatigue. Since tensile and flexural stresses exist in the fan simultaneously, a combined mode fatigue model is needed. The proposed model is based on high cycle flexural and tensile fatigue strengths, and tensile strength. It relates measurable strain to stress using temperature dependent flexural and tensile moduli, and treats underhood temperature and desired product life as variables.

  14. Characterization of Mode I fatigue crack growth in GFRP woven laminates at low temperatures

    SciTech Connect

    Shindo, Yasuhide . E-mail: shindo@material.tohoku.ac.jp; Inamoto, Akihiro; Narita, Fumio

    2005-03-01

    This paper describes an experimental and analytical study on the cryogenic fatigue behavior of glass fiber reinforced polymer woven laminates under Mode I loading. Fatigue crack growth rate tests were performed using compact tension specimens at room temperature, liquid nitrogen temperature (77 K), and liquid helium temperature (4 K). The fracture surfaces were also examined by scanning electron microscopy to correlate with the fatigue properties. A finite element method coupled with fatigue damage was adopted for the extensional analysis. The effects of temperature and loading condition on the fatigue crack growth rates are examined.

  15. Tensile and compressive failure modes of laminated composites loaded by fatigue with different mean stress

    NASA Technical Reports Server (NTRS)

    Rotem, Assa

    1990-01-01

    Laminated composite materials tend to fail differently under tensile or compressive load. Under tension, the material accumulates cracks and fiber fractures, while under compression, the material delaminates and buckles. Tensile-compressive fatigue may cause either of these failure modes depending on the specific damage occurring in the laminate. This damage depends on the stress ratio of the fatigue loading. Analysis of the fatigue behavior of the composite laminate under tension-tension, compression-compression, and tension-compression had led to the development of a fatigue envelope presentation of the failure behavior. This envelope indicates the specific failure mode for any stress ratio and number of loading cycles. The construction of the fatigue envelope is based on the applied stress-cycles to failure (S-N) curves of both tensile-tensile and compressive-compressive fatigue. Test results are presented to verify the theoretical analysis.

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

    NASA Astrophysics Data System (ADS)

    Miles, R. N.

    1992-03-01

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

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

    NASA Technical Reports Server (NTRS)

    Miles, R. N.

    1992-01-01

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

  18. The Harvard Fatigue Laboratory: contributions to World War II.

    PubMed

    Folk, G Edgar

    2010-09-01

    The war contributions of the Harvard Fatigue Laboratory in Cambridge, MA, were recorded in 169 Technical Reports, most of which were sent to the Office of the Quartermaster General. Earlier reports were sent to the National Research Council and the Office of Scientific Research and Development. Many of the reports from 1941 and later dealt with either physical fitness of soldiers or the energetic cost of military tasks in extreme heat and cold. New military emergency rations to be manufactured in large quantities were analyzed in the Fatigue Laboratory and then tested in the field. Newly designed cold weather clothing was tested in the cold chamber at -40 degrees F, and desired improvements were made and tested in the field by staff and soldiers in tents and sleeping bags. Electrically heated clothing was designed for high-altitude flight crews and tested both in laboratory chambers and field tests before being issued. This eye witness account of the Harvard Fatigue Laboratory during World War II was recorded by Dr. G. Edgar Folk, who is likely the sole surviving member of that famous laboratory.

  19. Fatigue

    MedlinePlus

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

  20. FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (UNIX VERSION)

    NASA Technical Reports Server (NTRS)

    Newman, J. C.

    1994-01-01

    Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied

  1. FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (IBM PC VERSION)

    NASA Technical Reports Server (NTRS)

    Newman, J. C.

    1994-01-01

    Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied

  2. Multi-Mode Excitation and Data Reduction for Fatigue Crack Characterization in Conducting Plates

    NASA Technical Reports Server (NTRS)

    Wincheski, B.; Namkung, M.; Fulton, J. P.; Clendenin, C. G.

    1992-01-01

    Advances in the technique of fatigue crack characterization by resonant modal analysis have been achieved through a new excitation mechanism and data reduction of multiple resonance modes. A non-contacting electromagnetic device is used to apply a time varying Lorentz force to thin conducting sheets. The frequency and direction of the Lorentz force are such that resonance modes are generated in the test sample. By comparing the change in frequency between distinct resonant modes of a sample, detecting and sizing of fatigue cracks are achieved and frequency shifts caused by boundary condition changes can be discriminated against. Finite element modeling has been performed to verify experimental results.

  3. Effects of friction and high torque on fatigue crack propagation in mode III. [AISI 4140 and 4340

    SciTech Connect

    Nayeb-Hashemi, H.; McClintock, F.A.; Ritchie, R.O.

    1982-12-01

    Turbo-generator and automotive shafts are often subjected to complex histories of high torques. To provide a basis for fatigue life estimation in such components, a study of fatigue crack propagation in Mode III (anti-plane shear) for a mill-annealed AISI 4140 steel (R /SUB B/ 88, 590 MN/m/sup 2/ tensile strength) has been undertaken, using torsionally-loaded, circumferentially-notched cylindrical specimens. As demonstrated previously for higher strength AISI 4340 steel, Mode III cyclic crack growth rates (dc/dN) /SUB III/ can be related to the alternating stress intensity factor ..delta..K /SUB III/ for conditions of small-scale yielding. However, to describe crack propagation behavior over an extended range of crack growth rates (about 10/sup -6/ to 10/sup -2/ mm per cycle), where crack growth proceeds under elastic-plastic and full plastic conditions, no correlation between (dc/dN) /SUB III/ and ..delta..K /SUB III/ is possible. Accordingly, a new parameter for torsional crack growth, termed the plastic strain intensity GAMMA /SUB III/, is introduced and is shown to provide a unique description of Mode III crack growth behavior for a wide range of testing conditions, provided a mean load reduces friction, abrasion, and interlocking between mating fracture surfaces A micro-mechanical model for the main radial Mode III growth is extended to high nominal stress levels, and predicts that Mode III fatigue crack propagation rates should be proportional to the range of plastic strain intensity (..delta..GAMMA /SUB III/) if local Mode II growth rates are proportional to the displacements. Such predictions are shown to be in agreement with measured growth rates in AISI 4140 steel from 10/sup -6/ to 10/sup -2/ mm per cycle.

  4. Fatigue

    MedlinePlus

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

  5. Effect of Buckling Modes on the Fatigue Life and Damage Tolerance of Stiffened Structures

    NASA Technical Reports Server (NTRS)

    Davila, Carlos G.; Bisagni, Chiara; Rose, Cheryl A.

    2015-01-01

    The postbuckling response and the collapse of composite specimens with a co-cured hat stringer are investigated experimentally and numerically. These specimens are designed to evaluate the postbuckling response and the effect of an embedded defect on the collapse load and the mode of failure. Tests performed using controlled conditions and detailed instrumentation demonstrate that the damage tolerance, fatigue life, and collapse loads are closely tied with the mode of the postbuckling deformation, which can be different between two nominally identical specimens. Modes that tend to open skin/stringer defects are the most damaging to the structure. However, skin/stringer bond defects can also propagate under shearing modes. In the proposed paper, the effects of initial shape imperfections on the postbuckling modes and the interaction between different postbuckling deformations and the propagation of skin/stringer bond defects under quasi-static or fatigue loads will be examined.

  6. Elastic-Plastic Finite Element Analysis of Fatigue Crack Growth in Mode 1 and Mode 2 Conditions

    NASA Technical Reports Server (NTRS)

    Nakagaki, M.; Atluri, S. N.

    1978-01-01

    Presented is an alternate cost-efficient and accurate elastic-plastic finite element procedure to analyze fatigue crack closure and its effects under general spectrum loading. Both Modes 1 and 2 type cycling loadings are considered. Also presented are the results of an investigation, using the newly developed procedure, of various factors that cause crack growth acceleration or retardation and delay effects under high-to-low, low-to-high, single overload, and constant amplitude type cyclic loading in a Mode 1 situation. Further, the results of an investigation of a centercracked panel under external pure shear (Mode 2) cyclic loading, of constant amplitude, are reported.

  7. Visualization of non-propagating Lamb wave modes for fatigue crack evaluation

    NASA Astrophysics Data System (ADS)

    An, Yun-Kyu; Sohn, Hoon

    2015-03-01

    This article develops a non-propagating Lamb wave mode (NPL) imaging technique for fatigue crack visualization. NPL has a great potential for crack evaluation in that it significantly contributes local mode amplitudes in the vicinity of a crack without spatial propagation. Such unique physical phenomenon is theoretically proven and experimentally measured through laser scanning. Although its measurement is a quite challenging work due to the fact that it is quite localized and coexists with complex propagating Lamb wave modes, a NPL filter proposed in this article overcomes the technical challenge by eliminating all propagating Lamb modes from laser scanned full Lamb wavefields. Through the NPL filtering process, only fatigue crack-induced NPLs can be measured and retained. To verify such physical observation and the corresponding NPL filter, a real micro fatigue crack is created by applying repeated tensile loading, and its detectability is tested using a surface-mounted piezoelectric transducer for generating Lamb waves and a laser Doppler vibrometer for measuring the corresponding responses. The experimental results confirm that even an invisible fatigue crack can be instantaneously visualized and effectively evaluated through the proposed NPL measurement and filtering processes.

  8. Fracture toughness of polycrystalline ceramics in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, Dileep; Shetty, Dinesh K.

    1989-01-01

    The present investigation of the fracture of alumina and zirconia polycrystalline ceramic specimens of precracked-disk type, in diametral compression, evaluated fracture toughness in pure mode I, combined mode I/mode II, and pure mode II, depending on the alignment of the center crack relative to the loading diameter. The mixed-mode fracture-toughness envelope thus obtained exhibits significant deviation to higher fracture toughness in mode II, relative to the predictions of linear elastic fracture mechanics theory. Crack-surface resistance due to grain-interlocking and abrasion are identified as the primary sources of increased fracture resistance in mode II loading of the polycrystalline ceramics.

  9. Thermomechanical fatigue, oxidation, and Creep: Part II. Life prediction

    NASA Astrophysics Data System (ADS)

    Neu, R. W.; Sehitoglu, Huseyin

    1989-09-01

    A life prediction model is developed for crack nucleation and early crack growth based on fatigue, environment (oxidation), and creep damage. The model handles different strain-temperature phasings (i.e., in-phase and out-of-phase thermomechanical fatigue, isothermal fatigue, and others, including nonproportional phasings). Fatigue life predictions compare favorably with experiments in 1070 steel for a wide range of test conditions and strain-temperature phasings. An oxide growth (oxide damage) model is based on the repeated microrupture process of oxide observed from microscopic measurements. A creep damage expression, which is stress-based, is coupled with a unified constitutive equation. A set of interrupted tests was performed to provide valuable damage progression information. Tests were performed in air and in helium atmospheres to isolate creep damage from oxidation damage.

  10. Relationship between fatigue of generation II image intensifier and input illumination

    NASA Astrophysics Data System (ADS)

    Chen, Qingyou

    1995-09-01

    If there is fatigue for an image intesifier, then it has an effect on the imaging property of the night vision system. In this paper, using the principle of Joule Heat, we derive a mathematical formula for the generated heat of semiconductor photocathode. We describe the relationship among the various parameters in the formula. We also discuss reasons for the fatigue of Generation II image intensifier caused by bigger input illumination.

  11. Assessment of Crack Path Prediction in Non-Proportional Mixed-Mode Fatigue

    NASA Technical Reports Server (NTRS)

    Highsmith, Shelby, Jr.; Johnson, Steve; Swanson, Gregory; Sayyah, Tarek; Pettit, Richard

    2008-01-01

    Non-proportional mixed-mode loading is present in many systems and a growing crack can experience any manner of mixed-mode loading. Prediction of the resulting crack path is important when assessing potential failure modes or when performing a failure investigation. Current crack path selection criteria are presented along with data for Inconel 718 under non-proportional mixed-mode loading. Mixed-mode crack growth can transition between path deflection mechanisms with very different orientations. Non-proportional fatigue loadings lack a single parameter for input to current crack path criteria. Crack growth transitions were observed in proportional and non-proportional FCG tests. Different paths displayed distinct fracture surface morphologies. New crack path drivers & transition criteria must be developed.

  12. Fatigue Behavior of Adhesively Bonded Joints. Volume II. Appendices.

    DTIC Science & Technology

    1980-04-01

    StressoAnayiFnt lmns tic, andc argh th eeemntinar violastrick3 - modelO foAGoES ne 1D 4. MONTOIN A EDITC O *AWL’ NO ADPO~IfSiftfl OBSOLETE lla Offce 1...and Ultra- sonic Holography", Vol. I, Nondestructive Inspection and Control, Eighth Edition, 1976, pp . 198-233. "Fatigue Behavior of Adhesively Bonded

  13. The Harvard Fatigue Laboratory: Contributions to World War II

    ERIC Educational Resources Information Center

    Folk, G. Edgar

    2010-01-01

    The war contributions of the Harvard Fatigue Laboratory in Cambridge, MA, were recorded in 169 Technical Reports, most of which were sent to the Office of the Quartermaster General. Earlier reports were sent to the National Research Council and the Office of Scientific Research and Development. Many of the reports from 1941 and later dealt with…

  14. Subcritical crack growth in soda-lime glass in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, Dileep; Shetty, Dinesh K.

    1990-01-01

    Subcritical crack growth under mixed-mode loading was studied in soda-lime glass. Pure mode I, combined mode I and mode II, and pure mode II loadings were achieved in precracked disk specimens by loading in diametral compression at selected angles with respect to the symmetric radial crack. Crack growth was monitored by measuring the resistance changes in a microcircuit grid consisting of parallel, electrically conducting grid lines deposited on the surface of the disk specimens by photolithography. Subcritical crack growth rates in pure mode I, pure mode II, and combined mode I and mode II loading could be described by an exponential relationship between crack growth rate and an effective crack driving force derived from a mode I-mode II fracture toughness envelope. The effective crack driving force was based on an empirical representation of the noncoplanar strain energy release rate. Stress intensities for kinked cracks were assessed using the method of caustics and an initial decrease and a subsequent increase in the subcritical crack growth rates of kinked cracks were shown to correlate with the variations of the mode I and the mode II stress intensities.

  15. Exercise muscle fatigue detection system implementation via wireless surface electromyography and empirical mode decomposition.

    PubMed

    Chang, Kang-Ming; Liu, Shing-Hong; Wang, Jia-Jung; Cheng, Da-Chuan

    2013-01-01

    Surface electromyography (sEMG) is an important measurement for monitoring exercise and fitness. A wireless Bluetooth transmission sEMG measurement system with a sampling frequency of 2 KHz is developed. Traditional muscle fatigue is detected from the median frequency of the sEMG power spectrum. The regression slope of the linear regression of median frequency is an important muscle fatigue index. As fatigue increases, the power spectrum of the sEMG shifts toward lower frequencies. The goal of this study is to evaluate the sensitivity of empirical mode decomposition (EMD) quantifying the electrical manifestations of the local muscle fatigue during exercising in health people. We also compared this method with the raw data and discrete wavelet transform (DWT). Five male and five female volunteers participated. Each subject was asked to run on a multifunctional pedaled elliptical trainer for about 30 minutes, twice a week, and there were a total of six recording times for each subject with a wireless EMG recording system. The results show that sensitivity of the highest frequency component of EMD is better than the highest frequency component of DWT, and raw data.

  16. Microstructural effects on fracture toughness of polycrystalline ceramics in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, D.; Shetty, D. K.

    1988-01-01

    Fracture toughness of polycrystalline alumina and ceria partially-stabilized tetragonal zirconia (CeO2-TZP) ceramics were assessed in combined mode I and mode II loading using precracked disk specimens in diametral compression. Stress states ranging from pure mode I, combined mode I and mode II, and pure mode II were obtained by aligning the center crack at specific angles relative to the loading diameter. The resulting mixed-mode fracture toughness envelope showed significant deviation to higher fracture toughness in mode II relative to the predictions of the linear elastic fracture mechanics theory. Critical comparison with corresponding results on soda-lime glass and fracture surface observations showed that crack surface resistance arising from grain interlocking and abrasion was the main source of the increased fracture toughness in mode II loading of the polycrystalline ceramics. The normalized fracture toughness for pure mode II loading, (KII/KIc), increased with increasing grain size for the CeO2-TZP ceramics. Quantitative fractography confirmed an increased percentage of transgranular fracture of the grains in mode II loading.

  17. Fatigue Failure Modes of the Grain Size Transition Zone in a Dual Microstructure Disk

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Kantzos, Pete T.; Palsa, Bonnie; Telesman, Jack; Gayda, John; Sudbrack, Chantal K.

    2012-01-01

    Mechanical property requirements vary with location in nickel-based superalloy disks. In order to maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored grain microstructures. In this study, fatigue failure modes of a grain size transition zone in a dual microstructure disk were evaluated. A specialized heat treatment method was applied to produce varying grain microstructure in the bore to rim portions of a powder metallurgy processed nickel-based superalloy disk. The transition in grain size was concentrated in a zone of the disk web, between the bore and rim. Specimens were extracted parallel and transversely across this transition zone, and multiple fatigue tests were performed at 427 C and 704 C. Grain size distributions were characterized in the specimens, and related to operative failure initiation modes. Mean fatigue life decreased with increasing maximum grain size, going out through the transition zone. The scatter in limited tests of replicates was comparable for failures of uniform gage specimens in all transition zone locations examined.

  18. Extending non-fatigue Mode I subcritical crack growth data to subcritical fatigue crack growth: Demonstration of the equivalence of the Charles' law and Paris law exponents

    NASA Astrophysics Data System (ADS)

    Keanini, Russell; Eppes, Martha-Cary

    2016-04-01

    Paris's law connects fatigue-induced subcritical crack growth and fatigue loading. Environmentally-driven subcritical crack growth, while a random process, can be decomposed into a spectrum of cyclic processes, where each spectral component is governed by Paris's law. Unfortunately, almost no data exists concerning the Paris law exponent, m; rather, the great majority of existing sub-critical crack growth measurements on rock have been carried out via Mode I tensile tests, where corresponding data are generally correlated using Charles' law, and where the latter, similar to Paris's law, exposes a power law relationship between crack growth rate and stress intensity. In this study, a statistical argument is used to derive a simple, rigorous relationship between the all-important Paris law and Charles law exponents, m and n. This result has a significant practical implication: subcritical fatigue crack growth in rock, driven by various random environmental weathering processes can now be predicted using available Mode I stress corrosion indices, n.

  19. Fatigue cracks in Eurofer 97 steel: Part II. Comparison of small and long fatigue crack growth

    NASA Astrophysics Data System (ADS)

    Kruml, T.; Hutař, P.; Náhlík, L.; Seitl, S.; Polák, J.

    2011-05-01

    The fatigue crack growth rate in the Eurofer 97 steel at room temperature was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch and no artificial crack starters. The growth of semicircular cracks of length between 10-2000 μm was followed in symmetrical cycling with constant strain amplitude ( R ɛ = -1). Long crack data were measured using standard CT specimen and ASTM methodology, i.e. R = 0.1. The growth of cracks having the length in the range of 10-30 mm was measured. It is shown that the crack growth rates of both types of cracks are in a very good agreement if J-integral representation is used and usual assumptions of the crack closure effects are taken into account.

  20. Mixed-mode static and fatigue crack growth in central notched and compact tension shear specimens

    SciTech Connect

    Shlyannikov, V.N.

    1999-07-01

    Elastic-plastic crack growth under mixed Mode I and 2 in six types of aluminum alloys and three types of steel were investigated. The experimental study of fatigue crack growth in six types of the aluminum alloys and one type of the steel is performed on biaxially loaded eight-petal specimens (EPS). All specimens for biaxial loading contained inclined through thickness central cracks. Mixed Mode I/2 static and fatigue crack growth experiments on the three types of steels and one type of the aluminum alloy used compact tension shear (CTS) specimens. Two approaches are developed for geometrical modeling of crack growth trajectories for the central notched and compact tension shear specimens respectively. The principal feature of such modeling is the determination of crack growth direction and the definition of crack length increment in this direction. On the basis of the analysis of the experimental data for the aluminum alloys and the steels an empirical crack reorientation criterion is suggested for both brittle and ductile materials. The damage process zone size concept is used for calculations and mixed-mode crack path. The influence of specimen geometry, biaxial loading and properties of the aluminum alloys and the steels on both crack growth direction and crack path at the macroscopic scale is discussed.

  1. Slow crack growth in glass in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Shetty, D. K.; Rosenfield, A. R.

    1991-01-01

    Slow crack growth in soda-lime glass under combined mode I and mode II loading was investigated in precracked disk specimens in which pure mode I, pure mode II, and various combinations of mode I and mode II were achieved by loading in diametral compression at selected angles with respect to symmetric radial cracks. It is shown that slow crack growth under these conditions can be described by a simple exponential relationship with elastic strain energy release rate as the effective crack-driving force parameter. It is possible to interpret this equation in terms of theoretical models that treat subcritical crack growth as a thermally activated bond-rupture process with an activation energy dependent on the environment, and the elastic energy release rate as the crack-driving force parameter.

  2. Standard solar model. II - g-modes

    NASA Technical Reports Server (NTRS)

    Guenther, D. B.; Demarque, P.; Pinsonneault, M. H.; Kim, Y.-C.

    1992-01-01

    The paper presents the g-mode oscillation for a set of modern solar models. Each solar model is based on a single modification or improvement to the physics of a reference solar model. Improvements were made to the nuclear reaction rates, the equation of state, the opacities, and the treatment of the atmosphere. The error in the predicted g-mode periods associated with the uncertainties in the model physics is predicted and the specific sensitivities of the g-mode periods and their period spacings to the different model structures are described. In addition, these models are compared to a sample of published observations. A remarkably good agreement is found between the 'best' solar model and the observations of Hill and Gu (1990).

  3. Damage type and strain mode associations in human compact bone bending fatigue.

    PubMed

    Boyce, T M; Fyhrie, D P; Glotkowski, M C; Radin, E L; Schaffler, M B

    1998-05-01

    When compact bone is subjected to fatigue loading, it develops matrix microdamage, which reduces the tissue's ability to resist fracture. The relative influence of different strain modes on damage and strength in compact bone has not been characterized, to our knowledge. In this study, the nonuniform strain field produced by four-point bending was used to introduce fatigue damage into tibial bending beam specimens from men 40-49 years old. The specimens were then bulk-stained with basic fuchsin to mark damage surfaces and were examined histologically and with confocal microscopy to describe damage morphologies and position relative to tension and compression-strained regions of the specimen. Histomorphometric methods were used to quantify the amounts of different types of bone microdamage. Three major types were observed. In regions subjected to tensile strains, the bone had focal regions of diffusely increased basic fuchsin staining (i.e., diffuse microdamage). Confocal microscopy of these regions showed them to be composed of extensive networks of fine, ultrastructural-level cracks. In compressive strain regions, the tissue developed linear microcracks in interstitial areas similar to those originally described by Frost. Fine, tearing-type (wispy-appearing) cracks were observed near and in the plane of the neutral axis. The paths of these fine cracks were not influenced by microstructural boundaries. Other minor damage morphologies (sector-stained osteons, delamination of regions of lamellae, and intraosteonal cracking) were observed, but their distribution was unrelated to local strain field. Thus. in fatigue of human compact bone, the principal mechanisms of matrix failure (i.e., linear microcrack, diffuse damage foci, and tearing-type damage) are strongly dependent on local strain type.

  4. Rogue Mode Shileding in NSLS-II Multipole Vacuum Chambers

    SciTech Connect

    Ferreira, M.; Blednykh, A.; Bacha, B.; Borrelli, A.; Hseuh, H.-C.; Kosciuk, B.; Krinsky, S.; Singh, O.; Vetter, K.

    2011-03-28

    Modes with transverse electric field (TE-modes) in the NSLS-II multipole vacuum chamber can be generated at frequencies above 450MHz due to its geometric dimensions. Since the NSLS-II BPM system monitors signals within 10 MHz band at RF frequency of 500 MHz, frequencies of higher-order modes (HOM) can be generated within the transmission band of the band pass filter. In order to avoid systematic errors in the NSLS-II BPM system, we introduced frequency shift of HOMs by using RF metal shielding located in the antechamber slot. We demonstrated numerical modeling and experimental studies of the spurious TE modes in the NSLS-II vacuum chambers with antechamber slot. Calculated frequencies of TE-modes in considered chambers with and without RF shielding were verified experimentally. Flexible BeCu RF shielding inside each chamber at proper location shifts frequencies of H{sub 10p}-modes above {approx}900MHz, except chambers S6 odd and even. These chambers need special attention because of synchrotron radiation from downstream magnets. S6 odd multipole vacuum chamber needs to be measured and the RF shielding length has to be optimized. RF shielding looks adequate for baseline design. Fifty percent of open space provides adequate pumping speed.

  5. Alternate Operating Modes For NDCX-II

    NASA Astrophysics Data System (ADS)

    Sharp, W. M.; Friedman, A.; Grote, D. P.; Cohen, R. H.; Lund, S. M.; Vay, J.-L.; Waldron, W. L.

    2012-10-01

    NDCX-II is a newly completed accelerator facility at LBNL, built to study ion-heated warm dense matter and aspects of ion-driven targets for inertial-fusion energy. The baseline design calls for using twelve induction cells to accelerate 40 nC of Li+ ions to 1.2 MeV. During commissioning, though, we plan to extend the source lifetime by extracting less total charge. For operational flexibility, the option of using a helium plasma source is also being investigated. Over time, we expect that NDCX-II will be upgraded to substantially higher energies, necessitating the use of heavier ions to keep a suitable deposition range in targets. Each of these options requires development of an alternate acceleration schedule and the associated transverse focusing. The schedules here are first worked out with a fast-running 1-D particle-in-cell code ASP, then 2-D and 3-D Warp simulations are used to verify the 1-D results and to design transverse focusing.

  6. Ren Shen Yangrong Tang for Fatigue in Cancer Survivors: A Phase I/II Open-Label Study

    PubMed Central

    Xu, Yichen; Chen, Yanzhi

    2015-01-01

    Abstract Objectives: This open-label, prospective, phase I/II trial was performed to establish the safety and efficacy of Traditional Chinese Medicine (TCM) herbal products for treating non–anemia-related fatigue in patients with cancer. Although this practice is widespread in China, it has not been confirmed in a prospective clinical study. Design: Thirty-three patients who had completed cancer treatment, had stable disease and no anemia, and reported moderate to severe fatigue (rated ≥4 on a 0–10 scale) were enrolled in a TCM outpatient clinic. Patients took Ren Shen Yangrong Tang (RSYRT) decoction, a soup containing 12 TCM herbs, twice a day for 6 weeks. RSYRT aims to correct qi deficiency. Fatigue was assessed before and after RSYRT therapy, which all patients completed. Results: No discomfort or toxicity was observed. Before the study, all patients had had fatigue for at least 4 months. Fatigue severity decreased significantly from before therapy to 6 weeks after therapy: from 7.06 to 3.30 on a 0–10 scale (p<0.001). Fatigue category (mild, moderate, severe) shifted significantly (p=0.024): Of 22 patients with severe fatigue (rated ≥7) before therapy, 11 had mild fatigue and 11 had moderate fatigue after TCM treatment. The time-to-fatigue-alleviation was 2–3 weeks. Conclusion: RSYRT therapy was safe and was associated with fatigue improvement in nonanemic cancer survivors, consistent with historical TCM clinical practice experience. Because of a possible placebo effect in this open-label study, decoction RSYRT warrants further study in randomized clinical trials to confirm its effectiveness for managing moderate to severe fatigue. PMID:25918996

  7. Phase II double-blind placebo-controlled randomized study of armodafinil for brain radiation-induced fatigue

    PubMed Central

    Page, Brandi R.; Shaw, Edward G.; Lu, Lingyi; Bryant, David; Grisell, David; Lesser, Glenn J.; Monitto, Drew C.; Naughton, Michelle J.; Rapp, Stephen R.; Savona, Steven R.; Shah, Sunjay; Case, Doug; Chan, Michael D.

    2015-01-01

    Background Common acute-term side effects of brain radiotherapy (RT) include fatigue, drowsiness, decreased physical functioning, and decreased quality of life (QOL). We hypothesized that armodafinil (a wakefulness-promoting drug known to reduce fatigue and increase cognitive function in breast cancer patients receiving chemotherapy) would result in reduced fatigue and sleepiness for patients receiving brain RT. Methods A phase II, multi-institutional, placebo-controlled randomized trial assessed feasibility of armodafinil 150 mg/day in participants receiving brain RT, from whom we obtained estimates of variability for fatigue, sleepiness, QOL, cognitive function, and treatment effect. Results From September 20, 2010, to October 20, 2012, 54 participants enrolled with 80% retention and 94% self-reported compliance. There were no grade 4–5 toxicities, and the incidence of grade 2–3 toxicities was similar between treatment arms, the most common of which were anxiety and nausea (15%), headaches (19%), and insomnia (20%). There were no statistically significant differences in end-RT or 4 week post-RT outcomes between armodafinil and placebo in any outcomes (Functional Assessment of Chronic Illness Therapy [FACIT]-Fatigue, Brief Fatigue Inventory, Epworth Sleepiness Scale, FACT-Brain, and FACIT-cognitive function). However, in participants with more baseline fatigue, those treated with armodafinil did better than those who received the placebo on the end-RT assessments for several outcomes. Conclusion Armodafinil 150 mg/day was well tolerated in primary brain tumor patients undergoing RT with good compliance. While there was no overall significant effect on fatigue, those with greater baseline fatigue experienced improved QOL and reduced fatigue when using armodafinil. These data suggest that a prospective, phase III randomized trial is warranted for patients with greater baseline fatigue. PMID:25972454

  8. Surface integrity evolution and fatigue evaluation after milling mode, shot-peening and polishing mode for TB6 titanium alloy

    NASA Astrophysics Data System (ADS)

    Yao, Changfeng; Wu, Daoxia; Ma, Lufei; Tan, Liang; Zhou, Zheng; Zhang, Jiyin

    2016-11-01

    Surface integrity is closely related to the service life of parts and components. Effects of four kinds of integration processes on surface integrity and fatigue life are studied. These four integration processes are M (milling), MP (milling and polishing), MPS (milling, polishing and shot-peening), and MPSP (milling, polishing, shot-peening and polishing). When roughness, micro-hardness, residual stress, micro-structure and fatigue were considered after the four integration processes, research results show that MPSP process can obtain the best surface topography and roughness, micro-hardness, and residual stress field distribution; MPSP process has the longest fatigue life, and the fatigue life of MPSP process is about 68 times of M process, 56 times of MP process, and 48 times of MPS process; The fatigue fracture of the specimen after MPSP process is flat, and the depth of the crack initiation site for MPSP specimen is approximately 150 μm below the surface.

  9. Comparison of Two Different Modes of Active Recovery on Muscles Performance after Fatiguing Exercise in Mountain Canoeist and Football Players

    PubMed Central

    Mika, Anna; Oleksy, Łukasz; Kielnar, Renata; Wodka-Natkaniec, Ewa; Twardowska, Magdalena; Kamiński, Kamil; Małek, Zbigniew

    2016-01-01

    Background The aim of this study is to assess if the application of different methods of active recovery (working the same or different muscle groups from those which were active during fatiguing exercise) results in significant differences in muscle performance and if the efficiency of the active recovery method is dependent upon the specific sport activity (training loads). Design A parallel group non-blinded trial with repeated measurements. Methods Thirteen mountain canoeists and twelve football players participated in this study. Measurements of the bioelectrical activity, torque, work and power of the vastus lateralis oblique, vastus medialis oblique, and rectus femoris muscles were performed during isokinetic tests at a velocity of 90°/s. Results Active legs recovery in both groups was effective in reducing fatigue from evaluated muscles, where a significant decrease in fatigue index was observed. The muscles peak torque, work and power parameters did not change significantly after both modes of active recovery, but in both groups significant decrease was seen after passive recovery. Conclusions We suggest that 20 minutes of post-exercise active recovery involving the same muscles that were active during the fatiguing exercise is more effective in fatigue recovery than active exercise using the muscles that were not involved in the exercise. Active arm exercises were less effective in both groups which indicates a lack of a relationship between the different training regimens and the part of the body which is principally used during training. PMID:27706260

  10. Effect of initial delamination on Mode 1 and Mode 2 interlaminar fracture toughness and fatigue fracture threshold

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen Bostaph; Martin, Roderick H.

    1991-01-01

    Static and fatigue double-cantilever beam (DCB) and end-notch flexure (ENF) tests were conducted to determine the effect of the simulated initial delamination in interlaminar fracture toughness, G(sub c), and fatigue fracture threshold, G(sub th). Unidirectional, 24-ply specimens of S2/SP250 glass/epoxy were tested using Kapton inserts of four different thickness - 13, 25, 75, and 130 microns, at the midplane at one end, or with tension or shear precracks, to simulate an initial delamination. To determine G(sub c), the fatigue fracture threshold below which no delamination growth would occur in less than 1 x 10(exp 6) cycles, fatigue tests were conducted by cyclically loading specimens until delamination growth was detected. Consistent values of model 1 fracture toughness, G(sub Ic), were measured from DCB specimens with inserts of thickness 75 microns or thinner, or with shear precracks. The fatigue DCB tests gave similar values of G(sub Ith) for the 13, 25, and 75 microns specimens. Results for the shear precracked specimens were significantly lower that for specimens without precracks. Results for both the static and fatigue ENF tests showed that measured G(IIc) and G(IIth) values decreased with decreasing insert thickness, so that no limiting thickness could be determined. Results for specimens with inserts of 75 microns or thicker were significantly higher than the results for precracked specimens or specimens with 13 or 25 microns inserts.

  11. NSLS-II BPM System Protection from Rogue Mode Coupling

    SciTech Connect

    Blednykh, A.; Bach, B.; Borrelli, A.; Ferreira, M.; Hseuh, H.-C.; Hetzel, C.; Kosciuk, B.; Krinsky, S.; Singh, O.; Vetter, K.

    2011-03-28

    Rogue mode RF shielding has been successfully designed and implemented into the production multipole vacuum chambers. In order to avoid systematic errors in the NSLS-II BPM system we introduced frequency shift of HOM's by using RF metal shielding located in the antechamber slot of each multipole vacuum chamber. To satisfy the pumping requirement the face of the shielding has been perforated with roughly 50 percent transparency. It stays clear of synchrotron radiation in each chamber.

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

    NASA Technical Reports Server (NTRS)

    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.

  13. Mode of action of lipid II-targeting lantibiotics.

    PubMed

    Bauer, R; Dicks, L M T

    2005-05-25

    The antimicrobial action of bacteriocins from Gram-positive bacteria is based on interaction with the cytoplasmic membrane of sensitive bacteria. Models based on studies with artificial membrane systems propose that nisin forms wedge-like poration complexes in the membrane by electrostatic interaction between the positively charged C terminus of the peptide and anionic membrane phospholipids. Nisin can also permeabilise membranes via a targeted mechanism by using lipid II, the bactoprenol-bound precursor of the bacterial cell wall, as a docking molecule. Another consequence of binding with lipid II is the inhibition of peptidoglycan biosynthesis. Mersacidine and actagardine also form a complex with lipid II, but binding only blocks the incorporation of lipid II into peptidoglycan, resulting in slow cell lysis rather than pore formation. Both peptides share a conserved sequence motif with plantaricin C and pediocin PD-1, which is most probably involved in the binding of these bacteriocins to lipid II. Although pediocin PD-1 and plantaricin C may inhibit peptidoglycan biosynthesis, pore formation is rather due to electrostatic interaction between the positively charged unbridged N-terminus and anionic phospholipids in the cytoplasmic membrane of sensitive cells. In the light of increased antibiotic resistance, this review focuses on the mode of action of lantibiotics that involve lipid II, possible candidates for the development of new-generation novel antibiotic drugs.

  14. Development of a numerical procedure for mixed mode K-solutions and fatigue crack growth in FCC single crystal superalloys

    NASA Astrophysics Data System (ADS)

    Ranjan, Srikant

    2005-11-01

    Fatigue-induced failures in aircraft gas turbine and rocket engine turbopump blades and vanes are a pervasive problem. Turbine blades and vanes represent perhaps the most demanding structural applications due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and jet engines because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. These materials have orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Computation of stress intensity factors (SIFs) and the ability to model fatigue crack growth rate at single crystal cracks subject to mixed-mode loading conditions are important parts of developing a mechanistically based life prediction for these complex alloys. A general numerical procedure has been developed to calculate SIFs for a crack in a general anisotropic linear elastic material subject to mixed-mode loading conditions, using three-dimensional finite element analysis (FEA). The procedure does not require an a priori assumption of plane stress or plane strain conditions. The SIFs KI, KII, and KIII are shown to be a complex function of the coupled 3D crack tip displacement field. A comprehensive study of variation of SIFs as a function of crystallographic orientation, crack length, and mode-mixity ratios is presented, based on the 3D elastic orthotropic finite element modeling of tensile and Brazilian Disc (BD) specimens in specific crystal orientations. Variation of SIF through the thickness of the specimens is also analyzed. The resolved shear stress intensity coefficient or effective SIF, Krss, can be computed as a function of crack tip SIFs and the

  15. Effects of Control Mode and R-Ratio on the Fatigue Behavior of a Metal Matrix Composite

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Composite Because of their high specific stiffness and strength at elevated temperatures, continuously reinforced metal matrix composites (MMC's) are under consideration for a future generation of aeropropulsion systems. Since components in aeropropulsion systems experience substantial cyclic thermal and mechanical loads, the fatigue behavior of MMC's is of great interest. Almost without exception, previous investigations of the fatigue behavior of MMC's have been conducted in a tension-tension, load-controlled mode. This has been due to the fact that available material is typically less than 2.5-mm thick and, therefore, unable to withstand high compressive loads without buckling. Since one possible use of MMC's is in aircraft skins, this type of testing mode may be appropriate. However, unlike aircraft skins, most engine components are thick. In addition, the transient thermal gradients experienced in an aircraft engine will impose tension-compression loading on engine components, requiring designers to understand how the MMC will behave under fully reversed loading conditions. The increased thickness of the MMC may also affect the fatigue life. Traditionally, low-cycle fatigue (LCF) tests on MMC's have been performed in load control. For monolithic alloys, low-cycle fatigue tests are more typically performed in strain control. Two reasons justify this choice: (1) the critical volume from which cracks initiate and grow is generally small and elastically constrained by the larger surrounding volume of material, and (2) load-controlled, low-cycle fatigue tests of monolithics invariably lead to unconstrained ratcheting and localized necking--an undesired material response because the failure mechanism is far more severe than, and unrelated to, the fatigue mechanism being studied. It is unknown if this is the proper approach to composite testing. However, there is a lack of strain-controlled data on which to base any decisions. Consequently, this study addresses the

  16. Association of chronic fatigue syndrome with human leucocyte antigen class II alleles

    PubMed Central

    Smith, J; Fritz, E L; Kerr, J R; Cleare, A J; Wessely, S; Mattey, D L

    2005-01-01

    Background: A genetic component to the development of chronic fatigue syndrome (CFS) has been proposed, and a possible association between human leucocyte antigen (HLA) class II antigens and chronic fatigue immune dysfunction has been shown in some, but not all, studies. Aims: To investigate the role of HLA class II antigens in CFS. Methods: Forty nine patients with CFS were genotyped for the HLA-DRB1, HLA-DQA1, and HLA-DQB1 alleles and the frequency of these alleles was compared with a control group comprising 102 normal individuals from the UK. All patients and controls were from the same region of England and, apart from two patients, were white. Results: Analysis by 2 × 2 contingency tables revealed an increased frequency of HLA-DQA1*01 alleles in patients with CFS (51.0% v 35%; odds ratio (OR), 1.93; p  =  0.008). HLA-DQB1*06 was also increased in the patients with CFS (30.2% v 20.0%; OR, 1.73, p  =  0.052). Only the association between HLA-DQA1*01 and CFS was significant in logistic regression models containing HLA-DQA1*01 and HLA-DRQB1*06, and this was independent of HLA-DRB1 alleles. There was a decreased expression of HLA-DRB1*11 in CFS, although this association disappeared after correction for multiple comparisons. Conclusions: CFS may be associated with HLA-DQA1*01, although a role for other genes in linkage disequilibrium cannot be ruled out. PMID:16049290

  17. Effets de l'humidite sur la propagation du delaminage dans un composite carbone/epoxy sollicite en mode mixte I/II

    NASA Astrophysics Data System (ADS)

    LeBlanc, Luc R.

    In industries such as aerospace, motorsports, and even sporting equipment, composite materials are used more than ever, primarily due to their high stiffness and strength to weight ratios. Studies have shown that moisture exposure on carbon/epoxy composite materials can affect their delamination toughness, initiation and growth rate. Of these studies, only a few demonstrated the effects of moisture on delamination toughness and initiation with mixed mode I/II loadings, while none have investigated the effects of moisture exposure of composites on delamination growth rate with mixed mode I/II loadings. The first part of this thesis studies the effects of moisture exposure on delamination growth in a carbon/epoxy composite using mixed mode I/II loadings. Coupons were cut from plates of unidirectional carbon/epoxy (040-800/5276-1) and were submerged in a 70°C distilled water bath until they reached saturation. Quasi -static experimental tests were performed using a range of mode mixities (0%, 25%, 50%, 75% and 1 00%) on dry and conditioned coupons to determine the effects of humidity on delamination toughness. Fatigue tests with the same mode mixities were performed to determine the effects of moisture on delamination initiation and growth rate. Results from tests with quasi-static loadings demonstrated that delamination toughness decreased for all loading modes studied except for mode I after composites are exposed to moisture. When a conditioned composite is subject to mode I loadings, its delamination toughness increases compared to non-conditioned composites. Composites exposed to moisture showed accelerated delamination initiation and growth rates for all mixed mode I/II fatigue loadings. Experimental data was used to determine which fracture criterion and growth rate model for mixed mode I/II delamination better represented the studied composite. A regression curve and regression surface was used to fit the experimental data to the delamination fracture

  18. Retroviral sequences related to human T-lymphotropic virus type II in patients with chronic fatigue immune dysfunction syndrome

    SciTech Connect

    DeFreitas, E.; Hilliard, B.; Cheney, P.R.; Bell, D.S.; Kiggundu, E.; Sankey, D.; Wroblewska, Z.; Palladino, M.; Woodward, J.P.; Koprowski, H. )

    1991-04-01

    Chronic fatigue immune dysfunction syndrome (CFIDS) is a recently recognized illness characterized by debilitating fatigue as well as immunological and neurological abnormalities. Once thought to be caused by Epstein-Barr virus, it is now thought to have a different but unknown etiology. The authors evaluted 30 adult and pediatric CFIDS patients from six eastern states for the presence of human T-lymphotropic virus (HTLV) types I and II by Western immunoblotting, polymerase chain reaction, and in situ hybridization of blood samples. The majority of patients were positive for HTLV antibodies by Western blotting and for HTLV-II gag sequences by polymerase chain reaction and in situ hybridization. Twenty nonexposure healthy controls were negative in all assays. These data support an association between an HTLV-II-like virus and CFIDS.

  19. Combined Mode I and Mode II Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

    2003-01-01

    The mode I, mode II, and combined mode I-mode II fracture behavior of ZrO2- 8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. Precracks were introduced in test specimens using the single-edge-v-notched beam (SEVNB) method incorporated with final diamond polishing to achieve sharp crack tips. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of K(sub I)/K(sub II) were also determined. The mixed-mode fracture behaviors of the coating material were compared with those of monolithic advanced ceramics determined previously. The mixed-mode fracture behavior of the plasma-sprayed thermal barrier coating material was predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

  20. Evaluation of Delamination Onset and Growth Characterization Methods under Mode I Fatigue Loading

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.

    2013-01-01

    Double-cantilevered beam specimens of IM7/8552 graphite/epoxy from two different manufacturers were tested in static and fatigue to compare the material characterization data and to evaluate a proposed ASTM standard for generating Paris Law equations for delamination growth. Static results were used to generate compliance calibration constants for reducing the fatigue data, and a delamination resistance curve, GIR, for each material. Specimens were tested in fatigue at different initial cyclic GImax levels to determine a delamination onset curve and the delamination growth rate. The delamination onset curve equations were similar for the two sources. Delamination growth rate was calculated by plotting da/dN versus GImax on a log-log scale and fitting a Paris Law. Two different data reduction methods were used to calculate da/dN. To determine the effects of fiber-bridging, growth results were normalized by the delamination resistance curves. Paris Law exponents decreased by 31% to 37% after normalizing the data. Visual data records from the fatigue tests were used to calculate individual compliance constants from the fatigue data. The resulting da/dN versus GImax plots showed improved repeatability for each source, compared to using averaged static data. The Paris Law expressions for the two sources showed the closest agreement using the individually fit compliance data.

  1. Accelerated fatigue crack growth behavior of PWA 1480 single crystal alloy and its dependence on the deformation mode

    NASA Technical Reports Server (NTRS)

    Telesman, Jack; Ghosn, Louis J.

    1988-01-01

    An investigation of the fatigue crack growth (FCG) behavior of PWA 1480 single crystal nickel base superalloy was conducted. Typical Paris region behavior was observed above a delta K of 8 MPa sq rt of m. However, below that stress intensity range, the alloy exhibited highly unusual behavior. This behavior consisted of a region where the crack growth rate became essentially independent of the applied stress intensity. The transition in the FCG behavior was related to a change in the observed crack growth mechanisms. In the Paris region, fatigue failure occurred along (111) facets; however, at the lower stress intensities, (001) fatigue failure was observed. A mechanism was proposed, based on barriers to dislocation motion, to explain the changes in the observed FCG behavior. The FCG data were also evaluated in terms of a recently proposed stress intensity parameter, K sub rss. This parameter, based on the resolved shear stresses on the slip planes, quantified the crack driving force as well as the mode I delta K, and at the same time was also able to predict the microscopic crack path under different stress states.

  2. Synergistic Effects of Temperature, Oxidation and Multicracking Modes on Damage Evolution and Life Prediction of 2D Woven Ceramic-Matrix Composites under Tension-Tension Fatigue Loading

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2016-11-01

    In this paper, the synergistic effects of temperature, oxidation and multicracking modes on damage evolution and life prediction in 2D woven ceramic-matrix composites (CMCs) have been investigated. The damage parameter of fatigue hysteresis dissipated energy and the interface shear stress were used to monitor the damage evolution inside of CMCs. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface/fiber oxidation model, interface wear model and fibers statistical failure model at elevated temperature, based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the load carried by broken and intact fibers satisfy the Global Load Sharing (GLS) criterion. When the broken fibers fraction approaches to the critical value, the composite fatigue fractures. The evolution of fatigue hysteresis dissipated energy, the interface shear stress and broken fibers fraction versus cycle number, and the fatigue life S-N curves of SiC/SiC at 1000, 1200 and 1300 °C in air and steam condition have been predicted. The synergistic effects of temperature, oxidation, fatigue peak stress, and multicracking modes on the evolution of interface shear stress and fatigue hysteresis dissipated energy versus cycle numbers curves have been analyzed.

  3. Adaptations to isolated shoulder fatigue during simulated repetitive work. Part II: Recovery.

    PubMed

    McDonald, Alison C; Tse, Calvin T F; Keir, Peter J

    2016-08-01

    The shoulder allows kinematic and muscular changes to facilitate continued task performance during prolonged repetitive work. The purpose of this work was to examine changes during simulated repetitive work in response to a fatigue protocol. Participants performed 20 one-minute work cycles comprised of 4 shoulder centric tasks, a fatigue protocol, followed by 60 additional cycles. The fatigue protocol targeted the anterior deltoid and cycled between static and dynamic actions. EMG was collected from 14 upper extremity and back muscles and three-dimensional motion was captured during each work cycle. Participants completed post-fatigue work despite EMG manifestations of muscle fatigue, reduced flexion strength (by 28%), and increased perceived exertion (∼3 times). Throughout the post-fatigue work cycles, participants maintained performance via kinematic and muscular adaptations, such as reduced glenohumeral flexion and scapular rotation which were task specific and varied throughout the hour of simulated work. By the end of 60 post-fatigue work cycles, signs of fatigue persisted in the anterior deltoid and developed in the middle deltoid, yet perceived exertion and strength returned to pre-fatigue levels. Recovery from fatigue elicits changes in muscle activity and movement patterns that may not be perceived by the worker which has important implications for injury risk.

  4. Evaluation of Delamination Growth Characterization Methods Under Mode I Fatigue Loading

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.

    2012-01-01

    Reliable delamination characterization data for laminated composites are needed for input to analytical models of structures to predict delamination. The double-cantilevered beam (DCB) specimen is used with laminated composites to measure fracture toughness, G(sub Ic), delamination onset strain energy release rate, and growth rate data under cyclic loading. In the current study, DCB specimens of IM7/8552 graphite/epoxy supplied by two different manufacturers were tested in static and fatigue to compare the measured characterization data from the two sources, and to evaluate a proposed ASTM standard for generating Paris Law equations. Static results were used to generate compliance calibration constants for the fatigue data, and a delamination resistance curve, G(sub IR), which was used to determine the effects of fiber-bridging on delamination growth. Specimens were tested in fatigue at a cyclic G(sub Imax) level equal to 50, 40 or 30% of G(sub Ic), to determine a delamination onset curve and delamination growth rate. The delamination onset curve equations had similar exponents and the same trends. Delamination growth rate was calculated by fitting a Paris Law to the da/dN versus G(sub Imax) data. Both a 2-point and a 7-point data reduction method were used and the Paris Law equations were compared. To determine the effects of fiber-bridging, growth rate results were normalized by the delamination resistance curve for each material and compared to the non-normalized results. Paris Law exponents were found to decrease by 31% to 37% due to normalizing the growth data. Normalizing the data also greatly reduced the amount of scatter between the different specimens. Visual data records from the fatigue testing were used to calculate individual compliance calibration constants from the fatigue data for some of the specimens. The resulting da/dN versus G(sub Imax) plots showed much improved repeatability between specimens. Gretchen

  5. Initiation and growth of mode II delamination in toughened composites

    NASA Astrophysics Data System (ADS)

    Russell, Alan J.

    The origins of nonlinearity in the mode-II delamination fracture of three organic-matrix carbon-fiber composite materials was investigated. This was accomplished by testing specimens with different types of starter cracks and by loading and unloading these specimens several times so that the change in nonlinearity as the delaminations grew could be measured. The load at which crack growth initiated was determined by acoustic emission. Slow crack growth as found to be the principal cause of nonlinearity in the materials tested. The crack velocity obeyed the same power law dependence on GII as is observed for slow crack growth in viscoelastic polymers. For the first loading from the end of the starter cracks, plastic deformation at the crack tip also contributed to the nonlinearity. Other sources of nonlinearity included an increasing fracture resistance in one of the materials as well as problems associated with producing a clean starter notch with a straight crack front.

  6. Combined Mode I and Mode II Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

    2003-01-01

    The mode I, mode II, and combined mode I-mode II fracture behavior of ZrO2 - 8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. Precracks were introduced in test specimens using the single-edge-v-notched beam (SEVNB) method incorporated with final diamond polishing to achieve sharp crack tips. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of KI/KII were also determined. The mixed-mode fracture behaviors of the coating material were compared with those of monolithic advanced ceramics determined previously. The mixed-mode fracture behavior of the plasma- sprayed thermal barrier coating material was predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

  7. Composite materials: Fatigue and fracture. Vol. 3

    NASA Technical Reports Server (NTRS)

    O'Brien, T. K. (Editor)

    1991-01-01

    The present volume discusses topics in the fields of matrix cracking and delamination, interlaminar fracture toughness, delamination analysis, strength and impact characteristics, and fatigue and fracture behavior. Attention is given to cooling rate effects in carbon-reinforced PEEK, the effect of porosity on flange-web corner strength, mode II delamination in toughened composites, the combined effect of matrix cracking and free edge delamination, and a 3D stress analysis of plain weave composites. Also discussed are the compression behavior of composites, damage-based notched-strength modeling, fatigue failure processes in aligned carbon-epoxy laminates, and the thermomechanical fatigue of a quasi-isotropic metal-matrix composite.

  8. Effect of Embedded Piezoelectric Sensors on Fracture Toughness and Fatigue Resistance of Composite Laminates Under Mode I Loading

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.

    2006-01-01

    Double-cantilevered beam (DCB) specimens of a glass/epoxy composite material with embedded piezoelectric sensors were tested both statically and under fatigue loading to determine the effect of the embedded material on the Mode I fracture toughness and fatigue resistance compared to baseline data without the embedded elements. A material known as LaRC-Macrofiber Composite (LaRC-MFC (TradeMark)), or MFC, was embedded at the midplane of the specimen during the layup. Specimens were manufactured with the embedded MFC material either at the loaded end of the specimen to simulate an initial delamination; or with the MFC material located at the delaminating interface, with a Teflon film at the loaded end to simulate an initial delamination. There were three types of specimens with the embedded material at the delaminating interface: co-cured with no added adhesive; cured with a paste adhesive applied to the embedded element; or cured with a film adhesive added to the embedded material. Tests were conducted with the sensors in both the passive and active states. Results were compared to baseline data for the same material without embedded elements. Interlaminar fracture toughness values (G(sub Ic)) for the passive condition showed little change when the MFC was at the insert end. Passive results varied when the MFC was at the delaminating interface. For the co-cured case and with the paste adhesive, G(sub Ic) decreased compared to the baseline toughness, whereas, for the film adhesive case, G(sub Ic) was significantly greater than the baseline toughness, but the failure was always catastrophic. When the MFC was in the active state, G(sub Ic) was generally lower compared to the passive results. Fatigue tests showed little effect of the embedded material whether it was active or passive compared to baseline values.

  9. Development and Application of Benchmark Examples for Mixed-Mode I/II Quasi-Static Delamination Propagation Predictions

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald

    2012-01-01

    The development of benchmark examples for quasi-static delamination propagation prediction is presented and demonstrated for a commercial code. The examples are based on finite element models of the Mixed-Mode Bending (MMB) specimen. The examples are independent of the analysis software used and allow the assessment of the automated delamination propagation prediction capability in commercial finite element codes based on the virtual crack closure technique (VCCT). First, quasi-static benchmark examples were created for the specimen. Second, starting from an initially straight front, the delamination was allowed to propagate under quasi-static loading. Third, the load-displacement relationship from a propagation analysis and the benchmark results were compared, and good agreement could be achieved by selecting the appropriate input parameters. Good agreement between the results obtained from the automated propagation analysis and the benchmark results could be achieved by selecting input parameters that had previously been determined during analyses of mode I Double Cantilever Beam and mode II End Notched Flexure specimens. The benchmarking procedure proved valuable by highlighting the issues associated with choosing the input parameters of the particular implementation. Overall the results are encouraging, but further assessment for mixed-mode delamination fatigue onset and growth is required.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  11. A MODEL STUDY OF TRANSVERSE MODE COUPLING INSTABILITY AT NATIONAL SYNCHROTRON LIGHT SOURCE-II (NSLS-II).

    SciTech Connect

    BLEDNYKH, A.; WANG, J.M.

    2005-05-15

    The vertical impedances of the preliminary designs of National Synchrotron Light Source II (NSLS-II) Mini Gap Undulators (MGU) are calculated by means of GdfidL code. The Transverse Mode Coupling Instability (TMCI) thresholds corresponding to these impedances are estimated using an analytically solvable model.

  12. Shear fatigue crack growth - A literature survey

    NASA Technical Reports Server (NTRS)

    Liu, H. W.

    1985-01-01

    Recent studies of shear crack growth are reviewed, emphasizing test methods and data analyses. The combined mode I and mode II elastic crack tip stress fields are considered. The development and design of the compact shear specimen are described, and the results of fatigue crack growth tests using compact shear specimens are reviewed. The fatigue crack growth tests are discussed and the results of inclined cracks in tensile panels, center cracks in plates under biaxial loading, cracked beam specimens with combined bending and shear loading, center-cracked panels and double edge-cracked plates under cyclic shear loading are examined and analyzed in detail.

  13. Treatment of Class II Division 2 Malocclusion Using the Forsus Fatigue Resistance Device and 5-Year Follow-Up

    PubMed Central

    Atik, Ezgi; Kocadereli, Ilken

    2016-01-01

    This case report presents the treatment of a 14-year-and-8-month-old boy with Class II division 2 mandibular retrusion, severe deep bite, and concave profile. The Forsus fatigue resistance device (FRD) was effective in correcting both skeletal and dental parameters. At 5-year posttreatment follow-up, the teeth were well aligned and the occlusion was stable. FRD application with appropriate treatment time can result with prominent changes in the facial profile and dentition, and the outcomes can be maintained at the long-term follow-up periods. PMID:27034855

  14. Development and Application of Benchmark Examples for Mixed-Mode I/II Quasi-Static Delamination Propagation Predictions

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald

    2012-01-01

    The development of benchmark examples for quasi-static delamination propagation prediction is presented. The example is based on a finite element model of the Mixed-Mode Bending (MMB) specimen for 50% mode II. The benchmarking is demonstrated for Abaqus/Standard, however, the example is independent of the analysis software used and allows the assessment of the automated delamination propagation prediction capability in commercial finite element codes based on the virtual crack closure technique (VCCT). First, a quasi-static benchmark example was created for the specimen. Second, starting from an initially straight front, the delamination was allowed to propagate under quasi-static loading. Third, the load-displacement as well as delamination length versus applied load/displacement relationships from a propagation analysis and the benchmark results were compared, and good agreement could be achieved by selecting the appropriate input parameters. The benchmarking procedure proved valuable by highlighting the issues associated with choosing the input parameters of the particular implementation. Overall, the results are encouraging, but further assessment for mixed-mode delamination fatigue onset and growth is required.

  15. Influence of fatigue testing and cementation mode on the load-bearing capability of bovine incisors restored with crowns and FRC posts.

    PubMed

    Nothdurft, Frank P; Schmitt, Thomas; Rupf, Stefan; Pospiech, Peter R

    2011-01-01

    The aim of the study was to evaluate the influence of fatigue and cementation mode on the fracture behaviour of endodontically treated bovine incisors restored with fiber-reinforced-composite (FRC) posts and crowns. Forty-eight endodontically treated incisors were restored with FRC posts, composite build-ups, and cast crowns. In 16 teeth, each of the posts were cemented conventionally with KetacCem (3M Espe) or adhesively with Panavia F (Kuraray) or RelyXUniCem (3M Espe). One-half of the specimens in each group were subjected to thermal cycling with 10,000 cycles at 5-55°C and mechanical aging, loading the specimens in 1,200,000 cycles with 50 N. Fracture resistance was determined by loading the specimens until fracture at an angle of 45°. The loading test showed that cementation mode and fatigue testing had an influence on the load bearing capability. Before fatigue testing no statistically significant differences between the different cementation modes could be detected. After fatigue testing, conventionally cemented FRC posts lead to statistically significant higher fracture loads compared to adhesively luted posts. Most specimens fractured in a favourable way, independent from the type of cementation.

  16. Suppression of fatigue inducing cavity acoustic modes on turbo fan engines

    NASA Astrophysics Data System (ADS)

    Benner, R. H.

    1990-10-01

    This paper discusses several methods of suppressing shear layer excitation of cavity acoustic modes on turbofan engines. The methods include the use of a Helmholtz resonator, reducing the cavity impingement length with vane-like dividers, and drawing the shear layer into the cavity. Empirical data and closed-form solutions were used to design baseline structures employed in each method. Full scale turbofan engine tests were used to measure their effectiveness. Each method significantly reduced the level to which cavity acoustic modes were excited by shear layer flow.

  17. Mission Crew Fatigue during RIVET JOINT Block II Demonstration/Evaluation.

    DTIC Science & Technology

    1980-11-01

    you feel RIGHT NOW. STATEMENT SETTER THAN SAME AS WORSE THAN 1. VERY LIVELY 2. EXTREMELY TIRED & QUITE FRESH & SLIGHTLY POOPED 0 S, EXTREMELY PEPPV 6...SOMEWHAT PRISMJ 7. PETERED OUT •Z L. VERY REFRESHED 9. FAIL.Y WELL POOPED Re IEADY TO DROP WE SAM roy’" 136 SUBJECTIVE FATIGUE CNECKCARDGaip 74 aa

  18. An analytical and experimental stress analysis of a practical mode II fracture-test specimen

    NASA Technical Reports Server (NTRS)

    Chisholm, D. B.; Jones, D. L.

    1975-01-01

    A boundary collocation method has been employed to determine the Mode II stress intensity factors for a pair of through-the-thickness edge cracks in a finite isotropic plate. An elastostatic analysis has been carried out in terms of the complete Williams stress function employing both even and odd components. The results of the numerical analysis were verified by a two-step procedure whereby the symmetric and antisymmetric portions of the solution were independently compared with existing solutions. The complete solution was verified by comparison with a photoelastic analysis. A compact shear specimen (CSS) of Hysol epoxy resin was loaded in a photoelastic experiment designed to study the isochromatic fringe patterns resulting from the Mode II crack tip stress distribution. The experiment verified that a pure Mode II stress distribution existed in the neighborhood of the crack tips and confirmed the accuracy of the boundary collocation solution for the Mode II stress intensity factors.

  19. An Acoustic Plate Mode Sensor for Biowarfare Toxins, Phase II

    DTIC Science & Technology

    1997-10-01

    Biological agents -- such as bacteria , bacterial toxins and viruses -- must be detected rapidly to allow their neutralization or the quick treatment of...Mode Sensor for Biowarfare Toxins PRINCIPAL INVESTIGATOR: Douglas J. McAllister, Ph.D. CONTRACTING ORGANIZATION: Biode, Incorporated Bangor, Maine...OF PAGES Acoustic Plate Mode, Biowarfare Toxins 54 16. PRICE CODE 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION

  20. Creep, Plasticity, and Fatigue of Single Crystal Superalloy. (Preprint)

    DTIC Science & Technology

    2011-07-01

    control mode ( 1R ) using servo- hydraulic machines. The test specimen was heated using a low frequency (10 kHz) induction generator. Tests were...1989), Thermomechanical Fatigue , Oxidation, and Creep. Part II. Life Prediction, Metallurgical Transactions A: Physical Metallurgy and Materials...AFRL-RX-WP-TP-2011-4223 CREEP, PLASTICITY, AND FATIGUE OF SINGLE CRYSTAL SUPERALLOY Alexander Staroselsky United Technologies

  1. A Novel Method for Characterizing Fatigue Delamination Growth Under Mode I Using the Double Cantilever Beam Specimen

    NASA Technical Reports Server (NTRS)

    Carvalho, Nelson; Murri, G.

    2014-01-01

    A novel method is proposed to obtain Mode I delamination growth rate from a Double Cantilever Beam (DCB) specimen. In the proposed method, Unidirectional (UD) DCB specimens are tested in fatigue at different initial maximum energy release rates levels. The growth rate data obtained in the first increments of crack growth at each maximum energy release rate level are used to generate a Paris Law equation, which characterizes delamination growth rate without fiber-bridging, and can also be used to determine a delamination onset curve. The remaining delamination growth rate data from each test are used to determine a modified Paris law, which characterizes the delamination growth rate in a DCB specimen, explicitly accounting for fiber-bridging. The proposed expression captures well the scatter in experimental data obtained using the DCB specimens, suggesting its adequacy. The Paris Law characterizing delamination growth rate without fiber-bridging predicts higher delamination growth rates for the same maximum energy release rate applied, leading to a conservative estimate for delamination growth. This is particularly relevant, since in generic ply interfaces, fiber-bridging is less predominant than in UD DCB specimens. Failing to account for fiber-bridging in UD DCB specimens may underestimate the delamination growth rate, yielding non-conservative predictions.

  2. The influence of load misalignment during uniaxial low-cycle fatigue testing. I - Modeling. II - Applications

    NASA Astrophysics Data System (ADS)

    Kandil, F. A.; Dyson, B. F.

    1993-05-01

    A quantitative model for predicting the extent of lifetime scatter in low-cycle fatigue due to the bending effect caused by load misalignment is proposed. The model is based on the bending mechanism and the type of extensometer used to control strain and the fatigue characteristics of the material. A consequence of a lateral offset in the center-lines of the load-train with respect to either a machine's frame or ram is found to be the most damaging bending mechanism. Two types of scatter under consideration include repeatability scatter due to testing practice within a single laboratory and reproducibility scatter among laboratories. The model is applied to four alloys, including AISI 316L, Nimonic 101, 9 Cr-1 Mo, and IN 718. Results show that in all four materials a major fraction of the data scatter could be attributed to bending. At the lowest strain range the predicted bending component represents the highest proportion of the experimental interlaboratory scatter.

  3. Magnetic antenna excitation of whistler modes. II. Antenna arrays

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2014-12-15

    The excitation of whistler modes from magnetic loop antennas has been investigated experimentally. The field topology of the excited wave driven by a single loop antenna has been measured for different loop orientations with respect to the uniform background field. The fields from two or more antennas at different locations are then created by superposition of the single-loop data. It is shown that an antenna array can produce nearly plane waves which cannot be achieved with single antennas. By applying a phase shift along the array, oblique wave propagation is obtained. This allows a meaningful comparison with plane wave theory. The Gendrin mode and oblique cyclotron resonance are demonstrated. Wave helicity and polarization in space and time are demonstrated and distinguished from the magnetic helicity of the wave field. The superposition of two oblique plane whistler modes produces in a “whistler waveguide” mode whose polarization and helicity properties are explained. The results show that single point measurements cannot properly establish the wave character of wave packets. The laboratory observations are relevant for excitation and detection of whistler modes in space plasmas.

  4. Magnetic antenna excitation of whistler modes. II. Antenna arrays

    NASA Astrophysics Data System (ADS)

    Stenzel, R. L.; Urrutia, J. M.

    2014-12-01

    The excitation of whistler modes from magnetic loop antennas has been investigated experimentally. The field topology of the excited wave driven by a single loop antenna has been measured for different loop orientations with respect to the uniform background field. The fields from two or more antennas at different locations are then created by superposition of the single-loop data. It is shown that an antenna array can produce nearly plane waves which cannot be achieved with single antennas. By applying a phase shift along the array, oblique wave propagation is obtained. This allows a meaningful comparison with plane wave theory. The Gendrin mode and oblique cyclotron resonance are demonstrated. Wave helicity and polarization in space and time are demonstrated and distinguished from the magnetic helicity of the wave field. The superposition of two oblique plane whistler modes produces in a "whistler waveguide" mode whose polarization and helicity properties are explained. The results show that single point measurements cannot properly establish the wave character of wave packets. The laboratory observations are relevant for excitation and detection of whistler modes in space plasmas.

  5. Resistive wall modes in the Reversatron II RFP

    SciTech Connect

    Barrick, G.; Greene, P.; Robertson, S.

    1990-01-01

    The Reversatron 2 RFP (R/a=50cm/8cm) has been operated with interchangeable shells to investigate resistive wall modes. Shell penetration times are 610, 100, and 4 {mu}sec (no shell). With the 610 {mu}sec shell, the plasma current is {le} 65 kA and the duration {le} 550 {mu}sec. With no shell, helium discharges are more resistive and hydrogen discharges cannot be sustained. An m=1, n=-6 mode resonant on axis grows to a relative amplitude of 20% during the setting-up phase. With the 100{mu}sec shell, deuterium discharges can be sustained but are degraded due to a broad spectrum of modes. The increased plasma resistance can be correlated with the flux intersecting the wall. 21 refs., 12 figs.

  6. Ductile fracture in HY100 steel under mixed mode I/mode II loading

    SciTech Connect

    Bhattacharjee, D. . Dept. of Materials Science and Metallurgy); Knott, J.F. . School of Metallurgy and Materials)

    1994-05-01

    A number of criteria have been proposed which predict the direction of cracking under mixed Mode 1/Mode 2 loading. All have been evaluated for brittle materials, in which a crack subjected to tension and shear propagates normal to the maximum tensile stress (i.e. fracture is of the Mode 1 type). In a ductile material, however, a notch subjected to mixed Mode 1/Mode 2 loading may initiate a crack in the direction of maximum shear. This paper shows that the profile of the notch tip changes with increasing mixed mode load in such a way that one side of the tip blunts while the other sharpens. Various specimens, subjected to the same mixed mode ratio, were unloaded from different points on the load-displacement curves to study the change in notch-tip profile. Studies under the Scanning Electron Microscope (SEM) have shown that cracks initiate at the sharpened end, along a microscopic shear band. Using a dislocation pile-up model for decohesion of the carbide-matrix interface, a micromechanical model has been proposed for crack initiation in the shear band. It is shown that a theoretical prediction of the shear strain required for decohesion gives a result that is, of magnitude, similar to that of the shear strain at crack initiation measured in the experiments.

  7. Vibrational relaxation pathways of amide I and amide II modes in N-methylacetamide.

    PubMed

    Piatkowski, L; Bakker, H J

    2012-04-28

    We studied the vibrational energy relaxation mechanisms of the amide I and amide II modes of N-methylacetamide (NMA) monomers dissolved in bromoform using polarization-resolved femtosecond two-color vibrational spectroscopy. The results show that the excited amide I vibration transfers its excitation energy to the amide II vibration with a time constant of 8.3 ± 1 ps. In addition to this energy exchange process, we observe that the excited amide I and amide II vibrations both relax to a final thermal state. For the amide I mode this latter process dominates the vibrational relaxation of this mode. We find that the vibrational relaxation of the amide I mode depends on frequency which can be well explained from the presence of two subbands with different vibrational lifetimes (~1.1 ps on the low frequency side and ~2.7 ps on the high frequency side) in the amide I absorption spectrum.

  8. A compendium of sources of fracture toughness and fatigue crack growth data for metallic alloys. II

    NASA Technical Reports Server (NTRS)

    Hudson, C. M.; Seward, S. K.

    1982-01-01

    A compendium is presented of sources for metallic alloy fracture toughness and fatigue crack growth data, which concentrates on technical reports as the primary source of references and updates the previous Hudson and Seward (1978) compendium references on technical journals. Where available, the accession numbers which are used as code numbers for the ordering of the reports from their publishers are given. The sources of these reports include the AIAA Technical Information Service, the Defense Technical Information Center, the National Technical Information Service, and NASA.

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

    NASA Astrophysics Data System (ADS)

    Arzoumanidis, Alexis Gerasimos

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

  10. Cooperative binding modes of Cu(II) in prion protein

    NASA Astrophysics Data System (ADS)

    Hodak, Miroslav; Chisnell, Robin; Lu, Wenchang; Bernholc, Jerry

    2007-03-01

    The misfolding of the prion protein, PrP, is responsible for a group of neurodegenerative diseases including mad cow disease and Creutzfeldt-Jakob disease. It is known that the PrP can efficiently bind copper ions; four high-affinity binding sites located in the octarepeat region of PrP are now well known. Recent experiments suggest that at low copper concentrations new binding modes, in which one copper ion is shared between two or more binding sites, are possible. Using our hybrid Thomas-Fermi/DFT computational scheme, which is well suited for simulations of biomolecules in solution, we investigate the geometries and energetics of two, three and four binding sites cooperatively binding one copper ion. These geometries are then used as inputs for classical molecular dynamics simulations. We find that copper binding affects the secondary structure of the PrP and that it stabilizes the unstructured (unfolded) part of the protein.

  11. Pulsatile Support Mode of BJUT-II Ventricular Assist Device (VAD) has Better Hemodynamic Effects on the Aorta than Constant Speed Mode: A Primary Numerical Study

    PubMed Central

    Gu, Kaiyun; Gao, Bin; Chang, Yu; Zeng, Yi

    2016-01-01

    Background BJUT-II VAD is a novel left ventricular assist device (LVADs), directly implanted into the ascending aorta. The pulsatile support mode is proposed to achieve better unloading performance than constant speed mode. However, the hemodynamic effects of this support mode on the aorta are still unclear. The aim of this study was to clarify the hemodynamic effects BJUT-II VAD under pulsatile support mode on the aorta. Material/Methods Computational fluid dynamics (CFD) studies, based on a patient-specific aortic geometric model, were conducted. Wall shear stress (WSS), averaged WSS (avWSS), oscillatory shear index (OSI), and averaged helicity density (Ha) were calculated to compare the differences in hemodynamic effects between pulsatile support mode and constant speed mode. Results The results show that avWSS under pulsatile support mode is significantly higher than that under constant speed mode (0.955Pa vs. 0.675Pa). Similarly, the OSI value under pulsatile mode is higher than that under constant speed mode (0.104 vs. 0.057). In addition, Ha under pulsatile mode for all selected cross-sections is larger than that under constant mode. Conclusions BJUT-II VAD, under pulsatile control mode, may prevent atherosclerosis lesions and aortic remodeling. The precise effects of pulsatile support mode on atherosclerosis and aortic remodeling need to be further studied in animal experiments. PMID:27363758

  12. Pulsatile Support Mode of BJUT-II Ventricular Assist Device (VAD) has Better Hemodynamic Effects on the Aorta than Constant Speed Mode: A Primary Numerical Study.

    PubMed

    Gu, Kaiyun; Gao, Bin; Chang, Yu; Zeng, Yi

    2016-07-01

    BACKGROUND BJUT-II VAD is a novel left ventricular assist device (LVADs), directly implanted into the ascending aorta. The pulsatile support mode is proposed to achieve better unloading performance than constant speed mode. However, the hemodynamic effects of this support mode on the aorta are still unclear. The aim of this study was to clarify the hemodynamic effects BJUT-II VAD under pulsatile support mode on the aorta. MATERIAL AND METHODS Computational fluid dynamics (CFD) studies, based on a patient-specific aortic geometric model, were conducted. Wall shear stress (WSS), averaged WSS (avWSS), oscillatory shear index (OSI), and averaged helicity density (Ha) were calculated to compare the differences in hemodynamic effects between pulsatile support mode and constant speed mode. RESULTS The results show that avWSS under pulsatile support mode is significantly higher than that under constant speed mode (0.955Pa vs. 0.675Pa). Similarly, the OSI value under pulsatile mode is higher than that under constant speed mode (0.104 vs. 0.057). In addition, Ha under pulsatile mode for all selected cross-sections is larger than that under constant mode. CONCLUSIONS BJUT-II VAD, under pulsatile control mode, may prevent atherosclerosis lesions and aortic remodeling. The precise effects of pulsatile support mode on atherosclerosis and aortic remodeling need to be further studied in animal experiments.

  13. Active-treatment effects of the Forsus fatigue resistant device during comprehensive Class II correction in growing patients

    PubMed Central

    Cacciatore, Giorgio; Alvetro, Lisa; Defraia, Efisio; Ghislanzoni, Luis Tomas Huanc

    2014-01-01

    Objective To evaluate the active-treatment effects of the Forsus fatigue resistant device (Forsus) during comprehensive correction of Class II malocclusion in growing patients. Methods Fifty-four patients (mean age, 12.5 ± 1.2 years) with Class II division 1 malocclusion were consecutively treated with fixed app-liances in combination with Forsus. Lateral cephalograms were analyzed at the beginning of the fixed treatment (T1), Forsus insertion (T2), its removal (T3), and end of the comprehensive therapy (T4). Statistical comparisons were carried out by repeated-measures ANOVA with Tukey's post-hoc test (p < 0.05). Results The overall therapeutic effects were mainly dentoalveolar and occurred mostly during the active treatment with Forsus (T2-T3, mean duration = 0.5 ± 0.1 years). The overjet and overbite decreased significantly (-3.5 and -1.5 mm, respectively) and the molar relationship improved by 4.3 mm. These changes were associated with significant retroclination of the maxillary incisors (-3.1°), proclination and intrusion of the mandibular incisors (+5.0° and -1.5 mm, respectively), and mesialization of the mandibular molars (+2.0 mm). Conclusions Forsus had mainly dentoalveolar effects and contributed largely to the overall therapeutic outcome. PMID:24892027

  14. Acoustic mode driven by fast electrons in TJ-II Electron Cyclotron Resonance plasmas

    NASA Astrophysics Data System (ADS)

    Sun, B. J.; Ochando, M. A.; López-Bruna, D.

    2016-08-01

    Intense harmonic oscillations in radiation signals (δ I/I∼ 5{%}) are commonly observed during Electron Cyclotron Resonance (ECR) heating in TJ-II stellarator plasmas at low line-averaged electron density, 0.15 < \\bar{n}e < 0.6 ×1019 \\text{m}-3 . The frequency agrees with acoustic modes. The poloidal modal structure is compatible with Geodesic Acoustic Modes (GAM) but an n \

  15. Mode-specific vibrational energy relaxation of amide I' and II' modes in N-methylacetamide/water clusters: intra- and intermolecular energy transfer mechanisms.

    PubMed

    Zhang, Yong; Fujisaki, Hiroshi; Straub, John E

    2009-04-02

    The mode-specific vibrational energy relaxation of the amide I' and amide II' modes in NMA-d(1)/(D(2)O)(n) (n = 0-3) clusters were studied using the time-dependent perturbation theory at the B3LYP/aug-cc-pvdz level. The amide modes were identified for each cluster based on the potential energy distribution of each mode. The vibrational population relaxation time constants were derived for the amide I' and II' modes. Results for the amide I' mode relaxation of NMA-d(1)/(D(2)O)(3) agree well with previous experimental results. The energy relaxation pathways were identified, and both intra- and intermolecular mechanisms were found to be important. The amide II' mode was identified in the energy transfer pathways from the excited amide I' mode of NMA-d(1)/(D(2)O)(n) (n = 1-3) clusters. The modes associated with methyl group deformation were found to play a role in the mechanism of energy transfer from both excited amide I' and II' modes. The kinetics of energy flow in the cluster were examined by solving a master equation describing the vibrational energy relaxation process from excited system mode as a multistep reaction with the third order Fermi resonance parameters as the reaction rate constants. The intramolecular energy transfer mechanism was found to dominate the short time energy flow dynamics, whereas the intermolecular mechanism was found to be dominant at longer times.

  16. A pentanuclear lead(II) complex based on a strapped porphyrin with three different coordination modes.

    PubMed

    Le Gac, Stéphane; Furet, Eric; Roisnel, Thierry; Hijazi, Ismail; Halet, Jean-François; Boitrel, Bernard

    2014-10-06

    We have previously described Pb(II) and Bi(III) bimetallic complexes with overhanging carboxylic acid strapped porphyrins in which one metal ion is bound to the N-core ("out-of-plane", OOP), whereas the second one is bound to the strap ("hanging-atop", HAT). In such complexes, the hemidirected coordination sphere of a HAT Pb(II) cation provides sufficient space for an additional binding of a neutral ligand (e.g., DMSO). Interestingly, investigations of the HAT metal coordination mode in a single strap porphyrin show that a HAT Pb(II) can also interact via intermolecular coordination bonds, allowing the self-assembly of two bimetallic complexes. In the pentanuclear Pb(II) complex we are describing in this Article, three different coordination modes were found. The OOP Pb(II) remains inert toward the supramolecular assembling process, whereas the HAT Pb(II) cation, in addition to its intramolecular carboxylate and regular exogenous acetate groups, coordinates an additional exogenous acetate. These two acetates are shared with a third lead(II) cation featuring a holo-directed coordination sphere, from which a centro-symmetric complex is assembled. Density functional theory calculations show some electron-density pockets in the vicinity of the hemidirected HAT Pb(II) atoms, which are associated with the presence of a stereochemically active lone pair of electrons. On the basis of the comparison with other HAT Pb(II) and Bi(III) systems, the "volume" of this lone pair correlates well with the bond distance distributions and the number of the proximal oxygen atoms tethered to the post-transition metal cation. It thus follows the order 6-coordinate Bi(III) > 6-coordinate Pb(II) > 5-coordinate Pb(II).

  17. Selection of stirling engine parameter and modes of joint operation with the Topaz II

    SciTech Connect

    Kirillov, E.Y.; Ogloblin, B.G.; Shalaev, A.I.

    1996-03-01

    In addition to a high-temperature thermionic conversion cycle, application of a low-temperature machine cycle, such as the Stirling engine, is being considered. To select the optimum mode for joint operation of the Topaz II system and Stirling engine, output electric parameters are obtained as a function of thermal power released in the TFE fuel cores. The hydraulic diagram used for joint operation of the Topaz II and the Stirling engine is considered. Requirements to hydraulic characteristics of the Stirling engine heat exchanges are formulated. Scope of necessary modifications to mount the Stirling Engine on the Topaz II is estimated. {copyright} {ital 1996 American Institute of Physics.}

  18. Influence of fatigue testing and cementation mode on the load-bearing capability of bovine incisors restored with crowns and zirconium dioxide posts.

    PubMed

    Nothdurft, F P; Schmitt, T; Motter, P J; Pospiech, P R

    2008-12-01

    The aim of the study was to evaluate the influence of fatigue and cementation mode on the fracture behavior of endodontically treated bovine incisors restored with zirconium dioxide posts and crowns. Forty-eight endodontically treated bovine primary incisors were restored with zirconium dioxide posts (Cerapost, Brasseler), composite build-ups, and crowns cast from a chromium cobalt alloy. In 16 teeth, each of the posts was cemented conventionally with KetacCem (3M ESPE) or adhesively with Panavia F (Kuraray) or RelyX UniCem (3M ESPE). One-half of the specimens in each group were subjected to thermocycling with 10,000 cycles at 5-55 degrees C and mechanical aging, loading the specimens at an angle of 45 degrees in 1,200,000 cycles with 50 N. Fracture resistance was determined by loading the specimens until fracture at an angle of 45 degrees to the long axis of the teeth. The loading test showed that neither cementation mode nor fatigue testing had an influence on the load bearing capability. Most specimens fractured in a favorable way, independent from the type of cementation.

  19. Low Cycle Fatigue Behavior of 316LN Stainless Steel Alloyed with Varying Nitrogen Content. Part II: Fatigue Life and Fracture Behavior

    NASA Astrophysics Data System (ADS)

    Prasad Reddy, G. V.; Sandhya, R.; Sankaran, S.; Mathew, M. D.

    2014-10-01

    Influence of nitrogen content on low cycle fatigue life and fracture behavior of 316LN stainless steel (SS) alloyed with 0.07 to 0.22 wt pct nitrogen is presented in this paper over a range of total strain amplitudes ( ±0.25 to 1.0 pct) in the temperature range from 773 K to 873 K (500 °C to 600 °C). The combined effect of nitrogen and strain amplitude on fatigue life is observed to be complex i.e., fatigue life either decreases/increases with increase in nitrogen content or saturates/peaks at 0.14 wt pct N depending on strain amplitude and temperature. Coffin-Manson plots (CMPs) revealed both single-slope and dual-slope strain-life curves depending on the test temperature and nitrogen content. 316LN SS containing 0.07 and 0.22 wt pct N showed nearly single-slope CMP at all test temperatures, while 316LN SS with 0.11 and 0.14 wt pct N exhibited marked dual-slope behavior at 773 K (500 °C) that changes to single-slope behavior at 873 K (600 °C). The changes in slope of CMP are found to be in good correlation with deformation substructural changes.

  20. Mode I, Mode II, and Mixed-Mode Fracture of Plasma-sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

    2003-01-01

    The mixed-mode fracture behavior of plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings was determined in air at 25 and 1316 C in asymmetric four-point flexure with single edge v-notched beam (SEVNB) test specimens. The mode I fracture toughness was found to be K(sub Ic) = 1.15 plus or minus 0.07 and 0.98 plus or minus 0.13 MPa the square root of m, respectively, at 25 and 1316 C. The respective mode II fracture toughness values were K(sub IIc) = 0.73 plus or minus 0.10 and 0.65 plus or minus 0.04 MPa the square root of m. Hence, there was an insignificant difference in either K(sub Ic or K(sub IIc) between 25 and 1316 C for the coating material, whereas there was a noticeable distinction between K(sub Ic) and K(sub IIc), resulting in K(sub IIc) per K(sub Ic) = 0.65 at both temperatures. The empirical mixed-mode fracture criterion best described the coatings' mixed-mode fracture behavior among the four mixed-mode fracture theories considered. The angle of crack propagation was in reasonable agreement with the minimum strain energy density criterion. The effect of the directionality of the coating material in on K(sub Ic) was observed to be insignificant, while its sintering effect at 1316 C on K(sub Ic) was significant.

  1. Small Fatigue Crack Growth and Failure Mode Transitions in a Ni-Base Superalloy at Elevated Temperature (Preprint)

    DTIC Science & Technology

    2010-02-01

    cavitation and oxidation at grain boundaries during the 6 second dwell. Figs. 3 (c) and (d) show SEM images for the fracture surfaces of small fatigue...in driving force due to crack branching along grain boundaries . These factors can be considered as being driven by the environmental exposure. At...oxidation at grain boundaries and the associated branching of the crack. The mechanism of dwell-time effect on the long crack behavior, which

  2. Bearing fatigue investigation 3

    NASA Technical Reports Server (NTRS)

    Nahm, A. H.; Bamberger, E. N.; Signer, H. R.

    1982-01-01

    The operating characteristics of large diameter rolling-element bearings in the ultra high speed regimes expected in advanced turbine engines for high performance aircraft were investigated. A high temperature lubricant, DuPont Krytox 143 AC, was evaluated at bearing speeds to 3 million DN. Compared to the results of earlier, similar tests using a MIL-L-23699 (Type II) lubricant, bearings lubricated with the high density Krytox fluid showed significantly higher power requirements. Additionally, short bearing lives were observed when this fluid was used with AISI M50 bearings in an air atmosphere. The primary mode of failure was corrosion initiated surface distress (fatigue) on the raceways. The potential of a case-carburized bearing to sustain a combination of high-tangential and hertzian stresses without experiencing race fracture was also investigated. Limited full scale bearing tests of a 120 mm bore ball bearing at a speed of 25,000 rpm (3 million DN) indicated that a carburized material could sustain spalling fatigue without subsequent propagation to fracture. Planned life tests of the carburized material had to be aborted, however, because of apparent processing-induced material defects.

  3. Damping Higher Order Modes in the PEP-II B-Factory Vertex Bellows

    SciTech Connect

    Weathersby, S.; Langton, J.; Novokhatski, A.; Seeman, J.; /SLAC

    2005-06-30

    Higher stored currents and shorter bunch lengths are requirements for increasing luminosity in colliding storage rings. As a result, more HOM power is generated in the IP region. This HOM power propagates to sensitive components causing undesirable heating, thus becoming a limiting issue for the PEP-II B-factory. HOM field penetration through RF shielding fingers has been shown to cause heating in bellows structures. To overcome these limitations, a proposal to incorporate ceramic absorbers within the bellows cavity to damp these modes is presented. Results show that the majority of modes of interest are damped, the effectiveness depending on geometrical considerations. An optimal configuration is presented for the PEP-II B-factory IR bellows component utilizing commercial grade ceramics with consideration for heat transfer requirements.

  4. Sliding mode control of the space nuclear reactor system TOPAZ II

    SciTech Connect

    Shtessel, Y.B.; Wyant, F.J.

    1996-03-01

    The Automatic Control System (ACS) of the space nuclear reactor power system TOPAZ II that generates electricity from nuclear heat using in-core thermionic converters is considered. Sliding Mode Control Technique was applied to the reactor system controller design in order to provide the robust high accuracy following of a neutron (thermal) power reference profile in a start up regime and a payload electric power (current) reference profile following in an operation regime. Extensive simulations of the TOPAZ II reactor system with the designed sliding mode controllers showed improved accuracy and robustness of the reactor system performances in a start up regime and in an electric power supply regime as well. {copyright} {ital 1996 American Institute of Physics.}

  5. Mode-II Crack Problem for a Long Rectangular Slab of Superconductor under an Electromagnetic Force

    NASA Astrophysics Data System (ADS)

    Gao, Zhi-Wen; Zhou, You-He

    2009-02-01

    We present a theoretical analysis to the fracture parameters of the large single domain YBCO superconductor with a tangential line crack under electromagnetic force. The mode-II fracture parameters are obtained due to coupled finite element and infinite element method, and the numerical results are conducted for two activation processes. For a zero-field cooling (ZFC) magnetization process, in the process of magnetic field descent, the larger the applied field is, the larger the stress intensity factors. In the case of field cooling (FC) magnetization process, the stress intensity factors have obvious differences between the two cases of bfc > 1 and bfc >= 1. Additionally, J-integral characteristic is obtained, and according to these results, the mode-II crack growth trend is predicted. These results are benefit for us to understand the fracture mechanism of superconductor both in theory and application.

  6. Mode II interlaminar fracture toughness of carbon fabric composite laminates with carbon nanotube oriented by magnet

    NASA Astrophysics Data System (ADS)

    Xu, Xinguang; Zhou, Zhenggang

    2017-03-01

    Inspired by the residual iron nanoparticles wrapped in the CNTs tips, we developed a method to induce efficient orientation of multiwalled CNTs bundles by relatively low magnetic fields. Laminates were fabricated to investigate the effect of magnet oriented CNTs on GIIC properties. Microstructure anisotropy of nanotube bundles demonstrated the orientation of CNT bundles by magnet. Furthermore, the application of magnet increased mode II interlaminar fracture toughness by 29% compared to plain laminates.

  7. Measurements and Analysis of Longitudinal HOM Driven Coupled Bunch Modes in PEP-II Rings

    SciTech Connect

    Mastorides, T; Rivetta, C.; Fox, J.D.; Winkle, D.Van; /SLAC

    2008-07-07

    The growth rates of the longitudinal higher-order impedance-driven beam modes have greatly increased since the initial PEP-II design and commissioning. This increase is attributed to the addition of 6 1.2MW RF stations with 8 accelerating cavities in the HER and 2 1.2MW RF stations with 4 accelerating cavities in the LER, which allowed operations at twice the design current and almost four times the luminosity. As a result, the damping requirements for the longitudinal feedback have greatly increased since the design, and the feedback filters and control schemes have evolved during PEP-II operations. In this paper, growth and damping rate data for the higher-order mode (HOM) driven coupled-bunch modes are presented from various PEP-II runs and are compared with historical estimates during commissioning. The effect of noise in the feedback processing channel is also studied. Both the stability and performance limits of the system are analyzed.

  8. Effective representation of amide III, II, I, and A modes on local vibrational modes: Analysis of ab initio quantum calculation results

    NASA Astrophysics Data System (ADS)

    Hahn, Seungsoo

    2016-10-01

    The Hamiltonian matrix for the first excited vibrational states of a protein can be effectively represented by local vibrational modes constituting amide III, II, I, and A modes to simulate various vibrational spectra. Methods for obtaining the Hamiltonian matrix from ab initio quantum calculation results are discussed, where the methods consist of three steps: selection of local vibrational mode coordinates, calculation of a reduced Hessian matrix, and extraction of the Hamiltonian matrix from the Hessian matrix. We introduce several methods for each step. The methods were assessed based on the density functional theory calculation results of 24 oligopeptides with four different peptide lengths and six different secondary structures. The completeness of a Hamiltonian matrix represented in the reduced local mode space is improved by adopting a specific atom group for each amide mode and reducing the effect of ignored local modes. The calculation results are also compared to previous models using C=O stretching vibration and transition dipole couplings. We found that local electric transition dipole moments of the amide modes are mainly bound on the local peptide planes. Their direction and magnitude are well conserved except amide A modes, which show large variation. Contrary to amide I modes, the vibrational coupling constants of amide III, II, and A modes obtained by analysis of a dipeptide are not transferable to oligopeptides with the same secondary conformation because coupling constants are affected by the surrounding atomic environment.

  9. Effective representation of amide III, II, I, and A modes on local vibrational modes: Analysis of ab initio quantum calculation results.

    PubMed

    Hahn, Seungsoo

    2016-10-28

    The Hamiltonian matrix for the first excited vibrational states of a protein can be effectively represented by local vibrational modes constituting amide III, II, I, and A modes to simulate various vibrational spectra. Methods for obtaining the Hamiltonian matrix from ab initio quantum calculation results are discussed, where the methods consist of three steps: selection of local vibrational mode coordinates, calculation of a reduced Hessian matrix, and extraction of the Hamiltonian matrix from the Hessian matrix. We introduce several methods for each step. The methods were assessed based on the density functional theory calculation results of 24 oligopeptides with four different peptide lengths and six different secondary structures. The completeness of a Hamiltonian matrix represented in the reduced local mode space is improved by adopting a specific atom group for each amide mode and reducing the effect of ignored local modes. The calculation results are also compared to previous models using C=O stretching vibration and transition dipole couplings. We found that local electric transition dipole moments of the amide modes are mainly bound on the local peptide planes. Their direction and magnitude are well conserved except amide A modes, which show large variation. Contrary to amide I modes, the vibrational coupling constants of amide III, II, and A modes obtained by analysis of a dipeptide are not transferable to oligopeptides with the same secondary conformation because coupling constants are affected by the surrounding atomic environment.

  10. A kinetic model for type I and II IP3R accounting for mode changes.

    PubMed

    Siekmann, Ivo; Wagner, Larry E; Yule, David; Crampin, Edmund J; Sneyd, James

    2012-08-22

    Based upon an extensive single-channel data set, a Markov model for types I and II inositol trisphosphate receptors (IP(3)R) is developed. The model aims to represent accurately the kinetics of both receptor types of IP(3)R depending on the concentrations of inositol trisphosphate (IP(3)), adenosine trisphosphate (ATP), and intracellular calcium (Ca(2+)). In particular, the model takes into account that for some combinations of ligands the IP(3)R switches between extended periods of inactivity alternating with intervals of bursting activity (mode changes). In a first step, the inactive and active modes are modeled separately. It is found that, within modes, both receptor types are ligand-independent. In a second step, the submodels are connected by transition rates. Ligand-dependent regulation of the channel activity is achieved by modulating these transitions between active and inactive modes. As a result, a compact representation of the IP(3)R is obtained that accurately captures stochastic single-channel dynamics including mode changes in a model with six states and 10 rate constants, only two of which are ligand-dependent.

  11. Elevated temperature biaxial fatigue

    NASA Technical Reports Server (NTRS)

    Jordan, E. H.

    1984-01-01

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

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

    NASA Astrophysics Data System (ADS)

    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.

  13. Isothermal fatigue of an aluminide-coated single-crystal superalloy: Part II. effects of brittle precracking

    NASA Astrophysics Data System (ADS)

    Totemeier, T. C.; Gale, W. F.; King, J. E.

    1996-02-01

    The effect of brittle coating precracking on the fatigue behavior of a high-activity aluminide-coated single-crystal nickel-base superalloy has been studied using hollow cylindrical specimens at test temperatures of 600 °, 800 °, and 1000 °. Three types of precrack were studied: narrow precracks formed at room temperature, wide precracks formed at room temperature, and narrow precracks formed at elevated temperature. The effect of precracking on fatigue life at 600 ° was found to depend strongly on the type of precrack. No failure was observed for specimens with narrow room-temperature precracks because of crack arrest via an oxidation-induced crack closure mechanism, while the behavior of wide precracks and precracks formed at elevated temperature mirrored the non-precracked behavior. Crack retardation also occurred for narrow room-temperature precracks tested at 800 °—in this case, fatigue cracks leading to failure initiated in a layer of recrystallized grains on the inside surface of the specimen. A significant reduction in fatigue life at 800 ° relative to non-precracked specimens was observed for wide precracks and elevated temperature precracks. The presence of precracks bypassed the initiation and growth of coating fatigue cracks necessary for failure in non-precracked material. No effect of precracking was observed at 1000 °.

  14. Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments. Part II. Microscopic behavior

    SciTech Connect

    Mills, W J; James, L A

    1981-05-01

    The microstructural features that influenced the room and elevated temperature fatigue-crack growth behavior of as-welded, conventional heat-treated, and modified heat-treated Alloy 718 GTA weldments were studied. Electron fractographic examination of fatigue fracture surfaces revealed that operative fatigue mechanisms were dependent on microstructure, temperature and stress intensity factor. All specimens exhibited three basic fracture surface appearances at temperatures up to 838{sup 0}C: crystallographic faceting at low stress intensity range ({Delta}K) levels, striation formation at intermediate values, and dimples coupled with striations in the highest {Delta}K regime. At 649{sup 0}C, the heat-treated welds exhibited extensive intergranular cracking. Laves and {delta}particles in the conventional heat-treated material nucleated microvoids ahead of the advancing crack front and caused an overall acceleration in crack growth rates at intermediate and high {Delta}K levels. The modified heat treatment removed many of these particles from the weld zone, thereby improving its fatigue resistance. The dramatically improved fatigue properties exhibited by the as-welded material was attributed to compressive residual stresses introduced by the welding process. 16 figures.

  15. Trapped modes in the PEP-II B-Factory Interaction Region

    SciTech Connect

    Henestroza, E.; Heifets, S.; Zolotorev, M.

    1995-04-01

    The design of the PEP-II B-Factory Interaction Region is based primarily on beam-stay-clear requirements and on synchrotron radiation background considerations (masks are required to shield the detector beam pipe from all sources of synchrotron radiation). A complicated 3-dimensional structure results from these requirements. A high intensity beam traversing this structure will generate wake fields that lead to energy deposition on the beam pipe, as well as to decelerating and deflecting forces acting back on the beam. Computation of wake fields and impedances in frequency-domain and time-domain using 2-D and 3-D electromagnetic codes revealed the existence of trapped modes in the interaction region, which if not controlled could enhance the higher order model heating of the beam pipe. We will present the simulation results and the design strategy to avoid resonant conditions between these trapped modes and the bunch train frequency.

  16. Subcritical crack growth under mode I, II, and III loading for Coconino sandstone

    NASA Astrophysics Data System (ADS)

    Ko, Tae Young

    In systems subjected to long-term loading, subcritical crack growth is the principal mechanism causing the time-dependent deformation and failure of rocks. Subcritical crack growth is environmentally-assisted crack growth, which can allow cracks to grow over a long period of time at stresses far smaller than their failure strength and at tectonic strain rates. The characteristics of subcritical crack growth can be described by a relationship between the stress intensity factor and the crack velocity. This study presents the results of studies conducted to validate the constant stress-rate test for determining subcritical crack growth parameters in Coconino sandstone, compared with the conventional testing method, the double torsion test. The results of the constant stress-rate test are in good agreement with the results of double torsion test. More importantly, the stress-rate tests can determine the parameter A with a much smaller standard deviation than the double torsion test. Thus the constant stress-rate test seems to be both a valid and preferred test method for determining the subcritical crack growth parameters in rocks. We investigated statistical aspects of the constant stress-rate test. The effects of the number of tests conducted on the subcritical crack growth parameters were examined and minimum specimen numbers were determined. The mean and standard deviation of the subcritical crack growth parameters were obtained by randomly selecting subsets from the original strength data. In addition, the distribution form of the subcritical crack growth parameters and the relation between the parameter n and A were determined. We extended the constant stress-rate test technique to modes II and III subcritical crack growth in rocks. The experimental results of the modes I, II and III tests show that the values of the subcritical crack growth parameters are similar to each other. The subcritical crack growth parameter n value for Coconino sandstone has the range

  17. Normal Modes for Dynamic Motions of a Topoisomerase II enzyme upon DNA-Binding and Bending

    NASA Astrophysics Data System (ADS)

    Mentes, Ahmet

    We have used Molecular Dynamics (MD) simulation methods and two analytical approaches (the Gaussian Network Model (GNM) and Anisotropic Network Model (ANM)) to investigate the internal dynamic motions of the S. cerevisiae Topoisomerase (TopoII) during the first step of its catalytic cycle. At the initial state of the first step of its catalytic cycle, the protein and a 34 bp straight-DNA structure have no interaction. At the final state of the cycle, we have the bended-DNA/TopoII complex where the protein binds to DNA and, at this stage, the protein binds and bends the DNA, just before the DNA cleavage by TopoII. Normal mode analysis is used to characterize the functional flexibility of the protein, especially the C-gate domain closing/opening during the DNA binding/bending process and before DNA cleavage. Because of its clinical importance, our study might be helpful to better understand the next steps of its catalytic cycle and may provide new insight into the dynamics and structure of other TopoII-DNA complexes.

  18. Characterization of Mode I and mixed-mode delamination growth in T300/5208 graphite/epoxy

    NASA Technical Reports Server (NTRS)

    Ramkumar, R. L.; Whitcomb, J. D.

    1985-01-01

    The roles played by Mode I and Mode II strain-energy release rates (G-I and G-II, respectively) in inducing delamination growth under static and fatigue loading were investigated, using T300/5208 graphite/epoxy specimens. Double cantilever beam (DCB) specimens and cracked lap shear (CLS) specimens were used for pure Mode I and mixed-mode tests, respectively. Fatigue-induced delamination growth was characterized by constant-amplitude fatigue tests at a minimum to maximum cyclic load ratio of 0.05 and a frequency of 10 Hz. During the tests, the maximum and minimum strain-energy release rates (Gmax, Gmin) and the delamination growth rate (da/dN) were monitored. Static tests on mixed-mode CLS specimens measured the total strain-energy release rate, which was broken into G-I and G-II components using finite-element analysis. A power-law relationship between da/dN and G-Imax, and da/dN and Gmax were obtained from fatigue test results on DCB and CLS specimens, respectively. The power law for a pure Mode II delamination was derived from CLS results by subtracting the contribution due to G-I.

  19. Effects of Temperature on Mode II Fracture Toughness of Multidirectional CFRP Laminates

    NASA Astrophysics Data System (ADS)

    Kim, Hyoung Soo; Wang, Wen Xue; Takao, Yoshihiro; Ben, Goichi

    End notched flexure (ENF) tests were performed to investigate the effects of temperature and fiber orientation on Mode II interlaminar fracture behavior, GIIC (GII at the crack initiation), of carbon fiber-reinforced epoxy composites, T800H/#3631. The values of GIIC for three kinds of laminates, [012//012], [22.5/-22.5/08/-22.5/22.5//-22.5/22.5/08/22.5/-22.5] and [45/-45/08/-45/45//-45/45/08/45/-45], with a pre-cracked interface, that is // in each laminate, were obtained at three temperatures, i.e. -100°C, 25°C and 150°C. It is shown that GIIC is obviously affected by the temperature and fiber orientation. The scanning electron microscope (SEM) observation was also carried out to investigate the fracture surface. SEM analysis suggested that the decreased Mode II interlaminar fracture toughness for all kinds of specimens at high temperature could be attributed to temperature-induced matrix property change or fiber-matrix interfacial weakening.

  20. Damage mechanisms and failure modes of cortical bone under components of physiological loading.

    PubMed

    George, W T; Vashishth, D

    2005-09-01

    Fatigue damage development in cortical bone was investigated in vitro under different mechanical components of physiological loading including tension, compression, and torsion. During each test, stress and strain data were collected continuously to monitor and statistically determine the occurrence of the primary, secondary, and tertiary stages associated with fatigue and/or creep failure of bone. The resultant microdamage and failure modes were identified by histological and fractographic analysis, respectively. The tensile group demonstrated Mode I cracking and the three classic stages of fatigue and creep suggesting a low crack initiation threshold, steady crack propagation and final failure by coalescence of microcracks. In contrast, the compressive group displayed Mode II cracking and a two-stage fatigue behavior with limited creep suggesting a high crack initiation threshold followed by a sudden fracture. The torsion group also displayed a two-stage fatigue profile but demonstrated extensive damage from mixed mode (Modes II and III) microcracking and predominant time-dependent damage. Thus, fatigue behavior of bone was found to be uniquely related to the individual mechanical components of physiological loading and the latter determined the specific damage mechanisms associated with fatigue fracture.

  1. Fatigue Behavior of a Cross-Ply Metal Matrix Composite at Elevated Temperature Under Strain Controlled Mode.

    DTIC Science & Technology

    1994-12-01

    the higher strains, matrix plasticity was predicted, but could not be experimentally confirmed. A large scatter in the elastic moduli for the 0/90...1991. 114 22. Nimmer, R. P. et al. "Fiber Array Geometry Effects Upon Composite Transverse Tensile Behavior," Titanium Aluminide Composites. February... Titanium , Silicon Carbide, Strain Control Mode 17. SECURITY CLASSIFICATION I18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFIKATION 20. LIMITATION OF

  2. Linear growth rates of types I and II convective modes within the rotating-cone boundary layer

    NASA Astrophysics Data System (ADS)

    Garrett, S. J.

    2010-04-01

    Experimental observations have shown that the transition characteristics of the boundary-layer flow over rotating cones depends on the cone half-angle. In particular, pairs of counter-rotating Görtler-type vortices are observed over cones with slender half-angles and co-rotating vortices are observed over broad cones. Garrett et al (2009 J. Fluid Mech. 622 209-32) have hypothesized the existence of a centrifugal instability mode over slender cones that is more dangerous than the types I (crossflow) and II (streamline curvature) modes which dominate over rotating disks and broad cones. Work is currently underway to clarify this alternative mode; however, a clear understanding of the growth rates of types I and II modes is crucial to the ultimate understanding of how the dominant mode changes with half-angle. In this paper, we demonstrate that the maximum growth rate for types I and II modes decreases with reduced half-angle, which clears the way for the dominance of the alternative instability mode. Furthermore, it is suggested that vortices travelling at 75% of the cone surface speed will be selected over smooth, clean rotating cones with half-angle such that the type I mode is dominant. Interestingly, this vortex speed has been experimentally observed by Kobayashi and Arai within the rotating-sphere boundary layer.

  3. Elevated temperature biaxial fatigue

    NASA Technical Reports Server (NTRS)

    Jordan, E. H.

    1985-01-01

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

  4. Materials characterization of silicon carbide reinforced titanium (Ti/SCS-6) metal matrix composites: Part I. Tensile and fatigue behavior

    NASA Astrophysics Data System (ADS)

    Liaw, P. K.; Diaz, E. S.; Chiang, K. T.; Loh, D. H.

    1995-12-01

    Flexural fatigue behavior was investigated on titanium (Ti-15V-3Cr) metal matrix composites reinforced with cross-ply, continuous silicon carbide (SiC) fibers. The titanium composites had an eightply (0, 90, +45, -45 deg) symmetric layup. Fatigue life was found to be sensitive to fiber layup sequence. Increasing the test temperature from 24 °C to 427 °C decreased fatigue life. Interface debonding and matrix and fiber fracture were characteristic of tensile behavior regardless of test temperature. In the tensile fracture process, interface debonding between SiC and the graphite coating and between the graphite coating and the carbon core could occur. A greater amount of coating degradation at 427 °C than at 24 °C reduced the Ti/SiC interface bonding integrity, which resulted in lower tensile properties at 427 °C. During tensile testing, a crack could initiate from the debonded Ti/SiC interface and extend to the debonded interface of the neighboring fiber. The crack tended to propagate through the matrix and the interface. Dimpled fracture was the prime mode of matrix fracture. During fatigue testing, four stages of flexural deflection behavior were observed. The deflection at stage I increased slightly with fatigue cycling, while that at stage II increased significantly with cycling. Interestingly, the deflection at stage III increased negligibly with fatigue cycling. Stage IV was associated with final failure, and the deflection increased abruptly. Interface debonding, matrix cracking, and fiber bridging were identified as the prime modes of fatigue mechanisms. To a lesser extent, fiber fracture was observed during fatigue. However, fiber fracture was believed to occur near the final stage of fatigue failure. In fatigued specimens, facet-type fracture appearance was characteristic of matrix fracture morphology. Theoretical modeling of the fatigue behavior of Ti/SCS-6 composites is presented in Part II of this series of articles.

  5. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part II. Fatigue crack growth rate

    NASA Astrophysics Data System (ADS)

    Margolin, B.; Minkin, A.; Smirnov, V.; Sorokin, A.; Shvetsova, V.; Potapova, V.

    2016-11-01

    The experimental data on the fatigue crack growth rate (FCGR) have been obtained for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various radiation swelling. The performed study of the fracture mechanisms for cracked specimens under cyclic loading has explained why radiation swelling affects weakly FCGR unlike its effect on fracture toughness. Mechanical modeling of fatigue crack growth has been carried out and the dependencies for prediction of FCGR in irradiated austenitic steel with and with no swelling are proposed and verified with the obtained experimental results. As input data for these dependencies, FCGR for unirradiated steel and the tensile mechanical properties for unirradiated and irradiated steels are used.

  6. Effect of TE Mode Power on the PEP II LER BPM System

    SciTech Connect

    Ng, Cho-K

    2011-08-26

    The beam chamber of the PEP-II B-Factory Low Energy Ring (LER) arc sections is connected to an antechamber for the absorption of synchrotron radiation on discrete photon stops. The presence of the antechamber substantially reduces the cutoff frequency of the vacuum chamber and, in particular, allows the propagation of higher-order-mode (HOM) TE power generated by beamline components at the BPM signal processing frequency. Calculations of the transmission properties of the TE mode in different sections of the vacuum chamber show that the power is trapped between widely separated bellows in the arc sections. Because of the narrow signal bandwidth and weak coupling of the TE mode to the BPM buttons, the noise contributed by the HOM TE power will not produce a noticeable effect on the BPM position signal voltage. The LER arc vacuum chamber employs an antechamber with a discrete photon stop for absorption of synchrotron radiation and with pumps for maintaining pressure below 10 nTorr [1]. The horizontal dimensions of the antechambers at the pumping chamber section and the magnet chamber section are larger or comparable to that of the beam chamber. Because of the increase in the horizontal dimension, the cutoff frequency of the TE10-like mode (in rectangular coordinates) of the vacuum chamber is considerably reduced and, in particular, is less than the BPM signal processing frequency at 952 MHz. TE power propagating in the vacuum chamber will penetrate through the BPM buttons and will affect the pickup signal if its magnitude is not properly controlled. It is the purpose of this note to clarify various issues pertaining to this problem. TE power is generated when the beam passes a noncylindrically symmetric beamline component such as the RF cavity, the injection region, the IR crotch and the IP region. The beampipes connected to these components have TE cutoff frequencies greater than 952 MHz (for example, the TE cutoff frequency of the RF cavity beampipe is 1.8 GHz

  7. Electron radiation effects on Mode II interlaminar fracture toughness of GFRP and CFRP composites

    SciTech Connect

    Takeda, N.; Tohdoh, M.; Takahashi, K.

    1989-01-01

    The degradation properties of epoxy-based fiber-reinforced-plastics (FRP) composites irradiated by high-energy electrons were studied using the Mode II interlaminar fracture toughness G/sub IIc/, measured by end-notched flexure tests. The radiation-induced degradation mechanisms were investigated through G/sub IIc/ and the scanning electron micrographs of fracture surfaces. For GFRP, the significant decrease in G/sub IIc/ was found. Debonding of glass fibers and epoxy matrix (or degradation of silane coupling agents) plays an important role in degradation in addition to resin degradation. Thus, the improvement of the radiation resistance of fiber-resin interfaces as well as matrix itself is of supreme importance in order to increase the radiation resistance of GFRP. For CFRP, on the other hand, no degradation in fiber-resin interfaces was found and the slight decrease in G/sub IIc/ seems to be due to the resin degradation. 18 references, 6 figures.

  8. In-plane response and mode II fracture response of Z-pin woven laminates

    NASA Astrophysics Data System (ADS)

    Huang, Hseng-Ji

    Textile composites are proven to be an attractive choice over traditional pre-preg based composites because of reduced manufacturing costs and improved transverse mechanical properties. However, similar to traditional pre-preg composites, 2D laminates consisting of multiple layers of laminae still suffer from delamination under impact or transverse loads. Z-pin (carbon fiber of small diameter inserted in the thickness direction-z) composites are a means to provide higher through-thethickness stiffness and strength that 2D woven composites lack. In this thesis, The influences of Z-pin density and Z-pin diameter on the response of Z-pin under in-plane loads (compression) and transverse loads (mode II fracture) are examined. Both experiments and numerical simulations were performed to address the problems. Compression tests were conducted first and failure mechanism in each loading scenario was identified, through optical and mechanical measurements, during and after the tests. This was followed by the development of different numerical models of varying degree of sophistication, which include in-plane 2D models, (used to study fiber distortion and damage due to Z-pin insertion), multi-layer 2D models, (used to provide an inexpensive multi-layer model to study the effect of phase difference due to stacking consolidation), and multi-layer-multi-cell models (used to provide a full 3D multi-layer and multi-representative unit cell description). The second part of this thesis investigates the mode II fracture response under static and dynamic loading. Discrete Cohesive Zone Model (DCZM) was adopted to obtain the fracture toughness in conjunction with experimental data. In dynamic test, a crack advance gage (CAG) was designed to capture the exact time when the crack begins to propagate. By use of these CAGs, the corresponding crack propagation speed between different CAGs can be computed accordingly. These observations are supplemented through high speed optical images

  9. Mixed-mode I+II fracture characterization of human cortical bone using the Single Leg Bending test.

    PubMed

    Silva, F G A; de Moura, M F S F; Dourado, N; Xavier, J; Pereira, F A M; Morais, J J L; Dias, M I R

    2016-02-01

    Mixed-mode I+II fracture characterization of human cortical bone was analyzed in this work. A miniaturized version of the Single Leg Bending test (SLB) was used owing to its simplicity. A power law criterion was verified to accurately describe the material fracture envelop under mixed-mode I+II loading. The crack tip opening displacements measured by digital image correlation were used in a direct method to determine the cohesive law mimicking fracture behavior of cortical bone. Cohesive zone modeling was used for the sake of validation. Several fracture quantities were compared with the experimental results and the good agreement observed proves the appropriateness of the proposed procedure for fracture characterization of human bone under mixed-mode I+II loading.

  10. Damping higher order modes in the PEP-II B-Factory storage ring collider

    NASA Astrophysics Data System (ADS)

    Weathersby, Stephen

    2007-05-01

    The PEP-II B-Factory storage ring collider at SLAC provides crucial experimental evidence for the physics of CP violation. To investigate rare B-meson decays requires high luminosity which comes mainly from increasing bunch currents and reducing bunch sizes. Electromagnetic effects of intense bunch fields in the form of wake fields couple into accelerator components, inducing Joule heating at levels detrimental to vacuum chamber components. Additionally, wake fields contribute to beam instability, decreasing luminosity. These effects are limiting B-factory performance. Computer simulations and experimental evidence indicate that beam collimators produce wake fields in the form of dipole and quadrupole waveguide modes which can propagate tens of meters from their source before depositing energy at remote locations. Simulations confirm that coupling through narrow slots into bellows cavities occurs for beam pipe modes. Two proposals are set forth to mitigate wake field effects. The first proposal is to reduce the quality factor of resonant structures with a water cooled dielectric lossy material. Electromagnetic energy coupling into resonant structures can be isolated and safely dissipated. Prototype devices have been built and have been shown to reduce resistive heating in large pumping chambers coupled to the beam chamber. Designs and simulations which incorporate such techiques into bellows devices are presented. The second proposal incorporates novel devices introduced in the accelerator vacuum chamber which selectively traps dipole and quadrupole propagating wake fields before they can couple into sensitive beam line components without introducing impedance to the beam. Scattering parameter analysis is used to tailor device response to specific modes. Dangerous modes are extracted from the beam chamber, trapped and dissipated in a water cooled lossy material. Modes which represent an impedance to the beam are not affected. After design optimization, production

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

    PubMed

    Rangan, Suresh; Van Dongen, Hans P A

    2013-02-01

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

  12. Analysis of the Numerical and Geometrical Parameters Influencing the Simulation of Mode I and Mode II Delamination Growth in Unidirectional and Textile Composites

    NASA Astrophysics Data System (ADS)

    Jacques, S.; De Baere, I.; Van Paepegem, W.

    2015-12-01

    The reliability of composite structures depends, among other damage mechanisms, on their ability to withstand delaminations. In order to have a better understanding of the cohesive zone method technique for delamination simulations, a complete analysis of the multiple parameters influencing the results is necessary. In this paper the work is concentrated on the cohesive zone method using cohesive elements. First a summary of the theory of the cohesive zone method is given. A numerical investigation on the multiple parameters influencing the numerical simulation of the mode I and mode II delamination tests has been performed. The parameters such as the stabilization method, the output frequency, the friction and the computational efficiency have been taken into account. The results will be compared to an analytical solution obtained by linear elastic fracture mechanics. Additionally the numerical simulation results will be compared to the experimental results of a glass-fibre reinforced composite material for the mode I Double Cantilever Beam (DCB) and to a carbon fibre 5-harness satin weave reinforced polyphenylene sulphide composite for the mode I DCB and mode II End Notched Flexure (ENF).

  13. Pseudo-type-II tuning behavior and mode identification in whispering gallery optical parametric oscillators.

    PubMed

    Meisenheimer, Sarah-Katharina; Fürst, Josef Urban; Schiller, Annelie; Holderied, Florian; Buse, Karsten; Breunig, Ingo

    2016-06-27

    Wavelength tuning of conventional mirror-based optical parametric oscillators (OPOs) exhibits parabolically-shaped tuning curves (type-0 and type-I phase matching) or tuning branches that cross each other with a finite slope (type-II phase matching). We predict and experimentally prove that whispering gallery OPOs based on type-0 phase matching show both tuning behaviors, depending on whether the mode numbers of the generated waves coincide or differ. We investigate the wavelength tuning of optical parametric oscillation in a millimeter-sized radially-poled lithium niobate disk pumped at 1 μm wavelength generating signal and idler waves between 1.7 and 2.6 μm wavelength. Our experimental findings excellently coincide with the theoretical predictions. The investigated whispering gallery optical parametric oscillator combines the employment of the highest nonlinear-optical coefficient of the material with a controlled type-II-like wavelength tuning and with the possibility of self-phase locking.

  14. FATIGUE OF DENTAL CERAMICS

    PubMed Central

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

    2013-01-01

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

  15. Creep-Fatigue Interaction Testing

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.

    2001-01-01

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

  16. Postdialysis fatigue.

    PubMed

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

    1996-11-01

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

  17. Fracture characterization of human cortical bone under mode II loading using the end-notched flexure test.

    PubMed

    Silva, F G A; de Moura, M F S F; Dourado, N; Xavier, J; Pereira, F A M; Morais, J J L; Dias, M I R; Lourenço, P J; Judas, F M

    2016-10-25

    Fracture characterization of human cortical bone under mode II loading was analyzed using a miniaturized version of the end-notched flexure test. A data reduction scheme based on crack equivalent concept was employed to overcome uncertainties on crack length monitoring during the test. The crack tip shear displacement was experimentally measured using digital image correlation technique to determine the cohesive law that mimics bone fracture behavior under mode II loading. The developed procedure was validated by finite element analysis using cohesive zone modeling considering a trapezoidal with bilinear softening relationship. Experimental load-displacement curves, resistance curves and crack tip shear displacement versus applied displacement were used to validate the numerical procedure. The excellent agreement observed between the numerical and experimental results reveals the appropriateness of the proposed test and procedure to characterize human cortical bone fracture under mode II loading. The proposed methodology can be viewed as a novel valuable tool to be used in parametric and methodical clinical studies regarding features (e.g., age, diseases, drugs) influencing bone shear fracture under mode II loading.

  18. Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-standing Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

    2003-01-01

    Strength, fracture toughness and fatigue behavior of free-standing thick thermal barrier coatings of plasma-sprayed ZrO2-8wt % Y2O3 were determined at ambient and elevated temperatures in an attempt to establish a database for design. Strength, in conjunction with deformation (stress-strain behavior), was evaluated in tension (uniaxial and trans-thickness), compression, and uniaxial and biaxial flexure; fracture toughness was determined in various load conditions including mode I, mode II, and mixed modes I and II; fatigue or slow crack growth behavior was estimated in cyclic tension and dynamic flexure loading. Effect of sintering was quantified through approaches using strength, fracture toughness, and modulus (constitutive relations) measurements. Standardization issues on test methodology also was presented with a special regard to material's unique constitutive relations.

  19. Particle simulation of radio frequency stabilization of the flute mode in a tandem mirror. II. Perpendicular antenna

    SciTech Connect

    Abe, H.; Kadoya, Y.

    1988-10-01

    A two-and-a-half-dimensional electromagnetic particle code PS2M (J. Phys. Soc. Jpn. 56, 3899 (1987)) is used to study how an electric field applied perpendicularly to the magnetic field affects the radio frequency stabilization of flute modes in a tandem mirror plasma. The electric field perpendicular to the magnetic field stabilizes or destabilizes the flute mode through the mechanism of the ponderomotive force acting on electrons and ions and through the mechanism of sideband coupling. In the simulations two typical examples have been shown: (i) when the sideband coupling effects (in which the electron terms are dominant) stabilize the flute modes and (ii) when the perpendicular ponderomotive force acting on the electrons destabilizes the flute modes.

  20. Interlaminar shear fracture toughness and fatigue thresholds for composite materials

    NASA Technical Reports Server (NTRS)

    Obrien, T. Kevin; Murri, Gretchen B.; Salpekar, Satish A.

    1987-01-01

    Static and cyclic end notched flexure tests were conducted on a graphite epoxy, a glass epoxy, and graphite thermoplastic to determine their interlaminar shear fracture toughness and fatigue thresholds for delamination in terms of limiting values of the mode II strain energy release rate, G-II, for delamination growth. The influence of precracking and data reduction schemes are discussed. Finite element analysis indicated that the beam theory calculation for G-II with the transverse shear contribution included was reasonably accurate over the entire range of crack lengths. Cyclic loading significantly reduced the critical G-II for delamination. A threshold value of the maximum cyclic G-II below which no delamination occurred after one million cycles was identified for each material. Also, residual static toughness tests were conducted on glass epoxy specimens that had undergone one million cycles without delamination. A linear mixed-mode delamination criteria was used to characterize the static toughness of several composite materials; however, a total G threshold criterion appears to characterize the fatigue delamination durability of composite materials with a wide range of static toughness.

  1. Interlaminar shear fracture toughness and fatigue thresholds for composite materials

    NASA Technical Reports Server (NTRS)

    O'Brien, T. Kevin; Murri, Gretchen B.; Salpekar, Satish A.

    1989-01-01

    Static and cyclic end notched flexure tests were conducted on a graphite epoxy, a glass epoxy, and graphite thermoplastic to determine their interlaminar shear fracture toughness and fatigue thresholds for delamination in terms of limiting values of the mode II strain energy release rate, G-II, for delamination growth. The influence of precracking and data reduction schemes are discussed. Finite element analysis indicated that the beam theory calculation for G-II with the transverse shear contribution included was reasonably accurate over the entire range of crack lengths. Cyclic loading significantly reduced the critical G-II for delamination. A threshold value of the maximum cyclic G-II below which no delamination occurred after one million cycles was identified for each material. Also, residual static toughness tests were conducted on glass epoxy specimens that had undergone one million cycles without delamination. A linear mixed-mode delamination criteria was used to characterize the static toughness of several composite materials; however, a total G threshold criterion appears to characterize the fatigue delamination durability of composite materials with a wide range of static toughness.

  2. Effect of magnetic configuration on frequency of NBI-driven Alfvén modes in TJ-II

    NASA Astrophysics Data System (ADS)

    Melnikov, A. V.; Ochando, M.; Ascasibar, E.; Castejon, F.; Cappa, A.; Eliseev, L. G.; Hidalgo, C.; Krupnik, L. I.; Lopez-Fraguas, A.; Liniers, M.; Lysenko, S. E.; de Pablos, J. L.; Perfilov, S. V.; Sharapov, S. E.; Spong, D. A.; Jimenez, J. A.; Ufimtsev, M. V.; Breizman, B. N.; HIBP Group; the TJ-II Team

    2014-12-01

    Excitation of modes in the Alfvénic frequency range, 30 kHz < fAE < 300 kHz, was observed in hydrogen plasma heated by hydrogen neutral beam injection (NBI) in the TJ-II heliac. Co-field and counter-field NBI were injected, and the components of the poloidal magnetic field were varied one by one and in combinations, in order to investigate the beam-driven modes over an extended range of the rotational transform values, 1.51<\\unicode{7548} (0)<1.67 . Taking advantage of the unique TJ-II capabilities, a dynamic magnetic configuration experiment with \\unicode{7548} (ρ , t) variation during discharges has shown strong effects on the mode frequency via both vacuum \\unicode{7548} changes and induced net plasma current. A drastic frequency increase from ˜50 to ˜250 kHz was observed for some modes when plasma current as low as ±2 kA was induced by small (10%) changes in the vertical field. A comprehensive set of diagnostics including a heavy ion beam probe, magnetic probes and a multi-chord bolometer made it possible to identify the spatial spread of the modes and deduce the internal amplitudes of their plasma density and magnetic field perturbations. A simple analytical model for fAE, based on the local Alfvén eigenmode (AE) dispersion relation, was proposed to characterize the observation. It was shown that all the observations, including vacuum iota and plasma current variations, may be fitted by the model, so the linear mode frequency dependence on \\unicode{7548} (plasma current) and one over square root density dependence present the major features of the NBI-induced AEs in TJ-II, and provide the framework for further experiment-to-theory comparison.

  3. Saturation of the f -mode instability in neutron stars. II. Applications and results

    NASA Astrophysics Data System (ADS)

    Pnigouras, Pantelis; Kokkotas, Kostas D.

    2016-07-01

    We present the first results on the saturation of the f -mode instability in neutron stars due to nonlinear mode coupling. Emission of gravitational waves drives the f -mode (fundamental mode) unstable in fast-rotating, newborn neutron stars. The initial growth phase of the mode is followed by its saturation, because of energy leaking to other modes of the star. The saturation point determines the strain of the generated gravitational-wave signal, which can then be used to extract information about the neutron star's equation of state. The parent (unstable) mode couples via parametric resonances with pairs of daughter modes, with the triplets' evolution exhibiting a rich variety of behaviors. We study both supernova- and merger-derived neutron stars, simply modeled as polytropes in a Newtonian context, and show that the parent may couple to many different daughter pairs during the star's evolution through the instability window, with the saturation amplitude changing by orders of magnitude.

  4. Spectral estimation of plasma fluctuations. II. Nonstationary analysis of edge localized mode spectra

    SciTech Connect

    Riedel, K.S.; Sidorenko, A. ); Bretz, N. ); Thomson, D.J. )

    1994-03-01

    Several analysis methods for nonstationary fluctuations are described and applied to the edge localized mode (ELM) instabilities of limiter H-mode plasmas. The microwave scattering diagnostic observes poloidal [ital k][sub [theta

  5. Effect of fast electrons on the stability of resistive interchange modes in the TJ-II stellarator

    NASA Astrophysics Data System (ADS)

    García, L.; Ochando, M. A.; Carreras, B. A.; Carralero, D.; Hidalgo, C.; van Milligen, B. Ph.

    2016-06-01

    In this paper, we report on electromagnetic phenomena in low-β plasmas at the TJ-II stellarator, controlled by external heating. To understand the observations qualitatively, we introduce a simple modification of the standard resistive MHD equations, to include the potential impact of fast electrons on instabilities. The dominant instabilities of the modeling regime are resistive interchange modes, and calculations are performed in a configuration with similar characteristics as the TJ-II stellarator. The main effect of the trapping of fast electrons by magnetic islands induced by MHD instabilities is to increase the magnetic component of the fluctuations, changing the character of the instability to tearing-like and modifying the frequency of the modes. These effects seem to be consistent with some of the experimental observations.

  6. ELECTROMAGNETIC FIELD MEASUREMENT OF FUNDAMENTAL AND HIGHER-ORDER MODES FOR 7-CELL CAVITY OF PETRA-II

    SciTech Connect

    Kawashima, Y.; Blednykh, A.; Cupolo, J.; Davidsaver, M.; Holub, B.; Ma, H.; Oliva, J.; Rose, J.; Sikora, R.; Yeddulla, M.

    2011-03-28

    The booster synchrotron for NSLS-II will include a 7-cell PETRA cavity, which was manufactured for the PETRA-II project at DESY. The cavity fundamental frequency operates at 500 MHz. In order to verify the impedances of the fundamental and higher-order modes (HOM), which were calculated by computer code, we measured the magnitude of the electromagnetic field of the fundamental acceleration mode and HOM using the bead-pull method. To keep the cavity body temperature constant, we used a chiller system to supply cooling water at 20 degrees C. The bead-pull measurement was automated with a computer. We encountered some issues during the measurement process due to the difficulty in measuring the electromagnetic field magnitude in a multi-cell cavity. We describe the method and apparatus for the field measurement, and the obtained results.

  7. Asteroseismology of the nearby SN II Progenitor Rigel. II. epsilon-mechanism Triggering Gravity-mode Pulsations?

    NASA Astrophysics Data System (ADS)

    Moravveji, Ehsan; Moya, Andres; Guinan, Edward F.

    2012-04-01

    The cores of luminous B- and A-type (BA) supergiant stars are the seeds of later core-collapse supernovae. Thus, constraining the near-core conditions in this class of stars can place tighter constraints on the size, mass, and chemical composition of supernova remnants. Asteroseismology of these massive stars is one possible approach into such investigations. Recently, Moravveji et al. in 2012 (hereafter Paper I) extracted 19 significant frequencies from a 6-year radial velocity monitoring of Rigel (β Ori, B8 Ia). The periods they determined broadly range from 1.22 to 74.74 days. Based on our differentially rotating stellar structure and evolution model, Rigel, at its current evolutionary state, is undergoing core He burning and shell H burning. Linear fully non-adiabatic non-radial stability analyses result in the excitation of a dense spectrum of non-radial gravity-dominated mixed modes. The fundamental radial mode (l = 0) and its overtones are all stable. When the hydrogen-burning shell is located even partially in the radiative zone, a favorable condition for destabilization of g-modes through the so-called epsilon-mechanism becomes viable. Only those g-modes that have high relative amplitudes in the hydrogen-burning (radiative) zone can survive the strong radiative damping. From the entire observed range of variability periods of Rigel (found in Paper I), and based on our model, only those modes with periods ranging between 21 and 127 days can be theoretically explained by the epsilon-mechanism. The origin of the short-period variations (found in Paper I) still remains unexplained. Because Rigel is similar to other massive BA supergiants, we believe that the epsilon-mechanism may be able to explain the long-period variations in α Cygni class of pulsating stars.

  8. Solar seismology. II - The stochastic excitation of the solar p-modes by turbulent convection

    NASA Technical Reports Server (NTRS)

    Goldreich, P.; Keeley, D. A.

    1977-01-01

    We test the hypothesis that the solar p-modes are stabilized by damping due to turbulent viscosity in the convective zone. Starting from the assumption that the modes are stable, we calculate expectation values for the modal energies. We find that the interaction between a p-mode and the turbulent convection is such that the modal energy tends toward equipartition with the kinetic energy of turbulent eddies whose lifetimes are comparable to the modal period. From the calculated values of the modal energies, we compute rms surface velocity amplitudes. Our predicted rms surface velocities range from 0.01 cm/sec for the fundamental radial mode to 0.6 cm/sec for the radial mode whose period is approximately 5 minutes. The predicted surface velocities for the low order p-modes are much smaller than the velocities inferred from recent observations.

  9. VCD Robustness of the Amide-I and Amide-II Vibrational Modes of Small Peptide Models.

    PubMed

    Góbi, Sándor; Magyarfalvi, Gábor; Tarczay, György

    2015-09-01

    The rotational strengths and the robustness values of amide-I and amide-II vibrational modes of For(AA)n NHMe (where AA is Val, Asn, Asp, or Cys, n = 1-5 for Val and Asn; n = 1 for Asp and Cys) model peptides with α-helix and β-sheet backbone conformations were computed by density functional methods. The robustness results verify empirical rules drawn from experiments and from computed rotational strengths linking amide-I and amide-II patterns in the vibrational circular dichroism (VCD) spectra of peptides with their backbone structures. For peptides with at least three residues (n ≥ 3) these characteristic patterns from coupled amide vibrational modes have robust signatures. For shorter peptide models many vibrational modes are nonrobust, and the robust modes can be dependent on the residues or on their side chain conformations in addition to backbone conformations. These robust VCD bands, however, provide information for the detailed structural analysis of these smaller systems.

  10. Oscillations of a vertically stratified dissipative atmosphere. II. Low frequency trapped modes

    NASA Astrophysics Data System (ADS)

    Rudenko, G. V.; Dmitrienko, I. S.

    2016-05-01

    Trapped atmosphere waves, such as IGW waveguide modes and Lamb modes, are described using dissipative solution above source (DSAS) (Dmitrienko and Rudenko, 2016). According to this description, the modes are disturbances penetrating without limit in the upper atmosphere and dissipating their energy throughout the atmosphere; leakage from a trapping region to the upper atmosphere is taken into consideration. The DSAS results are compared to those based on both accurate and WKB approximated dissipationless equations. It is shown that the spatial and frequency characteristics of modes in the upper atmosphere calculated by any of the methods are close to each other and are in good agreement with the observed characteristics of traveling ionospheric disturbances.

  11. Fatigue Life Prediction of Carbon Fiber-Reinforced Ceramic-Matrix Composites at Room and Elevated Temperatures. Part II: Experimental Comparisons

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2015-12-01

    This paper follows on from the earlier study (Part I) which investigated the fatigue behavior of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures. In this paper, a micromechanics approach to predict the fatigue life S-N curves of fiber-reinforced CMCs has been developed considering the fatigue damage mechanism of interface wear or interface oxidation. Upon first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. The two-parameter Weibull model is used to describe fibers strength distribution. The stress carried by broken and intact fibres on the matrix crack plane under fatigue loading is determined based on the Global Load Sharing (GLS) criterion. The fibres failure probabilities under fatigue loading considering the degradation of interface shear stress and fibres strength have been obtained. When the broken fibres fraction approaches critical value, the composite would fatigue fail. The fatigue life S-N curves of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures have been predicted. The predicted results agreed with experimental data.

  12. An engineering treatise on the CARE II dual mode and coverage models

    NASA Technical Reports Server (NTRS)

    1976-01-01

    A mathematical model used to calculate the reliability of any dual-mode, spare-switching computer system was described, and some illustrative examples were presented. The possibility of extending the resultant computer program further was also examined, enabling it, in particular, to accommodate computer configurations involving more than two modes of operation.

  13. Rossby normal modes in nonuniform background configurations. I Simple fields. II - Equinox and solstice conditions

    NASA Technical Reports Server (NTRS)

    Salby, M. L.

    1981-01-01

    An investigation is conducted regarding the influence of mean field variations on the realization of planetary normal modes, taking into account the mode response and structure in the presence of simple background nonuniformities. It is found that mean field variations have the combined effect of depressing, shifting, and broadening the characteristic response of Rossby normal modes. While nonuniformities in both the mean wind and temperature fields contribute to the reduction in peak response, the former are primarily responsible for translation and spectral broadening. An investigation is conducted to determine which modes may be realized in actual atmospheric configurations and which may be identified. For both the equinox and solstice configurations, response peaks corresponding to all of the first four modes of wavenumbers 1, 2, and 3 are readily visible above the noise.

  14. Physiological state, growth mode, and oxidative stress play a role in Cd(II)-mediated inhibition of Nitrosomonas europaea 19718.

    PubMed

    Chandran, Kartik; Love, Nancy G

    2008-04-01

    The goal of this study was to determine the impact of physiological growth states (batch exponential and batch stationary growth) and growth modes (substrate-limited chemostat, substrate-sufficient exponential batch, and substrate-depleted stationary batch growth) on several measures of growth and responses to Cd(II)-mediated inhibition of Nitrosomonas europaea strain 19718. The specific oxygen uptake rate (sOUR) was the most sensitive indicator of inhibition among the different responses analyzed, including total cell abundance, membrane integrity, intracellular 16S rRNA/DNA ratio, and amoA expression. This observation remained true irrespective of the physiological state, the growth mode, or the mode of Cd(II) exposure. Based on the sOUR, a strong time-dependent exacerbation of inhibition (in terms of an inhibition coefficient [K(i)]) in exponential batch cultures was observed. Long-term inhibition levels (based on K(i) estimates) in metabolically active chemostat and exponential batch cultures were also especially severe and comparable. In contrast, the inhibition level in stationary-phase cultures was 10-fold lower and invariable with exposure time. Different strategies for surviving substrate limitation (a 10-fold increase in amoA expression) and starvation (the retention of 16S rRNA levels) in N. europaea cultures were observed. amoA expression was most negatively impacted by Cd(II) exposure in the chemostat cultures, was less impacted in exponential batch cultures, and was least impacted in stationary batch cultures. Although the amoA response was consistent with that of the sOUR, the amoA response was not as strong. The intracellular 16S rRNA/DNA ratio, as determined by fluorescence in situ hybridization, also did not uniformly correlate with the sOUR under conditions of inhibition or no inhibition. Finally, Cd(II)-mediated inhibition of N. europaea was attributed partially to oxidative stress.

  15. Two-mode squeezed light source for quantum illumination and quantum imaging II

    NASA Astrophysics Data System (ADS)

    Masada, Genta

    2016-09-01

    Two-mode squeezed light is a macroscopic quantum entangled state of electro-magnetic fields and shows non-classical correlation between quadrature phase amplitudes in each optical mode. In this work the author is developing a high-quality two-mode squeezed light source for exploring the possibility of a quantum radar system based on a quantum illumination method and also expecting to apply it to quantum imaging. Two-mode squeezed light can be generated by combining two independent single-mode squeezed light beams using a beam splitter with a relative optical phase of 90 degrees between them. In current experimental progress the author developed two sub-threshold optical parametric oscillators to generate single-mode squeezed light beams. In the actual quantum radar or quantum imaging system, a turbulent atmosphere degrades quantum entanglement of a light source and affects performance of target detection. An optical loss is one of the simplest and most probable examples of environmental factors. In this work an evaluation method for quantum entanglement of two-mode squeezed light source is developed with consideration for the optical loss based on Duan's inseparability criteria.

  16. Chronic Fatigue Syndrome

    MedlinePlus

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

  17. Experiments on fracture toughness of thick-wall cylinder for modes I, II, III

    SciTech Connect

    Saegusa, T.; Urabe, N.; Ito, C.; Shirai, K.; Kosaki, A.

    1999-07-01

    There have been few data on fracture toughness for Mode 2 and 3 as compared with those for Mode 1. Experimental data on fracture toughness of plates made of ductile cast iron (ASTM A874-89) and forged steel (ASME SA350 LF5 C1.1) were obtained at a temperature range from 77K to 293K for Mode 1, 2 and 3. The results showed: J{sub IC} < J{sub IIC} < J{sub IIIC}, and K{sub IC} < K{sub IIC} K{sub IIIC}. Integrity of a thick-wall cylinder with artificial flaw was demonstrated against brittle fracture at 233K for Mode 1, 2 and 3, which is one of the design requirements of containers shipping radioactive materials.

  18. Tidal interactions of a Maclaurin spheroid - II. Resonant excitation of modes by a close, misaligned orbit

    NASA Astrophysics Data System (ADS)

    Braviner, Harry J.; Ogilvie, Gordon I.

    2015-02-01

    We model a tidally forced star or giant planet as a Maclaurin spheroid, decomposing the motion into the normal modes found by Bryan. We first describe the general prescription for this decomposition and the computation of the tidal power. Although this formalism is very general, forcing due to a companion on a misaligned, circular orbit is used to illustrate the theory. The tidal power is plotted for a variety of orbital radii, misalignment angles, and spheroid rotation rates. Our calculations are carried out including all modes of degree l ≤ 4, and the same degree of gravitational forcing. Remarkably, we find that for close orbits (a/R* ≈ 3) and rotational deformations that are typical of giant planets (e ≈ 0.4) the l = 4 component of the gravitational potential may significantly enhance the dissipation through resonance with surface gravity modes. There are also a large number of resonances with inertial modes, with the tidal power being locally enhanced by up to three orders of magnitude. For very close orbits (a/R* ≈ 3), the contribution to the power from the l = 4 modes is roughly the same magnitude as that due to the l = 3 modes.

  19. Effect of inclusion size on the high cycle fatigue strength and failure mode of a high V alloyed powder metallurgy tool steel

    NASA Astrophysics Data System (ADS)

    Yao, Jun; Qu, Xuan-hui; He, Xin-bo; Zhang, Lin

    2012-07-01

    The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was shown that brittle inclusions with large sizes above 30 μm prompted the occurrence of subsurface crack initiation and the reduction in fatigue strength. The fracture toughness and the stress amplitude both exerted a significant influence on the fish-eye size. A larger fish-eye area would form in the sample with a higher fracture toughness subjected to a lower stress amplitude. The stress intensity factor of the inclusion was found to lie above a typical value of the threshold stress intensity factor of 4 MPa·m1/2. The fracture toughness of the sample with a hardness above HRC 56 could be estimated by the mean value of the stress intensity factor of the fish-eye. According to fractographic evaluation, the critical inclusion size can be calculated by linear fracture mechanics.

  20. Structure of the human angiotensin II type 1 (AT1) receptor bound to angiotensin II from multiple chemoselective photoprobe contacts reveals a unique peptide binding mode.

    PubMed

    Fillion, Dany; Cabana, Jérôme; Guillemette, Gaétan; Leduc, Richard; Lavigne, Pierre; Escher, Emanuel

    2013-03-22

    Breakthroughs in G protein-coupled receptor structure determination based on crystallography have been mainly obtained from receptors occupied in their transmembrane domain core by low molecular weight ligands, and we have only recently begun to elucidate how the extracellular surface of G protein-coupled receptors (GPCRs) allows for the binding of larger peptide molecules. In the present study, we used a unique chemoselective photoaffinity labeling strategy, the methionine proximity assay, to directly identify at physiological conditions a total of 38 discrete ligand/receptor contact residues that form the extracellular peptide-binding site of an activated GPCR, the angiotensin II type 1 receptor. This experimental data set was used in homology modeling to guide the positioning of the angiotensin II (AngII) peptide within several GPCR crystal structure templates. We found that the CXC chemokine receptor type 4 accommodated the results better than the other templates evaluated; ligand/receptor contact residues were spatially grouped into defined interaction clusters with AngII. In the resulting receptor structure, a β-hairpin fold in extracellular loop 2 in conjunction with two extracellular disulfide bridges appeared to open and shape the entrance of the ligand-binding site. The bound AngII adopted a somewhat vertical binding mode, allowing concomitant contacts across the extracellular surface and deep within the transmembrane domain core of the receptor. We propose that such a dualistic nature of GPCR interaction could be well suited for diffusible linear peptide ligands and a common feature of other peptidergic class A GPCRs.

  1. Seismic transmission operator reciprocity - II: impedance-operator symmetry via elastic lateral modes

    NASA Astrophysics Data System (ADS)

    Thomson, C. J.

    2015-08-01

    The properties of the overburden transmission response are of particular interest for the analysis of reflectivity illumination or blurring in seismic depth imaging. The first step to showing a transmission-operator reciprocity property is to identify the symmetry of the so-called displacement-to-traction operators. The latter are analogous to Dirichlet-to-Neumann operators and they may also be called impedance operators. Their symmetry is deduced here after development of a formal spectral or modal theory of lateral wavefunctions in a laterally heterogeneous generally anisotropic elastic medium. The elastic lateral modes are displacement-traction 6-vectors and they are built from two auxiliary 3-vector lateral-mode bases. These auxiliary modes arise from Hermitian and anti-Hermitian operators, so they have familiar properties such as orthogonality. There is no assumption of down/up symmetry of the elasticity tensor, but basic assumptions are made about the existence and completeness of the elastic modes. A point-symmetry property appears and plays a central role. The 6-vector elastic modes have a symplectic orthogonality property, which facilitates the development of modal expansions for 6-vector functions of the lateral coordinates when completeness is assumed. While the elastic modal theory is consistent with the laterally homogeneous case, numerical work would provide confidence that it is correct in general. An appendix contains an introductory overview of acoustic lateral modes that were studied by other authors, given from the perspective of this new work. A distinction is drawn between unit normalization of scalar auxiliary modes and a separate energy-flux normalization of 2-vector acoustic modes. Neither is crucial to the form of acoustic pressure-to-velocity or impedance operators. This statement carries over to the elastic case for the 3-vector auxiliary- and 6-vector elastic-mode normalizations. The modal theory is used to construct the kernel of the

  2. Single-mode tapered optical fiber loop immunosensor II: assay of anti-cholera toxin immunoglobulins

    NASA Astrophysics Data System (ADS)

    Marks, Robert S.; Hale, Zoe M.; Levine, Myron M.; Lowe, C. R.; Payne, Frank P.

    1994-07-01

    An evanescent wave immunoassay for cholera antitoxin immunoglobulins was performed using a single mode tapered optical fiber loop sensor. The transducer was silanized with 3- glycidoxypropyltrimethoxysilane and chemically modified to link covalently either cholera toxin B subunit or a synthetic peptide derived from it, CTP3. The sensor was exposed to seral fluids, obtained from human volunteers having been exposed to live virulent Vibrio cholerae 01 and shown to produce rice-water stools. Other toxins of interest, such as Clostridium botulinum toxin A, have been tested on similar systems. The bound unlabelled immunoglobulins were then exposed to a mixture of FITC-anti-IgG and TRITC-anti-IgA, without requirement for a separation step. The emanating fluorescent emissions of fluorescein and rhodamine, excited by the input laser light, were coupled back into the guided mode of the tapered fiber, and used to determine the concentrations of the complementary antigens.

  3. Fatigue damage prognosis of internal delamination in composite plates under cyclic compression loadings using affine arithmetic as uncertainty propagation tool

    NASA Astrophysics Data System (ADS)

    Gbaguidi, Audrey J.-M.

    Structural health monitoring (SHM) has become indispensable for reducing maintenance costs and increasing the in-service capacity of a structure. The increased use of lightweight composite materials in aircraft structures drastically increased the effects of fatigue induced damage on their critical structural components and thus the necessity to predict the remaining life of those components. Damage prognosis, one of the least investigated fields in SHM, uses the current damage state of the system to forecast its future performance by estimating the expected loading environments. A successful damage prediction model requires the integration of technologies in areas like measurements, materials science, mechanics of materials, and probability theories, but most importantly the quantification of uncertainty in all these areas. In this study, Affine Arithmetic is used as a method for incorporating the uncertainties due to the material properties into the fatigue life prognosis of composite plates subjected to cyclic compressive loadings. When loadings are compressive in nature, the composite plates undergo repeated buckling-unloading of the delaminated layer which induces mixed modes I and II states of stress at the tip of the delamination in the plates. The Kardomateas model-based prediction law is used to predict the growth of the delamination, while the integration of the effects of the uncertainties for modes I and II coefficients in the fatigue life prediction model is handled using Affine arithmetic. The Mode I and Mode II interlaminar fracture toughness and fatigue characterization of the composite plates are first experimentally studied to obtain the material coefficients and fracture toughness, respectively. Next, these obtained coefficients are used in the Kardomateas law to predict the delamination lengths in the composite plates while using Affine Arithmetic to handle their uncertainties. At last, the fatigue characterization of the composite plates during

  4. Corrosion on Fatigue and Fatigue Crack Growth in Aircraft Structural Materials

    DTIC Science & Technology

    1979-06-01

    fatigue initiated by stress corrosion cracking and thus is not directly relevant o this work except that conceptually iL has similarities. The other paper...34 Corrosion Fatigue Initiated by Stress Corrosion Cracking ", personal coi’iuni cation. 12. II. Kitagaw,.:a, T. Fugita, K. Miyazawa, "Sniall Randomly...a result, extensive research on corrosion fatigue has led to the traditional model which superimposes the stress corrosion cracking phenomenon upon

  5. Measurements of higher-order mode damping in the PEP-II low-power test cavity

    SciTech Connect

    Rimmer, R.A.; Goldberg, D.A.

    1993-05-01

    The paper describes the results of measurements of the Higher-Order Mode (HOM) spectrum of the low-power test model of the PEP-II RF cavity and the reduction in the Q`s of the modes achieved by the addition of dedicated damping waveguides. All the longitudinal (monopole) and deflecting (dipole) modes below the beam pipe cut-off are identified by comparing their measured frequencies and field distributions with calculations using the URMEL code. Field configurations were determined using a perturbation method with an automated bead positioning system. The loaded Q`s agree well with the calculated values reported previously, and the strongest HOMs are damped by more than three orders of magnitude. This is sufficient to reduce the coupled-bunch growth rates to within the capability of a reasonable feedback system. A high power test cavity will now be built to validate the thermal design at the 150 kW nominal operating level, as described elsewhere at this conference.

  6. Nucleosynthesis Modes in the High-Entropy-Wind Scenario of Type II Supernovae

    SciTech Connect

    Farouqi, K.; Kratz, K.-L.; Cowan, J. J.; Mashonkina, L. I.; Pfeiffer, B.; Sneden, C.; Thielemann, F.-K.; Truran, J. W.

    2008-03-11

    In an attempt to constrain the astrophysical conditions for the nucleosynthesis of the classical r-process elements beyond Fe, we have performed large-scale dynamical network calculations within the model of an adiabatically expanding high- entropy wind (HEW) of type II supernovae (SN II). A superposition of several entropy-components (S) with model-inherent weightings results in an excellent reproduction of the overall Solar System (SS) isotopic r-process residuals (N{sub r,{center_dot}}), as well as the more recent observations of elemental abundances of metal-poor, r-process rich halo stars in the early Galaxy. For the heavy r-process elements beyond Sn, our HEW model predicts a robust abundance pattern up to the Th, U r-chronometer region. For the lighter neutron-capture region, an S-dependent superposition of (i) a normal {alpha}-component directly producing stable nuclei, including s-only isotopes, and (ii) a component from a neutron-rich {alpha}-freezeout followed by the rapid recapture of {beta}-delayed neutrons ({beta}dnrpar; emitted from the far-unstable seed nuclei is indicated. In agreement with several recent halo-star observations in the 60

  7. Phase effects in guided mode resonances II: measuring the angular phase of a surface plasmon polariton

    NASA Astrophysics Data System (ADS)

    Theisen, M. J.; Brown, T. G.

    2015-02-01

    We show how the phase of a resonant interaction between a focused beam and a guided mode can be directly observed in a pupil imaging experiment, in which the irradiance leaving the pupil of a standard microscope is relayed to an image sensor through a combination Wollaston prism, calcite beam splitter and polarizer. We apply the method to the observation of a surface plasmon polariton resonance excited in a corrugated silver film fabricated using electron beam lithography. We discuss how this particular imaging configuration could be adapted for applications in plasmonic optical sensing.

  8. A revisit to high-rate mode-II fracture characterization of composites with Kolsky bar techniques.

    SciTech Connect

    Lu, Wei-Yang; Song, Bo; Jin, Huiqing

    2010-03-01

    Nowadays composite materials have been extensively utilized in many military and industrial applications. For example, the newest Boeing 787 uses 50% composite (mostly carbon fiber reinforced plastic) in production. However, the weak delamination strength of fiber reinforced composites, when subjected to external impact such as ballistic impact, has been always potential serious threats to the safety of passengers. Dynamic fracture toughness is a critical indicator of the performance from delamination in such impact events. Quasi-static experimental techniques for fracture toughness have been well developed. For example, end notched flexure (ENF) technique, which is illustrated in Fig. 1, has become a typical method to determined mode-II fracture toughness for composites under quasi-static loading conditions. However, dynamic fracture characterization of composites has been challenging. This has resulted in conflictive and confusing conclusions in regard to strain rate effects on fracture toughness of composites.

  9. Characterization of fatigue mechanisms in nickel-based superalloys

    NASA Astrophysics Data System (ADS)

    Yablinsky, Clarissa A.

    Ni-based superalloys are important for turbine engine airfoil applications. Historically, creep has been the main failure mode and thus creep mechanisms have been the subject of numerous studies. However, modern airfoil designs maintain cooler temperatures, and consequently creep is no longer the primary failure mode. Rather, in the cooled components, experience and experimental studies have shown that fatigue is the life-limiting factor. The changing cause of failure highlighted the need for a comprehensive study of fatigue deformation mechanisms. Information about crack propagation and the associated deformation mechanisms has allowed appropriate design changes based on fatigue as a life-limiting factor. The focus of the study will be on a monocrystalline Ni-based superalloy, Rene N5, which is currently used for airfoils. Compact tension specimens were tested under cyclic loading conditions to determine the influence of microstructure and material properties on crack propagation and fatigue failure. The crack growth rate as a function of temperature, environment, frequency, and crystallographic orientation was determined. High resolution scanning electron microscopy was used to examine the fracture surface on length scales from nano to macro. Deformation mechanisms in the plastic zone ahead of the crack tip and within the plastic wake of the crack were studied using TEM and FIB techniques. Environment and frequency seem to have a larger effect on fatigue crack growth rates and threshold stress intensity factor ranges, while temperature and orientation effects are present, but not as dramatic. In the normal blade orientation, (001)[100], mode I crack propagation was prevalent, with mode II crack propagation found at higher DeltaK values. Interdendritic particles appear to be slowing crack growth rates in the threshold region of specimens tested in air. Microstructural analysis showed no change in gamma' precipitate size or morphology with temperature or stress

  10. Measurement of higher-order mode losses in SPEAR II by shift in synchrotron phase and increase in net cavity power

    SciTech Connect

    Not Available

    1988-01-01

    It has been estimated that the loss to higher-order cavity modes in SPEAR II will be 135 keV per cavity at 100 mA for a 10-cm bunch (sigma/sub z/ = 5 cm). This corresponds to a loss of 10 MeV for a 50-m PEP structure. The power lost to higher modes in each SPEAR II cavity at 100 mA would be 13.5 kW. A loss of this order can be measured by calorimetry. This loss is also large enough to cause a significant increase in the net rf power input into the cavities over the power input with no higher-mode excitation. In addition, the higher-mode loss can also produce a measurable shift in the synchronous phase angle. Numbers for these effects are computed in this paper.

  11. Failure of the human lumbar motion-segments resulting from anterior shear fatigue loading

    PubMed Central

    SKRZYPIEC, Daniel M.; NAGEL, Katrin; SELLENSCHLOH, Kay; KLEIN, Anke; PÜSCHEL, Klaus; MORLOCK, Michael M.; HUBER, Gerd

    2016-01-01

    An in-vitro experiment was designed to investigate the mode of failure following shear fatigue loading of lumbar motion-segments. Human male lumbar motion-segments (age 32–42 years, n=6) were immersed in Ringer solution at 37°C and repeatedly loaded, using a modified materials testing machine. Fatigue loading consisted of a sinusoidal shear load from 0 N to 1,500 N (750 N±750 N) applied to the upper vertebra of the motion-segment, at a frequency of 5 Hz. During fatigue experiments, several failure events were observed in the dynamic creep curves. Post-test x-ray, CT and dissection revealed that all specimens had delamination of the intervertebral disc. Anterior shear fatigue predominantly resulted in fracture of the apophyseal processes of the upper vertebrae (n=4). Exposure to the anterior shear fatigue loading caused motion-segment instability and resulted in vertebral slip corresponding to grade I and ‘mild’ grade II spondylolisthesis, as observed clinically. PMID:26829975

  12. Fatigue Damage in Composite Materials

    NASA Astrophysics Data System (ADS)

    Revuelta, D.; Miravete, A.

    2002-02-01

    The phenomenon of fatigue is critical for designing structures including elements made of composite materials. The accurate prediction of the life and fatigue resistance of laminated composites is one of the subjects of inquiry in materials science. The ability of predicting the life of laminates is important for designing, operation, and safety analysis of a composite structure under specific conditions. To predict reliably the life of structures, it is necessary to know the mechanisms of cyclic deformation and damage. It is also necessary to develop a qualitative theory of fatigue failure that should be based on the concepts of solids mechanics. Developing such a theory requires to evaluate the microscopic parameters and the macroscopic variables of the material at the level of a laminate and the structure and to determine exactly the load modes acting on the system.

  13. An assessment of BWR (boiling water reactor) Mark-II containment challenges, failure modes, and potential improvements in performance

    SciTech Connect

    Kelly, D.L.; Jones, K.R.; Dallman, R.J. ); Wagner, K.C. )

    1990-07-01

    This report assesses challenges to BWR Mark II containment integrity that could potentially arise from severe accidents. Also assessed are some potential improvements that could prevent core damage or containment failure, or could mitigate the consequences of such failure by reducing the release of fission products to the environment. These challenges and improvements are analyzed via a limited quantitative risk/benefit analysis of a generic BWR/4 reactor with Mark II containment. Point estimate frequencies of the dominant core damage sequences are obtained and simple containment event trees are constructed to evaluate the response of the containment to these severe accident sequences. The resulting containment release modes are then binned into source term release categories, which provide inputs to the consequence analysis. The output of the consequences analysis is used to construct an overall base case risk profile. Potential improvements and sensitivities are evaluated by modifying the event tree spilt fractions, thus generating a revised risk profile. Several important sensitivity cases are examined to evaluate the impact of phenomenological uncertainties on the final results. 75 refs., 25 figs., 65 tabs.

  14. The ice nucleating ability of pollen:. Part II. Laboratory studies in immersion and contact freezing modes

    NASA Astrophysics Data System (ADS)

    Diehl, K.; Matthias-Maser, S.; Jaenicke, R.; Mitra, S. K.

    Laboratory tests were conducted of the ice nucleating ability of four kinds of pollen in the immersion and the contact freezing modes. The diameters of the selected pollen were between 25 and 70 μm. The experiments were carried out at the Mainz vertical wind tunnel with freely suspended supercooled droplets at temperatures down to -28 °C. The immersion freezing experiments were conducted with drops of radii between 250 and 375 μm formed from distilled water with a defined amount of pollen added. The drops were freely floated in the wind tunnel while being supercooled. For the contact freezing experiments, a short burst of pollen was allowed to collide with freely suspended, supercooled pure water drops of 360-μm radius. The results showed that particle-free water drops in particle-free air in the wind tunnel did not freeze at temperatures above -28 °C while water drops containing pollen froze at temperatures as high as -9 °C, and water drops colliding with pollen froze at temperatures -5 °C and lower. Combined with earlier results about the ice nucleating ability of some bacteria, marine plankton, and leaf litters, the present results confirm the importance of biological aerosol particles as potential ice nuclei at relatively warm temperatures.

  15. Effects of ammonium sulfate aerosols on vegetation—II. Mode of entry and responses of vegetation

    NASA Astrophysics Data System (ADS)

    Gmur, Nicholas F.; Evans, Lance S.; Cunningham, Elizabeth A.

    These experiments were designed to provide information on the rates of aerosol deposition, mode of entry, and effects of deposition of submicrometer ammonium sulfate aerosols on foliage of Phaseolus vulgaris L. A deposition velocity of 3.2 × 10 3cms-1 was constant during 3-week exposures of plants to aerosol concentrations of 26mg m -3 (i.e. about two orders of magnitude above ambient episode concentrations). Mean deposition rate on foliage was 4.1 × 10 -11 μg cm -2s -1. Visible injury symptoms included leaf chlorosis, necrosis and loss of turgor. Chlorosis was most frequent near leaf margins causing epinasty and near major veins. Internal injury occurred initially in spongy mesophyll cells. Eventually abaxial epidermal and palisade parenchyma cells were injured. These results suggest that submicrometer aerosols enter abaxial stomata and affect more internal cells before affecting leaf surface cells. Exposure to aerosols decreased both abaxial and adaxial leaf resistances markedly. Although visible injury to foliage occurred, no changes in dry mass of roots and shoots or leaf area occurred. These results suggest that for the plant developmental stage studied, while leaf resistances decreased and cellular injury occurred in foliage, these factors were not significantly related to plant growth and development.

  16. Transit time instabilities in an inverted fireball. II. Mode jumping and nonlinearities

    SciTech Connect

    Stenzel, R. L.; Gruenwald, J.; Fonda, B.; Ionita, C.; Schrittwieser, R.

    2011-01-15

    A fireball is formed inside a highly transparent spherical grid immersed in a dc discharge plasma. The ambient plasma acts as a cathode and the positively biased grid as an anode. A strong nearly current-free double layer separates the two plasmas. Electrons are accelerated into the fireball, ionize, and establish a discharge plasma with plasma potential near the grid potential. Ions are ejected from the fireball. Since electrons are lost at the same rate as ions, most electrons accelerated into the fireball just pass through it. Thus, the electron distribution contains radially counterstreaming electrons. High-frequency oscillations are excited with rf period given by the electron transit time through the fireball. Since the frequency is well below the electron plasma frequency, no eigenmodes other than a beam space-charge wave exists. The instability is an inertial transit-time instability similar to the sheath-plasma instability or the reflex vircator instability. In contrast to vircators, there is no electron reflection from a space-charge layer but counterstreaming arises from spherical convergence and divergence of electrons. While the basic instability properties have been presented in a companion paper [R. L. Stenzel et al., Phys. Plasmas 18, 012104 (2011)], the present paper focuses on observed mode jumping and nonlinear effects. The former produce frequency jumps and different potential profiles, the latter produce harmonics associated with electron bunching at large amplitudes. In situ probe measurements are presented and interpreted.

  17. FORWARD MODELING OF STANDING KINK MODES IN CORONAL LOOPS. II. APPLICATIONS

    SciTech Connect

    Yuan, Ding; Doorsselaere, Tom Van

    2016-04-15

    Magnetohydrodynamic waves are believed to play a significant role in coronal heating, and could be used for remote diagnostics of solar plasma. Both the heating and diagnostic applications rely on a correct inversion (or backward modeling) of the observables into the thermal and magnetic structures of the plasma. However, due to the limited availability of observables, this is an ill-posed issue. Forward modeling is designed to establish a plausible mapping of plasma structuring into observables. In this study, we set up forward models of standing kink modes in coronal loops and simulate optically thin emissions in the extreme ultraviolet bandpasses, and then adjust plasma parameters and viewing angles to match three events of transverse loop oscillations observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. We demonstrate that forward models could be effectively used to identify the oscillation overtone and polarization, to reproduce the general profile of oscillation amplitude and phase, and to predict multiple harmonic periodicities in the associated emission intensity and loop width variation.

  18. Characterization of Solder Joint Reliability Using Cyclic Mechanical Fatigue Testing

    NASA Astrophysics Data System (ADS)

    Kim, Choong-Un; Bang, Woong-Ho; Xu, Huili; Lee, Tae-Kyu

    2013-10-01

    This article summarizes the mechanics of two mechanical fatigue methods, cyclic bending fatigue and shear fatigue, in inducing failure in solder joints in package assemblies, and it presents the characteristics of fatigue failures resulting from these methods using example cases of Sn-Pb eutectic and Sn-rich Pb-free solder alloys. Numerical simulation suggests that both testing configurations induce fatigue failure by the crack-opening mode. In the case of bending fatigue, the strain induced by the bending displacement is found to be sensitive to chip geometry, and it induces fatigue cracks mainly at the solder matrix adjacent to the printed circuit board interface. In case of shear fatigue, the failure location is firmly fixed at the solder neck, created by solder mask, where an abrupt change in the solder geometry occurs. Both methods conclude that the Coffin-Manson model is the most appropriate model for the isothermal mechanical fatigue of solder alloys. An analysis of fatigue characteristics using the frame of the Coffin-Manson model produces several insightful results, such as the reason why Pb-free alloys show higher fatigue resistance than Sn-Pb alloys even if they are generally more brittle. Our analysis suggests that it is related to higher work hardening. All these results indicate that mechanical fatigue can be an extremely useful method for fast screening of defective package structures and also in gaining a better understanding of fatigue failure mechanism and prediction of reliability in solder joints.

  19. Effect of Variation in the Burst Mode and Carrier Frequency of High Intensity Electrical Stimulation on Muscle Fatigue and Pain Perception of Healthy Subjects

    DTIC Science & Technology

    1988-10-22

    MVC; ( c ) Subjects pain tolerance is contingent upon the stimulating frequency and the amplitude of stimulation. Variations in either burst mode or...Body Weight and Force Data ..... ............. .132 C . Suoject Pain Ratings for all Combinations of Bursts and Carrier Frequencies...work supports the "size principle’ espoused by Henneman (1965) and confirmed by electromyographic studies using fine wire electrodes (Hannez, 1974

  20. Concentration-dependent mode of interaction of angiotensin II receptor blockers with uric acid transporter.

    PubMed

    Iwanaga, Takashi; Sato, Masanobu; Maeda, Tomoji; Ogihara, Toshio; Tamai, Ikumi

    2007-01-01

    Serum uric acid (SUA) is currently recognized as a risk factor for cardiovascular disease. It has been reported that an angiotensin II receptor blocker (ARB), losartan, decreases SUA level, whereas other ARBs, such as candesartan, have no lowering effect. Because the renal uric acid transporter (URAT1) is an important factor controlling the SUA level, we examined the involvement of URAT1 in those differential effects of various ARBs on SUA level at clinically relevant concentrations. This study was done by using URAT1-expressing Xenopus oocytes. Losartan, pratosartan, and telmisartan exhibited cis-inhibitory effects on the uptake of uric acid by URAT1, whereas at higher concentrations, only telmisartan did, and these ARBs reduced the uptake in competitive inhibition kinetics. On the other hand, candesartan, EXP3174 [2-n-butyl-4-chloro-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yI)methyl]imidazole-5-carboxylic acid] (a major metabolite of losartan), olmesartan, and valsartan were not inhibitory. Preloading of those ARBs in the oocytes enhanced the URAT1-mediated uric acid uptake, showing a trans-stimulatory effect. The present study is a first demonstration of the differential effects of ARBs on URAT1 that some ARBs are both cis-inhibitory and trans-stimulatory, depending on concentration, whereas others exhibit either a trans-stimulatory or cis-inhibitory effect alone, which could explain the clinically observed differential effects of ARBs on SUA level. Furthermore, it was found that such differential effects of ARBs on URAT1 could be predicted from the partial chemical structures of ARBs, which will be useful information for the appropriate use and development of ARBs without an increase of SUA.

  1. The effect of aging and cold working on the high-temperature low-cycle fatigue behavior of alloy 800h: part ii: continuous cyclic loading

    NASA Astrophysics Data System (ADS)

    Villagrana, R. E.; Kaae, J. L.; Ellis, J. R.

    1981-11-01

    The individual and combined effects of cold working (5 and 10 pct) and aging (4000 and 8000 h in the temperature range 538 to 760 °C) on the high-temperature low-cycle fatigue behavior of alloy 800H have been investigated. The specimens were tested at the aging temperatures. Both the saturation stress range and the fatigue life were found to be history dependent. A history-independent hardening mechanism, dynamic strain aging, was found to operate over the temperature range ~450 to 650°C and to be maximized at ~55O °C. It is speculated that carbon is responsible for this dynamic strain aging. Finally, at temperatures above 538 °C the Coffin-Manson plots show a history-independent deviation from linearity.

  2. Fatigue life extension

    NASA Technical Reports Server (NTRS)

    Matejczyk, D. E.; Lin, J.

    1985-01-01

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

  3. Improvement of the mode II interface fracture toughness of glass fiber reinforced plastics/aluminum laminates through vapor grown carbon fiber interleaves

    PubMed Central

    Ning, Huiming; Li, Yuan; Hu, Ning; Cao, Yanping; Yan, Cheng; Azuma, Takesi; Peng, Xianghe; Wu, Liangke; Li, Jinhua; Li, Leilei

    2014-01-01

    The effects of acid treatment, vapor grown carbon fiber (VGCF) interlayer and the angle, i.e., 0° and 90°, between the rolling stripes of an aluminum (Al) plate and the fiber direction of glass fiber reinforced plastics (GFRP) on the mode II interlaminar mechanical properties of GFRP/Al laminates were investigated. The experimental results of an end notched flexure test demonstrate that the acid treatment and the proper addition of VGCF can effectively improve the critical load and mode II fracture toughness of GFRP/Al laminates. The specimens with acid treatment and 10 g m−2 VGCF addition possess the highest mode II fracture toughness, i.e., 269% and 385% increases in the 0° and 90° specimens, respectively compared to those corresponding pristine ones. Due to the induced anisotropy by the rolling stripes on the aluminum plate, the 90° specimens possess 15.3%–73.6% higher mode II fracture toughness compared to the 0° specimens. The improvement mechanisms were explored by the observation of crack propagation path and fracture surface with optical, laser scanning and scanning electron microscopies. Moreover, finite element analyses were carried out based on the cohesive zone model to verify the experimental fracture toughness and to predict the interface shear strength between the aluminum plates and GFRP laminates. PMID:27877680

  4. Improvement of the mode II interface fracture toughness of glass fiber reinforced plastics/aluminum laminates through vapor grown carbon fiber interleaves.

    PubMed

    Ning, Huiming; Li, Yuan; Hu, Ning; Cao, Yanping; Yan, Cheng; Azuma, Takesi; Peng, Xianghe; Wu, Liangke; Li, Jinhua; Li, Leilei

    2014-06-01

    The effects of acid treatment, vapor grown carbon fiber (VGCF) interlayer and the angle, i.e., 0° and 90°, between the rolling stripes of an aluminum (Al) plate and the fiber direction of glass fiber reinforced plastics (GFRP) on the mode II interlaminar mechanical properties of GFRP/Al laminates were investigated. The experimental results of an end notched flexure test demonstrate that the acid treatment and the proper addition of VGCF can effectively improve the critical load and mode II fracture toughness of GFRP/Al laminates. The specimens with acid treatment and 10 g m(-2) VGCF addition possess the highest mode II fracture toughness, i.e., 269% and 385% increases in the 0° and 90° specimens, respectively compared to those corresponding pristine ones. Due to the induced anisotropy by the rolling stripes on the aluminum plate, the 90° specimens possess 15.3%-73.6% higher mode II fracture toughness compared to the 0° specimens. The improvement mechanisms were explored by the observation of crack propagation path and fracture surface with optical, laser scanning and scanning electron microscopies. Moreover, finite element analyses were carried out based on the cohesive zone model to verify the experimental fracture toughness and to predict the interface shear strength between the aluminum plates and GFRP laminates.

  5. Improvement of the mode II interface fracture toughness of glass fiber reinforced plastics/aluminum laminates through vapor grown carbon fiber interleaves

    NASA Astrophysics Data System (ADS)

    Ning, Huiming; Li, Yuan; Hu, Ning; Cao, Yanping; Yan, Cheng; Azuma, Takesi; Peng, Xianghe; Wu, Liangke; Li, Jinhua; Li, Leilei

    2014-06-01

    The effects of acid treatment, vapor grown carbon fiber (VGCF) interlayer and the angle, i.e., 0° and 90°, between the rolling stripes of an aluminum (Al) plate and the fiber direction of glass fiber reinforced plastics (GFRP) on the mode II interlaminar mechanical properties of GFRP/Al laminates were investigated. The experimental results of an end notched flexure test demonstrate that the acid treatment and the proper addition of VGCF can effectively improve the critical load and mode II fracture toughness of GFRP/Al laminates. The specimens with acid treatment and 10 g m-2 VGCF addition possess the highest mode II fracture toughness, i.e., 269% and 385% increases in the 0° and 90° specimens, respectively compared to those corresponding pristine ones. Due to the induced anisotropy by the rolling stripes on the aluminum plate, the 90° specimens possess 15.3%-73.6% higher mode II fracture toughness compared to the 0° specimens. The improvement mechanisms were explored by the observation of crack propagation path and fracture surface with optical, laser scanning and scanning electron microscopies. Moreover, finite element analyses were carried out based on the cohesive zone model to verify the experimental fracture toughness and to predict the interface shear strength between the aluminum plates and GFRP laminates.

  6. Fatigue Behavior of Inconel 718 TIG Welds

    NASA Astrophysics Data System (ADS)

    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.

  7. Analytic modeling of instabilities driven by higher-order modes in the HLS II RF system with a higher-harmonic cavity

    NASA Astrophysics Data System (ADS)

    Zhao, Yu-Ning; Li, Wei-Min; Wu, Cong-Feng; Wang, Lin

    2013-08-01

    The utility of a passive fourth-harmonic cavity plays a key role in suppressing longitudinal beam instabilities in the electron storage ring and lengthens the bunch by a factor of 2.6 for the phase II project of the Hefei Light Source (HLS II). Meanwhile, instabilities driven by higher-order modes (HOM) may limit the performance of the higher-harmonic cavity. In this paper, the parasitic coupled-bunch instability, which is driven by narrow band parasitic modes, and the microwave instability, which is driven by broadband HOM, are both modeled analytically. The analytic modeling results are in good agreement with those of our previous simulation study and indicate that the passive fourth-harmonic cavity suppresses parasitic coupled-bunch instabilities and microwave instability. The modeling suggests that a fourth-harmonic cavity may be successfully used at the HLS II.

  8. Analysis of fretting fatigue in aircraft structures: Stresses, stress intensity factors, and life predictions

    NASA Astrophysics Data System (ADS)

    McVeigh, Pamela Alison

    Clamped contacts subjected to cyclic loading are prone to fretting fatigue, a mechanism of crack nucleation and propagation. In aircraft, fretting fatigue occurs at the rivet/hole interface on the fuselage skin and at the dovetail joint in engine hardware where disk and blade meet. The ability to predict the lives of such components would be a great aid in preventing failures. Finite element models appropriate for the calculation of fretting fatigue stresses and stress intensity factors are developed for two different contact geometries. In addition, several less computationally expensive numerical methods are also studied. Agreement between the various solutions is good. A severe increase in the mode I stress intensity factor near the surface is discovered in both geometries. Mode II stress intensity factors are also detailed, illustrating the complex non-proportional loading of fretting-induced cracks. A comparison is made between results obtained from actual surface profiles and those generated from prescribed surface profiles; the differences are significant. Equivalent initial flaw sizes are calculated for two different metals using an approach which ignores the effect of mode II stress intensity factors. Life predictions based on the equivalent initial flaw size approach are found to agree reasonably well with those measured in the laboratory for contact geometries similar to the rivet/hole interface. More data is needed before a judgment can be made about life correlations for the dovetail joint contact geometry. The analysis methods described throughout can be easily implemented and integrated into a system aimed at designing against fretting fatigue.

  9. Viscoelastic-damage interface model formulation with friction to simulate the delamination growth in mode II shear

    NASA Astrophysics Data System (ADS)

    Goodarzi, Mohammad Saeed; Hosseini-Toudeshky, Hossein

    2017-02-01

    In this paper a formulation of a viscoelastic-damage interface model with friction in mode-II is presented. The cohesive constitutive law contains elastic and damage regimes. It has been assumed that the shear stress in the elastic regime follows the viscoelastic properties of the matrix material. The three element Voigt model has been used for the formulation of relaxation modulus of the material. Damage evolution proceeds according to the bilinear cohesive constitutive law combined with friction stress consideration. Combination of damage and friction is based on the presumption that the damaged area, related to an integration point, can be dismembered into the un-cracked area with the cohesive damage and cracked area with friction. Samples of a one element model have been presented to see the effect of parameters on the cohesive constitutive law. A comparison between the predicted results with available results of end-notched flexure specimens in the literature is also presented to verify the model. Transverse crack tension specimens are also simulated for different applied displacement velocities.

  10. Interlaminar fracture reinforcement under mode-II loading: Post-cure through-thickness reinforcement of graphite epoxy, unidirectional laminates

    NASA Astrophysics Data System (ADS)

    Jacobson, Joel B.

    A novel through-thickness reinforcement method proposed by S. Kravchenko et al., has been static tested under mode II loading using end notched flexure (ENF), unidirectional laminate specimens to determine the impact on the apparent critical fracture toughness (GIIc) for the material tested. Both experimental and numerical methods have been employed in an attempt to characterize and model these effects. Testing and analysis were conducted on two different specimen thickness, 2.34 mm and 3.54 mm nominally. ASTM D7905/7905M -- 14 was followed during the experimental portion of the thick specimens. Multiple reinforcing configurations using the proposed technique were experimentally tested including single, double, and quadruple rows of orthogonal, pultruded carbon/epoxy pins located within the crack and ahead of the crack (pristine material) to determine the effect on the apparent critical fracture toughness for each configuration. Both pre-cracked and no pre-cracked specimens were evaluated. The results of this study indicate that specimens pinned in the crack experienced the highest supportable reaction force such that the crack was completely arrested and most of the specimens failed in flexure. Pre-cracked specimens that were pinned in the body exhibited stable crack growth as well as a shadowing phenomenon. Both pins and the crack surface topography due to this phenomenon are attributed to the increased apparent fracture toughness for these specimens. Similar outcomes were observed through numerical simulations for the models simulated in this study.

  11. Role of large-scale slip in mode II fracture of bimaterial interface produced by diffusion bonding

    NASA Astrophysics Data System (ADS)

    Fox, M. R.; Ghosh, A. K.

    2001-08-01

    Bimaterial interfaces present in diffusion-bonded (and in-situ) composites are often not flat interfaces. The unevenness of the interface can result not only from interface reaction products but also from long-range waviness associated with the surfaces of the component phases bonded together. Experimental studies aimed at determining interface mechanical properties generally ignore the departure in the local stress due to waviness and assume a theoretically flat interface. Furthermore, the commonly used testing methods involving superimposed tension often renders the interface so extremely brittle that if microplastic effects were present it becomes impossible to perceive them. This article examines the role of waviness of the interface and microplastic effects on crack initiation. To do this, a test was selected that provides significant stability against crack growth by superimposing compressive stresses. Mode II interface fracture was studied for NiAl/Mo model laminates using a recently developed asymmetrically loaded shear (ALS) interface shear test. The ALS test may be viewed as opposite of the laminate bend test. In the bend test, shear at the interface is created via tension on one surface of the bend, while in the ALS test, shear is created by compression on one side of the interface relative to the other. Normal to the interface, near the crack tip, an initially compressive state is replaced by slight tension due to Poisson’s expansion of the unbonded part of the compressed beam.

  12. 3D-RISM-MP2 Approach to Hydration Structure of Pt(II) and Pd(II) Complexes: Unusual H-Ahead Mode vs Usual O-Ahead One.

    PubMed

    Aono, Shinji; Mori, Toshifumi; Sakaki, Shigeyoshi

    2016-03-08

    Solvation of transition metal complexes with water has been one of the fundamental topics in physical and coordination chemistry. In particular, Pt(II) complexes have recently attracted considerable interest for their relation to anticancer activity in cisplatin and its analogues, yet the interaction of the water molecule and the metal center has been obscured. The challenge from a theoretical perspective remains that both the microscopic solvation effect and the dynamical electron correlation (DEC) effect have to be treated simultaneously in a reasonable manner. In this work we derive the analytical gradient for the three-dimensional reference interaction site model Møller-Plesset second order (3D-RISM-MP2) free energy. On the basis of the three-regions 3D-RISM self-consistent field (SCF) method recently proposed by us, we apply a new layer of the Z-vector method to the CP-RISM equation as well as point-charge approximation to the derivatives with respect to the density matrix elements in the RISM-CPHF equation to remarkably reduce the computational cost. This method is applied to study the interaction of H2O with the d(8) square planar transition metal complexes in aqueous solution, trans-[Pt(II)Cl2(NH3)(glycine)] (1a), [Pt(II)(NH3)4](2+) (1b), [Pt(II)(CN)4](2-) (1c), and their Pd(II) analogues 2a, 2b, and 2c, respectively, to elucidate whether the usual H2O interaction through O atom (O-ahead mode) or unusual one through H atom (H-ahead mode) is stable in these complexes. We find that the interaction energy of the coordinating water and the transition metal complex changes little when switching from gas to aqueous phase, but the solvation free energy differs remarkably between the two interaction modes, thereby affecting the relative stability of the H-ahead and O-ahead modes. Particularly, in contrast to the expectation that the O-ahead mode is preferred due to the presence of positive charges in 1b, the H-ahead mode is also found to be more stable. The O

  13. Increased ventricular lactate in chronic fatigue syndrome measured by 1H MRS imaging at 3.0 T. II: comparison with major depressive disorder.

    PubMed

    Murrough, James W; Mao, Xiangling; Collins, Katherine A; Kelly, Chris; Andrade, Gizely; Nestadt, Paul; Levine, Susan M; Mathew, Sanjay J; Shungu, Dikoma C

    2010-07-01

    Chronic fatigue syndrome (CFS), a complex illness characterized by fatigue, impaired concentration, and musculoskeletal pain, is often misdiagnosed as a psychiatric illness due to the overlap of its symptoms with mood and anxiety disorders. Using proton magnetic resonance spectroscopic imaging ((1)H MRSI), we previously measured levels of the major brain metabolites in CFS, in generalized anxiety disorder (GAD), and in healthy control subjects, and found significantly higher levels of ventricular cerebrospinal fluid (CSF) lactate in CFS compared to the other two groups. In the present study, we sought to assess the specificity of this observation for CFS by comparing ventricular lactate levels in a new cohort of 17 CFS subjects with those in 19 healthy volunteers and in 21 subjects with major depressive disorder (MDD), which, like GAD, is a neuropsychiatric disorder that has significant symptom overlap with CFS. Ventricular CSF lactate was significantly elevated in CFS compared to healthy volunteers, replicating the major result of our previous study. Ventricular lactate measures in MDD did not differ from those in either CFS or healthy volunteers. We found a significant correlation between ventricular CSF lactate and severity of mental fatigue that was specific to the CFS group. In an exploratory analysis, we did not find evidence for altered levels of the amino acid neurotransmitters, gamma-aminobutyric acid (GABA) and glutamate + glutamine ('Glx'), in CFS compared to MDD or healthy controls. Future (1)H MRS studies with larger sample sizes and well-characterized populations will be necessary to further clarify the sensitivity and specificity of neurometabolic abnormalities in CFS and MDD.

  14. ECCI observations of dislocation structures around fatigue cracks in ferritic stainless steel single crystals

    NASA Astrophysics Data System (ADS)

    Taniguchi, T.; Kaneko, Y.; Hashimoto, S.

    2009-07-01

    Dislocation structures around the crack tips of ferritic stainless steel single crystals were observed with electron channelling contrast imaging (ECCI) method. The ECCI method enables us to observe dislocations lying near surface using a scanning electron microscope. Fatigue crack growth tests were conducted on compact tension (CT) specimens having loading axes of [221] and [110] directions. In the specimen having the [110] loading axis at which the fatigue crack having Mode I and II component propagated, a thin band-like structure consisting of dislocation wall array was observed ahead of the crack tip. On the other hand, the dislocation structures around the crack having Mode I and III components could be divided into three regions in the specimen with the [221] loading axis: the cell structure, the dislocation wall structure and the vein structure were observed in order of ascending distance from crack tip. Difference between the dislocation structures near the fatigue cracks could be understood from the crack mode by which edge and screw dislocation emissions from the crack tips are strongly affected.

  15. Cast Aluminum Structures Technology (CAST) Structural Test and Evaluation (Phase V). Part II. Fatigue and Fracture Properties of Cast Aluminum Bulkheads

    DTIC Science & Technology

    1980-04-01

    Solution heat treatment: 1010 + 10OF for 24 to 25 hours Quench delay: 10 seconds maximum Quenchant: 106 + 150 F water Natural aging : Room temperature for...16 to 24 hours Precipitation heat treatment ( aging ): 325 + 100 F for 7 to 8 hours Constant-amplitude fatigue specimens were obtained from each of the...SURF. TREAT. AS MILLED--- ýAANUFACTUREA BOEING NEAT NUMBER NA -SPEC. CONFIG. D6.-4671-626I -TEST TEMP. 7 ETEST WUMIDITY 2PTA YIELD STRESS 39.6 KSI MAX

  16. Surface enhanced Raman scattering, natural bond orbitals and Mulliken atomic charge distribution in the normal modes of diethyldithiocarbamate cadmium (II) complex, [Cd(DDTC)2

    NASA Astrophysics Data System (ADS)

    Téllez Soto, C. A.; Costa, A. C.; Versiane, O.; Lemma, T.; Machado, N. C. F.; Mondragón, M. A.; Martin, A. A.

    2015-07-01

    Theoretical and experimental bands have been assigned to the Fourier Transform Infrared (FT-IR) and FT-Raman spectra of the bis(diethyldithiocarbamate)Cd(II) complex, abbreviated as ([Cd(DDTC)2]). The calculations and spectral interpretation have been based on the DFT/B3LYP method, infrared and Raman second derivative spectra, and band deconvolution analysis to assist in the assignment of observed fundamentals. This study validated the unusual pseudo tetrahedral molecular structure formed around the Cd(II) cation. Surface-enhanced Raman scattering (SERS) was used to determine the interactions of the normal-modes of the diethyldithiocarbamate cadmium (II) complex on nano-structured silver surfaces. Natural bond orbital (NBO) analysis was also carried out to study the Cd(II) hybridization causing the pseudo tetrahedral geometry of the framework of the [Cd(DDTC)2] complex, and to confirm the charge transfer mechanisms through second order perturbation theory analysis of the Fox Matrix. In order to find out the electronic dispersion of the Mulliken atomic charges (MAC) in the normal modes, we calculated the MAC for each normal mode and correlated these values with the SERS effect. Experimental UV-Vis spectra were obtained and charge transfer bands were assigned. Good agreement between the calculated and experimental values for the vibrational and UV-Vis spectra was obtained.

  17. Binding mode and thermodynamic studies on the interaction of the anticancer drug dacarbazine and dacarbazine-Cu(II) complex with single and double stranded DNA.

    PubMed

    Temerk, Yassien; Ibrahim, Hossieny

    2014-07-01

    The binding mode and thermodynamic characteristics of the anticancer drug dacarbazine (Dac) with double and single stranded DNA were investigated in the absence and presence of Cu(II) using cyclic voltammetry, square wave voltammetry and fluorescence spectroscopy. The interaction of Dac and Dac-Cu(II) complex with dsDNA indicated their intercalation into the base stacking domain of dsDNA double helix and the strength of interaction is independent on the ionic strength. The interaction of Dac with dsDNA in the presence of Cu(II) leads to a much stronger intercalation. The interaction mode of Dac molecules with ssDNA is electrostatic attraction via negative phosphate on the exterior of the ssDNA with Dac. The binding constants, stoichiometric coefficients and thermodynamic parameters of Dac and Dac-Cu(II) complex with dsDNA and ssDNA were evaluated. Comparison of the mode interaction of Dac with dsDNA and ssDNA was discussed. The decrease of peak current of Dac was proportional to DNA concentration, which was applied for determination of dsDNA and ssDNA concentration.

  18. German experiences in local fatigue monitoring

    SciTech Connect

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

    2012-07-01

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

  19. Mathematical and numerical analysis of non-planer static mode-II crack in a two-layered medium

    NASA Astrophysics Data System (ADS)

    Hirano, S.; Yamashita, T.

    2009-12-01

    A crack in an infinite homogeneous medium is widely assumed as a model for earthquake fault. It is, however, well known that the earth's crust is heterogeneous and its structure is approximated well by a layered medium. Hence, such structure should be taken into account to model earthquake fault reasonably. We mathematically analyze the behavior of a 2-D static mode-II non-planar crack in a two-layered elastic medium in order to understand the effect of layer boundary on earthquake faulting. Although Rani and Singh (1993) and Rivalta et al.(2002) studied similar problems, focuses of their studies were quite narrow probably because of inherent mathematical difficulty. Actually the former assumed a planar crack with uniform slip and the latter assumed a planar crack perpendicular to the layer boundary. While a serious difficulty of the analysis of mode-II crack lies in the derivation of stress distribution due to point source as a kernel function, we first overcome the difficulty by writing its expression in a sequence of complex functions in the real (not the Fourier) domain. A very important characteristic in the sequence is that it has recursive property, which makes possible to derive the kernel function explicitly and to integrate it by parts; the integration by parts is required before the boundary integral equation method (BIEM) is applied. Our kernel function is much easier to treat than the expression given by Rani and Singh (1993). This enables us to analyze arbitrarily oriented non-planar crack in a two-layered medium. Next, we calculate the spatial distribution of stress due to crack that does not intersect the layer boundary using the above derived kernel function. We find in the calculation that the existence of layer boundary amplifies or reduces the stress at the crack tip when the crack is located close to the boundary; the stress is amplified when the crack exists in the layer with lower rigidity. Our method of analysis can easily be applied to the

  20. Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin; Minguet, Pierre J.

    2001-01-01

    A methodology is presented for determining the fatigue life of composite structures based on fatigue characterization data and geometric nonlinear finite element (FE) analyses. To demonstrate the approach, predicted results were compared to fatigue tests performed on specimens which represented a tapered composite flange bonded onto a composite skin. In a first step, tension tests were performed to evaluate the debonding mechanisms between the flange and the skin. In a second step, a 2D FE model was developed to analyze the tests. To predict matrix cracking onset, the relationship between the tension load and the maximum principal stresses transverse to the fiber direction was determined through FE analysis. Transverse tension fatigue life data were used to -enerate an onset fatigue life P-N curve for matrix cracking. The resulting prediction was in good agreement with data from the fatigue tests. In a third step, a fracture mechanics approach based on FE analysis was used to determine the relationship between the tension load and the critical energy release rate. Mixed mode energy release rate fatigue life data were used to create a fatigue life onset G-N curve for delamination. The resulting prediction was in good agreement with data from the fatigue tests. Further, the prediction curve for cumulative life to failure was generated from the previous onset fatigue life curves. The results showed that the methodology offers a significant potential to Predict cumulative fatigue life of composite structures.

  1. DAMPING THE HIGH ORDER MODES IN THE PUMPING CHAMBER OF THE PEP-II LOW ENERGY RING

    SciTech Connect

    Novokhatski, A

    2004-06-30

    The Low Energy Ring of the PEP-II B-factory operates with extremely high currents of short positron bunches. Any discontinuity in the vacuum chamber can excite a broad-band spectrum of high order modes (HOM). A temperature rise has been found in the vacuum chamber elements in one junction of straight and arc chambers. The power in the wake fields was high enough to char beyond use the feed-through for the titanium sublimation pump (TSP). This pumping section is 5.5 m long and consists of the beam chamber and an ante-chamber. Electromagnetic fields, excited in the beam chamber penetrate to the ante-chamber and then through the heater feed-through come out. To be sure that these electromagnetic fields are present a small ceramic tile with a high loss tangent was placed near the TSP feed-through outside of the pumping chamber. A thermocouple that was attached to this tile showed a strong temperature rise. A short wire antenna was also placed there. The antenna was connected directly to a spectrum analyzer. Measurements show a wide frequency HOM spectrum with a maximum in the 2-3 GHz region. Based on these measurements a special water cooled HOM absorber was designed and installed in the vacuum chamber. As a result, the HOM power in the section decreased and the temperature rise went down. The power loss in the absorber reaches 1200 W for a positron beam current of 2.4 A. The absorber helped to find the source of HOM. Steering the beam on the vertical collimators upstream of the absorber resulted in the significant HOM power change in the absorber.

  2. Near infra-red emission from a mer-Ru(II) complex: consequences of strong σ-donation from a neutral, flexible ligand with dual binding modes.

    PubMed

    Pal, Amlan K; Zaccheroni, Nelsi; Campagna, Sebastiano; Hanan, Garry S

    2014-07-04

    A rare example of dual coordination modes by a novel tridentate ligand gives rise to unique fac-and mer-Ru((II/III)) complexes. The mer-Ru(II)-complex displays the farthest red-shift of a triplet metal-to-ligand charge transfer ((3)MLCT) emission with a tridentate ligand for a mononuclear complex. This observation is a consequence of large bite angle and strong σ-donation by the ligand, the combined effect of which helps to separate the energy of the (3)MLCT and (3)MC states.

  3. Modeling axial compression fatigue in fiber ropes

    SciTech Connect

    Hearle, J.W.S.; Hobbs, R.E.; Overington, M.S.; Banfield, S.J.

    1995-12-31

    The modeling of long-term fatigue performance of twisted ropes has been extended to cover axial compression fatigue. This mode of failure has been observed in use and testing of ropes. It is characterized by sharp cooperative kinking of yarns, which leads to flex fatigue breakage of fibers. A model of pipeline buckling was modified to allow for plasticity in bending. An axial and lateral restraints, which influence the buckling, were derived from the existing rope mechanics model. Axial compression was introduced into the total computational model, in order to predict the form of buckling and the consequent fiber failure. An alternative use of the program is simply to detect conditions in which axial compression occurs as an indication of the occurrence of fatigue.

  4. Corrosion Fatigue

    DTIC Science & Technology

    1981-10-01

    the conditipn-fitrs to the structure (6-9). Even though this may appear to be a straight forward problem it is nott W. Schutz (8) discussed some of...AIL , •Ship; Offshore Structure; 0 vVl~t~1TJVlIi1t Automobile; Train 0 Transport Aircraft Wing 0 • Steel Rolling Mill Shaftt Disc of an -t Aircraft

  5. 76 FR 75435 - Fatigue Tolerance Evaluation of Metallic Structures

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-02

    ... evaluating the fatigue strength of transport category rotorcraft metallic primary structural elements. I... 2.9 11.2 56 9 25.4 2.9 22.5 100 03/16/2011 II. Background Rotorcraft fatigue strength reduction or... reduction in strength of any primary structural element can lead to a catastrophic failure, it is...

  6. Molecular interactions of DNA-topoisomerase I and II inhibitor with DNA and topoisomerases and in ternary complexes: binding modes and biological effects for intoplicine derivatives.

    PubMed

    Nabiev, I; Chourpa, I; Riou, J F; Nguyen, C H; Lavelle, F; Manfait, M

    1994-08-02

    Molecular interactions of intoplicine, dual DNA-topoisomerases (Topo) I and II inhibitor, with topoisomerases, plasmid DNA, in ternary cleavable complexes with enzymes and plasmid DNA, and in the reversed cleavable complexes were examined by means of surface-enhanced Raman scattering (SERS) and CD spectroscopy and by biochemical techniques. Detailed spectral analysis of intoplicine derivatives allowed us to assign SERS vibrational modes of chromophores and to propose the models for these complexes. Intoplicine was found to be able to interact specifically with the Topo II alone, but with Topo I only when in the presence of DNA. It shows at least two modes of binding to the DNA: the first was found to be dominant for its derivative 1c (most potent Topo I inhibitor), and the second was dominant for derivative 2a (most potent Topo II inhibitor). The possibility of forming these two types of complexes simultaneously is suggested to be one of the main factors enabling the drug to be a dual Topo I and Topo II inhibitor. The "deep intercalation mode" of the drug from the DNA minor groove with the long axis of the chromophore oriented roughly parallel to the dyad axis has been suggested to be responsible for induction of distortions of the DNA structure by the intercalating drug. Being involved in the formation of Topo I-mediated cleavable ternary complex, the molecules participating in the deep intercalation mode within the DNA do not change their molecular interactions as compared with their complex with the DNA alone. The stabilization of the Topo I-mediated cleavable complex was shown to be followed by the local denaturation of DNA in the AT-rich regions of the helix. When the ternary cleavable complex was reversed, the drug was shown to be in the complex with the plasmid. The "outside binding mode" from the DNA major groove via the hydroxyl group of the A-ring of the chromophore has been suggested to be responsible for Topo II inhibition. These molecules did not

  7. Improving the accuracy of derivation of the Williams’ series parameters under mixed (I+II) mode loading by compensation of measurement bias in the stress field components data

    NASA Astrophysics Data System (ADS)

    Lychak, Oleh V.; Holyns'kiy, Ivan S.

    2016-12-01

    A new method for compensation of bias in the stress field components measurement data used for Williams’ series parameters derivation was presented. Essential increase of accuracy of derivation of SIF-related leading terms in series under mixed (I+II) mode loading was demonstrated. It was shown that a relatively low value of bias in the stress field components data error could result in the essential deviation of the values of derived Williams’ coefficients and the crack tip coordinates.

  8. Fatigue of composites

    NASA Technical Reports Server (NTRS)

    Salkind, M. J.

    1972-01-01

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

  9. Low-cycle corrosion fatigue of Zircaloy-2 in iodine atmospheres

    NASA Astrophysics Data System (ADS)

    Kubo, T.; Motomiya, T.; Wakashima, Y.

    1986-09-01

    Low-cycle fatigue tests have been performed on Zircaloy-2 by a reversed-bending method in inert and iodine atmospheres at 623 K. Fatigue lives in both atmospheres followed the Coffin-Manson law. Cracks propagated by a transgranular shear mode, and the propagation was the process controlling fatigue life in an inert atmosphere. Fatigue life in a high concentration of iodine vapour was significantly shorter than in an inert atmosphere. The iodine vapour caused brittle fracture of a specimen mainly by the transgranular cleavage mode, and an accelerated crack propagation rate. The minimum vapour pressure of iodine to cause brittle fracture under fatigue conditions was about 27 Pa.

  10. A theoretical analysis of the coordination modes of CuII with penicillins: activation of the beta-lactam C-N bond.

    PubMed

    Campomanes, Pablo; Menéndez, M Isabel; López, Ramón; Sordo, Tomás L

    2005-02-01

    The interaction of CuII with 6-formylamino-3alpha-carboxypenam and 6-acetylamino-3alpha-carboxypenam was investigated by means of DFT calculations with the UB3LYP functional. Nine different modes of complexation between CuII and 6-formylamino-3alpha-carboxypenam were located. When two water molecules directly bonded to CuII are included in the calculations on 6-acetylamino-3alpha-carboxypenam as penicillin model, only six CuII(H2O)2-6-acetylamino-3alpha-carboxypenam complexes (1S-6S) are found. In solution the four most stable complexes obtained from our calculations, 6S, 1S, 2S, and 3S, exhibit CuII in square-planar coordination with at least one bond to the carboxylate group, in agreement with experimental evidence. Complexes 6S, 1S, and 3S were previously suggested by available experimental evidence. In three of the most stable complexes (6S, 2S, and 3S) the beta-lactam C-N bond is remarkably activated and displays C-N bond lengths similar to those found in some tetrahedral intermediates located for the hydrolysis of 2-azetidinones. This suggests that these kinds of complexes belong to the reaction coordinate for the degradation of beta-lactam antibiotics in the presence of CuII.

  11. Mechanical fatigue of thin copper foil

    SciTech Connect

    Merchant, H.D.; Minor, M.G.; Liu, Y.L.

    1999-09-01

    The electrodeposited and the rolled 12 to 35 {micro}m thick copper foils are subjected to the bending/unbending strain-controlled flex fatigue over a wide range of strain amplitudes. The fatigue life is associated with an increase in electrical resistance of the specimen beyond a preassigned threshold. For each foil type, in the rolled or as-deposited as well as in the (recrystallization-like) annealed conditions, the inverse Coffin-Manson (C-M) relationship between strain amplitude ({Delta}{epsilon}/2) and fatigue life (N{sub f}) is established in the high {Delta}{epsilon}/2 (low N{sub f}) and the low {Delta}{epsilon}/2 (high N{sub f}) regimes. The N{sub f}, {Delta}{epsilon}/2, and C-M slopes (c,b) are utilized to calculate the cyclic strain hardening (n{prime}) and fatigue ductility (D{sub f}) parameters. It is shown that for a given foil thickness, an universal relationship exists between D{sub f} and the strength ({sigma}) normalized fatigue life (N{sub f}/{sigma}). The propagation of fatigue crack through the foil thickness and across the sample width is related to the unique fine grain structure for each foil type: pancaked grains for the rolled foil and equiaxed grains for the electrodeposited foil. The fatal failure corresponds to convergence of the through-thickness and the across-the-width fatigue cracks. The variations in (i) electrical resistance, (ii) mid-thickness microhardness and grain structure and (iii) dislocation configurations with fatigue are monitored. Except for a small but significant fatigue induced softening (or hardening), nonconvincing evidence of strain localization (and the associated dislocation configurations generally observed for the bulk samples) has been found.

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

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.; Gabb, Timothy P.

    1990-01-01

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

  13. Fatigue handbook: Offshore steel structures

    SciTech Connect

    Almarnaess, A.

    1985-01-01

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

  14. Fatigue life prediction under service load considering strengthening effect of loads below fatigue limit

    NASA Astrophysics Data System (ADS)

    Zhao, Lihui; Zheng, Songlin; Feng, Jinzhi

    2014-11-01

    Lightweight design requires an accurate life prediction for structures and components under service loading histories. However, predicted life with the existing methods seems too conservative in some cases, leading to a heavy structure. Because these methods are established on the basis that load cycles would only cause fatigue damage, ignore the strengthening effect of loads. Based on Palmgren-Miner Rule (PMR), this paper introduces a new method for fatigue life prediction under service loadings by taking into account the strengthening effect of loads below the fatigue limit. In this method, the service loadings are classified into three categories: damaging load, strengthening load and none-effect load, and the process for fatigue life prediction is divided into two stages: stage I and stage II, according to the best strengthening number of cycles. During stage I, fatigue damage is calculated considering both the strengthening and damaging effect of load cycles. While during stage II, only the damaging effect is considered. To validate this method, fatigue lives of automobile half shaft and torsion beam rear axle are calculated based on the new method and traditional methods, such as PMR and Modified Miner Rule (MMR), and fatigue tests of the two components are conducted under service loading histories. The tests results show that the percentage errors of the predicted life with the new method to mean life of tests for the two components are -3.78% and -1.76% separately, much lesser than that with PMR and MMR. By considering the strengthening effect of loads below the fatigue limit, the new method can significantly improve the accuracy for fatigue life prediction. Thus lightweight design can be fully realized in the design stage.

  15. Strategies for Rapid Muscle Fatigue Reduction during FES Exercise in Individuals with Spinal Cord Injury: A Systematic Review

    PubMed Central

    Ibitoye, Morufu Olusola; Hamzaid, Nur Azah; Hasnan, Nazirah; Abdul Wahab, Ahmad Khairi; Davis, Glen M.

    2016-01-01

    Background Rapid muscle fatigue during functional electrical stimulation (FES)-evoked muscle contractions in individuals with spinal cord injury (SCI) is a significant limitation to attaining health benefits of FES-exercise. Delaying the onset of muscle fatigue is often cited as an important goal linked to FES clinical efficacy. Although the basic concept of fatigue-resistance has a long history, recent advances in biomedical engineering, physiotherapy and clinical exercise science have achieved improved clinical benefits, especially for reducing muscle fatigue during FES-exercise. This review evaluated the methodological quality of strategies underlying muscle fatigue-resistance that have been used to optimize FES therapeutic approaches. The review also sought to synthesize the effectiveness of these strategies for persons with SCI in order to establish their functional impacts and clinical relevance. Methods Published scientific literature pertaining to the reduction of FES-induced muscle fatigue was identified through searches of the following databases: Science Direct, Medline, IEEE Xplore, SpringerLink, PubMed and Nature, from the earliest returned record until June 2015. Titles and abstracts were screened to obtain 35 studies that met the inclusion criteria for this systematic review. Results Following the evaluation of methodological quality (mean (SD), 50 (6) %) of the reviewed studies using the Downs and Black scale, the largest treatment effects reported to reduce muscle fatigue mainly investigated isometric contractions of limited functional and clinical relevance (n = 28). Some investigations (n = 13) lacked randomisation, while others were characterised by small sample sizes with low statistical power. Nevertheless, the clinical significance of emerging trends to improve fatigue-resistance during FES included (i) optimizing electrode positioning, (ii) fine-tuning of stimulation patterns and other FES parameters, (iii) adjustments to the mode and

  16. Assessment of fatigue in Parkinson's disease: Indian perspective

    PubMed Central

    Paul, Birinder Singh; Singh, Amandeep; Jain, Dinesh; Singh, Gagandeep; Kaushal, Sandeep; Paul, Gunchan; Kaura, Karan

    2016-01-01

    Context: Fatigue is one of the most frequent nonmotor manifestations in Parkinson's disease (PD), having a major effect on quality of life but is not reported in Indian patients. Aims: To evaluate the frequency of fatigue in a cohort of PD population and its correlation with disease. Settings and Design: Fatigue Severity Scale (FSS) was translated and validated in local vernacular language. All patients of PD visiting neurology outpatient department of a tertiary care hospital. Subjects and Methods: A total of 150 patients were screened, and 104 were included in this study. They were divided into – Group I with fatigue (score of >4 in each item) and Group II without fatigue. Statistical Analysis: Data were analyzed by SPSS software version 20.0. Spearman correlation was used to evaluate the convergent validity of the FSS-Ind score with PD-related variables. The principal components analysis was applied to detect the domain structure of the FSS. Results: Of the total 104 patients, 68 (65.3%) patients experienced fatigue. The duration of disease was significantly more (P = 0.021) in Group I (4.39 ± 3.8 years) than in the Group II (3.13 ± 1.6 years). The severity of disease also showed a positive correlation with fatigue with 50.9% patients in H and Y stage >3 experiencing fatigue. 69.1% patients of tremor phenotype experienced fatigue as compared to 32.3% of rigid phenotype. There was no relation of fatigue with age, gender, H and Y stage, levodopa equivalent dose and mean Unified PD Rating Scale motor III score. Conclusions: Translated version of the FSS, FSS-Ind has high internal consistency and validity which supports its application as an effective tool in detecting fatigue in patients with PD. Fatigue in PD was related to duration and phenotype of the disease. PMID:27994352

  17. Fatigue Characterization of Functionally Graded Metallic Alloys

    NASA Astrophysics Data System (ADS)

    Silva, F. S.

    2008-02-01

    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.

  18. Fatigue Characterization of Functionally Graded Metallic Alloys

    SciTech Connect

    Silva, F. S.

    2008-02-15

    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.

  19. Numerical investigations with a hybrid isentropic-sigma model. I - Normal-mode characteristics. II - The inclusion of moist processes

    NASA Technical Reports Server (NTRS)

    Pierce, R. B.; Johnson, Donald R.; Reames, Fred M.; Zapotocny, Tom H.; Wolf, Bart J.

    1991-01-01

    The normal-mode characteristics of baroclinically amplifying disturbances were numerically investigated in a series of adiabatic simulations by a hybrid isentropic-sigma model, demonstrating the effect of coupling an isentropic-coordinate free atmospheric domain with a sigma-coordinate PBL on the normal-mode characteristics. Next, the normal-mode model was modified by including a transport equation for water vapor and adiabatic heating by condensation. Simulations with and without a hydrological component showed that the overall effect of latent heat release is to markedly enhance cyclogenesis and frontogenesis.

  20. High Frequency Fatigue of Turbine Blade Material.

    DTIC Science & Technology

    1982-10-01

    TESTS 83 APPENDIX II - S-N DATA FOR INCONEL - 718 99...amplitude tests were run on sheet Inconel - 718 at 650*C. The data is presented as da/dM vs AK o plots and in tabular maj or form. These tests are included in...Kip 98 APPENDIX II S-N DATA FOR INCONEL - 718 During the early stages of this program, several fatigue life tests , (S-N tests ), were run on Inconel - 718

  1. Study of NBI-driven chirping mode properties and radial location by the heavy ion beam probe in the TJ-II stellarator

    NASA Astrophysics Data System (ADS)

    Melnikov, A. V.; Eliseev, L. G.; Castejón, F.; Hidalgo, C.; Khabanov, P. O.; Kozachek, A. S.; Krupnik, L. I.; Liniers, M.; Lysenko, S. E.; de Pablos, J. L.; Sharapov, S. E.; Ufimtsev, M. V.; Zenin, V. N.; HIBP Group; TJ-II Team

    2016-11-01

    Alfvén eigenmodes (AEs) were studied in low magnetic shear flexible heliac TJ-II (B 0  =  0.95 T, R 0  =  1.5 m, < a>   =  0.22 m) neutral beam injection (NBI) heated plasmas (P NBI  ⩽  1.1 MW, E NBI  =  32 keV) using the heavy ion beam probe (HIBP). L-mode hydrogen plasmas heated with co-, counter- and balanced-NBI and electron cyclotron resonance heating (ECRH) were investigated in various magnetic configurations with rotational transform ι(a)/2π  =  1/q ~ 1.5-1.6. The HIBP diagnostic is capable of simultaneously measuring the oscillations of the plasma electric potential, density and poloidal magnetic field. In earlier studies chirping modes have been observed with 250 kHz  <  f AE  <  380 kHz in combined ECR and NBI heated plasmas at low density {{\\bar{n}}\\text{e}}   =  (0.3-1.5)  ×  1019 m-3. In this paper we report the observation of chirping modes obtained with NBI only in plasmas with densities similar to those of earlier studies and obtained after lithium evaporation in the vacuum vessel. The absence of ECRH in the discharges studied here shows that ECRH is not a necessary ingredient to obtain chirping modes in TJ-II but rather a tool for obtaining low-density discharges. Using the HIBP we deduce that the location of the AE chirping mode is  -0.8  <  ρ  <  0.8. Chirping modes have a specific spatial structure: electric potential perturbations have a ballooning character, while the density and B pol perturbations are nearly symmetric for both ECRH  +  NBI and NBI-only plasmas. On TJ-II, the dominant effect on the nonlinear evolution of the AE from the chirping state to the steady-frequency state is the magnetic configuration, determined by the vacuum ι and plasma current I pl.

  2. Fracture and fatigue in osteocytes.

    PubMed

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

    2014-11-01

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

  3. Clinical neurophysiology of fatigue.

    PubMed

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

    2008-01-01

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

  4. Cancer-related fatigue.

    PubMed

    Visovsky, Constance; Schneider, Susan M

    2003-01-01

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

  5. Fatigue of cellular materials

    SciTech Connect

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

    1996-01-01

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

  6. Accelerated Fatigue Test Rationale,

    DTIC Science & Technology

    1980-03-01

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

  7. The versatile binding mode of transition-state analogue inhibitors of tyrosinase towards dicopper(II) model complexes: experimental and theoretical investigations.

    PubMed

    Orio, Maylis; Bochot, Constance; Dubois, Carole; Gellon, Gisèle; Hardré, Renaud; Jamet, Hélène; Luneau, Dominique; Philouze, Christian; Réglier, Marius; Serratrice, Guy; Belle, Catherine

    2011-11-25

    We describe 2-mercaptopyridine-N-oxide (HSPNO) as a new and efficient competitive inhibitor of mushroom tyrosinase (K(IC) =3.7 μM). Binding studies of HSPNO and 2-hydroxypyridine-N-oxide (HOPNO) on dinuclear copper(II) complexes [Cu(2)(BPMP)(μ-OH)](ClO(4))(2) (1; HBPMP=2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol) and [Cu(2)(BPEP)(μ-OH)](ClO(4))(2)) (2; HBPEP=2,6-bis{bis[2-(2-pyridyl)ethyl]aminomethyl}-4-methylphenol), known to be functional models for the tyrosinase diphenolase activity, have been performed. A combination of structural data, spectroscopic studies, and DFT calculations evidenced the adaptable binding mode (bridging versus chelating) of HOPNO in relation to the geometry and chelate size of the dicopper center. For comparison, binding studies of HSPNO and kojic acid (5-hydroxy-2-(hydroxymethyl)-4-pyrone) on dinuclear complexes were performed. A theoretical approach has been developed and validated on HOPNO adducts to compare the binding mode on the model complexes. It has been applied for HSPNO and kojic acid. Although results for HSPNO were in line with those obtained with HOPNO, thus reflecting their chemical similarity, we showed that the bridging mode was the most preferential binding mode for kojic acid on both complexes.

  8. Fatigue behaviour of composites

    NASA Astrophysics Data System (ADS)

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

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

  9. Scalable High-Performance Algorithm for the Simulation of Exciton Dynamics. Application to the Light-Harvesting Complex II in the Presence of Resonant Vibrational Modes.

    PubMed

    Kreisbeck, Christoph; Kramer, Tobias; Aspuru-Guzik, Alán

    2014-09-09

    The accurate simulation of excitonic energy transfer in molecular complexes with coupled electronic and vibrational degrees of freedom is essential for comparing excitonic system parameters obtained from ab initio methods with measured time-resolved spectra. Several exact methods for computing the exciton dynamics within a density-matrix formalism are known but are restricted to small systems with less than 10 sites due to their computational complexity. To study the excitonic energy transfer in larger systems, we adapt and extend the exact hierarchical equation of motion (HEOM) method to various high-performance many-core platforms using the Open Compute Language (OpenCL). For the light-harvesting complex II (LHC II) found in spinach, the HEOM results deviate from predictions of approximate theories and clarify the time scale of the transfer process. We investigate the impact of resonantly coupled vibrations on the relaxation and show that the transfer does not rely on a fine-tuning of specific modes.

  10. Comparative internal kinematics of the H II regions in interacting and isolated galaxies: implications for massive star formation modes

    NASA Astrophysics Data System (ADS)

    Zaragoza-Cardiel, Javier; Beckman, John E.; Font, Joan; García-Lorenzo, Begoña; Camps-Fariña, Artemi; Fathi, Kambiz; James, Philip A.; Erroz-Ferrer, Santiago; Barrera-Ballesteros, Jorge; Cisternas, Mauricio

    2015-08-01

    We have observed 12 interacting galaxy pairs using the Fabry-Perot interferometer GH αFaS (Galaxy H α Fabry-Perot system) on the 4.2-m William Herschel Telescope at the Observatorio del Roque de los Muchachos, La Palma. We present here the Hα surface brightness, velocity and velocity dispersion maps for the 10 systems we have not previously observed using this technique, as well as the physical properties (sizes, Hα luminosities and velocity dispersion) of 1259 H II regions from the full sample. We also derive the physical properties of 1054 H II regions in a sample of 28 isolated galaxies observed with the same instrument in order to compare the two populations of H II regions. We find a population of the brightest H II regions for which the scaling relations, for example the relation between the Hα luminosity and the radius, are clearly distinct from the relations for the regions of lower luminosity. The regions in this bright population are more frequent in the interacting galaxies. We find that the turbulence, and also the star formation rate (SFR), are enhanced in the H II regions in the interacting galaxies. We have also extracted the Hα equivalent widths for the H II regions of both samples, and we have found that the distribution of H II region ages coincides for the two samples of galaxies. We suggest that the SFR enhancement is brought about by gas flows induced by the interactions, which give rise to gravitationally bound gas clouds which grow further by accretion from the flowing gas, producing conditions favourable to star formation.

  11. The monotonic and fatigue behavior of CFCCs

    SciTech Connect

    Miriyala, N.; Liaw, P.K.; McHargue, C.J.; Snead, L.L.

    1996-04-01

    Flexure tests were performed to study the fabric orientation effects on the monotonic and fatigue behavior of two commercially available continuous fiber reinforced ceramic composites (CFCCs), namely (i) Nicalon fiber fabric reinforced alumina (Al{sub 2}O{sub 3}) matrix composite fabricated by a direct molten metal oxidation (DIMOX) process and, (ii) Nicalon fiber fabric reinforced silicon carbide (SiC) matrix composite fabricated by an isothermal chemical vapor infiltration (ICVI) process. The fabric orientation effects on the monotonic and fatigue behavior were strong in the Nicalon/Al{sub 2}O{sub 3} composite, while they were relatively weak in the Nicalon/SiC composite.

  12. Bulk filling of Class II cavities with a dual-cure composite: Effect of curing mode and enamel etching on marginal adaptation

    PubMed Central

    Bortolotto, Tissiana; Roig, Miguel; Krejci, Ivo

    2014-01-01

    Objectives: This study attempted to find a simple adhesive restorative technique for class I and II cavities on posterior teeth. Study Design: The tested materials were a self-etching adhesive (Parabond, Coltène/Whaledent) and a dual-cure composite (Paracore, Coltène/Whaledent) used in bulk to restore the cavities. Class II MO cavities were performed and assigned to 4 groups depending on the orthophosphoric acid (H3PO4) conditioning of enamel and polymerization method used (chemical or dual). Specimens were subjected to quantitative marginal analysis before and after thermo-mechanical loading. Results: Higher percentages of marginal adaptation at the total margin length, both before and after thermo-mechanical loading, were found in groups in which enamel was etched with phosphoric acid, without significant differences between the chemically and dual-cured modes. The restorations performance was similar on enamel and dentin, obtaining low results of adaptation on occlusal enamel in the groups without enamel etching, the lowest scores were on cervical dentin in the group with no ortophosphoric acid and self-cured. Conclusions: A dual-cure composite applied in bulk on acid etched enamel obtained acceptable marginal adaptation results, and may be an alternative technique for the restoration of class II cavities. Key words:Dual-cure composite, bulk technique, class II restoration, selective enamel etching, marginal adaptation. PMID:25674316

  13. Computational micromechanics of fatigue of microstructures in the HCF–VHCF regimes

    SciTech Connect

    Castelluccio, Gustavo M.; Musinski, William D.; McDowell, David L.

    2016-05-19

    Advances in higher resolution experimental techniques have shown that metallic materials can develop fatigue cracks under cyclic loading levels significantly below the yield stress. Indeed, the traditional notion of a fatigue limit can be recast in terms of limits associated with nucleation and arrest of fatigue cracks at the microstructural scale. Though fatigue damage characteristically emerges from irreversible dislocation processes at sub-grain scales, the specific microstructure attributes, environment, and loading conditions can strongly affect the apparent failure mode and surface to subsurface transitions. This paper discusses multiple mechanisms that occur during fatigue loading in the high cycle fatigue (HCF) to very high cycle fatigue (VHCF) regimes. We compare these regimes, focusing on strategies to bridge experimental and modeling approaches exercised at multiple length scales and discussing particular challenges to modeling and simulation regarding microstructure-sensitive fatigue driving forces and thresholds. Finally, we discuss some of the challenges in predicting the transition of failure mechanisms at different stress and strain amplitudes.

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

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  15. Anticancer Activity and Modes of Action of (arene) ruthenium(II) Complexes Coordinated to C-, N-, and O-ligands.

    PubMed

    Biersack, Bernhard

    2016-01-01

    An overview of anticancer active (arene)ruthenium(II) complexes coordinated to period 2 element-based ligand systems, i.e., carbon-, nitrogen-, and oxygen-coordinated ligands, is provided in this mini-review. A bridge is forged from the large group of anticancer active ruthenium compounds with monodentate and chelating nitrogen ligands via complexes of O,O-chelating ligands to organometallic ruthenium derivatives coordinated to carbon. (Arene)ruthenium(II) complexes with reduced side-effects and enhanced efficacy against cancer are highlighted. Pertinent literature is covered up to 2014.

  16. An Evaluation of the Mode of Action Framework for MutagenicCarcinogens Case Study II: Chromium (VI).

    EPA Science Inventory

    In response to the 2005 revised U.S Environmental Protection Agency’s (EPA) Cancer Guidelines, a strategy is being developed to include all mutagenicity and other genotoxicity data with any additional information to determine whether a carcinogen operates through a mutagenic mode...

  17. Biaxial fatigue loading of notched composites

    NASA Technical Reports Server (NTRS)

    Francis, P. H.; Walrath, D. E.; Sims, D. F.; Weed, D. N.

    1977-01-01

    Thin walled, 2.54-cm (1-in.) diameter tubular specimens of T300/934 graphite/epoxy were fabricated and fatigue cycled in combinations of axial, torsional, and internal pressure loading. Two different four-ply layup configurations were tested: (0/90)S and (+ or - 45)S; all tubes contained a 0.48-cm (3/16-in.) diameter circular hole penetrating one wall midway along the tube length. S-N curves were developed to characterize fatigue behavior under pure axial, torsional, or internal pressure loading, as well as combined loading fatigue. A theory was developed based on the Hill plane stress model which enabled the S-N curve for combined stress states to be predicted from the S-N data for the uniaxial loading modes. Correlation of the theory with the experimental data proved to be remarkably good.

  18. Biaxial fatigue loading of notched composites

    NASA Technical Reports Server (NTRS)

    Francis, P. H.; Walrath, D. E.; Sims, D. F.; Weed, D. N.

    1977-01-01

    Thin-walled, 2.54-cm diameter tubular specimens of graphite/epoxy were fatigue cycled in combinations of axial, torsional, and internal pressure loading. Two different four-ply layup configurations were tested: (0-90)s and (+ or- 45)s; each tube contained a 0.48-cm diameter circular hole penetrating one wall midway along the tube length. S-N curves were developed to characterize fatigue behavior under pure axial, torsional, or internal pressure loading, as well as combined loading fatigue. A theory was developed based on a plane stress model which enabled the S-N curve for combined stress states to be predicted from the S-N data for the uniaxial loading modes. Correlation of the theory with the experimental data proved to be remarkably good.

  19. Aerodynamic Heating and Fatigue

    NASA Technical Reports Server (NTRS)

    Kroll, Wilhelmina D.

    1959-01-01

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

  20. Characterization of failure processes in tungsten copper composites under fatigue loading conditions

    NASA Technical Reports Server (NTRS)

    Kim, Yong-Suk; Verrilli, Michael J.; Gabb, Timothy P.

    1989-01-01

    A fractographic and metallographic investigation was performed on specimens of a tungsten fiber reinforced copper matrix composite (9 vol percent), which had experienced fatigue failures at elevated temperatures. Major failure modes and possible failure mechanisms, with an emphasis placed on characterizing fatigue damage accumulation, were determined. Metallography of specimens fatigued under isothermal cyclic loading suggested that fatigue damage initiates in the matrix. Cracks nucleated within the copper matrix at grain boundaries, and they propagated through cavity coalescence. The growing cracks subsequently interacted with the reinforcing tungsten fibers, producing a localized ductile fiber failure. Examinations of interrupted tests before final failure confirmed the suggested fatigue damage processes.

  1. Shear-flow trapped-ion-mode interaction revisited. II. Intermittent transport associated with low-frequency zonal flow dynamics

    SciTech Connect

    Ghizzo, A.; Palermo, F.

    2015-08-15

    We address the mechanisms underlying low-frequency zonal flow generation in turbulent system and the associated intermittent regime of ion-temperature-gradient (ITG) turbulence. This model is in connection with the recent observation of quasi periodic zonal flow oscillation at a frequency close to 2 kHz, at the low-high transition, observed in the ASDEX Upgrade [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)] and EAST tokamak [Xu et al., Phys. Rev. Lett 107, 125001 (2011)]. Turbulent bursts caused by the coupling of Kelvin-Helmholtz (KH) driven shear flows with trapped ion modes (TIMs) were investigated by means of reduced gyrokinetic simulations. It was found that ITG turbulence can be regulated by low-frequency meso-scale zonal flows driven by resonant collisionless trapped ion modes (CTIMs), through parametric-type scattering, a process in competition with the usual KH instability.

  2. Fatigue countermeasures in aviation.

    PubMed

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

    2009-01-01

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

  3. Coordination modes of a schiff base pentadentate derivative of 4-aminoantipyrine with cobalt(II), nickel(II) and copper(II) metal ions: synthesis, spectroscopic and antimicrobial studies.

    PubMed

    Chandra, Sulekh; Jain, Deepali; Sharma, Amit Kumar; Sharma, Pratibha

    2009-01-01

    Transition metal complexes of Co(II), Ni(II) and Cu(II) metal ions with general stoichiometry [M(L)X]X and [M(L)SO(4)], where M = Co(II), Ni(II) and Cu(II), L = 3,3'-thiodipropionic acid bis(4-amino-5-ethylimino-2,3-dimethyl-1-phenyl-3-pyrazoline) and X = NO(3)(-), Cl(-) and OAc(-), have been synthesized and structurally characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements and spectral techniques like IR, UV and EPR. The nickel(II) complexes were found to have octahedral geometry, whereas cobalt(II) and copper(II) complexes were of tetragonal geometry. The covalency factor (beta) and orbital reduction factor (k) suggest the covalent nature of the complexes. The ligand and its complexes have been screened for their antifungal and antibacterial activities against three fungi, i.e. Alternaria brassicae, Aspergillus niger and Fusarium oxysporum and two bacteria, i.e. Xanthomonas compestris and Pseudomonas aeruginosa.

  4. Low Cycle Fatigue and Creep-Fatigue Behavior of Alloy 617 at High Temperature

    SciTech Connect

    Cabet, Celine; Carroll, Laura; Wright, Richard

    2013-10-01

    Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the Very High Temperature Nuclear Reactor (VHTR), expected to have an outlet temperature as high as 950 degrees C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanism/s and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 degrees C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens, although evidence of grain boundary cavitation was not observed. Despite the absence of grain boundary cavitation to accelerate crack propagation, the addition of a hold time at peak tensile strain was detrimental to cycle life. This suggests that creepfatigue interaction may occur by a different mechanism or that the environment may be partially responsible for accelerating failure.

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

    SciTech Connect

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

    1994-02-01

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

  6. Probabilistic fatigue life prediction of metallic and composite materials

    NASA Astrophysics Data System (ADS)

    Xiang, Yibing

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

  7. Experimental study of thermodynamics propagation fatigue crack in metals

    NASA Astrophysics Data System (ADS)

    Vshivkov, A.; Iziumova, A.; Plekhov, O.

    2015-10-01

    This work is devoted to the development of an experimental method for studying the energy balance during cyclic deformation and fracture. The studies were conducted on 304 stainless steel AISE samples. The investigation of the fatigue crack propagation was carried out on flat samples with stress concentrators. The stress concentrator was three central holes. The heat flux sensor was developed based on the Seebeck effect. This sensor was used for measuring the heat dissipation power in the examined samples during the fatigue tests. The measurements showed that the rate of fatigue crack growth depends on the heat flux at the crack tip and there are two propagation mode of fatigue crack with different link between the propagation mode and heat flux from crack tip.

  8. Experimental study of thermodynamics propagation fatigue crack in metals

    SciTech Connect

    Vshivkov, A. Iziumova, A. Plekhov, O.

    2015-10-27

    This work is devoted to the development of an experimental method for studying the energy balance during cyclic deformation and fracture. The studies were conducted on 304 stainless steel AISE samples. The investigation of the fatigue crack propagation was carried out on flat samples with stress concentrators. The stress concentrator was three central holes. The heat flux sensor was developed based on the Seebeck effect. This sensor was used for measuring the heat dissipation power in the examined samples during the fatigue tests. The measurements showed that the rate of fatigue crack growth depends on the heat flux at the crack tip and there are two propagation mode of fatigue crack with different link between the propagation mode and heat flux from crack tip.

  9. TOXIC SUBSTANCES FROM COAL COMBUSTION--A COMPREHENSIVE ASSESSMENT, PHASE II: ELEMENT MODES OF OCCURRENCE FOR THE OHIO 5/6/7, WYODAK AND NORTH DAKOTA COAL SAMPLES

    SciTech Connect

    Allan Kolker; Stanley J. Mroczkowski; Curtis A. Palmer; Kristen O. Dennen; Robert B. Finkelman; John H. Bullock Jr.

    2002-05-30

    This study reports on the second phase (Phase II) of USGS research activities in support of DOE contract DE-AC22-95PC95101 ''Toxic Substances From Coal Combustion--A Comprehensive Assessment'', funded under DOE Interagency Agreement DE-AI22-95PC95145. The purpose of the study was to provide a quantitative and semi-quantitative characterization of the modes of occurrence of trace elements in coal samples investigated under Phase II, including (1) Ohio 5/6/7, an Ohio bituminous coal sample blended from the No.5, No.6, and No.7 beds; (2) North Dakota, a lignite sample from the Falkirk Mine, Underwood, ND, and (3) Wyodak, a sub-bituminous coal sample from the Cordero Mine, Gillette, WY. Samples from these coal beds were selected for their range in rank and commercial applicability. Results of this research provide basic information on the distribution of elements in Phase II coal samples, information needed for development of a commercial predictive model for trace-element behavior during coal combustion.

  10. Vibrational investigation on the copper(II) binding mode of carcinine and its pH dependence

    NASA Astrophysics Data System (ADS)

    Torreggiani, Armida; Reggiani, Matteo; Manco, Immacolata; Tinti, Anna

    2007-05-01

    A comparative FT-Raman and FT-IR study of Carcinine (Carc), a natural imidazole dipeptide, and its complexes with Cu(II) ions was performed at different pH's. Both Raman and IR spectra present marker bands useful for the identification of the predominant complexes; in particular, Raman spectroscopy appears useful for identifying the metal-coordination site of the imidazole ring (N π or N τ atoms) of Carc. Free Carc shows a strong network of H-bonds and tautomer I (N τ-H) is the preferred form of the imidazolic ring (bands at 1578, 1292 and 988 cm -1). The presence of Cu(II) does not affect the tautomeric equilibrium at pH 7, whereas the deprotonation of both N-imidazolic nitrogens is strongly induced at higher pH. Under neutral and alkaline conditions the primary amino group takes part to the Cu(II) chelation, whereas all the peptidic moieties are involved in coordination only at pH 7. Thus, Carc acts as a tri-dentate ligand at neutral pH, mainly giving a monomeric complex, [CuLH -1], containing tautomer I, whereas an oligonuclear complex, probably [Cu 4L 4H -8], where metal-imidazolate ions connect different ligand molecules, predominates at alkaline pH.

  11. Structures of mammalian ER α-glucosidase II capture the binding modes of broad-spectrum iminosugar antivirals

    PubMed Central

    Alonzi, Dominic S.; Marti, Lucia; Reca, Ida-Barbara; Kiappes, J. L.; Struwe, Weston B.; Cross, Alice; Basu, Souradeep; Lowe, Edward D.; Darlot, Benoit; Santino, Angelo; Zitzmann, Nicole

    2016-01-01

    The biosynthesis of enveloped viruses depends heavily on the host cell endoplasmic reticulum (ER) glycoprotein quality control (QC) machinery. This dependency exceeds the dependency of host glycoproteins, offering a window for the targeting of ERQC for the development of broad-spectrum antivirals. We determined small-angle X-ray scattering (SAXS) and crystal structures of the main ERQC enzyme, ER α-glucosidase II (α-GluII; from mouse), alone and in complex with key ligands of its catalytic cycle and antiviral iminosugars, including two that are in clinical trials for the treatment of dengue fever. The SAXS data capture the enzyme’s quaternary structure and suggest a conformational rearrangement is needed for the simultaneous binding of a monoglucosylated glycan to both subunits. The X-ray structures with key catalytic cycle intermediates highlight that an insertion between the +1 and +2 subsites contributes to the enzyme’s activity and substrate specificity, and reveal that the presence of d-mannose at the +1 subsite renders the acid catalyst less efficient during the cleavage of the monoglucosylated substrate. The complexes with iminosugar antivirals suggest that inhibitors targeting a conserved ring of aromatic residues between the α-GluII +1 and +2 subsites would have increased potency and selectivity, thus providing a template for further rational drug design. PMID:27462106

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

    PubMed

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

    2015-01-01

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

  13. Altered resting brain connectivity in persistent cancer related fatigue

    PubMed Central

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

    2015-01-01

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

  14. Dramatic increase in fatigue life in hierarchical graphene composites.

    PubMed

    Yavari, F; Rafiee, M A; Rafiee, J; Yu, Z-Z; Koratkar, N

    2010-10-01

    We report the synthesis and fatigue characterization of fiberglass/epoxy composites with various weight fractions of graphene platelets infiltrated into the epoxy resin as well as directly spray-coated on to the glass microfibers. Remarkably only ∼0.2% (with respect to the epoxy resin weight and ∼0.02% with respect to the entire laminate weight) of graphene additives enhanced the fatigue life of the composite in the flexural bending mode by up to 1200-fold. By contrast, under uniaxial tensile fatigue conditions, the graphene fillers resulted in ∼3-5-fold increase in fatigue life. The fatigue life increase (in the flexural bending mode) with graphene additives was ∼1-2 orders of magnitude superior to those obtained using carbon nanotubes. In situ ultrasound analysis of the nanocomposite during the cyclic fatigue test suggests that the graphene network toughens the fiberglass/epoxy-matrix interface and prevents the delamination/buckling of the glass microfibers under compressive stress. Such fatigue-resistant hierarchical materials show potential to improve the safety, reliability, and cost effectiveness of fiber-reinforced composites that are increasingly the material of choice in the aerospace, automotive, marine, sports, biomedical, and wind energy industries.

  15. Damage mechanisms in bithermal and thermomechanical fatigue of Haynes 188

    NASA Technical Reports Server (NTRS)

    Kalluri, Sreeramesh; Halford, Gary R.

    1992-01-01

    Post failure fractographic and metallographic studies were conducted on Haynes 188 specimens fatigued under bithermal and thermomechanical loading conditions between 316 and 760 C. Bithermal fatigue specimens examined included those tested under high strain rate in-phase and out-phase, tensile creep in-phase, and compressive creep out-of-phase loading conditions. Specimens tested under in-phase and out-of-phase thermomechanical fatigue were also examined. The nature of failure mode (transgrandular versus intergranular), the topography of the fracture surface, and the roles of oxidation and metallurgical changes were studied for each type of bithermal and thermomechanical test.

  16. Mechanisms of peripheral fatigue.

    PubMed

    Kirkendall, D T

    1990-08-01

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

  17. Wilsonville SRC-I pilot plant: I. Fractionation area corrosion studies; II. Hot vs. normal separation mode of operation

    SciTech Connect

    Lee, J.M.

    1981-04-01

    Extensive corrosion studies in solvent recovery columns have been done with different coals (mainly Kentucky number 9 Lafayette, Dotiki and Fies). Sodium carbonate (0.1 to 1.1% of coal) was added as neutralizer to control corrosion rate. Chloride balance runs were made for isolation of corrosive streams with high chlorine content. A caustic wash program of inlet streams has been developed for selective treatment of corrosive streams as an alternative means for possible replacement of sodium carbonate addition. High chlorine content coals such as Kentucky number 9 Lafayette and Dotiki (0.2 to 0.3%) were very corrosive, compared to low chlorine content coal, Kentucky number 9 Fies (< 0.1%). Sodium carbonate addition (0.6 to 0.7% of coal) reduced corrosion rate from 500 MPY to an insignificant level of less than 5 MPY. Caustic wash of solvents could reduce corrosion rate by 50%, removing most corrosive compounds present in the 440 to 480/sup 0/F boiling fraction. Extensive studies for the hot separator mode of operation have been done as a means of saving substantial energy by elimination of dissolver slurry cooling (0.3 MM Btu/hr) and reheating for solvent recovery (1 MM Btu/h). Impacts of the hot separator mode on plant operability, product quality and Kerr-McGee CSD Unit recovery have been studied. The hot separator mode of operation was carried out by controlling the V103 temperature to 740/sup 0/F. It was observed that preasphaltene contents increased in the SRC products such as V110 L/F SRC and CSD feed; CSD unit recovery was not affected significantly; solvent quality was not affected significantly.

  18. Motions in the interiors and atmospheres of Jupiter and Saturn. II - Barotropic instabilities and normal modes of an adiabatic planet

    NASA Technical Reports Server (NTRS)

    Ingersoll, A. P.; Miller, R. L.

    1986-01-01

    A rotating and adiabatic inviscid fluid planet possesses low frequency motions that are barotropic, quasi-geostrophic and quasi-columnar. The limiting curvature at which flow becomes unstable upon projection onto the planetary surface is negative, with an amplitude that is 3-4 times that for thin atmospheres, in planets in which density linearly decreases to zero at the surface. This result is shown to hold for all quasi-columnar perturbations. Both the phase speed of the normal mode oscillations and the barotropic stability criterion have features in common with Saturn and Jupiter oscillations.

  19. Fatigue 󈨛. Volume 2,

    DTIC Science & Technology

    1987-06-01

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

  20. Observing Exoplanets with High-dispersion Coronagraphy. II. Demonstration of an Active Single-mode Fiber Injection Unit

    NASA Astrophysics Data System (ADS)

    Mawet, D.; Ruane, G.; Xuan, W.; Echeverri, D.; Klimovich, N.; Randolph, M.; Fucik, J.; Wallace, J. K.; Wang, J.; Vasisht, G.; Dekany, R.; Mennesson, B.; Choquet, E.; Delorme, J.-R.; Serabyn, E.

    2017-04-01

    High-dispersion coronagraphy (HDC) optimally combines high-contrast imaging techniques such as adaptive optics/wavefront control plus coronagraphy to high spectral resolution spectroscopy. HDC is a critical pathway toward fully characterizing exoplanet atmospheres across a broad range of masses from giant gaseous planets down to Earth-like planets. In addition to determining the molecular composition of exoplanet atmospheres, HDC also enables Doppler mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as precise measurements of exoplanet rotational velocities. Here, we demonstrate an innovative concept for injecting the directly imaged planet light into a single-mode fiber, linking a high-contrast adaptively corrected coronagraph to a high-resolution spectrograph (diffraction-limited or not). Our laboratory demonstration includes three key milestones: close-to-theoretical injection efficiency, accurate pointing and tracking, and on-fiber coherent modulation and speckle nulling of spurious starlight signal coupling into the fiber. Using the extreme modal selectivity of single-mode fibers, we also demonstrated speckle suppression gains that outperform conventional image-based speckle nulling by at least two orders of magnitude.

  1. Nonaxisymmetric Dynamic Instabilities of Rotating Polytropes. II. Torques, Bars, and Mode Saturation with Applications to Protostars and Fizzlers

    NASA Astrophysics Data System (ADS)

    Imamura, James N.; Durisen, Richard H.; Pickett, Brian K.

    2000-01-01

    Dynamic nonaxisymmetric instabilities in rapidly rotating stars and protostars have a range of potential applications in astrophysics, including implications for binary formation during protostellar cloud collapse and for the possibility of aborted collapse to neutron star densities at late stages of stellar evolution (``fizzlers''). We have recently presented detailed linear analyses for polytropes of the most dynamically unstable global modes, the barlike modes. These produce bar distortions in the regions near the rotation axis but have trailing spiral arms toward the equator. In this paper, we use our linear eigenfunctions to predict the early nonlinear behavior of the dynamic instability and compare these ``quasi-linear'' predictions with several fully nonlinear hydrodynamics simulations. The comparisons demonstrate that the nonlinear saturation of the barlike instability is due to the self-interaction gravitational torques between the growing central bar and the spiral arms, where angular momentum is transferred outward from bar to arms. We also find a previously unsuspected resonance condition that accurately predicts the mass of the bar regions in our own simulations and in those published by other researchers. The quasi-linear theory makes other accurate predictions about consequences of instability, including properties of possible end-state bars and increases in central density, which can be large under some conditions. We discuss in some detail the application of our results to binary formation during protostellar collapse and to the formation of massive rotating black holes.

  2. Nondestructive Evaluation of Metal Fatigue.

    DTIC Science & Technology

    1977-02-01

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

  3. Unbound position II in MXCXXC metallochaperone model peptides impacts metal binding mode and reactivity: Distinct similarities to whole proteins.

    PubMed

    Shoshan, Michal S; Dekel, Noa; Goch, Wojciech; Shalev, Deborah E; Danieli, Tsafi; Lebendiker, Mario; Bal, Wojciech; Tshuva, Edit Y

    2016-06-01

    The effect of position II in the binding sequence of copper metallochaperones, which varies between Thr and His, was investigated through structural analysis and affinity and oxidation kinetic studies of model peptides. A first Cys-Cu(I)-Cys model obtained for the His peptide at acidic and neutral pH, correlated with higher affinity and more rapid oxidation of its complex; in contrast, the Thr peptide with the Cys-Cu(I)-Met coordination under neutral conditions demonstrated weaker and pH dependent binding. Studies with human antioxidant protein 1 (Atox1) and three of its mutants where S residues were replaced with Ala suggested that (a) the binding affinity is influenced more by the binding sequence than by the protein fold (b) pH may play a role in binding reactivity, and (c) mutating the Met impacted the affinity and oxidation rate more drastically than did mutating one of the Cys, supporting its important role in protein function. Position II thus plays a dominant role in metal binding and transport.

  4. Concurrent Structural Fatigue Damage Prognosis Under Uncertainty

    DTIC Science & Technology

    2014-04-30

    decomposition in time domain." Mechanical Systems and Signal Processing 28(0): 348-366. Lu, Z. and Y. Liu (2011). "Experimental investigation of...Structural response reconstruction based on empirical mode decomposition in time domain, Mechanical Systems and Signal Processing , 2012, 28, 348...and Signal Processing (under review) Xiang, Y., Liu, Y. An Equivalent Stress Transformation for Efficient Probabilistic Fatigue Crack Growth

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

    SciTech Connect

    Tai Asayama; Yukio Tachibana

    2007-09-30

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

  6. Fundamental parameters of RR Lyrae stars from multicolour photometry and Kurucz atmospheric models - II. Adaptation to double-mode stars

    NASA Astrophysics Data System (ADS)

    Barcza, S.; Benkő, J. M.

    2012-02-01

    Our photometric-hydrodynamic method is generalized to determine the fundamental parameters of multiperiodic radially pulsating stars. We report 302 UBV(RI)C Johnson-Kron-Cousins observations of GSC 4868-0831. Using these and the published photometric data of V372 Ser, we determine the metallicity, reddening, distance, mass, radius, equilibrium luminosity and effective temperature. The results underline the necessity of using multicolour photometry, including an ultraviolet band, to classify the subgroups of RR Lyrae stars properly. Our U observations might reveal that GSC 4868-0831 is a subgiant star pulsating in two radial modes and that V372 Ser is a giant star with the size and mass of an RRd star.

  7. Integrating a DNA Strand Displacement Reaction with a Whispering Gallery Mode Sensor for Label-Free Mercury (II) Ion Detection

    PubMed Central

    Wu, Fengchi; Wu, Yuqiang; Niu, Zhongwei; Vollmer, Frank

    2016-01-01

    Mercury is an extremely toxic chemical pollutant of our environment. It has attracted the world’s attention due to its high mobility and the ease with which it accumulates in organisms. Sensitive devices and methods specific for detecting mercury ions are, hence, in great need. Here, we have integrated a DNA strand displacement reaction with a whispering gallery mode (WGM) sensor for demonstrating the detection of Hg2+ ions. Our approach relies on the displacement of a DNA hairpin structure, which forms after the binding of mercury ions to an aptamer DNA sequence. The strand displacement reaction of the DNA aptamer provides highly specific and quantitative means for determining the mercury ion concentration on a label-free WGM sensor platform. Our approach also shows the possibility for manipulating the kinetics of a strand displacement reaction with specific ionic species. PMID:27483277

  8. DNA binding, DNA cleavage and cytotoxicity studies of a new water soluble copper(II) complex: The effect of ligand shape on the mode of binding

    NASA Astrophysics Data System (ADS)

    Kashanian, Soheila; Khodaei, Mohammad Mehdi; Roshanfekr, Hamideh; Shahabadi, Nahid; Mansouri, Ghobad

    2012-02-01

    The interaction of native calf thymus DNA (CT-DNA) with [Cu(ph 2phen)(phen-dione)Cl]Cl was studied at physiological pH by spectrophotometric, spectrofluorometric, circular dichroism, and viscometric techniques. Considerable hypochromicity and red shift are observed in the UV absorption band of the Cu complex. Binding constants ( Kb) of DNA with the complex were calculated at different temperatures. Thermodynamic parameters, enthalpy and entropy changes were calculated according to Van't Hoff equation, which indicated that reaction is predominantly enthalpically driven. All these results indicate that Cu(II) complex interacts with CT-DNA via intercalative mode. Also, this new complex induced cleavage in pUC18 plasmid DNA as indicated in gel electrophoresis and showed excellent antitumor activity against K562 (human chronic myeloid leukemia) and human T lymphocyte carcinoma-Jurkat cell lines.

  9. Coronal loop seismology using damping of standing kink oscillations by mode coupling. II. additional physical effects and Bayesian analysis

    NASA Astrophysics Data System (ADS)

    Pascoe, D. J.; Anfinogentov, S.; Nisticò, G.; Goddard, C. R.; Nakariakov, V. M.

    2017-04-01

    Context. The strong damping of kink oscillations of coronal loops can be explained by mode coupling. The damping envelope depends on the transverse density profile of the loop. Observational measurements of the damping envelope have been used to determine the transverse loop structure which is important for understanding other physical processes such as heating. Aims: The general damping envelope describing the mode coupling of kink waves consists of a Gaussian damping regime followed by an exponential damping regime. Recent observational detection of these damping regimes has been employed as a seismological tool. We extend the description of the damping behaviour to account for additional physical effects, namely a time-dependent period of oscillation, the presence of additional longitudinal harmonics, and the decayless regime of standing kink oscillations. Methods: We examine four examples of standing kink oscillations observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We use forward modelling of the loop position and investigate the dependence on the model parameters using Bayesian inference and Markov chain Monte Carlo (MCMC) sampling. Results: Our improvements to the physical model combined with the use of Bayesian inference and MCMC produce improved estimates of model parameters and their uncertainties. Calculation of the Bayes factor also allows us to compare the suitability of different physical models. We also use a new method based on spline interpolation of the zeroes of the oscillation to accurately describe the background trend of the oscillating loop. Conclusions: This powerful and robust method allows for accurate seismology of coronal loops, in particular the transverse density profile, and potentially reveals additional physical effects.

  10. Chronic Fatigue Syndrome

    MedlinePlus

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

  11. Chronic Fatigue Syndrome

    MedlinePlus

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

  12. Crystallographic studies of metal ion-DNA interactions: different binding modes of cobalt(II), copper(II) and barium(II) to N7 of guanines in Z-DNA and a drug-DNA complex.

    PubMed Central

    Gao, Y G; Sriram, M; Wang, A H

    1993-01-01

    Metal ion coordination to nucleic acids is not only required for charge neutralization, it is also essential for the biological function of nucleic acids. The structural impact of different metal ion coordinations of DNA helices is an open question. We carried out X-ray diffraction analyses of the interactions of the two transition metal ions Co(II) and Cu(II) and an alkaline earth metal ion Ba(II), with DNA of different conformations. In crystals, Co(II) ion binds exclusively at the N7 position of guanine bases by direct coordination. The coordination geometry around Co(II) is octahedral, although some sites have an incomplete hydration shell. The averaged Co-N7 bond distance is 2.3 A. The averaged Co-N7-C8 angle is 121 degrees, significantly smaller than the value of 128 degrees if the Co-N7 vector were to bisect the C5-N7-C8 bond angle. Model building of Co(II) binding to guanine N7 in B-DNA indicates that the coordinated waters in the axial positions would have a van der Waals clash with the neighboring base on the 5' side. In contrast, the major groove of A-DNA does not have enough room to accommodate the entire hydration shell. This suggests that Co(II) binding to either B-DNA or A-DNA may induce significant conformational changes. The Z-DNA structure of Cu(II)-soaked CGCGTG crystal revealed that the Cu(II) ion is bis-coordinated to N7 position of G10 and #G12 (# denotes a symmetry-related position) bases with a trigonal bipyramid geometry, suggesting a possible N7-Cu-N7 crosslinking mechanism. A similar bis-coordination to two guanines has also been seen in the interaction of Cu(II) in m5CGUAm5CG Z-DNA crystal and of Ba(II) with two other Z-DNA crystals. PMID:8371984

  13. Micromechanics of Fatigue.

    DTIC Science & Technology

    1992-06-01

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

  14. Fracture and Fatigue

    DTIC Science & Technology

    1988-04-01

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

  15. Fatigue and multiple sclerosis.

    PubMed

    Béthoux, F

    2006-07-01

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

  16. BIOMARKERS for CHRONIC FATIGUE

    PubMed Central

    Broderick, Gordon; Fletcher, Mary Ann

    2012-01-01

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

  17. DNA interaction studies of a copper (II) complex containing an antiviral drug, valacyclovir: the effect of metal center on the mode of binding.

    PubMed

    Shahabadi, Nahid; Fatahi, Parvin

    2012-07-01

    The water-soluble complex, [Cu(Val)(2)(NO(3))(2)]; in which Val = valacyclovir, an antiviral drug, has been synthesized and characterized by elemental analysis, furier transfer-infrared, hydrogen nuclear magnetic resonance (H NMR), and UV-Vis techniques. The binding of this Cu (II) complex to calf thymus DNA was investigated using fluorimetry, spectrophotometry, circular dichroism, and viscosimetry. In fluorimetric studies, the enthalpy and entropy of the reaction between the complex and calf-thymus DNA (CT-DNA) showed that the reaction is endothermic (ΔH = 208.22 kJ mol(-1); ΔS = 851.35 J mol(-1)K(-1)). The complex showed the absorption hyperchromism in its ultra violet-visible (UV-Vis) spectrum with DNA. The calculated binding constant, K(b), obtained from UV-Vis absorption studies was 2 × 10(5) M(-1). Moreover, the complex induced detectable changes in the circular dichroism spectrum of CT-DNA, as well as changes in its viscosity. The results suggest that this copper (II) complex interacts with CT-DNA via a groove-binding mode.

  18. Creep, fatigue and creep-fatigue interactions in modified 9% Chromium - 1% Molybdenum (P91) steels

    NASA Astrophysics Data System (ADS)

    Kalyanasundaram, Valliappa

    Grade P91 steel, from the class of advanced high-chrome ferritic steels, is one of the preferred materials for many elevated temperature structural components. Creep-fatigue (C-F) interactions, along with oxidation, can accelerate the kinetics of damage accumulation and consequently reduce such components' life. Hence, reliable C-F test data is required for meticulous consideration of C-F interactions and oxidation, which in turn is vital for sound design practices. It is also imperative to develop analytical constitutive models that can simulate and predict material response under various long-term in-service conditions using experimental data from short-term laboratory experiments. Consequently, the major objectives of the proposed research are to characterize the creep, fatigue and C-F behavior of grade P91 steels at 625 C and develop robust constitutive models for simulating/predicting their microstructural response under different loading conditions. This work will utilize experimental data from 16 laboratories worldwide that conducted tests (creep, fatigue and C-F) on grade P91 steel at 625°C in a round-robin (RR) program. Along with 7 creep deformation and rupture tests, 32 pure fatigue and 46 C-F tests from the RR are considered in this work. A phenomenological constitutive model formulated in this work needs just five fitting parameters to simulate/predict the monotonic, pure fatigue and C-F behavior of grade P91 at 625 C. A modified version of an existing constitutive model is also presented for particularly simulating its isothermal creep deformation and rupture behavior. Experimental results indicate that specimen C-F lives, as measured by the 2% load drop criterion, seem to decrease with increasing strain ranges and increasing hold times at 625°C. Metallographic assessment of the tested specimens shows that the damage mode in both pure fatigue and 600 seconds hold time cyclic tests is predominantly transgranular fatigue with some presence of

  19. CAD-II: the second version current-mode readout ASIC for high-resolution timing measurements

    NASA Astrophysics Data System (ADS)

    Yuan, Z. X.; Deng, Z.; Wang, Y.; Liu, Y. N.

    2016-07-01

    This paper presents the second version of a fully current-mode front-end ASIC, CAD (Current Amplifier and Discriminator), for MRPC detectors for TOF applications. Several upgrades have been made in this new version, including: 1). Using differential input stages with input impedance down to 30 Ω and LVDS compatible outputs; 2). Much higher current gain and bandwidth of 4.5 A/A and 380 MHz 3). Fabricated in 0.18 μ m CMOS process instead of 0.35 μ m CMOS technology used in CAD-I. The detailed design of the ASIC will be described as well as the measurement results. The single-ended input impedance could be as low as 32 Ω and the power consumption was measured to be 15 mW per channel. Input referred RMS noise current was about 0.56 μ A. The threshold could be set as low as 4.5 μ A referred to input, corresponding to 9 fC for the typical MRPC detector signal with 2 ns width. Sub-10 ps resolution has been measured for input signal above 200 μ A.

  20. Effects of Different Modes of Hot Cross-Rolling in 7010 Aluminum Alloy: Part II. Mechanical Properties Anisotropy

    NASA Astrophysics Data System (ADS)

    Mondal, Chandan; Singh, A. K.; Mukhopadhyay, A. K.; Chattopadhyay, K.

    2013-06-01

    The influence of microstructure and texture developed by different modes of hot cross-rolling on in-plane anisotropy ( A IP) of yield strength, work hardening behavior, and anisotropy of Knoop hardness (KHN) yield locus has been investigated. The A IP and work hardening behavior are evaluated by tensile testing at 0 deg, 45 deg, and 90 deg to the rolling direction, while yield loci have been generated by directional KHN measurements. It has been observed that specimens especially in the peak-aged temper, in spite of having a strong, rotated Brass texture, show low A IP. The results are discussed on the basis of Schmid factor analyses in conjunction with microstructural features, namely grain morphology and precipitation effects. For the specimen having a single-component texture, the yield strength variation as a function of orientation can be rationalized by the Schmid factor analysis of a perfectly textured material behaving as a quasi-single crystal. The work hardening behavior is significantly affected by the presence of solute in the matrix and the state of precipitation rather than texture, while yield loci derived from KHN measurements reiterate the low anisotropy of the materials. Theoretic yield loci calculated from the texture data using the visco-plastic self-consistent model and Hill's anisotropic equation are compared with that obtained experimentally.

  1. A Tropical Ocean Recharge Mechanism for Climate Variability. Part II: A Unified Theory for Decadal and ENSO Modes.

    NASA Astrophysics Data System (ADS)

    Wang, Xiaochun; Jin, Fei-Fei; Wang, Yuqing

    2003-11-01

    Decadal to interdecadal timescale variability in the Pacific region, commonly referred to as the Pacific decadal oscillation (PDO), is studied in this research using analytical and numerical models. A coupled analytical model is formulated to analyze the physical mechanism of both the PDO and ENSO. It has the equatorial β-plane dynamics of a reduced-gravity model coupled with the wind stress of fixed spatial patterns. The amplitude of the latter is proportional to the sea surface temperature (SST) anomaly in the eastern equatorial Pacific. The SST anomaly is governed by a simple thermal dynamic equation used for ENSO modeling. It is found that when a warm SST is coupled with cyclonic wind stress patterns in the eastern subtropical Pacific, an oscillation with a timescale of around 10 15 yr could be generated. In contrast, when a warm SST is coupled with only a westerly wind stress in the central equatorial Pacific, an ENSO-like oscillation could be generated with a timescale of around 3 5 yr. Thus the present research is potentially relevant to aspects of the PDO and the mechanism of the PDO may be understood as a weakly coupled decadal recharge oscillator similar to the recharge oscillator dynamics of ENSO. The sensitivity of these two kinds of coupled modes to different parameters is tested. Numerical integrations with the reduced-gravity shallow-water model in a rectangular basin and a similar coupled framework confirm the results of the analytical model.

  2. Reduction of RF accelerating voltage of Pohang Light Source-II superconducting RF cavity for stable top-up mode operation

    NASA Astrophysics Data System (ADS)

    Joo, Y.; Yu, I.; Park, I.; Chun, M. H.; Sohn, Y.

    2017-03-01

    The Pohang Light Source-II (PLS-II) is currently providing a top-up mode user-service operation with maximum available beam current of 400 mA and a beam emittance of below 10 nm-rad. The dimension of the beam bunch shortened to accomplish a low beam emittance of below 10 nm-rad from a high beam current of 400 mA increases the bunch charge density. As a result, the electron beam lifetime is significantly degraded and a high gradient of power is lost in the vacuum components of the storage ring. A study on how to reduce the bunch charge density without degrading beam emittance found that reducing the RF accelerating voltage (Vacc) can lower the bunch charge density by lengthening the bunch in the longitudinal direction. In addition, the Vacc required for stable operation with beam current of 400 mA can be reduced by lowering the external cavity quality factors (Qext values) of the superconducting cavities (SCs). To control the Qext values of SCs gradually without accessing the accelerator tunnel, a remote control motorized three-probe-tuner was installed in the transmission line of each SC. The optimum installation position of the three-probe-tuner was determined by using a finite-difference time-domain (FDTD) simulation and by experimenting on various installation positions of the three-probe-tuner. The Qext values of all the SCs were lowered to 1.40 × 105, and then, the Vacc required to store the beam current of 400 mA was decreased from 4.8 MV to 4.2 MV, which corresponds to 10% lengthening of the beam bunches. The stable operation with the reduced Vacc was confirmed during a 400 mA ten-day top-up mode user-service. Currently, the RF system of the PLS-II storage ring delivers the user-service operation with lowered Qext values to reduce the power loss at the vacuum components as well as the cryogenic heat load of SCs, and no significant problems have been found. This method of reducing the Vacc may also be applied in other synchrotron facilities.

  3. A Nitroxide-Tagged Platinum(II) Complex Enables the Identification of DNA G-Quadruplex Binding Mode

    PubMed Central

    Zhou, Yi-Wei; Wang, Hanqiang; Cao, Qian; Shen, Yong; Ji, Liang-Nian; Mao, Zong-Wan; Qin, Peter Z.

    2016-01-01

    We reported a novel strategy for investigating small molecule binding to G-quadruplexes (GQs). A newly synthesized dinuclear platinum(II) complex (Pt2L) containing a nitroxide radical was shown to selectively bind a GQ-forming sequence derived from human telomere (hTel). Using the nitroxide moiety as a spin label, electron paramagnetic resonance (EPR) spectroscopy was carried out to investigate binding between Pt2L and hTel GQ. Measurements indicated that two molecules of Pt2L bind with one molecule of hTel GQ. The inter-spin distance measured between the two bound Pt2L, together with molecular docking analyses, revealed that Pt2L predominately binds to the neighboring narrow and wide grooves of the G-tetrads as hTel adopts the antiparallel conformation. The design and synthesis of nitroxide tagged GQ binders, and the use of spin-labeling/EPR to investigate their interactions with GQs, will aid the development of small molecules for manipulating GQs involved in crucial biological processes. PMID:26845489

  4. Mode-coupling approach to polymer diffusion in an unentangled melt. II. The effect of viscoelastic hydrodynamic interactions

    NASA Astrophysics Data System (ADS)

    Farago, J.; Meyer, H.; Baschnagel, J.; Semenov, A. N.

    2012-05-01

    A mode-coupling theory (MCT) version (called hMCT thereafter) of a recently presented theory [Farago, Meyer, and Semenov, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.107.178301 107, 178301 (2011)] is developed to describe the diffusional properties of a tagged polymer in a melt. The hMCT accounts for the effect of viscoelastic hydrodynamic interactions (VHIs), that is, a physical mechanism distinct from the density-based MCT (dMCT) described in the first paper of this series. The two versions of the MCT yield two different contributions to the asymptotic behavior of the center-of-mass velocity autocorrelation function (c.m. VAF). We show that in most cases the VHI mechanism is dominant; for long chains and prediffusive times it yields a negative tail ∝-N-1/2t-3/2 for the c.m. VAF. The case of non-momentum-conserving dynamics (Langevin or Monte Carlo) is discussed as well. It generally displays a distinctive behavior with two successive relaxation stages: first -N-1t-5/4 (as in the dMCT approach), then -N-1/2t-3/2. Both the amplitude and the duration of the first t-5/4 stage crucially depend on the Langevin friction parameter γ. All results are also relevant for the early time regime of entangled melts. These slow relaxations of the c.m. VAF, thus account for the anomalous subdiffusive regime of the c.m. mean square displacement widely observed in numerical and experimental works.

  5. Probabilistic Fatigue: Computational Simulation

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.

    2002-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1994-02-01

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

  7. Fatigue crack growth in lithium hydride

    SciTech Connect

    Healy, T.E.

    1993-09-01

    Subcritical fatigue crack growth, from cyclic tensile loading, was demonstrated in warm pressed Polycrystalline lithium hydride. Experiments were performed with cyclic tension-tension crack opening (mode I) loads applied to a pre-cracked compact type specimen in an argon environment at a temperature of 21C (70F). The fatigue crack growth was found to occur between 7.56 {times} 10{sup {minus}ll} M/cycle (2.98 {times} l0{sup {minus}9} in/cycle) and 2.35 {times} l0{sup {minus}8} m/cycle (9.24{times}10{sup {minus}7} in/cycle) for a range of stress intensity factors between 1.04 MPa{center_dot}{radical}m (0.95 ksi{center_dot}{radical}in) and 1.49 MPa{center_dot}{radical}m (1.36 ksi{center_dot}{radical}in). The rate of fatigue crack growth from cyclic tensile loading was found to be in excess of crack growth from sustained loading at an equivalent stress intensity factor. Furthermore, a fatigue threshold was not evident from the acquired data.

  8. Fatigue properties of shuttle thermal protection system

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

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

  9. Operational Risk Management of Fatigue Effects II

    DTIC Science & Technology

    2008-08-01

    promotes wakefulness, enhances vigilance performance and lessens feelings of weariness. The half- life for caffeine metabolism is typically 5-6 hours...excellent-quality sleep. Time of Day The period of concern is between midnight and 06:00 on the body clock. If mental work is to be performed during...10 In this case, the ability to perform such functions as logical reasoning and mental arithmetic. 41 Approved for public

  10. Isothermal fatigue of low tin lead based solder

    NASA Astrophysics Data System (ADS)

    Vayman, Semyon; Fine, Morris E.; Jeannotte, Dexter A.

    1988-04-01

    Low tin lead based solder fails by intergranular and/or transgranular modes depending upon experimental conditions. At low frequency and in tests with hold times separation of grains is the main mode of fracture. In the 5 to 100 °C temperature range at high frequency (> 10-2 Hz) and at high total strain range (0.75 pct) the failure mode is mixed transgranular-intergranular; at a low total strain range (0.3 pct) the mode of failure is intergranular. Change in failure mode leads to a bend in the Coffin-Manson plot. Tensile hold time and combined tensile and compressive hold times are found to reduce dramatically the fatigue cycles to failure of this solder. A simple mathematical relation between the fatigue life of the solder and ramp time, tensile, and compressive hold times is developed.

  11. Illuminating heterogeneous anisotropic upper mantle: testing a new anisotropic teleseismic body-wave tomography code - part II: Inversion mode

    NASA Astrophysics Data System (ADS)

    Munzarova, Helena; Plomerova, Jaroslava; Kissling, Edi

    2015-04-01

    necessary step before AniTomo is applied to real datasets. We examine various aspects coming along with anisotropic tomography such as setting a starting anisotropic model and parameters controlling the inversion, and particularly influence of a ray coverage on resolvability of individual anisotropic parameters. Synthetic testing also allows investigation of the well-known trade-off between effects of P-wave anisotropy and isotropic heterogeneities. Therefore, the target synthetic models are designed to represent schematically different heterogeneous anisotropic structures of the upper mantle. Testing inversion mode of the AniTomo code, considering an azimuthally quasi-equal distribution of rays and teleseismic P-wave incidences, shows that a separation of seismic anisotropy and isotropic velocity heterogeneities is plausible and that the correct orientation of the symmetry axes in a model can be found within three iterations for well-tuned damping factors.

  12. Evaluation of Fatigue Performance of Asphalt Based on Constant Strain DSR Test

    NASA Astrophysics Data System (ADS)

    Zhu, H. Z.; Yan, E. H.; Lu, Z. T.

    2017-02-01

    Asphalt performance has important effect on the fatigue resistance performance of asphalt mixture. This research based on the DSR time scanning mode, investigated the constant strain performance of 70 # matrix asphalt and SBS modified asphalt. Based on 50% G* 0 to simulate the fatigue performance of two kinds of the asphalt.

  13. Thermal fatigue of beryllium

    SciTech Connect

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

    1995-09-01

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

  14. Inspiratory muscles experience fatigue faster than the calf muscles during treadmill marching.

    PubMed

    Perlovitch, Renana; Gefen, Amit; Elad, David; Ratnovsky, Anat; Kramer, Mordechai R; Halpern, Pinchas

    2007-04-16

    The possibility that respiratory muscles may fatigue during extreme physical activity and thereby become a limiting factor leading to exhaustion is debated in the literature. The aim of this study was to determine whether treadmill marching exercise induces respiratory muscle fatigue, and to compare the extent and rate of respiratory muscle fatigue to those of the calf musculature. To identify muscle fatigue, surface electromyographic (EMG) signals of the inspiratory (sternomastoid, external intercostals), expiratory (rectus abdominis and external oblique) and calf (gastrocnemius lateralis) muscles were measured during a treadmill march of 2 km at a constant velocity of 8 km/h. The extent of fatigue was assessed by determining the increase in root-mean-square (RMS) of EMG over time, and the rate of fatigue was assessed from the slope of the EMG RMS versus time curve. Results indicated that (i) the inspiratory and calf muscles are the ones experiencing the most dominant fatigue during treadmill marching, (ii) the rate of fatigue of each muscle group was monotonic between the initial and terminal phases of exercise, and (iii) the inspiratory muscles fatigue significantly faster than the calf at the terminal phase of exercise, and are likely to fatigue faster during the initial exercise as well. Accordingly, this study supports the hypothesis that fatigue of the inspiratory muscles may be a limiting factor during exercise.

  15. An indentation fatigue strength law

    NASA Astrophysics Data System (ADS)

    Xu, Baoxing; Yonezu, Akio; Chen, Xi

    2010-05-01

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

  16. Low-cycle thermal fatigue

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1986-01-01

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

  17. Chronic Fatigue Syndrome (CFS): Symptoms

    MedlinePlus

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

  18. Fatigue and fracture overview

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.

    1986-01-01

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

  19. Fatigue and Barkhausen effect

    NASA Astrophysics Data System (ADS)

    Tong, Wei

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

  20. Molecular recognition modes between adenine or adeniniun(1+) ion and binary M(II)(pdc) chelates (MCoZn; pdc=pyridine-2,6-dicarboxylate(2-) ion).

    PubMed

    Del Pilar Brandi-Blanco, María; Choquesillo-Lazarte, Duane; Domínguez-Martín, Alicia; Matilla-Hernández, Antonio; González-Pérez, Josefa María; Castiñeiras, Alfonso; Niclós-Gutiérrez, Juan

    2013-10-01

    Mixed ligand M(II)-complexes (MCoZn) with pyridine-2,6-dicarboxylate(2-) chelator (pdc) and adenine (Hade) have been synthesized and studied by X-ray diffraction and other spectral and thermal methods: [Cu(pdc)(H(N9)ade)(H2O)] (1), [Cu2(pdc)2(H2O)2(μ2-N3,N7-H(N9)ade)]·3H2O (2), trans-[M(pdc)(H(N9)ade)(H2O)2]·nH2O for MCo (3-L, 3-M, 3-H) or Zn (4-L, 4-H), where n is 0, 1 or 3 for the 'lowest' (L), 'medium' (M) and 'highest' (H) hydrated forms, and the salt trans-[Ni(pdc)(H2(N1,N9)ade)(H2O)2]Cl·2H2O (5). In all the nine compounds, both neutral and cationic adenine exist as their most stable tautomer and the molecular recognition pattern between the metal-pdc chelates and the adenine or adeninium(1+) ligands involves the MN7 bond in cooperation with an intra-molecular N6H⋯O(coordinated carboxylate) interligand interaction. In addition the dinuclear copper(II) compound (2) has the CuN3 bond and the N9H⋯O(coord. carboxylate) interaction. The structures of mononuclear ternary complexes proved that the molecular recognition pattern is the same irrespective of (a) the coordination geometry of the complex molecule, (b) the different hydrated forms of crystals with Co or Zn, and (c) the neutral of cationic form of the adenine ligand. These features are related to the mer-NO2 chelating ligand conformation (imposed by the planar rigidity of pdc) as a driving force for the observed metal binding mode.

  1. Ferrocene and (arene)ruthenium(II) complexes of the natural anticancer naphthoquinone plumbagin with enhanced efficacy against resistant cancer cells and a genuine mode of action.

    PubMed

    Spoerlein-Guettler, Cornelia; Mahal, Katharina; Schobert, Rainer; Biersack, Bernhard

    2014-09-01

    A series of ferrocene and (arene)ruthenium(II) complexes attached to the naturally occurring anticancer naphthoquinones plumbagin and juglone was tested for efficacy against various cancer cell lines and for alterations in the mode of action. The plumbagin ferrocene and (p-cymene)Ru(II) conjugates 1c and 2a overcame the multi-drug drug resistance of KB-V1/Vbl cervix carcinoma cells and showed IC50 (72 h) values around 1 μM in growth inhibition assays using 3-(4,5-dimethyl-2-yl)-2,5-diphenyltetrazolium bromide (MTT). They were further investigated for their influence on the cell cycle of KB-V1/Vbl and HCT-116 colon carcinoma cells, on the generation of reactive oxygen species (ROS) by the latter cell line, for their substrate character for the P-glycoprotein drug eflux pump via the calcein-AM efflux assays, and for DNA affinity by the electrophoretic mobility shift assay (EMSA). The derivatives 1c and 2a increased the number of dead cancer cells (sub-G0/G1 fraction) in a dose- and time-dependent manner. ROS levels were significantly increased upon treatment with 1c and 2a. These compounds also showed a greater affinity to linear DNA than plumbagin. While plumbagin did not affect calcein-AM transport by P-glycoprotein the derivatives 1c and 2a exhibited a 50% or 80% inhibition of the P-glycoprotein-mediated calcein-AM efflux relative to the clinically established sensitizer verapamil.

  2. The influence of mode of delivery, obstetric analgesia and anaesthesia on the response of isolated human chorionic plate arteries to angiotensin II.

    PubMed

    Odum, C U; Pipkins, F B

    1989-01-01

    A six point concentration: response curved of the contractile effect of angiotensin II (AII) on helically-cut strips of human chorionic plate artery strips were established at final concentrations of between 10(-14) to 10(-9) M. The tissues were obtained from the placentae of primigravid patients who had normal pregnancy, and also from those with pregnancy induced hypertension (PIH). The tissue response were then related to mode of delivery, obstetric analgesia, and anaesthesia. A total of 36 chorionic plate arteries from 12 primigravid patients were studied. i) The overall initial EC50s of the tissues ranged from 8.0 x 10(-13) M and 4.5 x 10(-13) M. The tissues from PIH patients were significantly more sensitive to AII, when compared with tissues from the normotensive subjects (P greater than or equal to 0.01 less than or equal to 0.05). ii) The tissues from epidural vaginal deliveries were also significantly more sensitive to AII, than those from both normal vaginal deliveries and caesarean deliveries respectively. The median gradients of the semi-log transformed concentration response curved were 2.4 +/- 0.18; 1.27 +/- 0.37, and 1.5 +/- 0.49, for epidural, Caeserean and normal vaginal deliveries respectively. iii) It is suggested that whilst Lumbar epidural analgesia may be of great value in pain relief in labour and in the control of intrapartum hypertension in pre-eclampsia, this procedure may be associated with hypersensitivity and perhaps vasospasm of the placental vasculature to vasoactive agents invivo.

  3. The application of probabilistic design theory to high temperature low cycle fatigue

    NASA Technical Reports Server (NTRS)

    Wirsching, P. H.

    1981-01-01

    Metal fatigue under stress and thermal cycling is a principal mode of failure in gas turbine engine hot section components such as turbine blades and disks and combustor liners. Designing for fatigue is subject to considerable uncertainty, e.g., scatter in cycles to failure, available fatigue test data and operating environment data, uncertainties in the models used to predict stresses, etc. Methods of analyzing fatigue test data for probabilistic design purposes are summarized. The general strain life as well as homo- and hetero-scedastic models are considered. Modern probabilistic design theory is reviewed and examples are presented which illustrate application to reliability analysis of gas turbine engine components.

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

    PubMed

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

    2010-12-01

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

  5. The Nature of Fatigue in Chronic Fatigue Syndrome.

    PubMed

    Olson, Karin; Zimka, Oksana; Stein, Eleanor

    2015-10-01

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

  6. Fatigue of notched fiber composite laminates. Part 1: Analytical model

    NASA Technical Reports Server (NTRS)

    Mclaughlin, P. V., Jr.; Kulkarni, S. V.; Huang, S. N.; Rosen, B. W.

    1975-01-01

    A description is given of a semi-empirical, deterministic analysis for prediction and correlation of fatigue crack growth, residual strength, and fatigue lifetime for fiber composite laminates containing notches (holes). The failure model used for the analysis is based upon composite heterogeneous behavior and experimentally observed failure modes under both static and fatigue loading. The analysis is consistent with the wearout philosophy. Axial cracking and transverse cracking failure modes are treated together in the analysis. Cracking off-axis is handled by making a modification to the axial cracking analysis. The analysis predicts notched laminate failure from unidirectional material fatique properties using constant strain laminate analysis techniques. For multidirectional laminates, it is necessary to know lamina fatique behavior under axial normal stress, transverse normal stress and axial shear stress. Examples of the analysis method are given.

  7. Criterion for mixed mode fracture in composite bonded joints

    NASA Technical Reports Server (NTRS)

    Mall, S.; Kochhar, N. K.

    1986-01-01

    A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite-epoxy composite adherends bonded with a toughened epoxy adhesive. The mode I, mode II and mixed mode I-II fracture energies of the tested adhesives were found to be equal to each other. The criterion for mixed mode fracture in composite bonded joints was found.

  8. The impact of hygrothermal preconditioning on mode II interlaminar fracture toughness in unidirectional carbon fiber reinforced epoxy composites: An experimental investigation

    NASA Astrophysics Data System (ADS)

    Hempowicz, Michael L.

    The correlation between the interlaminar Mode II fracture toughness (GIIC) of a carbon fiber reinforced epoxy and other material properties across different conditioning regimes was investigated. Specimens were preconditioned using select hygrothermal criteria to evaluate how changes in the material and mechanical properties in a carbon fiber/epoxy composite correlations with changes in GIIC for each regime. An increase in GIIC from baseline values was demonstrated across all conditions from end-notched flexure (ENF) testing. Dynamic mechanical analysis (DMA) and tensile tests had varying responses based on preconditioning environment. Since tensile and some DMA properties rely on fiber strength and show property loss with increased plasticization, fiber strength may not have a large impact on GIIC properties. Test data also implied that the GIIC increased when consolidation of the polymer chains occurred in the arid condition as well as when crosslink density increased in the moisture exposed conditions. From these results it is believed that the chemical and physical changes in matrix cohesion are more important to GIIC behavior prediction than fiber behavior.

  9. Control over the Self-Assembly Modes of Pt(II) Complexes by Alkyl Chain Variation: From Slipped to Parallel π-Stacks.

    PubMed

    Allampally, Naveen Kumar; Mayoral, María José; Chansai, Sarayute; Lagunas, María Cristina; Hardacre, Christopher; Stepanenko, Vladimir; Albuquerque, Rodrigo Q; Fernández, Gustavo

    2016-06-01

    We report the self-assembly of a new family of hydrophobic, bis(pyridyl) Pt(II) complexes featuring an extended oligophenyleneethynylene-derived π-surface appended with six long (dodecyloxy (2)) or short (methoxy (3)) side groups. Complex 2, containing dodecyloxy chains, forms fibrous assemblies with a slipped arrangement of the monomer units (dPt⋅⋅⋅Pt ≈14 Å) in both nonpolar solvents and the solid state. Dispersion-corrected PM6 calculations suggest that this organization is driven by cooperative π-π, C-H⋅⋅⋅Cl and π-Pt interactions, which is supported by EXAFS and 2D NMR spectroscopic analysis. In contrast, nearly parallel π-stacks (dPt⋅⋅⋅Pt ≈4.4 Å) stabilized by multiple π-π and C-H⋅⋅⋅Cl contacts are obtained in the crystalline state for 3 lacking long side chains, as shown by X-ray analysis and PM6 calculations. Our results reveal not only the key role of alkyl chain length in controlling self-assembly modes but also show the relevance of Pt-bound chlorine ligands as new supramolecular synthons.

  10. Muscle Deoxygenation Causes Muscle Fatigue

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

  11. Influence of microstructure on high-cycle fatigue of Ti-6Al-4V: Bimodal vs. lamellar structures

    NASA Astrophysics Data System (ADS)

    Nalla, R. K.; Ritchie, R. O.; Boyce, B. L.; Campbell, J. P.; Peters, J. O.

    2002-03-01

    The high-cycle fatigue (HCF) of titanium alloy turbine engine components remains a principal cause of failures in military aircraft engines. A recent initiative sponsored by the United States Air Force has focused on the major drivers for such failures in Ti-6Al-4V, a commonly used turbine blade alloy, specifically for fan and compressor blades. However, as most of this research has been directed toward a single processing/heat-treated condition, the bimodal (solution-treated and overaged (STOA)) microstructure, there have been few studies to examine the role of microstructure. Accordingly, the present work examines how the overall resistance to high-cycle fatigue in Ti-6Al-4V compares between the bimodal microstructure and a coarser lamellar ( β-annealed) microstructure. Several aspects of the HCF problem are examined. These include the question of fatigue thresholds for through-thickness large and short cracks; microstructurally small, semi-elliptical surface cracks; and cracks subjected to pure tensile (mode I) and mixed-mode (mode I+II) loading over a range of load ratios (ratio of minimum to maximum load) from 0.1 to 0.98, together with the role of prior damage due to sub-ballistic impacts (foreign-object damage (FOD)). Although differences are not large, it appears that the coarse lamellar microstructure has improved smooth-bar stress-life (S-N) properties in the HCF regime and superior resistance to fatigue-crack propagation (in pure mode I loading) in the presence of cracks that are large compared to the scale of the microstructure; however, this increased resistance to crack growth compared to the bimodal structure is eliminated at extremely high load ratios. Similarly, under mixed-mode loading, the lamellar microstructure is generally superior. In contrast, in the presence of microstructurally small cracks, there is little difference in the HCF properties of the two microstructures. Similarly, resistance to HCF failure following FOD is comparable in the

  12. Hysteresis and Fatigue

    NASA Astrophysics Data System (ADS)

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

    1993-06-01

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

  13. Incompatibility and Mental Fatigue

    ERIC Educational Resources Information Center

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

    2011-01-01

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

  14. Fatigue Characterization of Fire Resistant Syntactic Foam Core Material

    NASA Astrophysics Data System (ADS)

    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

  15. Defect-induced fatigue microcrack formation in cement mantle.

    PubMed

    Qi, Gang; Li, Jihui; Mouchon, W Paul; Lewis, Gladius

    2005-11-01

    Acoustic emission (AE) was used to monitor the progress of the fatigue damage process in the cement mantles of two cemented femur stem constructs that contained naturally occurring defects. After the fatigue tests, morphological features of the defects were investigated using an environmental scanning electron microscope. It showed that the regions with no visible defects were mainly microcrack free, whereas the defect regions were the main sources generating microcracks. Two types of microcracks were identified: type I and type II. Signal energies associated with type I microcracks were about an order of magnitude higher than that of type II. The microstructural investigations of the defects and the areas in the vicinity of the defects suggested their categorization into stable and unstable. The accumulative energy-time relationships revealed that stable and unstable microcrack curves had convex [formula: see text], and concave [formula: see text] shapes, respectively. The progress of fatigue microcrack formation occurred over three distinct phases: initiation, transition, and stableness.

  16. Fatigue of notched fiber composite laminates. Part 2: Analytical and experimental evaluation

    NASA Technical Reports Server (NTRS)

    Kulkarni, S. V.; Mclaughlin, P. V., Jr.; Pipes, R. B.

    1976-01-01

    The analytical/experimental correlation study was performed to develop an understanding of the behavior of notched Boron/epoxy laminates subjected to tension/tension fatigue loading. It is postulated that the fatigue induced property changes (stiffness as well as strength) of the laminate can be obtained from the lamina fatigue properties. To that end, the Boron/epoxy lamina static and fatigue data (lifetime, residual stiffness and strength) were obtained initially. The longitudinal and transverse tension data were determined from the (0) and (90) laminate tests while the in-plane shear data were obtained from the (+ or - 45) sub s laminates. The static tests obtained the notched strength and mode of failure while the fatigue tests determined lifetime, damage propagation and residual strength. The failure in static tension occurred in a transverse crack propagation mode.

  17. Fatigue Crack Growth of Age-Hardened Al Alloy Under Ultrasonic Loading

    NASA Astrophysics Data System (ADS)

    Chen, Q.; Kawagoishi, N.; Kariya, K.; Nu, Y.; Goto, M.

    An age-hardened and extruded Al alloy 7075-T6 was fatigued under both ultrasonic loading (20kHz) and rotating bending (50Hz) in the environments of controlled humidity, distilled water and oxygen gas respectively, to investigate the availability of ultrasonic fatigue test as a time-saving tool for the reliability evaluation of materials subjected to conventional frequency loading. Although fatigue strength decreased slightly at relative humidity below 60-70%, it degraded significantly when the humidity was increased beyond that level, irrespective of the loading frequency. However, the mechanisms of strength degradation involved in high humidity are quite different. Under rotating bending, fatigue strength decreased because crack growth was accelerated due to brittle fracture, whileas the decrease in fatigue strength under ultrasonic loading was caused by crack propagation transition from tensile mode to shear mode cracking.

  18. Issues related to SPR joints subjected to fatigue loads

    NASA Astrophysics Data System (ADS)

    De Luca, A.; Senatore, F.; Greco, A.

    2016-05-01

    SPR joints will represent an alternative solution to spot welding in automotive field. However, their fatigue behavior shows several critical issues. After a brief introduction of this new solution, different crack modes are described, emphasizing the parameters that characterize them, i.e. the applied loads, the geometry of the joint and other phenomenon as fretting, vibration and corrosion.

  19. 14 CFR 29.571 - Fatigue evaluation of structure.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ..., fuselage, fixed and movable control surfaces, engine and transmission mountings, landing gear, and their... must be shown by analysis supported by test evidence and, if available, service experience to be of... determination of the probable locations and modes of damage caused by fatigue, considering environmental...

  20. Fatigue Life Methodology for Tapered Hybrid Composite Flexbeams

    NASA Technical Reports Server (NTRS)

    urri, Gretchen B.; Schaff, Jeffery R.

    2006-01-01

    Nonlinear-tapered flexbeam specimens from a full-size composite helicopter rotor hub flexbeam were tested under combined constant axial tension and cyclic bending loads. Two different graphite/glass hybrid configurations tested under cyclic loading failed by delamination in the tapered region. A 2-D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. The analysis results from two geometrically nonlinear finite element codes, ANSYS and ABAQUS, are presented and compared. Strain energy release rates (G) associated with simulated delamination growth in the flexbeams are presented from both codes. These results compare well with each other and suggest that the initial delamination growth from the tip of the ply-drop toward the thick region of the flexbeam is strongly mode II. The peak calculated G values were used with material characterization data to calculate fatigue life curves for comparison with test data. A curve relating maximum surface strain to number of loading cycles at delamination onset compared well with the test results.

  1. Fatigue Life Analysis of Tapered Hybrid Composite Flexbeams

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.; Schaff, Jeffery R.; Dobyns, Alan L.

    2002-01-01

    Nonlinear-tapered flexbeam laminates from a full-size composite helicopter rotor hub flexbeam were tested under combined constant axial tension and cyclic bending loads. The two different graphite/glass hybrid configurations tested under cyclic loading failed by delamination in the tapered region. A 2-D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. The analysis results from two geometrically nonlinear finite element codes, ANSYS and ABAQUS, are presented and compared. Strain energy release rates (G) obtained from the above codes using the virtual crack closure technique (VCCT) at a resin crack location in the flexbeams are presented for both hybrid material types. These results compare well with each other and suggest that the initial delamination growth from the resin crack toward the thick region of the flexbeam is strongly mode II. The peak calculated G values were used with material characterization data to calculate fatigue life curves and compared with test data. A curve relating maximum surface strain to number of loading cycles at delamination onset compared reasonably well with the test results.

  2. Monitoring of fatigue crack growth using guided ultrasonic waves

    NASA Astrophysics Data System (ADS)

    Masserey, B.; Kostson, E.; Fromme, P.

    2010-04-01

    Varying loading conditions of aircraft structures result in stress concentration at fastener holes, where multi layer components are connected, possibly leading to the development of fatigue cracks. Guided ultrasonic waves propagating along a structure allow in principle for the efficient non-destructive testing of large plate-like structures, such as aircraft wings. This contribution presents a study of the detection and monitoring of fatigue crack growth using both low frequency and higher frequency guided ultrasonic wave modes. Two types of structures were used, single layer aluminum tensile specimens, and multi layer structures consisting of two adhesively bonded aluminum plate-strips. Fatigue experiments were carried out and it was shown that fatigue crack detection and growth monitoring at a fastener hole during cyclic loading using both guided wave types is possible. The sensitivity and repeatability of the measurements were ascertained, having the potential for fatigue crack detection at critical and difficult to access fastener locations. Good agreement was observed between the experimental results and predictions from full three-dimensional numerical simulations of the scattering of the low frequency guided ultrasonic wave at the fastener hole and crack. The robustness of the methodology for practical in-situ ultrasonic monitoring of fatigue crack growth is discussed.

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

    PubMed

    Lloyd, A R

    1998-09-28

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

  4. Fatigue Assessment: Subjective Peer-to-Peer Fatigue Scoring (Reprint)

    DTIC Science & Technology

    2013-10-01

    basis for sleepiness and fatigue, as well as potential performance defi cits associ- ated with fatigued states. There are many biomathematical models ...in current use with most fundamentally infl uenced by the two or three-process model ( 7 , 9 , 12 ). Yet models are subject to many limitations...7 ). Thus, models have potential to be of great value, but also lack many independent variables that may be im- portant in fatigue and related

  5. [Childhood chronic fatigue syndrome].

    PubMed

    Miike, Teruhisa

    2007-06-01

    Chronic fatigue syndrome in childhood and adolescents(CCFS) is a complex and debilitation with severe morbidity and confusion. It is common condition with up to 3-5% of children and adolescents showing strange fatigue and confusion for more than 30 days. In this condition, four major symptoms are important: sleep disorders, easy fatigability, disturbed learning and memorization and immunological problems. Routine laboratory studies are similar to adult CFS, although abnormalities can be seen on serum pyruvic acid level, OGTT pattern, deep body temperature rhythm, hormonal secretion rhythm, and cerebral blood flow. For a diagnosis of CCFS, a research group supported by Japanese ministry of health, labor and welfare developed CCFS case definition on 2004. Treatment focused to correct disrupted circadian rhythms and supply of energy.

  6. Probabilistic Mesomechanical Fatigue Model

    NASA Technical Reports Server (NTRS)

    Tryon, Robert G.

    1997-01-01

    A probabilistic mesomechanical fatigue life model is proposed to link the microstructural material heterogeneities to the statistical scatter in the macrostructural response. The macrostructure is modeled as an ensemble of microelements. Cracks nucleation within the microelements and grow from the microelements to final fracture. Variations of the microelement properties are defined using statistical parameters. A micromechanical slip band decohesion model is used to determine the crack nucleation life and size. A crack tip opening displacement model is used to determine the small crack growth life and size. Paris law is used to determine the long crack growth life. The models are combined in a Monte Carlo simulation to determine the statistical distribution of total fatigue life for the macrostructure. The modeled response is compared to trends in experimental observations from the literature.

  7. Helicopter Fatigue Design Guide

    DTIC Science & Technology

    1983-11-01

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

  8. Chronic Fatigue Syndrome

    PubMed Central

    Leyton, Edward; Pross, Hugh

    1992-01-01

    To determine the effect of certain herbal and homeopathic preparations on symptoms, lymphocyte markers, and cytotoxic function of the lymphocytes in patients with chronic fatigue syndrome, we studied six outpatients diagnosed with the disease by their family physicians. Patients were given herbal and homeopathic preparations after a 3-week symptom-recording period. After treatment, symptoms were again recorded. Blood samples were taken before and after treatment. None of the values showed any significant change after treatment. PMID:21221272

  9. [Fatigue and anemia].

    PubMed

    Ivanova, K; Zeller, A

    2009-12-02

    We herein report on an 80-year old male patient with a history of muscle weakness, fatigue and weight loss since several months. Because of a pathologic synacthen test in combination with decreased levels of ACTH, we diagnosed a secondary chronic adrenal insufficiency. Because of a normochromic, normocytic, and hypo-proliferative anemia, bone marrow puncture was performed, showing an anemia of chronic disease. We initiated hydrocortisone and anemia and patients' symptoms were fully reconstituted.

  10. Effects of R-ratio on fatigue crack growth in a Ti-24Al-11Nb alloy

    NASA Technical Reports Server (NTRS)

    Bae, K.; Nelson, H. G.

    1993-01-01

    The microscopic fatigue crack behavior in a Ti-24Al-11Nb alloy was investigated. Particular attention was given to the path of the fatigue crack through the microstructure, the fracture mode, and the effects of R-ratio and crack closure on the fatigue crack growth behavior. The FCGR of the alloy at R = 0.5 was an order of magnitude higher than that at R = 0.1.

  11. Hysteresis and fatigue

    SciTech Connect

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

    1993-06-01

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

  12. Fatigue syndrome in sarcoidosis.

    PubMed

    Górski, Witold; Piotrowski, Wojciech J

    2016-01-01

    Sarcoidosis is an inflammatory disease of unknown etiology. Most commonly it results in the formation of non-caseating granulomas in intrathoracic lymph nodes and lung parenchyma, but the clinical course and picture may be complicated by extrapulmonary involvement and many non-respiratory signs and symptoms which are directly related to the disease. In addition, sarcoidosis patients may suffer from a plethora of symptoms of uncertain or unknown origin. Fatigue is one of these symptoms, and according to some authors it is reported by the majority of patients with active sarcoidosis, but also by a smaller proportion of patients with inactive sarcoidosis, or even with complete clinical and radiological remission. Therefore the term fatigue syndrome is frequently used to name this clinical problem. The definition of fatigue syndrome in sarcoidosis is imprecise and the syndrome is usually recognized by use of validated questionnaires. In this review the uptodate knowledge in this field was presented and different challenges connected with this syndrome were described.

  13. Fatigue in systemic lupus erythematosus.

    PubMed

    Ahn, Grace E; Ramsey-Goldman, Rosalind

    2012-04-01

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

  14. Fracture mechanics and corrosion fatigue.

    NASA Technical Reports Server (NTRS)

    Mcevily, A. J.; Wei, R. P.

    1972-01-01

    Review of the current state-of-the-art in fracture mechanics, particularly in relation to the study of problems in environment-enhanced fatigue crack growth. The usefulness of this approach in developing understanding of the mechanisms for environmental embrittlement and its engineering utility are discussed. After a brief review of the evolution of the fracture mechanics approach and the study of environmental effects on the fatigue behavior of materials, a study is made of the response of materials to fatigue and corrosion fatigue, the modeling of the mechanisms of the fatigue process is considered, and the application of knowledge of fatigue crack growth to the prediction of the high cycle life of unnotched specimens is illustrated.

  15. Probabilistic Fatigue Damage Program (FATIG)

    NASA Technical Reports Server (NTRS)

    Michalopoulos, Constantine

    2012-01-01

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

  16. Gear Fatigue Diagnostics and Prognostics

    DTIC Science & Technology

    2013-01-01

    one for single gear tooth fatigue, and one for gear-on-gear dynamometer-based tester ) we have been collecting crack initiation and crack propagation...fatigue tester ); and torque, angular speed, vibration, temperature, and crack-propagation (gear-on-gear dynamometer-based tester ). The main outcome...Description The test consists of two set of tests on a dynamometer and one set of test on the fatigue tester and some additional activities. Fig

  17. Fatigue failure of metal components as a factor in civil aircraft accidents

    NASA Technical Reports Server (NTRS)

    Holshouser, W. L.; Mayner, R. D.

    1972-01-01

    A review of records maintained by the National Transportation Safety Board showed that 16,054 civil aviation accidents occurred in the United States during the 3-year period ending December 31, 1969. Material failure was an important factor in the cause of 942 of these accidents. Fatigue was identified as the mode of the material failures associated with the cause of 155 accidents and in many other accidents the records indicated that fatigue failures might have been involved. There were 27 fatal accidents and 157 fatalities in accidents in which fatigue failures of metal components were definitely identified. Fatigue failures associated with accidents occurred most frequently in landing-gear components, followed in order by powerplant, propeller, and structural components in fixed-wing aircraft and tail-rotor and main-rotor components in rotorcraft. In a study of 230 laboratory reports on failed components associated with the cause of accidents, fatigue was identified as the mode of failure in more than 60 percent of the failed components. The most frequently identified cause of fatigue, as well as most other types of material failures, was improper maintenance (including inadequate inspection). Fabrication defects, design deficiencies, defective material, and abnormal service damage also caused many fatigue failures. Four case histories of major accidents are included in the paper as illustrations of some of the factors invovled in fatigue failures of aircraft components.

  18. Fatigue Reliability of Gas Turbine Engine Structures

    NASA Technical Reports Server (NTRS)

    Cruse, Thomas A.; Mahadevan, Sankaran; Tryon, Robert G.

    1997-01-01

    The results of an investigation are described for fatigue reliability in engine structures. The description consists of two parts. Part 1 is for method development. Part 2 is a specific case study. In Part 1, the essential concepts and practical approaches to damage tolerance design in the gas turbine industry are summarized. These have evolved over the years in response to flight safety certification requirements. The effect of Non-Destructive Evaluation (NDE) methods on these methods is also reviewed. Assessment methods based on probabilistic fracture mechanics, with regard to both crack initiation and crack growth, are outlined. Limit state modeling techniques from structural reliability theory are shown to be appropriate for application to this problem, for both individual failure mode and system-level assessment. In Part 2, the results of a case study for the high pressure turbine of a turboprop engine are described. The response surface approach is used to construct a fatigue performance function. This performance function is used with the First Order Reliability Method (FORM) to determine the probability of failure and the sensitivity of the fatigue life to the engine parameters for the first stage disk rim of the two stage turbine. A hybrid combination of regression and Monte Carlo simulation is to use incorporate time dependent random variables. System reliability is used to determine the system probability of failure, and the sensitivity of the system fatigue life to the engine parameters of the high pressure turbine. 'ne variation in the primary hot gas and secondary cooling air, the uncertainty of the complex mission loading, and the scatter in the material data are considered.

  19. Determinants of fatigue and stress

    PubMed Central

    2011-01-01

    Background Fatigue can be triggered by previous perceived stress which may lead to impairment of performance and function. The purpose of the study was to investigate the relationship between fatigue and perceived stress. Method Health determinants including sociodemographic factors for associations between fatigue and perceived stress in the general population (N = 2,483) are outlined. Fatigue and stress were assessed with the Chalder Fatigue Scale (CFS) and the Perceived Stress Questionnaire (PSQ). Results Within the general population, 25.9% of male and 34.5% of female respondents reported moderate fatigue during the last six months; 9.7% of subjects reported substantial fatigue lasting six months or longer. An adjusted regression analysis (R2corr = .28, p < .001) showed that fatigue is highest associated with perceived stress and self-perceived health status. The following factors were correlated with increased rates of fatigue and perceived stress: female gender, divorce/separation, low social class and poor health status. Conclusion We conclude that the two conditions overlap most in terms of socio-economic status and self-perceived health status. PMID:21774803

  20. Ultrasonic Evaluation of Fatigue Damage

    NASA Astrophysics Data System (ADS)

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

    2004-02-01

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

  1. Cryogenic fatigue data developed for Inconel 718

    NASA Technical Reports Server (NTRS)

    Schmidt, E. H.

    1967-01-01

    Data were obtained on the cryogenic fatigue properties of Inconel 718 bar using axial loading and rotating beam fatigue tests. Results also disclosed the fatigue properties of Inconel 718 sheet materials.

  2. Fatigue Life Analysis of a Turboprop Reduction Gearbox.

    DTIC Science & Technology

    1985-01-01

    Bearing fatigue life is a major factor in the evaluation of gearbox life. The fatigue life model proposed by Lundberg and Palmgren (refs. 4 to 6) is the...power train consists of eleven bearings (defined in table I) and nine gears (defined in table II). The lubri- cant for the gearbox conforms to MIL-L...stress cycles of the bearing in which 90 B percent will survive. n10 can be determined from the Lundberg- Palmgren B theory using equation (5) where C8

  3. Fatigue damage characterization using surface acoustic wave nonlinearity in aluminum alloy AA7175-T7351

    NASA Astrophysics Data System (ADS)

    Jaya Rao, V. V. S.; Kannan, Elankumaran; Prakash, Raghu V.; Balasubramaniam, Krishnan

    2008-12-01

    Nonlinear ultrasonic (NLU) harmonic generation system was used to characterize the fatigue damage in a flat hour-glass, high strength Al-Cu-Zn-Mg alloy, AA7175-T7351 specimens. Experiments were carried out to introduce controlled levels of fatigue damage under constant amplitude loading to determine the NLU response using surface acoustic wave (or Rayleigh mode) at regular intervals of fatigue life. The NLU parameter (A2/A12) plotted as a function of percentage of fatigue life shows two peaks for all the samples tested, independent of the amplitude of fatigue loading. The first peak appeared between 40%-50% of fatigue life and the second peak between 80%-90% of fatigue life. Among the two flat surfaces of the specimen, a higher nonlinearity response was observed on the surface which had the first crack initiation. The appearance of two peaks in the nonlinear response during fatigue damage progression is explained based on the dislocation dynamics and dislocation-crack interaction present in the specimens during the fatigue process.

  4. Different effects of verapamil and low calcium on repetitive contractile activity of frog fatigue-resistant and easily-fatigued muscle fibres.

    PubMed

    Lipská, E; Radzyukevich, T

    1999-06-01

    The effects of low calcium and verapamil on contractility of two muscle fibre types (m. iliofibularis, Rana temporaria) upon different stimulation protocols were been compared. Verapamil (0.02 mmol/l) induced temporal excitation-contraction coupling failure during single tetanic stimulation and enhanced the decline of tetanic force during 30 s repetitive tetanic stimulation in both fatigue-resistant fibres and easily-fatigued fibres. In contrast to verapamil, low extracellular calcium (0.02 mmol/l) only enhanced the decline of tetanic force in fatigue-resistant during repetitive tetanic stimulation but had no effect on easily-fatigued fibres. The effect of verapamil on the decline of tetanic force in fatigue-resistant fibres was more profound in low calcium conditions. Both verapamil and low calcium eliminated twitch facilitation that appeared after prolonged contractile activity in fatigue-resistant fibres. 4mmol/l Ni+2, used as calcium channel antagonist, had effects similar to low calcium medium. It could be concluded that (i) extracellular Ca2+-requirements for excitation-contraction coupling are different in fatigue-resistant and easily-fatigued fibres; (ii) the effects of verapamil on force performance are not entirely dependent upon calcium channel blockade.

  5. Fatigue Testing of TBC on Structural Steel by Cyclic Bending

    NASA Astrophysics Data System (ADS)

    Musalek, Radek; Kovarik, Ondrej; Medricky, Jan; Curry, Nicholas; Bjorklund, Stefan; Nylen, Per

    2015-01-01

    For applications with variable loading, fatigue performance of coated parts is of utmost importance. In this study, fatigue performance of conventional structural steel coated with thermal barrier coating (TBC) was evaluated in cyclic bending mode by "SF-Test" device. Testing was carried out at each stage of the TBC preparation process, i.e., for as-received and grit-blasted substrates, as well as for samples with Ni-based bond-coat and complete TBC: bond-coat with YSZ-based top-coat. Comparison of results obtained for different loading amplitudes supplemented by fractographic analysis enabled identification of dominating failure mechanisms and demonstrated applicability of the high-frequency resonant bending test for evaluation of fatigue resistance alteration at each stage of the TBC deposition process.

  6. Probabilistic finite elements for fracture and fatigue analysis

    NASA Technical Reports Server (NTRS)

    Liu, W. K.; Belytschko, T.; Lawrence, M.; Besterfield, G. H.

    1989-01-01

    The fusion of the probabilistic finite element method (PFEM) and reliability analysis for probabilistic fracture mechanics (PFM) is presented. A comprehensive method for determining the probability of fatigue failure for curved crack growth was developed. The criterion for failure or performance function is stated as: the fatigue life of a component must exceed the service life of the component; otherwise failure will occur. An enriched element that has the near-crack-tip singular strain field embedded in the element is used to formulate the equilibrium equation and solve for the stress intensity factors at the crack-tip. Performance and accuracy of the method is demonstrated on a classical mode 1 fatigue problem.

  7. Fatigue and fracture: Overview

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1984-01-01

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

  8. Fatigue 󈨛. Volume 3,

    DTIC Science & Technology

    1987-06-01

    Figure 5 appears to be composed of fibrils or crazes which have been torn in the fracture process. There is little of this rough fibrous material on the...their work on the role of crazes in the fatigue of polycarbonate. They suggested that the smooth area evident at the edge of an untreated sample is a...remnant of a single craze which first formed during cyclic loading at a point of high local surface stress. Under cyclic loading, this craze grew, as

  9. Reversal bending fatigue testing

    DOEpatents

    Wang, Jy-An John; Wang, Hong; Tan, Ting

    2014-10-21

    Embodiments for apparatuses for testing reversal bending fatigue in an elongated beam are disclosed. Embodiments are configured to be coupled to first and second end portions of the beam and to apply a bending moment to the beam and create a pure bending condition in an intermediate portion of the beam. Embodiments are further configured to cyclically alternate the direction of the bending moment applied to the beam such that the intermediate portion of the beam cyclically bends in opposite directions in a pure bending condition.

  10. Improving turbine blade fatigue life

    NASA Technical Reports Server (NTRS)

    Buddenbohm, H. W.

    1988-01-01

    Turbine airfoil design, materials, and cooling system management are variables which, when optimized, can contribute to longer turbine component lives. These advancements have been identified as redesign techniques to improve the turbine fatigue life of the SSME High Pressure Fuel Turbopump. This paper discusses the general program approach toward improving turbine fatigue life.

  11. Caffeine to Sustain Operational Fatigue

    DTIC Science & Technology

    2000-03-01

    It Caffeine is the most widely used psychostimulant and provided data about the most commonly used may be useful in operational fatigue-coping...palpitation, psychomotor agitation. Caffeine candy 05 withdrawal may cause headache, fatigue, anxiety, soda 04 insomnia, nausea, performance impainnents. snuff

  12. Fatigue monitoring in Nuclear Power Plants

    SciTech Connect

    Ware, A.G.; Shah, V.N.

    1995-04-01

    This paper summarizes fatigue monitoring methods and surveys their application in the nuclear power industry. The paper is based on a review of the technical literature. Two main reasons for fatigue monitoring are more frequent occurrence of some transients than that assumed in the fatigue design analysis and the discovery of stressors that were not included in the fatigue design analysis but may cause significant fatigue damage at some locations. One fatigue monitoring method involves use of plant operating data and procedures to update the fatigue usage. Another method involves monitoring of plant operating parameters using existing, or if needed, supplementary plant instrumentation for online computation of fatigue usage. Use of fatigue monitoring has better defined the operational transients. Most operational transients have been found less severe and fewer in numbers than anticipated in the design fatigue analysis. Use of fatigue monitoring has assisted in quantifying newly discovered stressors and has helped in detecting the presence of thermal stratification of unsuspected locations.

  13. High frequency guided waves for hidden fatigue crack growth monitoring in multi-layer aerospace structures

    NASA Astrophysics Data System (ADS)

    Chan, Henry; Fromme, Paul

    2015-03-01

    Varying loading conditions of aircraft structures result in stress concentration at fastener holes, where multi-layered components are connected, possibly leading to the development of fatigue cracks. High frequency guided waves propagating along the structure allow for the non-destructive testing of such components, e.g., aircraft wings. However, the sensitivity for the detection of small, potentially hidden, fatigue cracks has to be ascertained. The type of multi-layered model structure investigated consists of two adhesively bonded aluminium plate-strips. Fatigue experiments were carried out. The sensitivity of the high frequency guided wave modes to monitor fatigue crack growth at a fastener hole during cyclic loading was investigated, using both standard pulse-echo equipment and laser interferometry. The sensitivity and repeatability of the measurements were ascertained, having the potential for fatigue crack growth monitoring at critical and difficult to access fastener locations from a stand-off distance.

  14. Effects of fine porosity on the fatigue behavior of a powder metallurgy superalloy

    NASA Technical Reports Server (NTRS)

    Miner, R. V., Jr.; Dreshfield, R. L.

    1980-01-01

    Hot isostatically pressed powder metallurgy Astroloy was obtained which contained 1.4 percent fine porosity at the grain boundaries produced by argon entering the powder container during pressing. This material was tested at 650 C in fatigue, creep fatigue, tension, and stress-rupture and the results compared with previous data on sound Astroloy. The pores averaged about 2 micrometers diameter and 20 micrometers spacing. They did influence fatigue crack initiation and produced a more intergranular mode of propagation. However, fatigue life was not drastically reduced. A large 25 micrometers pore in one specimen resulting from a hollow particle did not reduce life by 60 percent. Fatigue behavior of the porous material showed typical correlation with tensile behavior. The plastic strain range life relation was reduced proportionately with the reduction in tensile ductility, but the elastic strain range-life relation was little changed reflecting the small reduction in sigma sub u/E for the porous material.

  15. Effects of fine porosity on the fatigue behavior of a powder metallurgy superalloy

    NASA Technical Reports Server (NTRS)

    Miner, R. V.; Dreshfield, R. L.

    1980-01-01

    Hot-isostatically-pressed powder-metallurgy Astroloy was obtained which contained 1.4 percent porosity at the grain boundaries produced by argon entering the powder container during pressing. This material was tested at 650 C in fatigue, creep-fatigue, tension, and stress-rupture and the results compared with data on sound Astroloy. They influenced fatigue crack initiation and produced a more intergranular mode of propagation but fatigue life was not drastically reduced. Fatigue behavior of the porous material showed typical correlation with tensile behavior. The plastic strain range-life relation was reduced proportionately with the reduction in tensile ductility, but the elastic strain range-life relation was changed little.

  16. Fatigue strengths of particulate filler composites reinforced with fibers.

    PubMed

    Bae, Ji-Myung; Kim, Kyoung-Nam; Hattori, Masayuki; Hasegawa, Koji; Yoshinari, Masao; Kawada, Eiji; Oda, Yutaka

    2004-06-01

    The aim of this study was to evaluate the dynamic fatigue strengths at 10(5) cycles and the strains of particulate filler composite resins with and without reinforcing fibers. An UHMWPE (Ribbond), a polyaromatic polyamide fiber (Fibreflex), and three glass fibers (GlasSpan, FibreKor, Vectris Frame) were used to reinforce the particulate filler composite resins. The fatigue properties were measured in three-point bending mode using a servohydraulic universal testing machine at a frequency of 5 Hz, until failure occurred or 10(5) cycles had been completed. The fatigue strengths at 10(5) cycles were determined by the staircase method. The fractured aspects of specimens were evaluated by an optical and scanning electron microscope. The fatigue strengths of particulate filler composite resins were 49-57 MPa, and those of fiber-reinforced were 90-209 MPa. Unidirectional glass fibers showed higher reinforcing effects on the fatigue strengths of composite resins. The strain of UHMWPE-reinforced composite was largest.

  17. Fatigue enhancement of concrete beam with ECC layer

    SciTech Connect

    Leung, Christopher K.Y. . E-mail: ckleung@ust.hk; Cheung, Y.N.; Zhang Jun

    2007-05-15

    The pseudo strain-hardening behavior of Engineered Cementitious Composites (ECC) is a desirable characteristic for it to replace concrete to suppress brittle failure. This widespread use of ECC in the industry is, however, limited by its high cost. To achieve higher performance/cost, ECC can be strategically applied in parts of a structure that is under relatively high stress and strain. In this paper, layered ECC-concrete beams subjected to static and fatigue flexural loads were investigated by experiments. The static test results showed that the application of a layer of ECC on the tensile side of a flexural beam increased its flexural strength and the degree of improvement increased with the thickness of ECC applied. In addition, the layer of ECC enhanced the ductility of the beam and the failure mode changed from brittle to ductile. Under four-point cyclic loading, the ECC layer significantly improved the fatigue life of the beam. Moreover, in comparison to plain concrete beams, layered ECC beams could sustain fatigue loading at a larger deflection without failure. The great improvement in fatigue performance was attributed to the effectiveness of ECC in controlling the growth of small cracks. The experimental findings reflect the feasibility of using ECC strategically in critical locations for the control of fatigue crack growth.

  18. Probabilistic Simulation for Combined Cycle Fatigue in Composites

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.

    2010-01-01

    A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multifactor interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

  19. Understanding postoperative fatigue.

    PubMed

    Rose, E A; King, T C

    1978-07-01

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

  20. Studies in interactive communication. II - The effects of four communication modes on the linguistic performance of teams during cooperative problem solving

    NASA Technical Reports Server (NTRS)

    Chapanis, A.; Parrish, R. N.; Ochsman, R. B.; Weeks, G. D.

    1977-01-01

    Two-man teams solved credible, 'real world' problems for which computer assistance has been or could be useful. Conversations were carried on in one of four modes of communication: typewriting, handwriting, voice, and natural unrestricted communication. Performance was assessed on three classes of dependent measures: time to solution, behavioral measures of activity, and linguistic measures. Significant differences among the communication modes were found in each of the three classes. This paper is concerned mainly with the results of the linguistic analyses. Linguistic performance was assessed with 182 measures, most of which turned out to be redundant and some of which were useless or meaningless. Those that remain show that although problems can be solved faster in the oral modes than in the hard-copy modes, the oral modes are characterized by many more messages, sentences, words, and unique words; much higher communication rates; but lower type-token ratios. Although a number of significant problem and job-role effects were found, there were relatively few significant interactions of modes with thsse variables. It appears, therefore, that the mode effects hold for both problems and for both job roles assigned to the subjects.

  1. Muscle fatigue examined at different temperatures in experiments on intact mammalian (rat) muscle fibers

    PubMed Central

    Roots, H.; Ball, G.; Talbot-Ponsonby, J.; King, M.; McBeath, K.; Ranatunga, K. W.

    2009-01-01

    In experiments on small bundles of intact fibers from a rat fast muscle, in vitro, we examined the decline in force in repeated tetanic contractions; the aim was to characterize the effect of shortening and of temperature on the initial phase of muscle fatigue. Short tetanic contractions were elicited at a control repetition rate of 1/60 s, and fatigue was induced by raising the rate to 1/5 s for 2–3 min, both in isometric mode (no shortening) and in shortening mode, in which each tetanic contraction included a ramp shortening at a standard velocity. In experiments at 20°C (n = 12), the force decline during a fatigue run was 25% in the isometric mode but was significantly higher (35%) in the shortening mode. In experiments at different temperatures (10–30°C, n = 11), the tetanic frequency and duration were adjusted as appropriate, and for shortening mode, the velocity was adjusted for maximum power output. In isometric mode, fatigue of force was significantly less at 30°C (∼20%) than at 10°C (∼30%); the power output (force × velocity) was >10× higher at 30°C than at 10°C, and power decline during a fatigue run was less at 30°C (∼20–30%) than at 10°C (∼50%). The finding that the extent of fatigue is increased with shortening contractions and is lower at higher temperatures is consistent with the view that force depression by inorganic phosphate, which accumulates within fibers during activity, may be a primary cause of initial muscle fatigue. PMID:19057001

  2. Fatigue and corrosion fatigue of beryllium-copper spring materials

    SciTech Connect

    Bagheri, R.; Miller, G.A. )

    1993-03-01

    Fine gage, 0.006-in. d(0.15-mm) thick, beryllium-copper (Be-Cu) spring materials with tensile strength in the range of 70 to 145 ksi were subjected to cyclic loading in air and salt water environments. Plain and notched (center hole) hour glass specimens were subjected to sinusoidal loading with R = (minimum/maximum) stress = 0.1 at cyclic frequencies of 50 Hz in air and 1 Hz in salt water. Fatigue life was typically from 10[sup 4] to 10[sup 6] cycles with crack initiation as the dominant fatigue process. The excellence fatigue performance of Be-Cu alloys in salt water is well-known, however, current findings demonstrate 10 to 37% reduction in fatigue strength of unnotched specimens in this environment for a life of 3 x 10[sup 5] cycles. This strength degradation is attributed to the use of a lower cyclic frequency for present than for previous tests, i.e., 1 versus about 20 Hz. There was no effect of salt water on crack initiation in notched specimens. The ratios of the fatigue strengths, namely (cold-rolled/annealed) and (aged/annealed), for plain and notched specimens tested in air, decreased from 2 to about 1.4 as fatigue life increased from 10[sup 4] to 10[sup 6] cycles. This effect is attributed to cyclic hardening of the annealed material. The fatigue stress concentration factor, K[sub f] = (plain/notched) fatigue strength, increased by about 30% as fatigue cycles increased from 10[sup 4] to 10[sup 6]. The ranking of K[sub f] values of the various material conditions from highest to lowest was: cold-rolled, aged, and annealed.

  3. Neuromuscular Fatigue During 200 M Breaststroke

    PubMed Central

    Conceição, Ana; Silva, António J.; Barbosa, Tiago; Karsai, István; Louro, Hugo

    2014-01-01

    The aims of this study were: i) to analyze activation patterns of four upper limb muscles (duration of the active and non-active phase) in each lap of 200m breaststroke, ii) quantify neuromuscular fatigue, with kinematics and physiologic assessment. Surface electromyogram was collected for the biceps brachii, deltoid anterior, pectoralis major and triceps brachii of nine male swimmers performing a maximal 200m breaststroke trial. Swimming speed, SL, SR, SI decreased from the 1st to the 3rd lap. SR increased on the 4th lap (35.91 ± 2.99 stroke·min-1). Peak blood lactate was 13.02 ± 1.72 mmol·l-1 three minutes after the maximal trial. The EMG average rectified value (ARV) increased at the end of the race for all selected muscles, but the deltoid anterior and pectoralis major in the 1st lap and for biceps brachii, deltoid anterior and triceps brachii in the 4th lap. The mean frequency of the power spectral density (MNF) decreased at the 4th lap for all muscles. These findings suggest the occurrence of fatigue at the beginning of the 2nd lap in the 200m breaststroke trial, characterized by changes in kinematic parameters and selective changes in upper limb muscle action. There was a trend towards a non-linear fatigue state. Key Points Fatigue in the upper limbs occurs in different way as it described by 100m swimming events. Neuromuscular fatigue was estimated by analyzing the physiological changes (high blood lactate concentrations), biomechanical changes in the swimming stroke characteristics (decreased in swimming velocity), and by the changes in the EMG amplitude and frequency parameters at the end of the swimming bout. The amplitude signal of EMG provided by the ARV demonstrated an increase at the end with the respect to the beginning for all muscles under study, excepted for the muscle deltoid anterior. The mean frequency (MNF) in our study decrease at the end of the swimming in the 4th lap relative to the 1st lap for all muscles under observation, along the

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

    NASA Technical Reports Server (NTRS)

    Sarkar, Bhaskar; Lisagor, W. B.

    1992-01-01

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

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

    SciTech Connect

    Sarkar, B.; Lisagor, W.B. NASA, Langley Research Center, Hampton, VI )

    1992-01-01

    The dependence of strength, fracture resistance, and fatigue crack growth rate on the aging conditions of two alloy compositions based on Al-3.7Cu-1.85Mg-0.2Mn is investigated. Mechanical properties were evaluated in two heat treatment conditions and in two orientations (longitudinal and transverse). Compact tension specimens were used to determine fatigue crack growth characteristics and fracture resistance. The aging response was monitored on coupons using hardness measurements determined with a standard Rockwell hardness tester. Fracture resistance is found to increase with increasing yield strength during artificial aging of age-hardenable 2124-Zr alloys processed by powder metallurgy techniques. Fatigue crack growth rate increases with increasing strength. It is argued that these changes are related to deformation modes of the alloys; a homogeneous deformation mode tends to increase fracture resistance and to decrease the resistance to the fatigue crack propagation rate. 12 refs.

  6. THE DEVELOPMENT OF MICROSTRUCTURAL DAMAGE DURING HIGH TEMPERATURE CREEP-FATIGUE OF A NICKEL ALLOY

    SciTech Connect

    L.J. Carroll; M.C. Carroll; C. Cabet; R.N. Wright

    2013-02-01

    Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include hold times up to 9000 s at maximum tensile strain were conducted at 950 degrees C. The fatigue resistance decreased when a hold time was added at peak tensile strain, owing to the mechanisms resulting in a change in fracture mode from transgranular in pure fatigue to intergranular in creep–fatigue. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep–fatigue resistance. An analysis of the evolving failure modes was facilitated by interrupting tests during cycling for ex situ microstructural investigation.

  7. Dynamical response of the Galileo Galilei on the ground rotor to test the equivalence principle: Theory, simulation, and experiment. II. The rejection of common mode forces

    NASA Astrophysics Data System (ADS)

    Comandi, G. L.; Toncelli, R.; Chiofalo, M. L.; Bramanti, D.; Nobili, A. M.

    2006-03-01

    "Galileo Galilei on the ground" (GGG) is a fast rotating differential accelerometer designed to test the equivalence principle (EP). Its sensitivity to differential effects, such as the effect of an EP violation, depends crucially on the capability of the accelerometer to reject all effects acting in common mode. By applying the theoretical and simulation methods reported in Part I of this work, and tested therein against experimental data, we predict the occurrence of an enhanced common mode rejection of the GGG accelerometer. We demonstrate that the best rejection of common mode disturbances can be tuned in a controlled way by varying the spin frequency of the GGG rotor.

  8. Dynamical response of the Galileo Galilei on the ground rotor to test the equivalence principle: Theory, simulation, and experiment. II. The rejection of common mode forces

    SciTech Connect

    Comandi, G.L.; Toncelli, R.; Chiofalo, M.L.; Bramanti, D.; Nobili, A.M.

    2006-03-15

    'Galileo Galilei on the ground' (GGG) is a fast rotating differential accelerometer designed to test the equivalence principle (EP). Its sensitivity to differential effects, such as the effect of an EP violation, depends crucially on the capability of the accelerometer to reject all effects acting in common mode. By applying the theoretical and simulation methods reported in Part I of this work, and tested therein against experimental data, we predict the occurrence of an enhanced common mode rejection of the GGG accelerometer. We demonstrate that the best rejection of common mode disturbances can be tuned in a controlled way by varying the spin frequency of the GGG rotor.

  9. The fracture morphology of nickel-base superalloys tested in fatigue and creep-fatigue at 650 C

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Miner, R. V.

    1981-01-01

    The fracture surfaces of compact tension specimens from seven nickel-base superalloys fatigue tested at 650 C were studied by scanning electron microscopy and optical metallography to determine the nature and morphology of the crack surface in the region of stable growth. Crack propagation testing was performed as part of an earlier study at 650 C in air using a 0.33 Hz fatigue cycle and a creep-fatigue cycle incorporating a 900 second dwell at maximum load. In fatigue, alloys with a grain size greater than 20 micrometers, HIP Astroloy, Waspaloy, and MERL 76, exhibited transgranular fracture. MERL 76 also displayed numerous fracture sites which were associated with boundaries of prior powder particles. The two high strength, fine grain alloys, IN 100 and NASA IIB-7, exhibited intergranular fracture. Rene 95 and HIP plus forged Astroloy displayed a mixed failure mode that was transgranular in the coarse grains and intergranular in the fine grains. Under creep-fatigue conditions, fracture was found to be predominantly intergranular in all seven alloys.

  10. Development of the electrochemical fatigue sensor for evaluating fatigue damage

    SciTech Connect

    Li, Y.F.; Wang, J.; Wang, M.Z.; DeLuccia, J.; Laird, C.

    1999-07-01

    The Electrochemical Fatigue Sensor (EFS) is a device which operates by an electrochemical-mechanical interaction and which can sense the type and extent of fatigue damage both before and after crack initiation. It was initially explored through studies on soft metals. Here the authors report efforts to determine the ability of the device to read damage in hardened commercial alloys: 7075 aluminum alloy, 4130 steel and Ti-6Al-4V. They also demonstrate that the device, which uses an electrolytic medium, does not degrade the fatigue properties if care is used in electrolyte selection.

  11. The copper(II) and zinc(II) coordination mode of HExxH and HxxEH motif in small peptides: the role of carboxylate location and hydrogen bonding network.

    PubMed

    Grasso, Giuseppe; Magrì, Antonio; Bellia, Francesco; Pietropaolo, Adriana; La Mendola, Diego; Rizzarelli, Enrico

    2014-01-01

    Copper(II) and zinc(II) complexes with two hexapeptides encompassing HExxH and HxxEH motif were characterized by means of a combined experimental and theoretical approach. Parallel tempering and density functional theory (DFT) investigations show the presence of different hydrogen bonding networks between the copper(II) and zinc(II) complexes with the two peptides, suggesting a significant contribution of these non-covalent interactions to the stability constant values. The glutamate carboxylate group has a direct role in metal ion binding. The location of this amino acid along the sequence of the investigated peptides is critical to determine thermodynamic and spectroscopic features of the copper(II) complex species, whereas is less relevant in the zinc(II) complexes formation. Electrospray ionization mass spectrometry (ESI-MS) characterization of the zinc(II) complex species show that in the [ZnH-2L] two deprotonated amide nitrogen atoms are involved in the metal coordination environment, an uncommon behavior in zinc(II) complexes for multi-histidine ligands.

  12. Coordination mode of pentadentate ligand derivative of 5-amino-1,3,4-thiadiazole-2-thiol with nickel(II) and copper(II) metal ions: Synthesis, spectroscopic characterization, molecular modeling and fungicidal study

    NASA Astrophysics Data System (ADS)

    Chandra, Sulekh; Gautam, Seema; Kumar, Amit; Madan, Molly

    2015-02-01

    Complexes of nickel(II), and copper(II) were synthesized with pantadentate ligand i.e. 3,3‧-thiodipropionicacid-bis(5-amino-1,3,4-thiadiazole-2-thiol) (L). The ligand was synthesized by the condensation of thiodipropionic acid and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio, respectively. Synthesized ligand was characterized by elemental analysis, mass, 1H NMR, IR, and molecular modeling. All the complexes were characterized by elemental analysis, molar conductance, magnetic moment, IR, electronic spectra, ESR, and molecular modeling. The newly synthesized complexes possessed general composition [M(L)X2] where M = Ni(II), Cu(II), L = pantadentate ligand and X = Cl-, CH3COO-. The IR spectral data indicated that the ligand behaved as a pantadentate ligand and coordinated to the metal ion through N2S3 donor atoms. The molar conductance value of Ni(II), and Cu(II) complexes in DMSO corresponded to their electrolytic behavior. On the basis of spectral study, octahedral and tetragonal geometry was assigned for Ni(II) and Cu(II) complexes, respectively. In vitro fungicidal study of ligand and its complexes was investigated against fungi Candida albicans, Candida parapsilosis, Candidia krusei, and Candida tropicalis by means of well diffusion method.

  13. Coordination mode of pentadentate ligand derivative of 5-amino-1,3,4-thiadiazole-2-thiol with nickel(II) and copper(II) metal ions: synthesis, spectroscopic characterization, molecular modeling and fungicidal study.

    PubMed

    Chandra, Sulekh; Gautam, Seema; Kumar, Amit; Madan, Molly

    2015-02-05

    Complexes of nickel(II), and copper(II) were synthesized with pantadentate ligand i.e. 3,3'-thiodipropionicacid-bis(5-amino-1,3,4-thiadiazole-2-thiol) (L). The ligand was synthesized by the condensation of thiodipropionic acid and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio, respectively. Synthesized ligand was characterized by elemental analysis, mass, (1)H NMR, IR, and molecular modeling. All the complexes were characterized by elemental analysis, molar conductance, magnetic moment, IR, electronic spectra, ESR, and molecular modeling. The newly synthesized complexes possessed general composition [M(L)X2] where M = Ni(II), Cu(II), L = pantadentate ligand and X = Cl(-), CH3COO(-). The IR spectral data indicated that the ligand behaved as a pantadentate ligand and coordinated to the metal ion through N2S3 donor atoms. The molar conductance value of Ni(II), and Cu(II) complexes in DMSO corresponded to their electrolytic behavior. On the basis of spectral study, octahedral and tetragonal geometry was assigned for Ni(II) and Cu(II) complexes, respectively. In vitro fungicidal study of ligand and its complexes was investigated against fungi Candida albicans, Candida parapsilosis, Candidia krusei, and Candida tropicalis by means of well diffusion method.

  14. Spatially distributed sequential stimulation reduces fatigue in paralyzed triceps surae muscles: a case study.

    PubMed

    Nguyen, Robert; Masani, Kei; Micera, Silvestro; Morari, Manfred; Popovic, Milos R

    2011-12-01

    Functional electrical stimulation (FES) is limited by the rapid onset of muscle fatigue caused by localized nerve excitation repeatedly activating only a subset of motor units. The purpose of this study was to investigate reducing fatigue by sequentially changing, pulse by pulse, the area of stimulation using multiple surface electrodes that cover the same area as one electrode during conventional stimulation. Paralyzed triceps surae muscles of an individual with complete spinal cord injury were stimulated, via the tibial nerve, through four active electrodes using spatially distributed sequential stimulation (SDSS) that was delivered by sending a stimulation pulse to each electrode one after another with 90° phase shift between successive electrodes. For comparison, single electrode stimulation was delivered through one active electrode. For both modes of stimulation, the resultant frequency to the muscle as a whole was 40 Hz. Isometric ankle torque was measured during fatiguing stimulations lasting 2 min. Each mode of stimulation was delivered a total of six times over 12 separate days. Three fatigue measures were used for comparison: fatigue index (final torque normalized to maximum torque), fatigue time (time for torque to drop by 3 dB), and torque-time integral (over the entire trial). The measures were all higher during SDSS (P < 0.001), by 234, 280, and 171%, respectively. The results are an encouraging first step toward addressing muscle fatigue, which is one of the greatest problems for FES.

  15. Multiaxial and Thermomechanical Fatigue of Materials: A Historical Perspective and Some Future Challenges

    NASA Technical Reports Server (NTRS)

    Kalluri, Sreeramesh

    2013-01-01

    Structural materials used in engineering applications routinely subjected to repetitive mechanical loads in multiple directions under non-isothermal conditions. Over past few decades, several multiaxial fatigue life estimation models (stress- and strain-based) developed for isothermal conditions. Historically, numerous fatigue life prediction models also developed for thermomechanical fatigue (TMF) life prediction, predominantly for uniaxial mechanical loading conditions. Realistic structural components encounter multiaxial loads and non-isothermal loading conditions, which increase potential for interaction of damage modes. A need exists for mechanical testing and development verification of life prediction models under such conditions.

  16. Nonlinear ultrasonic imaging of thermal fatigue cracks of several tens nm gap in glass plates

    NASA Astrophysics Data System (ADS)

    Hertl, M.; Kawashima, K.; Sekino, K.; Yasui, H.; Aida, T.

    2015-10-01

    Thermal fatigue crack of which gap distance is several tens nm in glass plate is imaged by using an immersion higher harmonic imaging technique. Some parts of the thermal fatigue crack are clearly imaged by the third harmonic amplitude of the 3.5 MHz burst wave by angular incidence. For through-transmission mode across the crack face, the seventh harmonic of a through-thickness resonant frequency also visualizes the thermal fatigue crack. If spatial resolution will reach to a few micron meters, the technique could be applied for detection of disbonds in bonded wafers.

  17. Detection and characterization of fatigue cracks in thin metal plates by low frequency resonant model analysis

    NASA Technical Reports Server (NTRS)

    Wincheski, B.; Namkung, M.; Birt, E. A.

    1992-01-01

    Low-frequency resonant model analysis, a technique for the detection and characterization of fatigue cracks in thin metal plates, which could be adapted to rapid scan or large area testing, is considered. Experimental data displaying a direct correlation between fatigue crack geometry and resonance frequency for the second vibrational plate mode are presented. FEM is used to calculate the mechanical behavior of the plates, and provides a comparison basis for the experimentally determined resonance frequency values. The waveform of the acoustic emission generated at the resonant frequency is examined; it provides the basis for a model of the interaction of fatigue crack faces during plate vibration.

  18. A new, model-free calculation method to determine the coordination modes and distribution of copper(II) among the metal binding sites of multihistidine peptides using circular dichroism spectroscopy.

    PubMed

    Osz, Katalin

    2008-12-01

    A new calculation method to determine microscopic protonation processes from CD spectra measured at different pH and Cu(II):ligand ratios was developed and used to give the relative binding strengths for the three histidines of hsPrP(84-114), a 31-mer polypeptide modeling the N-terminal copper(II) binding region of human (homo sapiens) prion protein. Mutants of hsPrP(84-114) with two or one histidyl residues have also been synthesized and their copper(II) complexes studied by CD spectroscopy. The 1-His models were analyzed first, and the molar CD spectra for the different coordination modes on the different histidines were calculated using the general computational program PSEQUAD. These spectra were deconvoluted into the sum of Gaussian curves and used as a first parameter set to calculate the molar spectra for the different coordination modes (3N and 4N coordination) and coordination positions (His85, His96 and His111) of the 2-His peptides. The calculation method therefore does not require the direct use of CD spectra measured in the smaller peptide models. This is a significant improvement over earlier calculation methods. In the same runs, the stepwise deprotonation pK(mic) values were refined and the pH-dependent distribution of copper(II) between the two histidines was determined. The results revealed the high, but different copper(II) binding affinities of the three separate histidines in the following order: His85 < His96His111. The calculation also showed that molar CD spectra which belong to the same coordination mode and coordination position in different ligands have very similar transition energies but different intensities. For this reason, direct transfer of molar CD spectra between different ligands may be a source of error, but the pK(mic) values and the copper(II) binding preferences are transferable from the 2-His peptides to the 3-His hsPrP(84-114).

  19. Fatigue management in the workplace

    PubMed Central

    Sadeghniiat-Haghighi, Khosro; Yazdi, Zohreh

    2015-01-01

    Workers’ fatigue is a significant problem in modern industry, largely because of high demand jobs, long duty periods, disruption of circadian rhythms, and accumulative sleep debt that are common in many industries. Fatigue is the end result of integration of multiple factors such as time awake, time of day, and workload. Then, the full understanding of circadian biologic clock, dynamics of transient and cumulative sleep loss, and recovery is required for effective management of workplace fatigue. It can be more investigated in a new field of sleep medicine called occupational sleep medicine. Occupational sleep medicine is concerned with maintaining best productivity and safety in the industrial settings. The fatigue risk management system (FRMS) is a comprehensive approach that is based on applying scientific evidence of sleep knowledge to manage workers fatigue. It is developing rapidly in the highly safety demand jobs; especially truck drivers, pilots, and power plant workers. The objective of this review is to explain about fatigue in the workplace with emphasis on its association work performance and errors/accidents. Also, we discussed about different methods of fatigue measurement and management. PMID:26257477

  20. Fatigue management in the workplace.

    PubMed

    Sadeghniiat-Haghighi, Khosro; Yazdi, Zohreh

    2015-01-01

    Workers' fatigue is a significant problem in modern industry, largely because of high demand jobs, long duty periods, disruption of circadian rhythms, and accumulative sleep debt that are common in many industries. Fatigue is the end result of integration of multiple factors such as time awake, time of day, and workload. Then, the full understanding of circadian biologic clock, dynamics of transient and cumulative sleep loss, and recovery is required for effective management of workplace fatigue. It can be more investigated in a new field of sleep medicine called occupational sleep medicine. Occupational sleep medicine is concerned with maintaining best productivity and safety in the industrial settings. The fatigue risk management system (FRMS) is a comprehensive approach that is based on applying scientific evidence of sleep knowledge to manage workers fatigue. It is developing rapidly in the highly safety demand jobs; especially truck drivers, pilots, and power plant workers. The objective of this review is to explain about fatigue in the workplace with emphasis on its association work performance and errors/accidents. Also, we discussed about different methods of fatigue measurement and management.

  1. Computational micromechanics of fatigue of microstructures in the HCF–VHCF regimes

    DOE PAGES

    Castelluccio, Gustavo M.; Musinski, William D.; McDowell, David L.

    2016-05-19

    Advances in higher resolution experimental techniques have shown that metallic materials can develop fatigue cracks under cyclic loading levels significantly below the yield stress. Indeed, the traditional notion of a fatigue limit can be recast in terms of limits associated with nucleation and arrest of fatigue cracks at the microstructural scale. Though fatigue damage characteristically emerges from irreversible dislocation processes at sub-grain scales, the specific microstructure attributes, environment, and loading conditions can strongly affect the apparent failure mode and surface to subsurface transitions. This paper discusses multiple mechanisms that occur during fatigue loading in the high cycle fatigue (HCF) tomore » very high cycle fatigue (VHCF) regimes. We compare these regimes, focusing on strategies to bridge experimental and modeling approaches exercised at multiple length scales and discussing particular challenges to modeling and simulation regarding microstructure-sensitive fatigue driving forces and thresholds. Finally, we discuss some of the challenges in predicting the transition of failure mechanisms at different stress and strain amplitudes.« less

  2. Effect of lubricant extreme pressure additives on rolling element fatigue life

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Zaretsky, E. V.

    1973-01-01

    The effects of surface active additives on rolling-element fatigue life were investigated with the five-ball fatigue tester at conditions where classical subsurface initiated rolling-element fatigue is the sole mode of failure. Test balls of AISI 52100, AISI M-50, and AISI 1018 were run with an acid-treated white oil containing either 2.5 percent sulfurized terpene, 1 percent didodecyl phosphite, or 5 percent chlorinated wax. In general, it was found that the influence of surface active additives was detrimental to rolling-element fatigue life. The chlorinated-wax additive significantly reduced fatigue life by a factor of 7. The base oil with the 2.5 percent sulfurized-terpene additive can reduce fatigue life by as much as 50 percent. No statistical change in fatigue life occurred with the base oil having the 1 percent didodecyl-phosphite additive. The additives used with the base oil did not change the ranking of the bearing steels where rolling-element fatigue life was of subsurface origin.

  3. Fatigue Crack Propagation Behavior According Tofiber Arraying Direction for Load Direction Inwoven CFRP Composite

    NASA Astrophysics Data System (ADS)

    Choi, Jung-Hun; Kang, Min-Sung; Koo, Jae-Mean; Seok, Chang-Sung; Kim, Hyung-Ick

    The fatigue crack propagation of CFRP (carbon fiber reinforced composite material) laminates is of current interest, particularly with regard to their durability under fatigue loading. Recently, carbon fiber reinforced composite materials (Woven fabric) are widely used in various fields of engineering because of its advanced properties. Then, many researchers have studied woven fabric CFRP materials but fatigue crack propagation behaviors for composites have not been still standardized . It shows the different crack propagation behavior according to load and fiber direction. Therefore, there is a need to consider fatigue crack propagation behavior in conformity with fiber arraying direction to load direction at designing structure using woven CFRP materials. In this study, therefore, the fatigue crack propagation for plain woven CFRP composite materials was investigated under two different fiber array direction (fiber arraying direction to load : 0°, 45°). Fatigue crack propagation tests of the woven CFRP composite were conducted under sinusoidal wave-form with stress ratios of 0.3 at a frequency of 10Hz, respectively. As a result of test, fatigue crack propagation rates (da/dN) were plotted against the stress-intensity factor amplitude (ΔK) and other factor. Also we compared ΔK with other factor that considering in-plain anisotropy. All of tests of fatigue crack propagation were carried out under mode I opening loading by using compact tension specimens.

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    The fatigue crack initiation resistance of an alloy is determined by conducting a series of tests over a range of values of stress amplitude or strain range. The observed number of cycles to failure is plotted against the stress amplitude or strain range to obtain a fatigue curve. The fatigue properties quoted for an alloy are typically the constants used in the equation(s) that describe the fatigue curve. Fatigue lives of interest may be as low as 10(exp 2) or higher than 10(exp 9) cycles. Because of the enormous scatter associated with fatigue, dozens of tests may be needed to confidently establish a fatigue curve, and the cost may run into several thousands of dollars. To further establish the effects on fatigue life of the test temperature, environment, alloy condition, mean stress effects, creep-fatigue effects, thermomechanical cycling, etc. requires an extraordinarily large and usually very costly test matrix. The total effort required to establish the fatigue resistance of an alloy should not be taken lightly. Fatigue crack initiation tests are conducted on relatively small and presumed to be initially crack-free, samples of an alloy that are intended to be representative of the alloy's metallurgical and physical condition. Generally, samples are smooth and have uniformly polished surfaces within the test section. Some may have intentionally machined notches of well-controlled geometry, but the surface at the root of the notch is usually not polished. The purpose of polishing is to attain a reproducible surface finish. This is to eliminate surface finish as an uncontrolled variable. Representative test specimen geometries will be discussed later. Test specimens are cyclically loaded until macroscopically observable cracks initiate and eventually grow to failure. Normally, the fatigue failure life of a specimen is defined as the number of cycles to separation of the specimen into two pieces. Alternative definitions are becoming more common, particularly for

  5. Evaluation of composite flattened tubular specimen. [fatigue tests

    NASA Technical Reports Server (NTRS)

    Liber, T.; Daniel, I. M.

    1978-01-01

    Flattened tubular specimens of graphite/epoxy, S-glass/epoxy, Kevlar-49/epoxy, and graphite/S-glass/epoxy hybrid materials were evaluated under static and cyclic uniaxial tensile loading and compared directly with flat coupon data of the same materials generated under corresponding loading conditions. Additional development for the refinement of the flattened specimen configuration and fabrication was required. Statically tested graphite/epoxy, S-glass/epoxy, and Kevlar 49/epoxy flattened tube specimens exhibit somewhat higher average strengths than their corresponding flat coupons. Flattened tube specimens of the graphite/S-glass/epoxy hybrid and the graphite/epoxy flattened tube specimens failed in parasitic modes with consequential lower strength than the corresponding flat coupons. Fatigue tested flattened tube specimens failed in parasitic modes resulting in lower fatigue strengths than the corresponding flat coupons.

  6. Atlas of fatigue curves

    SciTech Connect

    Boyer, H.E.

    1986-01-01

    This Atlas was developed to serve engineers who are looking for fatigue data on a particular metal or alloy. Having these curves compiled in a single book will also facilitate the computerization of the involved data. It is pointed out that plans are under way to make the data in this book available in ASCII files for analysis by computer programs. S-N curves which typify effects of major variables are considered along with low-carbon steels, medium-carbon steels, alloy steels, HSLA steels, high-strength alloy steels, heat-resisting steels, stainless steels, maraging steels, cast irons, and heat-resisting alloys. Attention is also given to aluminum alloys, copper alloys, magnesium alloys, molybdenum, tin alloys, titanium and titanium alloys, zirconium, steel castings, closed-die forgings, powder metallurgy parts, composites, effects of surface treatments, and test results for component parts.

  7. Peculiar double-periodic pulsation in RR Lyrae stars of the OGLE collection - II. Short-period stars with a dominant radial fundamental mode

    NASA Astrophysics Data System (ADS)

    Prudil, Z.; Smolec, R.; Skarka, M.; Netzel, H.

    2017-03-01

    We report the discovery of a new group of double-periodic stars in the OGLE Galactic bulge photometry. In 38 stars identified as fundamental-mode RR Lyrae and four classified as first-overtone RR Lyrae, we detected an additional shorter periodicity. The periods of the dominant variability in the newly discovered group are 0.28 < PD < 0.41 d. Period ratios (0.68-0.72) are smaller than the period ratios of the Galactic bulge RRd stars. The typical amplitude ratio (of the additional to the dominant periodicity) is 20 per cent for the stars identified as fundamental-mode RR Lyrae and 50 per cent for stars classified as first-overtone RR Lyrae. 10 stars from our sample exhibit equidistant peaks in the frequency spectrum, which suggests the Blazhko-type modulation of the main pulsation frequency and/or additional periodicity. The Fourier coefficients R21 and R31 are some of the lowest among fundamental-mode RR Lyrae stars, but among the highest for the first-overtone pulsators. For the phase Fourier coefficients φ21 and φ31, our stars lie between RRab and RRc stars. The stars discussed were compared with radial linear pulsation models. Their position in the Petersen diagram cannot be reproduced by assuming that two radial modes are excited and their physical parameters are like those characteristic of RR Lyrae stars. The non-radial-mode scenario also faces difficulties. We conclude that the dominant variability is most likely due to pulsation in the radial fundamental mode, which applies to stars classified as first-overtone mode pulsators. At this point, we cannot explain the nature of the additional periodicity. Even more, the classification of the stars as RR Lyrae should be treated as tentative.

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

    NASA Astrophysics Data System (ADS)

    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.

  9. Coping with cancer - managing fatigue

    MedlinePlus

    ... cause fatigue. Simply having cancer can drain your energy: Some cancers release proteins called cytokines that can ... tumors can change the way your body uses energy and leave you feeling tired. Many cancer treatments ...

  10. Pilot Fatigue and Circadian Desynchronosis

    NASA Technical Reports Server (NTRS)

    1981-01-01

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

  11. Fatigue of internal combustion engines

    NASA Technical Reports Server (NTRS)

    Dumanois, P

    1924-01-01

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

  12. Chronic Fatigue Syndrome (For Parents)

    MedlinePlus

    ... help reduce symptoms of fatigue. acupuncture, massage, stretching, yoga, and tai chi, which have been helpful for ... that antidepressant medications can help ease the symptoms. Pain medications and anti-inflammatory drugs, such as ibuprofen, ...

  13. Resolving the frustration of fatigue.

    PubMed

    Harpham, W S

    1999-01-01

    Fatigue is a ubiquitous side effect of many cancer therapies. Nevertheless, after treatment is complete, many survivors continue to feel a profound tiredness that affects almost all aspects of life. Even after recovery, patients are often frustrated by their continuing need for extra rest. In this deeply personal, first-person account, a physician relates the various ways that cancer-related fatigue can affect family dynamics, job responsibilities, social interactions, finances, and intimacy. Clinicians can help by searching for treatable medical conditions, but also by taking cancer-related fatigue, and the frustrations it causes, seriously. Patients should be reassured that the fatigue they feel is real, and that by learning personal energy conservation, they should be able to improve their abilities to function, to socialize, to interact with others, and ultimately to adjust to a "new normal" baseline.

  14. Copper complexes relevant to the catalytic cycle of copper nitrite reductase: electrochemical detection of NO(g) evolution and flipping of NO2 binding mode upon Cu(II) → Cu(I) reduction.

    PubMed

    Maji, Ram Chandra; Barman, Suman Kumar; Roy, Suprakash; Chatterjee, Sudip K; Bowles, Faye L; Olmstead, Marilyn M; Patra, Apurba K

    2013-10-07

    Copper complexes of the deprotonated tridentate ligand, N-2-methylthiophenyl-2'-pyridinecarboxamide (HL1), were synthesized and characterized as part of our investigation into the reduction of copper(II) o-nitrito complexes into the related copper nitric oxide complexes and subsequent evolution of NO(g) such as occurs in the enzyme copper nitrite reductase. Our studies afforded the complexes [(L1)Cu(II)Cl]n (1), [(L1)Cu(II)(ONO)] (2), [(L1)Cu(II)(H2O)](ClO4)·H2O (3·H2O), [(L1)Cu(II)(CH3OH)](ClO4) (4), [(L1)Cu(II)(CH3CO2)]·H2O (5·H2O), and [Co(Cp)2][(L1)Cu(I)(NO2)(CH3CN)] (6). X-ray crystal structure determinations revealed distorted square-pyramidal coordination geometry around Cu(II) ion in 1-5. Substitution of the H2O of 3 by nitrite quantitatively forms 2, featuring the κ(2)-O,O binding mode of NO2(-) to Cu(II). Reduction of 2 generates two Cu(I) species, one with κ(1)-O and other with the κ(1)-N bonded NO2(-) group. The Cu(I) analogue of 2, compound 6, was synthesized. The FTIR spectrum of 6 reveals the presence of κ(1)-N bonded NO2(-). Constant potential electrolysis corresponding to Cu(II) → Cu(I) reduction of a CH3CN solution of 2 followed by reaction with acids, CH3CO2H or HClO4 generates 5 or 3, and NO(g), identified electrochemically. The isolated Cu(I) complex 6 independently evolves one equivalent of NO(g) upon reaction with acids. Production of NO(g) was confirmed by forming [Co(TPP)NO] in CH2Cl2 (λ(max) in CH2Cl2: 414 and 536 nm, ν(NO) = 1693 cm(-1)).

  15. Thermal-mechanical fatigue behavior of nickel-base superalloys

    NASA Technical Reports Server (NTRS)

    Pelloux, R. M.; Marchand, N.

    1986-01-01

    The main achievements of a 36-month research program are presented. The main objective was to gain more insight into the problem of crack growth under thermal mechanical fatigue (TMF) conditions. This program was conducted at M.I.T. for the period of September 1982 to September 1985. The program was arranged into five technical tasks. Under Task I, the literature of TMF data was reviewed. The goal was to identify the crack propagation conditions in aircraft engines (hot section) and to assess the validity of conventional fracture mechanics parameters to address TMF crack growth. The second task defined the test facilities, test specimen and the testing conditions needed to establish the effectiveness of data correlation parameters identified in Task I. Three materials (Inconel X-750, Hastelloy-X, and B-1900) were chosen for the program. Task II was accomplished in collaboration with Pratt & Whitney Aircraft engineers. Under Task III, a computerized testing system to measure the TMF behavior (LCF and CG behaviors) of various alloys systems was built. The software used to run isothermal and TMF tests was also developed. Built around a conventional servohydraulic machine, the system is capable of push-pull tests under stress or strain and temperature controlled conditions in the temperature range of 25C to 1050C. A crack propagation test program was defined and conducted under Task IV. The test variables included strain range, strain rate (frequency) and temperature. Task V correlated and generalized the Task IV data for isothermal and variable temperature conditions so that several crack propagation parameters could be compared and evaluated. The structural damage (mode of cracking and dislocation substructure) under TMF cycling was identified and contrasted with the isothermal damage to achieve a sound fundamental mechanistic understanding of TMF.

  16. Prediction of fatigue life of high-heat-load components made of oxygen-free copper by comparing with Glidcop.

    PubMed

    Takahashi, Sunao; Sano, Mutsumi; Watanabe, Atsuo; Kitamura, Hideo

    2013-01-01

    Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep-fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep-fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment.

  17. Prediction of fatigue life of high-heat-load components made of oxygen-free copper by comparing with Glidcop

    PubMed Central

    Takahashi, Sunao; Sano, Mutsumi; Watanabe, Atsuo; Kitamura, Hideo

    2013-01-01

    Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep–fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep–fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment. PMID:23254657

  18. Fatigue and the criminal law.

    PubMed

    Jones, Christopher B; Dorrian, Jillian; Rajaratnam, Shanthakumar M W

    2005-01-01

    Fatigue is an increasingly recognised risk factor for transportation accidents. In light of this, there is the question of whether driving whilst fatigued should be a criminal offence. This paper discusses the current legal position, including the problems of voluntary conduct and self awareness. Three models for reform are proposed. The manner in which scientific research can inform legal consideration and future directions for research are discussed.

  19. Fatigue and Fracture of Titanium Aluminides. Volume 2

    DTIC Science & Technology

    1990-02-01

    WRDC-TR-89-4145 Volume II FATIGUE AND FRACTURE OF TITANIUM ALUMINIDES M.L. Gambone V) Allison Gas Turbine Division fl General Motors Corporation RO...77 I1 TITLE (Include Securty Classficaton) Fat igue & Fracture of Titanium Aluminides 12. PERSONAL AUTHOR(S) M.L. Gambone 13& TYPE OF REPORT 13b. TIME...CODES 18. SUBJECT TERMS (Continue on reuerse it neceuar’y and identify by block numberi FIELD GROUP SUB GR. Metal matrix composites, titanium aluminide

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

    NASA Astrophysics Data System (ADS)

    Fiedler, Brent Alan

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

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

    NASA Astrophysics Data System (ADS)

    Jiang, Xiuping

    2007-12-01

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

  2. Compressive fatigue limit of four types of dental restorative materials.

    PubMed

    Chen, Song; Öhman, Caroline; Jefferies, Steven R; Gray, Holly; Xia, Wei; Engqvist, Håkan

    2016-08-01

    The purpose of this study was to evaluate the quasi-static compressive strength and the compressive fatigue limit of four different dental restorative materials, before and after aging in distilled water for 30 days. A conventional glass ionomer cement (Fuji IX GP; IG), a zinc-reinforced glass ionomer cement (Chemfil rock; CF), a light curable resin-reinforced glass ionomer cement (Fuji II LC; LC) and a resin-based composite (Quixfil; QF) were investigated. Cylindrical specimens (4mm in diameter and 6mm in height) were prepared according to the manufacturer׳s instructions. The compressive fatigue limit was obtained using the staircase method. Samples were tested in distilled water at 37°C, at a frequency of 10Hz with 10(5) cycles set as run-out. 17 fatigue samples were tested for each group. Two-way ANOVA and one-way ANOVA followed by Tukey׳s post-hoc test were used to analyze the results. Among the four types of materials, the resin-based composite exhibited the highest compressive strength (244±13.0MPa) and compressive fatigue limit (134±7.8MPa), followed by the light-cured resin reinforced glass ionomer cement (168±8.5MPa and 92±6.6MPa, respectively) after one day of storage in distilled water. After being stored for 30 days, all specimens showed an increase in compressive strength. Aging showed no effect on the compressive fatigue limit of the resin-based composite and the light-cured resin reinforced glass ionomer cement, however, the conventional glass ionomer cements showed a drastic decrease (37% for IG, 31% for CF) in compressive fatigue limit. In conclusion, in the present study, resin modified GIC and resin-based composite were found to have superior mechanical properties to conventional GIC.

  3. Fabric orientation effects on the monotonic and fatigue behavior of continuous fiber-reinforced ceramic-matrix composites (CFCCs)

    NASA Astrophysics Data System (ADS)

    Miriyala, Narendernath

    Fabric orientation effects on the monotonic and fatigue behavior of two commercially available continuous fiber-reinforced ceramic-matrix composites (CFCCs) were investigated by performing flexure tests at room temperature in air, and at 1,000sp°C in an argon environment. The two CFCCs used in the study were: (i) a Nicalon woven-fabric reinforced alumina (Alsb2Osb3) matrix composite fabricated by the directed metal oxidation (DIMOX) process, and (ii) a Nicalon woven-fabric reinforced silicon carbide (SiC) matrix composite fabricated by an isothermal chemical vapor infiltration (ICVI) process. Specimens of square cross-section (3 mm x 3 mm of Nicalon/Alsb2Osb3 and 2 mm x 2 mm of Nicalon/SiC) were subjected to four-point bending loads to perform the monotonic and fatigue tests at room and elevated temperatures. The specimen configurations were designated as edge-on and transverse, depending on whether the load was applied parallel or perpendicular to the fabric plies, respectively. The monotonic and fatigue behavior of the Nicalon/Alsb2Osb3 composite was remarkably affected by the fabric orientation at room and elevated temperatures. The ultimate flexural strength (UFS) was significantly higher in the edge-on orientation, as compared to that in the transverse orientation, at RT and 1,000sp°C. Also, the stress at which the samples survived one million load cycles was higher in the edge-on orientation, relative to that in the transverse orientation, particularly at RT. Under monotonic and fatigue loadings, the samples tested in the edge-on orientation failed by specimen severance into two pieces, while the transversely oriented samples failed by specimen collapse. Due to the interlaminar weakness of the material, delamination cracks propagated in the transversely oriented samples, and the specimens failed by a complex combination of tensile, compressive and shear stresses. In contrast, the specimens tested in the edge-on orientation failed in a predominantly tensile

  4. Fatigue after Stroke: The Patient's Perspective.

    PubMed

    Barbour, Victoria Louise; Mead, Gillian Elizabeth

    2012-01-01

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

  5. Fatigue in advanced cancer: a prospective study.

    PubMed

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

    2008-01-01

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

  6. Assessment of fatigue in cancer patients.

    PubMed

    Jacobsen, Paul B

    2004-01-01

    Increased recognition of the problem of fatigue in cancer patients can be attributed, in part, to the development of measures that have provided researchers with the tools necessary for quantifying and characterizing fatigue and exploring its etiology and treatment. Although a consensus regarding the definition of fatigue is lacking, there is general agreement that it is a subjective and multidimensional phenomenon whose assessment requires the use of self-report methods. Consistent with this view, several multidimensional measures of fatigue have been developed and validated for use with cancer patients. These measures differ considerably in their format and content and, as with the definition of fatigue, there is no consensus at the present time regarding the dimensional structure of fatigue. In addition to measuring fatigue on a continuum along one or more dimensions, it may also be possible to assess a clinical syndrome of cancer-related fatigue. Criteria for assessing fatigue in this manner have been proposed and are currently undergoing evaluation. Despite the progress that has been made, there are several important unresolved issues in the assessment of fatigue in cancer patients. These include how to distinguish fatigue from depression, how to use self-reports of fatigue in clinical decision-making, how to capture temporal changes in fatigue, and how best to address the continuing lack of consensus regarding the conceptualization and measurement of fatigue.

  7. Mode of death and hospitalization from the Second Follow-up Serial Infusions of Nesiritide (FUSION II) trial and comparison of clinical events committee adjudicated versus investigator reported outcomes.

    PubMed

    O'Connor, Christopher M; Fiuzat, Mona; Lindenfeld, Joann; Miller, Alan; Lombardi, Carlo; Carson, Peter; Shaw, Linda K; Wang, Li-Joy; Connolly, Patricia; Mills, Roger; Yancy, Clyde; Mahaffey, Kenneth

    2011-11-15

    The aim of this study was to evaluate the mode of death and hospitalizations in advanced heart failure (HF) patients with renal dysfunction and to examine the rate of concordance between events reported by the clinical events committee and site investigators (using case report forms) in the Second Follow-Up Serial Infusions of Nesiritide (FUSION II) trial. Little is known about the cause of death and hospitalization in patients with advanced HF. FUSION II was a randomized, double-blind, placebo-controlled trial evaluating outpatient nesiritide infusions versus placebo, with 911 patients with advanced HF (New York Heart Association class III or IV) and renal dysfunction enrolled. There were 151 deaths and 1,041 hospitalizations at 24 weeks. The clinical events committee classified events as cardiac, renal, cardiorenal, other or noncardiovascular, or unknown. Kappa statistics and McNemar tests were used to assess agreement (overall and by individual modes of death and hospitalization indications). In conclusion, the most common cause of death or hospitalization was cardiac related, with 70% of deaths and 60% of hospitalizations due to cardiac causes. There was 74% agreement (26% disagreement) on cardiac cause of death (κ = 0.40, McNemar p = 0.001) and 75% agreement (25% disagreement) between the investigators and the clinical events committee on cardiac classification for hospitalization (κ = 0.49, McNemar p <0.0001).

  8. Monitoring of hidden fatigue crack growth in multi-layer aircraft structures using high frequency guided waves

    NASA Astrophysics Data System (ADS)

    Chan, H.; Masserey, B.; Fromme, P.

    2015-03-01

    Varying loading conditions of aircraft structures result in stress concentration at fastener holes, where multi-layered components are connected, potentially leading to the development of hidden fatigue cracks in inaccessible layers. High frequency guided waves propagating along the structure allow for the structural health monitoring (SHM) of such components, e.g., aircraft wings. Experimentally the required guided wave modes can be easily excited using standard ultrasonic wedge transducers. However, the sensitivity for the detection of small, potentially hidden, fatigue cracks has to be ascertained. The type of multi-layered model structure investigated consists of two adhesively bonded aluminum plate-strips with a sealant layer. Fatigue experiments were carried out and the growth of fatigue cracks at the fastener hole in one of the metallic layers was monitored optically during cyclic loading. The influence of the fatigue cracks of increasing size on the scattered guided wave field was evaluated. The sensitivity and repeatability of the high frequency guided wave modes to detect and monitor the fatigue crack growth was investigated, using both standard pulse-echo equipment and a laser interferometer. The potential for hidden fatigue crack growth monitoring at critical and difficult to access fastener locations from a stand-off distance was ascertained. The robustness of the methodology for practical in situ ultrasonic monitoring of fatigue crack growth is discussed.

  9. [Emergy value evaluation on rice-duck organic farming mode].

    PubMed

    Xi, Yunguan; Qin, Pei

    2006-02-01

    Employing emergy value evaluation method, this paper compared the ecological and economic benefits of rice-duck organic farming system (mode I) and conventional rice-wheat rotation system (mode II) in Shanghai suburb. The results showed that mode I had better emergy benefits, higher self-organizing ability and sustainability, and higher product safety. The net emergy yield ratio (EYR), feedback ratio of yield emergy (FYE), and emergy sustainable index (ESI) of mode I were respectively 1.57, 14.1, and 8.71 times as much as those of mode II, and the emergy index of product safety (EIPS) was 0 in mode I but -0.66 in mode II. The emergy investment ratio (EIR) and environmental loading ratio (ELR) of mode I were 40.1% and 18.3% of mode II, respectively, suggesting that mode I had less environmental pressure than mode II. Mode I had lower economic benefits than mode II. The economic output, gross income, and net income of mode I were 15.7%, 9.6%, and 29.6% less than those of mode II , respectively. As for Em dollars, the output, gross income, and net income of mode I were respectively 50%, 102.6%, and 136.4% higher than those of mode II. With the system optimization and the development of organic food market, mode I had the potential to improve its economic benefits.

  10. The Role of Microtexture on the Fatigue Behavior of an alpha + beta Titanium Alloy, Ti-6Al-2Sn-4Zr-6Mo (Preprint)

    DTIC Science & Technology

    2011-03-01

    Hall. Fatigue crack initiation in alpha-beta titanium alloys, International Journal of Fatigue, 31 (Suppl. 1), (1997) S23–S37. [ 4 ] G. Lutjering...Power Research Institute - October 1983. [ 6 ] F. Larson, A. Zarkades. Properties of Textured Titanium Alloys, MCIC Report - MCIC·74- 20 – Metals and...Figure 3 and 4 . Table II. The cycle count and relative rankings of fatigue crack growth rates measured from the cracks shown in Figure 5 and 6

  11. The Fatigue of Powder Metallurgy Alloys.

    DTIC Science & Technology

    2014-09-26

    MPavffi) Fig. 5. Fatigue crack growth rates as a function of A for P/M and I/M alloys (R =0.05). * -9- X 7090 T-L -RM05 NODS0 13 X 7091 L-T /O Ra 16 -6 1077... 16 - IN9021-T4 Kc , Ul "I . II gD I / .2 .4 .6 8 10 R (Kmin/Kmax) Fig. 12. Kmax’ K’tn and Kop as a function of R for the INgO2-T4 alloy. In this...19- X7091 T-L 10- -R=Q05 3.5% NaCI o K-decreasing * K-increasing o 0 0a 00 E0 010 1 50-62 R i o • AK (MPa ifr ) Ftg

  12. Rolling element fatigue testing of gear materials

    NASA Technical Reports Server (NTRS)

    Nahm, A. H.

    1978-01-01

    Rolling element fatigue lives of eleven alloys were evaluated. The eleven alloys studied were three nitriding alloys (Super Nitralloy, Nitralloy 135, and Nitralloy N), four case carburizing alloys (AISI 9310, CBS 600, CBS 1000M and Vasco X-2), and four throughhardening alloys (Vasco Matrix II,AISI W-1, AISI S-2 and AISI O-2). Several different heat treatments and/or melting processes were studied on the three carburizing alloy steels. Metallurgical analyses were made before and after the RC rig tests. Test data were statistically analyzed using the Weibull distribution function. B-10 lives were compared versus VIM-VAR AISI M-50 and carburized VAR AISI 9310, as reference alloys.

  13. Blood-Borne Markers of Fatigue in Competitive Athletes – Results from Simulated Training Camps

    PubMed Central

    Hecksteden, Anne; Skorski, Sabrina; Schwindling, Sascha; Hammes, Daniel; Pfeiffer, Mark; Kellmann, Michael; Ferrauti, Alexander; Meyer, Tim

    2016-01-01

    Assessing current fatigue of athletes to fine-tune training prescriptions is a critical task in competitive sports. Blood-borne surrogate markers are widely used despite the scarcity of validation trials with representative subjects and interventions. Moreover, differences between training modes and disciplines (e.g. due to differences in eccentric force production or calorie turnover) have rarely been studied within a consistent design. Therefore, we investigated blood-borne fatigue markers during and after discipline-specific simulated training camps. A comprehensive panel of blood-born indicators was measured in 73 competitive athletes (28 cyclists, 22 team sports, 23 strength) at 3 time-points: after a run-in resting phase (d 1), after a 6-day induction of fatigue (d 8) and following a subsequent 2-day recovery period (d 11). Venous blood samples were collected between 8 and 10 a.m. Courses of blood-borne indicators are considered as fatigue dependent if a significant deviation from baseline is present at day 8 (Δfatigue) which significantly regresses towards baseline until day 11 (Δrecovery). With cycling, a fatigue dependent course was observed for creatine kinase (CK; Δfatigue 54±84 U/l; Δrecovery -60±83 U/l), urea (Δfatigue 11±9 mg/dl; Δrecovery -10±10 mg/dl), free testosterone (Δfatigue -1.3±2.1 pg/ml; Δrecovery 0.8±1.5 pg/ml) and insulin linke growth factor 1 (IGF-1; Δfatigue -56±28 ng/ml; Δrecovery 53±29 ng/ml). For urea and IGF-1 95% confidence intervals for days 1 and 11 did not overlap with day 8. With strength and high-intensity interval training, respectively, fatigue-dependent courses and separated 95% confidence intervals were present for CK (strength: Δfatigue 582±649 U/l; Δrecovery -618±419 U/l; HIIT: Δfatigue 863±952 U/l; Δrecovery -741±842 U/l) only. These results indicate that, within a comprehensive panel of blood-borne markers, changes in fatigue are most accurately reflected by urea and IGF-1 for cycling and by CK

  14. A study on the influence of microstructure on small fatigue cracks

    NASA Astrophysics Data System (ADS)

    Castelluccio, Gustavo M.

    In spite of its significance in industrial applications, the prediction of the influence of microstructure on the early stages of crack formation and growth in engineering alloys remains underdeveloped. The formation and early growth of fatigue cracks in the high cycle fatigue regime lasts for much of the fatigue life, and it is strongly influenced by microstructural features such as grain size, twins and morphological and crystallographic texture. However, most fatigue models do not predict the in uence of the microstructure on early stages of crack formation, or they employ parameters that should be calibrated with experimental data from specimens with microstructures of interest. These post facto strategies are adequate to characterize materials, but they are not fully appropriate to aid in the design of fatigue-resistant engineering alloys. This thesis considers finite element computational models that explicitly render the microstructure of selected FCC metallic systems and introduces a fatigue methodology that estimates transgranular and intergranular fatigue growth for microstructurally small cracks. The driving forces for both failure modes are assessed by means of fatigue indicators, which are used along with life correlations to estimate the fatigue life. Furthermore, cracks with meandering paths are modeled by considering crack growth on a grain-by-grain basis with a damage model embedded analytically to account for stress and strain redistribution as the cracks extend. The methodology is implemented using a crystal plasticity constitutive model calibrated for studying the effect of microstructure on early fatigue life of a powder processed Ni-base RR1000 superalloy at elevated temperature under high cycle fatigue conditions. This alloy is employed for aircraft turbine engine disks, which undergo a thermomechanical production process to produce a controlled bimodal grain size distribution. The prediction of the fatigue life for this complex

  15. Transients from initial conditions based on Lagrangian perturbation theory in N-body simulations II: the effect of the transverse mode

    SciTech Connect

    Tatekawa, Takayuki

    2014-04-01

    We study the initial conditions for cosmological N-body simulations for precision cosmology. In general, Zel'dovich approximation has been applied for the initial conditions of N-body simulations for a long time. These initial conditions provide incorrect higher-order growth. These error caused by setting up the initial conditions by perturbation theory is called transients. We investigated the impact of transient on non-Gaussianity of density field by performing cosmological N-body simulations with initial conditions based on first-, second-, and third-order Lagrangian perturbation theory in previous paper. In this paper, we evaluates the effect of the transverse mode in the third-order Lagrangian perturbation theory for several statistical quantities such as power spectrum and non-Gaussianty. Then we clarified that the effect of the transverse mode in the third-order Lagrangian perturbation theory is quite small.

  16. In situ fatigue loading stage inside scanning electron microscope

    NASA Technical Reports Server (NTRS)

    Telesman, Jack; Kantzos, Peter; Brewer, David

    1988-01-01

    A fatigue loading stage inside a scanning electron microscopy (SEM) was developed. The stage allows dynamic and static high-magnification and high-resolution viewing of the fatigue crack initiation and crack propagation processes. The loading stage is controlled by a closed-loop servohydraulic system. Maximum load is 1000 lb (4450 N) with test frequencies ranging up to 30 Hz. The stage accommodates specimens up to 2 inches (50 mm) in length and tolerates substantial specimen translation to view the propagating crack. At room temperature, acceptable working resolution is obtainable for magnifications ranging up to 10,000X. The system is equipped with a high-temperature setup designed for temperatures up to 2000 F (1100 C). The signal can be videotaped for further analysis of the pertinent fatigue damage mechanisms. The design allows for quick and easy interchange and conversion of the SEM from a loading stage configuration to its normal operational configuration and vice versa. Tests are performed entirely in the in-situ mode. In contrast to other designs, the NASA design has greatly extended the life of the loading stage by not exposing the bellows to cyclic loading. The loading stage was used to investigate the fatigue crack growth mechanisms in the (100)-oriented PWA 1480 single-crystal, nickel-based supperalloy. The high-magnification observations revealed the details of the crack growth processes.

  17. Fatigue and fracture of fiber composites under combined interlaminar stresses

    SciTech Connect

    DeTeresa, S J; Freeman, D C; Groves, S E

    1998-06-25

    As part of efforts to develop a three-dimensional failure model for composites, a study of failure and fatigue due to combined interlaminar stresses was conducted. The combined stresses were generated using a hollow cylindrical specimen, which was subjected to normal compression and torsion. For both glass and carbon fiber composites, normal compression resulted in a significant enhancement in the interlaminar shear stress and strain at failure. Under moderate compression levels, the failure mode transitioned from elastic to plastic. The observed failure envelope could not be adequately captured using common ply- level failure models. Alternate modeling approaches were examined and it was found that a pressure-dependent failure criterion was required to reproduce the experimental results. The magnitude of the pressure-dependent terms of this model was found to be material dependent. The interlaminar shear fatigue behavior of a carbon/epoxy system was also studied using the cylindrical specimen. Preliminary results indicate that a single S/N curve which is normalized for interlaminar shear strength may be able to reproduce the effects of both temperature and out-of-plane compression on fatigue life. The results demonstrate that there are significant gains to be made in improving interlaminar strengths of composite structures by applying out-of-plane compression. This effect could be exploited for improved strength and fatigue life of composite joints and other regions in structures where interlaminar stress states are critical.

  18. A review on strengthening steel beams using FRP under fatigue.

    PubMed

    Kamruzzaman, Mohamed; Jumaat, Mohd Zamin; Sulong, N H Ramli; Islam, A B M Saiful

    2014-01-01

    In recent decades, the application of fibre-reinforced polymer (FRP) composites for strengthening structural elements has become an efficient option to meet the increased cyclic loads or repair due to corrosion or fatigue cracking. Hence, the objective of this study is to explore the existing FRP reinforcing techniques to care for fatigue damaged structural steel elements. This study covers the surface treatment techniques, adhesive curing, and support conditions under cyclic loading including fatigue performance, crack propagation, and failure modes with finite element (FE) simulation of the steel bridge girders and structural elements. FRP strengthening composites delay initial cracking, reduce the crack growth rate, extend the fatigue life, and decrease the stiffness decay with residual deflection. Prestressed carbon fibre-reinforced polymer (CFRP) is the best strengthening option. End anchorage prevents debonding of the CRRP strips at the beam ends by reducing the local interfacial shear and peel stresses. Hybrid-joint, nanoadhesive, and carbon-flex can also be attractive for strengthening systems.

  19. A Review on Strengthening Steel Beams Using FRP under Fatigue

    PubMed Central

    Jumaat, Mohd Zamin; Ramli Sulong, N. H.

    2014-01-01

    In recent decades, the application of fibre-reinforced polymer (FRP) composites for strengthening structural elements has become an efficient option to meet the increased cyclic loads or repair due to corrosion or fatigue cracking. Hence, the objective of this study is to explore the existing FRP reinforcing techniques to care for fatigue damaged structural steel elements. This study covers the surface treatment techniques, adhesive curing, and support conditions under cyclic loading including fatigue performance, crack propagation, and failure modes with finite element (FE) simulation of the steel bridge girders and structural elements. FRP strengthening composites delay initial cracking, reduce the crack growth rate, extend the fatigue life, and decrease the stiffness decay with residual deflection. Prestressed carbon fibre-reinforced polymer (CFRP) is the best strengthening option. End anchorage prevents debonding of the CRRP strips at the beam ends by reducing the local interfacial shear and peel stresses. Hybrid-joint, nanoadhesive, and carbon-flex can also be attractive for strengthening systems. PMID:25243221

  20. FTIR spectra and normal-mode analysis of a tetranuclear Manganese adamantane-like complex in two electrochemically prepared oxidation states: Relevance to the oxygen-evolving complex of Photosystem II

    SciTech Connect

    Visser, Hendrik; Dube, Christopher E.; Armstrong, William H.; Sauer, Kenneth; Yachandra, Vittal K.

    2002-03-19

    The IR spectra and normal-mode analysis of the adamantane-like compound [Mn4O6(bpea)4]n+ in two oxidation states, MnIV4 and MnIIIMnIV3, that are relevant to the oxygen-evolving complex of photosystem II are presented. Mn-O vibrational modes are identified with isotopic exchange, 16O->18O, of the mono-(mu)-oxo bridging atoms in the complex. IR spectra of the MnIIIMnIV3 species are obtained by electrochemical reduction of the MnIV4 species using a spectroelectrochemical cell, based on attenuated total reflection [Visser et al. Anal Chem 2001, 73, 4374-4378]. A novel method of subtraction is used to reduce background contributions from solvent and ligand modes, and the difference and double-difference spectra are used in identifying Mn-O bridging modes that are sensitive to oxidation state change. Two strong IR bands are observed for the MnIV4 species at 745 and 707 cm-1 and a weaker band at 510 cm-1. Upon reduction, the MnIIIMnIV3 species exhibits two strong IR bands at 745 and 680 cm-1, and several weaker bands are observed in the 510 - 425 cm-1 range. A normal mode analysis is performed to assign all the relevant bridging modes in the oxidized MnIV4 and reduced MnIIIMnIV3 species. The calculated force constants for the MnIV4 species are = 3.15 mdynAngstrom, = 0.55 mdyn/Angstrom, and = 0.20 mdyn/Angstrom. The force constants for the MnIIIMnIV3 species are = 3.10 mdyn/Angstrom, = 2.45 mdyn/Angstrom, = 0.40, and = 0.15 mdyn/Angstrom. This study provides insights for the identification of Mn-O modes in the IR spectra of the photosynthetic oxygen-evolving complex during its catalytic cycle.

  1. FTIR Spectra and Normal-Mode Analysis of a Tetranuclear Manganese Adamantane-like Complex in Two Electrochemically Prepared Oxidation States: Relevance to the Oxygen-Evolving Complex of Photosystem II

    PubMed Central

    Visser, Hendrik; Dubé, Christopher E.; Armstrong, William H.; Sauer, Kenneth; Yachandra, Vittal K.

    2014-01-01

    The IR spectra and normal-mode analysis of the adamantane-like compound [Mn4O6(bpea)4]n+ (bpea = N,N-bis(2-pyridylmethyl)ethylamine) in two oxidation states, MnIV4 and MnIIIMnIV3, that are relevant to the oxygen-evolving complex of photosystem II are presented. Mn–O vibrational modes are identified with isotopic exchange, 16O→18O, of the mono-μ-oxo bridging atoms in the complex. IR spectra of the MnIIIMnIV3 species are obtained by electrochemical reduction of the MnIV4 species using a spectroelectrochemical cell, based on attenuated total reflection [Visser, H.; et al. Anal. Chem. 2001, 73, 4374–4378]. A novel method of subtraction is used to reduce background contributions from solvent and ligand modes, and the difference and double-difference spectra are used in identifying Mn–O bridging modes that are sensitive to oxidation state change. Two strong IR bands are observed for the MnIV4 species at 745 and 707 cm−1, and a weaker band is observed at 510 cm−1. Upon reduction, the MnIIIMnIV3 species exhibits two strong IR bands at 745 and 680 cm−1, and several weaker bands are observed in the 510–425 cm−1 range. A normal-mode analysis is performed to assign all the relevant bridging modes in the oxidized MnIV4 and reduced MnIIIMnIV3 species. The calculated force constants for the MnIV4 species are frIV = 3.15 mdyn/Å, frOr = 0.55 mdyn/Å, and frMnr = 0.20 mdyn/Å. The force constants for the MnIIIMnIV3 species are frIV = 3.10 mdyn/Å, frIII = 2.45 mdyn/Å, frOr = 0.40 mdyn/Å, and frMnr = 0.15 mdyn/Å. This study provides insights for the identification of Mn–O modes in the IR spectra of the photosynthetic oxygen-evolving complex during its catalytic cycle. PMID:12224948

  2. FTIR spectra and normal-mode analysis of a tetranuclear manganese adamantane-like complex in two electrochemically prepared oxidation states: relevance to the oxygen-evolving complex of photosystem II.

    PubMed

    Visser, Hendrik; Dubé, Christopher E; Armstrong, William H; Sauer, Kenneth; Yachandra, Vittal K

    2002-09-18

    The IR spectra and normal-mode analysis of the adamantane-like compound [Mn(4)O(6)(bpea)(4)](n+) (bpea = N,N-bis(2-pyridylmethyl)ethylamine) in two oxidation states, Mn(IV)(4) and Mn(III)Mn(IV)(3), that are relevant to the oxygen-evolving complex of photosystem II are presented. Mn-O vibrational modes are identified with isotopic exchange, (16)O-->(18)O, of the mono-micro-oxo bridging atoms in the complex. IR spectra of the Mn(III)Mn(IV)(3) species are obtained by electrochemical reduction of the Mn(IV)(4) species using a spectroelectrochemical cell, based on attenuated total reflection [Visser, H.; et al. Anal. Chem. 2001, 73, 4374-4378]. A novel method of subtraction is used to reduce background contributions from solvent and ligand modes, and the difference and double-difference spectra are used in identifying Mn-O bridging modes that are sensitive to oxidation state change. Two strong IR bands are observed for the Mn(IV)(4) species at 745 and 707 cm(-1), and a weaker band is observed at 510 cm(-1). Upon reduction, the Mn(III)Mn(IV)(3) species exhibits two strong IR bands at 745 and 680 cm(-1), and several weaker bands are observed in the 510-425 cm(-1) range. A normal-mode analysis is performed to assign all the relevant bridging modes in the oxidized Mn(IV)(4) and reduced Mn(III)Mn(IV)(3) species. The calculated force constants for the Mn(IV)(4) species are f(r)(IV)= 3.15 mdyn/A, f(rOr) = 0.55 mdyn/A, and f(rMnr) = 0.20 mdyn/A. The force constants for the Mn(III)Mn(IV)(3) species are f(r)(IV)= 3.10 mdyn/A, f(r)(III)= 2.45 mdyn/A, f(rOr) = 0.40 mdyn/A, and f(rMnr) = 0.15 mdyn/A. This study provides insights for the identification of Mn-O modes in the IR spectra of the photosynthetic oxygen-evolving complex during its catalytic cycle.

  3. Mechanisms for fatigue and wear of polysilicon structural thinfilms

    SciTech Connect

    Alsem, Daniel Henricus

    2006-01-01

    Fatigue and wear in micron-scale polysilicon structural films can severely impact the reliability of microelectromechanical systems (MEMS). Despite studies on fatigue and wear behavior of these films, there is still an on-going debate regarding the precise physical mechanisms for these two important failure modes. Although macro-scale silicon does not fatigue, this phenomenon is observed in micron-scale silicon. It is shown that for polysilicon devices fabricated in the MUMPs foundry and SUMMiT process stress-lifetime data exhibits similar trends in ambient air, shorter lifetimes in higher relative humidity environments and no fatigue failure at all in high vacuum. Transmission electron microscopy of the surface oxides of the samples show an approximate four-fold thickening of the oxide at stress concentrations after fatigue failure, but no thickening after fracture in air or after fatigue cycling in vacuo. It is found that such oxide thickening and fatigue failure (in air) occurs in devices with initial oxide thicknesses of ~4-20 nm. Such results are interpreted and explained by a reaction layer fatigue mechanism; specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure. Polysilicon specimens from the SUMMiT process are used to study wear mechanisms in micron-scale silicon in ambient air. Worn parts are examined by analytical scanning and transmission electron microscopy, while temperature changes are monitored using infrared microscopy. These results are compared with the development of values of static coefficients of friction (COF) with number of wear cycles. Observations show amorphous debris particles (~50-100 nm) created by fracture through the silicon grains (~500 nm), which subsequently oxidize, agglomerate into clusters and create plowing tracks. A nano-crystalline layer (~20-200 nm) forms at worn regions. No dislocations or

  4. Mechanisms for fatigue and wear of polysilicon structural thin films

    NASA Astrophysics Data System (ADS)

    Alsem, Daniel Henricus

    Fatigue and wear in micron-scale polysilicon structural films can severely impact the reliability of microelectromechanical systems (MEMS). Despite studies on fatigue and wear behavior of these films, there is still an on-going debate regarding the precise physical mechanisms for these two important failure modes. Although macro-scale silicon does not fatigue, this phenomenon is observed in micron-scale silicon. It is shown that for polysilicon devices fabricated in the MUMPs foundry and SUMMiT(TM) process stress-lifetime data exhibits similar trends in ambient air, shorter lifetimes in higher relative humidity environments and no fatigue failure at all in high vacuum. Transmission electron microscopy of the surface oxides of the samples show an approximate four-fold thickening of the oxide at stress concentrations after fatigue failure, but no thickening after fracture in air or after fatigue cycling in vacuo . It is found that such oxide thickening and fatigue failure (in air) occurs in devices with initial oxide thicknesses of ˜4-20 nm. Such results are interpreted and explained by a reaction-layer fatigue mechanism; specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure. Polysilicon specimens from the SUMMiT(TM) process are used to study wear mechanisms in micron-scale silicon in ambient air. Worn parts are examined by analytical scanning and transmission electron microscopy, while temperature changes are monitored using infrared microscopy. These results are compared with the development of values of static coefficients of friction (COF) with number of wear cycles. Observations show amorphous debris particles (˜50-100 nm) created by fracture through the silicon grains (˜500 nm), which subsequently oxidize, agglomerate into clusters and create plowing tracks. A nano-crystalline layer (˜20-200 nm) forms at worn regions. No

  5. Degradation in the fatigue crack growth resistance of human dentin by lactic acid.

    PubMed

    Orrego, Santiago; Xu, Huakun; Arola, Dwayne

    2017-04-01

    The oral cavity frequently undergoes localized changes in chemistry and level of acidity, which threatens the integrity of the restorative material and supporting hard tissue. The focus of this study was to evaluate the changes in fatigue crack growth resistance of dentin and toughening mechanisms caused by lactic acid exposure. Compact tension specimens of human dentin were prepared from unrestored molars and subjected to Mode I opening mode cyclic loads. Fatigue crack growth was achieved in samples from mid- and outer-coronal dentin immersed in either a lactic acid solution or neutral conditions. An additional evaluation of the influence of sealing the lumens by dental adhesive was also conducted. A hybrid analysis combining experimental results and finite element modeling quantified the contribution of the toughening mechanisms for both environments. The fatigue crack growth responses showed that exposure to lactic acid caused a significant reduction (p≤0.05) of the stress intensity threshold for cyclic crack extension, and a significant increase (p≤0.05) in the incremental fatigue crack growth rate for both regions of coronal dentin. Sealing the lumens had negligible influence on the fatigue resistance. The hybrid analysis showed that the acidic solution was most detrimental to the extrinsic toughening mechanisms, and the magnitude of crack closure stresses operating in the crack wake. Exposing dentin to acidic environments contributes to the development of caries, but it also increases the chance of tooth fractures via fatigue-related failure and at lower mastication forces.

  6. Characterising fatigue crack in an aluminium plate using guided elastic waves

    NASA Astrophysics Data System (ADS)

    Zhou, Chao; Su, Zhongqing; Cheng, Li

    2011-04-01

    Integrity of in-service engineering structures is prone to fatigue damage over their lifespan. Majority of the currently existing elastic-wave-based damage identification techniques have been developed and validated for damage at macroscopic levels, by canvassing linear properties of elastic waves such as attenuation, transmission, reflection and mode conversion. However the real damage in engineering structures often initiates from fatigue crack, presenting highly nonlinear characteristics under cyclic loads. It is of great significance but vast challenge to detect fatigue damage of small dimension at its initial stage. In this study, traditional elastic-wave-based damage identification techniques were first employed with an attempt to detect fatigue crack initiated from a notch in an aluminium plate with the assistance of a signal correlation analysis, to observe the deficiency of the approach. Then the higher-order harmonic wave generation was used to exploit the nonlinear characteristics of acousto-ultrasonic waves (Lamb waves), whereby the fatigue damage was characterised. Results show that nonlinear characteristics of acousto-ultrasonic waves can facilitate more effective detection of fatigue damage than linear signal features such as wave reflection, transmission or mode conversion.

  7. Muscle fatigue during high-intensity exercise in children.

    PubMed

    Ratel, Sébastien; Duché, Pascale; Williams, Craig A

    2006-01-01

    Children are able to resist fatigue better than adults during one or several repeated high-intensity exercise bouts. This finding has been reported by measuring mechanical force or power output profiles during sustained isometric maximal contractions or repeated bouts of high-intensity dynamic exercises. The ability of children to better maintain performance during repeated high-intensity exercise bouts could be related to their lower level of fatigue during exercise and/or faster recovery following exercise. This may be explained by muscle characteristics of children, which are quantitatively and qualitatively different to those of adults. Children have less muscle mass than adults and hence, generate lower absolute power during high-intensity exercise. Some researchers also showed that children were equipped better for oxidative than glycolytic pathways during exercise, which would lead to a lower accumulation of muscle by-products. Furthermore, some reports indicated that the lower ability of children to activate their type II muscle fibres would also explain their greater resistance to fatigue during sustained maximal contractions. The lower accumulation of muscle by-products observed in children may be suggestive of a reduced metabolic signal, which induces lower ratings of perceived exertion. Factors such as faster phosphocreatine resynthesis, greater oxidative capacity, better acid-base regulation, faster readjustment of initial cardiorespiratory parameters and higher removal of metabolic by-products in children could also explain their faster recovery following high-intensity exercise.From a clinical point of view, muscle fatigue profiles are different between healthy children and children with muscle and metabolic diseases. Studies of dystrophic muscles in children indicated contradictory findings of changes in contractile properties and the muscle fatigability. Some have found that the muscle of boys with Duchenne muscular dystrophy (DMD) fatigued less

  8. Thermomechanical Fatigue of Ductile Cast Iron and Its Life Prediction

    NASA Astrophysics Data System (ADS)

    Wu, Xijia; Quan, Guangchun; MacNeil, Ryan; Zhang, Zhong; Liu, Xiaoyang; Sloss, Clayton

    2015-06-01

    Thermomechanical fatigue (TMF) behaviors of ductile cast iron (DCI) were investigated under out-of-phase (OP), in-phase (IP), and constrained strain-control conditions with temperature hold in various temperature ranges: 573 K to 1073 K, 723 K to 1073 K, and 433 K to 873 K (300 °C to 800 °C, 450 °C to 800 °C, and 160 °C to 600 °C). The integrated creep-fatigue theory (ICFT) model was incorporated into the finite element method to simulate the hysteresis behavior and predict the TMF life of DCI under those test conditions. With the consideration of four deformation/damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement, (iii) creep, and (iv) oxidation, as revealed from the previous study on low cycle fatigue of the material, the model delineates the contributions of these physical mechanisms in the asymmetrical hysteresis behavior and the damage accumulation process leading to final TMF failure. This study shows that the ICFT model can simulate the stress-strain response and life of DCI under complex TMF loading profiles (OP and IP, and constrained with temperature hold).

  9. Creep and Environmental Effects on High Temperature Creep-Fatigue Behavior of Alloy 617

    SciTech Connect

    L. J. Carroll; C. Cabet; R. Madland; R. Wright

    2011-06-01

    Alloy 617 is the leading candidate material for Intermediate Heat Exchanger (IHX) of a Very High Temperature Reactor (VHTR), expected to have an outlet temperature as high as 950 C. System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior in both air and impure helium, representative of the VHTR primary coolant. Strain controlled LCF tests including hold times at maximum tensile strain were conducted at total strain range of 0.3% in air at 950 C. Creep-fatigue testing was also performed in a simulated VHTR impure helium coolant for selected experimental conditions. The fatigue resistance decreased when a hold time was added at peak tensile stress, consistent with the observed change in fracture mode from transgranular to intergranular with introduction of a tensile hold. Increases in the tensile hold time, beyond 180 sec, was not detrimental to the creep-fatigue resistance. Grain boundary damage in the form of grain boundary cracking was present in the bulk of the creep-fatigue specimens. This bulk cracking was quantified and found to be similar for hold times of up to 1800 sec consistent with the saturation in failure lives and rapid stress relaxation observed during the creep portion of the creep-fatigue cycle.

  10. A temperature dependent fatigue failure criterion for graphite/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Rotem, A.; Nelson, H. G.

    1979-01-01

    A fatigue failure criterion applicable to composite materials is developed and applied to predict the fatigue behavior of graphite/epoxy laminates with particular emphasis on the influence of temperature. Tensile stress-strain curves and tension-tension fatigue curves for various unidirectional, angle-ply and symmetrically balanced laminates were developed at test temperatures of 25 C, 74 C and 114 C. In general for most laminates a reduction in both static strength and fatigue strength is observed with increasing temperature. This reduction appeared more severe in fatigue loading than in static tensile loading and most severe where the shear stress in the lamina is the dominant failure mode. Through an analytical formulation of shifting functions for the influences of temperature, all fatigue data are shown to be capable of being reduced to a single reference curve at some temperature. Additionally, examples are given which demonstrate the capability of the fatigue failure criterion to predict failure of complex symmetrically balanced laminates from relevant parameters obtained from the observed behavior of unidirectional and angle-ply laminates.

  11. A temperature dependent fatigue failure criterion for graphite/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Rotem, A.; Nelson, H. G.

    1978-01-01

    A fatigue failure criterion applicable to composite materials is developed and applied to predict the fatigue behavior of graphite/epoxy laminates with particular emphasis on the influence of temperature. Tensile stress-strain curves and tension-tension fatigue curves for various unidirectional, angle-ply and symmetrically balanced laminates were developed at test temperatures of 25 C, 74 C, and 114 C. For most laminates a reduction in both static strength and fatigue strength is observed with increasing temperature. This reduction appeared more severe in fatigue loading than in static tensile loading and most severe where the shear stress in the lamina is the dominate failure mode. Through an analytical formulation of shifting functions for the influences of temperature, all fatigue data are shown to be capable of being reduced to a single reference curve at some temperature. Examples are given which demonstrate the capability of the fatigue failure criterion to predict failure of complex symmetrically balanced laminates from relevant parameters obtained from the observed behavior of unidirectional and angle-ply laminates.

  12. Spatially distributed sequential stimulation reduces muscle fatigue during neuromuscular electrical stimulation.

    PubMed

    Sayenko, Dimitry G; Popovic, Milos R; Masani, Kei

    2013-01-01

    A critical limitation with neuromuscular electrical stimulation (NMES) approach is the rapid onset of muscle fatigue during repeated contractions, which results in the muscle force decay and slowing of muscle contractile properties. In our previous study, we demonstrated that spatially distributed sequential stimulation (SDSS) show a drastically greater fatigue-reducing ability compared to a conventional, single active electrode stimulation (SES) with an individual with spinal cord injury when applied for plantar flexors. The purpose of the present study is to explore the fatigue-reducing ability of SDSS for major lower limb muscle groups in the able-bodied population as well as individuals with spinal cord injury (SCI). SDSS was delivered through four active electrodes applied to the muscle of interest, sending a stimulation pulse to each electrode one after another with 90° phase shift between successive electrodes. For comparison, SES was delivered through one active electrode. For both modes of stimulation, the resultant frequency to the muscle as a whole was 40 Hz. Using corresponding protocols for the fatiguing stimulation, we demonstrated the fatigue-reducing ability of SDSS by higher fatigue indices as compared with single active electrode setup for major leg muscles in both subject groups. The present work verifies and extends reported findings on the effectiveness of using spatially distributed sequential stimulation in the leg muscles to reduce muscle fatigue. Application of this technique can improve the usefulness of NMES during functional movements in the clinical setup.

  13. Noncontact monitoring of fatigue crack growth using high frequency guided waves

    NASA Astrophysics Data System (ADS)

    Masserey, B.; Fromme, P.

    2014-03-01

    The development of fatigue cracks at fastener holes due to stress concentration is a common problem in aircraft maintenance. This contribution investigates the use of high frequency guided waves for the non-contact monitoring of fatigue crack growth in tensile, aluminium specimens. High frequency guided ultrasonic waves have a good sensitivity for defect detection and can propagate along the structure, thus having the potential for the inspection of difficult to access parts by means of non-contact measurements. Experimentally the required guided wave modes are excited using standard wedge transducers and measured using a laser interferometer. The growth of fatigue cracks during cyclic loading was monitored optically and the resulting changes in the signal caused by crack growth are quantified. Full three-dimensional simulation of the scattering of the high frequency guided ultrasonic waves at the fastener hole and crack has been implemented using the Finite Difference (FD) method. The comparison of the results shows a good agreement of the measured and predicted scattered field of the guided wave at quarter-elliptical and through-thickness fatigue cracks. The measurements show a good sensitivity for the early detection of fatigue damage and for the monitoring of fatigue crack growth at a fastener hole. The sensitivity and repeatability are ascertained, and the robustness of the methodology for practical in-situ ultrasonic monitoring of fatigue crack growth is discussed.

  14. Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1988-01-01

    A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

  15. Two coordination modes of CuII in a binuclear complex with N-(pyridin-2-yl­carbon­yl)pyridine-2-carboxamidate ligands

    PubMed Central

    Campos-Gaxiola, José J.; Morales-Morales, David; Höpfl, Herbert; Parra-Hake, Miguel; Reyes-Martínez, Reyna

    2012-01-01

    In the title dinuclear complex, (acetonitrile-1κN)[μ-N-(pyri­din-2-ylcarbonyl)pyridine-2-carboxamidato-1:2κ5 N,N′,N′′:O,O′][N-(pyridin-2-ylcarbonyl)pyridine-2-carboxamidato-2κ3 N,N′,N′′]bis(trifluoromethanesulfonato-1κO)dicopper(II), [Cu2(C12H8N3O2)2(CF3O3S)2(CH3CN)], one of the CuII ions is five-coordinated in a distorted square-pyramidal N3O2 environment provided by two N-(pyridin-2-ylcarbon­yl)pyridine-2-carboxamidate (bpca) ligands, while the second CuII ion is six-coordinated in a distorted octa­hedral N4O2 environment provided by one bpca ligand, two trifluoro­methansulfonate ligands and one acetonitrile mol­ecule. Weak inter­molecular C—H⋯O and C—H⋯F hydrogen bonds and π–π stacking inter­actions with centroid–centroid distances of 3.6799 (15) and 3.8520 (16) Å stabilize the crystal packing and lead to a three-dimensional network. PMID:23125602

  16. Two coordination modes of Cu(II) in a binuclear complex with N-(pyridin-2-yl-carbon-yl)pyridine-2-carboxamidate ligands.

    PubMed

    Campos-Gaxiola, José J; Morales-Morales, David; Höpfl, Herbert; Parra-Hake, Miguel; Reyes-Martínez, Reyna

    2012-10-01

    In the title dinuclear complex, (acetonitrile-1κN)[μ-N-(pyri-din-2-ylcarbonyl)pyridine-2-carboxamidato-1:2κ(5)N,N',N'':O,O'][N-(pyridin-2-ylcarbonyl)pyridine-2-carboxamidato-2κ(3)N,N',N'']bis(trifluoromethanesulfonato-1κO)dicopper(II), [Cu(2)(C(12)H(8)N(3)O(2))(2)(CF(3)O(3)S)(2)(CH(3)CN)], one of the Cu(II) ions is five-coordinated in a distorted square-pyramidal N(3)O(2) environment provided by two N-(pyridin-2-ylcarbon-yl)pyridine-2-carboxamidate (bpca) ligands, while the second Cu(II) ion is six-coordinated in a distorted octa-hedral N(4)O(2) environment provided by one bpca ligand, two trifluoro-methansulfonate ligands and one acetonitrile mol-ecule. Weak inter-molecular C-H⋯O and C-H⋯F hydrogen bonds and π-π stacking inter-actions with centroid-centroid distances of 3.6799 (15) and 3.8520 (16) Å stabilize the crystal packing and lead to a three-dimensional network.

  17. High-Cycle Fatigue of High-Strength Low Alloy Steel Q345 Subjected to Immersion Corrosion for Mining Wheel Applications

    NASA Astrophysics Data System (ADS)

    Dicecco, Sante; Altenhof, William; Hu, Henry; Banting, Richard

    2017-03-01

    In an effort to better understand the impact of material degradation on the fatigue life of mining wheels made of a high-strength low alloy carbon steel (Q345), this study seeks to evaluate the effect of surface corrosion on the high-cycle fatigue behavior of the Q345 alloy. The fatigue behavior of the polished and corroded alloy was investigated. Following exposure to a 3.5 wt.% NaCl saltwater solution, polished and corroded fatigue specimens were tested using an R.R. Moore rotating-bending fatigue apparatus. Microstructural analyses via both optical microscopy and scanning electron microscopy (SEM) revealed that one major phase, α-iron phase, ferrite, and one minor phase, colony pearlite, existed in the extracted Q345 alloy. The results of the fatigue testing showed that the polished and corroded specimens had an endurance strength of approximately 295 and 222 MPa, respectively, at 5,000,000 cycles. The corroded surface condition resulted in a decrease in the fatigue strength of the Q345 alloy by 24.6%. Scanning electron microscope fractography indicated that failure modes for polished and corroded fatigue specimens were consistent in the high-cycle low loading fatigue regime. Conversely, SEM fractography of low-cycle high-loading fatigue specimens found considerable differences in fracture surfaces between the corroded and polished fatigue specimens.

  18. Criterion for mixed mode fracture in composite bonded joints

    NASA Technical Reports Server (NTRS)

    Mall, S.; Kochhar, N. K.

    1986-01-01

    A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite/epoxy (T300/5208) composite adherends bonded with a toughened epoxy (EC 3445) adhesive. The mode I, mode II and mixed-mode I-II fracture energies of the tested adhesive were found to be equal to each other. Furthermore, the criterion for mixed mode fracture in composite bonded joints was determined.

  19. Fatigue as it Affects Nursing.

    PubMed

    2016-08-01

    : Editor's note: From its first issue in 1900 through to the present day, AJN has unparalleled archives detailing nurses' work and lives over more than a century. These articles not only chronicle nursing's growth as a profession within the context of the events of the day, but they also reveal prevailing societal attitudes about women, health care, and human rights. Today's nursing school curricula rarely include nursing's history, but it's a history worth knowing. To this end, From the AJN Archives highlights articles selected to fit today's topics and times.In this month's article from the January 1935 issue, Lillian M. Gilbreth, a highly respected psychologist and industrial engineer, examines the problem of fatigue in nursing. A nonnurse expert, Gilbreth notes the negative effects of fatigue on skills, a problem "enormously more serious when the product of the work is human comfort and sometimes even human life, as it often is with the work of the nurse." In their article in this issue, "Health Care Worker Fatigue," Lea Anne Gardner and Deborah Dubeck of the Pennsylvania Patient Safety Authority share examples of fatigue-related adverse events and discuss the need for both personal and institutional fatigue risk management strategies.

  20. Competing fatigue mechanisms in Nickel-base superalloy Rene 88DT

    NASA Astrophysics Data System (ADS)

    Chang, Paul N.

    Nickel base superalloys exhibit superior high temperature mechanical properties required for aircraft engine components. It has been known that the processing of these alloys by the powder metallurgy route introduces inclusions inside the material. The presence of such inclusions often leads to competing failure modes in fatigue that is described by a step-wise or two distinct S-N curves involving both the surface and internally-initiated cracks, resulting in large uncertainties of fatigue life. A clear understanding of such behavior is yet to be established. The principal objective of this research is to examine the effect of inclusions on the extent of fatigue failure competition from surface and internal initiators at two different specimen test volumes. Experimental fatigue testing has been performed to explore how the presence of inclusions affects the competing fatigue failure modes. In addition, how the competing failure modes will behave with changes in the specimen size was also studied. Two groups of material each with two different specimen sizes were used in this study. It has been shown that the two crack initiation mechanisms occurred in the small unseeded Rene 88DT specimens tested at 650ºC over the stress range tested. Additionally, the fatigue lives were reduced with increase in specimen volume. All fatigue failures in seeded material occurred due to crack initiations from the seeded inclusions. In the fatigue life of seeded material, two competing and separate S-N curves were found in small test volume, whereas, in the large test volume, the regions were separated by a "step" in S-N curve. It has been found that the largest inclusion size observed in metallographic surfaces was smaller than the size determined from the fatigue failure origin. An analysis method based on extreme value statistics developed by Murakami was used to predict the largest size of inclusion in the test volume. The results of this study clearly show that competition for

  1. Ischemia causes muscle fatigue

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    The purpose of this investigation was to determine whether ischemia, which reduces oxygenation in the extensor carpi radialis (ECR) muscle, causes a reduction in muscle force production. In eight subjects, muscle oxygenation (TO2) of the right ECR was measured noninvasively and continuously using near infrared spectroscopy (NIRS) while muscle twitch force was elicited by transcutaneous electrical stimulation (1 Hz, 0.1 ms). Baseline measurements of blood volume, muscle oxygenation and twitch force were recorded continuously, then a tourniquet on the upper arm was inflated to one of five different pressure levels: 20, 40, 60 mm Hg (randomized order) and diastolic (69 +/- 9.8 mm Hg) and systolic (106 +/- 12.8 mm Hg) blood pressures. Each pressure level was maintained for 3-5 min, and was followed by a recovery period sufficient to allow measurements to return to baseline. For each respective tourniquet pressure level, mean TO2 decreased from resting baseline (100% TO2) to 99 +/- 1.2% (SEM), 96 +/- 1.9%, 93 +/- 2.8%, 90 +/- 2.5%, and 86 +/- 2.7%, and mean twitch force decreased from resting baseline (100% force) to 99 +/- 0.7% (SEM), 96 +/- 2.7%, 93 +/- 3.1%, 88 +/- 3.2%, and 86 +/- 2.6%. Muscle oxygenation and twitch force at 60 mm Hg tourniquet compression and above were significantly lower (P < 0.05) than baseline value. Reduced twitch force was correlated in a dose-dependent manner with reduced muscle oxygenation (r = 0.78, P < 0.001). Although the correlation does not prove causation, the results indicate that ischemia leading to a 7% or greater reduction in muscle oxygenation causes decreased muscle force production in the forearm extensor muscle. Thus, ischemia associated with a modest decline in TO2 causes muscle fatigue.

  2. Defeating feature fatigue.

    PubMed

    Rust, Roland T; Thompson, Debora Viana; Hamilton, Rebecca W

    2006-02-01

    Consider a coffeemaker that offers 12 drink options, a car with more than 700 features on the dashboard, and a mouse pad that's also a clock, calculator, and FM radio. All are examples of "feature bloat", or "featuritis", the result of an almost irresistible temptation to load products with lots of bells and whistles. The problem is that the more features a product boasts, the harder it is to use. Manufacturers that increase a product's capability--the number of useful functions it can perform--at the expense of its usability are exposing their customers to feature fatigue. The authors have conducted three studies to gain a better understanding of how consumers weigh a product's capability relative to its usability. They found that even though consumers know that products with more features are harder to use, they initially choose high-feature models. They also pile on more features when given the chance to customize a product for their needs. Once consumers have actually worked with a product, however, usability starts to matter more to them than capability. For managers in consumer products companies, these findings present a dilemma: Should they maximize initial sales by designing high-feature models, which consumers consistently choose, or should they limit the number of features in order to enhance the lifetime value of their customers? The authors' analytical model guides companies toward a happy middle ground: maximizing the net present value of the typical customer's profit stream. The authors also advise companies to build simpler products, help consumers learn which products suit their needs, develop products that do one thing very well, and design market research in which consumers use actual products or prototypes.

  3. Influences of semiconductor morphology on the mechanical fatigue behavior of flexible organic electronics

    NASA Astrophysics Data System (ADS)

    Lee, Young-Joo; Uk Lee, Yong; Yeon, Han-Wool; Shin, Hae-A.-Seul; Evans, Louise A.; Joo, Young-Chang

    2013-12-01

    The influence of crystalline morphology on the mechanical fatigue of organic semiconductors (OSCs) was investigated using 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as a crystalline OSC and poly(triarylamine) (PTAA) as an amorphous OSC. During cyclic bending, resistances of the OSCs were monitored using the transmission-line method on a metal-semiconductor-metal structure. The resistance of the TIPS-pentacene increased under fatigue damage in tensile-stress mode, but no such degradation was observed in the PTAA. Both OSCs were stable under compressive bending fatigue. The formation of intergranular cracks at the domain boundaries of the TIPS-pentacene was responsible for the degradation of its electrical properties under tensile bending fatigue.

  4. Fatigue of Nitinol: The state-of-the-art and ongoing challenges.

    PubMed

    Mahtabi, M J; Shamsaei, Nima; Mitchell, M R

    2015-10-01

    Nitinol, a nearly equiatomic alloy of nickel and titanium, has been considered for a wide range of applications including medical and dental devices and implants as well as aerospace and automotive components and structures. The realistic loading condition in many of these applications is cyclic; therefore, fatigue is often the main failure mode for such components and structures. The fatigue behavior of Nitinol involves many more complexities compared with traditional metal alloys arising from its uniqueness in material properties such as superelasticity and shape memory effects. In this paper, a review of the present state-of-the-art on the fatigue behavior of superelastic Nitinol is presented. Various aspects of fatigue of Nitinol are discussed and microstructural effects are explained. Effects of material preparation and testing conditions are also reviewed. Finally, several conclusions are made and recommendations for future works are offered.

  5. Local fatigue behavior in tapered areas of large offshore wind turbine blades

    NASA Astrophysics Data System (ADS)

    Aydin Raeis Hosseiny, Seyed; Jakobsen, Johnny

    2016-07-01

    Thickness transitions in load carrying elements lead to improved geometries and efficient material utilization. However, these transitions may introduce localized areas with high stress concentrations and may act as crack initiators that could potentially cause delamination and further catastrophic failure of an entire blade structure. The local strength degradation under an ultimate static loading, subsequent to several years of fatigue, is predicted for an offshore wind turbine blade. Fatigue failure indexes of different damage modes are calculated using a sub-modeling approach. Multi axial stresses are accounted for using a developed failure criterion with residual strengths instead of the virgin strengths. Damage initiation is predicted by including available Wohler curve data of E-Glass fabrics and epoxy matrix into multi-axial fatigue failure criteria. As a result of this study, proper knock-down factors for ply-drop effects in wind turbine blades under multi-axial static and fatigue loadings can be obtained.

  6. Creep-Fatigue Behavior of Alloy 617 at 850 and 950°C, Revision 2

    SciTech Connect

    Carroll, L.; Carroll, M.

    2015-05-01

    Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests including hold times up to 9000 s at maximum tensile strain were conducted at 850 and 950 degrees C. At both temperatures, the fatigue resistance decreased when a hold time was added at peak tensile strain. The magnitude of this effect depended on the specific mechanisms and whether they resulted in a change in fracture mode from transgranular in pure fatigue to intergranular in creep-fatigue for a particular temperature and strain range combination. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep-fatigue resistance at 950 degrees C but did continue to degrade the lifetimes at 850 degrees C.

  7. Influences of semiconductor morphology on the mechanical fatigue behavior of flexible organic electronics

    SciTech Connect

    Lee, Young-Joo; Yeon, Han-Wool; Shin, Hae-A-Seul; Joo, Young-Chang; Uk Lee, Yong; Evans, Louise A.

    2013-12-09

    The influence of crystalline morphology on the mechanical fatigue of organic semiconductors (OSCs) was investigated using 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as a crystalline OSC and poly(triarylamine) (PTAA) as an amorphous OSC. During cyclic bending, resistances of the OSCs were monitored using the transmission-line method on a metal-semiconductor-metal structure. The resistance of the TIPS-pentacene increased under fatigue damage in tensile-stress mode, but no such degradation was observed in the PTAA. Both OSCs were stable under compressive bending fatigue. The formation of intergranular cracks at the domain boundaries of the TIPS-pentacene was responsible for the degradation of its electrical properties under tensile bending fatigue.

  8. Evaluation of fatigue damage in steel structural components by magnetoelastic Barkhausen signal analysis

    SciTech Connect

    Govindaraju, M.R.; Strom, A.; Jiles, D.C.; Biner, S.B.; Chen, Z. )

    1993-05-15

    This paper is concerned with using a magnetic technique for the evaluation of fatigue damage in steel structural components. It is shown that Barkhausen effect measurements can be used to indicate impending failure due to fatigue under certain conditions. The Barkhausen signal amplitude is known to be highly sensitive to changes in density and distribution of dislocations in materials. The sensitivity of Barkhausen signal amplitude to fatigue damage has been studied in the low-cycle fatigue regime using smooth tensile specimens of a medium strength steel. The Barkhausen measurements were taken at depths of penetration of 0.02, 0.07, and 0.2 mm. It was found that changes in magnetic properties are sensitive to microstructural changes taking place at the surface of the material throughout the fatigue life. The changes in the Barkhausen signals have been attributed to distribution of dislocations in stage I and stage II of fatigue life and the formation of a macrocrack in the final stage of fatigue.

  9. Fatigue life of laser cut metals

    NASA Technical Reports Server (NTRS)

    Martin, M. R.

    1986-01-01

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

  10. High Speed Research Program Sonic Fatigue

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  11. Exercise Helps Counter Cancer-Linked Fatigue

    MedlinePlus

    ... and physical activity for the ACS. She said exercise has many benefits, not just helping to ease fatigue. "But because ... fatigue and gain some of the many other benefits of exercise [both during and after treatment]: reduced stress, less ...

  12. Chronic Fatigue Syndrome (CFS): Who's at Risk?

    MedlinePlus

    ... please visit this page: About CDC.gov . Chronic Fatigue Syndrome (CFS) Share Compartir Who's at Risk? More ... explore this possibility Related Links Disability and Chronic Fatigue Syndrome Print page View page in: Español (Spanish) ...

  13. Monitoring fatigue crack growth and opening using antenna sensors

    NASA Astrophysics Data System (ADS)

    Mohammad, I.; Huang, H.

    2010-05-01

    Fatigue cracking is one of the most common failure modes of various load-bearing structures. Even though sensors of many different types have been developed for crack detection, very few can monitor crack growth with a high sensitivity. This paper presents an antenna sensor that is capable of monitoring the growth of fatigue cracks with a sub-millimeter resolution. According to microstrip patch antenna theory, the resonant frequencies of a dual-frequency patch antenna are inversely proportional to the electrical lengths of the corresponding antenna radiation modes. The presence of a crack in the ground plane or the elongation of the antenna patch due to crack opening increases the electric length, thereby causing a shift in its corresponding resonant frequency. As a result, crack propagation and opening can be monitored from the resonant frequency shifts of the patch antenna. The patch antenna's capability of monitoring crack growth was validated using fatigue testing of a compact tension specimen. The specimen preparation, sensor fabrication, and experimental procedure are presented. The experimental results demonstrated that the corresponding resonant frequency of the antenna sensor shifted linearly with crack growth. On average, 1 mm crack growth caused the antenna frequency to shift by 22.1 MHz. The orientation of the crack and the effect of crack closure on the resonant frequencies of the antenna sensor are also discussed.

  14. Fatigue response of notched graphite/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Kress, G. R.; Stinchcomb, W. W.

    1985-01-01

    Tests were performed to determine the damage states in quasi-isotropic graphite/epoxy laminates with center holes caused by cyclic tensile loading. The influence of the stacking sequence on the initiation and interaction of damage modes and the relationship between damage, strength, stiffness, and life of the laminates were also studied. X-ray radiography, moire interferometry, and stiffness change were used to monitor damage. Fatigue damage in both laminates began with matrix cracks around the holes leading to delaminations. In laminates cycled at the same percent of notched tensile strength the stacking sequence influenced the density of the matrix cracks and the modes and distribution of the damage. Ply cracking was also caused by the stacking sequence. The damage states in the two laminates produced stiffness changes of 15 to 20 percent, different rates of change in residual strength, and a factor of two to four difference in fatigue life. It was determined that continued cyclic loading produced matrix cracks which led to fatigue of the laminates.

  15. structured exploratory data analysis (SEDA) for determining mode of inheritance of quantitative traits. II. simulation studies on the effect of ascertaining families through high-valued probands.

    PubMed Central

    Karlin, S; Williams, P T

    1981-01-01

    An understanding of the effect of selecting families through a high-valued proband on the major gene index (MGI), the offspring between parents function (OBP), and the pairwise midparental correlation coefficient (MPCC) is developed. It is shown that the interpretations of these statistics must be carefully modified to adjust for the biases created by the selection criteria. Computer simulations are used to examine sporadic, multifactorial, and major gene models, under moderate (85%) and extreme (95%) proband selection. Additional insights may be acquired into the nature of mode of inheritance by comparing and contrasting selected and unselected of populations. PMID:7211842

  16. structured exploratory data analysis (SEDA) for determining mode of inheritance of quantitative traits. II. simulation studies on the effect of ascertaining families through high-valued probands.

    PubMed

    Karlin, S; Williams, P T

    1981-03-01

    An understanding of the effect of selecting families through a high-valued proband on the major gene index (MGI), the offspring between parents function (OBP), and the pairwise midparental correlation coefficient (MPCC) is developed. It is shown that the interpretations of these statistics must be carefully modified to adjust for the biases created by the selection criteria. Computer simulations are used to examine sporadic, multifactorial, and major gene models, under moderate (85%) and extreme (95%) proband selection. Additional insights may be acquired into the nature of mode of inheritance by comparing and contrasting selected and unselected of populations.

  17. Development of an isothermal titration microcalorimetric system with digital control and dynamic power peltier compensation. II. Characterization and operation mode. Myoglobin adsorption onto polymeric latex particles

    NASA Astrophysics Data System (ADS)

    Velázquez-Campoy, A.; López-Mayorga, O.; Cabrerizo-Vílchez, M. A.

    2000-04-01

    In a previous article a comprehensive description of an isothermal titration microcalorimeter with Peltier compensation was reported. This work deals with the characterization procedure and the operation mode. The transfer function parameters (time constants, calibration constants, and thermal properties of the system components) have been determined using a rigorous physical model for the microcalorimeter. To check the good performance of the instrument, titration experiments of cytidine and adenosine protonation have been carried out. Finally, as an example of the instrument applicability, differential heat measurements of myoglobin adsorption onto polymeric (polystyrene) latex particles are presented.

  18. Peridynamic model for fatigue cracking.

    SciTech Connect

    Silling, Stewart Andrew; Abe Askari

    2014-10-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  20. Fatigue and Comorbidities in Multiple Sclerosis

    PubMed Central

    Fiest, Kirsten M.; Fisk, John D.; Patten, Scott B.; Tremlett, Helen; Wolfson, Christina; Warren, Sharon; McKay, Kyla A.; Berrigan, Lindsay I.

    2016-01-01

    Abstract Background: Fatigue is commonly reported by people with multiple sclerosis (MS). Comorbidity is also common in MS, but its association with the presence of fatigue or fatigue changes over time is poorly understood. Methods: Nine hundred forty-nine people with definite MS were recruited from four Canadian centers. The Fatigue Impact Scale for Daily Use and a validated comorbidity questionnaire were completed at three visits over 2 years. Participants were classified into groups with no fatigue versus any fatigue. Logistic regression was used to determine the relationship between fatigue and each comorbidity at baseline, year 1, year 2, and overall. Results: The incidence of fatigue during the study was 38.8%. The prevalence of fatigue was greater in those who were older (P = .0004), had a longer time since symptom onset (P = .005), and had greater disability (P < .0001). After adjustment, depression (odds ratio [OR], 2.58; 95% confidence interval [CI], 2.03–3.27), irritable bowel syndrome (OR, 1.71; 95% CI, 1.18–2.48), migraine (OR, 1.69; 95% CI, 1.27–2.27), and anxiety (OR, 1.57; 95% CI, 1.15–2.16) were independently associated with fatigue that persisted during the study. There was also an individual-level effect of depression on worsening fatigue (OR, 1.49; 95% CI, 1.08–2.07). Conclusions: Comorbidity is associated with fatigue in MS. Depression is associated with fatigue and with increased risk of worsening fatigue over 2 years. However, other comorbid conditions commonly associated with MS are also associated with persistent fatigue, even after accounting for depression. Further investigation is required to understand the mechanisms by which comorbidities influence fatigue. PMID:27134583

  1. Fatigue Lives Of Laser-Cut Metals

    NASA Technical Reports Server (NTRS)

    Martin, Michael R.

    1988-01-01

    Fatigue lives made to approach those attainable by traditional grinding methods. Fatigue-test specimens prepared from four metallic alloys, and material removed from specimens by manual grinding, by Nd:glass laser, and by Nd:YAG laser. Results of fatigue tests of all specimens indicated reduction of fatigue strengths of laser-fired specimens. Laser machining holds promise for improved balancing of components of gas turbines.

  2. Effect of Load History on Fatigue Life.

    DTIC Science & Technology

    1980-06-01

    A number of different loading histories will be investigated to determine their effects on constant amplitude fatigue properties of the selected...previous test results, and at each of the two R ratios. The effect of overloads on constant ampli- tude fatigue life and damage will be investigated ...be investigated . 5.1 FATIGUE TEST RESULTS Constant amplitude fatigue tests were conducted at four R ratios (+0.5, 0.0, -0.5, -1.0) using the

  3. Study of the Neurophysiology of Central Fatigue

    DTIC Science & Technology

    2014-11-05

    objective cognitive fatigue using event related potentials (ERPs). 2) To determine the neurophysiologic mechanisms underlying objective cognitive fatigue ...Study of the Neurophysiology of Central Fatigue The views, opinions and/or findings contained in this report are those of the author(s) and should not...AGENCY NAME(S) AND ADDRESS (ES) U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 cognitive, fatigue , fatigability

  4. Porous Ti6Al4V alloys with enhanced normalized fatigue strength for biomedical applications.

    PubMed

    Li, Fuping; Li, Jinshan; Kou, Hongchao; Zhou, Lian

    2016-03-01

    In this paper, porous Ti6Al4V alloys for biomedical applications were fabricated by diffusion bonding of alloy meshes. The compression-compression fatigue behavior was studied. It results that porous Ti6Al4V alloys show enhanced normalized fatigue strength which is in the range of 0.5-0.55 at 10(6)cycles. The porosity has some effect on the absolute S-N curves but minor effect on the normalized S-N curves. The relationship between strain per cycle and number of cycles shows three distinct stages and the value of strain per cycle is constant in stage II. The reasons for the higher normalized fatigue strength of porous Ti6Al4V alloys are discussed based on the fatigue crack initiation and propagation.

  5. Creep-fatigue of High Temperature Materials for VHTR: Effect of Cyclic Loading and Environment

    SciTech Connect

    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.

  6. Prediction of Petermann I and II Spot Sizes for Single-mode Dispersion-shifted and Dispersion-flattened Fibers by a Simple Technique

    NASA Astrophysics Data System (ADS)

    Kamila, Kiranmay; Panda, Anup Kumar; Gangopadhyay, Sankar

    2013-09-01

    Employing the series expression for the fundamental modal field of dispersion-shifted trapezoidal and dispersion-flattened graded and step W fibers, we present simple but accurate analytical expressions for Petermann I and II spot sizes of such kind of fibers. Choosing some typical dispersion-shifted trapezoidal and dispersion-flattened graded and step W fibers as examples, we show that our estimations match excellently with the exact numerical results. The evaluation of the concerned propagation parameters by our formalism needs very little computations. This accurate but simple formalism will benefit the system engineers working in the field of all optical technology.

  7. Time and temperature dependence on flexural fatigue behavior of unidirectional CFRP laminates using pitch-based carbon fibers

    SciTech Connect

    Miyano, Yasushi; Daichou, Noboru; Nakada, Masayuki; Mohri, Michihiro

    1996-12-31

    The flexural fatigue behavior of two kinds of unidirectional pitch-based CFRP laminates, which have different types of matrix resin, were evaluated at several levels of frequency and temperature. The fatigue behavior of both CFRPs was found to be remarkably dependent on time and temperature. The time-temperature superposition principle for the viscoelastic behavior of the matrix resin holds for the fatigue strength as well as the static strength of the CFRPs. The master curves of fatigue strength for the CFRPs can be divided into three distinct groups of curves, each corresponding to a different mode of fracture. The time and temperature dependence of the fatigue behavior of the CFRP laminates is not only controlled by the viscoelastic behavior of the matrix resin, even though the static behavior is dominated by the viscoelastic behavior of matrix resin.

  8. Fatigue-Resistant Photochromic Plastics

    NASA Astrophysics Data System (ADS)

    Chu, Nori Y. C.

    1989-03-01

    The optical switching properties of a photochromic spirooxazine compound in retrofit polyester film and in poly (vinyl butyral) have been measured. The light fatigue resistance of these two optical switching elements were tested by an accelerated method. The length of photochromic activity of the optical switching elements can be improved by various organonickel and hindered amine light stabilizers. The effectiveness and optimal concentration for each light stabilizer in these host materials has been determined. These two types of light stabilizers act synergistically in improving the light fatigue resistance of the optical switching elements significantly.

  9. The problem of alarm fatigue.

    PubMed

    Tanner, Tanya

    2013-01-01

    Up to 99 percent of alarms sounding on hospital units are false alarms signaling no real danger to patients. These false alarms can lead to alarm fatigue and alarm burden, and may divert health care providers' attention away from significant alarms heralding actual or impending harm. As the health care environment continues to become more dependent upon technological monitoring devices used for patient care, nurses must become aware of the possibility and consequences of alarm fatigue and ways to prevent it from negatively affecting their practice, as well as the possible consequences for patient care.

  10. Capturing Uncertainty in Fatigue Life Data

    DTIC Science & Technology

    2014-09-18

    Several parameters can be investigated in fatigue testing . Factors such as loading, specimen geometry, material behavior, and thermal or chemical...of time they have spent with me discussing material sciences, fatigue testing , and their modeling efforts. Finally, a considerable amount of thanks...pricing structures for insurance policies. In fatigue , engineers can characterize metal alloys, quantify material responses to testing conditions, and

  11. 10 CFR 26.211 - Fatigue assessments.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 1 2014-01-01 2014-01-01 false Fatigue assessments. 26.211 Section 26.211 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Managing Fatigue § 26.211 Fatigue assessments. (a) Licensees... addition to any other test or determination of fitness that may be required under §§ 26.31(c) and 26.77,...

  12. 10 CFR 26.211 - Fatigue assessments.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 1 2013-01-01 2013-01-01 false Fatigue assessments. 26.211 Section 26.211 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Managing Fatigue § 26.211 Fatigue assessments. (a) Licensees... addition to any other test or determination of fitness that may be required under §§ 26.31(c) and 26.77,...

  13. 10 CFR 26.211 - Fatigue assessments.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 1 2012-01-01 2012-01-01 false Fatigue assessments. 26.211 Section 26.211 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Managing Fatigue § 26.211 Fatigue assessments. (a) Licensees... addition to any other test or determination of fitness that may be required under §§ 26.31(c) and 26.77,...

  14. 10 CFR 26.211 - Fatigue assessments.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 1 2011-01-01 2011-01-01 false Fatigue assessments. 26.211 Section 26.211 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Managing Fatigue § 26.211 Fatigue assessments. (a) Licensees... addition to any other test or determination of fitness that may be required under §§ 26.31(c) and 26.77,...

  15. 10 CFR 26.211 - Fatigue assessments.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 1 2010-01-01 2010-01-01 false Fatigue assessments. 26.211 Section 26.211 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Managing Fatigue § 26.211 Fatigue assessments. (a) Licensees... addition to any other test or determination of fitness that may be required under §§ 26.31(c) and 26.77,...

  16. 14 CFR 23.627 - Fatigue strength.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Fatigue strength. 23.627 Section 23.627... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service....

  17. 14 CFR 23.627 - Fatigue strength.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Fatigue strength. 23.627 Section 23.627... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service....

  18. 14 CFR 23.627 - Fatigue strength.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Fatigue strength. 23.627 Section 23.627... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service....

  19. 14 CFR 23.627 - Fatigue strength.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Fatigue strength. 23.627 Section 23.627... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service....

  20. Atomic simulation of cracks under mixed mode loading

    NASA Technical Reports Server (NTRS)

    Mullins, M.

    1984-01-01

    A discrete atomic model of a crack tip in iron under mixed mode loads is examined. The results indicate that the behavior of the crack at the atomic scale as a function of the ratio of mode I to mode II component of load is quite complex. In general, crack tip plasticity appears to increase as the mode II component of load increases.

  1. Mixed-Mode-Bending Delamination Apparatus

    NASA Technical Reports Server (NTRS)

    Crews, John H., Jr.; Reeder, James R.

    1991-01-01

    Mixed-mode-bending delamination apparatus generates two types of delamination stress simultaneously in specimen from single externally applied point load. In technique, indivial mode I and mode II contributions to delamination in specimen analyzed by use of simple beam-theory equations, eliminating need for time-consuming, difficult numerical analysis. Allows wider range of mode I/mode II ratios than possible with many other methods. Mixed-mode delamination testing of interest in all fields utilizing composite materials, used mostly in aerospace field, but also used in automobiles, lightweight armored military vehicles, boats, and sporting equipment. Useful in general lumber, plywood, and adhesive industries, as well.

  2. Fracture and fatigue of discontinuously reinforced copper/tungsten composites

    NASA Technical Reports Server (NTRS)

    Harris, B.; Ramani, S. V.

    1975-01-01

    The strength, toughness and resistance to cyclic crack propagation of composites consisting of copper reinforced with short tungsten wires of various lengths have been studied and the results compared with the behavior of continuously reinforced composites manufactured by the same method, i.e., by vacuum hot-pressing. It has been found that whereas the resistance to fatigue crack growth of continuously reinforced composites is very similar to that of continuous Al/stainless steel composites reported elsewhere, the addition of short fibers completely changes the mode of fracture, and no direct comparisons are possible. In effect, short fibers inhibit single crack growth by causing plastic flow to be distributed rather than localized, and although these composites are much less strong than continuous fiber composites, they nevertheless have much greater fatigue resistance.

  3. Fatigue of pseudoelastic NiTi within the stress-induced transformation regime: a modified Coffin-Manson approach

    NASA Astrophysics Data System (ADS)

    Maletta, C.; Sgambitterra, E.; Furgiuele, F.; Casati, R.; Tuissi, A.

    2012-11-01

    Strain controlled fatigue tests of a pseudoelastic nickel-titanium (NiTi) shape memory alloy (SMA) have been carried out in this investigation. In particular, flat dog-bone shaped specimens, obtained from commercial NiTi sheets, have been analyzed, under pull-pull loading conditions, in two subsequent steps: (i) material stabilization and (ii) fatigue life estimation. The first step was carried out to obtain a stable pseudoelastic response of the SMA, i.e. with no residual deformations upon unloading, and it can be regarded as a preliminary processing condition of the alloy. Results on functional fatigue, i.e. in terms of stabilized pseudoelastic response, and on structural fatigue, in terms of cycles to failure, are reported and discussed. Furthermore, a modified Coffin-Manson approach for fatigue life estimation of SMAs is proposed, which takes into account the strain mechanisms involved during repeated stress-induced martensitic transformations.

  4. Fatigue biomarker index: an objective salivary measure of fatigue level.

    PubMed

    Michael, Darren J; Daugherty, Sheena; Santos, Adrienne; Ruby, Brent C; Kalns, John E

    2012-03-01

    Fatigue changed the composition of the small-molecular weight (sMW) proteome of saliva during a 10h session of moderate (70% of maximum ventilatory threshold) physical exertion. Saliva samples were collected from nine recreationally trained cyclists participating in a cross-over study designed to simulate prolonged manual labor, a military operation or wildfire-suppression work. During each hour of the study, participants performed an exercise program that included upper and lower body exercises separated by short periods of recovery. Over the course of the study, fatigue level increased as suggested by a significant increase in the participants' relative perceived exertion. The composition of the sMW proteome was investigated using reversed-phase liquid chromatography with mass-spectrometric detection. Isotopes of acetic anhydride were used for mass-specific labeling of samples and subsequent identification of ions with significant changes in intensity. Cluster analysis was used to identify a pair of peptides with concentrations that changed in opposite directions with fatigue level, i.e. concentration of one peptide increased while concentration of the other decreased. The sequences of the two peptides were determined by high-resolution mass spectrometry. The ratio of the ion intensities of these two peptides, referred to as the fatigue biomarker index, was calculated for subjects throughout the study. The FBI values from the start of the study likely arose from a different distribution than the FBI values measured at the end of the study (Mann-Whitney test, P<.05). While this study is restricted to a small population of recreationally trained cyclists performing exercise under controlled conditions, it holds promise for the development of an objective salivary measurement of fatigue that is applicable to a much broader population performing in uncontrolled environments.

  5. Modal analysis for characterization of fatigue cracks in thin metal plates

    NASA Technical Reports Server (NTRS)

    Wincheski, B.; Namkung, M.

    1991-01-01

    Detailed experimental investigation and numerical analysis were performed on the characterization of fatigue cracks in thin aluminum alloys by a low frequency resonant modal analysis technique. The resonance frequency of plate modes is altered by the presence of fatigue cracks. This frequency shift was analyzed using a finite element approach and the results were compared to experimental data. Acoustic sensors were used to detect the fatigue cracks which were stimulated by standing waves in 0.1 cm aluminum alloy plates. The response of several different sensors to the crack noise was studied, as was the response at higher order modes. It was found that critical crack information can be obtained from the amplitude and phase of the emitted signal with respect to that of the external driving force.

  6. High frequency guided ultrasonic waves for hidden fatigue crack growth monitoring in multi-layer model aerospace structures

    NASA Astrophysics Data System (ADS)

    Chan, Henry; Masserey, Bernard; Fromme, Paul

    2015-02-01

    Especially for ageing aircraft the development of fatigue cracks at fastener holes due to stress concentration and varying loading conditions constitutes a significant maintenance problem. High frequency guided waves offer a potential compromise between the capabilities of local bulk ultrasonic measurements with proven defect detection sensitivity and the large area coverage of lower frequency guided ultrasonic waves. High frequency guided waves have energy distributed through all layers of the specimen thickness, allowing in principle hidden (2nd layer) fatigue damage monitoring. For the integration into structural health monitoring systems the sensitivity for the detection of hidden fatigue damage in inaccessible locations of the multi-layered components from a stand-off distance has to be ascertained. The multi-layered model structure investigated consists of two aluminium plate-strips with an epoxy sealant layer. During cyclic loading fatigue crack growth at a fastener hole was monitored. Specific guided wave modes (combination of fundamental A0 and S0 Lamb modes) were selectively excited above the cut-off frequencies of higher modes using a standard ultrasonic wedge transducer. Non-contact laser measurements close to the defect were performed to qualify the influence of a fatigue crack in one aluminium layer on the guided wave scattering. Fatigue crack growth monitoring using laser interferometry showed good sensitivity and repeatability for the reliable detection of small, quarter-elliptical cracks. Standard ultrasonic pulse-echo equipment was employed to monitor hidden fatigue damage from a stand-off distance without access to the damaged specimen layer. Sufficient sensitivity for the detection of fatigue cracks located in the inaccessible aluminium layer was verified, allowing in principle practical in situ ultrasonic monitoring of fatigue crack growth.

  7. Microstructural aspects of fatigue in Ni-base superalloys.

    PubMed

    Antolovich, Stephen D

    2015-03-28

    Nickel-base superalloys are primarily used as components in jet engines and land-based turbines. While compositionally complex, they are microstructurally simple, consisting of small (50-1000 nm diameter), ordered, coherent Ni(3)(Al,Ti)-type L1(2) or Ni(3)Nb-type DO(22) precipitates (called γ(') and γ(''), respectively) embedded in an FCC substitutional solid solution consisting primarily of Ni and other elements which confer desired properties depending upon the application. The grain size may vary from as small as 2 μm for powder metallurgy alloys used in discs to single crystals the actual size of the component for turbine blades. The fatigue behaviour depends upon the microstructure, deformation mode, environment and cycle time. In many cases, it can be controlled or modified through small changes in composition which may dramatically change the mechanism of damage accumulation and the fatigue life. In this paper, the fundamental microstructural, compositional, environmental and deformation mode factors which affect fatigue behaviour are critically reviewed. Connections are made across a range of studies to provide more insight. Modern approaches are pointed out in which the wealth of available microstructural, deformation and damage information is used for computerized life prediction. The paper ends with a discussion of the very important and highly practical subject of thermo-mechanical fatigue (TMF). It is shown that physics-based modelling leads to significantly improved life prediction. Suggestions are made for moving forward on the critical subject of TMF life prediction in notched components.

  8. Fatigue Life Methodology for Tapered Composite Flexbeam Laminates

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.; OBrien, T. Kevin; Rousseau, Carl Q.

    1997-01-01

    The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delamination fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to non-linear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axial-tension and transverse cyclic bending. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen. Continued cycling resulted in multiple delaminations. A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed. The global responses of the model and test specimens agreed very well in terms of the transverse displacement. The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode 2, whereas delamination growth toward the thin region was almost completely mode 1. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.

  9. Fatigue Life Methodology for Tapered Composite Flexbeam Laminates

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.; O''Brien, T. Kevin; Rousseau, Carl Q.

    1997-01-01

    The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delamination fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to nonlinear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axial-tension and transverse cyclic bending loads. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen. Continued cycling resulted in multiple delaminations. A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed. The global responses of the model and test specimens agreed very well in terms of the transverse flexbeam tip-displacement and flapping angle. The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode 2, whereas delamination growth toward the thin region was almost completely mode 1. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.

  10. Interaction between impact damage and fatigue in fibre reinforced plastics

    NASA Astrophysics Data System (ADS)

    Beheshty, M. H.

    This study has been designed to investigate the interaction between impact damage and fatigue, which is necessarily a complex one and of current interest to the aerospace industry, and to predict the fatigue response for virgin and impact-damaged materials by using a constant-life model. In order to achieve these goals, measurements have been made of the residual tensile and compressive strengths after low-velocity impacts of 1, 2, 3 and 5 Joules of two modem carbon-fibre composites, viz., HTA/982A and HTA/913, and a glass-fibre laminate, E-Glass/913, all having the common lay-up [(45,02)2]s. The impact damage was assessed by transient thermography, ultrasonic C-scan and optical microscopy. The modes of failure under low-velocity impacts of 1-3J were found to be matrix cracking and mainly delamination. Only a 5J impact energy event caused some fibre fractures in CFRP laminates. Measurement of post-impact mechanical properties has shown that impact damage in the range 1-5J had little effect on the residual tensile strength although the compressive strength was markedly reduced. Replicate stress/life fatigue data were obtained at different stress ratios, R, for sound and impact-damaged materials. Results show that impact energies in the range 1-3J had no effect on the tensile fatigue behaviour at R = +0.l. At R = -1.5 and +10, on the other hand, the stress/life curves are markedly affected. And as the compression component of stress increases the slope of the S/N curve decreases, which indicates less sensitivity to fatigue. The fatigue tests results have been analysed by using a constant-life model previously developed at Bath. A new relationship between constant-life model parameters and material properties has been found. The model has been modified to predict the fatigue response of fibre composite materials in the virgin condition and after damage by low-velocity impact by using only the tensile and compressive strengths of composite in question. Results show

  11. Fatigue Fighters in Sjogren's Syndrome

    MedlinePlus

    ... to help you with tasks. Ask friends and family members to be prepared to do one or two chores for you on your fatigue days. Give them specific instructions in advance and be reasonable with your expectations. Get at least eight hours of sleep every ...

  12. Muscular fatigue: considerations for dance.

    PubMed

    Wyon, Matthew A; Koutedakis, Yiannis

    2013-01-01

    Muscular fatigue can be defined as the failure to maintain an expected power output. It is a multifaceted phenomenon that incorporates metabolic, neural and neuromuscular components, among others. Metabolic causes of fatigue are associated with the ability to maintain energy supply during exercise, the speed at which homeostasis is achieved post-exercise, and the effects of high intensity exercise by-products on the peripheral neuromuscular system. Research has indicated that the central nervous system plays a protective role in preventing catastrophic muscle damage by reducing the intensity and frequency of propagation founded on biofeedback from the muscle cells. The duration and particularly the type of physical activity play a role in the development of muscle fatigue, with impact or weightbearing exercises, such as dance, producing increased symptoms compared to non-impact or non-weightbearing equivalents. The effects of prolonged exercise and the associated increased levels of muscle fatigue that may lead to compromises in neuromuscular propagation need to be considered in dance.

  13. TV fatigue crack monitoring system

    NASA Technical Reports Server (NTRS)

    Exton, R. J. (Inventor)

    1977-01-01

    An apparatus is disclosed for monitoring the development and growth of fatigue cracks in a test specimen subjected to a pulsating tensile load. A plurality of television cameras photograph a test specimen which is illuminated at the point of maximum tensile stress. The television cameras have a modified vidicon tube which has an increased persistence time thereby eliminating flicker in the displayed images.

  14. "Holocaust Fatigue" in Teaching Today

    ERIC Educational Resources Information Center

    Schweber, Simone

    2006-01-01

    In this article, the author discusses the problems faced by educators in teaching about the Holocaust. She relates that because the Holocaust is now frequently taught in middle schools and in upper elementary grades, by the time it is taught in high schools, students will experience "Holocaust fatigue." As such, teachers face the challenge of…

  15. FATIGUE OF BIOMATERIALS: HARD TISSUES

    PubMed Central

    Arola, D.; Bajaj, D.; Ivancik, J.; Majd, H.; Zhang, D.

    2009-01-01

    The fatigue and fracture behavior of hard tissues are topics of considerable interest today. This special group of organic materials comprises the highly mineralized and load-bearing tissues of the human body, and includes bone, cementum, dentin and enamel. An understanding of their fatigue behavior and the influence of loading conditions and physiological factors (e.g. aging and disease) on the mechanisms of degradation are essential for achieving lifelong health. But there is much more to this topic than the immediate medical issues. There are many challenges to characterizing the fatigue behavior of hard tissues, much of which is attributed to size constraints and the complexity of their microstructure. The relative importance of the constituents on the type and distribution of defects, rate of coalescence, and their contributions to the initiation and growth of cracks, are formidable topics that have not reached maturity. Hard tissues also provide a medium for learning and a source of inspiration in the design of new microstructures for engineering materials. This article briefly reviews fatigue of hard tissues with shared emphasis on current understanding, the challenges and the unanswered questions. PMID:20563239

  16. Ultrasonic absortion in fatigued materials

    NASA Astrophysics Data System (ADS)

    Dugan, S.; Arnold, W.

    2013-01-01

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

  17. Biomechanical evaluation of an integrated fixation cage during fatigue loading: a human cadaver study.

    PubMed

    Palepu, Vivek; Peck, Jonathan H; Simon, David D; Helgeson, Melvin D; Nagaraja, Srinidhi

    2017-04-01

    OBJECTIVE Lumbar cages with integrated fixation screws offer a low-profile alternative to a standard cage with anterior supplemental fixation. However, the mechanical stability of integrated fixation cages (IFCs) compared with a cage with anterior plate fixation under fatigue loading has not been investigated. The purpose of this study was to compare the biomechanical stability of a screw-based IFC with a standard cage coupled with that of an anterior plate under fatigue loading. METHODS Eighteen functional spinal units were implanted with either a 4-screw IFC or an anterior plate and cage (AP+C) without integrated fixation. Flexibility testing was conducted in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) on intact spines, immediately after device implantation, and post-fatigue up to 20,000 cycles of FE loading. Stability parameters such as range of motion (ROM) and lax zone (LZ) for each loading mode were compared between the 2 constructs at multiple stages of testing. In addition, construct loosening was quantified by subtracting post-instrumentation ROM from post-fatigue ROM. RESULTS IFC and AP+C configurations exhibited similar stability (ROM and LZ) at every stage of testing in FE (p ≥ 0.33) and LB (p ≥ 0.23) motions. In AR, however, IFCs had decreased ROM compared with AP+C constructs at pre-fatigue (p = 0.07) and at all post-fatigue time points (p ≤ 0.05). LZ followed a trend similar to that of ROM in AR. ROM increased toward intact motion during fatigue cycling for AP+C and IFC implants. IFC specimens remained significantly (p < 0.01) more rigid than specimens in the intact condition during fatigue for each loading mode, whereas AP+C construct motion did not differ significantly (p ≥ 0.37) in FE and LB and was significantly greater (p < 0.01) in AR motion compared with intact specimens after fatigue. Weak to moderate correlations (R(2) ≤ 56%) were observed between T-scores and construct loosening, with lower T

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

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

  20. Effect of fabric orientation on the monotonic and fatigue behavior of a Nicalon{trademark}/alumina composite

    SciTech Connect

    Miriyala, N.; Liaw, P.K.; McHargue, C.J.

    1996-12-31

    Monotonic and cyclic fatigue tests were performed on a Nicalon{trademark} fiber reinforced alumina composite fabricated by the direct metal oxidation (DIMOX{trademark}) process, using four-point bend specimens at ambient temperature. It was observed that both monotonic flexural strength and fatigue threshold of the composite were higher when the load was applied parallel to the fabric plane, compared to loading normal to the fabric plane. The modulus reduction during the fatigue tests was also monitored. Fracture surfaces were examined to gain an insight into the composite failure modes.