DOE Office of Scientific and Technical Information (OSTI.GOV)

Mandell, John F.; Ashwill, Thomas D.; Wilson, Timothy J.

This report presents an analysis of trends in fatigue results from the Montana State University program on the fatigue of composite materials for wind turbine blades for the period 2005-2009. Test data can be found in the SNL/MSU/DOE Fatigue of Composite Materials Database which is updated annually. This is the fifth report in this series, which summarizes progress of the overall program since its inception in 1989. The primary thrust of this program has been research and testing of a broad range of structural laminate materials of interest to blade structures. The report is focused on current types of infusedmore » and prepreg blade materials, either processed in-house or by industry partners. Trends in static and fatigue performance are analyzed for a range of materials, geometries and loading conditions. Materials include: sixteen resins of three general types, five epoxy based paste adhesives, fifteen reinforcing fabrics including three fiber types, three prepregs, many laminate lay-ups and process variations. Significant differences in static and fatigue performance and delamination resistance are quantified for particular materials and process conditions. When blades do fail, the likely cause is fatigue in the structural detail areas or at major flaws. The program is focused strongly on these issues in addition to standard laminates. Structural detail tests allow evaluation of various blade materials options in the context of more realistic representations of blade structure than do the standard test methods. Types of structural details addressed in this report include ply drops used in thickness tapering, and adhesive joints, each tested over a range of fatigue loading conditions. Ply drop studies were in two areas: (1) a combined experimental and finite element study of basic ply drop delamination parameters for glass and carbon prepreg laminates, and (2) the development of a complex structured resin-infused coupon including ply drops, for comparison studies of various resins, fabrics and pry drop thicknesses. Adhesive joint tests using typical blade adhesives included both generic testing of materials parameters using a notched-lap-shear test geometry developed in this study, and also a series of simulated blade web joint geometries fabricated by an industry partner.« less

Impact of a 10-Week Individualized Exercise Program on Physical Function and Fatigue of People with Multiple Sclerosis

PubMed Central

Elgelid, Staffan; Bolger, Shannon; Parsons, Caroline; Quashnoc, Rachel; Raymor, Johanna

2011-01-01

Research has found that people with multiple sclerosis (MS) who engage in exercise programs experience improvements in physical and psychological health, resulting in enhanced quality of life. These studies have involved structured exercise protocols, but few have examined the effects of an individualized exercise program allowing for peer socialization. The purpose of this study was to investigate the effects of a 10-week individualized exercise program offering opportunities to socialize with peers on fatigue and physical functioning in people with MS. Thirteen individuals with a physician diagnosis of MS were enrolled in a 10-week exercise program at Nazareth College in Rochester, New York. Eleven participants (9 female, 2 male; mean ± SD age, 55.0 ± 7.06 years) completed the study. The following qualitative and quantitative measures were used for evaluation before and after the exercise program: Multiple Sclerosis Quality of Life–54 (MSQOL-54), Activities-specific Balance Confidence (ABC) scale, Modified Fatigue Impact Scale (MFIS), Timed Up and Go (TUG) test, Timed 10-Meter Walk (T10MW) test, functional reach test, and single-leg stance (SLS) test. Statistically significant differences were found for the TUG (P = .005), T10MW (P = .014), and MFIS physical functioning subscore (P = .039). The results showed significant increases in gait speed and mobility as well as decreased impact of fatigue on physical functioning after the 10-week exercise program. PMID:24453715

Corrosion fatigue of high strength fastener materials in seawater. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tipton, D.G.

1983-12-01

Environmental effects can significantly reduce the fatigue life of metals. As such, corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L40 high strength steel blade-to-hub attachment bolt at the MOD-0A 200 kW wind turbine generator in Oahu, Hawaii prompted the current test program. Tests were undertaken to confirm the dramatic reduction of fatigue strength of AISI 41L40 in marine environments and to obtain similar corrosion fatigue data for candidate replacement materials. AISI 41L40, AISI 4140, PH 13-8Mo stainless steel, alloy 718 and alloy MP-35Nmore » were tested in axial fatigue at a frequency of 20 Hz in dry air and natural seawater. The fatigue data were fitted by regression equations to allow determination of fatigue strength for a given number of cycles to failure.« less

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.

Computer programs to characterize alloys and predict cyclic life using the total strain version of strainrange partitioning: Tutorial and users manual, version 1.0

NASA Technical Reports Server (NTRS)

Saltsman, James F.

1992-01-01

This manual presents computer programs for characterizing and predicting fatigue and creep-fatigue resistance of metallic materials in the high-temperature, long-life regime for isothermal and nonisothermal fatigue. The programs use the total strain version of Strainrange Partitioning (TS-SRP). An extensive database has also been developed in a parallel effort. This database is probably the largest source of high-temperature, creep-fatigue test data available in the public domain and can be used with other life prediction methods as well. This users manual, software, and database are all in the public domain and are available through COSMIC (382 East Broad Street, Athens, GA 30602; (404) 542-3265, FAX (404) 542-4807). Two disks accompany this manual. The first disk contains the source code, executable files, and sample output from these programs. The second disk contains the creep-fatigue data in a format compatible with these programs.

Improved cognitive functioning in obese adolescents after a 30-week inpatient weight loss program.

PubMed

Vantieghem, Stijn; Bautmans, Ivan; Guchtenaere, Ann De; Tanghe, Ann; Provyn, Steven

2018-06-15

Studies linked obesity with a large number of medical conditions including decreased cognitive functioning. The relation between BMI and cognition was proven in adults, but in adolescents the results are conflicting. Further, limited data are available on the impact of weight loss on cognition. This study analyzed the impact of a 30-week lasting weight loss program on cognition and determined the impact of changes in body composition and self-perceived fatigue on changes in cognition. Sixty-two obese adolescents were evaluated at baseline and after 30 weeks. Stroop test (ST; selective attention), Continuous Performance Test (CPT; sustained attention) and Ray Auditory verbal learning test (RAVLT; short-term memory) were assessed. Additionally, body composition parameters and fatigue (MFI-20) were evaluated. Improved reaction times were found for ST and CPT after the intervention, but were independent for reductions in BMI, fat mass, fat%, and fatigue. Short memory also improved with decreased fatigue as an influencing parameter. Accuracy of ST and CPT showed no significant changes. A 30-week lasting inpatient weight loss program improved selective attention, sustained attention, and short-term memory. Changes in body composition did not explain the improvements in cognitive functioning. Decreased fatigue resulted in improved aspects of cognition.

FLAPS (Fatigue Life Analysis Programs): Computer Programs to Predict Cyclic Life Using the Total Strain Version of Strainrange Partitioning and Other Life Prediction Methods. Users' Manual and Example Problems, Version 1.0

NASA Technical Reports Server (NTRS)

Arya, Vinod K.; Halford, Gary R. (Technical Monitor)

2003-01-01

This manual presents computer programs FLAPS for characterizing and predicting fatigue and creep-fatigue resistance of metallic materials in the high-temperature, long-life regime for isothermal and nonisothermal fatigue. The programs use the Total Strain version of Strainrange Partitioning (TS-SRP), and several other life prediction methods described in this manual. The user should be thoroughly familiar with the TS-SRP and these life prediction methods before attempting to use any of these programs. Improper understanding can lead to incorrect use of the method and erroneous life predictions. An extensive database has also been developed in a parallel effort. The database is probably the largest source of high-temperature, creep-fatigue test data available in the public domain and can be used with other life-prediction methods as well. This users' manual, software, and database are all in the public domain and can be obtained by contacting the author. The Compact Disk (CD) accompanying this manual contains an executable file for the FLAPS program, two datasets required for the example problems in the manual, and the creep-fatigue data in a format compatible with these programs.

Time-dependent reliability analysis of ceramic engine components

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.

1993-01-01

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing either the power or Paris law relations. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Two example problems demonstrating proof testing and fatigue parameter estimation are given.

Lifetime Reliability Evaluation of Structural Ceramic Parts with the CARES/LIFE Computer Program

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.; Powers, Lynn M.; Janosik, Lesley A.; Gyekenyesi, John P.

1993-01-01

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing the power law, Paris law, or Walker equation. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), Weibull's normal stress averaging method (NSA), or Batdorf's theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Two example problems demonstrating cyclic fatigue parameter estimation and component reliability analysis with proof testing are included.

Experimental and theoretical investigation of fatigue life in reusable rocket thrust chambers

NASA Technical Reports Server (NTRS)

Hannum, N. P.; Kasper, H. J.; Pavli, A. J.

1976-01-01

During a test program to investigate low-cycle thermal fatigue, 13 rocket combustion chambers were fabricated and cyclically test fired to failure. Six oxygen-free, high-conductivity (OFHC) copper and seven Amzirc chambers were tested. The failures in the OFHC copper chambers were not typical fatigue failures but are described as creep rupture enhanced by ratcheting. The coolant channels bulged toward the chamber centerline, resulting in progressive thinning of the wall during each cycle. The failures in the Amzirc alloy chambers were caused by low-cycle thermal fatigue. The zirconium in this alloy was not evenly distributed in the chamber materials. The life that was achieved was nominally the same as would have been predicted from OFHC copper isothermal test data.

Reliability aspects of a composite bolted scarf joint. [in wing skin splice

NASA Technical Reports Server (NTRS)

Reed, D. L.; Eisenmann, J. R.

1975-01-01

The design, fabrication, static test, and fatigue test of both tension and compression graphite-epoxy candidates for a wing splice representative of a next-generation transport aircraft was the objective of the reported research program. A single-scarf bolted joint was selected as the design concept. Test specimens were designed and fabricated to represent an upper-surface and a lower-surface panel containing the splice. The load spectrum was a flight-by-flight random-load history including ground-air-ground loads. The results of the fatigue testing indicate that, for this type of joint, the inherent fatigue resistance of the laminate is reflected in the joint behavior and, consequently, the rate of damage accumulation is very slow under realistic fatigue loadings.

A systems approach to solder joint fatigue in spacecraft electronic packaging

NASA Technical Reports Server (NTRS)

Ross, R. G., Jr.

1991-01-01

Differential expansion induced fatigue resulting from temperature cycling is a leading cause of solder joint failures in spacecraft. Achieving high reliability flight hardware requires that each element of the fatigue issue be addressed carefully. This includes defining the complete thermal-cycle environment to be experienced by the hardware, developing electronic packaging concepts that are consistent with the defined environments, and validating the completed designs with a thorough qualification and acceptance test program. This paper describes a useful systems approach to solder fatigue based principally on the fundamental log-strain versus log-cycles-to-failure behavior of fatigue. This fundamental behavior has been useful to integrate diverse ground test and flight operational thermal-cycle environments into a unified electronics design approach. Each element of the approach reflects both the mechanism physics that control solder fatigue, as well as the practical realities of the hardware build, test, delivery, and application cycle.

Statistical complex fatigue data for SAE 4340 steel and its use in design by reliability

NASA Technical Reports Server (NTRS)

Kececioglu, D.; Smith, J. L.

1970-01-01

A brief description of the complex fatigue machines used in the test program is presented. The data generated from these machines are given and discussed. Two methods of obtaining strength distributions from the data are also discussed. Then follows a discussion of the construction of statistical fatigue diagrams and their use in designing by reliability. Finally, some of the problems encountered in the test equipment and a corrective modification are presented.

Cyclic fatigue analysis of rocket thrust chambers. Volume 1: OFHC copper chamber low cycle fatigue

NASA Technical Reports Server (NTRS)

Miller, R. W.

1974-01-01

A three-dimensional finite element elasto-plastic strain analysis was performed for the throat section of a regeneratively cooled rocket combustion chamber. The analysis employed the RETSCP finite element computer program. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the chamber operating cycle. The analysis was performed for chamber configuration and operating conditions corresponding to a hydrogen-oxygen combustion chamber which was fatigue tested to failure. The computed strain range at typical chamber operating conditions was used in conjunction with oxygen-free, high-conductivity (OHFC) copper isothermal fatigue test data to predict chamber low-cycle fatigue life.

Solder creep-fatigue interactions with flexible leaded parts

NASA Technical Reports Server (NTRS)

Ross, R. G., Jr.; Wen, L. C.; Mon, G. R.; Jetter, E.

1992-01-01

With flexible leaded parts, the solder-joint failure process involves a complex interplay of creep and fatigue mechanisms. To better understand the role of creep in typical multi-hour cyclic loading conditions, a specialized non-linear finite-element creep simulation computer program has been formulated. The numerical algorithm includes the complete part-lead-solder-PWB system, accounting for strain-rate dependence of creep on applied stress and temperature, and the role of the part-lead dimensions and flexibility that determine the total creep deflection (solder strain range) during stress relaxation. The computer program has been used to explore the effects of various solder creep-fatigue parameters such as lead height and stiffness, thermal-cycle test profile, and part/board differential thermal expansion properties. One of the most interesting findings is the strong presence of unidirectional creep-ratcheting that occurs during thermal cycling due to temperature dominated strain-rate effects. To corroborate the solder fatigue model predictions, a number of carefully controlled thermal-cycle tests have been conducted using special bimetallic test boards.

Using Wii Fit to reduce fatigue among African American women with systemic lupus erythematosus: a pilot study.

PubMed

Yuen, H K; Holthaus, K; Kamen, D L; Sword, D O; Breland, H L

2011-10-01

Fatigue and physical deconditioning are common, difficult to treat conditions among patients with systemic lupus erythematosus (SLE). The aim of this pilot study was to evaluate the effectiveness of a home-based exercise program using the Wii Fit system in patients with SLE. Fifteen sedentary African American women with SLE experiencing moderate to severe fatigue participated in a home exercise program using the Wii Fit 3 days a week for 30 minutes each for 10 weeks. A one-group pretest-post test design was used to evaluate the effectiveness of this program. Primary outcome measure was severity of fatigue. Secondary outcome measures were body weight, waist circumference, fatigue-related symptoms of distress, activity level, and physical fitness. At the completion of the 10-week Wii Fit exercise program, participants perceived fatigue severity as measured by the Fatigue Severity Scale to be significantly decreased (p = 0.002), and body weight and waist circumference were significantly reduced (p = 0.01). In addition, anxiety level, as measured by Hospital Anxiety and Depression Scale, and overall intensity of total pain experience, as measured by Short-form of the McGill Pain Questionnaire, were also significantly reduced (p < 0.05). Findings provide preliminary evidence that the Wii Fit motivates this population to exercise, which leads to alleviation of fatigue and reduced body weight, waist circumference, anxiety level, and overall intensity of total pain experience.

High Cycle Fatigue (HCF) Science and Technology Program 2000 Annual Report

DTIC Science & Technology

2000-01-01

in an area of deep compressive stress. • Results of industry and government testing have indicated the ability to stop crack initiation and...fatigue crack nucleation process with the cyclic deformation behavior of the alloy for different microstructures and crystallographic texture ... texture combinations investigated, bimodal fine uni-rolled and lamellar cross-rolled displayed superior fatigue properties to the remaining four

Small Crack Growth and Fatigue Life Predictions for High-Strength Aluminium Alloys. Part 1; Experimental and Fracture Mechanics Analysis

NASA Technical Reports Server (NTRS)

Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.

1998-01-01

The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.

Experimental Evaluation of Fatigue Crack Initiation from Corroded Hemispherical Notches in Aerospace Structural Materials

NASA Technical Reports Server (NTRS)

Garcia, Daniel B.; Forman, Royce; Shindo, David

2010-01-01

A test program was developed and executed to evaluate the influence of corroded hemispherical notches on the fatigue crack initiation and propagation in aluminum 7075-T7351, 4340 steel, and D6AC steel. Surface enhancements such as shot peening and laser shock peening were also incorporated as part of the test effort with the intent of improving fatigue performance. In addition to the testing, fracture mechanics and endurance limit based analysis methods were evaluated to characterize the results with the objective of challenging typical assumptions used in modeling fatigue cracks from corrosion pits. The results specifically demonstrate that the aluminum and steel alloys behave differently with respect to fatigue crack initiation from hemispherical corrosion pits. The aluminum test results were bounded by the fracture mechanics and endurance limit models while exhibiting a general insensitivity to the residual stress field generated by shot peening. The steel specimens were better characterized by the endurance limit fatigue properties and did exhibit sensitivities to residual stresses from the shot peening and laser shock peening

Elevated Temperature Fatigue Endurance of Three Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Verrilli, Michael J.

2007-01-01

High-cycle fatigue endurance of three candidate materials for the acoustic liners of the Enabling Propulsion Materials Nozzle Program was investigated. The ceramic matrix composite materials investigated were N720/AS (Nextel 720, 3M Corporation), Sylramic S200 (Dow Corning), and UT 22. High-cycle fatigue tests were conducted in air at 910 C on as-machined specimens and on specimens subjected to tensile cyclic load excursions every 160 hr followed by thermal exposure at 910 C in a furnace up to total exposure times of 2066 and 4000 hr. All the fatigue tests were conducted in air at 100 Hz with a servohydraulic test machine. In the as-machined condition, among the three materials investigated only the Sylramic S200 exhibited a deterministic type of high-cycle fatigue behavior. Both the N720/AS and UT-22 exhibited significant scatter in the experimentally observed high-cycle fatigue lives. Among the thermally exposed specimens, N720/AS and Sylramic S200 materials exhibited a reduction in the high-cycle fatigue lives, particularly at the exposure time of 4000 hr.

Fatigue Crack Growth Rate Test Results for Al-Li 2195 Parent Metal, Variable Polarity Plasma Arc Welds and Friction Stir Welds

NASA Technical Reports Server (NTRS)

Hafley, Robert A.; Wagner, John A.; Domack, Marcia S.

2000-01-01

The fatigue crack growth rate of aluminum-lithium (Al-Li) alloy 2195 plate and weldments was determined at 200-F, ambient temperature and -320-F. The effects of stress ratio (R), welding process, orientation and thickness were studied. Results are compared with plate data from the Space Shuttle Super Lightweight Tank (SLWT) allowables program. Data from the current series of tests, both plate and weldment, falls within the range of data generated during the SLWT allowables program.

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.

Eye-activity measures of fatigue and napping as a fatigue countermeasure : tech brief.

DOT National Transportation Integrated Search

2011-08-01

This report presents the test plan for collecting and analyzing safety data for the Atlanta Congestion Reduction Demonstration (CRD) under the United States Department of Transportation (U.S. DOT) Urban Partnership Agreement (UPA) and CRD Programs. T...

An Axial-Torsional, Thermomechanical Fatigue Testing Technique

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Bonacuse, Peter J.

1995-01-01

A technique for conducting strain-controlled, thermomechanical, axial-torsional fatigue tests on thin-walled tubular specimens was developed. Three waveforms of loading, namely, the axial strain waveform, the engineering shear strain waveform, and the temperature waveform were required in these tests. The phasing relationships between the mechanical strain waveforms and the temperature and axial strain waveforms were used to define a set of four axial-torsional, thermomechanical fatigue (AT-TMF) tests. Real-time test control (3 channels) and data acquisition (a minimum of 7 channels) were performed with a software program written in C language and executed on a personal computer. The AT-TMF testing technique was used to investigate the axial-torsional thermomechanical fatigue behavior of a cobalt-base superalloy, Haynes 188. The maximum and minimum temperatures selected for the AT-TMF tests were 760 and 316 C, respectively. Details of the testing system, calibration of the dynamic temperature profile of the thin-walled tubular specimen, thermal strain compensation technique, and test control and data acquisition schemes, are reported. The isothermal, axial, torsional, and in- and out-of-phase axial-torsional fatigue behaviors of Haynes 188 at 316 and 760 C were characterized in previous investigations. The cyclic deformation and fatigue behaviors of Haynes 188 in AT-TMF tests are compared to the previously reported isothermal axial-torsional behavior of this superalloy at the maximum and minimum temperatures.

7075-T6 and 2024-T351 Aluminum Alloy Fatigue Crack Growth Rate Data

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Wright, Christopher W.; Johnston, William M., Jr.

2005-01-01

Experimental test procedures for the development of fatigue crack growth rate data has been standardized by the American Society for Testing and Materials. Over the past 30 years several gradual changes have been made to the standard without rigorous assessment of the affect these changes have on the precision or variability of the data generated. Therefore, the ASTM committee on fatigue crack growth has initiated an international round robin test program to assess the precision and variability of test results generated using the standard E647-00. Crack growth rate data presented in this report, in support of the ASTM roundrobin, shows excellent precision and repeatability.

Perceived stress and fatigue among students in a doctor of chiropractic training program.

PubMed

Kizhakkeveettil, Anupama; Vosko, Andrew M; Brash, Marissa; Ph, Dr; Philips, Michael A

2017-03-01

High levels of stress and fatigue are associated with decreased academic success, well-being, and quality of life. The objective of this research was to quantify levels of perceived stress and fatigue among chiropractic students to identify sources of and student coping mechanisms for perceived stress and fatigue and to identify the relationship between students' perceived stress and fatigue. A survey comprised of the Perceived Stress Scale, the Undergraduate Sources of Stress Survey, and the Piper Fatigue Scale was administered to chiropractic students in their 2nd, 5th, and 8th trimesters of doctoral study. Data were analyzed by descriptive statistics, 1-way analysis of variance, and linear correlation tests. Students reported having moderate to high levels of stress and fatigue, with higher levels of stress and fatigue seen in women than in men. A nonsignificant difference among stress scores and a significant difference among fatigue scores were observed based on program term. Levels of stress predicted levels of fatigue, and stress was strongly correlated with psychological health, relationships with family members, mood, and need for learning accommodations. Fatigue was strongly correlated with psychological health, academic demands, and conflicts between studies and other activities. There are differences in the reporting of perceived stress and fatigue levels in this chiropractic student population based on gender. The correlation between fatigue and stress also suggests that measures that may alleviate one may likely affect the other.

Program for Weibull Analysis of Fatigue Data

NASA Technical Reports Server (NTRS)

Krantz, Timothy L.

2005-01-01

A Fortran computer program has been written for performing statistical analyses of fatigue-test data that are assumed to be adequately represented by a two-parameter Weibull distribution. This program calculates the following: (1) Maximum-likelihood estimates of the Weibull distribution; (2) Data for contour plots of relative likelihood for two parameters; (3) Data for contour plots of joint confidence regions; (4) Data for the profile likelihood of the Weibull-distribution parameters; (5) Data for the profile likelihood of any percentile of the distribution; and (6) Likelihood-based confidence intervals for parameters and/or percentiles of the distribution. The program can account for tests that are suspended without failure (the statistical term for such suspension of tests is "censoring"). The analytical approach followed in this program for the software is valid for type-I censoring, which is the removal of unfailed units at pre-specified times. Confidence regions and intervals are calculated by use of the likelihood-ratio method.

Effects of blurring and vertical misalignment on visual fatigue of stereoscopic displays

NASA Astrophysics Data System (ADS)

Baek, Sangwook; Lee, Chulhee

2015-03-01

In this paper, we investigate two error issues in stereo images, which may produce visual fatigue. When two cameras are used to produce 3D video sequences, vertical misalignment can be a problem. Although this problem may not occur in professionally produced 3D programs, it is still a major issue in many low-cost 3D programs. Recently, efforts have been made to produce 3D video programs using smart phones or tablets, which may present the vertical alignment problem. Also, in 2D-3D conversion techniques, the simulated frame may have blur effects, which can also introduce visual fatigue in 3D programs. In this paper, to investigate the relationship between these two errors (vertical misalignment and blurring in one image), we performed a subjective test using simulated 3D video sequences that include stereo video sequences with various vertical misalignments and blurring in a stereo image. We present some analyses along with objective models to predict the degree of visual fatigue from vertical misalignment and blurring.

Fatigue behavior of AAR Class A railroad wheel steel at ambient and elevated temperatures.

DOT National Transportation Integrated Search

2006-12-01

This report documents a test program to determine the material properties (chemical composition, tensile, and fatigue) at ambient and elevated temperatures of a Class A wheel steel as designated by the Association of American Railroads. The 3 tempera...

Gear crack propagation investigations

NASA Technical Reports Server (NTRS)

Lewicki, David G.; Ballarini, Roberto

1996-01-01

Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRacture ANalysis Code) computer program was used to simulate crack propagation. The FRANC program used principles of linear elastic fracture mechanics, finite element modeling, and a unique re-meshing scheme to determine crack tip stress distributions, estimate stress intensity factors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gears were installed with special crack propagation gages in the tooth fillet region to measure bending fatigue crack growth. Good correlation between predicted and measured crack growth was achieved when the fatigue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear tooth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.

Fatigue and durability of Nitinol stents.

PubMed

Pelton, A R; Schroeder, V; Mitchell, M R; Gong, Xiao-Yan; Barney, M; Robertson, S W

2008-04-01

Nitinol self-expanding stents are effective in treating peripheral artery disease, including the superficial femoral, carotid, and renal arteries. However, fracture occurrences of up to 50% have been reported in some stents after one year. These stent fractures are likely due to in vivo cyclic displacements. As such, the cyclic fatigue and durability properties of Nitinol-based endovascular stents are discussed in terms of an engineering-based experimental testing program. In this paper, the combined effects of cardiac pulsatile fatigue and stent-vessel oversizing are evaluated for application to both stents and stent subcomponents. In particular, displacement-controlled fatigue tests were performed on stent-like specimens processed from Nitinol microtubing. Fatigue data were collected with combinations of simulated oversizing conditions and pulsatile cycles that were identified by computer modeling of the stent that mimic in vivo deformation conditions. These data are analyzed with non-linear finite element computations and are illustrated with strain-life and strain-based constant-life diagrams. The utility of this approach is demonstrated in conjunction with 10 million cycle pulsatile fatigue tests of Cordis SMART Control((R)) Nitinol self-expanding stents to calculate fatigue safety factors and thereby predict in vivo fatigue resistance. These results demonstrate the non-linear constant fatigue-life response of Nitinol stents, whereby, contrary to conventional engineering materials, the fatigue life of Nitinol is observed to increase with increasing mean strain.

Evaluation of a compassion fatigue resiliency program for oncology nurses.

PubMed

Potter, Patricia; Deshields, Teresa; Berger, Julia Allen; Clarke, Marty; Olsen, Sarah; Chen, Ling

2013-03-01

To evaluate a resiliency program designed to educate oncology nurses about compassion fatigue. Descriptive pilot study. A National Cancer Institute-designated comprehensive cancer center in the midwestern United States. 13 oncology nurses employed in an outpatient infusion center. Nurses attended a five-week program involving five 90-minute sessions on compassion fatigue resiliency. A pre- and post-test design, using repeated measures, was conducted over six months. Scores on the Professional Quality of Life (ProQOL) IV, Maslach Burnout Inventory-Human Services Survey, Impact of Event Scale-Revised (IES-R), and the Nursing Job Satisfaction Scale. Long-term benefits were realized from the program. Secondary traumatization scores on the ProQOL IV declined immediately after the program, remained down at three months, and then dropped again at six months, with a statistically significant mean difference compared with baseline. The average IES-R total scores improved significantly overall and for each of the three postintervention time points. Participants evaluated the program positively with respect to their ability to apply and benefit from resiliency techniques. This is the first reported study to show benefits gained from a compassion fatigue intervention program. Participants received useful strategies for managing stress at work and home. Compassion fatigue is a prevalent condition among healthcare providers. Development of resiliency to compassion fatigue may improve decision making, clarity of communication, and patient and nurse satisfaction. Self-regulation offers an approach to reduce stress during a perceived threat. Working by intention reduces reactivity in the workplace and makes communication more intentional and, therefore, effective.

Disk Alloy Development

NASA Technical Reports Server (NTRS)

Gabb, Tim; Gayda, John; Telesman, Jack

2001-01-01

The advanced powder metallurgy disk alloy ME3 was designed using statistical screening and optimization of composition and processing variables in the NASA HSR/EPM disk program to have extended durability at 1150 to 1250 "Fin large disks. Scaled-up disks of this alloy were produced at the conclusion of this program to demonstrate these properties in realistic disk shapes. The objective of the UEET disk program was to assess the mechanical properties of these ME3 disks as functions of temperature, in order to estimate the maximum temperature capabilities of this advanced alloy. Scaled-up disks processed in the HSR/EPM Compressor / Turbine Disk program were sectioned, machined into specimens, and tested in tensile, creep, fatigue, and fatigue crack growth tests by NASA Glenn Research Center, in cooperation with General Electric Engine Company and Pratt & Whitney Aircraft Engines. Additional sub-scale disks and blanks were processed and tested to explore the effects of several processing variations on mechanical properties. Scaled-up disks of an advanced regional disk alloy, Alloy 10, were used to evaluate dual microstructure heat treatments. This allowed demonstration of an improved balance of properties in disks with higher strength and fatigue resistance in the bores and higher creep and dwell fatigue crack growth resistance in the rims. Results indicate the baseline ME3 alloy and process has 1300 to 1350 O F temperature capabilities, dependent on detailed disk and engine design property requirements. Chemistry and process enhancements show promise for further increasing temperature capabilities.

Fatigue and fail-safe design features of the DC-10 airplane

NASA Technical Reports Server (NTRS)

Stone, M. E.

1972-01-01

The philosophy and methods used in the design of the DC-10 aircraft to assure structural reliability against cracks under repeated service loads are described in detail. The approach consists of three complementary parts: (1) the structure is designed to be fatigue resistant for a crack-free life of 60,000 flight hours; (2) inasmuch as small undetected cracks could develop from other sources, such as material flaws and manufacturing preloads, the structure also is designed to arrest and control cracks within a reasonable service-inspection interval; and (3) a meaningful service-inspection program has been defined on the basis of analysis and test experience from the design development program. This service-inspection program closes the loop to assure the structural integrity of the DC-10 airframe. Selected materials, fasteners, and structural arrangements are used to achieve these design features with minimum structural weight and with economy in manufacturing and maintenance. Extensive analyses and testing were performed to develop and verify the design. The basic design considerations for fatigue-resistant structure are illustrated in terms of material selection, design loads spectra, methods for accurate stress and fatigue damage analysis, and proven concepts for efficient detail design.

Fatigue behavior of railcar wheel steel at ambient and elevated temperature

DOT National Transportation Integrated Search

2003-08-01

This report presents the results of a material property test program undertaken on a Class B railcar wheel steel. This work was performed to obtain relevant fatigue data that may be used in support of a larger effort exploring the applicability of fa...

The Effect of Hole Quality on the Fatigue Life of 2024-T3 Aluminum Alloy Sheet

NASA Technical Reports Server (NTRS)

Everett, Richard A., Jr.

2004-01-01

This paper presents the results of a study whose main objective was to determine which type of fabrication process would least affect the fatigue life of an open-hole structural detail. Since the open-hole detail is often the fundamental building block for determining the stress concentration of built-up structural parts, it is important to understand any factor that can affect the fatigue life of an open hole. A test program of constant-amplitude fatigue tests was conducted on five different sets of test specimens each made using a different hole fabrication process. Three of the sets used different mechanical drilling procedures while a fourth and fifth set were mechanically drilled and then chemically polished. Two sets of specimens were also tested under spectrum loading to aid in understanding the effects of residual compressive stresses on fatigue life. Three conclusions were made from this study. One, the residual compressive stresses caused by the hole-drilling process increased the fatigue life by two to three times over specimens that were chemically polished after the holes were drilled. Second, the chemical polishing process does not appear to adversely affect the fatigue life. Third, the chemical polishing process will produce a stress-state adjacent to the hole that has insignificant machining residual stresses.

High temperature fatigue behavior of Haynes 188

NASA Technical Reports Server (NTRS)

Halford, Gary R.; Saltsman, James F.; Kalluri, Sreeramesh

1988-01-01

The high temperature, creep-fatigue behavior of Haynes 188 was investigated as an element in a broader thermomechanical fatigue life prediction model development program at the NASA-Lewis. The models are still in the development stage, but the data that were generated possess intrinsic value on their own. Results generated to date is reported. Data were generated to characterize isothermal low cycle fatigue resistance at temperatures of 316, 704, and 927 C with cyclic failure lives ranging from 10 to more than 20,000. These results follow trends that would be predicted from a knowledge of tensile properties, i.e., as the tensile ductility varies with temperature, so varies the cyclic inelastic straining capacity. Likewise, as the tensile strength decreases, so does the high cyclic fatigue resistance. A few two-minute hold-time cycles at peak compressive strain were included in tests at 760 C. These results were obtained in support of a redesign effort for the Orbital Maneuverable System engine. No detrimental effects on cyclic life were noted despite the added exposure time for creep and oxidation. Finally, a series of simulated thermal fatigue tests, referred to as bithermal fatigue tests, were conducted using 316 C as the minimum and 760 C as the maximum temperature. Only out-of-phase bithermal tests were conducted to date. These test results are intended for use as input to a more general thermomechanical fatigue life prediction model based on the concepts of the total strain version of Strainrange Partitioning.

Fatigue crack growth equations for TC-128B tank car steel

DOT National Transportation Integrated Search

2006-10-01

In an effort to develop relevant data for use in applying damage tolerance analysis concepts to railroad tank cars, the fatigue crack growth (FCG) behavior of TC-128B tank car steel was investigated by SwRI in a previous test program conducted for th...

Effects of exercise, patient education, and resource support on women with fibromyalgia: An extended long-term study.

PubMed

Karper, William B

2016-01-01

This research examined whether a long-term, multi-component program positively affected physical fitness, pain and fatigue in seven women with fibromyalgia syndrome. These women lived independently in the community. They attended a university-based program 3 days per week, 1 hour per session, year-around for many years. They were evaluated periodically with a fitness test and rating scale regarding pain and fatigue. Results from when they began the program versus most recently are provided. All of these women showed various positive results from participation in the program.

The Mechanical Property Data Base from an Air Force/Industry Cooperative Test Program on Advanced Aluminum Alloys

DTIC Science & Technology

1993-12-01

Longitudinal) E3 Fatigue Crack Growth Rate Data for Alcan 8090-T8 160 1 " x 4" Extrusion ( L-T Orientation). Grumman E4 Fatigue Crack Growth Rate...Data for Alcan 8090-T8 161 1 " x 4" Extrusion (T-L Orientation). Grumman E5 Fatigue Crack Growth Rate Data for Alcan 8090-T651 162 1 "x 4" Extrusion (L-T...Orientation). Northrop E6 Fatigue Crack Growth Rate for Alcan 8090-T651 163 1 " x 4" Extrusion (T-L Orientation). Northrop E7 Fatigue Crack Growth Rate

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a “sandwich structure” as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50–55% of ultimate tensile strength). The dynamic modulus (E⁎) was found to stay almost constant at 47 GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials.

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a "sandwich structure" as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50-55% of ultimate tensile strength). The dynamic modulus (E(⁎)) was found to stay almost constant at 47GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials. Copyright © 2014 Elsevier Ltd. All rights reserved.

Creep fatigue life prediction for engine hot section materials (isotropic)

NASA Technical Reports Server (NTRS)

Nelson, R. S.; Levan, G. W.; Harvey, P. R.

1992-01-01

This Final Report covers the activities completed under the optional program of the NASA HOST Contract, NAS3-23288. The initial effort of the optional program was report-in NASA CR189221, which consisted of high temperature strain controlled fatigue tests to study the effects of thermomechanical fatigue, multiaxial loading, reactive environments, and imposed stresses. The baseline alloy used in the tests included B1900+Hf (with or without coating) and wrought INCO 718. Tests conducted on B1900+Hf included environmental tests using various atmospheres (75 psig oxygen, purified argon, or block exposures) and specimen tests of wrought INCO 718 included tensile, creep, stress rupture, TMF, multiaxial, and mean stress tests. Results of these testings were used to calibrate a CDA model for INCO 718 alloy and to develop modifications or corrections to the CDA model to handle additional failure mechanisms. The Socie parameter was found to provide the best correlation for INCO multiaxial loading. Microstructural evaluations consisting of optical, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) techniques, and surface replication techniques to determine crack initiation lives provided data which were used to develop life prediction models.

Crack propagation modelling for high strength steel welded structural details

NASA Astrophysics Data System (ADS)

Mecséri, B. J.; Kövesdi, B.

2017-05-01

Nowadays the barrier of applying HSS (High Strength Steel) material in bridge structures is their low fatigue strength related to yield strength. This paper focuses on the fatigue behaviour of a structural details (a gusset plate connection) made from NSS and HSS material, which is frequently used in bridges in Hungary. An experimental research program is carried out at the Budapest University of Technology and Economics to investigate the fatigue lifetime of this structural detail type through the same test specimens made from S235 and S420 steel grades. The main aim of the experimental research program is to study the differences in the crack propagation and the fatigue lifetime between normal and high strength steel structures. Based on the observed fatigue crack pattern the main direction and velocity of the crack propagation is determined. In parallel to the tests finite element model (FEM) are also developed, which model can handle the crack propagation. Using the measured strain data in the tests and the calculated values from the FE model, the approximation of the material parameters of the Paris law are calculated step-by-step, and their calculated values are evaluated. The same material properties are determined for NSS and also for HSS specimens as well, and the differences are discussed. In the current paper, the results of the experiments, the calculation method of the material parameters and the calculated values are introduced.

Fatigue of die cast zinc alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schrems, K.K.; Dogan, O.N.; Goodwin, F.E.

2006-04-01

The rotating bending fatigue limit of die cast zinc alloy 2, alloy 3, alloy 5, AcuZinc 5, and ZA-8 were determined as a part of an on-going program by ILZRO into the mechanical properties of die cast zinc. The stress-life (S-N) curves of alloys 3, 5, AcuZinc 5, and ZA-8 were determined previously. This presentation reports the results of the S-N curve for Alloy 2 and the calculated fatigue limits for all five alloys. During the previous stress-life testing, the samples were stopped at 10 million cycles and the fatigue limit for alloy 3, alloy 5, and AcuZinc 5 appearedmore » to be higher and the fatigue limit for ZA-8 appeared to be lower than the values reported in the literature. This was further investigated in alloy 5 and ZA-8 by testing continuous cast bulk alloy 5 and ZA-8.« less

Effects of an individual 12-week community-located "start-to-run" program on physical capacity, walking, fatigue, cognitive function, brain volumes, and structures in persons with multiple sclerosis.

PubMed

Feys, Peter; Moumdjian, Lousin; Van Halewyck, Florian; Wens, Inez; Eijnde, Bert O; Van Wijmeersch, Bart; Popescu, Veronica; Van Asch, Paul

2017-11-01

Exercise therapy studies in persons with multiple sclerosis (pwMS) primarily focused on motor outcomes in mid disease stage, while cognitive function and neural correlates were only limitedly addressed. This pragmatic randomized controlled study investigated the effects of a remotely supervised community-located "start-to-run" program on physical and cognitive function, fatigue, quality of life, brain volume, and connectivity. In all, 42 pwMS were randomized to either experimental (EXP) or waiting list control (WLC) group. The EXP group received individualized training instructions during 12 weeks (3×/week), to be performed in their community aiming to participate in a running event. Measures were physical (VO 2max , sit-to-stand test, Six-Minute Walk Test (6MWT), Multiple Sclerosis Walking Scale-12 (MSWS-12)) and cognitive function (Rao's Brief Repeatable Battery (BRB), Paced Auditory Serial Attention Test (PASAT)), fatigue (Fatigue Scale for Motor and Cognitive Function (FSMC)), quality of life (Multiple Sclerosis Impact Scale-29 (MSIS-29)), and imaging. Brain volumes and diffusion tensor imaging (DTI) were quantified using FSL-SIENA/FIRST and FSL-TBSS. In all, 35 pwMS completed the trial. Interaction effects in favor of the EXP group were found for VO 2max , sit-to-stand test, MSWS-12, Spatial Recall Test, FSMC, MSIS-29, and pallidum volume. VO 2max improved by 1.5 mL/kg/min, MSWS-12 by 4, FSMC by 11, and MSIS-29 by 14 points. The Spatial Recall Test improved by more than 10%. Community-located run training improved aerobic capacity, functional mobility, visuospatial memory, fatigue, and quality of life and pallidum volume in pwMS.

Effect of Fatigue Protocols on Lower Limb Neuromuscular Function and Implications for Anterior Cruciate Ligament Injury Prevention Training: A Systematic Review.

PubMed

Barber-Westin, Sue D; Noyes, Frank R

2017-12-01

Approximately two-thirds of anterior cruciate ligament (ACL) tears are sustained during noncontact situations when an athlete is cutting, pivoting, decelerating, or landing from a jump. Some investigators have postulated that fatigue may result in deleterious alterations in lower limb biomechanics during these activities that could increase the risk of noncontact ACL injuries. However, prior studies have noted a wide variation in fatigue protocols, athletic tasks studied, and effects of fatigue on lower limb kinetics and kinematics. First, to determine if fatigue uniformly alters lower limb biomechanics during athletic tasks that are associated with noncontact ACL injuries. Second, to determine if changes should be made in ACL injury prevention training programs to alter the deleterious effects of fatigue on lower limb kinetics and kinematics. Systematic review; Level of evidence, 4. A systematic review of the literature using MEDLINE was performed. Key terms were fatigue, neuromuscular, exercise, hop test, and single-legged function tests. Inclusion criteria were original research studies involving healthy participants, use of a fatigue protocol, study of at least 1 lower limb task that involved landing from a hop or jump or cutting, and analysis of at least 1 biomechanical variable. Thirty-seven studies involving 806 athletes (485 female, 321 male; mean age, 22.7 years) met the inclusion criteria. General fatigue protocols were used in 20 investigations, peripheral protocols were used in 17 studies, and 21 different athletic tasks were studied (13 single-legged, 8 double-legged). There was no consistency among investigations regarding the effects of fatigue on hip, knee, or ankle joint angles and moments or surface electromyography muscle activation patterns. The fatigue protocols typically did not produce statistically significant changes in ground-reaction forces. Published fatigue protocols did not uniformly produce alterations in lower limb neuromuscular factors that heighten the risk of noncontact ACL injuries. Therefore, justification does not currently exist for major changes in ACL injury prevention training programs to account for potential fatigue effects. However, the effect of fatigue related to ACL injuries is worthy of further investigation, including the refinement of protocols and methods of analysis.

Implementation and Validation of the Viscoelastic Continuum Damage Theory for Asphalt Mixture and Pavement Analysis in Brazil

NASA Astrophysics Data System (ADS)

Nascimento, Luis Alberto Herrmann do

This dissertation presents the implementation and validation of the viscoelastic continuum damage (VECD) model for asphalt mixture and pavement analysis in Brazil. It proposes a simulated damage-to-fatigue cracked area transfer function for the layered viscoelastic continuum damage (LVECD) program framework and defines the model framework's fatigue cracking prediction error for asphalt pavement reliability-based design solutions in Brazil. The research is divided into three main steps: (i) implementation of the simplified viscoelastic continuum damage (S-VECD) model in Brazil (Petrobras) for asphalt mixture characterization, (ii) validation of the LVECD model approach for pavement analysis based on field performance observations, and defining a local simulated damage-to-cracked area transfer function for the Fundao Project's pavement test sections in Rio de Janeiro, RJ, and (iii) validation of the Fundao project local transfer function to be used throughout Brazil for asphalt pavement fatigue cracking predictions, based on field performance observations of the National MEPDG Project's pavement test sections, thereby validating the proposed framework's prediction capability. For the first step, the S-VECD test protocol, which uses controlled-on-specimen strain mode-of-loading, was successfully implemented at the Petrobras and used to characterize Brazilian asphalt mixtures that are composed of a wide range of asphalt binders. This research verified that the S-VECD model coupled with the GR failure criterion is accurate for fatigue life predictions of Brazilian asphalt mixtures, even when very different asphalt binders are used. Also, the applicability of the load amplitude sweep (LAS) test for the fatigue characterization of the asphalt binders was checked, and the effects of different asphalt binders on the fatigue damage properties of the asphalt mixtures was investigated. The LAS test results, modeled according to VECD theory, presented a strong correlation with the asphalt mixtures' fatigue performance. In the second step, the S-VECD test protocol was used to characterize the asphalt mixtures used in the 27 selected Fundao project test sections and subjected to real traffic loading. Thus, the asphalt mixture properties, pavement structure data, traffic loading, and climate were input into the LVECD program for pavement fatigue cracking performance simulations. The simulation results showed good agreement with the field-observed distresses. Then, a damage shift approach, based on the initial simulated damage growth rate, was introduced in order to obtain a unique relationship between the LVECD-simulated shifted damage and the pavement-observed fatigue cracked areas. This correlation was fitted to a power form function and defined as the averaged reduced damage-to-cracked area transfer function. The last step consisted of using the averaged reduced damage-to-cracked area transfer function that was developed in the Fundao project to predict pavement fatigue cracking in 17 National MEPDG project test sections. The procedures for the material characterization and pavement data gathering adopted in this step are similar to those used for the Fundao project simulations. This research verified that the transfer function defined for the Fundao project sections can be used for the fatigue performance predictions of a wide range of pavements all over Brazil, as the predicted and observed cracked areas for the National MEPDG pavements presented good agreement, following the same trends found for the Fundao project pavement sites. Based on the prediction errors determined for all 44 pavement test sections (Fundao and National MEPDG test sections), the proposed framework's prediction capability was determined so that reliability-based solutions can be applied for flexible pavement design. It was concluded that the proposed LVECD program framework has very good fatigue cracking prediction capability.

The influence of modifications of a fatigue loading history program on fatigue lifetime

NASA Technical Reports Server (NTRS)

Branger, J.

1972-01-01

Rectangular specimens of 7075 and 2014 aluminum alloys with two holes (stress concentration factor of 3.24) have been tested under axial fatigue loading on a six-rod test bed with modifications of the loading program, the surface particulars, and the frequency. The length of the precrack stage was investigated by use of a new crack detector. In most cases the two alloys behaved similarly, with similar life to crack start under the same loading. Some overloads lengthened the life. Truncation by omission of the lowest peak loads should be limited to about 20 percent of the ultimate load. Simplifying counting methods gave misleading results. Very thin surface layers of anodizing, protection by vinyl, dry nitrogen atmosphere, as well as stepwise reaming or grinding the surface of the holes, lengthened the life; thick anodized layers shortened the life. Compressing the hole surface by rolling had no influence. Frequencies at about 210 to 240 cpm produced shorter lives than those at 40 cpm. At 5.4 cpm the life was considerably longer. A model to better understand the precrack-stage fatigue mechanism is discussed.

Physical fitness and physical activity in fatigued and non-fatigued inflammatory bowel disease patients.

PubMed

Vogelaar, Lauran; van den Berg-Emons, Rita; Bussmann, Hans; Rozenberg, Robert; Timman, Reinier; van der Woude, Christien J

2015-01-01

To assess physical fitness and physical activity in inflammatory bowel disease (IBD) patients and whether fatigue is associated with impaired physical fitness and impaired physical activity. Ten patients with quiescent IBD and fatigue (fatigue group [FG]) based on the Checklist Individual Strength-Fatigue score of ≥35 were matched for age (±5 years) and sex with a non-fatigue group (NFG) with IBD. Physical fitness was measured with a cyclo-ergometric-based maximal exercise test, a submaximal 6-min walk test, and a dynamometer test to quantify the isokinetic muscle strength of the knee extensors and flexors. Level of physical activity was measured with an accelerometer-based activity monitor. The patients in both groups did not differ in regard to medication use, clinical characteristics, and body composition. However, medium-to-large effect sizes for impaired physical fitness (both cardiorespiratory fitness and muscle strength) and physical activity were seen between the patients in the FG and the NFG. Especially, intensity of physical activity was significantly lower in the FG patients compared with the NFG patients (effect size: 1.02; p = 0.037). Similar results were seen when outcomes of the FG and NFG were compared with reference values of the normal population. Fatigued IBD patients show an impaired physical fitness and physical activity compared with non-fatigued IBD patients. This gives directions for a physical component in fatigue in IBD patients. Therefore, these new insights into fatigue indicate that these patients might benefit from an exercise program to improve physical fitness and physical activity.

The role of insomnia in the treatment of chronic fatigue.

PubMed

Kallestad, Håvard; Jacobsen, Henrik B; Landrø, Nils Inge; Borchgrevink, Petter C; Stiles, Tore C

2015-05-01

The definition of Chronic Fatigue Syndrome (CFS) overlaps with definitions of insomnia, but there is limited knowledge about the role of insomnia in the treatment of chronic fatigue. To test if improvement of insomnia during treatment of chronic fatigue was associated with improved outcomes on 1) fatigue and 2) cortisol recovery span during a standardized stress exposure. Patients (n = 122) with chronic fatigue received a 3.5-week inpatient return-to-work rehabilitation program based on Acceptance and Commitment Therapy, and had been on paid sick leave>8 weeks due their condition. A physician and a psychologist examined the patients, assessed medication use, and SCID-I diagnoses. Patients completed self-report questionnaires measuring fatigue, pain, depression, anxiety, and insomnia before and after treatment. A subgroup (n = 25) also completed the Trier Social Stress Test for Groups (TSST-G) before and after treatment. Seven cortisol samples were collected during each test and cortisol spans for the TSST-G were calculated. A hierarchical regression analysis in nine steps showed that insomnia improvement predicted improvement in fatigue, independently of age, gender, improvement in pain intensity, depression and anxiety. A second hierarchical regression analysis showed that improvement in insomnia significantly predicted the cortisol recovery span after the TSST-G independently of improvement in fatigue. Improvement in insomnia severity had a significant impact on both improvement in fatigue and the ability to recover from a stressful situation. Insomnia severity may be a maintaining factor in chronic fatigue and specifically targeting this in treatment could increase treatment response. Copyright © 2014. Published by Elsevier Inc.

Low cycle fatigue behaviour of a plasma-sprayed coating material

NASA Technical Reports Server (NTRS)

Gayda, J.; Gabb, T. P.; Miner, R. V.

1986-01-01

Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

The low cycle fatigue behavior of a plasma-sprayed coating material

NASA Technical Reports Server (NTRS)

Gayda, J.; Gabb, T. P.; Miner, R. V., Jr.

1986-01-01

Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C, but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

High-Frequency Axial Fatigue Test Procedures for Spectrum Loading

DTIC Science & Technology

2016-07-20

histories can be performed at frequencies much higher than standard servo-hydraulic test frames by using a test frame that is optimized to run at higher...by using a test frame that is optimized to run at higher frequencies. AIR 4.3 has conducted a research program to develop a test capability for...Applied Research (BAR) program (219BAR-10-008) was initiated in 2010. The program investigated the influence of a generic rotorcraft main rotor blade root

Results of inphase axial-torsional fatigue experiments on 304 stainless steel

NASA Technical Reports Server (NTRS)

Bonacuse, Peter J.; Kalluri, Sreeramesh

1989-01-01

A series of axial-torsional, inphase, strain-controlled, low-cycle fatigue tests were performed at room temperature on tubular specimens of 304 stainless steel. The program was conducted in cooperation with the task group on multiaxial fatigue research of ASTM committee E-09. The objective was to quantify the variability in multiaxial test results among several laboratories. Only included is data which was generated at the NASA Lewis Research Center's High Temperature Fatigue and Structures Laboratory. The experimental equipment and procedures used are described. The tubular specimens were polished on the outer surface to aid in the use of a cellulose film surface replication technique for crack detection. However, cracking initiated predominantly on the internal surface for all specimens. Honing of the bore of the tubular specimens lessened but did not entirely eliminate this problem. The observed fatigue lives are compared with lives calculated from three multiaxial life models. Constants for the life prediction models were obtained from uniaxial and torsional tests performed on the same heat of material. The observed fatigue lives agreed with calculated lives to within a factor of two for all but one of the life prediction models.

Development of load spectra for Airbus A330/A340 full scale fatigue tests

NASA Technical Reports Server (NTRS)

Schmidt, H.-J.; Nielsen, Thomas

1994-01-01

For substantiation of the recently certified medium range Airbus A330 and long range A340 the full scale fatigue tests are in progress. The airframe structures of both aircraft types are tested by one set of A340 specimens. The development of the fatigue test spectra for the two major test specimens which are the center fuselage and wing test and the rear fuselage test is described. The applied test load spectra allow a realistic simulation of flight, ground and pressurization loads and the finalization of the tests within the pre-defined test period. The paper contains details about the 1 g and incremental flight and ground loads and the establishment of the flight-by-flight test program, i.e., the definition of flight types, distribution of loads within the flights and randomization of flight types in repeated blocks. Special attention is given to procedures applied for acceleration of the tests, e.g. omission of lower spectrum loads and a general increase of all loads by ten percent.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohanty, Subhasish; Soppet, William; Majumdar, Saurin

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

Development of composite carrythrough bulkhead

NASA Technical Reports Server (NTRS)

Ehlen, R. J.; Libeskind, M.

1992-01-01

A structural development program was recently completed in which the weight and fatigue advantages of an all composite major load carrying bulkhead was successfully demonstrated. Fabrication of a full scale article, including static and fatigue testing of the carry-through beam portion verified the producibility, strength and durability of this design, thereby presenting the opportunity for use on aircraft upgrades and new aircraft. A 15% weight saving is achievable and, more importantly, the fatigue problems that normally plague metal bulkheads are virtually eliminated.

A Review of Australian and New Zealand Investigations on Aeronautical Fatigue During the Period April 2005 to March 2007

DTIC Science & Technology

2007-04-01

possessed better fatigue properties than the 2024T3 series alloys . It was also possible to develop a fracture mechanic approach which could match...Mechanical Properties of 7050-T7451 Aluminium Alloy . (J.Calero, DSTO) - Paper to be presented at ICAF 2007 Symposium Abstract “It is not uncommon...conductivity, strength, fatigue life and fracture toughness properties of 7050- T7451 aluminium alloy . The test program investigated temperatures ranging

Effect of Stress Ratio on Fatigue Crack Growth Rate at Notched Hole in 7075-T6 Aluminum Alloy Under Biaxial Fatigue

DTIC Science & Technology

2016-08-18

Taylor and Lee studied the effect of in-plane stress biaxility on the fatigue life [22]. Research in this subject is going on but no research done to...closer picture to the hole, notch, pre -crack and the crack in one of the specimens in Abaqus program...which is the scope of this research , using fracture mechanics approach. 6 To achieve the purpose of this study , the specimen has to be test

Relationships between compassion fatigue, burnout, and turnover intention in Korean hospital nurses.

PubMed

Sung, Kiwol; Seo, Youngsook; Kim, Jee Hee

2012-12-01

This study aimed to identify relationships between compassion fatigue, burnout, and turnover intention in Korean hospital nurses. In total, 142 hospital nurses were surveyed as part of data collection. Data related to compassion fatigue, burnout, and turnover intention were collected using a questionnaire between May 2011 and September 2011. The data analysis was performed using PASW 19.0 program, which included one-way ANOVA, independent t-tests, Pearson's correlation coefficient, and hierarchical regression analysis. This study detected a positive correlation between compassion fatigue and burnout(r=.37, p<.001), and turnover intention(r=.55, p<.001). Compassion fatigue accounted for 29.6% of the variance for turnover intention among Korean hospital nurses. The results indicate that it is necessary to reduce compassion fatigue, and turnover intention among Korean hospital nurses.

The Purpose of Generating Fatigue Crack Growth Threshold Data

NASA Technical Reports Server (NTRS)

Forth, Scott

2006-01-01

Test data shows that different width and thickness C(T), M(T) and ESE(T) specimens generate different thresholds Structures designed for "infinite life" are being re-evaluated: a) Threshold changes from 6 to 3 ksi in(sup 1/2); b) Computational life changes from infinite to 4 missions. Multi-million dollar test programs required to substantiate operation. Using ASTM E647 as standard guidance to generate threshold data is not practical. A threshold test approach needs to be standardized that will provide positive margin for high cycle fatigue applications.

Computerized fracture critical and specialized bridge inspection program with NDE applications

NASA Astrophysics Data System (ADS)

Fish, Philip E.

1998-03-01

Wisconsin Department of Transportation implemented a Fracture Critical & Specialized Inspection Program in 1987. The program has a strong emphasis on Nondestructive Testing (NDT). The program is also completely computerized, using laptop computers to gather field data, digital cameras for pictures, and testing equipment with download features. Final inspection reports with detailed information can be delivered within days of the inspection. The program requires an experienced inspection team and qualified personnel. Individuals performing testing must be licensed ASNT (American Society for Nondestructive Testing) Level III and must be licensed Certified Weld Inspectors (American Welding Society). Several critical steps have been developed to assure that each inspection identifies all possible deficiencies that may be possible on a Fracture Critical or Unique Bridge. They include; review of all existing plans and maintenance history; identification of fracture critical members, identification of critical connection details, welds, & fatigue prone details, development of visual and NDE inspection plan; field inspection procedures; and a detailed formal report. The program has found several bridges with critical fatigue conditions which have resulted in replacement or major rehabilitation. In addition, remote monitoring systems have been installed on structures with serious cracking to monitor for changing conditions.

NDE detectability of fatigue-type cracks in high-strength alloys: NDI reliability assessments

NASA Technical Reports Server (NTRS)

Christner, Brent K.; Long, Donald L.; Rummel, Ward D.

1988-01-01

This program was conducted to generate quantitative flaw detection capability data for the nondestructive evaluation (NDE) techniques typically practiced by aerospace contractors. Inconel 718 and Haynes 188 alloy test specimens containing fatigue flaws with a wide distribution of sizes were used to assess the flaw detection capabilities at a number of contractor and government facilities. During this program 85 inspection sequences were completed presenting a total of 20,994 fatigue cracks to 53 different inspectors. The inspection sequences completed included 78 liquid penetrant, 4 eddy current, and 3 ultrasonic evaluations. The results of the assessment inspections are presented and discussed. In generating the flaw detection capability data base, procedures for data collection, data analysis, and specimen care and maintenance were developed, demonstrated, and validated. The data collection procedures and methods that evolved during this program for the measurement of flaw detection capabilities and the effects of inspection variables on performance are discussed. The Inconel 718 and Haynes 188 test specimens that were used in conducting this program and the NDE assessment procedures that were demonstrated, provide NASA with the capability to accurately assess the flaw detection capabilities of specific inspection procedures being applied or proposed for use on current and future fracture control hardware program.

Hybrid test on building structures using electrodynamic fatigue test machine

NASA Astrophysics Data System (ADS)

Xu, Zhao-Dong; Wang, Kai-Yang; Guo, Ying-Qing; Wu, Min-Dong; Xu, Meng

2017-01-01

Hybrid simulation is an advanced structural dynamic experimental method that combines experimental physical models with analytical numerical models. It has increasingly been recognised as a powerful methodology to evaluate structural nonlinear components and systems under realistic operating conditions. One of the barriers for this advanced testing is the lack of flexible software for hybrid simulation using heterogeneous experimental equipment. In this study, an electrodynamic fatigue test machine is made and a MATLAB program is developed for hybrid simulation. Compared with the servo-hydraulic system, electrodynamic fatigue test machine has the advantages of small volume, easy operation and fast response. A hybrid simulation is conducted to verify the flexibility and capability of the whole system whose experimental substructure is one spring brace and numerical substructure is a two-storey steel frame structure. Experimental and numerical results show the feasibility and applicability of the whole system.

The Effects of Shot and Laser Peening on Fatigue Life and Crack Growth in 2024 Aluminum Alloy and 4340 Steel

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.; Matthews, W. T.; Prabhakaran, R.; Newman, J. C., Jr.; Dubberly, M. J.

2001-01-01

Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life.

Current activities in standardization of high-temperature, low-cycle-fatigue testing techniques in the United States

NASA Technical Reports Server (NTRS)

Verrilli, Michael J.; Ellis, J. Rodney; Swindeman, Robert W.

1990-01-01

The American Society for Testing and Materials (ASTM) standard E606-80 is the most often used recommended testing practice for low-cycle-fatigue (LCF) testing in the United States. The standard was first adopted in 1977 for LCF testing at room temperature and was modified in 1980 to include high-temperature testing practices. Current activity within ASTM is aimed at extending the E606-80 recommended practices to LCF under thermomechanical conditions, LCF in high-pressure hydrogen, and LCF in metal-matrix composite materials. Interlaboratory testing programs conducted to generate a technical base for modifying E606-80 for the aforementioned LCF test types are discussed.

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.

Effects of a Training Program Involving Body Cooling on Physical and Cognitive Capacities and Quality of Life in Multiple Sclerosis Patients: A Pilot Study.

PubMed

Gonzales, Benoit; Chopard, Gilles; Charry, Benjamin; Berger, Eric; Tripard, Julien; Magnin, Eloi; Groslambert, Alain

2017-01-01

Two methods using exercise and body cooling could influence the well-being of patients with multiple sclerosis (PwMS). The aim of this study was to determine whether wearing a cooling vest during a physical training program could increase the cognitive and physical capacities and quality of life in PwMS. Eighteen PwMS (49.6 ± 8 years; Expanded Disability Status Score 5.0 ± 1.0) were randomly assigned to a cooling or control group. PwMS underwent a 7-week physical training program. In the cooling group, PwMS wore a cooling vest during each training session, whereas in the control group, PwMS wore a cotton T-shirt. Before and after the training program, both groups completed the Isaacs Set Test (IST), Trail Making Test A-B (TMT A-B), SEP-59, Multidimensional Fatigue Inventory and performed a 6-minute walk test (6MWT). The cooling group showed significantly (p < 0.05) improved performance for IST, TMT A and 6MWT. Their emotional well-being and cognitive functions investigated in SEP-59 were significantly (p < 0.05) improved, and general and physical fatigue significantly (p < 0.05) decreased. This physical training program combined with a cooling strategy could have a significant positive influence on both cognitive and physical performances, perceived fatigue and emotional well-being in heat-sensitive PwMS. © 2017 S. Karger AG, Basel.

Fatigue Crack Growth Threshold Testing of Metallic Rotorcraft Materials

NASA Technical Reports Server (NTRS)

Newman, John A.; James, Mark A.; Johnson, William M.; Le, Dy D.

2008-01-01

Results are presented for a program to determine the near-threshold fatigue crack growth behavior appropriate for metallic rotorcraft alloys. Four alloys, all commonly used in the manufacture of rotorcraft, were selected for study: Aluminum alloy 7050, 4340 steel, AZ91E Magnesium, and Titanium alloy Ti-6Al-4V (beta-STOA). The Federal Aviation Administration (FAA) sponsored this research to advance efforts to incorporate damage tolerance design and analysis as requirements for rotorcraft certification. Rotorcraft components are subjected to high cycle fatigue and are typically subjected to higher stresses and more stress cycles per flight hour than fixed-wing aircraft components. Fatigue lives of rotorcraft components are generally spent initiating small fatigue cracks that propagate slowly under near-threshold cracktip loading conditions. For these components, the fatigue life is very sensitive to the near-threshold characteristics of the material.

Fatigue damage characterization of braided and woven fiber reinforced polymer matrix composites at room and elevated temperatures

NASA Astrophysics Data System (ADS)

Montesano, John

The use of polymer matrix composites (PMC) for manufacturing primary load-bearing structural components has significantly increased in many industrial applications. Specifically in the aerospace industry, PMCs are also being considered for elevated temperature applications. Current aerospace-grade composite components subjected to fatigue loading are over-designed due to insufficient understanding of the material failure processes, and due to the lack of available generic fatigue prediction models. A comprehensive literature survey reveals that there are few fatigue studies conducted on woven and braided fabric reinforced PMC materials, and even fewer at elevated temperatures. It is therefore the objective of this study to characterize and subsequently model the elevated temperature fatigue behaviour of a triaxial braided PMC, and to investigate the elevated temperature fatigue properties of two additional woven PMCs. An extensive experimental program is conducted using a unique test protocol on the braided and woven composites, which consists of static and fatigue testing at various test temperatures. The development of mechanically-induced damage is monitored using a combination of non-destructive techniques which included infrared thermography, fiber optic sensors and edge replication. The observed microscopic damage development is quantified and correlated to the exhibited macroscopic material behaviour at all test temperatures. The fiber-dominated PMC materials considered in this study did not exhibit notable time- or temperature-dependent static properties. However, fatigue tests reveal that the local damage development is in fact notably influenced by temperature. The elevated temperature environment increases the toughness of the thermosetting polymers, which results in consistently slower fatigue crack propagation rates for the respective composite materials. This has a direct impact on the stiffness degradation rate and the fatigue lives for the braided and woven composites under investigation. The developed analytical fatigue damage prediction model, which is based on actual observed damage mechanisms, accurately predicted the development of damage and the corresponding stiffness degradation for the braided PMC, for all test temperatures. An excellent correlation was found between the experimental and the predicted results to within a 2% accuracy. The prediction model adequately captured the local temperature-induced phenomenon exhibited by the braided PMC material. The results presented in this study are novel for a braided composite material subjected to elevated temperature fatigue.

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

NASA Astrophysics Data System (ADS)

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

2005-08-01

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

Biaxial tests of flat graphite/epoxy laminates

NASA Technical Reports Server (NTRS)

Liebowitz, H.; Jones, D. L.

1981-01-01

The influence of biaxially applied loads on the strength of composite materials containing holes was analyzed. The analysis was performed through the development of a three dimensional, finite element computer program that is capable of evaluating fiber breakage, delamination, and matrix failure. Realistic failure criteria were established for each of the failure modes, and the influence of biaxial loading on damage accumulation under monotonically increasing loading was examined in detail. Both static and fatigue testing of specially designed biaxial specimens containing central holes were performed. Static tests were performed to obtain an understanding of the influence of biaxial loads on the fracture strength of composite materials and to provide correlation with the analytical predictions. The predicted distributions and types of damage are in reasonable agreement with the experimental results. A number of fatigue tests were performed to determine the influence of cyclic biaxial loads on the fatigue life and residual strength of several composite laminates.

Influence of creep damage on the low cycle thermal-mechanical fatigue behavior of two tantalum base alloys

NASA Technical Reports Server (NTRS)

Sheffler, K. D.; Doble, G. S.

1972-01-01

Low cycle fatigue tests have been performed on the tantalum base alloys T-111 and ASTAR 811C with synchronized, independently programmed temperature and strain cycling. The thermal-mechanical cycles applied fell into three basic categories: these were isothermal cycling, in-phase thermal cycling, and out-of-phase thermal cycling. In-phase cycling was defined as tensile deformation associated with high temperature and compressive deformation with low temperature, while out-of-phase thermal cycling was defined as the reverse case. The in-phase thermal cycling had a pronounced detrimental influence on the fatigue life of both alloys, with the life reduction being greater in the solid solution strengthened T-111 alloy than in the carbide strengthened ASTAR 811C alloy. The out-of-phase tests also showed pronounced effects on the fatigue life of both alloys, although not as dramatic.

Exercising Impacts on Fatigue, Depression, and Paresthesia in Female Patients with Multiple Sclerosis.

PubMed

Razazian, Nazanin; Yavari, Zeinab; Farnia, Vahid; Azizi, Akram; Kordavani, Laleh; Bahmani, Dena Sadeghi; Holsboer-Trachsler, Edith; Brand, Serge

2016-05-01

Multiple sclerosis (MS) is a chronic progressive autoimmune disease impacting both body and mind. Typically, patients with MS report fatigue, depression, and paresthesia. Standard treatment consists of immune modulatory medication, though there is growing evidence that exercising programs have a positive influence on fatigue and psychological symptoms such as depression. We tested the hypothesis that, in addition to the standard immune regulatory medication, either yoga or aquatic exercise can ameliorate both fatigue and depression, and we examined whether these interventions also influence paresthesia compared with a nonexercise control condition. Fifty-four women with MS (mean age: M = 33.94 yr, SD = 6.92) were randomly assigned to one of the following conditions: yoga, aquatic exercise, or nonexercise control. Their existing immune modulatory therapy remained unchanged. Participants completed questionnaires covering symptoms of fatigue, depression, and paresthesia, both at baseline and on completion of the study 8 wk later. Compared with the nonexercise control condition and over time, fatigue, depression, and paresthesia decreased significantly in the yoga and aquatic exercise groups. On study completion, the likelihood of reporting moderate to severe depression was 35-fold higher in the nonexercise control condition than in the intervention conditions (yoga and aquatic exercising values collapsed). The pattern of results suggests that for females with MS and treated with standard immune regulatory medication, exercise training programs such as yoga and aquatic exercising positively impact on core symptoms of MS, namely, fatigue, depression, and paresthesia. Exercise training programs should be considered in the future as possible complements to standard treatments.

Short-crack growth behaviour in an aluminum alloy: An AGARD cooperative test program

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Edwards, P. R.

1988-01-01

An AGARD Cooperative Test Program on the growth of short fatigue cracks was conducted to define the significance of the short-crack effect, to compare test results from various laboratories, and to evaluate an existing analytical crack-growth prediction model. The initiation and growth of short fatigue cracks (5 micrometer to 2 mm) from the surface of a semi-circular notch in 2024-T3 aluminum alloy sheet material were monitored under various load histories. The cracks initiated from inclusion particle clusters or voids on the notch surface and generally grew as surface cracks. Tests were conducted under several constant-amplitude (stress ratios of -2, -1, 0, and 0.5) and spectrum (FALSTAFF and Gaussian) loading conditions at 3 stress levels each. Short crack growth was recorded using a plastic-replica technique. Over 250 edge-notched specimens were fatigue tested and nearly 950 cracks monitored by 12 participants from 9 countries. Long crack-growth rate data for cracks greater than 2 mm in length were obtained over a wide range in rates (10 to the -8 to 10 to the -1 mm/cycle) for all constant-amplitude loading conditions. Long crack-growth rate data for the FALSTAFF and Gaussian load sequences were also obtained.

Remote monitoring and prognosis of fatigue cracking in steel bridges with acoustic emission

NASA Astrophysics Data System (ADS)

Yu, Jianguo Peter; Ziehl, Paul; Pollock, Adrian

2011-04-01

Acoustic emission (AE) monitoring is desirable to nondestructively detect fatigue damage in steel bridges. Investigations of the relationship between AE signals and crack growth behavior are of paramount importance prior to the widespread application of passive piezoelectric sensing for monitoring of fatigue crack propagation in steel bridges. Tests have been performed to detect AE from fatigue cracks in A572G50 steel. Noise induced AE signals were filtered based on friction emission tests, loading pattern, and a combined approach involving Swansong II filters and investigation of waveforms. The filtering methods based on friction emission tests and load pattern are of interest to the field evaluation using sparse datasets. The combined approach is suitable for data filtering and interpretation of actual field tests. The pattern recognition program NOESIS (Envirocoustics) was utilized for the evaluation of AE data quality. AE parameters are associated with crack length, crack growth rate, maximum stress intensity and stress intensity range. It is shown that AE hits, counts, absolute energy, and signal strength are able to provide warnings at the critical cracking level where cracking progresses from stage II (stable propagation) to stage III (unstable propagation which may result in failure). Absolute energy rate and signal strength rate may be better than count rate to assess the remaining fatigue life of inservice steel bridges.

In-air and pressurized water reactor environment fatigue experiments of 316 stainless steel to study the effect of environment on cyclic hardening

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohanty, Subhasish; Soppet, William K.; Majumdar, Saurindranath

Argonne National Laboratory (ANL), under the sponsorship of Department of Energy’s Light Water Reactor Sustainability (LWRS) program, is trying to develop a mechanistic approach for more accurate life estimation of LWR components. In this context, ANL has conducted many fatigue experiments under different test and environment conditions on type 316 stainless steel (316SS) material which is widely used in the US reactors. Contrary to the conventional S~N curve based empirical fatigue life estimation approach, the aim of the present DOE sponsored work is to develop an understanding of the material ageing issues more mechanistically (e.g. time dependent hardening and softening)more » under different test and environmental conditions. Better mechanistic understanding will help develop computer-based advanced modeling tools to better extrapolate stress-strain evolution of reactor components under multi-axial stress states and hence help predict their fatigue life more accurately. In this paper (part-I) the fatigue experiments under different test and environment conditions and related stress-strain results for 316 SS are discussed. In a second paper (part-II) the related evolutionary cyclic plasticity material modeling techniques and results are discussed.« less

Muscular Activity and Fatigue in Lower-Limb and Trunk Muscles during Different Sit-To-Stand Tests.

PubMed

Roldán-Jiménez, Cristina; Bennett, Paul; Cuesta-Vargas, Antonio I

2015-01-01

Sit-to-stand (STS) tests measure the ability to get up from a chair, reproducing an important component of daily living activity. As this functional task is essential for human independence, STS performance has been studied in the past decades using several methods, including electromyography. The aim of this study was to measure muscular activity and fatigue during different repetitions and speeds of STS tasks using surface electromyography in lower-limb and trunk muscles. This cross-sectional study recruited 30 healthy young adults. Average muscle activation, percentage of maximum voluntary contraction, muscle involvement in motion and fatigue were measured using surface electrodes placed on the medial gastrocnemius (MG), biceps femoris (BF), vastus medialis of the quadriceps (QM), the abdominal rectus (AR), erector spinae (ES), rectus femoris (RF), soleus (SO) and the tibialis anterior (TA). Five-repetition STS, 10-repetition STS and 30-second STS variants were performed. MG, BF, QM, ES and RF muscles showed differences in muscle activation, while QM, AR and ES muscles showed significant differences in MVC percentage. Also, significant differences in fatigue were found in QM muscle between different STS tests. There was no statistically significant fatigue in the BF, MG and SO muscles of the leg although there appeared to be a trend of increasing fatigue. These results could be useful in describing the functional movements of the STS test used in rehabilitation programs, notwithstanding that they were measured in healthy young subjects.

Development of a full-scale transmission testing procedure to evaluate advanced lubricants

NASA Technical Reports Server (NTRS)

Lewicki, David G.; Decker, Harry J.; Shimski, John T.

1992-01-01

Experimental tests were performed on the OH-58A helicopter main rotor transmission in the NASA Lewis 500-hp Helicopter Transmission Test Stand. The testing was part of a joint Navy/NASA/Army lubrication program. The objective of the program was to develop a separate lubricant for gearboxes and demonstrate an improved performance in life and load-carrying capacity. The goal of the experiments was to develop a testing procedure to fail certain transmission components using a MIL-L-23699 base reference oil, then run identical tests with improved lubricants and demonstrate performance. The tests were directed at failing components that the Navy has had problems with due to marginal lubrication. These failures included mast shaft bearing micropitting, sun gear and planet bearing fatigue, and spiral bevel gear scoring. A variety of tests were performed and over 900 hours of total run time accumulated for these tests. Some success was achieved in developing a testing procedure to produce sun gear and planet bearing fatigue failures. Only marginal success was achieved in producing mast shaft bearing micropitting and spiral bevel gear scoring.

Mobile phone text messaging intervention to improve alertness and reduce sleepiness and fatigue during shiftwork among emergency medicine clinicians: study protocol for the SleepTrackTXT pilot randomized controlled trial.

PubMed

Patterson, Paul Daniel; Moore, Charity G; Weaver, Matthew D; Buysse, Daniel J; Suffoletto, Brian P; Callaway, Clifton W; Yealy, Donald M

2014-06-21

Mental and physical fatigue while at work is common among emergency medical services (EMS) shift workers. Extended shifts (for example 24 hours) and excessive amounts of overtime work increase the likelihood of negative safety outcomes and pose a challenge for EMS fatigue-risk management. Text message-based interventions are a potentially high-impact, low-cost platform for sleep and fatigue assessment and distributing information to workers at risk of negative safety outcomes related to sleep behaviors and fatigue. We will conduct a pilot randomized trial with a convenience sample of adult EMS workers recruited from across the United States using a single study website. Participants will be allocated to one of two possible arms for a 90-day study period. The intervention arm will involve text message assessments of sleepiness, fatigue, and difficulty with concentration at the beginning, during, and end of scheduled shifts. Intervention subjects reporting high levels of sleepiness or fatigue will receive one of four randomly selected intervention messages promoting behavior change during shiftwork. Control subjects will receive assessment only text messages. We aim to determine the performance characteristics of a text messaging tool for the delivery of a sleep and fatigue intervention. We seek to determine if a text messaging program with tailored intervention messages is effective at reducing perceived sleepiness and/or fatigue among emergency medicine clinician shift workers. Additional aims include testing whether a theory-based behavioral intervention, delivered by text message, changes 'alertness behaviors'. The SleepTrackTXT pilot trial could provide evidence of compliance and effectiveness that would support rapid widespread expansion in one of two forms: 1) a stand-alone program in the form of a tailored/individualized sleep monitoring and fatigue reduction support service for EMS workers; or 2) an add-on to a multi-component fatigue risk management program led and maintained by employers or by safety and risk management services. Clinicaltrials.gov NCT02063737, Registered on 10 January 2014.

Mobile phone text messaging intervention to improve alertness and reduce sleepiness and fatigue during shiftwork among emergency medicine clinicians: study protocol for the SleepTrackTXT pilot randomized controlled trial

PubMed Central

2014-01-01

Background Mental and physical fatigue while at work is common among emergency medical services (EMS) shift workers. Extended shifts (for example 24 hours) and excessive amounts of overtime work increase the likelihood of negative safety outcomes and pose a challenge for EMS fatigue-risk management. Text message-based interventions are a potentially high-impact, low-cost platform for sleep and fatigue assessment and distributing information to workers at risk of negative safety outcomes related to sleep behaviors and fatigue. Methods/Design We will conduct a pilot randomized trial with a convenience sample of adult EMS workers recruited from across the United States using a single study website. Participants will be allocated to one of two possible arms for a 90-day study period. The intervention arm will involve text message assessments of sleepiness, fatigue, and difficulty with concentration at the beginning, during, and end of scheduled shifts. Intervention subjects reporting high levels of sleepiness or fatigue will receive one of four randomly selected intervention messages promoting behavior change during shiftwork. Control subjects will receive assessment only text messages. We aim to determine the performance characteristics of a text messaging tool for the delivery of a sleep and fatigue intervention. We seek to determine if a text messaging program with tailored intervention messages is effective at reducing perceived sleepiness and/or fatigue among emergency medicine clinician shift workers. Additional aims include testing whether a theory-based behavioral intervention, delivered by text message, changes ‘alertness behaviors’. Discussion The SleepTrackTXT pilot trial could provide evidence of compliance and effectiveness that would support rapid widespread expansion in one of two forms: 1) a stand-alone program in the form of a tailored/individualized sleep monitoring and fatigue reduction support service for EMS workers; or 2) an add-on to a multi-component fatigue risk management program led and maintained by employers or by safety and risk management services. Trial Registration Clinicaltrials.gov NCT02063737, Registered on 10 January 2014 PMID:24952387

In-air and pressurized water reactor environment fatigue experiments of 316 stainless steel to study the effect of environment on cyclic hardening

NASA Astrophysics Data System (ADS)

Mohanty, Subhasish; Soppet, William K.; Majumdar, Saurindranath; Natesan, Krishnamurti

2016-05-01

Argonne National Laboratory (ANL), under the sponsorship of Department of Energy's Light Water Reactor Sustainability (LWRS) program, is trying to develop a mechanistic approach for more accurate life estimation of LWR components. In this context, ANL has conducted many fatigue experiments under different test and environment conditions on type 316 stainless steel (316 SS) material which is widely used in the US reactors. Contrary to the conventional S ∼ N curve based empirical fatigue life estimation approach, the aim of the present DOE sponsored work is to develop an understanding of the material ageing issues more mechanistically (e.g. time dependent hardening and softening) under different test and environmental conditions. Better mechanistic understanding will help develop computer-based advanced modeling tools to better extrapolate stress-strain evolution of reactor components under multi-axial stress states and hence help predict their fatigue life more accurately. Mechanics-based modeling of fatigue such as by using finite element (FE) tools requires the time/cycle dependent material hardening properties. Presently such time-dependent material hardening properties are hardly available in fatigue modeling literature even under in-air conditions. Getting those material properties under PWR environment, are even harder. Through this work we made preliminary attempt to generate time/cycle dependent stress-strain data both under in-air and PWR water conditions for further study such as for possible development of material models and constitutive relations for FE model implementation. Although, there are open-ended possibility to further improve the discussed test methods and related material estimation techniques we anticipate that the data presented in this paper will help the metal fatigue research community particularly, the researchers who are dealing with mechanistic modeling of metal fatigue such as using FE tools. In this paper the fatigue experiments under different test and environment conditions and related stress-strain results for 316 SS are discussed.

Small-crack effects in high-strength aluminum alloys

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Wu, X. R.; Venneri, S. L.; Li, C. G.

1994-01-01

The National Aeronautics and Space Administration and the Chinese Aeronautical Establishment participated in a Fatigue and Fracture Mechanics Cooperative Program. The program objectives were to identify and characterize crack initiation and growth of small cracks (10 microns to 2 mm long) in commonly used US and PRC aluminum alloys, to improve fracture mechanics analyses of surface- and corner-crack configurations, and to develop improved life-prediction methods. Fatigue and small-crack tests were performed on single-edgenotch tension (SENT) specimens and large-crack tests were conducted on center-crack tension specimens for constant-amplitude (stress ratios of -1, 0, and 0.5) and Mini-TWIST spectrum loading. The plastic replica method was used to monitor the initiation and growth of small fatigue cracks at the semicircular notch. Crack growth results from each laboratory on 7075-T6 bare and LC9cs clad aluminum alloys agreed well and showed that fatigue life was mostly crack propagation from a material defect (inclusion particles or void) or from the cladding layer. Finite-element and weight-function methods were used to determine stress intensity factors for surface and corner cracks in the SENT specimens. Equations were then developed and used in a crack growth and crack-closure model to correlate small- and large-crack data and to make life predictions for various load histories. The cooperative program produced useful experimental data and efficient analysis methods for improving life predictions. The results should ultimately improve aircraft structural reliability and safety.

Fatigue of titanium alloys in a supersonic-cruise airplane environment

NASA Technical Reports Server (NTRS)

Imig, L. A.

1976-01-01

The test programs conducted by several aerospace companies and NASA, summarized in this paper, studied several titanium materials previously identified as having high potential for application to supersonic cruise airplane structures. These studies demonstrate that the temperature (560 K) by itself produced no significant degradation of the materials. However, the fatigue resistance of titanium-alloy structures, in which thermal and loading effects are combined, has been studied insufficiently. The predominant topic for future study of fatigue problems in Mach 3 structures should be the influences of thermal stress particularly, the effects of thermal stress on failure location.

Creep fatigue life prediction for engine hot section materials (isotropic)

NASA Technical Reports Server (NTRS)

Moreno, V.

1983-01-01

The Hot Section Technology (HOST) program, creep fatigue life prediction for engine hot section materials (isotropic), is reviewed. The program is aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components. Significant results include: (1) cast B1900 and wrought IN 718 selected as the base and alternative materials respectively; (2) fatigue test specimens indicated that measurable surface cracks appear early in the specimen lives, i.e., 15% of total life at 871 C and 50% of life at 538 c; (3) observed crack initiation sites are all surface initiated and are associated with either grain boundary carbides or local porosity, transgrannular cracking is observed at the initiation site for all conditions tested; and (4) an initial evaluation of two life prediction models, representative of macroscopic (Coffin-Mason) and more microscopic (damage rate) approaches, was conducted using limited data generated at 871 C and 538 C. It is found that the microscopic approach provides a more accurate regression of the data used to determine crack initiation model constants, but overpredicts the effect of strain rate on crack initiation life for the conditions tested.

Space Shuttle Crawler Transporter Vibration Analysis in Support of Rollout Fatigue Load Spectra Verification Program

NASA Technical Reports Server (NTRS)

Margasahayam, Ravi N.; Meyer, Karl A.; Nerolich, Shaun M.; Burton, Roy C.; Gosselin, Armand M.

2004-01-01

The Crawler Transporter (CT), designed and built for the Apollo Program in the 1960's and surpassing its initial operational life, has become an integral part of the Space Shuttle Program (SSP). The CT transports the Space Shuttle Vehicle (SSV) stack, atop the Mobile Launch Platform (MLP), from the Vehicle Assembly Building (VAB) to the launch pad. This support structure provides hydraulic jacking, leveling and load equalization for the 12 million pound stack on its 3.5-5.0 mile rollout to the launch pad. Major elements of the SSV, consisting of the orbiter, solid rocket boosters (SRB) and external tank (ET) have required fatigue analyses as part of the mission life certification. Compared to rollout vibration, the SSV sees relatively high vibration loads during launch, ascent, descent and landing phases of the mission. Although preliminary measured SRB vibration levels during rollout were of low amplitude and frequency, the duration of the rollout phase is typically high, from 5-6 hours. As part of an expanded mission life assessment, additional certification effort was initiated to define fatigue load spectra for rollout. This study addresses the CT vibration analyses in support of the rollout fatigue study. Structural models developed for modal and vibration analyses were used to identify unique CT, CT/MLP and CT/MLP/SRB vibration characteristics for comparison to instrumented rollout tests. Whereas the main structural and vibration characteristics of the SSV are well defined, minimum analytical and vibration test data on the Crawler Transporter were available. Unique vibration characteristics of the CT are attributable to the drive mechanism, hydraulic jacking system, structural framing and the CT-to-MLP support pad restraints. Initial tests performed on the CT/MLP/SRB configuration showed reasonable correlation with predicted mode shapes and frequencies.

[Effects of Foot-Reflexology Massage on Fatigue, Stress and Postpartum Depression in Postpartum Women].

PubMed

Choi, Mi Son; Lee, Eun Ja

2015-08-01

To identify the effects of foot reflexology massage on fatigue, stress and depression of postpartum women. A nonequivalent control group pre-post design was used. A total of 70 women in a postpartum care center were recruited and were assigned to the experimental group (35) or control group (35). Foot reflexology massage was provided to the experimental group once a day for three days. Data were collected before and after the intervention program which was carried out from December, 2013 to February, 2014. Data were analyzed using Chi-square test, Fisher's exact test, and t-test. The level of fatigue in the experimental group was significantly lower than the control group (t=-2.74, p=.008). The level of cortisol in the urine of women in the experimental group was significantly lower than the control group (t=-2.19, p=.032). The level of depression in the experimental group was significantly lower than the control group (t=-3.00, p=.004). The results show that the foot reflexology massage is an effective nursing intervention to relieve fatigue, stress, and depression for postpartum women.

Assessment of microalloying effects on the high temperature fatigue behavior of NiAl

NASA Technical Reports Server (NTRS)

Noebe, R. D.; Lerch, B. A.; Rao, K. B. S.

1995-01-01

Binary NiAl suffers from a lack of strength and poor creep properties at and above 1000 K. Poor creep resistance in turn affects low cycle fatigue (LCF) lives at low strain ranges due to the additional interactions of creep damage. One approach for improving these properties involved microalloying with either Zr or N. As an integral part of a much larger alloying program the low cycle fatigue behavior of Zr and N doped nickel aluminides produced by extrusion of prealloyed powders has been investigated. Strain controlled LCF tests were performed in air at 1000 K. The influence of these microalloying additions on the fatigue life and cyclic stress response of polycrystalline NiAl are discussed.

Impact of the Arthritis Foundation’s Walk With Ease Program on Arthritis Symptoms in African Americans

PubMed Central

Wyatt, Brooke; Mingo, Chivon A.; Waterman, Mary B.; White, Patience; Cleveland, Rebecca J.

2014-01-01

Introduction Inadequate program design and lack of access to evidence-based programs are major barriers to the management of chronic diseases such as arthritis, particularly for African Americans. This study evaluates the effectiveness of the Arthritis Foundation’s Walk With Ease Program (WWE) in a subsample of African Americans who were part of a larger study that established evidence of the program’s efficacy. Methods Participants were African Americans (N = 117) with self-reported arthritis who chose to participate in either a self-directed (n = 68) or group (n = 49) 6-week WWE program. Arthritis-related symptoms (ie, pain, fatigue, stiffness; measured using visual analog scales) were assessed at baseline, 6 weeks, and 1 year. Independent samples t tests were conducted to examine group differences (ie, self-directed vs group) in arthritis-related symptoms at baseline, and paired sample t tests were conducted to examine differences over time (ie, baseline to 6 weeks and baseline to 1 year) in symptoms. Satisfaction was examined by descriptive statistics. Results Younger, more educated individuals chose the self-directed format (P < .001, P = .008; respectively). After the 6-week intervention, participants reported a decrease in pain (P < .001), fatigue (P = .002), and stiffness (P < .001). At 1 year, the decrease in pain (P = .04) and stiffness (P = .002) remained constant. Overall, participants were satisfied with both program formats. Conclusion The individualized and group formats of the WWE program improved arthritis-related pain, fatigue, and stiffness in African Americans. Culturally appealing arthritis interventions ultimately may increase the use of existing arthritis interventions. PMID:25393747

A root-mean-square approach for predicting fatigue crack growth under random loading

NASA Technical Reports Server (NTRS)

Hudson, C. M.

1981-01-01

A method for predicting fatigue crack growth under random loading which employs the concept of Barsom (1976) is presented. In accordance with this method, the loading history for each specimen is analyzed to determine the root-mean-square maximum and minimum stresses, and the predictions are made by assuming the tests have been conducted under constant-amplitude loading at the root-mean-square maximum and minimum levels. The procedure requires a simple computer program and a desk-top computer. For the eleven predictions made, the ratios of the predicted lives to the test lives ranged from 2.13 to 0.82, which is a good result, considering that the normal scatter in the fatigue-crack-growth rates may range from a factor of two to four under identical loading conditions.

High Cycle Fatigue (HCF) Science and Technology Program 2002 Annual Report

DTIC Science & Technology

2003-08-01

Turbine Engine Airfoils, Phase I 4.3 Probabilistic Design of Turbine Engine Airfoils, Phase II 4.4 Probabilistic Blade Design System 4.5...XTL17/SE2 7.4 Conclusion 8.0 TEST AND EVALUATION 8.1 Characterization Test Protocol 8.2 Demonstration Test Protocol 8.3 Development of Multi ...transparent and opaque overlays for processing. The objective of the SBIR Phase I program was to identify and evaluate promising methods for

Crew Factors in Flight Operations X: Alertness Management in Flight Operations

NASA Technical Reports Server (NTRS)

Rosekind, Mark R.; Gander, Philippa H.; Connell, Linda J.; Co, Elizabeth L.

1999-01-01

In response to a 1980 congressional request, NASA Ames Research Center initiated a Fatigue/Jet Lag Program to examine fatigue, sleep loss, and circadian disruption in aviation. Research has examined fatigue in a variety of flight environments using a range of measures (from self-report to performance to physiological). In 1991, the program evolved into the Fatigue Countermeasures Program, emphasizing the development and evaluation of strategies to maintain alertness and performance in operational settings. Over the years, the Federal Aviation Administration (FAA) has become a collaborative partner in support of fatigue research and other Program activities. From the inception of the Program, a principal goal was to return the information learned from research and other Program activities to the operational community. The objectives of this Education and Training Module are to explain what has been learned about the physiological mechanisms that underlie fatigue, demonstrate the application of this information in flight operations, and offer some specific fatigue counter-measure recommendations. It is intended for all segments of the aeronautics industry, including pilots, flight attendants, managers, schedulers, safety and policy personnel, maintenance crews, and others involved in an operational environment that challenges human physiological capabilities because of fatigue, sleep loss, and circadian disruption.

Crew Factors in Flight Operations X: Alertness Management in Flight Operations

NASA Technical Reports Server (NTRS)

Rosekind, Mark R.; Gander, Philippa H.; Connell, Linda J.; Co, Elizabeth L.

2001-01-01

In response to a 1980 congressional request, NASA Ames Research Center initiated a Fatigue/Jet Lag Program to examine fatigue, sleep loss, and circadian disruption in aviation. Research has examined fatigue in a variety of flight environments using a range of measures (from self-report to performance to physiological). In 1991, the program evolved into the Fatigue Countermeasures Program, emphasizing the development and evaluation of strategies to maintain alertness and performance in operational settings. Over the years, the Federal Aviation Administration (FAA) has become a collaborative partner in support of fatigue research and other Program activities. From the inception of the Program, a principal goal was to return the information learned from research and other Program activities to the operational community. The objectives of this Education and Training Module are to explain what has been learned about the physiological mechanisms that underlie fatigue, demonstrate the application of this information in flight operations, and offer some specific fatigue countermeasure recommendations. It is intended for all segments of the aeronautics industry, including pilots, flight attendants, managers, schedulers, safety and policy personnel, maintenance crews, and others involved in an operational environment that challenges human physiological capabilities because of fatigue, sleep loss, and circadian disruption.

Effects of a dance-based aquatic exercise program in obese postmenopausal women with knee osteoarthritis: a randomized controlled trial.

PubMed

Casilda-López, Jesús; Valenza, Marie Carmen; Cabrera-Martos, Irene; Díaz-Pelegrina, Ana; Moreno-Ramírez, Maria Paz; Valenza-Demet, Gerald

2017-07-01

To evaluate the effects of a dance-based aquatic exercise program on functionality, cardiorespiratory capacity, postexercise heart rate, and fatigue in obese postmenopausal women with knee osteoarthritis. A randomized controlled trial was performed. In all, 34 obese women diagnosed with knee osteoarthritis participated. Women were randomly allocated to an experimental group (n = 17) or a control group (n = 17). Participants in the experimental group were included in an 8-week dance-based aquatic exercise program conducted in community swimming pools. Those in the control group underwent a global aquatic exercise program. The primary outcome measure was functionality assessed with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Secondary outcomes were cardiorespiratory capacity evaluated with the 6-minute walk test, and postexercise heart rate and fatigue assessed using a visual analog scale. Variables were measured at baseline, after the intervention, and at 3-month follow-up. A between-group analysis showed significant postintervention differences in functionality (aggregate postintervention WOMAC score of 37.30 ± 16.61 vs 41.83 ± 13.69; P = 0.048) in favor of the experimental group. In addition, significant between-group differences were found after the 8 weeks in cardiorespiratory capacity, postexercise heart rate, and fatigue. Follow-up continued to show significant differences between groups in function (aggregate WOMAC score of 38.60 ± 13.61 vs 42.60 ± 9.05; P = 0.038), postexercise heart rate, and fatigue. An 8-week dance-based exercise program significantly improved function and cardiorespiratory capacity, and decreased postexercise heart rate and fatigue. Most of these improvements were maintained at 3-month follow-up in obese postmenopausal women.

Modeling and Prediction of Corrosion-Fatigue Failures in AF1410 Steel Test Specimens

DTIC Science & Technology

2009-01-12

PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Structures Division, Code 4.3.3 University of Dayton Research Bldg. 2187 Room 2340A Institute Naval...AND ADDRESS(ES) Office of Naval Research One Liberty Center 875 North Randolph St., Suite 1425 Arlington, VA 22203-1995 11. SPONSOR/MONITOR’S...costs. To address these issues, NAVAIR has initiated a multiyear research program to investigate and quantify the fatigue life reduction due to

Microstructurally based variations on the dwell fatgue life of titanium alloy IMI 834

NASA Technical Reports Server (NTRS)

Thomsen, Mark L.; Hoeppner, David W.

1994-01-01

An experimental study was undertaken to determine the role of microstructure on the fatigue life reduction observed in titanium alloy IMI 834 under dwell loading conditions. The wave forms compared were a trapezoid with 15 and 30 second hold times at the maximum test load and a baseline, 10 Hertz, haversine. The stress ratio for both loading wave forms was 0.10. The fatigue loading of each specimen was conducted in a vacuum within a scanning electron microscope chamber which minimized the possibility that the laboratory environment would adversely affect the material behavior. Two microstructural conditions were investigated in the experimental program. The first involved standard 'disk' material with equiaxed alpha in a transformed beta matrix. The second material was cut from the same disk forging as the first but was heat treated to obtain a martensitic alpha prime microstructure. Tensile tests were performed prior to the onset of the fatigue loading portion of the study, and it was determined that the yield strengths of the specimens from both material conditions were within ten percent. The maximum fatigue loads were chosen to be 72 percent of the average yield strength for both materials as determined from the tensile tests. It was found that the cycles to failure from the 10 Hertz loading wave form were reduced by a factor of approximately five when the loading was changed to the trapezoidal wave form for the standard 'disk' material. The fatigue life reduction for the martensitic structure under identical test conditions was approximately 1.75. The improvement observed with the martensitic structure also was accompanied by an increase in overall fatigue life for the wave forms tested. This paper will review the results and conclusions of this effort.

Successful Solutions to SSME/AT Development Turbine Blade Distress

NASA Technical Reports Server (NTRS)

Montgomery, Stuart K.

1999-01-01

As part of the High-Pressure Fuel Turbopump/Alternate Turbopump (HPFTP/AT) turbine blade development program, unique turbine blade design features were implemented to address 2nd stage turbine blade high cycle fatigue distress and improve turbine robustness. Features included the addition of platform featherseal dampers, asymmetric blade tip seal segments, gold plating of the blade attachments, and airfoil tip trailing edge modifications. Development testing shows these features have eliminated turbine blade high cycle fatigue distress and consequently these features are currently planned for incorporation to the flight configuration. Certification testing will begin in 1999. This presentation summarizes these features.

Creep fatigue life prediction for engine hot section materials (isotropic)

NASA Technical Reports Server (NTRS)

Moreno, Vito; Nissley, David; Lin, Li-Sen Jim

1985-01-01

The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.

Evaluating of NASA-Langley Research Center explosion seam welding

NASA Technical Reports Server (NTRS)

Otto, H. E.; Wittman, R.

1977-01-01

An explosion bonding technique to meet current fabrication requirements was demonstrated. A test program was conducted on explosion bonded joints, compared to fusion joints in 6061-T6 aluminum. The comparison was made in required fixtures, non-destructive testing, static strength and fatigue strength.

Effects of a resistance training program on balance and fatigue perception in patients with Parkinson's disease: A randomized controlled trial.

PubMed

Ortiz-Rubio, Araceli; Cabrera-Martos, Irene; Torres-Sánchez, Irene; Casilda-López, Jesús; López-López, Laura; Valenza, Marie Carmen

2017-11-22

Fatigue and balance impairment leads to a loss of independence and are important to adequately manage. The objective of this study was to examine the effects of a resistance training program on dynamic balance and fatigue in patients with Parkinson's disease (PD). Randomized controlled trial. Forty-six patients with PD were randomly allocated to an intervention group receiving a 8-week resistance training program focused on lower limbs or to a control group. Balance was assessed using the Mini-BESTest and fatigue was assessed by the Piper Fatigue Scale. Patients in the intervention group improved significantly (p<0.05) on dynamic balance (reactive postural control and total values) and perceived fatigue. An 8-week resistance training program was found to be effective at improving dynamic balance and fatigue in patients with PD. Copyright © 2017 Elsevier España, S.L.U. All rights reserved.

Review of sonic fatigue technology

NASA Technical Reports Server (NTRS)

Clarkson, B. L.

1994-01-01

From the early-1960s until the mid-1980s, there was very little theoretical development for sonic fatigue prediction. Design nomographs based on simple theoretical models and results of specially designed tests were developed for most common aircraft structures. The use of advanced composites in the 1980s, however, generated an increased interest in development of more sophisticated theoretical models because of the possibilities for a much wider range of structural designs. The purpose of this report is to review sonic fatigue technology and, in particular, to assess recent developments. It also suggests a plan for a coordinated program of theoretical and experimental work to meet the anticipated needs of future aerospace vehicles.

Examination of Broad Symptom Improvement Resulting From Mindfulness-Based Stress Reduction in Breast Cancer Survivors: A Randomized Controlled Trial

PubMed Central

Reich, Richard R.; Paterson, Carly L.; Ramesar, Sophia; Park, Jong Y.; Alinat, Carissa; Johnson-Mallard, Versie; Moscoso, Manolete; Budhrani-Shani, Pinky; Miladinovic, Branko; Jacobsen, Paul B.; Cox, Charles E.; Goodman, Matthew; Kip, Kevin E.

2016-01-01

Purpose The purpose of this randomized trial was to evaluate the efficacy of the Mindfulness-Based Stress Reduction for Breast Cancer (MBSR[BC]) program in improving psychological and physical symptoms and quality of life among breast cancer survivors (BCSs) who completed treatment. Outcomes were assessed immediately after 6 weeks of MBSR(BC) training and 6 weeks later to test efficacy over an extended timeframe. Patients and Methods A total of 322 BCSs were randomly assigned to either a 6-week MBSR(BC) program (n = 155) or a usual care group (n = 167). Psychological (depression, anxiety, stress, and fear of recurrence) and physical symptoms (fatigue and pain) and quality of life (as related to health) were assessed at baseline and at 6 and 12 weeks. Linear mixed models were used to assess MBSR(BC) effects over time, and participant characteristics at baseline were also tested as moderators of MBSR(BC) effects. Results Results demonstrated extended improvement for the MBSR(BC) group compared with usual care in both psychological symptoms of anxiety, fear of recurrence overall, and fear of recurrence problems and physical symptoms of fatigue severity and fatigue interference (P < .01). Overall effect sizes were largest for fear of recurrence problems (d = 0.35) and fatigue severity (d = 0.27). Moderation effects showed BCSs with the highest levels of stress at baseline experienced the greatest benefit from MBSR(BC). Conclusion The MBSR(BC) program significantly improved a broad range of symptoms among BCSs up to 6 weeks after MBSR(BC) training, with generally small to moderate overall effect sizes. PMID:27247219

[Effects of self-foot reflexology on stress, fatigue, skin temperature and immune response in female undergraduate students].

PubMed

Lee, Young-Mee

2011-02-01

The purpose of this study was to evaluate the effects of self-foot reflexology on stress (perceived stress, urine cortisol level, and serum cortisol level), fatigue, skin temperature and immune response in female undergraduate students. The research design was a nonequivalent control group pretest-post test design. Participants were 60 university students: 30 in the experiment group and 30 in the control group. The period of this study was from April to June 2010. The program was performed for 1 hr a session, three times a week for 6 weeks. The data were analyzed using the SPSS/WIN 17.0 program. The results showed that self-foot reflexology was effective in reducing perceived stress and fatigue, and raised skin temperature in female undergraduate students. But cortisol levels and immune response were not statistically significant different. The results of this study indicate that self-foot reflexology is an effective nursing intervention in reducing perceived stress and fatigue and, in improving skin temperature. Therefore, it is recommended that this be used in clinical practice as an effective nursing intervention for in female undergraduate students.

Mechanisms of deformation and fracture in high temperature low cycle fatigue of Rene 80 and IN 100

NASA Technical Reports Server (NTRS)

Romanoski, G. R., Jr.

1982-01-01

Specimens tested for the AGARD strain range partitioning program were investigated. Rene 80 and IN 100 were tested in air and in vacuum; at 871 C, 925 C, and 1000 C; and in the coated and uncoated condition. The specimens exhibited a multiplicity of high-temperature low-cycle fatigue damage. Observations of the various forms of damage were consistent with material and testing conditions and were generally in agreement with previous studies. In every case observations support a contention that failure occurs at a particular combination of crack length and maximum stress. A failure criterion which is applicable in the regime of testing studied is presented. The predictive capabilities of this criterion are straight forward.

Fatigue and fracture assessment of cracks in steel elements using acoustic emission

NASA Astrophysics Data System (ADS)

Nemati, Navid; Metrovich, Brian; Nanni, Antonio

2011-04-01

Single edge notches provide a very well defined load and fatigue crack size and shape environment for estimation of the stress intensity factor K, which is not found in welded elements. ASTM SE(T) specimens do not appear to provide ideal boundary conditions for proper recording of acoustic wave propagation and crack growth behavior observed in steel bridges, but do provide standard fatigue crack growth rate data. A modified versions of the SE(T) specimen has been examined to provide small scale specimens with improved acoustic emission(AE) characteristics while still maintaining accuracy of fatigue crack growth rate (da/dN) versus stress intensity factor (ΔK). The specimens intend to represent a steel beam flange subjected to pure tension, with a surface crack growing transverse to a uniform stress field. Fatigue test is conducted at low R ratio. Analytical and numerical studies of stress intensity factor are developed for single edge notch test specimens consistent with the experimental program. ABAQUS finite element software is utilized for stress analysis of crack tips. Analytical, experimental and numerical analysis were compared to assess the abilities of AE to capture a growing crack.

Graphite fiber reinforced thermoplastic resins

NASA Technical Reports Server (NTRS)

Navak, R. C.

1977-01-01

The results of a program designed to optimize the fabrication procedures for graphite thermoplastic composites are described. The properties of the composites as a function of temperature were measured and graphite thermoplastic fan exit guide vanes were fabricated and tested. Three thermoplastics were included in the investigation: polysulfone, polyethersulfone, and polyarylsulfone. Type HMS graphite was used as the reinforcement. Bending fatigue tests of HMS graphite/polyethersulfone demonstrated a gradual shear failure mode which resulted in a loss of stiffness in the specimens. Preliminary curves were generated to show the loss in stiffness as a function of stress and number of cycles. Fan exit guide vanes of HMS graphite polyethersulfone were satisfactorily fabricated in the final phase of the program. These were found to have stiffness and better fatigue behavior than graphite epoxy vanes which were formerly bill of material.

Materials research for high-speed civil transport and generic hypersonics: Composites durability

NASA Technical Reports Server (NTRS)

Allen-Lilly, Heather; Cregger, Eric; Hoffman, Daniel; Mccool, Jim

1995-01-01

This report covers a portion of an ongoing investigation of the durability of composites for the High Speed Civil Transport (HSCT) program. Candidate HSCT composites need to possess the high-temperature capability required for supersonic flight. This program was designed to initiate the design, analysis, fabrication, and testing of equipment intended for use in validating the long-term durability of materials for the HSCT. This equipment includes thermally actuated compression and tension fixtures, hydraulic-actuated reversible load fixtures, and thermal chambers. This equipment can be used for the durability evaluation of both composite and adhesive materials. Thermally actuated fixtures are recommended for fatigue cycling when long-term thermomechanical fatigue (TMF) data are required on coupon-sized tension or compression specimens. Long term durability testing plans for polymer matrix composite specimens are included.

Cancer-related fatigue management: evaluation of a patient education program with a large-scale randomised controlled trial, the PEPs fatigue study.

PubMed

Bourmaud, A; Anota, A; Moncharmont, C; Tinquaut, F; Oriol, M; Trillet-Lenoir, V; Bajard, A; Parnalland, S; Rotonda, C; Bonnetain, F; Pérol, D; Chauvin, F

2017-03-28

To assess the efficacy of a patient educational program built according to guidelines that aims at reducing cancer-related fatigue (CRF). Randomised controlled trial, multicentre, comparing a patient education program, vs the standard of care. Patients were adult cancer outpatients with any tumour site. The primary outcome was fatigue severity assessed with a visual analogical scale (VAS), between the day of randomisation and week 7. Secondary outcomes were fatigue assessed with other scales, health-related quality of life, anxiety and depression. The time to fatigue severity deterioration was assessed. Analyses were performed in a modified intent-to-treat way, that is, including all patients with at least one baseline and 1 week 7 score. A total of 212 patients were included. Fatigue severity assessment was made on 79 patients in the experimental group and 65 in the control group. Between randomisation and week 7, the fatigue (VAS) improved by 0.96 (2.85) points in the experimental group vs 1.63 (2.63) points in the control group (P=0.15). No differences with the secondary outcomes were highlighted between two groups. No other factors were found to be associated with fatigue severity deterioration. Despite rigorous methodology, this study failed to highlight the program efficacy in fatigue reduction for cancer patients. Other assessment tools should be developed to measure the effect of the program on CRF and behaviour. The implementation of the program should also be explored in order to identify its mechanisms and longer-term impact.

Cancer-related fatigue management: evaluation of a patient education program with a large-scale randomised controlled trial, the PEPs fatigue study

PubMed Central

Bourmaud, A; Anota, A; Moncharmont, C; Tinquaut, F; Oriol, M; Trillet-Lenoir, V; Bajard, A; Parnalland, S; Rotonda, C; Bonnetain, F; Pérol, D; Chauvin, F

2017-01-01

Background: To assess the efficacy of a patient educational program built according to guidelines that aims at reducing cancer-related fatigue (CRF). Methods: Randomised controlled trial, multicentre, comparing a patient education program, vs the standard of care. Patients were adult cancer outpatients with any tumour site. The primary outcome was fatigue severity assessed with a visual analogical scale (VAS), between the day of randomisation and week 7. Secondary outcomes were fatigue assessed with other scales, health-related quality of life, anxiety and depression. The time to fatigue severity deterioration was assessed. Analyses were performed in a modified intent-to-treat way, that is, including all patients with at least one baseline and 1 week 7 score. Results: A total of 212 patients were included. Fatigue severity assessment was made on 79 patients in the experimental group and 65 in the control group. Between randomisation and week 7, the fatigue (VAS) improved by 0.96 (2.85) points in the experimental group vs 1.63 (2.63) points in the control group (P=0.15). No differences with the secondary outcomes were highlighted between two groups. No other factors were found to be associated with fatigue severity deterioration. Conclusions: Despite rigorous methodology, this study failed to highlight the program efficacy in fatigue reduction for cancer patients. Other assessment tools should be developed to measure the effect of the program on CRF and behaviour. The implementation of the program should also be explored in order to identify its mechanisms and longer-term impact. PMID:28196066

Feasibility, Validity, and Reliability of the Italian Pediatric Quality of Life Inventory Multidimensional Fatigue Scale for Adults in Inpatients with Severe Obesity

PubMed Central

Manzoni, Gian Mauro; Rossi, Alessandro; Marazzi, Nicoletta; Agosti, Fiorenza; De Col, Alessandra; Pietrabissa, Giada; Castelnuovo, Gianluca; Molinari, Enrico; Sartorio, Allessandro

2018-01-01

Objective This study was aimed to examine the feasibility, validity, and reliability of the Italian Pediatric Quality of Life Inventory Multidimensional Fatigue Scale (PedsQL™ MFS) for adult inpatients with severe obesity. Methods 200 inpatients (81% females) with severe obesity (BMI ≥ 35 kg/m2) completed the PedsQL MFS (General Fatigue, Sleep/Rest Fatigue and Cognitive Fatigue domains), the Fatigue Severity Scale, and the Center for Epidemiologic Studies Depression Scale immediately after admission to a 3-week residential body weight reduction program. A randomized subsample of 48 patients re-completed the PedsQL MFS after 3 days. Results Confirmatory factor analysis showed that a modified hierarchical model with two items moved from the Sleep/Rest Fatigue domain to the General Fatigue domain and a second-order latent factor best fitted the data. Internal consistency and test-retest reliabilities were acceptable to high in all scales, and small to high statistically significant correlations were found with all convergent measures, with the exception of BMI. Significant floor effects were found in two scales (Cognitive Fatigue and Sleep/Rest Fatigue). Conclusion The Italian modified PedsQL MFS for adults showed to be a valid and reliable tool for the assessment of fatigue in inpatients with severe obesity. Future studies should assess its discriminant validity as well as its responsiveness to weight reduction. PMID:29402854

Education and Training Module in Alertness Management

NASA Technical Reports Server (NTRS)

Mallis, M. M.; Brandt, S. L.; Oyung, R. L.; Reduta, D. D.; Rosekind, M. R.

2006-01-01

The education and training module (ETM) in alertness management has now been integrated as part of the training regimen of the Pilot Proficiency Awards Program ("WINGS") of the Federal Aviation Administration. Originated and now maintained current by the Fatigue Countermeasures Group at NASA Ames Research Center, the ETM in Alertness Management is designed to give pilots the benefit of the best and most recent research on the basics of sleep physiology, the causes of fatigue, and strategies for managing alertness during flight operations. The WINGS program is an incentive program that encourages pilots at all licensing levels to participate in recurrent training, upon completion of which distinctive lapel or tie pins (wings) and certificates of completion are awarded. In addition to flight training, all WINGS applicants must attend at least one FAA-sponsored safety seminar, FAA-sanctioned safety seminar, or industry recurrent training program. The Fatigue Countermeasures Group provides an FAA-approved industry recurrent training program through an on-line General Aviation (GA) WINGS ETM in alertness management to satisfy this requirement. Since 1993, the Fatigue Countermeasures Group has translated fatigue and alertness information to operational environments by conducting two-day ETM workshops oriented primarily toward air-carrier operations subject to Part 121 of the Federal Aviation Regulations pertaining to such operations. On the basis of the information presented in the two-day ETM workshops, an ETM was created for GA pilots and was transferred to a Web-based version. To comply with the requirements of the WINGS Program, the original Web-based version has been modified to include hypertext markup language (HTML) content that makes information easily accessible, in-depth testing of alertness-management knowledge, new interactive features, and increased informational resources for GA pilots. Upon successful completion of this training module, a participant receives a computer- screen display of a certificate of completion. The certificate, which includes the pilot s name and an identifying number, can be printed out and submitted, for ground training credit, with the pilot s WINGS application.

Randomized Controlled Trial to Examine the Impact of Aquatic Exercise Training on Functional Capacity, Balance, and Perceptions of Fatigue in Female Patients With Multiple Sclerosis.

PubMed

Kargarfard, Mehdi; Shariat, Ardalan; Ingle, Lee; Cleland, Joshua A; Kargarfard, Mina

2018-02-01

To assess the effects of an 8-week aquatic exercise training program on functional capacity, balance, and perceptions of fatigue in women with multiple sclerosis (MS). Randomized controlled design. Referral center of an MS society. Women (N=32; mean age ± SD, 36.4±8.2y) with diagnosed relapsing-remitting MS. After undergoing baseline testing by a neurologist, participants were allocated to either an intervention (aquatic training program, n=17) or a control group (n=15). The intervention consisted of an 8-week aquatic training program (3 supervised training sessions per week; session duration, 45-60min; 50%-75% estimated maximum heart rate). Six-minute walk test (6-MWT), balance (Berg Balance Scale [BBS]), and perceptions of fatigue (Modified Fatigue Impact Scale; [MFIS]) at baseline and after the 8-week intervention. Differences over time between the experimental and control groups were assessed by a 2×2 (group by time) repeated-measures analysis of variance. Thirty-two women completed the 8-week aquatic training intervention (experimental group, n=17; control group, n=15). All outcome measures improved in the experimental group: 6-MWT performance (pretest mean ± SD, 451±58m; posttest mean ± SD, 503±57m; P<.001); BBS (pretest mean ± SD, 53.59±1.70; posttest mean ± SD, 55.18±1.18; P<.001), and MFIS (pretest mean ± SD, 43.1±14.6; posttest mean ± SD, 32.8±5.9; P<.01). A significant group-by-time interaction was evident between the experimental and control groups for 6-MWT (P<.001, partial eta 2 [η p 2 ]=.551), BBS (P<.001, η p 2 =.423), and MFIS (P<.001, η p 2 =.679). Aquatic exercise training improved functional capacity, balance, and perceptions of fatigue in women with MS. Copyright © 2017 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

Resilient modulus and fatigue life characterization of asphalt concrete mixtures used in the Ohio Test Road : special student study

DOT National Transportation Integrated Search

1998-05-01

The performance of flexible and rigid pavements depends not only on the effects of traffic but also on environmental effects. As part of the Federal Highway Administration's (FHWA) Strategic Highway Research Program (SHRP), a test road was recently c...

Thermal fatigue and oxidation data for alloy/braze combinations

NASA Technical Reports Server (NTRS)

Hill, V. L.; Humphreys, V. E.

1977-01-01

Thermal fatigue and oxidation data were obtained for 62 brazed specimens of 3 iron-, 3 nickel-, and 1 cobalt-base alloy. Fluidized bed thermal cycling was conducted over the range 740/25 C employing 10 cm long single-edge wedge specimens. Immersion time was always 4 minutes in each bed. Types of test specimens employed in the program include those with brazed overlays on the specimen radius, those butt brazed at midspan and those with a brazed foil overlay on the specimen radius. Of the 18 braze overlay specimens, 5 generated fatigue cracks by 7000 cycles. Thermal cracking of butt brazed specimens occurred exclusively through the butt braze. Of the 23 butt brazed specimens, 7 survived 11,000 thermal cycles without cracking. Only 2 of the 21 foil overlaid specimens exhibiting cracking in 7,000 cycles. Blistering of the foil did occur for 2 alloys by 500 cycles. Oxidation of the alloy/braze combination was limited at the test maximum test temperature of 740 C.

A multicenter randomized controlled trial of two group education programs for fatigue in multiple sclerosis: Long-term (12-month) follow-up at one site.

PubMed

Hugos, Cinda L; Cameron, Michelle H; Chen, Zunqiu; Chen, Yiyi; Bourdette, Dennis

2018-05-01

A four-site RCT of Fatigue: Take Control (FTC), a multicomponent group program, found no significant differences from a control program, MS: Take Control (MSTC), in fatigue on the Modified Fatigue Impact Scale (MFIS) through 6 months. Assess FTC for a delayed effect on fatigue. Of 78 subjects at one site, 74 randomized to FTC or MSTC completed the MFIS at 12 months. Compared to baseline, FTC produced greater improvements in MFIS scores than MSTC (FTC -8.9 (confidence interval (CI): 32.2, 45), MSTC -2.5 (CI 39.6, 47.7), p = 0.03) at 12 months. The delayed effect of FTC on fatigue suggests the need for longer follow-up when assessing interventions for fatigue.

Shot peening for Ti-6Al-4V alloy compressor blades

NASA Technical Reports Server (NTRS)

Carek, Gerald A.

1987-01-01

A text program was conducted to determine the effects of certain shot-peening parameters on the fatigue life of the Ti-6Al-4V alloys as well as the effect of a demarcation line on a test specimen. This demarcation line, caused by an abrupt change from untreated surface to shot-peened surface, was thought to have caused the failure of several blades in a multistage compressor at the NASA Lewis Research Center. The demarcation line had no detrimental effect upon bending fatigue specimens tested at room temperature. Procedures for shot peening Ti-6Al-4V compressor blades are recommended for future applications.

NASA Langley Research Center's Contributions to International Active Buffeting Alleviation Programs

NASA Technical Reports Server (NTRS)

Moses, Robert W.

2000-01-01

Buffeting is an aeroelastic phenomenon which plagues high performance aircraft, especially those with twin vertical tails like the F/A-18, at high angles of attack. This buffeting is a concern from fatigue and inspection points of view. By means of wind-tunnel and flight tests, this phenomenon is well studied to the point that buffet loads can be estimated and fatigue life can be increased by structural enhancements to the airframe. In more recent years, buffeting alleviation through active control of smart materials has been highly researched in wind-tunnel proof-of-concept demonstrations and full-scale ground tests using the F/A-18 as a test bed. Because the F/A-18 resides in fleets outside as well as inside the United States, these tests have evolved into international collaborative research activities with Australia and Canada, coordinated by the Air Force Research Laboratory (AFRL) and conducted under the auspices of The Technical Cooperation Program (TTCP). With the recent successes and advances in smart materials, the main focus of these buffeting alleviation tests has also evolved to a new level: utilize the F/A-18 as a prototype to mature smart materials for suppressing vibrations of aerospace structures. The role of the NASA Langley Research Center (LaRC) in these programs is presented.

Contributions to Active Buffeting Alleviation Programs by the NASA Langley Research Center

NASA Technical Reports Server (NTRS)

Moses, Robert W.

1999-01-01

Buffeting is an aeroelastic phenomenon which plagues high performance aircraft, especially those with twin vertical tails like the F/A-18, at high angles of attack. This buffeting is a concern from fatigue and inspection points of view. By means of wind-tunnel and flight tests, this phenomenon is well studied to the point that buffet loads can be estimated and fatigue life can be increased by structural enhancements to the airframe. In more recent years, buffeting alleviation through active control of smart materials has been highly researched in wind-tunnel proof-of-concept demonstrations and full-scale ground tests using the F/A-18 as a test bed. Because the F/A-18 resides in fleets outside as well as inside the United States, these tests have evolved into international collaborative research activities with Australia and Canada, coordinated by the Air Force Research Laboratory (AFRL) and conducted under the auspices of The Technical Cooperation Program (TTCP). With the recent successes and advances in smart materials, the main focus of these buffeting alleviation tests has also evolved to a new level: utilize the F/A-18 as a prototype to mature smart materials for suppressing vibrations of aerospace structures. The role of the NASA Langley Research Center (LaRC) in these programs is presented.

Effects of High Mean Stress on High-cycle Fatigue Behavior of PWA 1480

NASA Technical Reports Server (NTRS)

Majumdar, S.; Antolovich, S. D.; Milligan, W. W.

1985-01-01

PWA 1480 is a potential candidate material for use in the high-pressure fuel turbine blade of the space shuttle main engine. As an engine material it will be subjected to high-cycle fatigue loading superimposed on a high mean stress due to combined centrifugal and thermal loadings. The present paper describes the results obtained in an ongoing program at the Argonne National Laboratory, sponsored by NASA Lewis, to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material. Straight-gauge high-cycle fatigue specimens, 0.2 inch in diameter and with the specimen axis in the 001 direction, were supplied by NASA Lewis. The nominal room temperature yield and ultimate strength of the material were 146 and 154 ksi, respectively. Each specimen was polished with 1-micron diamond paste prior to testing. However, the surface of each specimen contained many pores, some of which were as large as 50 micron. In the initial tests, specimens were subjected to axial-strain-controlled cycles. However, very little cyclic plasticity was observed.

Fracture mechanics life analytical methods verification testing

NASA Technical Reports Server (NTRS)

Favenesi, J. A.; Clemons, T. G.; Riddell, W. T.; Ingraffea, A. R.; Wawrzynek, P. A.

1994-01-01

The objective was to evaluate NASCRAC (trademark) version 2.0, a second generation fracture analysis code, for verification and validity. NASCRAC was evaluated using a combination of comparisons to the literature, closed-form solutions, numerical analyses, and tests. Several limitations and minor errors were detected. Additionally, a number of major flaws were discovered. These major flaws were generally due to application of a specific method or theory, not due to programming logic. Results are presented for the following program capabilities: K versus a, J versus a, crack opening area, life calculation due to fatigue crack growth, tolerable crack size, proof test logic, tearing instability, creep crack growth, crack transitioning, crack retardation due to overloads, and elastic-plastic stress redistribution. It is concluded that the code is an acceptable fracture tool for K solutions of simplified geometries, for a limited number of J and crack opening area solutions, and for fatigue crack propagation with the Paris equation and constant amplitude loads when the Paris equation is applicable.

Low dynamic muscle strength and its associations with fatigue, functional performance, and quality of life in premenopausal patients with systemic lupus erythematosus and low disease activity: a case–control study

PubMed Central

2013-01-01

Background The purpose of the present study was to compare dynamic muscle strength, functional performance, fatigue, and quality of life in premenopausal systemic lupus erythematosus (SLE) patients with low disease activity versus matched-healthy controls and to determine the association of dynamic muscle strength with fatigue, functional performance, and quality of life in SLE patients. Methods We evaluated premenopausal (18–45 years) SLE patients with low disease activity (Systemic lupus erythematosus disease activity index [SLEDAI]: mean 1.5 ± 1.2). The control (n = 25) and patient (n = 25) groups were matched by age, physical characteristics, and the level of physical activities in daily life (International Physical Activity Questionnaire IPAQ). Both groups had not participated in regular exercise programs for at least six months prior to the study. Dynamic muscle strength was assessed by one-repetition maximum (1-RM) tests. Functional performance was assessed by the Timed Up and Go (TUG), in 30-s test a chair stand and arm curl using a 2-kg dumbbell and balance test, handgrip strength and a sit-and-reach flexibility test. Quality of life (SF-36) and fatigue were also measured. Results The SLE patients showed significantly lower dynamic muscle strength in all exercises (leg press 25.63%, leg extension 11.19%, leg curl 15.71%, chest press 18.33%, lat pulldown 13.56%, 1-RM total load 18.12%, P < 0.001-0.02) compared to the controls. The SLE patients also had lower functional performance, greater fatigue and poorer quality of life. In addition, fatigue, SF-36 and functional performance accounted for 52% of the variance in dynamic muscle strength in the SLE patients. Conclusions Premenopausal SLE patients with low disease activity showed lower dynamic muscle strength, along with increased fatigue, reduced functional performance, and poorer quality of life when compared to matched controls. PMID:24011222

Lower rate-pressure product during submaximal walking: a link to fatigue improvement following a physical activity intervention among breast cancer survivors.

PubMed

Carter, Stephen J; Hunter, Gary R; McAuley, Edward; Courneya, Kerry S; Anton, Philip M; Rogers, Laura Q

2016-10-01

Research showing a link between exercise-induced changes in aerobic fitness and reduced fatigue after a cancer diagnosis has been inconsistent. We evaluated associations of fatigue and rate-pressure product (RPP), a reliable index of myocardial oxygen demand, at rest and during submaximal walking following a physical activity intervention among post-primary treatment breast cancer survivors (BCS). Secondary analyses of 152 BCS in a randomized controlled trial testing a physical activity intervention (INT) versus usual care (UC) were performed. The INT group completed counseling/group discussions along with supervised exercise sessions tapered to unsupervised exercise. Evaluations were made at baseline and immediately post-intervention (M3) on measures of physical activity (accelerometry), graded walk test, and average fatigue over the previous 7 days. RPP was calculated by dividing the product of heart rate and systolic blood pressure by 100. Resting and submaximal RPPs were significantly improved in both groups at M3; however, the magnitude of change (∆) was greater in the INT group from stage 1 (∆RPP1; INT -13 ± 17 vs. UC -7 ± 18; p = 0.03) through stage 4 (∆RPP4; INT -21 ± 26 vs. UC -9 ± 24; p < 0.01) of the walk test. The INT group reported significantly reduced fatigue (INT -0.7 ± 2.0 vs. UC +0.1 ± 2.0; p = 0.02) which was positively associated with ∆RPP during stages 2-4 of the walk test but not ∆aerobic fitness. Lower RPP during submaximal walking was significantly associated with reduced fatigue in BCS. Exercise/physical activity training programs that lower the physiological strain during submaximal walking may produce the largest improvements in reported fatigue.

Effectiveness of a tailored neck training program on neck strength, movement, and fatigue in under-19 male rugby players: a randomized controlled pilot study.

PubMed

Barrett, Matthew D; McLoughlin, Terence F; Gallagher, Kieran R; Gatherer, Don; Parratt, Michael Tr; Perera, Jonathan R; Briggs, Tim Wr

2015-01-01

To investigate the effect of a tailored neck muscle conditioning program on neck muscle strength, neck muscle fatigue, and range of neck movement in 16-18-year-old male rugby players. Thirty-four male rugby players were divided into forward and back playing positions and randomized within these groups. Seventeen players were randomly assigned to each group. The test group was given a tailored 6-week exercise regime based on their baseline measurements to be performed three times a week in addition to their normal training and playing. The control group trained and played as normal. The outcome measures used were cervical spine range of movement, neck strength, and neck muscle fatigability. There were no clinically relevant statistically significant differences between the two groups. Trends identified between the two groups suggest that a tailored neck exercise program increases neck strength, particularly neck extension, and increases resistance to fatigue, as well as influencing right- and left-sided neck muscle balance. A reduction in range of movement was also demonstrated in the test group. There was a great deal of variability in range of movement and strength within this age group. No previously undiagnosed neck conditions were detected, and there were no adverse events reported. This study has shown that neck strength, range of movement, and susceptibility of the neck muscles to fatigue can be influenced using a focused neck training regime. It forms an important basis for a larger, multicenter study to ensure the neck is given due attention in rugby training and receives the same focus of conditioning as other parts of the body.

Fatigue of graphite/epoxy buffer strip panels with center cracks

NASA Technical Reports Server (NTRS)

Bigelow, C. A.

1985-01-01

The effects of fatigue loading on the behavior of graphite/epoxy panels with either S-Glass or Kevlar-49 buffer strips is studied. Buffer strip panels are fatigued and tested in tension to measure their residual strength with crack-like damage. Panels are made with 45/0/-45/90 sub 2s layup with either S-Glass or Kevlar-49 buffer strip material. The buffer strips are parallel to the loading direction and made by replacing narrow strips of the 0-degree graphite plies with strips of either 0-degree S-Glass/epoxy or Kevlar-49/epoxy on a one-for-one basis. The panels are subjected to a fatigue loading spectrum MINITWIST, the shortened version of the standardized load program for the wing lower surface of a transport aircraft. Two levels of maximum strain are used in the spectrum with three durations of the fatigue spectrum. One group of panels is preloaded prior to the application of the fatigue cycling. The preload consists of statistically loading the spectrum in tension until the crack-tip damage zone reaches the ajacent buffer strips. After fatigue loading, all specimens are statistically loaded in tension to failure to determine their residual strengths.

Boron/aluminum skins for the DC-10 aft pylon

NASA Technical Reports Server (NTRS)

Elliott, S. Y.

1975-01-01

Boron/aluminum pylon boat tail skins were designed and fabricated and installed on the DC-10 aircraft for a 5-year flight service demonstration test. Inspection and tests of the exposed skins will establish the ability of the boron/aluminum composite to withstand long time flight service conditions, which include exposure to high temperatures, sonic fatigue, and flutter. The results of a preliminary testing program yield room temperature and elevated temperature data on the tension, compression, in-plane shear, interlaminar shear, bolt bearing, and tension fatigue properties of the boron/aluminum laminates. Present technology was used in the fabrication of the skins. Although maximum weight saving was not sought, weight of the constant thickness boron/aluminum skin is 26% less than the chemically milled titanium skin.

Protocol for the "four steps to control your fatigue (4-STEPS)" randomised controlled trial: a self-regulation based physical activity intervention for patients with unexplained chronic fatigue

PubMed Central

2012-01-01

Background Unexplained Chronic Fatigue is a medical condition characterized by the presence of persistent, severe and debilitating medically unexplained fatigue, leading to impaired functioning and lower quality of life. Research suggests that physical activity can contribute to the reduction of fatigue and other somatic symptoms and can thus significantly improve physical functioning and quality of life in these patients. Based on the self-regulation (SR) theory of behaviour change, we developed a brief physical activity program for patients suffering from unexplained chronic fatigue which focuses on the training of self-regulation skills, the "4-STEPS to control your fatigue" program. Methods/Design This is a multi-centre, randomised controlled trial (RCT) that will be carried out in local primary care centres and at the Portuguese Fibromyalgia and Chronic Fatigue Syndrome Patients Association. Patients aged between 18 and 65 and fulfilling operationalized criteria for Idiopathic Chronic Fatigue (ICF) and Chronic Fatigue Syndrome (CFS) will be recruited and randomly allocated to standard care (SC) or standard care plus a self-regulation based physical activity program (4-STEPS). Patients will be assessed at baseline, after the intervention (3 months) and at 12 months follow-up. The primary outcome is fatigue severity. Discussion The results of the RCT will provide information about the effectiveness of a brief self-regulation intervention for promoting physical activity in patients with unexplained chronic fatigue. If the program proves to be effective, it may be considered as an adjunctive treatment for these patients. Trial Registration ISRCTN: ISRCTN70763996 PMID:22429404

Fatigue Countermeasures: Alertness Management in Flight Operations

NASA Technical Reports Server (NTRS)

Co, E. L.; Rosekind, M. R.; Johnson, J. M.; Weldon, K. J.; Smith, R. M.; Gregory, K. G.; Miller, D. L.; Gander, P. H.; Lebacqz, J. V.; Statler, Irving C. (Technical Monitor)

1994-01-01

Since 1980, the NASA Ames Fatigue Countermeasures Program has studied the effects and impact of fatigue on flight operations . Sleep loss and circadian disruption are two of the primary physiological factors that underlie fatigue in flight operations. The Program has developed an array of fatigue countermeasure recommendations that can be used to combat the effects of fatigue and continues to research potential new countermeasures. For example, one such strategy involved a NASA/FAA study on the effects of planned cockpit rest to improve crewmember alertness and performance. Based partly on the study results, the FAA is currently reviewing a proposed Advisory Circular for controlled rest on the flight deck. Since there is no simple answer to the issue of fatigue in aviation, an Education and Training Module has been developed to provide the industry with pertinent information on sleep, circadian rhythms, how flight operations affect these physiological factors, and recommendations for fatigue countermeasures. The Module will be updated as the Program's continued research efforts uncover new information and develop new countermeasure strategies,

Feasibility, Validity, and Reliability of the Italian Pediatric Quality of Life Inventory Multidimensional Fatigue Scale for Adults in Inpatients with Severe Obesity.

PubMed

Manzoni, Gian Mauro; Rossi, Alessandro; Marazzi, Nicoletta; Agosti, Fiorenza; De Col, Alessandra; Pietrabissa, Giada; Castelnuovo, Gianluca; Molinari, Enrico; Sartorio, Allessandro

2018-01-01

This study was aimed to examine the feasibility, validity, and reliability of the Italian Pediatric Quality of Life Inventory Multidimensional Fatigue Scale (PedsQL™ MFS) for adult inpatients with severe obesity. 200 inpatients (81% females) with severe obesity (BMI ≥ 35 kg/m2) completed the PedsQL MFS (General Fatigue, Sleep/Rest Fatigue and Cognitive Fatigue domains), the Fatigue Severity Scale, and the Center for Epidemiologic Studies Depression Scale immediately after admission to a 3-week residential body weight reduction program. A randomized subsample of 48 patients re-completed the PedsQL MFS after 3 days. Confirmatory factor analysis showed that a modified hierarchical model with two items moved from the Sleep/Rest Fatigue domain to the General Fatigue domain and a second-order latent factor best fitted the data. Internal consistency and test-retest reliabilities were acceptable to high in all scales, and small to high statistically significant correlations were found with all convergent measures, with the exception of BMI. Significant floor effects were found in two scales (Cognitive Fatigue and Sleep/Rest Fatigue). The Italian modified PedsQL MFS for adults showed to be a valid and reliable tool for the assessment of fatigue in inpatients with severe obesity. Future studies should assess its discriminant validity as well as its responsiveness to weight reduction. © 2018 The Author(s) Published by S. Karger GmbH, Freiburg.

Hydraulic Fatigue-Testing Machine

NASA Technical Reports Server (NTRS)

Hodo, James D.; Moore, Dennis R.; Morris, Thomas F.; Tiller, Newton G.

1987-01-01

Fatigue-testing machine applies fluctuating tension to number of specimens at same time. When sample breaks, machine continues to test remaining specimens. Series of tensile tests needed to determine fatigue properties of materials performed more rapidly than in conventional fatigue-testing machine.

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.

Quiet Clean Short-haul Experimental Engine (QCSEE) under-the-wing engine composite fan blade: Preliminary design test report

NASA Technical Reports Server (NTRS)

1975-01-01

Results of tests conducted on preliminary design polymeric-composite fan blade for the under the wing (UTW) OCSEE engine are presented. During this phase of the program a total of 17preliminary OCSEE UTW composite fan blades were manufactured for various component tests including frequency characteristics, strain distribution, bench fatigue, dovetail pull, whirligig overspeed and whirligig impact. All tests were successfully completed with the exception of whirligig impact tests. Improvements in local impact capability are being evaluated for the OCSEE blade under other NASA and related programs.

Effects of soluble milk protein or casein supplementation on muscle fatigue following resistance training program: a randomized, double-blind, and placebo-controlled study

PubMed Central

2014-01-01

Background The effects of protein supplementation on muscle thickness, strength and fatigue seem largely dependent on its composition. The current study compared the effects of soluble milk protein, micellar casein, and a placebo on strength and fatigue during and after a resistance training program. Methods Sixty-eight physically active men participated in this randomized controlled trial and underwent 10 weeks of lower-body resistance training. Participants were randomly assigned to the Placebo (PLA), Soluble Milk Protein (SMP, with fast digestion rate) or Micellar Casein (MC, with slow digestion rate) group. During the 10-week training period, participants were instructed to take 30 g of the placebo or protein twice a day, or three times on training days. Tests were performed on quadriceps muscles at inclusion (PRE), after 4 weeks (MID) and after 10 weeks (POST) of training. They included muscle endurance (maximum number of repetitions during leg extensions using 70% of the individual maximal load), fatigue (decrease in muscle power after the endurance test), strength, power and muscle thickness. Results Muscle fatigue was significantly lower (P < 0.05) in the SMP group at MID and POST (-326.8 ± 114.1 W and -296.6 ± 130.1 W, respectively) as compared with PLA (-439.2 ± 153.9 W and -479.2 ± 138.1 W, respectively) and MC (-415.1 ± 165.1 W and -413.7 ± 139.4 W, respectively). Increases in maximal muscle power, strength, endurance and thickness were not statistically different between groups. Conclusions The present study demonstrated that protein composition has a large influence on muscular performance after prolonged resistance training. More specifically, as compared with placebo or micellar casein, soluble milk protein (fast digestible) appeared to significantly reduce muscle fatigue induced by intense resistance exercise. PMID:25057266

Effects of soluble milk protein or casein supplementation on muscle fatigue following resistance training program: a randomized, double-blind, and placebo-controlled study.

PubMed

Babault, Nicolas; Deley, Gaëlle; Le Ruyet, Pascale; Morgan, François; Allaert, François André

2014-01-01

The effects of protein supplementation on muscle thickness, strength and fatigue seem largely dependent on its composition. The current study compared the effects of soluble milk protein, micellar casein, and a placebo on strength and fatigue during and after a resistance training program. Sixty-eight physically active men participated in this randomized controlled trial and underwent 10 weeks of lower-body resistance training. Participants were randomly assigned to the Placebo (PLA), Soluble Milk Protein (SMP, with fast digestion rate) or Micellar Casein (MC, with slow digestion rate) group. During the 10-week training period, participants were instructed to take 30 g of the placebo or protein twice a day, or three times on training days. Tests were performed on quadriceps muscles at inclusion (PRE), after 4 weeks (MID) and after 10 weeks (POST) of training. They included muscle endurance (maximum number of repetitions during leg extensions using 70% of the individual maximal load), fatigue (decrease in muscle power after the endurance test), strength, power and muscle thickness. Muscle fatigue was significantly lower (P < 0.05) in the SMP group at MID and POST (-326.8 ± 114.1 W and -296.6 ± 130.1 W, respectively) as compared with PLA (-439.2 ± 153.9 W and -479.2 ± 138.1 W, respectively) and MC (-415.1 ± 165.1 W and -413.7 ± 139.4 W, respectively). Increases in maximal muscle power, strength, endurance and thickness were not statistically different between groups. The present study demonstrated that protein composition has a large influence on muscular performance after prolonged resistance training. More specifically, as compared with placebo or micellar casein, soluble milk protein (fast digestible) appeared to significantly reduce muscle fatigue induced by intense resistance exercise.

Damage tolerance certification of a fighter horizontal stabilizer

NASA Astrophysics Data System (ADS)

Huang, Jia-Yen; Tsai, Ming-Yang; Chen, Jong-Sheng; Ong, Ching-Long

1995-05-01

A review of the program for the damage tolerance certification test of a composite horizontal stabilizer (HS) of a fighter is presented. The object of this program is to certify that the fatigue life and damage tolerance strength of a damaged composite horizontal stabilizer meets the design requirements. According to the specification for damage tolerance certification, a test article should be subjected to two design lifetimes of flight-by-flight load spectra simulating the in-service fatigue loading condition for the aircraft. However, considering the effect of environmental change on the composite structure, one additional lifetime test was performed. In addition, to evaluate the possibilities for extending the service life of the structure, one more lifetime test was carried out with the spectrum increased by a factor of 1.4. To assess the feasibility and reliability of repair technology on a composite structure, two damaged areas were repaired after two lifetimes of damage tolerance test. On completion of four lifetimes of the damage tolerance test, the static residual strength was measured to check whether structural strength after repair met the requirements. Stiffness and static strength of the composite HS with and without damage were evaluated and compared.

A randomized controlled trial of qigong exercise on fatigue symptoms, functioning, and telomerase activity in persons with chronic fatigue or chronic fatigue syndrome.

PubMed

Ho, Rainbow T H; Chan, Jessie S M; Wang, Chong-Wen; Lau, Benson W M; So, Kwok Fai; Yuen, Li Ping; Sham, Jonathan S T; Chan, Cecilia L W

2012-10-01

Chronic fatigue is common in the general population. Complementary therapies are often used by patients with chronic fatigue or chronic fatigue syndrome to manage their symptoms. This study aimed to assess the effect of a 4-month qigong intervention program among patients with chronic fatigue or chronic fatigue syndrome. Sixty-four participants were randomly assigned to either an intervention group or a wait list control group. Outcome measures included fatigue symptoms, physical functioning, mental functioning, and telomerase activity. Fatigue symptoms and mental functioning were significantly improved in the qigong group compared to controls. Telomerase activity increased in the qigong group from 0.102 to 0.178 arbitrary units (p < 0.05). The change was statistically significant when compared to the control group (p < 0.05). Qigong exercise may be used as an alternative and complementary therapy or rehabilitative program for chronic fatigue and chronic fatigue syndrome.

Mechanics Methodology for Textile Preform Composite Materials

NASA Technical Reports Server (NTRS)

Poe, Clarence C., Jr.

1996-01-01

NASA and its contractors have completed a program to develop a basic mechanics underpinning for textile composites. Three major deliverables were produced by the program: 1. A set of test methods for measuring material properties and design allowables; 2. Mechanics models to predict the effects of the fiber preform architecture and constituent properties on engineering moduli, strength, damage resistance, and fatigue life; and 3. An electronic data base of coupon type test data. This report describes these three deliverables.

Analysis of Global Ultrasonic Sensor Data from a Full Scale Wing Panel Test

NASA Astrophysics Data System (ADS)

Michaels, Jennifer E.; Michaels, Thomas E.; Martin, Ramaldo S.

2009-03-01

A full scale wing panel fatigue test was undertaken in 2007 as a part of the DARPA Structural Integrity Prognosis System (SIPS) program. Both local and global ultrasonic sensors were installed on the wing panel and data were recorded periodically over a period of about seven weeks. The local ultrasonic sensors interrogated a small number of selected fastener holes, and the global ultrasonic sensors were arranged in a spatially distributed array surrounding an area encompassing multiple fastener holes of interest. The global ultrasonic sensor data is the focus of the work reported here. Waveforms were recorded from all pitch-catch sensor pairs as a function of static load while fatiguing was paused. The time windows over which the waveforms were recorded were long enough to include most of the reverberating energy. Partway through the test simulated defects were temporarily introduced by gluing masses onto the surface of the wing panel, and waveforms were recorded immediately before their attachment and after their removal. The overall fatigue test was terminated while cracks originating from the fastener holes were still relatively small and before they reached the surface of the wing panel. Both detection and localization results are shown for the artificial damage, and the overall repeatability and stability of the signals are analyzed. Also shown is an analysis of how the reverberating signals change as a function of applied load. The fastener hole fatigue cracks were not detected by the global transducer array, which is not surprising given the final sizes of the cracks as determined by later destructive analysis. However, signals were stable throughout the entire fatigue test, and effects of load on the received signals were significant, both in the short-time and long-time signal regimes.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohanty, Subhasish; Soppet, William; Majumdar, Saurin

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

Establishment of new design criteria for GlidCop ® X-ray absorbers

DOE PAGES

Collins, Jeff T.; Nudell, Jeremy; Navrotski, Gary; ...

2017-02-20

Here, an engineering research program has been conducted at the Advanced Photon Source (APS) in order to determine the thermomechanical conditions that lead to crack formation in GlidCop ®, a material commonly used to fabricate X-ray absorbers at X-ray synchrotron facilities. This dispersion-strengthened copper alloy is a proprietary material and detailed technical data of interest to the synchrotron community is limited. The results from the research program have allowed new design criteria to be established for GlidCop ® X-ray absorbers based upon the thermomechanically induced fatigue behavior of the material. X-ray power from APS insertion devices was used to exposemore » 30 GlidCop ® samples to 10000 thermal loading cycles each under various beam power conditions, and all of the samples were metallurgically examined for crack presence/geometry. In addition, an independent testing facility was hired to measure temperature-dependent mechanical data and uniaxial mechanical fatigue data for numerous GlidCop ® samples. Data from these studies support finite element analysis (FEA) simulation and parametric models, allowing the development of a thermal fatigue model and the establishment of new design criteria so that the thermomechanically induced fatigue life of X-ray absorbers may be predicted. It is also demonstrated how the thermal fatigue model can be used as a tool to geometrically optimize X-ray absorber designs.« less

Establishment of new design criteria for GlidCop ® X-ray absorbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, Jeff T.; Nudell, Jeremy; Navrotski, Gary

Here, an engineering research program has been conducted at the Advanced Photon Source (APS) in order to determine the thermomechanical conditions that lead to crack formation in GlidCop ®, a material commonly used to fabricate X-ray absorbers at X-ray synchrotron facilities. This dispersion-strengthened copper alloy is a proprietary material and detailed technical data of interest to the synchrotron community is limited. The results from the research program have allowed new design criteria to be established for GlidCop ® X-ray absorbers based upon the thermomechanically induced fatigue behavior of the material. X-ray power from APS insertion devices was used to exposemore » 30 GlidCop ® samples to 10000 thermal loading cycles each under various beam power conditions, and all of the samples were metallurgically examined for crack presence/geometry. In addition, an independent testing facility was hired to measure temperature-dependent mechanical data and uniaxial mechanical fatigue data for numerous GlidCop ® samples. Data from these studies support finite element analysis (FEA) simulation and parametric models, allowing the development of a thermal fatigue model and the establishment of new design criteria so that the thermomechanically induced fatigue life of X-ray absorbers may be predicted. It is also demonstrated how the thermal fatigue model can be used as a tool to geometrically optimize X-ray absorber designs.« less

National Transonic Facility Fan Blade prepreg material characterization tests

NASA Technical Reports Server (NTRS)

Klich, P. J.; Richards, W. H.; Ahl, E. L., Jr.

1981-01-01

The test program for the basic prepreg materials used in process development work and planned fabrication of the national transonic facility fan blade is presented. The basic prepreg materials and the design laminate are characterized at 89 K, room temperature, and 366 K. Characterization tests, test equipment, and test data are discussed. Material tests results in the warp direction are given for tensile, compressive, fatigue (tension-tension), interlaminar shear and thermal expansion.

Fatigue Life Estimation under Cumulative Cyclic Loading Conditions

NASA Technical Reports Server (NTRS)

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

1999-01-01

The cumulative fatigue behavior of a cobalt-base superalloy, Haynes 188 was investigated at 760 C in air. Initially strain-controlled tests were conducted on solid cylindrical gauge section specimens of Haynes 188 under fully-reversed, tensile and compressive mean strain-controlled fatigue tests. Fatigue data from these tests were used to establish the baseline fatigue behavior of the alloy with 1) a total strain range type fatigue life relation and 2) the Smith-Wastson-Topper (SWT) parameter. Subsequently, two load-level multi-block fatigue tests were conducted on similar specimens of Haynes 188 at the same temperature. Fatigue lives of the multi-block tests were estimated with 1) the Linear Damage Rule (LDR) and 2) the nonlinear Damage Curve Approach (DCA) both with and without the consideration of mean stresses generated during the cumulative fatigue tests. Fatigue life predictions by the nonlinear DCA were much closer to the experimentally observed lives than those obtained by the LDR. In the presence of mean stresses, the SWT parameter estimated the fatigue lives more accurately under tensile conditions than under compressive conditions.

Diagnostic Reasoning for ST-Segment Elevation Myocardial Infarction (STEMI) Interpretation Is Preserved Despite Fatigue

PubMed Central

Kellogg, Adam R.; Coute, Ryan A.; Garra, Gregory

2015-01-01

Background Fatigue and sleepiness contribute to medical errors, although the effect of circadian disruption and fatigue on diagnostic reasoning skills is largely unknown. Objective To determine whether circadian disruption and fatigue negatively affect the emergency medicine (EM) resident's ability to make important clinical decisions based on electrocardiogram (ECG) interpretation. Methods Senior EM residents at 2 programs completed a questionnaire consisting of various measures of fatigue followed by an ECG test packet of ST-segment elevation myocardial infarction (STEMI) and STEMI mimics. Participants were asked to examine each ECG and determine whether cardiac catheterization laboratory activation (CLA) was indicated, and to report their confidence in their decision making on an 11-point, numeric rating scale. The primary outcome measured was a pairwise difference in accuracy of CLA between daytime and overnight testing. Results A total of 23 residents were enrolled in 2011 and 2012. Subjects demonstrated significant differences in multiple measures of sleepiness and fatigue during overnight periods. The median (interquartile range [IQR]) accuracy of CLA was not significantly different between daytime and overnight (70% [IQR, 50–80] versus 70% [IQR, 60–70], P  =  .82). There were no significant differences in the median number of overcalls (CLA when not a STEMI) and undercalls (no CLA when a STEMI was present; P  =  .57 and .37, respectively). Diagnostic confidence and confidence in CLA were not statistically different between daytime and overnight. Conclusions Despite a measurable degree of fatigue, senior EM residents experienced no decrease in their ability to accurately make CLA decisions based on ECG interpretation. PMID:26217418

Diagnostic Reasoning for ST-Segment Elevation Myocardial Infarction (STEMI) Interpretation Is Preserved Despite Fatigue.

PubMed

Kellogg, Adam R; Coute, Ryan A; Garra, Gregory

2015-03-01

Fatigue and sleepiness contribute to medical errors, although the effect of circadian disruption and fatigue on diagnostic reasoning skills is largely unknown. To determine whether circadian disruption and fatigue negatively affect the emergency medicine (EM) resident's ability to make important clinical decisions based on electrocardiogram (ECG) interpretation. Senior EM residents at 2 programs completed a questionnaire consisting of various measures of fatigue followed by an ECG test packet of ST-segment elevation myocardial infarction (STEMI) and STEMI mimics. Participants were asked to examine each ECG and determine whether cardiac catheterization laboratory activation (CLA) was indicated, and to report their confidence in their decision making on an 11-point, numeric rating scale. The primary outcome measured was a pairwise difference in accuracy of CLA between daytime and overnight testing. A total of 23 residents were enrolled in 2011 and 2012. Subjects demonstrated significant differences in multiple measures of sleepiness and fatigue during overnight periods. The median (interquartile range [IQR]) accuracy of CLA was not significantly different between daytime and overnight (70% [IQR, 50-80] versus 70% [IQR, 60-70], P  =  .82). There were no significant differences in the median number of overcalls (CLA when not a STEMI) and undercalls (no CLA when a STEMI was present; P  =  .57 and .37, respectively). Diagnostic confidence and confidence in CLA were not statistically different between daytime and overnight. Despite a measurable degree of fatigue, senior EM residents experienced no decrease in their ability to accurately make CLA decisions based on ECG interpretation.

Analysis of SNL/MSU/DOE Fatigue Database Trends for Wind Turbine Blade Materials 2010-2015.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mandell, John F.; Samborsky, Daniel D.; Miller, David A.

Wind turbine blades are designed to several major structural conditions, including tip deflection, strength and b uckling during severe loading, as well as very high numbers of fatigue cycles and various service environments. The MSU Database Program has, since 1989, addressed the broad range of properties needed for current and potential blade materials through stati c and fatigue testing and test development in cooperation with Sandia National Laboratories and wind industry and supplier partners. This report is the latest in a series, giving test results and analysis for the period 2010 - 2015. Program data are compiled in a publicmore » database [1] and other reports and publications given in the cited references. The report begins with an executive summary and introductory material including background discussion of previous related studies. Section 3 describes experimental methods including processing, test methods, instrumentation and test development. Section 4 provides static tension, compression and shear stress - strain properties in three directions using coupons sectioned from a thick infused unidirectional glass/epoxy laminate. The nonlinear, shear dominated static properties were characterized with loading - u nloading - reloading (LUR) tests in tension and compression to increasing load levels, for +-45O laminates. Section 5 explores the origins of tensile fatigue sensitivity in glass fiber dominated laminates with variations in fabric architecture including speci ally prepared fabrics and aligned strand laminates. Several types of resins are considered, with variations in resin toughness and bonding to fibers, as well as cure cycle variations for an epoxy. Conclusions are drawn as to the limits of tensile fatigue r esistance and the effects of resin type and fabric architecture, including the behavior of a commercial aligned glass strand product. Interactions between cyclic fatigue response and creep are addressed for off - axis (+-45O) glass/epoxy laminates in Sectio n 6. The nonlinear fatigue and creep stress - strain and cumulative strain response are characterized in tension and compression as a function of stress level, cycles and cumulative time, using square and sinewave loading over a broad range of frequency. The results are analyzed in terms of the cycles and cumulative time under load. A cumulative strain failure criterion is established, and used to construct shear and tension constant life diagrams (CLD's) with data for nine R - values. The effects of a more duc tile urethne resin are also explored. A previous study of thick adhesives testing is extended to mixed mode fracture mechanics testing in Section 7. Mechanisms of static and fatigue crack extension near the laminate adherend interface are reported in deta il. Data are presented for mixed mode adhesive fracture, compared to mixed mode fracture in ply delamination. Fatigue crack growth exponents are also developed for a mixed mode cracked lap shear coupon. The data for fatigue trends and relative failure stra ins and exponents are compared for various blade component materials in Section 8. The effects of temperature and seawater saturation are considered for selected materials of interest for wind and hydrokinetic turbine blades in Section 9. Section 10 gives detailed conclusions for each section. A cknowledgements The research presented in this report was carried out under Sandia National Laboratories purchase orders 1325028 an d 1543945 between 2010 and 2015, with support from the DOE Wind and Water Technologies Office . In addition to the authors listed, significant contributions were made by Patrick Flaherty, Pancastya Agastra, Michael Schuster, and Michael Voth. Industry m aterials suppliers include Vectorply, Saertex, OCV, AGY, Bayer, Ashland, 3M and Nextel. Industry suppliers with significant contributions to the study were Hexion, PPG, Reichhold, Gurit and NEPTCO. Intentionally Left Blank« less

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

Fatigue strength reduction model: RANDOM3 and RANDOM4 user manual. Appendix 2: Development of advanced methodologies for probabilistic constitutive relationships of material strength models

NASA Technical Reports Server (NTRS)

Boyce, Lola; Lovelace, Thomas B.

1989-01-01

FORTRAN programs RANDOM3 and RANDOM4 are documented in the form of a user's manual. Both programs are based on fatigue strength reduction, using a probabilistic constitutive model. The programs predict the random lifetime of an engine component to reach a given fatigue strength. The theoretical backgrounds, input data instructions, and sample problems illustrating the use of the programs are included.

Managing Neuropsychological Impairment in Multiple Sclerosis

PubMed Central

Lau, Stephanie; Penner, Iris; Heesen, Christoph; Moritz, Steffen

2015-01-01

Background: Multiple sclerosis (MS) is an inflammatory and neurodegenerative disease of the central nervous system of potential autoimmune origin that is frequently associated with psychological disorders and cognitive deficits, as well as with fatigue, stress, and psychosocial burden. These factors often cause decreased quality of life, social withdrawal, and unemployment. We describe the development of a cognitive-behavioral group intervention based on the concept of metacognition and evaluation of the feasibility and acceptance of the program as a rehabilitation tool. Methods: Metacognitive Training in MS (MaTiMS) consists of six modules, each 90 minutes in duration. We tested acceptance and design of the program in six focus groups (entire sample, n = 27). Framework analysis of transcripts was used to identify key topics and categories. Program modules were revised in accordance with appropriate recommendations of focus group members. We subsequently evaluated MaTiMS in two groups (n = 5, n = 6) in a rehabilitation center. Neuropsychological functioning as well as coping self-efficacy, depression, stress, perceived cognitive deficit, fatigue, and quality of life were assessed. Acceptance of MaTiMS from the patient perspective was also studied. Results: The modules were highly accepted by patients. Pre-post assessments showed significant improvements in the Coping Self Efficacy Scale (P = .007), the Würzburger Fatigue Inventory for MS Score (P = .028), and the Hamburg Quality of Life Questionnaire in Multiple Sclerosis Mood subscale (P = .046). Conclusions: These preliminary results suggest that MaTiMS represents a feasible psychological group training program that may foster improvements in self-efficacy, fatigue, and mood. The next step will be an evaluation of the program in a randomized controlled trial. PMID:26052258

Full-scale transmission testing to evaluate advanced lubricants

NASA Technical Reports Server (NTRS)

Lewicki, David G.; Decker, Harry J.; Shimski, John T.

1992-01-01

Experimental tests were performed on the OH-58A helicopter main rotor transmission in the NASA Lewis 500 hp helicopter transmission test stand. The testing was part of a lubrication program. The objectives are to develop and show a separate lubricant for gearboxes with improved performance in life and load carrying capacity. The goal was to develop a testing procedure to fail certain transmission components using a MIL-L-23699 based reference oil and then to run identical tests with improved lubricants and show improved performance. The tests were directed at parts that failed due to marginal lubrication from Navy field experience. These failures included mast shaft bearing micropitting, sun gear and planet bearing fatigue, and spiral bevel gear scoring. A variety of tests were performed and over 900 hrs of total run time accumulated for these tests. Some success was achieved in developing a testing procedure to produce sun gear and planet bearing fatigue failures. Only marginal success was achieved in producing mast shaft bearing micropitting and spiral bevel gear scoring.

Cumulative fatigue damage behavior of MAR M-247

NASA Technical Reports Server (NTRS)

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

1991-01-01

The objective was to examine the room temperature fatigue and nonlinear cumulative fatigue damage behavior of the cast nickel-based superalloy, MAR M-247. The fatigue test matrix consisted of single-level, fully reversed fatigue experiments. Two series of tests were performed: one of the two baseline fatigue LCF (Low-Cycle Fatigue) life levels was used in the first loading block, and the HCF (High-Cycle Fatigue) baseline loading level was used in the second block in each series. For each series, duplicate tests were performed at each applied LCF life fraction.

Effect of outdoor exposure at ambient and elevated temperatures on fatigue life of Ti-6Al-4V titanium alloy sheet in the annealed and the solution treated and aged condition

NASA Technical Reports Server (NTRS)

Phillips, E. P.

1974-01-01

Specimens of Ti-6Al-4V titanium alloy sheet in the annealed and the solution-treated and aged heat-treatment condition were exposed outdoors at ambient and 560 K (550 F) temperatures to determine the effect of outdoor exposure on fatigue life. Effects of exposure were determined by comparing fatigue lives of exposed specimens to those of unexpected specimens. Two procedures for fatigue testing the exposed specimens were evaluated: (1) fatigue tests conducted outdoors by applying 1200 load cycles per week until failure occurred and (2) conventional fatigue tests (continuous cycling until failure occurred) conducted indoors after outdoor exposure under static load. The exposure period ranged from 9 to 28 months for the outdoor fatigue-test group and was 24 months for the static-load group. All fatigue tests were constant-amplitude bending of specimens containing a drilled hole (stress concentration factor of 1.6). The results of the tests indicate that the fatigue lives of solution-treated and aged specimens were significantly reduced by the outdoor exposure at 560 K but not by the exposure at ambient temperature. Fatigue lives of the annealed specimens were essentially unaffected by the outdoor exposure at either temperature. The two test procedures - outdoor fatigue test and indoor fatigue test after outdoor exposure - led to the same conclusions about exposure effects.

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

PubMed Central

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

2016-01-01

Background: Subjective cognitive impairments are frequent, but poorly understood in patients with chronic fatigue. We hypothesized that maladaptive metacognitive beliefs at baseline were associated with baseline subjective cognitive impairments, that they predict subjective cognitive impairments at treatment termination, and that a reduction in maladaptive metacognitive beliefs was associated with less subjective cognitive impairments at treatment termination, independent of changes in fatigue, pain, insomnia, depression, and anxiety. Methods: In this non-controlled study, patients (n = 137) on sick leave due to chronic fatigue received a 3.5-week inpatient RTW rehabilitation program. Of these patients 69 (50.4%) was referred with a ICPC-2 diagnosis of chronic fatigue. Patients completed questionnaires about metacognitive beliefs, somatic complaints, psychological complaints, and cognitive impairments before and after treatment. To test the hypotheses we performed paired t-tests of change, as well as seven hierarchical linear regressions. Results: Results showed that baseline maladaptive metacognitive beliefs were significantly associated with subjective cognitive impairments at baseline, controlling for symptoms. Score on baseline metacognitive beliefs did not predict impairments post-treatment. Testing specific maladaptive beliefs, pre-treatment scores on cognitive confidence were associated with subjective cognitive impairments both pre and post-treatment, controlling for symptoms. Post-treatment metacognitive beliefs and post-treatment cognitive confidence were associated with post-treatment subjective cognitive impairments, controlling for pre-treatment impairments and pre-treatment metacognitive beliefs, as well as pre and post-scores on symptom measures. Conclusion: This study reports associations between maladaptive metacognitive beliefs and subjective cognitive impairments in patients with chronic fatigue. Targeting metacognitive beliefs could prove an effective therapeutic intervention for subjective cognitive impairments in these patients. PMID:27242634

The effectiveness of an educational program on preventing and treating compassion fatigue in emergency nurses.

PubMed

Flarity, Kathleen; Gentry, J Eric; Mesnikoff, Nathan

2013-01-01

The purpose of this qualitative study was to examine the treatment effectiveness of a multifaceted education program to decrease compassion fatigue (CF) and burnout (BO) symptoms and increase compassion satisfaction of emergency nurses participating in the training. The goal of the CF multifaceted intervention program was to demonstrate a statistically significant improvement in the 3 CF subscales: an increase on the Compassion Satisfaction (CS) subscale and a decrease on the Secondary Traumatic Stress (STS) and BO subscales in the participants' pretest and posttest scores as measured by The Professional Quality of Life test (B. H. , ). The study sites were 2 emergency departments in Colorado Springs, CO. A convenience sample consisted of emergency nurses who self-selected to participate in the study. Univariate statistics were used, and data were examined for normalcy of distribution. Because these data were not distributed normally, Wilcoxon signed-rank tests were used to evaluate the differences between the baseline and postintervention groups. The multifaceted education program resulted in a statistically significant increase in CS (p = 0.004) and a decrease in BO (p = 0.001 or less) and STS (p = 0.001) symptoms.

Comparison of measured and calculated dynamic loads for the Mod-2 2.5 mW wind turbine system

NASA Technical Reports Server (NTRS)

Zimmerman, D. K.; Shipley, S. A.; Miller, R. D.

1995-01-01

The Boeing Company, under contract to the Electric Power Research Institute (EPRI), has completed a test program on the Mod-2 wind turbines at Goodnoe Hills, Washington. The objectives were to update fatigue load spectra, discern site and machine differences, measure vortex generator effects, and to evaluate rotational sampling techniques. This paper shows the test setup and loads instrumentation, loads data comparisons and test/analysis correlations. Test data are correlated with DYLOSAT predictions using both the NASA interim turbulence model and rotationally sampled winds as inputs. The latter is demonstrated to have the potential to improve the test/analysis correlations. The paper concludes with an assessment of the importance of vortex generators, site dependence, and machine differences on fatigue loads. The adequacy of prediction techniques used are evaluated and recommendations are made for improvements to the methodology.

Passive Orbital Disconnect Strut (PODS 3) structural test program

NASA Technical Reports Server (NTRS)

Parmley, R. T.

1985-01-01

A passive orbital disconnect strut (PODS-3) was analyzed structurally and thermally. Development tests on a graphite/epoxy orbit tube and S glass epoxy launch tube provided the needed data to finalize the design. A detailed assembly procedure was prepared. One strut was fabricated. Shorting loads in both the axial and lateral direction (vs. load angle and location) were measured. The strut was taken to design limit loads at both ambient and 78 K (cold end only). One million fatigue cycles were performed at predicted STS loads (half in tension, half in compression) with the cold end at 78 K. The fatigue test was repeated at design limit loads. Six struts were then fabricated and tested as a system. Axial loads, side loads, and simulated asymmetric loads due to temperature gradients around the vacuum shell were applied. Shorting loads were measured for all tests.

Development of a high-frequency and large-stroke fatigue testing system for rubber

NASA Astrophysics Data System (ADS)

Chen, Gang; Wu, Hao; Gao, Jianwen; Lin, Qiang

2017-04-01

The limited capabilities of current fatigue testing machines have resulted in studies on the fatigue behavior of rubber under large-displacement amplitude and high frequency being very sparse. In this study, a fatigue testing system that can carry out large-displacement amplitude and high-frequency fatigue tests on rubber was developed using a moving magnet voice coil motor (MMVCM) actuator, with finite element analysis applied to analyze the thrust of the MMVCM actuator. The results of a series of cyclic tension tests conducted on vulcanized natural rubber specimens using the developed fatigue testing system verify that it has high precision, low noise, large-stroke, and high-frequency characteristics. Further, the load frame with the developed MMVCM actuator is feasible for material testing, especially for large-stroke and high-frequency fatigue tests.

78 FR 40263 - Agency Information Collection Activities: Requests for Comments; Clearance of Renewed Approval of...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-07-03

... Program (Widespread Fatigue Damage) AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Notice and... information collection. The ``Aging Aircraft Program (Widespread Fatigue Damage)'' final rule (75 FR 69745... preclude widespread fatigue damage in those airplanes. DATES: Written comments should be submitted by...

78 FR 55327 - Agency Information Collection Activities: Requests for Comments; Clearance of Renewed Approval of...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-10

... Program (Widespread Fatigue Damage) AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Notice and... 40263-40264. The ``Aging Aircraft Program (Widespread Fatigue Damage)'' final rule (75 FR 69745) amended... widespread fatigue damage in those airplanes. DATES: Written comments should be submitted by October 10, 2013...

Fatigue tests on big structure assemblies of concorde aircraft

NASA Technical Reports Server (NTRS)

Nguyen, V. P.; Perrais, J. P.

1972-01-01

Fatigue tests on structural assemblies of the Concorde supersonic transport aircraft are reported. Two main sections of the aircraft were subjected to pressure, mechanical load, and thermal static tests. The types of fatigue tests conducted and the results obtained are discussed. It was concluded that on a supersonic aircraft whose structural weight is a significant part of the weight analysis, many fatigue and static strength development tests should be made and fatigue and thermal tests of the structures are absolutely necessary.

Development tests for the 2.5 megawatt Mod-2 wind turbine generator

NASA Technical Reports Server (NTRS)

Andrews, J. S.; Baskin, J. M.

1982-01-01

The 2.5 megawatt MOD-2 wind turbine generator test program is discussed. The development of the 2.5 megawatt MOD-2 wind turbine generator included an extensive program of testing which encompassed verification of analytical procedures, component development, and integrated system verification. The test program was to assure achievement of the thirty year design operational life of the wind turbine system as well as to minimize costly design modifications which would otherwise have been required during on site system testing. Computer codes were modified, fatigue life of structure and dynamic components were verified, mechanical and electrical component and subsystems were functionally checked and modified where necessary to meet system specifications, and measured dynamic responses of coupled systems confirmed analytical predictions.

A combined inspiratory and expiratory muscle training program improves respiratory muscle strength and fatigue in multiple sclerosis.

PubMed

Ray, Andrew D; Udhoji, Supriya; Mashtare, Terry L; Fisher, Nadine M

2013-10-01

To determine the effects of a short-duration, combined (inspiratory and expiratory), progressive resistance respiratory muscle training (RMT) protocol on respiratory muscle strength, fatigue, health-related quality of life, and functional performance in individuals with mild-to-moderate multiple sclerosis (MS). Quasi-experimental before-after trial. University rehabilitation research laboratory. Volunteers with MS (N=21) were divided into 2 groups: RMT (n=11; 9 women, 2 men; mean age ± SD, 50.9 ± 5.7y, mean Expanded Disability Status Scale score ± SD, 3.2 ± 1.9) and a control group that did not train (n=10; 7 women, 3 men; mean age ± SD, 56.2 ± 8.8y, mean Expanded Disability Status Scale score ± SD, 4.4 ± 2.1). Expanded Disability Status Scale scores ranged from 1 to ≤6.5. No patients withdrew from the study. Training was a 5-week combined progressive resistance RMT program, 3d/wk, 30 minutes per session. The primary outcome measures were maximal inspiratory pressure and expiratory pressure and the Modified Fatigue Impact Scale. All subjects completed secondary measures of pulmonary function, the six-minute walk test, the timed stair climb, the Multiple Sclerosis Self-Efficacy Scale, the Medical Outcomes Study 36-Item Short-Form Health Survey, and the Physical Activity Disability Scale. Maximal inspiratory pressure and expiratory pressure (mean ± SD) increased 35% ± 22% (P<.001) and 26% ± 17% (P<.001), respectively, whereas no changes were noted in the control group (12% ± 23% and -4% ± 17%, respectively). RMT improved fatigue (Modified Fatigue Impact Scale, P<.029), with no change or worsening in the control group. No changes were noted in the six-minute walk test, stair climb, Multiple Sclerosis Self-Efficacy Scale, or Physical Activity Disability Scale in the RMT group. The control group had decreases in emotional well-being and general health (Medical Outcomes Study 36-Item Short-Form Health Survey). A short-duration, combined RMT program improved inspiratory and expiratory muscle strength and reduced fatigue in patients with mild to moderate MS. Copyright © 2013 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

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.

The NASA Ames Fatigue Countermeasures Program: The Next Generation

NASA Technical Reports Server (NTRS)

Rosekind, Mark R.; Neri, David F.; Miller, Donna L.; Gregory, Kevin B.; Webbon, Lissa L.; Oyung, Ray L.

1997-01-01

Twenty-four hour, global aviation operations pose unique challenges to humans. Physiological requirements related to sleep, the internal circadian clock, and human fatigue are critical factors that are known to affect safety, performance, and productivity. Understanding the human operators' physiological capabilities, and limitations, will be important to address these issues as global demand for aviation activities continues to increase. In 1980, in response to a Congressional request, the National Aeronautics and Space Administration (NASA) Ames Research Center initiated a Fatigue/Jet Lag Program to examine the role of fatigue in flight operations. Originally established by Dr. John K. Lauber and Dr. Charles E. Billings, the Program was designed to address three objectives: (1) determine the extent of fatigue, sleep loss, and circadian disruption in flight operations; (2) determine how fatigue affected flight crew performance; and (3) develop strategies to maximize performance and alertness during flight operations.

The Philosophy which underlies the structural tests of a supersonic transport aircraft with particular attention to the thermal cycle

NASA Technical Reports Server (NTRS)

Ripley, E. L.

1972-01-01

The information presented is based on data obtained from the Concorde. Much of this data also applies to other supersonic transport aircraft. The design and development of the Concorde is a joint effort of the British and French, and the structural test program is shared, as are all the other activities. Vast numbers of small specimens have been tested to determine the behavior of the materials used in the aircraft. Major components of the aircraft structure, totalling almost a complete aircraft, have been made and are being tested to help the constructors in each country in the design and development of the structure. Tests on two complete airframes will give information for the certification of the aircraft. A static test was conducted in France and a fatigue test in the United Kingdom. Fail-safe tests are being made to demonstrate the crack-propagation characteristics of the structure and its residual strength. Aspects of the structural test program are described in some detail, dealing particularly with the problems associated with the thermal cycle. The biggest of these problems is the setting up of the fatigue test on the complete airframe; therefore, this is covered more extensively with a discussion about how the test time can be shortened and with a description of the practical aspects of the test.

Fatigue Characterization of Alloy 10: a 1300F Disk Alloy for Small Gas Turbine Engines

NASA Technical Reports Server (NTRS)

Gayda, John

2000-01-01

A detailed fatigue characterization of Alloy 10, a high strength nickel-based disk alloy, was conducted on test coupons machined from a 'pancake' forging. Smooth bar, strain controlled fatigue testing at various R-ratios was run at representative bore, 750 F, and rim, 1300 F, temperatures. This was followed by notch fatigue testing (Kt=2) run under load control. Analysis of the fatigue data using a Smith-Watson-Topper approach and finite element analysis of the notch root was employed to understand material behavior in these tests. Smooth bar fatigue data showed a significant R-ratio dependence at either test temperature which could be accounted for using a Smith-Watson-Topper parameter (SWT). In general, fatigue life was longer at 750 F than 1300 F for a given SWT. For notch fatigue tests, life was longer at 750 F than 1300 F but only at higher stresses. This was attributed to differences in alloy strength. At lower stresses, finite element analysis suggested that convergence of fatigue life at both temperatures resulted from relaxation of stresses at the notch root in the 1300 F tests.

The high frequency light load fatigue testing machine based on giant magnetostrictive material and stroke multiplier

NASA Astrophysics Data System (ADS)

Wang, M. D.; Li, D. S.; Huang, Y.; Zhang, C.; Zhong, K. M.; Sun, L. N.

2013-08-01

In the notebook and clamshell mobile phone, data communication wire often requires repeated bending. Generally, communication wire with the actual application conditions, the test data cannot assess bending resistance performance of data communication wire is tested conventionally using wires with weights of 90 degree to test bending number, this test method and device is not fully reflect the fatigue performance in high frequency and light load application condition, at the same time it has a large difference between the test data of the long-term reliability of high frequency and low load conditions. In this paper, high frequency light load fatigue testing machine based on the giant magnetostrictive material and stroke multiplier is put forward, in which internal reflux stroke multiplier is driven by giant magnetostrictive material to realize the rapid movement of light load. This fatigue testing device has the following advantages: (1) When the load is far less than the friction, reducing friction is very effective to improve the device performance. Because the body is symmetrical, the friction loss of radial does not exist in theory, so the stress situation of mechanism is good with high transmission efficiency and long service life. (2) The installation position of the output hydraulic cylinder, can be arranged conveniently as ordinary cylinder. (3) Reciprocating frequency, displacement and speed of high frequency movement can be programmed easily to change with higher position precision. (4)Hydraulic oil in this device is closed to transmit, which does not produce any environment pollution. The device has no hydraulic pump and tank, and less energy conversion processes, so it is with the trend of green manufacturing.

The effect of yoga exercise on improving depression, anxiety, and fatigue in women with breast cancer: a randomized controlled trial.

PubMed

Taso, Chao-Jung; Lin, Huey-Shyan; Lin, Wen-Li; Chen, Shu-Ming; Huang, Wen-Tsung; Chen, Shang-Wen

2014-09-01

Depression, anxiety, and fatigue are among the most significant problems that influence the quality of life of patients with breast cancer who receive adjuvant chemotherapy. Although evidence has shown yoga to decrease anxiety, depression, and fatigue in patients with cancer, few studies on the effects of yoga have targeted patients with breast cancer. Yoga interventions should be tested to promote the psychological and physical health of women with breast cancer. This study examines the effectiveness of an 8-week yoga exercise program in promoting the psychological and physical health of women with breast cancer undergoing adjuvant chemotherapy in terms of depression, anxiety, and fatigue. A sample of 60 women with nonmetastatic breast cancer was recruited. Participants were randomly assigned into either the experimental group (n = 30) or the control group (n = 30). A 60-minute, twice-per-week yoga exercise was implemented for 8 weeks as the intervention for the participants in the experimental group. The control group received standard care only. Analysis using the Johnson-Neyman procedure found that the yoga exercise reduced overall fatigue and the interference of fatigue in everyday life for the experimental group participants. Significant reductions were obtained after 4 weeks of intervention participation for those experimental group patients with relatively low starting baseline values (baseline item mean value < 3.31 and 3.22, respectively) and after 8 weeks for most patients (approximately 75%) with moderate starting baseline values (baseline item mean value < 7.30 and 5.34, respectively). The 8-week intervention did not significantly improve the levels of depression (F = 1.29, p > .05) or anxiety (F = 2.7, p > .05). The 8-week yoga exercise program developed in this study effectively reduced fatigue in patients with breast cancer but did not reduce depression or anxiety. Oncology nurses should strengthen their clinical health education and apply yoga to reduce the fatigue experienced by patients with breast cancer who undergo adjuvant chemotherapy.

A transient plasticity study and low cycle fatigue analysis of the Space Station Freedom photovoltaic solar array blanket

NASA Technical Reports Server (NTRS)

Armand, Sasan C.; Liao, Mei-Hwa; Morris, Ronald W.

1990-01-01

The Space Station Freedom photovoltaic solar array blanket assembly is comprised of several layers of materials having dissimilar elastic, thermal, and mechanical properties. The operating temperature of the solar array, which ranges from -75 to +60 C, along with the material incompatibility of the blanket assembly components combine to cause an elastic-plastic stress in the weld points of the assembly. The weld points are secondary structures in nature, merely serving as electrical junctions for gathering the current. The thermal mechanical loading of the blanket assembly operating in low earth orbit continually changes throughout each 90 min orbit, which raises the possibility of fatigue induced failure. A series of structural analyses were performed in an attempt to predict the fatigue life of the solar cell in the Space Station Freedom photovoltaic array blanket. A nonlinear elastic-plastic MSC/NASTRAN analysis followed by a fatigue calculation indicated a fatigue life of 92,000 to 160,000 cycles for the solar cell weld tabs. Additional analyses predict a permanent buckling phenomenon in the copper interconnect after the first loading cycle. This should reduce or eliminate the pulling of the copper interconnect on the joint where it is welded to the silicon solar cell. It is concluded that the actual fatigue life of the solar array blanket assembly should be significantly higher than the calculated 92,000 cycles, and thus the program requirement of 87,500 cycles (orbits) will be met. Another important conclusion that can be drawn from the overall analysis is that, the strain results obtained from the MSC/NASTRAN nonlinear module are accurate to use for low-cycle fatigue analysis, since both thermal cycle testing of solar cells and analysis have shown higher fatigue life than the minimum program requirement of 87,500 cycles.

Low visual information-processing speed and attention are predictors of fatigue in elementary and junior high school students

PubMed Central

2011-01-01

Background Fatigue is a common complaint among elementary and junior high school students, and is known to be associated with reduced academic performance. Recently, we demonstrated that fatigue was correlated with decreased cognitive function in these students. However, no studies have identified cognitive predictors of fatigue. Therefore, we attempted to determine independent cognitive predictors of fatigue in these students. Methods We performed a prospective cohort study. One hundred and forty-two elementary and junior high school students without fatigue participated. They completed a variety of paper-and-pencil tests, including list learning and list recall tests, kana pick-out test, semantic fluency test, figure copying test, digit span forward test, and symbol digit modalities test. The participants also completed computerized cognitive tests (tasks A to E on the modified advanced trail making test). These cognitive tests were used to evaluate motor- and information-processing speed, immediate and delayed memory function, auditory and visual attention, divided and switching attention, retrieval of learned material, and spatial construction. One year after the tests, a questionnaire about fatigue (Japanese version of the Chalder Fatigue Scale) was administered to all the participants. Results After the follow-up period, we confirmed 40 cases of fatigue among 118 students. In multivariate logistic regression analyses adjusted for grades and gender, poorer performance on visual information-processing speed and attention tasks was associated with increased risk of fatigue. Conclusions Reduced visual information-processing speed and poor attention are independent predictors of fatigue in elementary and junior high school students. PMID:21672212

Low visual information-processing speed and attention are predictors of fatigue in elementary and junior high school students.

PubMed

Mizuno, Kei; Tanaka, Masaaki; Fukuda, Sanae; Yamano, Emi; Shigihara, Yoshihito; Imai-Matsumura, Kyoko; Watanabe, Yasuyoshi

2011-06-14

Fatigue is a common complaint among elementary and junior high school students, and is known to be associated with reduced academic performance. Recently, we demonstrated that fatigue was correlated with decreased cognitive function in these students. However, no studies have identified cognitive predictors of fatigue. Therefore, we attempted to determine independent cognitive predictors of fatigue in these students. We performed a prospective cohort study. One hundred and forty-two elementary and junior high school students without fatigue participated. They completed a variety of paper-and-pencil tests, including list learning and list recall tests, kana pick-out test, semantic fluency test, figure copying test, digit span forward test, and symbol digit modalities test. The participants also completed computerized cognitive tests (tasks A to E on the modified advanced trail making test). These cognitive tests were used to evaluate motor- and information-processing speed, immediate and delayed memory function, auditory and visual attention, divided and switching attention, retrieval of learned material, and spatial construction. One year after the tests, a questionnaire about fatigue (Japanese version of the Chalder Fatigue Scale) was administered to all the participants. After the follow-up period, we confirmed 40 cases of fatigue among 118 students. In multivariate logistic regression analyses adjusted for grades and gender, poorer performance on visual information-processing speed and attention tasks was associated with increased risk of fatigue. Reduced visual information-processing speed and poor attention are independent predictors of fatigue in elementary and junior high school students. © 2011 Mizuno et al; licensee BioMed Central Ltd.

A prospective evaluation of an interdisciplinary nutrition–rehabilitation program for patients with advanced cancer

PubMed Central

Gagnon, B.; Murphy, J.; Eades, M.; Lemoignan, J.; Jelowicki, M.; Carney, S.; Amdouni, S.; Di Dio, P.; Chasen, M.; MacDonald, N.

2013-01-01

Background Cancer can affect many dimensions of a patient’s life, and in turn, it should be targeted using a multimodal approach. We tested the extent to which an interdisciplinary nutrition–rehabilitation program can improve the well-being of patients with advanced cancer. Methods Between January 10, 2007, and September 29, 2010, 188 patients with advanced cancer enrolled in the 10–12-week program. Body weight, physical function, symptom severity, fatigue dimensions, distress level, coping ability, and overall quality of life were assessed at the start and end of the program. Results Of the enrolled patients, 70% completed the program. Patients experienced strong improvements in the physical and activity dimensions of fatigue (effect sizes: 0.8–1.1). They also experienced moderate reductions in the severity of weakness, depression, nervousness, shortness of breath, and distress (effect sizes: 0.5–0.7), and moderate improvements in Six Minute Walk Test distance, maximal gait speed, coping ability, and quality of life (effect sizes: 0.5–0.7) Furthermore, 77% of patients either maintained or increased their body weight. Conclusions Interdisciplinary nutrition–rehabilitation can be advantageous for patients with advanced cancer and should be considered an integrated part of standard palliative care. PMID:24311946

Feasibility of a Telehealth Educational Program on Self-Management of Pain and Fatigue in Adult Cancer Patients.

PubMed

Rocque, Gabrielle B; Halilova, Karina I; Varley, Allyson L; Williams, Courtney P; Taylor, Richard A; Masom, David G; Wright, William J; Partridge, Edward E; Kvale, Elizabeth A

2017-06-01

Pain and fatigue are common symptoms among cancer patients and often lead to substantial distress. Innovative self-management programs for pain and fatigue are needed. The primary objective was to assess the feasibility of a telehealth pain and fatigue self-management program among adult cancer patients. Secondary objectives included assessment of differences in patient characteristics, recruitment, and retention of patients based on two screening strategies: 1) navigator-collected, patient-reported pain or fatigue and 2) in-clinic, physician-identified pain or fatigue. This prospective, nonrandomized, pre-post evaluation assessed feasibility, which was defined as 50% of eligible patients choosing to participate and completing the intervention. Patient demographics and patient-reported outcomes (patient activation, distress, symptoms, and quality of life) were collected at baseline and study completion. Differences in baseline characteristics were compared between cohorts and for patients who did vs. did not graduate from the program. The program did not meet feasibility requirements because of only 34% of eligible patients choosing to participate. However, 50% of patients starting the program graduated. Differences in baseline characteristics and retention rates were noted by recruitment strategy. At baseline, 27.3% of navigated patients were at the highest activation level compared with 7.1% in the physician-referred, non-navigated patients (P = 0.17); more than 15% of non-completers were at the lowest activation level compared with 9% of completers (P = 0.85). Telehealth self-management program for pain and fatigue may be better accepted among selected segments of cancer patients. Larger scale studies are needed to assess the efficacy of this program in a more selective activated population. Copyright © 2017 American Academy of Hospice and Palliative Medicine. Published by Elsevier Inc. All rights reserved.

AISI/DOE Technology Roadmap Program: Cold Work Embrittlement of Interstitial Free Steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

John T Bowker; Pierre Martin

2002-10-31

This work addresses the issues of measurement of secondary cold work embrittlement (SCWE) of an IF steel in deep-drawn parts using laboratory tests, and its correlation with real part fracture. It aimed at evaluating the influence of the steel chemistry and processing condition, microstructure, and test conditions, on SCWE as well as the effect of SCWE on fatigue properties. Size 6-in. cups produced with various draw ratios or trimmed at different heights were tested to determine the ductile-to-brittle-transition temperature (DBTT) as a function of strain. The 2-in. cup/expansion test, bend test and fracture of notched specimens were also used tomore » generate information complementary to that provided by the 6-inch cup/expansion test. The relationship between laboratory tests and fracture in real parts was established by testing large-scale parts. The fatigue behavior was investigated in the as-rolled and deep drawn (high stain) conditions, using prestrained specimens taken from the wall of a formed part.« less

Durability evaluation of ceramic components using CARES/LIFE

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.; Powers, Lynn M.; Janosik, Lesley A.; Gyekenyesi, John P.

1994-01-01

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing the power law, Paris law, or Walker equation. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Application of this design methodology is demonstrated using experimental data from alumina bar and disk flexure specimens which exhibit SCG when exposed to water.

Durability evaluation of ceramic components using CARES/LIFE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nemeth, N.N.; Janosik, L.A.; Gyekenyesi, J.P.

1996-01-01

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing the power law, Paris law, or Walker equation. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength andmore » fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Application of this design methodology is demonstrated using experimental data from alumina bar and disk flexure specimens, which exhibit SCG when exposed to water.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skochko, G.W.; Herrmann, T.P.

Axial load cycling fatigue tests of threaded fasteners are useful in determining fastener fatigue failure or design properties. By using appropriate design factors between the failure and design fatigue strengths, such tests are used to establish fatigue failure and design parameters of fasteners for axial and bending cyclic load conditions. This paper reviews the factors which influence the fatigue strength of low Alloy steel threaded fasteners, identifies those most significant to fatigue strength, and provides design guidelines based on the direct evaluation of fatigue tests of threaded fasteners. Influences on fatigue strength of thread manufacturing process (machining and rolling ofmore » threads), effect of fastener membrane and bending stresses, thread root radii, fastener sizes, fastener tensile strength, stress relaxation, mean stress, and test temperature are discussed.« less

Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

NASA Technical Reports Server (NTRS)

Forman, Royce G.; Figert, J.; Beek, J.; Ventura, J.; Martinez, J.; Samonski, F.

2011-01-01

This presentation describes results obtained from a research project conducted at the NASA Johnson Space Center (JSC) that was jointly supported by the FAA Technical Center and JSC. The JSC effort was part of a multi-task FAA program involving several U.S. laboratories and initiated for the purpose of developing enhanced analysis tools to assess damage tolerance of rotorcraft and aircraft propeller systems. The research results to be covered in this presentation include a new understanding of the behavior of fatigue crack growth in the threshold region. This behavior is important for structural life analysis of aircraft propeller systems and certain rotorcraft structural components (e.g., the mast). These components are often designed to not allow fatigue crack propagation to exceed an experimentally determined fatigue crack growth threshold value. During the FAA review meetings for the program, disagreements occurred between the researchers regarding the observed fanning (spread between the da/dN curves of constant R) in the threshold region at low stress ratios, R. Some participants believed that the fanning was a result of the ASTM load shedding test method for threshold testing, and thus did not represent the true characteristics of the material. If the fanning portion of the threshold value is deleted or not included in a life analysis, a significant penalty in the calculated life and design of the component would occur. The crack growth threshold behavior was previously studied and reported by several research investigators in the time period: 1970-1980. Those investigators used electron microscopes to view the crack morphology of the fatigue fracture surfaces. Their results showed that just before reaching threshold, the crack morphology often changed from a striated to a faceted or cleavage-like morphology. This change was reported to have been caused by particular dislocation properties of the material. Based on the results of these early investigations, a program was initiated at JSC to repeat these examinations on a number of aircraft structural alloys that were currently being tested for obtaining fatigue crack growth properties. These new scanning electron microscope (SEM) examinations of the fatigue fracture faces confirmed the change in crack morphology in the threshold crack tip region. In addition, SEM examinations were further performed in the threshold crack-tip region before breaking the specimens open (not done in the earlier published studies). In these examinations, extensive crack forking and even 90-degree crack bifurcations were found to have occurred in the final threshold crack-tip region. The forking and bifurcations caused numerous closure points to occur that prevented full crack closure in the threshold region, and thus were the cause of the fanning at low-R values. Therefore, we have shown that the fanning behavior was caused by intrinsic dislocation properties of the different alloy materials and were not the result of a plastic wake that remains from the load-shedding test phase. Also, to accommodate the use of da/dN data which includes fanning at low R-values, an updated fanning factor term has been developed and will be implemented into the NASGRO fatigue crack growth software. The term can be set to zero if it is desired that the fanning behavior is not be modeled for particular cases, such as when fanning is not a result of the intrinsic properties of a material.

Assessing fatigue in inflammatory bowel disease: comparison of three fatigue scales.

PubMed

Norton, C; Czuber-Dochan, W; Bassett, P; Berliner, S; Bredin, F; Darvell, M; Forbes, A; Gay, M; Ream, E; Terry, H

2015-07-01

Fatigue is commonly reported by patients with inflammatory bowel disease (IBD), both in quiescent and active disease. Few fatigue scales have been tested in IBD. To assess three fatigue assessment scales in IBD and to determine correlates of fatigue. Potential participants (n = 2131) were randomly selected from an IBD organisation's members' database; 605 volunteered and were posted three fatigue scales: Inflammatory Bowel Disease Fatigue scale, Multidimensional Fatigue Inventory and Multidimensional Assessment Fatigue scale and questionnaires assessing anxiety, depression, quality of life (QoL) and IBD activity. The questionnaires were tested for stability over time with another group (n = 70) of invited participants. Internal consistency was measured by Cronbach's alpha and test-retest reliability by the intraclass correlation coefficient (ICC). Four hundred and sixty-five of 605 (77%) questionnaires were returned; of 70 invited, 48/70 returned test (68.6%) and 41/70 (58.6%) returned retest. The three scales are highly correlated (P < 0.001). Test-retest suggests reasonable agreement with ICC values between 0.65 and 0.84. Lower age, female gender, IBD diagnosis, anxiety, depression and QoL were associated with fatigue (P < 0.001) on univariable analysis. However, on multivariable analysis only depression and low QoL were consistently associated with fatigue, while female gender was associated on most scales. IBD diagnosis, age and other factors were not consistently associated with severity or impact of fatigue once other variables were controlled for. All three fatigue scales are likely to measure IBD fatigue adequately. Responsiveness to change has not been tested. Depression, poorer QoL and probably female gender are the major associations of fatigue in IBD. © 2015 John Wiley & Sons Ltd.

Life prediction and constitutive models for engine hot section anisotropic materials program

NASA Technical Reports Server (NTRS)

Swanson, G. A.; Linask, I.; Nissley, D. M.; Norris, P. P.; Meyer, T. G.; Walker, K. P.

1986-01-01

This report presents the results of the first year of a program designed to develop life prediction and constitutive models for two coated single crystal alloys used in gas turbine airfoils. The two alloys are PWA 1480 and Alloy 185. The two oxidation resistant coatings are PWA 273, an aluminide coating, and PWA 286, an overlay NiCoCrAlY coating. To obtain constitutive and/or fatigue data, tests were conducted on coated and uncoated PWA 1480 specimens tensilely loaded in the 100 , 110 , 111 , and 123 directions. A literature survey of constitutive models was completed for both single crystal alloys and metallic coating materials; candidate models were selected. One constitutive model under consideration for single crystal alloys applies Walker's micromechanical viscoplastic formulation to all slip systems participating in the single crystal deformation. The constitutive models for the overlay coating correlate the viscoplastic data well. For the aluminide coating, a unique test method is under development. LCF and TMF tests are underway. The two coatings caused a significant drop in fatigue life, and each produced a much different failure mechanism.

Using Wii Fit to reduce fatigue among African American women with systemic lupus erythematosus: A pilot study

PubMed Central

Yuen, Hon K.; Holthaus, Katy; Kamen, Diane L.; Sword, David; Breland, Hazel L.

2012-01-01

Fatigue and physical deconditioning are common, difficult to treat conditions among patients with systemic lupus erythematosus (SLE). The aim of this pilot study is to evaluate the effectiveness of a home-based exercise program using the Wii Fit system in patients with SLE. Fifteen sedentary African American women with SLE experiencing moderate to severe fatigue participated in a home exercise program using the Wii Fit 3 days a week for 30 minutes each for 10 weeks. A one-group pretest-posttest design was used to evaluate the effectiveness of this program. Primary outcome measure was severity of fatigue. Secondary outcome measures were body weight, waist circumference, fatigue-related symptoms of distress, activity level and physical fitness. At the completion of the 10-week Wii Fit exercise program, participants perceived fatigue severity as measured by the Fatigue Severity Scale to be significantly decreased (P=0.002), body weight and waist circumference were significantly reduced (Ps=0.01). In addition, anxiety level as measured by Hospital Anxiety and Depression Scale, and overall intensity of total pain experience as measured by Short-form of the McGill Pain Questionnaire were also significantly reduced (Ps<0.05). Findings provide preliminary support that the Wii Fit motivates this population to exercise which leads to alleviation of fatigue and reduced body weight, waist circumference, anxiety level, and overall intensity of total pain experience. PMID:21700656

Low cycle fatigue and creep-fatigue behavior of Ni-based alloy 230 at 850 C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A

Strain-controlled low cycle fatigue (LCF) and creep-fatigue testing of Ni-based alloy 230 were carried out at 850 C. The material creep-fatigue life decreased compared with its low cycle fatigue life at the same total strain range. Longer hold time at peak tensile strain further reduced the material creep-fatigue life. Based on the electron backscatter diffraction, a novel material deformation characterization method was applied, which revealed that in low cycle fatigue testing as the total strain range increased, the deformation was segregated to grain boundaries since the test temperature was higher than the material equicohesive temperature and grain boundaries became weakermore » regions compared with grains. Creep-fatigue tests enhanced the localized deformation, resulting in material interior intergranular cracking, and accelerated material damage. Precipitation in alloy 230 helped slip dispersion, favorable for fatigue property, but grain boundary cellular precipitates formed after material exposure to the elevated temperature had a deleterious effect on the material low cycle fatigue and creep-fatigue property.« less

[Counseling in the prevention of fatigue in psychiatric nurses].

PubMed

Greeff, M; Poggenpoel, M

1991-12-01

Nursing is a stressful activity and therefore it is necessary for nurses to develop effective coping mechanisms, or to strengthen existing ones in a healthy manner, in order to be capable of dealing with stress, arising from their personal and professional lives. It is, however, not solely stress itself which predisposes nurses to fatigue (physical, psychological and emotional exhaustion) but rather the chronic nature and excessive amount of stressors which place excessive demands on the energy resources and coping, mechanisms of nurses resulting in the ineffective handling of stress which in turn leads to the eventual development of fatigue. The detrimental results of this experience are, however, not confined to the nurse herself, but extends further to the patient and the organization. Thus, if fatigue is not controlled or dealt with, all parties and organizations concerned could suffer. This research covers the accompaniment function of the psychiatric nurse specialist in the prevention of fatigue in psychiatric nurses by strengthening their mental preparedness. As a possible solution to the experience of fatigue, a structured, accompanied program of three days was offered to a group of psychiatric nurses. The Solomon four group design was followed in order to eliminate influences on the subjects resulting from the completion of the self-evaluation scale as pre-test. The data which was obtained from the test results was statistically compared. Results showed that there was a definite decrease in the levels of fatigue experienced by the experimental group that received the structured accompanied programme, but no real change occurred in the control group that had merely been provided with relevant literature.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Different Levels of Localized Muscle Fatigue on Knee Position Sense

PubMed Central

Gear, William S.

2011-01-01

There is little information available regarding how proprioceptive abilities decline as the amount of exertion increases during exercise. The purpose of this study was to determine the role of different levels of fatigue on knee joint position sense. A repeated measures design was used to examine changes in active joint reposition sense (AJRS) prior to and following three levels of fatigue. Eighteen participants performed knee extension and flexion isokinetic exercise until torque output was 90%, 70%, or 50% of the peak hamstring torque for three consecutive repetitions. Active joint reposition sense at 15, 30, or 45 degrees was tested following the isokinetic exercise session. Following testing of the first independent measure, participants were given a 20 minute rest period. Testing procedures were repeated for two more exercise sessions following the other levels of fatigue. Testing of each AJRS test angle was conducted on three separate days with 48 hours between test days. Significant main effect for fatigue was indicated (p = 0.001). Pairwise comparisons indicated a significant difference between the pre-test and following 90% of peak hamstring torque (p = 0.02) and between the pre-test and following 50% of peak hamstring torque (p = 0.02). Fatigue has long been theorized to be a contributing factor in decreased proprioceptive acuity, and therefore a contributing factor to joint injury. The findings of the present study indicate that fatigue may have an effect on proprioception following mild and maximum fatigue. Key points A repeated measures design was used to examine the effect of different levels of fatigue on active joint reposition sense (AJRS) of the knee at joint angles of 15°, 30° and 45° of flexion. A statistically significant main effect for fatigue was found, specifically between no fatigue and mild fatigue and no fatigue and maximum fatigue. A statistically significant interaction effect between AJRS and fatigue was not found. Secondary analysis of the results indicated a potential plateau effect of AJRS as fatigue continues to increase. Further investigation of the effect of increasing levels of fatigue on proprioception is warranted. PMID:24149565

Effect of different levels of localized muscle fatigue on knee position sense.

PubMed

Gear, William S

2011-01-01

There is little information available regarding how proprioceptive abilities decline as the amount of exertion increases during exercise. The purpose of this study was to determine the role of different levels of fatigue on knee joint position sense. A repeated measures design was used to examine changes in active joint reposition sense (AJRS) prior to and following three levels of fatigue. Eighteen participants performed knee extension and flexion isokinetic exercise until torque output was 90%, 70%, or 50% of the peak hamstring torque for three consecutive repetitions. Active joint reposition sense at 15, 30, or 45 degrees was tested following the isokinetic exercise session. Following testing of the first independent measure, participants were given a 20 minute rest period. Testing procedures were repeated for two more exercise sessions following the other levels of fatigue. Testing of each AJRS test angle was conducted on three separate days with 48 hours between test days. Significant main effect for fatigue was indicated (p = 0.001). Pairwise comparisons indicated a significant difference between the pre-test and following 90% of peak hamstring torque (p = 0.02) and between the pre-test and following 50% of peak hamstring torque (p = 0.02). Fatigue has long been theorized to be a contributing factor in decreased proprioceptive acuity, and therefore a contributing factor to joint injury. The findings of the present study indicate that fatigue may have an effect on proprioception following mild and maximum fatigue. Key pointsA repeated measures design was used to examine the effect of different levels of fatigue on active joint reposition sense (AJRS) of the knee at joint angles of 15°, 30° and 45° of flexion.A statistically significant main effect for fatigue was found, specifically between no fatigue and mild fatigue and no fatigue and maximum fatigue.A statistically significant interaction effect between AJRS and fatigue was not found.Secondary analysis of the results indicated a potential plateau effect of AJRS as fatigue continues to increase.Further investigation of the effect of increasing levels of fatigue on proprioception is warranted.

Fatigue data for polyether ether ketone (PEEK) under fully-reversed cyclic loading

PubMed Central

Shrestha, Rakish; Simsiriwong, Jutima; Shamsaei, Nima

2016-01-01

In this article, the data obtained from the uniaxial fully-reversed fatigue experiments conducted on polyether ether ketone (PEEK), a semi-crystalline thermoplastic, are presented. The tests were performed in either strain-controlled or load-controlled mode under various levels of loading. The data are categorized into four subsets according to the type of tests, including (1) strain-controlled fatigue tests with adjusted frequency to obtain the nominal temperature rise of the specimen surface, (2) strain-controlled fatigue tests with various frequencies, (3) load-controlled fatigue tests without step loadings, and (4) load-controlled fatigue tests with step loadings. Accompanied data for each test include the fatigue life, the maximum (peak) and minimum (valley) stress–strain responses for each cycle, and the hysteresis stress–strain responses for each collected cycle in a logarithmic increment. A brief description of the experimental method is also given. PMID:26937465

Fatigue data for polyether ether ketone (PEEK) under fully-reversed cyclic loading.

PubMed

Shrestha, Rakish; Simsiriwong, Jutima; Shamsaei, Nima

2016-03-01

In this article, the data obtained from the uniaxial fully-reversed fatigue experiments conducted on polyether ether ketone (PEEK), a semi-crystalline thermoplastic, are presented. The tests were performed in either strain-controlled or load-controlled mode under various levels of loading. The data are categorized into four subsets according to the type of tests, including (1) strain-controlled fatigue tests with adjusted frequency to obtain the nominal temperature rise of the specimen surface, (2) strain-controlled fatigue tests with various frequencies, (3) load-controlled fatigue tests without step loadings, and (4) load-controlled fatigue tests with step loadings. Accompanied data for each test include the fatigue life, the maximum (peak) and minimum (valley) stress-strain responses for each cycle, and the hysteresis stress-strain responses for each collected cycle in a logarithmic increment. A brief description of the experimental method is also given.

Predicting Fatigue Lives Of Metal-Matrix/Fiber Composites

NASA Technical Reports Server (NTRS)

Bartolotta, Paul A.

1994-01-01

Method of prediction of fatigue lives of intermetallic-matrix/fiber composite parts at high temperatures styled after method of universal slopes. It suffices to perform relatively small numbers of fatigue tests. Data from fatigue tests correlated with tensile-test data by fitting universal-slopes equation to both sets of data. Thereafter, universal-slopes equation used to predict fatigue lives from tensile properties.

Experimental and modeling results of creep fatigue life of Inconel 617 and Haynes 230 at 850 C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiang; Sokolov, Mikhail A; Sham, Sam

Creep fatigue testing of Ni-based superalloy Inconel 617 and Haynes 230 were conducted in the air at 850 C. Tests were performed with fully reversed axial strain control at a total strain range of 0.5%, 1.0% or 1.5% and hold time at maximum tensile strain for 3, 10 or 30 min. In addition, two creep fatigue life prediction methods, i.e. linear damage summation and frequency-modified tensile hysteresis energy modeling, were evaluated and compared with experimental results. Under all creep fatigue tests, Haynes 230 performed better than Inconel 617. Compared to the low cycle fatigue life, the cycles to failure formore » both materials decreased under creep fatigue test conditions. Longer hold time at maximum tensile strain would cause a further reduction in both material creep fatigue life. The linear damage summation could predict the creep fatigue life of Inconel 617 for limited test conditions, but considerably underestimated the creep fatigue life of Haynes 230. In contrast, frequency-modified tensile hysteresis energy modeling showed promising creep fatigue life prediction results for both materials.« less

Evaluation of fatigue life of CRM-reinforced SMA and its relationship to dynamic stiffness.

PubMed

Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati; Koting, Suhana

2014-01-01

Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400 kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture.

Experimental and modeling results of creep-fatigue life of Inconel 617 and Haynes 230 at 850 °C

NASA Astrophysics Data System (ADS)

Chen, Xiang; Sokolov, Mikhail A.; Sham, Sam; Erdman, Donald L., III; Busby, Jeremy T.; Mo, Kun; Stubbins, James F.

2013-01-01

Creep-fatigue testing of Ni-based superalloy Inconel 617 and Haynes 230 were conducted in the air at 850 °C. Tests were performed with fully reversed axial strain control at a total strain range of 0.5%, 1.0% or 1.5% and hold time at maximum tensile strain for 3, 10 or 30 min. In addition, two creep-fatigue life prediction methods, i.e. linear damage summation and frequency-modified tensile hysteresis energy modeling, were evaluated and compared with experimental results. Under all creep-fatigue tests, Haynes 230 performed better than Inconel 617. Compared to the low cycle fatigue life, the cycles to failure for both materials decreased under creep-fatigue test conditions. Longer hold time at maximum tensile strain would cause a further reduction in both material creep-fatigue life. The linear damage summation could predict the creep-fatigue life of Inconel 617 for limited test conditions, but considerably underestimated the creep-fatigue life of Haynes 230. In contrast, frequency-modified tensile hysteresis energy modeling showed promising creep-fatigue life prediction results for both materials.

Cast iron-base alloy for cylinder/regenerator housing

NASA Technical Reports Server (NTRS)

Witter, Stewart L.; Simmons, Harold E.; Woulds, Michael J.

1985-01-01

NASACC-1 is a castable iron-base alloy designed to replace the costly and strategic cobalt-base X-40 alloy used in the automotive Stirling engine cylinder/generator housing. Over 40 alloy compositions were evaluated using investment cast test bars for stress-rupture testing. Also, hydrogen compatibility and oxygen corrosion resistance tests were used to determine the optimal alloy. NASACC-1 alloy was characterized using elevated and room temperature tensile, creep-rupture, low cycle fatigue, heat capacity, specific heat, and thermal expansion testing. Furthermore, phase analysis was performed on samples with several heat treated conditions. The properties are very encouraging. NASACC-1 alloy shows stress-rupture and low cycle fatigue properties equivalent to X-40. The oxidation resistance surpassed the program goal while maintaining acceptable resistance to hydrogen exposure. The welding, brazing, and casting characteristics are excellent. Finally, the cost of NASACC-1 is significantly lower than that of X-40.

Comparative Study of Nondestructive Pavement Testing, MacDill Air Force Base, Florida

DTIC Science & Technology

1987-07-01

a deflection-basin fitting program that prodicts moduli of the pavement layers and subgrade. A layered-elastic program AIRPOD is used in a fatigue...Layered-elastic Limiting stress in PCC; of pavement layers ( AIRPOD ) limiting strain in AC from deflection basin (ELSYM-5) (BASFIT) AFESC Elastic moduli of...need not be made. 121. Pavement evaluation computations were next accomplished using a series of computer programs referred to as ELSYM-5 and AIRPOD

Fatigue crack identification method based on strain amplitude changing

NASA Astrophysics Data System (ADS)

Guo, Tiancai; Gao, Jun; Wang, Yonghong; Xu, Youliang

2017-09-01

Aiming at the difficulties in identifying the location and time of crack initiation in the castings of helicopter transmission system during fatigue tests, by introducing the classification diagnostic criteria of similar failure mode to find out the similarity of fatigue crack initiation among castings, an engineering method and quantitative criterion for detecting fatigue cracks based on strain amplitude changing is proposed. This method is applied on the fatigue test of a gearbox housing, whose results indicates: during the fatigue test, the system alarms when SC strain meter reaches the quantitative criterion. The afterwards check shows that a fatigue crack less than 5mm is found at the corresponding location of SC strain meter. The test result proves that the method can provide accurate test data for strength life analysis.

A task-oriented circuit training in multiple sclerosis: a feasibility study

PubMed Central

2014-01-01

Background The aim of this study was to evaluate the safety, feasibility and preliminary effects of a high-intensity rehabilitative task-oriented circuit training (TOCT) in a sample of multiple sclerosis (MS) subjects on walking competency, mobility, fatigue and health-related quality of life (HRQoL). Methods 24 MS subjects (EDSS 4.89 ± 0.54, 17 female and 7 male, 52.58 ± 11.21 years, MS duration 15.21 ± 8.68 years) have been enrolled and randomly assigned to 2 treatment groups: (i) experimental group received 10 TOCT sessions over 2 weeks (2 hours/each session) followed by a 3 months home exercise program, whereas control group did not receive any specific rehabilitation intervention. A feasibility patient-reported questionnaire was administered after TOCT. Functional outcome measures were: walking endurance (Six Minute Walk Test), gait speed (10 Meter Walk Test), mobility (Timed Up and Go test) and balance (Dynamic Gait Index). Furthermore, self-reported questionnaire of motor fatigue (Fatigue Severity Scale), walking ability (Multiple Sclerosis Walking Scale – 12) and health-related quality of life (Multiple Sclerosis Impact Scale – 29) were included. Subjects’ assessments were delivered at baseline (T0), after TOCT (T1) and 3 months of home-based exercise program (T2). Results After TOCT subjects reported a positive global rating on the received treatment. At 3 months, we found a 58.33% of adherence to the home-exercise program. After TOCT, walking ability and health-related quality of life were improved (p < 0.05) with minor retention after 3 months. The control group showed no significant changes in any variables. Conclusions This two weeks high-intensity task-oriented circuit class training followed by a three months home-based exercise program seems feasible and safe in MS people with moderate mobility impairments; moreover it might improve walking abilities. Trial registration NCT01464749 PMID:24906545

Deformation history and load sequence effects on cumulative fatigue damage and life predictions

NASA Astrophysics Data System (ADS)

Colin, Julie

Fatigue loading seldom involves constant amplitude loading. This is especially true in the cooling systems of nuclear power plants, typically made of stainless steel, where thermal fluctuations and water turbulent flow create variable amplitude loads, with presence of mean stresses and overloads. These complex loading sequences lead to the formation of networks of microcracks (crazing) that can propagate. As stainless steel is a material with strong deformation history effects and phase transformation resulting from plastic straining, such load sequence and variable amplitude loading effects are significant to its fatigue behavior and life predictions. The goal of this study was to investigate the effects of cyclic deformation on fatigue behavior of stainless steel 304L as a deformation history sensitive material and determine how to quantify and accumulate fatigue damage to enable life predictions under variable amplitude loading conditions for such materials. A comprehensive experimental program including testing under fully-reversed, as well as mean stress and/or mean strain conditions, with initial or periodic overloads, along with step testing and random loading histories was conducted on two grades of stainless steel 304L, under both strain-controlled and load-controlled conditions. To facilitate comparisons with a material without deformation history effects, similar tests were also carried out on aluminum 7075-T6. Experimental results are discussed, including peculiarities observed with stainless steel behavior, such as a phenomenon, referred to as secondary hardening characterized by a continuous increase in the stress response in a strain-controlled test and often leading to runout fatigue life. Possible mechanisms for secondary hardening observed in some tests are also discussed. The behavior of aluminum is shown not to be affected by preloading, whereas the behavior of stainless steel is greatly influenced by prior loading. Mean stress relaxation in strain control and ratcheting in load control and their influence on fatigue life are discussed. Some unusual mean strain test results are presented for stainless steel 304L, where in spite of mean stress relaxation fatigue lives were significantly longer than fully-reversed tests. Prestraining indicated no effect on either deformation or fatigue behavior of aluminum, while it induced considerable hardening in stainless steel 304L and led to different results on fatigue life, depending on the test control mode. In step tests for stainless steel 304L, strong hardening induced by the first step of a high-low sequence significantly affects the fatigue behavior, depending on the test control mode used. For periodic overload tests of stainless steel 340L, hardening due to the overloads was progressive throughout life and more significant than in high-low step tests. For aluminum, no effect on deformation behavior was observed due to periodic overloads. However, the direction of the overloads was found to affect fatigue life, as tensile overloads led to longer lives, while compressive overloads led to shorter lives. Deformation and fatigue behaviors under random loading conditions are also presented and discussed for the two materials. The applicability of a common cumulative damage rule, the linear damage rule, is assessed for the two types of material, and for various loading conditions. While the linear damage rule associated with a strain-life or stress-life curve is shown to be fairly accurate for life predictions for aluminum, it is shown to poorly represent the behavior of stainless steel, especially in prestrained and high-low step tests, in load control. In order to account for prior deformation effects and achieve accurate fatigue life predictions for stainless steel, parameters including both stress and strain terms are required. The Smith-Watson-Topper and Fatemi-Socie approaches, as such parameters, are shown to correlate most test data fairly accurately. For damage accumulation under variable amplitude loading, the linear damage rule associated with strain-life or stress-life curves can lead to inaccurate fatigue life predictions, especially for materials presenting strong deformation memory effect, such as stainless steel 304L. The inadequacy of this method is typically attributed to the linear damage rule itself. On the contrary, this study demonstrates that damage accumulation using the linear damage rule can be accurate, provided that the linear damage rule is used in conjunction with parameters including both stress and strain terms. By including both loading history and response of the material in damage quantification, shortcomings of the commonly used linear damage rule approach can be circumvented in an effective manner. In addition, cracking behavior was also analyzed under various loading conditions. Results on microcrack initiation and propagation are presented in relation to deformation and fatigue behaviors of the materials. Microcracks were observed to form during the first few percent of life, indicating that most of the fatigue life of smooth specimens is spent in microcrack formation and growth. Analyses of fractured specimens showed that microcrack formation and growth is dependent on the loading history, and less important in aluminum than stainless steel 304L, due to the higher toughness of this latter material.

Influence of type D personality on job stress and job satisfaction in clinical nurses: the mediating effects of compassion fatigue, burnout, and compassion satisfaction.

PubMed

Kim, Yeon Hee; Kim, Sung Reul; Kim, Yeo Ok; Kim, Ji Young; Kim, Hyun Kyung; Kim, Hye Young

2017-04-01

To test a hypothetical path model evaluating the influence of type D personality on job stress and job satisfaction and to identify the mediating effects of compassion fatigue, burnout, and compassion satisfaction among clinical nurses in South Korea. Personalities susceptible to stress, compassion fatigue, and burnout in clinical nurses have negative effects on the job stress and job satisfaction. A correlational, cross-sectional design was used. A convenience sample of 875 clinical nurses was recruited between December 2014 - February 2015. The structured questionnaires included the Type D personality scale-14, Professional Quality of Life, job stress, job satisfaction, and general characteristics. To test the hypothetical path model, we performed a path analysis by using the AMOS 18·0 program. Based on the path model, type D personality was significantly associated with compassion fatigue, burnout, and compassion satisfaction in our study subjects. Type D personality was significantly associated with job stress and job satisfaction via the effect of burnout, compassion satisfaction, and job stress. Since type D personality is associated with job stress and job satisfaction, identifying personalities vulnerable to stress would help to address job stress and to enhance job satisfaction when nurses have a high level of compassion fatigue and burnout and a low level of compassion satisfaction. The development of interventions that can reduce negative affect and social inhibition of nurses with type D personality and investigation of methods to decrease their compassion fatigue and burnout and to increase compassion satisfaction should be encouraged. © 2016 John Wiley & Sons Ltd.

Learning to live on a Mars day: fatigue countermeasures during the Phoenix Mars Lander mission.

PubMed

Barger, Laura K; Sullivan, Jason P; Vincent, Andrea S; Fiedler, Edna R; McKenna, Laurence M; Flynn-Evans, Erin E; Gilliland, Kirby; Sipes, Walter E; Smith, Peter H; Brainard, George C; Lockley, Steven W

2012-10-01

To interact with the robotic Phoenix Mars Lander (PML) spacecraft, mission personnel were required to work on a Mars day (24.65 h) for 78 days. This alien schedule presents a challenge to Earth-bound circadian physiology and a potential risk to workplace performance and safety. We evaluated the acceptability, feasibility, and effectiveness of a fatigue management program to facilitate synchronization with the Mars day and alleviate circadian misalignment, sleep loss, and fatigue. Operational field study. PML Science Operations Center. Scientific and technical personnel supporting PML mission. Sleep and fatigue education was offered to all support personnel. A subset (n = 19) were offered a short-wavelength (blue) light panel to aid alertness and mitigate/reduce circadian desynchrony. They were assessed using a daily sleep/work diary, continuous wrist actigraphy, and regular performance tests. Subjects also completed 48-h urine collections biweekly for assessment of the circadian 6-sulphatoxymelatonin rhythm. Most participants (87%) exhibited a circadian period consistent with adaptation to a Mars day. When synchronized, main sleep duration was 5.98 ± 0.94 h, but fell to 4.91 ± 1.22 h when misaligned (P < 0.001). Self-reported levels of fatigue and sleepiness also significantly increased when work was scheduled at an inappropriate circadian phase (P < 0.001). Prolonged wakefulness (≥ 21 h) was associated with a decline in performance and alertness (P < 0.03 and P < 0.0001, respectively). The ability of the participants to adapt successfully to the Mars day suggests that future missions should utilize a similar circadian rhythm and fatigue management program to reduce the risk of sleepiness-related errors that jeopardize personnel safety and health during critical missions.

Surface protection overview

NASA Technical Reports Server (NTRS)

Levine, S. R.

1982-01-01

A first-cut integrated environmental attack life prediction methodology for hot section components is addressed. The HOST program is concerned with oxidation and hot corrosion attack of metallic coatings as well as their degradation by interdiffusion with the substrate. The effects of the environment and coatings on creep/fatigue behavior are being addressed through a joint effort with the Fatigue sub-project. An initial effort will attempt to scope the problem of thermal barrier coating life prediction. Verification of models will be carried out through benchmark rig tests including a 4 atm. replaceable blade turbine and a 50 atm. pressurized burner rig.

Fatigue life of high-speed ball bearings with silicon nitride balls

NASA Technical Reports Server (NTRS)

Parker, R. J.; Zaretsky, E. V.

1974-01-01

Hot-pressed silicon nitride was evaluated as a rolling-element bearing material. The five-ball fatigue tester was used to test 12.7-mm- diameter silicon nitride balls at maximum Hertz stresses ranging from 4.27 x 10 to the 9th power n/sq m to 6.21 x 10 to the 9th power n/sq m at a race temperature of 328K. The fatigue life of NC-132 hot-pressed silicon nitride was found to be equal to typical bearing steels and much greater than other ceramic or cermet materials at the same stress levels. A digital computer program was used to predict the fatigue life of 120-mm- bore angular-contact ball bearings containing either steel or silicon nitride balls. The analysis indicates that there is no improvement in the lives of bearings of the same geometry operating at DN values from 2 to 4 million where silicon nitride balls are used in place of steel balls.

[Effects of aroma self-foot reflexology massage on stress and immune responses and fatigue in middle-aged women in rural areas].

PubMed

Kim, Ja Ok; Kim, In Sook

2012-10-01

This study was done to examine the effects of aroma self-foot reflexology massage on stress and immune responses and fatigue in middle-aged women in rural areas. The study was a nonequivalent control group pre-post test design. The participants were 52 middle-aged women from rural areas of which 26 were assigned to the experimental group and 26 to the control group. Data were collected from July to September, 2011 and analyzed using SPSS Win 17.0 version program. The intervention was conducted 3 times a week for six weeks. There were significant differences in reported perceived stress, systolic blood pressure, diastolic blood pressure and fatigue between the two groups. However, the issue of salivary cortisol and immune response were not significant. Aroma self-foot reflexology massage can be utilized as an effective intervention for perceived stress, systolic blood pressure, diastolic blood pressure and fatigue in middle-aged woman in rural areas.

Effects of Acute Fatigue of the Hip Flexor Muscles on Hamstring Muscle Extensibility.

PubMed

Muyor, José M; Arrabal-Campos, Francisco M

2016-12-01

The purpose of the present study was to evaluate the influence of acute fatigue of the hip flexor muscles on scores attained in tests frequently used in literature to measure hamstring muscle extensibility, namely the passive straight leg raise (PSLR), active straight leg raise (ASLR), passive knee extension (PKE), active knee extension (AKE), sit-and-reach (SR) and toe-touch (TT) tests. A total of seventy-five healthy and recreationally active adults voluntarily participated in this study. To reach fatigue, the participants actively lifted their legs alternately as many times as possible. In the passive tests, the results were 7.10 ± 5.21° and 5.68 ± 4.54° higher (p < 0.01) for PSLR and PKE tests, respectively, after acute fatigue. However, in the ASLR test, the results were lower post-fatigue than pre-fatigue (mean difference = -5.30° ± 9.51°; p < 0.01). The AKE, SR and TT tests did not show significant differences between pre- and post-fatigue (p > 0.05). Moderate (r = 0.40) to high (r = 0.97) correlation coefficients were found, which were statistically significant among all the measured flexibility tests both pre- and post-fatigue. In conclusion, the active implication of the hip flexor muscles until reaching fatigue had acute influences on the results of the PSLR, PKE and ASLR tests, but not on the results of the AKE, SR and TT tests. It is recommended to use the AKE test to assess hamstring muscle extensibility in situations where athletes show fatigue in their hip flexor muscles.

Strain energy release rate as a function of temperature and preloading history utilizing the edge delamination fatique test method

NASA Technical Reports Server (NTRS)

Zimmerman, Richard S.; Adams, Donald F.

1989-01-01

Static laminate and tension-tension fatigue tests of IM7/8551-7 composite materials was performed. The Edge Delamination Test (EDT) was utilized to evaluate the temperature and preloading history effect on the critical strain energy release rate. Static and fatigue testing was performed at room temperature and 180 F (82 C). Three preloading schemes were used to precondition fatigue test specimens prior to performing the normal tension-tension fatigue EDT testing. Computer software was written to perform all fatigue testing while monitoring the dynamic modulus to detect the onset of delamination and record the test information for later retrieval and reduction.

Is the Sørensen test valid to assess muscle fatigue of the trunk extensor muscles?

PubMed

Demoulin, Christophe; Boyer, Mathieu; Duchateau, Jacques; Grosdent, Stéphanie; Jidovtseff, Boris; Crielaard, Jean-Michel; Vanderthommen, Marc

2016-01-01

Very few studies have quantified the degree of fatigue characterized by the decline in the maximal voluntary contraction (MVC) force of the trunk extensors induced by the widely used Sørensen test. Measure the degree of fatigue of the trunk extensor muscles induced by the Sørensen test. Eighty young healthy subjects were randomly divided into a control group (CG) and an experimental group (EG), each including 50% of the two genders. The EG performed an isometric MVC of the trunk extensors (pre-fatigue test) followed by the Sørensen test, the latter being immediately followed by another MVC (post-fatigue test). The CG performed only the pre- and post-fatigue tests without any exertion in between. The comparison of the pre- and post-fatigue tests revealed a significant (P< 0.05) decrease in MVC force normalized by body mass (-13%) in the EG, whereas a small increase occurred in the CG (+2.7%, P= 0.001). This study shows that the Sørensen test performed until failure in a young healthy population results in a reduced ability of the trunk extensor muscles to generate maximal force, and indicates that this test is valid for the assessment of fatigue in trunk extensor muscles.

Evaluation of Fatigue Life of CRM-Reinforced SMA and Its Relationship to Dynamic Stiffness

PubMed Central

Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati

2014-01-01

Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400 kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture. PMID:25050406

Best Practices for Fatigue Risk Management in Non-Traditional Shiftwork

NASA Technical Reports Server (NTRS)

Flynn-Evans, Erin E.

2016-01-01

Fatigue risk management programs provide effective tools to mitigate fatigue among shift workers. Although such programs are effective for typical shiftwork scenarios, where individuals of equal skill level can be divided into shifts to cover 24 hour operations, traditional programs are not sufficient for managing sleep loss among individuals with unique skill sets, in occupations where non-traditional schedules are required. Such operations are prevalent at NASA and in other high stress occupations, including among airline pilots, military personnel, and expeditioners. These types of operations require fatigue risk management programs tailored to the specific requirements of the mission. Without appropriately tailored fatigue risk management, such operations can lead to an elevated risk of operational failure, disintegration of teamwork, and increased risk of accidents and incidents. In order to design schedules for such operations, schedule planners must evaluate the impact of a given operation on circadian misalignment, acute sleep loss, chronic sleep loss and sleep inertia. In addition, individual-level factors such as morningness-eveningness preference and sleep disorders should be considered. After the impact of each of these factors has been identified, scheduling teams can design schedules that meet operational requirements, while also minimizing fatigue.

Strength and endurance training reduces the loss of eccentric hamstring torque observed after soccer specific fatigue.

PubMed

Matthews, Martyn J; Heron, Kate; Todd, Stefanie; Tomlinson, Andrew; Jones, Paul; Delextrat, Anne; Cohen, Daniel D

2017-05-01

To investigate the effect of two hamstring training protocols on eccentric peak torque before and after soccer specific fatigue. Twenty-two university male soccer players. Isokinetic strength tests were performed at 60°/s pre and post fatigue, before and after 2 different training interventions. A 45-min soccer specific fatigue modified BEAST protocol (M-BEAST) was used to induce fatigue. Players were randomly assigned to a 4 week hamstrings conditioning intervention with either a maximum strength (STR) or a muscle endurance (END) emphasis. The following parameters were evaluated: Eccentric peak torque (EccPT), angle of peak torque (APT), and angle specific torques at knee joint angles of 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80° and 90°. There was a significant effect of the M-BEAST on the Eccentric torque angle profile before training as well as significant improvements in post-fatigue torque angle profile following the effects of both strength and muscle endurance interventions. Forty-five minutes of simulated soccer activity leads to reduced eccentric hamstring torque at longer muscle lengths. Short-term conditioning programs (4-weeks) with either a maximum strength or a muscular endurance emphasis can equally reduce fatigue induced loss of strength over this time period. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fatigue Strength and Related Characteristics of Aircraft Joints I : Comparison of Spot-Weld and Rivet Patterns in 24s-t Alclad and 75s-t Alclad

NASA Technical Reports Server (NTRS)

Russell, H W; Jackson, L R; Grover, H J; Beaver, W W

1944-01-01

Report contains detailed results of a number of fatigue tests on spot-welded joints in aluminum alloys. The tests described include: (1) fatigue tests on spot-welded lap joints in sheets of unequal thickness of alclad 24s-t. These tests indicate that the fatigue strength of a spot-welded joint in sheets of two different gages is slightly higher than that of a similar joint in two sheets of the thinner gage but definitely lower than that of a similar joint in two sheets of the thicker gage. (2) Fatigue tests on spot-welded alclad 75s-t spot-welded lap-joint specimens of alclad 75s-t were not any stronger in fatigue than similar specimens of alclad 24s-t. (3) Fatigue tests on lap-joint specimens spot -welded after various surface preparations--these included ac welding wire-brushed surfaces, dc welding wire-brushed surfaces, and dc welding chemically cleaned surfaces. While the ac welds were strongest statically, the dc welds on wire-brushed surfaces were strongest in fatigue. Specimens prepared in this way were very nearly as strong as the best riveted specimens tested for comparison. (4) Fatigue tests on specimens spot-welded with varying voltage so as to include a wide range of static spot-weld strengths. The fatigue strengths were in the same order as the static strengths but showed less range. (author)

Simulation of Fatigue Crack Initiation at Corrosion Pits With EDM Notches

NASA Technical Reports Server (NTRS)

Smith, Stephen W.; Newman, John A.; Piascik, Robert S.

2003-01-01

Uniaxial fatigue tests were conducted to compare the fatigue life of laboratory produced corrosion pits, similar to those observed in the shuttle main landing gear wheel bolt-hole, and an electro-discharged-machined (EDM) flaw. EDM Jaws are used to simulate corrosion pits during shuttle wheel (dynamometer) testing. The aluminum alloy, (AA 7050) laboratory fatigue tests were conducted to simulate the local stress level contained in the wheel bolt-hole. Under this high local stress condition, the EDM notch produced a fatigue life similar to test specimens containing corrosion pits of similar size. Based on the laboratory fatigue test results, the EDM Jaw (semi-circular disc shaped) produces a local stress state similar to corrosion pits and can be used to simulate a corrosion pit during the shuttle wheel dynamometer tests.

CARES/LIFE Ceramics Analysis and Reliability Evaluation of Structures Life Prediction Program

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.; Powers, Lynn M.; Janosik, Lesley A.; Gyekenyesi, John P.

2003-01-01

This manual describes the Ceramics Analysis and Reliability Evaluation of Structures Life Prediction (CARES/LIFE) computer program. The program calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. CARES/LIFE is an extension of the CARES (Ceramic Analysis and Reliability Evaluation of Structures) computer program. The program uses results from MSC/NASTRAN, ABAQUS, and ANSYS finite element analysis programs to evaluate component reliability due to inherent surface and/or volume type flaws. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing the power law, Paris law, or Walker law. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled by using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. The probabilistic time-dependent theories used in CARES/LIFE, along with the input and output for CARES/LIFE, are described. Example problems to demonstrate various features of the program are also included.

Early Experience with a Brief, Multimodal, Multidisciplinary Treatment Program for Fibromyalgia

PubMed Central

Vincent, Ann; Whipple, Mary O.; Oh, Terry H.; Guderian, Janet A.; Barton, Debra L.; Luedtke, Connie A.

2014-01-01

Fibromyalgia is a complex, heterogeneous disorder for which a multidisciplinary individualized approach is currently advocated. We executed a 1 week multidisciplinary fibromyalgia clinical program with 7 patients, based on our previous experience with our existing 1.5 day multidisciplinary fibromyalgia program that has demonstrated both short- and long-term benefits. The current expanded program was not designed as a clinical study, but rather as a clinical feasibility assessment and was multidisciplinary in nature, with cognitive behavioral therapy, activity pacing and graded exercise therapy as major components. We assessed changes in individual patients at 1 week and 3 months following the program utilizing validated self-report measures of pain, fatigue, and self-efficacy. All patients indicated at least small improvements in pain and physical symptoms both at 1 week and 3 months and all but one patient showed improvement in self-efficacy at 1 week and 3 months. Similar trends were observed for fatigue. Based on our early clinical experience, we conclude that the 1 week multidisciplinary fibromyalgia program is logistically feasible and has potential for clinical efficacy. Further research is needed and is planned to test the clinical efficacy of this program and compare it with other interventions. PMID:24315246

Reversal of Refractory Ulcerative Colitis and Severe Chronic Fatigue Syndrome Symptoms Arising from Immune Disturbance in an HLADR/DQ Genetically Susceptible Individual with Multiple Biotoxin Exposures

PubMed Central

Gunn, Shelly R.; Gibson Gunn, G.; Mueller, Francis W.

2016-01-01

Patient: Male, 25 Final Diagnosis: Ulcerative colitis and chronic fatigue syndrome Symptoms: Colitis • profound fatigue • multi-joint pain • cognitive impairment • corneal keratitis Medication: — Clinical Procedure: VIP replacement therapy Specialty: Family Medicine Objective: Unusual clinical course Background: Patients with multisymptom chronic conditions, such as refractory ulcerative colitis (RUC) and chronic fatigue syndrome (CFS), present diagnostic and management challenges for clinicians, as well as the opportunity to recognize and treat emerging disease entities. In the current case we report reversal of co-existing RUC and CFS symptoms arising from biotoxin exposures in a genetically susceptible individual. Case Report: A 25-year-old previously healthy male with new-onset refractory ulcerative colitis (RUC) and chronic fatigue syndrome (CFS) tested negative for autoimmune disease biomarkers. However, urine mycotoxin panel testing was positive for trichothecene group and air filter testing from the patient’s water-damaged rental house identified the toxic mold Stachybotrys chartarum. HLA-DR/DQ testing revealed a multisusceptible haplotype for development of chronic inflammation, and serum chronic inflammatory response syndrome (CIRS) biomarker testing was positive for highly elevated TGF-beta and a clinically undetectable level of vasoactive intestinal peptide (VIP). Following elimination of biotoxin exposures, VIP replacement therapy, dental extractions, and implementation of a mind body intervention-relaxation response (MBI-RR) program, the patient’s symptoms resolved. He is off medications, back to work, and resuming normal exercise. Conclusions: This constellation of RUC and CFS symptoms in an HLA-DR/DQ genetically susceptible individual with biotoxin exposures is consistent with the recently described CIRS disease pathophysiology. Chronic immune disturbance (turbatio immuno) can be identified with clinically available CIRS biomarkers and may represent a treatable underlying disease etiology in a subset of genetically susceptible patients with RUC, CFS, and other immune disorders. PMID:27165859

High temperature, low-cycle fatigue of copper-base alloys for rocket nozzles. Part 2: Strainrange partitioning and low-cycle fatigue results at 538 deg C

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1976-01-01

Low-cycle fatigue tests of 1/2 Hard AMZIRC Copper and NARloy Z were performed in argon at 538 C to determine partitioned strain range versus life relationships. Strain-controlled low-cycle fatigue tests of a Zr-Cr-Mg copper-base alloy were also performed. Strain ranges, lower than those employed in previous tests, were imposed in order to extend the fatigue life curve out to approximately 400,000 cycles. An experimental copper alloy and an experimental silver alloy were also studied. Tensile tests were performed in air at room temperature and in argon at 538 C. Strain-controlled low-cycle fatigue tests were performed at 538 C in argon to define the fatigue life over the regime from 300 to 3,000 cycles. For the silver alloy, three additional heat treatments were introduced, and a limited evaluation of the short-term tensile and low-cycle fatigue behavior at 538 C was performed.

Notched fatigue of single crystal PWA 1480 at turbine attachment temperatures

NASA Technical Reports Server (NTRS)

Meyer, T. G.; Nissley, D. M.; Swanson, G. A.

1989-01-01

The focus is on the lower temperature, uncoated and notched features of gas turbine blades. Constitutive and fatigue life prediction models applicable to these regions are being developed. Fatigue results are presented which were obtained thus far. Fatigue tests are being conducted on PWA 1480 single crystal material using smooth strain controlled specimens and three different notched specimens. Isothermal fatigue tests were conducted at 1200, 1400, and 1600 F. The bulk of the tests were conducted at 1200 F. The strain controlled tests were conducted at 0.4 percent per second strain rate and the notched tests were cycled at 1.0 cycle per second. A clear orientation dependence is observed in the smooth strain controlled fatigue results. The fatigue lifes of the thin, mild notched specimens agree fairly well with this smooth data when elastic stress range is used as a correlating parameter. Finite element analyses were used to calculate notch stresses. Fatigue testing will continue to further explore the trends observed thus far. Constitutive and life prediction models are being developed.

Prediction of Mean and Design Fatigue Lives of Self Compacting Concrete Beams in Flexure

NASA Astrophysics Data System (ADS)

Goel, S.; Singh, S. P.; Singh, P.; Kaushik, S. K.

2012-02-01

In this paper, result of an investigation conducted to study the flexural fatigue characteristics of self compacting concrete (SCC) beams in flexure are presented. An experimental programme was planned in which approximately 60 SCC beam specimens of size 100 × 100 × 500 mm were tested under flexural fatigue loading. Approximately 45 static flexural tests were also conducted to facilitate fatigue testing. The flexural fatigue and static flexural strength tests were conducted on a 100 kN servo-controlled actuator. The fatigue life data thus obtained have been used to establish the probability distributions of fatigue life of SCC using two-parameter Weibull distribution. The parameters of the Weibull distribution have been obtained by different methods of analysis. Using the distribution parameters, the mean and design fatigue lives of SCC have been estimated and compared with Normally vibrated concrete (NVC), the data for which have been taken from literature. It has been observed that SCC exhibits higher mean and design fatigue lives compared to NVC.

Detecting Gear Tooth Fatigue Cracks in Advance of Complete Fracture

NASA Technical Reports Server (NTRS)

Zakrajsek, James J.; Lewicki, David G.

1996-01-01

Results of using vibration-based methods to detect gear tooth fatigue cracks are presented. An experimental test rig was used to fail a number of spur gear specimens through bending fatigue. The gear tooth fatigue crack in each test was initiated through a small notch in the fillet area of a tooth on the gear. The primary purpose of these tests was to verify analytical predictions of fatigue crack propagation direction and rate as a function of gear rim thickness. The vibration signal from a total of three tests was monitored and recorded for gear fault detection research. The damage consisted of complete rim fracture on the two thin rim gears and single tooth fracture on the standard full rim test gear. Vibration-based fault detection methods were applied to the vibration signal both on-line and after the tests were completed. The objectives of this effort were to identify methods capable of detecting the fatigue crack and to determine how far in advance of total failure positive detection was given. Results show that the fault detection methods failed to respond to the fatigue crack prior to complete rim fracture in the thin rim gear tests. In the standard full rim gear test all of the methods responded to the fatigue crack in advance of tooth fracture; however, only three of the methods responded to the fatigue crack in the early stages of crack propagation.

Creep-fatigue life prediction for engine hot section materials (isotropic)

NASA Technical Reports Server (NTRS)

Moreno, V.

1982-01-01

The objectives of this program are the investigation of fundamental approaches to high temperature crack initiation life prediction, identification of specific modeling strategies and the development of specific models for component relevant loading conditions. A survey of the hot section material/coating systems used throughout the gas turbine industry is included. Two material/coating systems will be identified for the program. The material/coating system designated as the base system shall be used throughout Tasks 1-12. The alternate material/coating system will be used only in Task 12 for further evaluation of the models developed on the base material. In Task II, candidate life prediction approaches will be screened based on a set of criteria that includes experience of the approaches within the literature, correlation with isothermal data generated on the base material, and judgements relative to the applicability of the approach for the complex cycles to be considered in the option program. The two most promising approaches will be identified. Task 3 further evaluates the best approach using additional base material fatigue testing including verification tests. Task 4 consists of technical, schedular, financial and all other reporting requirements in accordance with the Reports of Work clause.

Comparison of structural response and fatigue endurance of aircraft flap-like box structures subjected to acoustic loading

NASA Astrophysics Data System (ADS)

Xiao, Y.; White, R. G.; Aglietti, G. S.

2005-05-01

The results of an extensive test program to characterize the behavior of typical aircraft structures under acoustic loading and to establish their fatigue endurance are presented. The structures tested were the three flap-like box-type of structures. Each structure consisted of one flat (bottom) and one curved (top) stiffener stiffened skin panel, front, and rear spars, and ribs that divided the structures into three bays. The three structures, constructed from three different materials (aircraft standard aluminum alloy, Carbon Fibre Reinforced Plastic, and a Glass Fibre Metal Laminate, i.e., GLARE) had the same size and configuration, with only minor differences due to the use of different materials. A first set of acoustic tests with excitations of intensity ranging from 140 to 160 dB were carried out to obtain detailed data on the dynamic response of the three structures. The FE analysis of the structures is also briefly described and the results compared with the experimental data. The fatigue endurance of the structures was then determined using random acoustic excitation with an overall sound pressure level of 161 dB, and details of crack propagation are reported. .

Damage Tolerance Characterisitics of Composite Sandwich Structures

DTIC Science & Technology

2000-02-01

requirements impose strict test program is devised and carried out, with hundreds of tests at constraints on the design of composite aircraft... design A particular effort was dedicated to the study of delamination methodologies, as well as static and fatigue strength and growth under...partition according to the theoretical tools, the industries are more or less forced, for the fundamental modes. design of primary composite structures

Investigating the effects of maximal anaerobic fatigue on dynamic postural control using the Y-Balance Test.

PubMed

Johnston, William; Dolan, Kara; Reid, Niamh; Coughlan, Garrett F; Caulfield, Brian

2018-01-01

The Y Balance Test is one of the most commonly used dynamic balance assessments, providing an insight into the integration of the sensorimotor subsystems. In recent times, there has been an increase in interest surrounding it's use in various clinical populations demonstrating alterations in motor function. Therefore, it is important to examine the effect physiological influences such as fatigue play in dynamic postural control, and establish a timeframe for its recovery. Descriptive laboratory study. Twenty male and female (age 23.75±4.79years, height 174.12±8.45cm, mass 69.32±8.76kg) partaking in competitive sport, completed the Y Balance Test protocol at 0, 10 and 20min, prior to a modified 60s Wingate fatiguing protocol. Post-fatigue assessments were then completed at 0, 10 and 20 min post-fatiguing intervention. Intraclass correlation coefficients demonstrated excellent intra-session reliability (0.976-0.982) across the three pre-fatigue YBT tests. Post-hoc paired sample t-tests demonstrated that all three reach directions demonstrated statistically significant differences between pre-fatigue and the first post-fatigue measurement (anterior; p=0.019, posteromedial; p=0.019 & posterolateral; p=0.003). The anterior reach direction returned to pre-fatigue levels within 10min (p=0.632). The posteromedial reach direction returned to pre-fatigue levels within 20min (p=0.236), while the posterolateral direction maintained a statistically significant difference at 20min (p=0.023). Maximal anaerobic fatigue has a negative effect on normalised Y balance test scores in all three directions. Following the fatiguing protocol, dynamic postural control returns to pre-fatigue levels for the anterior (<10min), posteromedial (<20min) and posterolateral (>20min). Copyright © 2017 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

Feeling Well Rested and Wide Awake When it Counts

NASA Technical Reports Server (NTRS)

2006-01-01

Responding to a congressional concern about aviation safety, NASA's Ames Research Center created the Ames Fatigue/Jet Lag Program in 1980 to examine the extent to which fatigue, sleep loss, and circadian disruption affect pilot performance. The program s primary research was conducted in field settings, as well as in a variety of aviation, controlled laboratory, and full-mission flight-simulation environments, to study fatigue factors and circadian disruption in short-haul, long-haul, military, cargo, and helicopter operations. In 1990, NASA changed the program s name to the Fatigue Countermeasures Group, to provide a greater emphasis on the development and evaluation of countermeasures that would mitigate the adverse effects of fatigue and maximize flight crew performance and alertness. The research conducted by this group at Ames included field studies of cockpit rest, quantity and quality of onboard sleep, and performance changes associated with long-haul flights.

Improvement of fatigue in multiple sclerosis by physical exercise is associated to modulation of systemic interferon response.

PubMed

Mulero, Patricia; Almansa, Raquel; Neri, María José; Bermejo-Martin, Jesús Francisco; Archanco, Miguel; Arenillas, Juan Francisco; Téllez, Nieves

2015-03-15

Mechanisms underlying multiple sclerosis (MS) fatigue and the causes of the beneficial effect of exercise on this symptom are not clarified. Our aim was to evaluate gene expression profiles in MS patients who improved their fatigue status after an exercise program and to compare them with healthy controls (HC). Gene expression in whole blood was profiled at baseline in 7 HC and also in 7 fatigued-MS patients. Patients underwent an exercise program for 6 months, and their fatigue status and gene expression profiles were again analyzed. MS patients showed a significant activation of genes participating in the systemic interferon response in comparison with HC that disappeared at the end of the program. Our results provide a biological basis for the observed benefit of exercise in MS. Copyright © 2015 Elsevier B.V. All rights reserved.

Comments on the origin of acoustic emission in fatigue testing of aluminum alloys

NASA Astrophysics Data System (ADS)

Heiple, C. R.; Carpenter, S. H.; Armentrout, D. L.

The size of acoustic emission (AE) signals expected from inclusion fracture during fatigue testing of 7075 aluminum has been estimated on the basis of previous measurements of AE produced by the fracture of boron particles incorporated into 2219 aluminum. The AF signal size expected from deformation in the plastic zone ahead of the fatigue crack was estimated from the results of tensile tests on 7075 aluminum. The signals predicted from both processes are near or below the noise level in the fatigue experiments and are therefore far too small to account for the signals actually observed. Nearly simultaneous fracture of multiple inclusions could produce signals as large as those observed in fatigue tests of 7075 aluminum, however, fatigue tests of 7050 aluminum produced signals as large or larger than in 7075. Since 7050 has substantially fewer inclusions than 7075, the simultaneous failure of multiple inclusions is unlikely to be a major AE source in fatigue testing of either aluminum alloy. Thus, the most probable source of acoustic emission during fatigue testing of 7075 and 7050 aluminum is the crack advance itself. The measured crack advance per cycle is large enough to release sufficient elastic energy to account for the AE signals observed.

NASA - easyJet Collaboration on the Human Factors Monitoring Program (HFMP) Study

NASA Technical Reports Server (NTRS)

Srivistava, Ashok N.; Barton, Phil

2012-01-01

This is the first annual report jointly prepared by NASA and easyJet on the work performed under the agreement to collaborate on a study of the many factors entailed in flight - and cabin-crew fatigue and documenting the decreases in performance associated with fatigue. The objective of this Agreement is to generate reliable, automated procedures that improve understanding of the levels and characteristics of flight - and cabin-crew fatigue factors, both latent and proximate, whose confluence will likely result in unacceptable flight crew performance. This study entails the analyses of numerical and textual data collected during operational flights. NASA and easyJet are both interested in assessing and testing NASA s automated capabilities for extracting operationally significant information from very large, diverse (textual and numerical) databases, much larger than can be handled practically by human experts.

Second Interim Report NASA - easyJet Collaboration on the Human Factors Monitoring Program (HFMP) Study

NASA Technical Reports Server (NTRS)

Srivistava, Ashok N.; Barton, Phil

2012-01-01

This is the second interim report jointly prepared by NASA and easyJet on the work performed under the agreement to collaborate on a study of the factors entailed in flight and cabin-crew fatigue, and decreases in performance associated with fatigue. The objective of this Agreement is to generate reliable procedures that aid in understanding the levels and characteristics of flight and cabin-crew fatigue factors, both latent and proximate, whose confluence will likely result in unacceptable crew performance. This study entails the analyses of numerical and textual data collected during operational flights. NASA and easyJet are both interested in assessing and testing NASA s automated capabilities for extracting operationally significant information from very large, diverse (textual and numerical) databases; much larger than can be handled practically by human experts.

Definition and Modeling of Critical Flaws in Graphite Fiber Reinforced Resin Matrix Composite Materials

DTIC Science & Technology

1979-08-28

11 EXPERIMENTAL PROGRAM .......................................*16 SHEAR TESTS ON THICK DISBONDED LAMINATES .... ....... 16 COMPRESSIVE BUCKLING OF...DISBONDED LAMINATES ...... .. 17 MECHANICAL CHARACTERIZATION FOR MOISTURE CONDITIONING EFFECTS .................................. 19 ULTRASONIC WAVE...SHEAR OF THICK LAMINATED BEAMS . . . ....... 24 PROPAGATION OF DISBOND IN FATIGUE ..... ............ .. 26 BUCKLING OF DISBONDED COMPRESSION SKIN

Development of a remote-controlled fatigue test machine using a laser extensometer for investigation of irradiation effect on fatigue properties

NASA Astrophysics Data System (ADS)

Yonekawa, M.; Ishii, T.; Ohmi, M.; Takada, F.; Hoshiya, T.; Niimi, M.; Ioka, I.; Miwa, Y.; Tsuji, H.

2002-12-01

In order to investigate effects of neutron irradiation on fatigue properties of nuclear materials, a remote-controlled high temperature fatigue test machine was developed at the hot laboratory of the Japan Materials Testing Reactor (JMTR) in the Japan Atomic Energy Research Institute (JAERI). A small-sized fatigue specimen having double blades to measure strain with a laser extensometer was designed for this machine. A strain amplitude in fatigue tests of a completely reversed push-pull type using a triangular wave was controlled with an accuracy of ±3% of the total strain range during test. Low cycle fatigue tests of type 304 stainless steel irradiated in JMTR at 823 K up to a fast neutron fluence of 1×10 25 n/m 2 ( E>1 MeV) were performed in total strain ranges of 0.7-1.4% at 823 K using the designed small-sized specimens.

75 FR 75882 - Airworthiness Directives; British Aerospace Regional Aircraft Models Jetstream Series 3101 and...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-07

... describes the unsafe condition as: As a result of the fatigue-testing programme on the Jetstream fatigue... result of the fatigue-testing programme on the Jetstream fatigue test specimen, it has been identified....S. registry. We also estimate that it will take about 15 work-hours per product to comply with the...

A literature review and inventory of the effects of environment on the fatigue behavior of metals

NASA Technical Reports Server (NTRS)

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

1976-01-01

The current state of knowledge of the effects of gas environments (at atmospheric pressure and below) on the fatigue behavior of metals is reviewed. Among the topics considered are the mechanisms proposed to explain the differences observed in the fatigue behavior of vacuum- and air-tested specimens, the effects of environment on the surface topography of fatigue cycled specimens, the effect of environment on the various phases of the fatigue phenomenon, the effect of prolonged exposure to vacuum on fatigue life, the variation of fatigue life with decreasing gas pressure, and gas evolution during fatigue cycling. Analysis of the findings of this review indicates that hydrogen embrittlement is primarily responsible for decreased fatigue resistance in humid environments, and that dislocations move more easily during tests in vacuum than during test in air. It was found that fatigue cracks generally initiated and propagated more rapidly in air than in vacuum. Prolonged exposure to vacuum does not adversely affect fatigue resistance. The variation of fatigue life with decreasing gas pressure is sometimes stepped and sometimes continuous.

Fatigue Behavior of Steel Fiber Reinforced High-Strength Concrete under Different Stress Levels

NASA Astrophysics Data System (ADS)

Zhang, Chong; Gao, Danying; Gu, Zhiqiang

2017-12-01

The investigation was conducted to study the fatigue behavior of steel fiber reinforced high-strength concrete (SFRHSC) beams. A series of 5 SFRHSC beams was conducted flexural fatigue tests at different stress level S of 0.5, 0.55, 0.6, 0.7 and 0.8 respectively. Static test was conducted to determine the ultimate static capacity prior to fatigue tests. Fatigue modes and S-N curves were analyzed. Besides, two fatige life prediction model were analyzed and compared. It was found that stress level S significantly influenced the fatigue life of SFRHSC beams and the fatigue behavior of SFRHSC beams was mainly determined by the tensile reinforcement.

Tension and fatigue behavior of 316LVM 1x7 multi-strand cables used as implantable electrodes.

PubMed

Lewandowski, John J; Varadarajan, Ravikumar; Smith, Brian; Tuma, Chris; Shazly, Mostafa; Vatamanu, Luciano O

2008-07-15

The mechanical behavior of 316LVM 1x7 cables were evaluated in uniaxial tension, and in cyclic strain-controlled fatigue with the use of a Flex tester operated to provide fully reversed bending fatigue. The magnitude of cyclic strains imparted to each cable tested was controlled via the use of different diameter mandrels. Smaller diameter mandrels produced higher values of cyclic strain and lower fatigue life. Multiple samples were tested and analyzed via scanning electron microscopy. The fatigue results were analyzed via a Coffin-Manson-Basquin approach and compared to fatigue data obtained from the literature where testing was conducted on similar materials, but under rotating bending fatigue conditions.

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.

A comparison of muscle strength and endurance, exercise capacity, fatigue perception and quality of life in patients with chronic obstructive pulmonary disease and healthy subjects: a cross-sectional study.

PubMed

Calik-Kutukcu, Ebru; Savci, Sema; Saglam, Melda; Vardar-Yagli, Naciye; Inal-Ince, Deniz; Arikan, Hulya; Aribas, Zeynep; Ozer, Ozge; Bosnak-Guclu, Meral; Coplu, Lutfi

2014-01-27

Chronic obstructive pulmonary disease (COPD) has significant systemic effects that substantially impact quality of life and survival. The purpose of this study was to assess and compare peripheral muscle strength and endurance, exercise capacity, fatigue perception and quality of life between patients with COPD and healthy subjects. Twenty COPD patients (mean FEV1 49.3 ± 19.2%) and 20 healthy subjects were included in the study. Pulmonary function testing and six-minute walk test (6MWT) were performed. Peripheral muscle strength was measured with a hand-held dynamometer, peripheral muscle endurance was evaluated with sit-ups, squats and modified push-ups tests. Fatigue perception was assessed using the Fatigue Impact Scale (FIS) and Fatigue Severity Scale (FSS). General quality of life was determined with the Nottingham Health Profile (NHP), and cough-specific quality of life was evaluated with the Leicester Cough Questionnaire (LCQ). Pulmonary functions, strength of shoulder abductor and flexor muscles, numbers of sit-ups and squats, 6MWT distance and 6MWT% were significantly lower in COPD patients than in healthy subjects (p < 0.05). FIS psychosocial sub-dimension and total scores, NHP scores for all sub-dimensions except pain sub-dimension of the COPD group were significantly higher than those of healthy subjects (p < 0.05). The LCQ physical, psychological and social sub-dimensions and total scores were significantly lower in COPD patients than in healthy subjects (p < 0.05). Pulmonary functions, peripheral muscle strength and endurance, exercise capacity and quality of life were adversely affected in patients with COPD. There are greater effect of fatigue on psychosocial functioning and general daily life activities and effect of cough on the quality of life in patients with COPD. This study supports the idea that COPD patients must be evaluated in a comprehensive manner for planning pulmonary rehabilitation programs.

A comparison of muscle strength and endurance, exercise capacity, fatigue perception and quality of life in patients with chronic obstructive pulmonary disease and healthy subjects: a cross-sectional study

PubMed Central

2014-01-01

Background Chronic obstructive pulmonary disease (COPD) has significant systemic effects that substantially impact quality of life and survival. The purpose of this study was to assess and compare peripheral muscle strength and endurance, exercise capacity, fatigue perception and quality of life between patients with COPD and healthy subjects. Methods Twenty COPD patients (mean FEV1 49.3 ± 19.2%) and 20 healthy subjects were included in the study. Pulmonary function testing and six-minute walk test (6MWT) were performed. Peripheral muscle strength was measured with a hand-held dynamometer, peripheral muscle endurance was evaluated with sit-ups, squats and modified push-ups tests. Fatigue perception was assessed using the Fatigue Impact Scale (FIS) and Fatigue Severity Scale (FSS). General quality of life was determined with the Nottingham Health Profile (NHP), and cough-specific quality of life was evaluated with the Leicester Cough Questionnaire (LCQ). Results Pulmonary functions, strength of shoulder abductor and flexor muscles, numbers of sit-ups and squats, 6MWT distance and 6MWT% were significantly lower in COPD patients than in healthy subjects (p < 0.05). FIS psychosocial sub-dimension and total scores, NHP scores for all sub-dimensions except pain sub-dimension of the COPD group were significantly higher than those of healthy subjects (p < 0.05). The LCQ physical, psychological and social sub-dimensions and total scores were significantly lower in COPD patients than in healthy subjects (p < 0.05). Conclusions Pulmonary functions, peripheral muscle strength and endurance, exercise capacity and quality of life were adversely affected in patients with COPD. There are greater effect of fatigue on psychosocial functioning and general daily life activities and effect of cough on the quality of life in patients with COPD. This study supports the idea that COPD patients must be evaluated in a comprehensive manner for planning pulmonary rehabilitation programs. PMID:24468029

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

NASA Astrophysics Data System (ADS)

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

2016-03-01

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

Spectrum Fatigue of 7075-T651 Aluminum Alloy under Overloading and Underloading

DTIC Science & Technology

2016-03-15

underload, stress ratio, and environment on fatigue crack growth. Fatigue crack growth tests were conducted with a 7075-T651 aluminum alloy under constant...the UniGrow equation, the variation of crack length with number of loading cycle was predicted. The prediction and the fatigue test life were found to...Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39-18 REPORT NO. NAWCADPAX/TIM-2015/282 ii SUMMARY Fatigue tests of 7075-T651

Investigation of Gear and Bearing Fatigue Damage Using Debris Particle Distributions

NASA Technical Reports Server (NTRS)

Dempsey, Paula J.; Lewicki, David G.; Decker, Harry J.

2004-01-01

A diagnostic tool was developed for detecting fatigue damage to spur gears, spiral bevel gears, and rolling element bearings. This diagnostic tool was developed and evaluated experimentally by collecting oil debris data from fatigue tests performed in the NASA Glenn Spur Gear Fatigue Rig, Spiral Bevel Gear Test Facility, and the 500hp Helicopter Transmission Test Stand. During each test, data from an online, in-line, inductance type oil debris sensor was monitored and recorded for the occurrence of pitting damage. Results indicate oil debris alone cannot discriminate between bearing and gear fatigue damage.

Influence of sustained submaximal clenching fatigue test on electromyographic activity and maximum voluntary bite forces in healthy subjects and patients with temporomandibular disorders.

PubMed

Xu, L; Fan, S; Cai, B; Fang, Z; Jiang, X

2017-05-01

This study aimed to investigate whether the fatigue induced by sustained motor task in the jaw elevator muscles differed between healthy subjects and patients with temporomandibular disorder (TMD). Fifteen patients with TMD and thirteen age- and sex-matched healthy controls performed a fatigue test consisting of sustained clenching contractions at 30% maximal voluntary clenching intensity until test failure (the criterion for terminating the fatigue test was when the biting force decreased by 10% or more from the target force consecutively for >3 s). The pre- and post-maximal bite forces (MBFs) were measured. Surface electromyographic signals were recorded from the superficial masseter muscles and anterior temporal muscles bilaterally, and the median frequency at the beginning, middle and end of the fatigue test was calculated. The duration of the fatigue test was also quantified. Both pre- and post-MBFs were lower in patients with TMD than in controls (P < 0·01). No significant difference was found in the percentage change in MBF between groups. The duration of the fatigue test in TMD patients was significantly shorter than that of the controls (P < 0·05). Our results suggest that, compared to healthy subjects, patients with TMD become more easily fatigued, but the electromyographic activation process during the fatigue test is similar between healthy subjects and patients with TMD. However, the mechanisms involved in this process remain unclear, and further research is warranted. © 2017 John Wiley & Sons Ltd.

Cyclic Fatigue Life of Two Single File Engine-Driven Systems in Simulated Curved Canals.

PubMed

Nabavizadeh, Mohammad Reza; Sedigh-Shams, Mahdi; Abdolrasoulnia, Sara

2018-01-01

This study aimed to evaluate the cyclic fatigue resistance of two single file engine-driven instruments, Reciproc and NeoNiTi, in simulated root canals. Two groups of 15 NiTi endodontic instruments with an identical tip size of 0.25 mm were tested: Reciproc R25 (group A) and NeoNiTi A1 (group B). Cyclic fatigue testing was performed in a stainless steel artificial canal. The simulated canals had a 60 ° angle and 5-mm radius curvature. The Reciproc instruments were operated using the preset program on torque control electric motor specific for the Reciproc instruments, while the NeoNiTi instruments were operated using the manufacturer recommendation. All instruments were rotated until fracture occurred, and the number of cycles to fracture (NCF) and the length of the fractured tip were recorded and registered. Means and standard deviations of NCF and fragment length were calculated for each system and data were subjected to Student's t test ( P <0.05). A statistically significant difference ( P <0.05) was noted between Reciproc and NeoNiTi instruments. NeoNiTi A1 instruments were associated with a significantly higher mean NCF as compared to Reciproc R25 instruments (833±176 vs. 318±87 NCF). There was no significant difference ( P >0.05) in the mean length of the fractured fragments between the instruments. NeoNiTi instruments were associated with a significantly higher cyclic fatigue resistance than Reciproc instruments.

Extrapulmonary features of bronchiectasis: muscle function, exercise capacity, fatigue, and health status.

PubMed

Ozalp, Ozge; Inal-Ince, Deniz; Calik, Ebru; Vardar-Yagli, Naciye; Saglam, Melda; Savci, Sema; Arikan, Hulya; Bosnak-Guclu, Meral; Coplu, Lutfi

2012-06-11

There are limited number of studies investigating extrapulmonary manifestations of bronchiectasis. The purpose of this study was to compare peripheral muscle function, exercise capacity, fatigue, and health status between patients with bronchiectasis and healthy subjects in order to provide documented differences in these characteristics for individuals with and without bronchiectasis. Twenty patients with bronchiectasis (43.5 ± 14.1 years) and 20 healthy subjects (43.0 ± 10.9 years) participated in the study. Pulmonary function, respiratory muscle strength (maximal expiratory pressure - MIP - and maximal expiratory pressure - MEP), and dyspnea perception using the Modified Medical Research Council Dyspnea Scale (MMRC) were determined. A six-minute walk test (6MWT) was performed. Quadriceps muscle, shoulder abductor, and hand grip strength (QMS, SAS, and HGS, respectively) using a hand held dynamometer and peripheral muscle endurance by a squat test were measured. Fatigue perception and health status were determined using the Fatigue Severity Scale (FSS) and the Leicester Cough Questionnaire (LCQ), respectively. Number of squats, 6MWT distance, and LCQ scores as well as lung function testing values and respiratory muscle strength were significantly lower and MMRC and FSS scores were significantly higher in patients with bronchiectasis than those of healthy subjects (p < 0.05). In bronchiectasis patients, QMS was significantly associated with HGS, MIP and MEP (p < 0.05). The 6MWT distance was significantly correlated to LCQ psychological score (p < 0.05). The FSS score was significantly associated with LCQ physical and total and MMRC scores (p < 0.05). The LCQ psychological score was significantly associated with MEP and 6MWT distance (p < 0.05). Peripheral muscle endurance, exercise capacity, fatigue and health status were adversely affected by the presence of bronchiectasis. Fatigue was associated with dyspnea and health status. Respiratory muscle strength was related to peripheral muscle strength and health status, but not to fatigue, peripheral muscle endurance or exercise capacity. These findings may provide insight for outcome measures for pulmonary rehabilitation programs for patients with bronchiectasis.

Thermal-Mechanical Fatigue Testing of a Titanium-Aluminide Alloy.

DTIC Science & Technology

1987-12-01

DIMSTRIBUTION STA Approved for pubi robing e% dQ *- AFIT/GAB/AA/87D-18 THERMAL-MECHANICAL FATIGUE TESTING OF A TITANIUM - ALUMINIDE ALLOY THESIS John J...THERMAL-MECHANICAL FATIGUE TESTING OF A TITANIUM - ALUMINIDE ALLOY THESIS Presented to the Faculty of the School of Engineering of the Air Force Institute...develop a Thermal-Mechanical Fatigue (TMF) testing system for titanium - aluminide compact tension specimens. I could not have accomplished this without the

Single-leg hop testing following fatiguing exercise: reliability and biomechanical analysis.

PubMed

Augustsson, J; Thomeé, R; Lindén, C; Folkesson, M; Tranberg, R; Karlsson, J

2006-04-01

A fatiguing exercise protocol was combined with single-leg hop testing to improve the possibilities of evaluating the effects of training or rehabilitation interventions. In the first test-retest experiment, 11 healthy male subjects performed two trials of single-leg hops under three different test conditions: non-fatigued and following fatiguing exercise, which consisted of unilateral weight machine knee extensions at 80% and 50%, respectively, of 1 repetition maximum (1 RM) strength. Intraclass correlation coefficients ranged from 0.75 to 0.98 for different hop test conditions, indicating that all tests were reliable. For the second experiment, eight healthy male subjects performed the fatiguing exercise protocol to investigate how fatigue influences lower-extremity joint kinematics and kinetics during single-leg hops. Hip, knee and ankle joint angles, moments and powers, as well as ground-reaction forces were recorded with a six-camera, motion-capture system and a force platform. Recovery of hop performance following the fatiguing exercise was also measured. During the take-off for the single-leg hops, hip and knee flexion angles, generated powers for the knee and ankle joints, and ground-reaction forces decreased for the fatigued hop conditions compared with the non-fatigued condition (P<0.05). Compared with landing during the non-fatigued condition, hip moments and ground-reaction forces were lower for the fatigued hop conditions (P<0.05). The negative joint power was two to three times greater for the knee than for the hip and five to 10 times greater for the knee than for the ankle during landing for all test conditions (P<0.05). Most measured variables had recovered three minutes post-exercise. It is concluded that the fatiguing exercise protocol combined with single-leg hop testing was a reliable method for investigating functional performance under fatigued test conditions. Further, subjects utilized an adapted hop strategy, which employed less hip and knee flexion and generated powers for the knee and ankle joints during take-off, and less hip joint moments during landing under fatigued conditions. The large negative power values observed at the knee joint during the landing phase of the single-leg hop, during which the quadriceps muscle activates eccentrically, indicate that not only hop distance but also the ability to perform successful landings should be investigated when assessing dynamic knee function.

Experimental Investigation and Finite Element Analysis on Fatigue Behavior of Aluminum Alloy 7050 Single-Lap Joints

NASA Astrophysics Data System (ADS)

Zhou, Bing; Cui, Hao; Liu, Haibo; Li, Yang; Liu, Gaofeng; Li, Shujun; Zhang, Shangzhou

2018-03-01

The fatigue behavior of single-lap four-riveted aluminum alloy 7050 joints was investigated by using high-frequency fatigue test and scanning electron microscope (SEM). Stress distributions obtained by finite element (FE) analysis help explain the fatigue performance. The fatigue test results showed that the fatigue lives of the joints depend on cold expansion and applied cyclic loads. FE analysis and fractography indicated that the improved fatigue lives can be attributed to the reduction in maximum stress and evolution of fatigue damage at the critical location. The beneficial effects of strengthening techniques result in tearing ridges or lamellar structure on fracture surface, decrease in fatigue striations spacing, delay of fatigue crack initiation, crack deflection in fatigue crack propagation and plasticity-induced crack closure.

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.

"A Group of Me's": Adult Learning through Group Process: The Experiences of Participants in a Teleconference Delivered Multiple Sclerosis Fatigue Management Program

ERIC Educational Resources Information Center

Preissner, Katharine L.

2013-01-01

Multiple sclerosis (MS) is a chronic, progressive neurological disorder that affects approximately 2.1 million people worldwide. Fatigue is one of the most common and most disabling symptoms of MS. One well-established approach to address fatigue is fatigue management education provided by an occupational therapist. Fatigue management education is…

Cumulative Axial and Torsional Fatigue: An Investigation of Load-Type Sequencing Effects

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Bonacuse, Peter J.

2000-01-01

Cumulative fatigue behavior of a wrought cobalt-base superalloy, Haynes 188 was investigated at 538 C under various single-step sequences of axial and torsional loading conditions. Initially, fully-reversed, axial and torsional fatigue tests were conducted under strain control at 538 C on thin-walled tubular specimens to establish baseline fatigue life relationships. Subsequently, four sequences (axial/axial, torsional/torsional, axial/torsional, and torsional/axial) of two load-level fatigue tests were conducted to characterize both the load-order (high/low) and load-type sequencing effects. For the two load-level tests, summations of life fractions and the remaining fatigue lives at the second load-level were computed by the Miner's Linear Damage Rule (LDR) and a nonlinear Damage Curve Approach (DCA). In general, for all four cases predictions by LDR were unconservative. Predictions by the DCA were within a factor of two of the experimentally observed fatigue lives for a majority of the cumulative axial and torsional fatigue tests.

Rolling-element fatigue life of AMS 5749 corrosion resistant, high temperature bearing steel

NASA Technical Reports Server (NTRS)

Parker, R. J.; Hodder, R. S.

1977-01-01

The rolling element fatigue lives of AMS 5749 and AISI M-50 were compared in tests run in the five ball fatigue tester and the rolling contact fatigue tester. The effects of double vacuum melting and retained austenite on the life of AMS 5749 were determined in five ball fatigue tests. The double vacuum melting process consisted of induction vacuum melting followed by vacuum arc remelting (VIM-VAR). In the five ball tests, VIM-VAR AMS 5749 gave lives at least six times that of VIM-VAR AISI M-50. Similar tests in the rolling contact fatigue tester showed no significant difference in the lives of the two materials. The rolling element fatigue life of VIM-VAR AMS 5749 was at least 14 times that of vacuum induction melted AMS 5749. A trend toward increased rolling element fatigue life with decreased retained austenite is apparent, but the confidence that all experimental differences are significant is not great.

Shift work and employee fatigue: implications for occupational health nursing.

PubMed

Yumang-Ross, Doreen J; Burns, Candace

2014-06-01

Long work hours and irregular shifts are part of the nation's 24-hour society and contribute to employee fatigue. Factors affecting employee fatigue are circadian rhythm, sleep quality and quantity, individual health, the environment, and work tasks. Employee fatigue contributes to accidents and injuries, and affects occupational performance, safety, and health. These findings should be used by occupational health nurses to address fatigue management and develop comprehensive fatigue management programs. Copyright 2014, SLACK Incorporated.

Fatigue and physical fitness of mildly disabled persons with multiple sclerosis: a cross-sectional study.

PubMed

Valet, Maxime; Lejeune, Thierry; Glibert, Yumiko; Hakizimana, Jean C; Van Pesch, Vincent; El Sankari, Souraya; Detrembleur, Christine; Stoquart, Gaëtan

2017-09-01

Fatigue is frequent and disabling in persons with multiple sclerosis (pwMS) with mild neurological disability. These patients also have impaired physical fitness. Whether mildly disabled pwMS are deconditioned, and this deconditioning is linked to fatigue, remains unknown. Our aim is to determine the physical fitness of mildly disabled patients with multiple sclerosis and study its relationship with perceived fatigue and to link perceived fatigue with other parameters. Twenty patients (14 women; mean age: 45.5 years) with mild disability (Expanded Disability Status Scale 0-4) underwent a 2-min walking test, Timed Up-and-Go test, aerobic capacity testing, and isometric knee extension testing to assess strength and neuromuscular fatigability. They completed questionnaires assessing perceived fatigue, psychological status, and physical activity. Correlation coefficients and multivariate regression were used to analyze the relationships among variables. Seventeen (85%) patients reported a high level of fatigue. Thirteen (65%) patients had subnormal aerobic capacity. Fatigue was weakly to moderately associated with aerobic capacity, mobility, walking capacity, depression, and neuromuscular fatigability. An association of disease duration, aerobic capacity, and the neuromuscular fatigability index explained 65.1% of fatigue. A high proportion of pwMS with mild neurological disability are fatigued and deconditioned. Perceived fatigue is linked to aerobic capacity, neuromuscular fatigability, depression, mobility, and walking capacity. Focusing on these parameters could help in the management of fatigue.

Probabilistic Flexural Fatigue in Plain and Fiber-Reinforced Concrete

PubMed Central

Ríos, José D.

2017-01-01

The objective of this work is two-fold. First, we attempt to fit the experimental data on the flexural fatigue of plain and fiber-reinforced concrete with a probabilistic model (Saucedo, Yu, Medeiros, Zhang and Ruiz, Int. J. Fatigue, 2013, 48, 308–318). This model was validated for compressive fatigue at various loading frequencies, but not for flexural fatigue. Since the model is probabilistic, it is not necessarily related to the specific mechanism of fatigue damage, but rather generically explains the fatigue distribution in concrete (plain or reinforced with fibers) for damage under compression, tension or flexion. In this work, more than 100 series of flexural fatigue tests in the literature are fit with excellent results. Since the distribution of monotonic tests was not available in the majority of cases, a two-step procedure is established to estimate the model parameters based solely on fatigue tests. The coefficient of regression was more than 0.90 except for particular cases where not all tests were strictly performed under the same loading conditions, which confirms the applicability of the model to flexural fatigue data analysis. Moreover, the model parameters are closely related to fatigue performance, which demonstrates the predictive capacity of the model. For instance, the scale parameter is related to flexural strength, which improves with the addition of fibers. Similarly, fiber increases the scattering of fatigue life, which is reflected by the decreasing shape parameter. PMID:28773123

Probabilistic Flexural Fatigue in Plain and Fiber-Reinforced Concrete.

PubMed

Ríos, José D; Cifuentes, Héctor; Yu, Rena C; Ruiz, Gonzalo

2017-07-07

The objective of this work is two-fold. First, we attempt to fit the experimental data on the flexural fatigue of plain and fiber-reinforced concrete with a probabilistic model (Saucedo, Yu, Medeiros, Zhang and Ruiz, Int. J. Fatigue, 2013, 48, 308-318). This model was validated for compressive fatigue at various loading frequencies, but not for flexural fatigue. Since the model is probabilistic, it is not necessarily related to the specific mechanism of fatigue damage, but rather generically explains the fatigue distribution in concrete (plain or reinforced with fibers) for damage under compression, tension or flexion. In this work, more than 100 series of flexural fatigue tests in the literature are fit with excellent results. Since the distribution of monotonic tests was not available in the majority of cases, a two-step procedure is established to estimate the model parameters based solely on fatigue tests. The coefficient of regression was more than 0.90 except for particular cases where not all tests were strictly performed under the same loading conditions, which confirms the applicability of the model to flexural fatigue data analysis. Moreover, the model parameters are closely related to fatigue performance, which demonstrates the predictive capacity of the model. For instance, the scale parameter is related to flexural strength, which improves with the addition of fibers. Similarly, fiber increases the scattering of fatigue life, which is reflected by the decreasing shape parameter.

Research on the Fatigue Flexural Performance of RC Beams Attacked by Salt Spray

NASA Astrophysics Data System (ADS)

Mao, Jiang-hong; Xu, Fang-yuan; Jin, Wei-liang; Zhang, Jun; Wu, Xi-xi; Chen, Cai-sheng

2018-04-01

The fatigue flexural performance of RC beams attacked by salt spray was studied. A testing method involving electro osmosis, electrical accelerated corrosion and salt spray was proposed. This corrosion process method effectively simulates real-world salt spray and fatigue loading exerted by RC components on sea bridges. Four RC beams that have different stress amplitudes were tested. It is found that deterioration by corrosion and fatigue loading reduces the fatigue life of the RC and decreases the ability of deformation. The fatigue life and deflection ability could be reduced by increasing the stress amplitude and the corrosion duration time. The test result demonstrates that this experimental method can couple corrosion deterioration and fatigue loading reasonably. This procedure may be applied to evaluate the fatigue life and concrete durability of RC components located in a natural salt spray environment.

Assessment of corrosion fatigue damage by acoustic emission and periodic proof tests

NASA Astrophysics Data System (ADS)

Mehdizadeh, P.

1976-03-01

The development of a better nondestructive inspection method for detecting corrosion fatigue damage based on acoustic emission (AE) and periodic proof testing (PPT) is studied for corrosion fatigue tests in salt water solution under tension-tension loading. It is shown that PPT combined with AE monitoring can be a sensitive method for assessing the progress of corrosion fatigue damage as the continuous AE monitoring method. The AE-PPT technique is shown to be dependent on the geometry and size of the crack relative to the test specimen. A qualitative method based on plateauing of acoustic emission counts during proof tests due to changes in the fracture mode is used to predict the remaining fatigue life up to 70% of the actual values. PPT is shown to have no adverse effect on fatigue performance in salt water.

Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl

NASA Technical Reports Server (NTRS)

Lerch, Brad; Draper, Sue; Pereira, J. Mike

2002-01-01

High cycle fatigue strength testing of gamma TiAl by the step test method is investigated. A design of experiments was implemented to determine if the coaxing effect occurred during testing. Since coaxing was not observed, step testing was deemed a suitable method to define the fatigue strength at 106 cycles.

Results of a Cyclic Load Test of an RB-47E Airplane

NASA Technical Reports Server (NTRS)

Huston, Wilber B.

1959-01-01

Results of a cyclic load test made by NASA on an EB-47E airplane are given. The test reported on is for one of three B-47 airplanes in a test program set up by the U. S. Air Force to evaluate the effect of wing structural reinforcements on fatigue life. As a result of crack development in the upper fuselage longerons of the other two airplanes in the program, a longeron and fuselage skin modification was incorporated early in the test. Fuselage strain-gage measurements made before and after the longeron modification and wing strain-gage measurements made only after wing reinforcement are summarized. The history of crack development and repair is given in detail. Testing was terminated one sequence short of the planned end of the program with the occurrence of a major crack in the lower right wing skin.

Oxygen uptake during peak graded exercise and single-stage fatigue tests of wheelchair propulsion in manual wheelchair users and the able-bodied.

PubMed

Keyser, R E; Rodgers, M M; Gardner, E R; Russell, P J

1999-10-01

To determine if a single-stage, submaximal fatigue test on a wheelchair ergometer would result in higher than expected energy expenditure. An experimental survey design contrasting physiologic responses during peak graded exercise tests and fatigue tests. A rehabilitation science laboratory that included a prototypical wheelchair ergometer, open-circuit spirometry system, and heart rate monitor. Nine able-bodied non-wheelchair users (the NWC group: 6 men and 3 women, mean +/- SD age 30 +/- 7yrs) and 15 manual wheelchair users (the WC group: 12 men and 3 women, age 40 +/- 9yrs, time in wheelchair 16 +/- 9yrs). No subject had any disease, medication regimen, or upper body neurologic, orthopedic, or other condition that would limit wheelchair exercise. Peak oxygen uptake (VO2) for graded exercise testing and during fatigue testing, using a power output corresponding to 75% peak aerobic capacity on graded exercise test. In the WC group, VO2 at 6 minutes of fatigue testing was not significantly different from peak VO2. In the NWC group, VO2 was similar to the expected level throughout fatigue testing. Energy expenditure was higher than expected in the WC group but not in the NWC group. Fatigue testing may provide a useful evaluation of cardiorespiratory status in manual wheelchair users.

Repeatability of testing procedures for resilient modulus and fatigue : appendices.

DOT National Transportation Integrated Search

1989-04-01

The article is the appendices of "Repeatability of testing procedures for resilient modulus and fatigue". : Extensive use of diametral resilient modulus and fatigue testing is made by the Oregon State Highway Division to evaluate asphaltic concrete m...

Three-dimensional measurements of fatigue crack closure

NASA Technical Reports Server (NTRS)

Ray, S. K.; Grandt, A. F., Jr.

1984-01-01

Fatigue crack growth and retardation experiments conducted in polycarbonate test specimen are described. The transparent test material allows optical interferometry measurements of the fatigue crack opening (and closing) profiles. Crack surface displacements are obtained through the specimen thickness and three dimensional aspects of fatigue crack closure are discussed.

High Frequency Vibration Based Fatigue Testing of Developmental Alloys

NASA Astrophysics Data System (ADS)

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

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

Computer program to assess impact of fatigue and fracture criteria on weight and cost of transport aircraft

NASA Technical Reports Server (NTRS)

Tanner, C. J.; Kruse, G. S.; Oman, B. H.

1975-01-01

A preliminary design analysis tool for rapidly performing trade-off studies involving fatigue, fracture, static strength, weight, and cost is presented. Analysis subprograms were developed for fatigue life, crack growth life, and residual strength; and linked to a structural synthesis module which in turn was integrated into a computer program. The part definition module of a cost and weight analysis program was expanded to be compatible with the upgraded structural synthesis capability. The resultant vehicle design and evaluation program is named VDEP-2. It is an accurate and useful tool for estimating purposes at the preliminary design stage of airframe development. A sample case along with an explanation of program applications and input preparation is presented.

Effect of fatigue loading on critical current in stainless steel-laminated DI-BSCCO superconducting composite tape

NASA Astrophysics Data System (ADS)

Hojo, M.; Osawa, K.; Adachi, T.; Inoue, Y.; Osamura, K.; Ochiai, S.; Ayai, N.; Hayashi, K.

2010-11-01

Tensile strain tolerance of the critical current in (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) composite superconductor is dramatically improved when the tape is laminated with stainless steel. For practical applications, it is important to understand whether this reinforcement by lamination is effective under fatigue loading. In the present study, we carried out fatigue tests in LN2 and measured the critical current at the specific fatigue cycles to clarify the strain tolerance of the critical current in stainless steel-laminated drastically innovative Bi2223 (DI-BSCCO®) tapes. The fatigue tests were carried out using a computer-controlled 10 kN servo-hydraulic fatigue testing machine with a load cell capacity of 2.5 kN. Tests under static loading showed that the irreversible stress at which the critical current is reduced by 1% from the original value (tensile stress at Ic/Ic0 = 0.99) was 315 MPa when measured at unloading state. The present fatigue tests results indicated that the critical current was maintained at over 98% of the original value at unloading state after stress cycles of 106 when the static irreversible stress was selected as the maximum stress under fatigue loading. Thus, laminated DI-BSCCO tapes showed excellent mechanical properties even under fatigue loading.

Axial-Load Fatigue Tests on 17-7 PH Stainless Steel Under Constant-Amplitude Loading

NASA Technical Reports Server (NTRS)

Leybold, Herbert A.

1960-01-01

Axial-load fatigue tests were conducted at room temperature on notched and unnotched sheet specimens of 17-7 PH stainless steel in Condition TH 1050. The notched specimens had theoretical stress-concentration factors of 2.32, 4.00, and 5.00. All specimens were tested under completely reversed loading. S-N curves are presented for each specimen configuration and ratios of fatigue strengths of unnotched specimens to those of notched specimens are given. Predictions of the fatigue behavior of notched specimens near the fatigue limit were made.

Development of advanced structural analysis methodologies for predicting widespread fatigue damage in aircraft structures

NASA Technical Reports Server (NTRS)

Harris, Charles E.; Starnes, James H., Jr.; Newman, James C., Jr.

1995-01-01

NASA is developing a 'tool box' that includes a number of advanced structural analysis computer codes which, taken together, represent the comprehensive fracture mechanics capability required to predict the onset of widespread fatigue damage. These structural analysis tools have complementary and specialized capabilities ranging from a finite-element-based stress-analysis code for two- and three-dimensional built-up structures with cracks to a fatigue and fracture analysis code that uses stress-intensity factors and material-property data found in 'look-up' tables or from equations. NASA is conducting critical experiments necessary to verify the predictive capabilities of the codes, and these tests represent a first step in the technology-validation and industry-acceptance processes. NASA has established cooperative programs with aircraft manufacturers to facilitate the comprehensive transfer of this technology by making these advanced structural analysis codes available to industry.

Development of a decision support system for analysis and solutions of prolonged standing in the workplace.

PubMed

Halim, Isa; Arep, Hambali; Kamat, Seri Rahayu; Abdullah, Rohana; Omar, Abdul Rahman; Ismail, Ahmad Rasdan

2014-06-01

Prolonged standing has been hypothesized as a vital contributor to discomfort and muscle fatigue in the workplace. The objective of this study was to develop a decision support system that could provide systematic analysis and solutions to minimize the discomfort and muscle fatigue associated with prolonged standing. The integration of object-oriented programming and a Model Oriented Simultaneous Engineering System were used to design the architecture of the decision support system. Validation of the decision support system was carried out in two manufacturing companies. The validation process showed that the decision support system produced reliable results. The decision support system is a reliable advisory tool for providing analysis and solutions to problems related to the discomfort and muscle fatigue associated with prolonged standing. Further testing of the decision support system is suggested before it is used commercially.

Development of a Decision Support System for Analysis and Solutions of Prolonged Standing in the Workplace

PubMed Central

Halim, Isa; Arep, Hambali; Kamat, Seri Rahayu; Abdullah, Rohana; Omar, Abdul Rahman; Ismail, Ahmad Rasdan

2014-01-01

Background Prolonged standing has been hypothesized as a vital contributor to discomfort and muscle fatigue in the workplace. The objective of this study was to develop a decision support system that could provide systematic analysis and solutions to minimize the discomfort and muscle fatigue associated with prolonged standing. Methods The integration of object-oriented programming and a Model Oriented Simultaneous Engineering System were used to design the architecture of the decision support system. Results Validation of the decision support system was carried out in two manufacturing companies. The validation process showed that the decision support system produced reliable results. Conclusion The decision support system is a reliable advisory tool for providing analysis and solutions to problems related to the discomfort and muscle fatigue associated with prolonged standing. Further testing of the decision support system is suggested before it is used commercially. PMID:25180141

An Experimental Investigation of the Influence of the Lubricant Viscosity and Additives on Gear Wear

NASA Technical Reports Server (NTRS)

Krantz, Timothy L.; Kahraman, Ahmet

2005-01-01

The influence of lubricant viscosity and additives on the average wear rate of spur gear pairs was investigated experimentally. The gear specimens of a comprehensive gear durability test program that made use of seven lubricants covering a range of viscosities were examined to measure gear tooth wear. The measured wear was related to the as-manufactured surface roughness, the elastohydrodynamic film thickness, and the experimentally determined contact fatigue lives of the same specimens. In general, the wear rate was found to be inversely proportional to the viscosity of the lubricant and to the lambda ratio (also sometimes called the specific film thickness). The data also show an exponential trend between the average wear rates and the surface fatigue lives. Lubricants with similar viscosities but differing additives and compositions had somewhat differing gear surface fatigue lives and wear rates.

Strain-controlled fatigue of acrylic bone cement.

PubMed

Carter, D R; Gates, E I; Harris, W H

1982-09-01

Monotonic tensile tests and tension-compression fatigue tests were conducted of wet acrylic bone cement specimens at 37 degrees C. All testing was conducted in strain control at a strain rate of 0.02/s. Weibull analysis of the tensile tests indicated that monotonic fracture was governed more strongly by strain than stress. The number of cycles to fatigue failure was also more strongly controlled by strain amplitude than stress amplitude. Specimen porosity distribution played a major role in determining the tensile and fatigue strengths. The degree of data scatter suggests that Weibull analysis of fatigue data may be useful in developing design criteria for the surgical use of bone cement.

Characterization of fatigue behavior of 2-D woven fabric reinforced ceramic matrix composite at elevated temperature. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Groner, D.J.

This study investigated the fatigue behavior and associated damage mechanisms in notched and unnotched enhanced SiC/SiC ceramic matrix composite specimens at 1100 deg C. Stiffness degradation, strain variation, and hysteresis were evaluated to characterize material behavior. Microscopic examination was performed to characterize damage mechanisms. During high cycle/low stress fatigue tests, far less fiber/matrix interface debond was evident than in low cycle/high stress fatigue tests. Notched specimens exhibited minimal stress concentration during monotonic tensile testing and minimal notch sensitivity during fatigue testing. Damage mechanisms were also similar to unnotched.

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.

Probabilistic analysis for fatigue strength degradation of materials

NASA Technical Reports Server (NTRS)

Royce, Lola

1989-01-01

This report presents the results of the first year of a research program conducted for NASA-LeRC by the University of Texas at San Antonio. The research included development of methodology that provides a probabilistic treatment of lifetime prediction of structural components of aerospace propulsion systems subjected to fatigue. Material strength degradation models, based on primitive variables, include both a fatigue strength reduction model and a fatigue crack growth model. Linear elastic fracture mechanics is utilized in the latter model. Probabilistic analysis is based on simulation, and both maximum entropy and maximum penalized likelihood methods are used for the generation of probability density functions. The resulting constitutive relationships are included in several computer programs, RANDOM2, RANDOM3, and RANDOM4. These programs determine the random lifetime of an engine component, in mechanical load cycles, to reach a critical fatigue strength or crack size. The material considered was a cast nickel base superalloy, one typical of those used in the Space Shuttle Main Engine.

Fatigue-environment interactions in a SiC/Ti-15-3 composite

NASA Technical Reports Server (NTRS)

Gayda, J.; Gabb, T. P.; Lerch, B. A.

1993-01-01

Load-controlled isothermal and nonisothermal fatigue lives of a (0-deg)s SiC/Ti-15-3 were evaluated at temperatures between 150 and 550 C and a target strain range of about 0.45 percent. In nonisothermal fatigue tests, load was first cycled at minimum temperature and then temperature was cycled at zero load. For fatigue tests with peak temperatures at or above 300 C, fatigue life was dramatically reduced compared to that at 150 C. The shortest life was produced by the nonisothermal test with the greatest temperature range (Delta T = 400 C) and highest peak temperature (T(max) = 550 C). Vacuum testing showed that much of the life reduction under isothermal and nonisothermal conditions was related to environmental effects, although the nature of the fatigue-environment interaction was decidedly different for the isothermal and nonisothermal test cycles which were studied.

Study the Cyclic Plasticity Behavior of 508 LAS under Constant, Variable and Grid-Load-Following Loading Cycles for Fatigue Evaluation of PWR Components

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohanty, Subhasish; Barua, Bipul; Soppet, William K.

This report provides an update of an earlier assessment of environmentally assisted fatigue for components in light water reactors. This report is a deliverable in September 2016 under the work package for environmentally assisted fatigue under DOE’s Light Water Reactor Sustainability program. In an April 2016 report, we presented a detailed thermal-mechanical stress analysis model for simulating the stress-strain state of a reactor pressure vessel and its nozzles under grid-load-following conditions. In this report, we provide stress-controlled fatigue test data for 508 LAS base metal alloy under different loading amplitudes (constant, variable, and random grid-load-following) and environmental conditions (in airmore » or pressurized water reactor coolant water at 300°C). Also presented is a cyclic plasticity-based analytical model that can simultaneously capture the amplitude and time dependency of the component behavior under fatigue loading. Results related to both amplitude-dependent and amplitude-independent parameters are presented. The validation results for the analytical/mechanistic model are discussed. This report provides guidance for estimating time-dependent, amplitude-independent parameters related to material behavior under different service conditions. The developed mechanistic models and the reported material parameters can be used to conduct more accurate fatigue and ratcheting evaluation of reactor components.« less

Isothermal and thermal-mechanical fatigue of VVER-440 reactor pressure vessel steels

NASA Astrophysics Data System (ADS)

Fekete, Balazs; Trampus, Peter

2015-09-01

The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of VVER-440 reactor pressure vessel under completely reserved total strain controlled low cycle fatigue tests were investigated. An advanced test facility was developed for GLEEBLE-3800 physical simulator which was able to perform thermomechanical fatigue experiments under in-service conditions of VVER nuclear reactors. The low cycle fatigue results were evaluated with the plastic strain based Coffin-Manson law, and plastic strain energy based model as well. It was shown that both methods are able to predict the fatigue life of reactor pressure vessel steels accurately. Interrupted fatigue tests were also carried out to investigate the kinetic of the fatigue evolution of the materials. On these samples microstructural evaluation by TEM was performed. The investigated low cycle fatigue behavior can provide reference for remaining life assessment and lifetime extension analysis.

Non-pharmacological interventions to manage fatigue and psychological stress in children and adolescents with cancer: an integrative review.

PubMed

Lopes-Júnior, L C; Bomfim, E O; Nascimento, L C; Nunes, M D R; Pereira-da-Silva, G; Lima, R A G

2016-11-01

Cancer-related fatigue (CRF) is the most stressful and prevalent symptom in paediatric oncology patients. This integrative review aimed to identify, analyse and synthesise the evidence of non-pharmacological intervention studies to manage fatigue and psychological stress in a paediatric population with cancer. Eight electronic databases were used for the search: PubMed, Web of Science, CINAHL, LILACS, EMBASE, SCOPUS, PsycINFO and the Cochrane Library. Initially, 273 articles were found; after the exclusion of repeated articles, reading of the titles, abstracts and the full articles, a final sample of nine articles was obtained. The articles were grouped into five categories: physical exercise, healing touch, music therapy, therapeutic massage, nursing interventions and health education. Among the nine studies, six showed statistical significance regarding the fatigue and/or stress levels, showing that the use of the interventions led to symptoms decrease. The most frequently tested intervention was programmed physical exercises. It is suggested that these interventions are complementary to conventional treatment and that their use can indicate an improvement in CRF and psychological stress. © 2015 John Wiley & Sons Ltd.

Thermal-Mechanical Stress Analysis of PWR Pressure Vessel and Nozzles under Grid Load-Following Mode: Interim Report on the Effect of Cyclic Hardening Material Properties and Pre-existing Cracks on Stress Analysis Results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohanty, Subhasish; Soppet, William; Majumdar, Saurin

This report provides an update on an assessment of environmentally assisted fatigue for light water reactor components under extended service conditions. This report is a deliverable under the work package for environmentally assisted fatigue as part of DOE’s Light Water Reactor Sustainability Program. In a previous report (September 2015), we presented tensile and fatigue test data and related hardening material properties for 508 low-alloys steel base metal and other reactor metals. In this report, we present thermal-mechanical stress analysis of the reactor pressure vessel and its hot-leg and cold-leg nozzles based on estimated material properties. We also present results frommore » thermal and thermal-mechanical stress analysis under reactor heat-up, cool-down, and grid load-following conditions. Analysis results are given with and without the presence of preexisting cracks in the reactor nozzles (axial or circumferential crack). In addition, results from validation stress analysis based on tensile and fatigue experiments are reported.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

MANDELL, JOHN F.; SAMBORSKY, DANIEL D.; CAIRNS, DOUGLAS

This report presents the major findings of the Montana State University Composite Materials Fatigue Program from 1997 to 2001, and is intended to be used in conjunction with the DOE/MSU Composite Materials Fatigue Database. Additions of greatest interest to the database in this time period include environmental and time under load effects for various resin systems; large tow carbon fiber laminates and glass/carbon hybrids; new reinforcement architectures varying from large strands to prepreg with well-dispersed fibers; spectrum loading and cumulative damage laws; giga-cycle testing of strands; tough resins for improved structural integrity; static and fatigue data for interply delamination; andmore » design knockdown factors due to flaws and structural details as well as time under load and environmental conditions. The origins of a transition to increased tensile fatigue sensitivity with increasing fiber content are explored in detail for typical stranded reinforcing fabrics. The second focus of the report is on structural details which are prone to delamination failure, including ply terminations, skin-stiffener intersections, and sandwich panel terminations. Finite element based methodologies for predicting delamination initiation and growth in structural details are developed and validated, and simplified design recommendations are presented.« less

Effectiveness and cost-effectiveness of a self-management group program to improve social participation in patients with neuromuscular disease and chronic fatigue: protocol of the Energetic study.

PubMed

Veenhuizen, Yvonne; Cup, Edith H C; Groothuis, Jan T; Hendriks, Jan C M; Adang, Eddy M M; van Engelen, Baziel G M; Geurts, Alexander C H

2015-04-19

Chronic fatigue is present in more than 60% of the patients with a neuromuscular disease and can be their most disabling symptom. In combination with other impairments, fatigue often results in low levels of physical activity and decreased social participation, leading to high societal costs. 'Energetic' is a self-management group program aimed at improving social participation, physical endurance and alleviating fatigue in these patients. The primary aim of this study is to evaluate the effectiveness and cost-effectiveness of the Energetic program. A multicentered, assessor-blinded, two-armed randomized controlled trial is conducted with evaluations at inclusion and four, seven and fifteen months later. The study includes patients with a neuromuscular disease and chronic fatigue and, when present, their caregivers. The participants are randomized (ratio 1:1) to either an intervention group, receiving the Energetic program, or a control group, receiving usual care (i.e., no specific intervention). The Energetic program covers four months and includes four modules: 1) individually tailored aerobic exercise training; 2) education about aerobic exercise; 3) self-management training in applying energy conservation strategies; and 4) implementation and relapse prevention in daily life. Two months after cessation of the program a booster session is provided. The primary outcome is the perceived performance score of the Canadian Occupational Performance Measure (COPM). Secondary outcomes include the COPM-satisfaction score, and measures of fatigue, physical endurance, activity engagement, mood, and self-efficacy. Caregiver burden is also evaluated as a secondary outcome. Health-related quality of life and medical and societal costs are assessed to estimate cost-effectiveness of the program. The Energetic study is the first randomized controlled trial to evaluate the effectiveness and cost-effectiveness of a combined physical and self-management group training program for improving social participation, physical endurance and alleviating fatigue in patients with neuromuscular diseases. It will generate new insights in (cost-)effective rehabilitation strategies for these incurable conditions. Clinicaltrials.gov NCT02208687 .

Fatigue limit and Hysteresis Behavior of Type 304L Stainless Steel in Air and PWR Water, at 150°C and 300°C

NASA Astrophysics Data System (ADS)

Solomon, H. D.; Amzallag, C.; Vallee, A. J.; DeLair, R. E.

This is a study of the 107 cycle fatigue limit of Type 304L Stainless Steel, as measured in fully reversed (R=-1) load-controlled tests, at 150°C and 300°C, in air and PWR water. The staircase method was used to determine the fatigue limit. The tests run here utilized a cycle frequency of 1.818Hz and are compared to other tests from the literature that were run at 30Hz. The fatigue limit measured in the tests run at the high frequency was higher than that measured here. This is explained by measurements of the strain developed during cycling, using the different cycle frequencies. The tests run at the higher frequencies yielded lower strains for a given stress and, as expected, this resulted in higher fatigue limits. Using 107 cycles to define a run-out also led to a lower fatigue limit. These results are important as most previous fatigue limit measurements utilized 106 cycles or less to define a run-out, and when lives as long as 107 cycles are used the tests are generally run at high cycle frequencies, thus leading to higher fatigue limits than those measured here.

Fatigue Crack Growth Behavior Evaluation of Grainex Mar-M 247 for NASA's High Temperature, High Speed Turbine Seal Test Rig

NASA Technical Reports Server (NTRS)

Delgado, Irebert R.; Steinetz, Bruce M.; Rimnac, Clare M.; Lewandowski, John J.

2008-01-01

The fatigue crack growth behavior of Grainex Mar-M 247 is evaluated for NASA s Turbine Seal Test Facility. The facility is used to test air-to-air seals primarily for use in advanced jet engine applications. Because of extreme seal test conditions of temperature, pressure, and surface speeds, surface cracks may develop over time in the disk bolt holes. An inspection interval is developed to preclude catastrophic disk failure by using experimental fatigue crack growth data. By combining current fatigue crack growth results with previous fatigue strain-life experimental work, an inspection interval is determined for the test disk. The fatigue crack growth life of the NASA disk bolt holes is found to be 367 cycles at a crack depth of 0.501 mm using a factor of 2 on life at maximum operating conditions. Combining this result with previous fatigue strain-life experimental work gives a total fatigue life of 1032 cycles at a crack depth of 0.501 mm. Eddy-current inspections are suggested starting at 665 cycles since eddy current detection thresholds are currently at 0.381 mm. Inspection intervals are recommended every 50 cycles when operated at maximum operating conditions.

Proof test and fatigue crack growth modeling on 2024-T3 aluminum alloy

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Poe, C. C., Jr.; Dawicke, D. S.

1990-01-01

Pressure proof testing of aircraft fuselage structures has been suggested as a means of screening critical crack sizes and of extending their useful life. The objective of this paper is to study the proof-test concept and to model the crack-growth process on a ductile material. Simulated proof and operational fatigue life tests have been conducted on cracked panels made of 2024-T3 aluminum alloy sheet material. A fatigue crack-closure model was modified to simulate the proof test and operational fatigue cycling. Using crack-growth rate and resistance-curve data, the model was able to predict crack growth during and after the proof load. These tests and analyses indicate that the proof test increases fatigue life; but the beneficial life, after a 1.33 or 1.5 proof, was less than a few hundred cycles.

Factors Influencing Dwell Fatigue Cracking in Notches of Powder Metallurgy Superalloys

NASA Technical Reports Server (NTRS)

Gabb, T. P.; Telesman, J.; Ghosn, L.; Garg, A.; Gayda, J.

2011-01-01

The influences of heat treatment and cyclic dwells on the notch fatigue resistance of powder metallurgy disk superalloys were investigated for low solvus high refractory (LSHR) and ME3 disk alloys. Disks were processed to produce material conditions with varied microstructures and associated mechanical properties. Notched specimens were first subjected to baseline dwell fatigue cycles having a dwell at maximum load, as well as tensile, stress relaxation, creep rupture, and dwell fatigue crack growth tests at 704 C. Several material heat treatments displayed a bimodal distribution of fatigue life with the lives varying by two orders-of-magnitude, while others had more consistent fatigue lives. This response was compared to other mechanical properties, in search of correlations. The wide scatter in baseline dwell fatigue life was observed only for material conditions resistant to stress relaxation. For selected materials and conditions, additional tests were then performed with the dwells shifted in part or in total to minimum tensile load. The tests performed with dwells at minimum load exhibited lower fatigue lives than max dwell tests, and also exhibited early crack initiation and a substantial increase in the number of initiation sites. These results could be explained in part by modeling evolution of peak stresses in the notch with continued dwell fatigue cycling. Fatigue-environment interactions were determined to limit life for the fatigue cycles with dwells.

The influence of cyclic shear fatigue on the bracket-adhesive-enamel complex: an in vitro study.

PubMed

Daratsianos, Nikolaos; Musabegovic, Ena; Reimann, Susanne; Grüner, Manfred; Jäger, Andreas; Bourauel, Christoph

2013-05-01

To describe the effect of fatigue on the strength of the bracket-adhesive-enamel complex and characterize the fatigue behavior of the materials tested. Upper central incisor brackets (Discovery(®), Dentaurum) were bonded with a light-curing (Transbond XT™, 3M Unitek) and a chemically-curing adhesive (Concise™, 3M Unitek) on bovine teeth embedded in cylindrical resign bases and stored in water at 37(±2)°C for 24 (±2)h. The first 15 specimens were tested with a universal testing machine ZMART.PRO(®) (Zwick GmbH & Co. KG, Ulm, Germany) for ultimate shear bond strength according to the DIN-13990-2-standard. The remaining three groups of 20 specimens underwent fatigue staircase testing of 100, 1000 and 3000 cycles at 1Hz with a self-made testing machine. The survived specimens were subjected to shear strength testing. The fatigued specimens showed decreased shear strength with both adhesives at all cycle levels. The shear strength after fatigue for 100, 1000 and 3000 cycles was in the Concise™-groups 34.8%, 59.0%, 47.3% and in the Transbond™ XT-groups 33.6%, 23.1%, 27.3% relative to the ultimate shear strength. The fatigue life of the Concise™-groups decreased with increasing stress and Transbond™ XT showed lower fatigue ratio with no obvious trend. The specimens bonded with Transbond™ XT showed typically favorable fracture modes in contrary to Concise™. Fatigue of the bracket-adhesive-enamel complex decreased its shear strength. The staircase method can provide a standardized experimental protocol for fatigue studies, however testing at various cycle numbers is recommended. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Experimental Study on Fatigue Performance of Foamed Lightweight Soil

NASA Astrophysics Data System (ADS)

Qiu, Youqiang; Yang, Ping; Li, Yongliang; Zhang, Liujun

2017-12-01

In order to study fatigue performance of foamed lightweight soil and forecast its fatigue life in the supporting project, on the base of preliminary tests, beam fatigue tests on foamed lightweight soil is conducted by using UTM-100 test system. Based on Weibull distribution and lognormal distribution, using the mathematical statistics method, fatigue equations of foamed lightweight soil are obtained. At the same time, according to the traffic load on real road surface of the supporting project, fatigue life of formed lightweight soil is analyzed and compared with the cumulative equivalent axle loads during the design period of the pavement. The results show that even the fatigue life of foamed lightweight soil has discrete property, the linear relationship between logarithmic fatigue life and stress ratio still performs well. Especially, the fatigue life of Weibull distribution is more close to that derived from the lognormal distribution, in the instance of 50% guarantee ratio. In addition, the results demonstrated that foamed lightweight soil as subgrade filler has good anti-fatigue performance, which can be further adopted by other projects in the similar research domain.

Bithermal fatigue: A simplified alternative to thermomechanical fatigue

NASA Technical Reports Server (NTRS)

Verrilli, Michael J.

1988-01-01

A bithermal fatigue test technique was proposed as a simplified alternative to the thermomechanical fatigue test. Both the thermomechanical cycle and the bithermal technique can be used to study nonisothermal fatigue behavior. The difference between the two cycles is that in a conventional thermomechanical fatigue cycle the temperature is continuously varied concurrently with the applied mechanical strains, but in the bithermal fatigue cycle the specimen is held at zero load during the temperature excursions and all the loads are applied at the two extreme temperatures of the cycle. Experimentally, the bithermal fatigue test technique offers advantages such as ease in synchronizing the temperature and mechanical strain waveforms, in minimizing temperature gradients in the specimen gauge length, and in reducing and interpreting thermal fatigue such as the influence of alternate high and low temperatures on the cyclic stress-strain response characteristics, the effects of thermal state, and the possibility of introducing high- and low-temperature deformation mechanisms within the same cycle. The bithermal technique was used to study nonisothermal fatigue behavior of alloys such as single-crystal PWA 1480, single-crystal Rene N4, cast B1900+Hf, and wrought Haynes 188.

The effects of 6-week training programs on throwing accuracy, proprioception, and core endurance in baseball.

PubMed

Lust, Kathleen R; Sandrey, Michelle A; Bulger, Sean M; Wilder, Nathan

2009-08-01

With a limited number of outcomes-based studies, only recommendations for strength-training and rehabilitation programs can be made. To determine the extent to which throwing accuracy, core stability, and proprioception improved after completion of a 6-week training program that included open kinetic chain (OKC), closed kinetic chain (CKC), and/or core-stability exercises. A 2 x 3 factorial design. Division III college. 19 healthy baseball athletes with a control group of 15. Two 6-week programs including OKC, CKC, and core-stabilization exercises that were progressed each week. Functional throwing-performance index, closed kinetic chain upper extremity stability test, back-extensor test, 45 degrees abdominal-fatigue test, and right- and left-side bridging test. There was no significant difference between groups. An increase was evident in all pretest-to-posttest results, with improvement ranging from 1.36% to 140%. Both of the 6-week training programs could be used to increase throwing accuracy, core stability, and proprioception in baseball.

Effects of a Short Physical Exercise Intervention on Patients with Multiple Sclerosis (MS).

PubMed

Kerling, Arno; Keweloh, Karin; Tegtbur, Uwe; Kück, Momme; Grams, Lena; Horstmann, Hauke; Windhagen, Anja

2015-07-10

The aim of this prospective randomized controlled trial was to investigate if a short-term endurance or combined endurance/resistance exercise program was sufficient to improve aerobic capacity and maximum force in adult patients (18-65 years) with multiple sclerosis (MS). All patients performed a three-month exercise program consisting of two training sessions per week, lasting 40 min each, with moderate intensity. All patients had a maximum value of 6 (low to moderate disability) on the Expanded Disability Status Scale (EDSS). One group (combined workout group (CWG); 15 females, 4 males) completed a combined endurance/resistance workout (20 min on a bicycle ergometer, followed by 20 min of resistance training), while the other group (endurance workout group (EWG); 13 females, 5 males) completed a 40 min endurance training program. Aerobic capacity was assessed as peak oxygen uptake, ventilatory anaerobic threshold, and workload expressed as Watts. Maximum force of knee and shoulder extensors and flexors was measured using isokinetic testing. Quality of life was assessed with the SF-36 questionnaire, and fatigue was measured using the Modified Fatigue Impact Scale. Both training groups increased in aerobic capacity and maximum force. EWG, as well as CWG, showed improvement in several subscales of the SF-36 questionnaire and decrease of their fatigue. A short exercise intervention increased both aerobic capacity and maximum force independent of whether endurance or combined endurance/resistance workouts were performed.

Developments in new aircraft tire tread materials. [fatigue life of elastomeric materials

NASA Technical Reports Server (NTRS)

Yager, T. J.; Mccarty, J. L.; Riccitiello, S. R.; Golub, M. A.

1976-01-01

Comparative laboratory and field tests were conducted on experimental and state-of-the-art aircraft tire tread materials in a program aimed at seeking new elastomeric materials which would provide improved aircraft tire tread wear, traction, and blowout resistance in the interests of operational safety and economy. The experimental stock was formulated of natural rubber and amorphous vinyl polybutadiene to provide high thermal-oxidative resistance, a characteristic pursued on the premise that thermal oxidation is involved both in the normal abrasion or wear of tire treads and probably in the chain of events leading to blowout failures. Results from the tests demonstrate that the experimental stock provided better heat buildup (hysteresis) and fatigue properties, at least equal wet and dry traction, and greater wear resistance than the state-of-the-art stock.

Futurepath: The Story of Research and Technology at NASA Lewis Research Center. Structures for Flight Propulsion, ARC Sprayed Monotape, National Aero-Space Plane

NASA Technical Reports Server (NTRS)

1989-01-01

The story of research and technology at NASA Lewis Research Center's Structures Division is presented. The job and designs of the Structures Division needed for flight propulsion is described including structural mechanics, structural dynamics, fatigue, and fracture. The video briefly explains why properties of metals used in structural mechanics need to be tested. Examples of tests and simulations used in structural dynamics (bodies in motion) are briefly described. Destructive and non-destructive fatigue/fracture analysis is also described. The arc sprayed monotape (a composite material) is explained, as are the programs in which monotape plays a roll. Finally, the National Aero-Space Plane (NASP or x-30) is introduced, including the material development and metal matrix as well as how NASP will reduce costs for NASA.

Corrosion fatigue in nitrocarburized quenched and tempered steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karim Khani, M.; Dengel, D.

1996-05-01

In order to investigate the fatigue strength and fracture mechanism of salt bath nitrocarburized steels, specimens of the steels SAE 4135 and SAE 4140, in a quenched and tempered state, and additionally in a salt bath nitrocarburized and oxidizing cooled state as well as in a polished (after the oxidizing cooling) and renewed oxidized state, were subjected to comparative rotating bending fatigue tests in inert oil and 5 pct NaCl solution. In addition, some of the quenched and tempered specimens of SAE 4135 material were provided with an approximately 50-{mu}m-thick electroless Ni-P layer, in order to compare corrosion fatigue behaviormore » between the Ni-P layer and the nitride layers. Long-life corrosion fatigue tests of SAE 4135 material were carried out under small stresses in the long-life range up to 10{sup 8} cycles with a test frequency of 100 Hz. Fatigue tests of SAE 4140 material were carried out in the range of finite life (low-cycle range) with a test frequency of 13 Hz. The results show that the 5 pct NaCl environment drastically reduced fatigue life, but nitrocarburizing plus oxidation treatment was found to improve the corrosion fatigue life over that of untreated and Ni-P coated specimens. The role of inclusions in initiating fatigue cracks was investigated. It was found that under corrosion fatigue conditions, the fatigue cracks started at cavities along the interfaces of MnS inclusions and matrix in the case of quenched and tempered specimens. The nitrocarburized specimens, however, showed a superposition of pitting corrosion and corrosion fatigue in which pores and nonmetallic inclusions in the compound layer play a predominant role concerning the formation of pits in the substrate.« less

Creep-fatigue of low cobalt superalloys

NASA Technical Reports Server (NTRS)

Halford, G. R.

1982-01-01

Testing for the low cycle fatigue and creep fatigue resistance of superalloys containing reduced amounts of cobalt is described. The test matrix employed involves a single high temperature appropriate for each alloy. A single total strain range, again appropriate to each alloy, is used in conducting strain controlled, low cycle, creep fatigue tests. The total strain range is based upon the level of straining that results in about 10,000 cycles to failure in a high frequency (0.5 Hz) continuous strain-cycling fatigue test. No creep is expected to occur in such a test. To bracket the influence of creep on the cyclic strain resistance, strain hold time tests with ore minute hold periods are introduced. One test per composition is conducted with the hold period in tension only, one in compression only, and one in both tension and compression. The test temperatures, alloys, and their cobalt compositions that are under study are given.

Compassion Fatigue in the Military Caregiver

DTIC Science & Technology

2009-03-01

Compassion Fatigue/ Burnout Syndrome Figley, C (1995; 97)19 Sprang, Clark, and Whitt-Woosley in their article, “Compassion Fatigue, Compassion...alternative or additional programs, process or intervention to address compassion fatigue, burnout , stress disorder or other debilitating post-traumatic...effects. 15. SUBJECT TERMS Caregiver, Care Provider, Secondary Traumatic Stress, Combat Trauma, Shared Trauma, Posttraumatic Stress Disorder, Burnout 16

30 CFR 250.908 - What are the minimum structural fatigue design requirements?

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 2 2010-07-01 2010-07-01 false What are the minimum structural fatigue design... Platform Approval Program § 250.908 What are the minimum structural fatigue design requirements? (a) API RP... (incorporated by reference as specified in 30 CFR 250.198), requires that the design fatigue life of each joint...

Investigation of fatigue failure in bituminous base mixes.

DOT National Transportation Integrated Search

1980-01-01

A correlation between the results obtained with the fatigue test and those from the indirect tensile test on two base mixes was attempted in anticipation of the possible use of the latter test to design base mixes for maximum fatigue life. Two base m...

Cyclic fatigue damage characteristics observed for simple loadings extended to multiaxial life prediction

NASA Technical Reports Server (NTRS)

Jones, David J.; Kurath, Peter

1988-01-01

Fully reversed uniaxial strain controlled fatigue tests were performed on smooth cylindrical specimens made of 304 stainless steel. Fatigue life data and cracking observations for uniaxial tests were compared with life data and cracking behavior observed in fully reversed torsional tests. It was determined that the product of maximum principle strain amplitude and maximum principle stress provided the best correlation of fatigue lives for these two loading conditions. Implementation of this parameter is in agreement with observed physical damage and it accounts for the variation of stress-strain response, which is unique to specific loading conditions. Biaxial fatigue tests were conducted on tubular specimens employing both in-phase and out-of-phase tension torsion cyclic strain paths. Cracking observations indicated that the physical damage which occurred in the biaxial tests was similar to the damage observed in uniaxial and torsional tests. The Smith, Watson, and Topper parameter was then extended to predict the fatigue lives resulting from the more complex loading conditions.

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

NASA Technical Reports Server (NTRS)

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

2008-01-01

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

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

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

Microstructure-based approach for predicting crack initiation and early growth in metals.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cox, James V.; Emery, John M.; Brewer, Luke N.

2009-09-01

Fatigue cracking in metals has been and is an area of great importance to the science and technology of structural materials for quite some time. The earliest stages of fatigue crack nucleation and growth are dominated by the microstructure and yet few models are able to predict the fatigue behavior during these stages because of a lack of microstructural physics in the models. This program has developed several new simulation tools to increase the microstructural physics available for fatigue prediction. In addition, this program has extended and developed microscale experimental methods to allow the validation of new microstructural models formore » deformation in metals. We have applied these developments to fatigue experiments in metals where the microstructure has been intentionally varied.« less

Fatigue life prediction of liquid rocket engine combustor with subscale test verification

NASA Astrophysics Data System (ADS)

Sung, In-Kyung

Reusable rocket systems such as the Space Shuttle introduced a new era in propulsion system design for economic feasibility. Practical reusable systems require an order of magnitude increase in life. To achieve this improved methods are needed to assess failure mechanisms and to predict life cycles of rocket combustor. A general goal of the research was to demonstrate the use of subscale rocket combustor prototype in a cost-effective test program. Life limiting factors and metal behaviors under repeated loads were surveyed and reviewed. The life prediction theories are presented, with an emphasis on studies that used subscale test hardware for model validation. From this review, low cycle fatigue (LCF) and creep-fatigue interaction (ratcheting) were identified as the main life limiting factors of the combustor. Several life prediction methods such as conventional and advanced viscoplastic models were used to predict life cycle due to low cycle thermal stress, transient effects, and creep rupture damage. Creep-fatigue interaction and cyclic hardening were also investigated. A prediction method based on 2D beam theory was modified using 3D plate deformation theory to provide an extended prediction method. For experimental validation two small scale annular plug nozzle thrusters were designed, built and tested. The test article was composed of a water-cooled liner, plug annular nozzle and 200 psia precombustor that used decomposed hydrogen peroxide as the oxidizer and JP-8 as the fuel. The first combustor was tested cyclically at the Advanced Propellants and Combustion Laboratory at Purdue University. Testing was stopped after 140 cycles due to an unpredicted failure mechanism due to an increasing hot spot in the location where failure was predicted. A second combustor was designed to avoid the previous failure, however, it was over pressurized and deformed beyond repair during cold-flow test. The test results are discussed and compared to the analytical and numerical predictions. A detailed comparison was not performed, however, due to the lack of test data resulting from a failure of the test article. Some theoretical and experimental aspects such as fin effect and round corner were found to reduce the discrepancy between prediction and test results.

Sleep Disorders as a Cause of Motor Vehicle Collisions

PubMed Central

de Mello, Marco Túlio; Narciso, Fernanda Veruska; Tufik, Sergio; Paiva, Teresa; Spence, David Warren; BaHammam, Ahmed S.; Verster, Joris C.; Pandi-Perumal, Seithikurippu R.

2013-01-01

Studies have shown that a large proportion of traffic accidents around the world are related to inadequate or disordered sleep. Recent surveys have linked driver fatigue to 16% to 20% of serious highway accidents in the UK, Australia, and Brazil. Fatigue as a result of sleep disorders (especially obstructive sleep apnea), excessive workload and lack of physical and mental rest, have been shown to be major contributing factors in motor vehicle accidents. A number of behavioral, physiological, and psychometric tests are being used increasingly to evaluate the impact of fatigue on driver performance. These include the oculography, polysomnography, actigraphy, the maintenance of wakefulness test, and others. Various strategies have been proposed for preventing or reducing the impact of fatigue on motor vehicle accidents. These have included: Educational programs emphasizing the importance of restorative sleep and the need for drivers to recognize the presence of fatigue symptoms, and to determine when to stop to sleep; The use of exercise to increase alertness and to promote restorative sleep; The use of substances or drugs to promote sleep or alertness (i.e. caffeine, modafinil, melatonin and others), as well as specific sleep disorders treatment; The use of CPAP therapy for reducing excessive sleepiness among drivers who have been diagnosed with obstructive sleep apnea. The evidence cited in this review justifies the call for all efforts to be undertaken that may increase awareness of inadequate sleep as a cause of traffic accidents. It is strongly recommended that, for the purpose of promoting highway safety and saving lives, all disorders that cause excessive sleepiness should be investigated and monitored. PMID:23626880

Face Gear Technology for Aerospace Power Transmission Progresses

NASA Technical Reports Server (NTRS)

2005-01-01

The use of face gears in an advanced rotorcraft transmission design was first proposed by the McDonnell Douglas Helicopter Company during their contracted effort with the U.S. Army under the Advanced Rotorcraft Transmission (ART) program. Face gears would be used to turn the corner between the horizontal gas turbine engine and the vertical output rotor shaft--a function currently done by spiral bevel gears. This novel gearing arrangement would substantially lower the drive system weight partly because a face gear mesh would be used to split the input power between two output gears. However, the use of face gears and their ability to operate successfully at the speeds and loads required for an aerospace environment was unknown. Therefore a proof-of-concept phase with an existing test stand at the NASA Lewis Research Center was pursued. Hardware was designed that could be tested in Lewis' Spiral Bevel Gear Test Rig. The initial testing indicated that the face gear mesh was a feasible design that could be used at high speeds and load. Surface pitting fatigue was the typical failure mode, and that could lead to tooth fracture. An interim project was conducted to see if slight modifications to the gear tooth geometry or an alternative heat treating process could overcome the surface fatigue problems. From the initial and interim tests, it was apparent that for the surface fatigue problems to be overcome the manufacturing process used for this component would have to be developed to the level used for spiral bevel gears. The current state of the art for face gear manufacturing required using less than optimal gear materials and manufacturing techniques because the surface of the tooth form does not receive final finishing after heat treatment as it does for spiral bevel gears. This resulted in less than desirable surface hardness and manufacturing tolerances. An Advanced Research and Projects Agency (ARPA) Technology Reinvestment Project has been funded to investigate the effects of manufacturing process improvements on the operating characteristics of face gears. The program is being conducted with McDonnell Douglas Helicopter Co., Lucas Western Inc., the University of Illinois at Chicago, and a NASA/U.S. Army team. The goal of the project is develop the grinding process, experimentally verify the improvement in face gear fatigue life, and conduct a full-scale helicopter transmission test. The theory and methodology to grind face gears has been completed, and manufacture of the test hardware is ongoing. Experimental verification on test hardware is scheduled to begin in fiscal 1996.

Initiation and growth of multiple-site damage in the riveted lap joint of a curved stiffened fuselage panel: An experimental and analytical study

NASA Astrophysics Data System (ADS)

Ahmed, Abubaker Ali

As part of the structural integrity research of the National Aging Aircraft Research Program, a comprehensive study on multiple-site damage (MSD) initiation and growth in a pristine lap-joint fuselage panel has been conducted. The curved stiffened fuselage panel was tested at the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration William J. Hughes Technical Center. A strain survey test was conducted to verify proper load application. The panel was then subjected to a fatigue test with constant-amplitude cyclic loading. The applied loading spectrum included underload marker cycles so that crack growth history could be reconstructed from post-test fractographic examinations. Crack formation and growth were monitored via nondestructive and high-magnification visual inspections. Strain gage measurements recorded during the strain survey tests indicated that the inner surface of the skin along the upper rivet row of the lap joint experienced high tensile stresses due to local bending. During the fatigue loading, cracks were detected by eddy-current inspections at multiple rivet holes along the upper rivet row. Through-thickness cracks were detected visually after about 80% of the fatigue life. Once MSD cracks from two adjacent rivet holes linked up, there was a quick deterioration in the structural integrity of the lap joint. The linkup resulted in a 2.87" (72.9-mm) lead fatigue crack that rapidly propagated across 12 rivet holes and crossed over into the next skin bay, at which stage the fatigue test was terminated. A post-fatigue residual strength test was then conducted by loading the panel quasi-statically up to final failure. The panel failed catastrophically when the crack extended instantaneously across three additional bays. Post-test fractographic examinations of the fracture surfaces in the lap joint of the fuselage panel were conducted to characterize subsurface crack initiation and growth. Results showed evidence of fretting damage and crack initiation at multiple locations near the rivet holes along the faying surface of the skin. The subsurface cracks grew significantly along the faying surface before reaching the outer surface of the skin, forming elliptical crack fronts. A finite element model (FE) of the panel was constructed and geometrically-nonlinear analyses conducted to determine strain distribution under the applied loads. The FE model was validated by comparing the analysis results with the strain gage measurements recorded during the strain survey test. The validated FE model was then used to determine stress-intensity factors at the crack tips. Stress-intensity factor results indicated that crack growth in the lap joint was under mixed-mode; however, the opening-mode stress intensity factor was dominant. The stress-intensity factors computed from the FE analysis were used to conduct cycle-by-cycle integration of fatigue crack growth. In the cycle-by-cycle integration, the NASGRO crack growth model was used with its parameters selected to account for the effects of plasticity-induced crack closure and the test environment on crack growth rate. Fatigue crack growth predictions from cycle-by-cycle computation were in good agreement with the experimental measured crack growth data. The results of the study provide key insights into the natural development and growth of MSD cracks in the pristine lap joint. The data provided by the study represent a valuable source for the evaluation and validation of analytical methodologies used for predicting MSD crack initiation and growth.

Effects of an 8-Week Outdoor Brisk Walking Program on Fatigue in Hi-Tech Industry Employees: A Randomized Control Trial.

PubMed

Wu, Li-Ling; Wang, Kuo-Ming; Liao, Po-I; Kao, Yu-Hsiu; Huang, Yi-Ching

2015-10-01

Over 73% of hi-tech industry employees in Taiwan lack regular exercise. They are exposed to a highly variable and stressful work environment for extended periods of time, and may subsequently experience depression, detrimental to workers' physiological and mental health. In this cross-sectional survey, the authors explored the effect of an 8-week brisk walking program on the fatigue of employees in the hi-tech industry. The participants, from a hi-tech company in northern Taiwan, were randomly assigned to an experimental group (EG; 41 subjects, Mage = 33.34 ± 6.40) or control group (CG; 45 subjects, Mage = 29.40 ± 3.60). Following the 8-week brisk walking program, the EG showed significantly lower scores for subjective fatigue, working motivation, attention, and overall fatigue. The authors confirmed that the 8-week outdoor brisk walking program significantly improved the level of fatigue among employees of the hi-tech industry. The finding serves as an important reference for health authorities in Taiwan and provides awareness of workplace health promotion in the hi-tech industry. © 2015 The Author(s).

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

PubMed Central

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

2014-01-01

Objective Fibromyalgia is a condition characterized by chronic widespread muscle pain and fatigue. The primary objective of this study was to determine if pain, perceived cognitive fatigue, and perceived physical fatigue were enhanced in participants with fibromyalgia compared to healthy controls during a cognitive fatigue task, a physical fatigue task and a dual fatigue task. Methods Twenty four people with fibromyalgia and 33 healthy controls completed pain, fatigue and function measures. A cognitive fatigue task (Controlled Oral Word Association Test) and physical fatigue task (Valpar peg test) were done individually and combined for a dual fatigue task. Resting pain, perceived cognitive fatigue and perceived physical fatigue were assessed during each task using visual analogue scales. Function was assessed with shoulder range of motion and grip. Results People with fibromyalgia had significantly higher increases in pain, cognitive fatigue and physical fatigue when compared to healthy controls after completion of a cognitive fatigue task, a physical fatigue task, or a dual fatigue task (p<0.01). People with fibromyalgia performed equivalently on measures of physical performance and cognitive performance on the physical and cognitive fatigue tasks, respectively. Conclusions These data show that people with fibromyalgia show larger increases in pain, perceived cognitive fatigue and perceived physical fatigue to both cognitive and physical fatigue tasks compared to healthy controls. The increases in pain and fatigue during cognitive and physical fatigue tasks could influence subject participation in daily activities and rehabilitation. PMID:25074583

Laboratory Study on the Fatigue Resistance of Asphaltic Concrete Containing Titanium Dioxide

NASA Astrophysics Data System (ADS)

Buhari, Rosnawati; Ezree Abdullah, Mohd; Khairul Ahmad, Mohd; Azhar Tajudin, Saiful; Khatijah Abu Bakar, Siti

2018-03-01

This study aims to evaluate the fatigue performance of modified asphalt mixture using Indirect Tensile Fatigue Test. Titanium Dioxide (TiO2) powder in a form of rutile was used for producing asphalt concrete with lower mixing and compaction temperature compared to conventional hot mix asphalt without reducing its physical and mechanical also resistance to fatigue. The characteristic of the asphalt and modified asphalt was evaluated using penetration test, softening test and rotational viscosity test. Titanium dioxide of 2%, 4%, 6%, 8% and 10% by weight of asphalt has been incorporated into unaged 80/100 asphalt mix in order to improvise its performance and to fulfill the objectives of this experimental study. As a result, TiO2 as an additive is potential to decrease the penetration and increasing the softening point of the asphalt. In terms of fatigue performance testing, addition TiO2 additive does help in improving the fatigue properties as it shows greater result than the control asphalt. In conclusion, TiO2 is great in improving fatigue properties.

High temperature, low cycle fatigue of copper-base alloys in argon. Part 3: Zirconium-copper; thermal-mechanical strain cycling, hold-time and notch fatigue results

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1973-01-01

The low-cycle fatigue characteristics of smooth bar and notched bar specimens (hourglass shape) of zirconium-copper, 1/2 Hard, material (R-2 Series) were evaluated at room temperature in axial strain control. Over the fatigue life range from about 300 to 3000 cycles the ratio of fatigue life for smooth bar to fatigue life for notched bar remained constant at a value of about 6.0. Some additional hold-time data for the R-2 alloy tested in argon at 538 C are reported. An analysis of the relaxation data obtained in these hold-time tests is also reported and it is shown that these data yield a fairly consistent correlation in terms of instantaneous stress rate divided by instantaneous stress. Two thermal-mechanical strain cycling tests were also performed using a cyclic frequency of 4.5 cycles per hour and a temperature cycling interval from 260 to 538 C. The fatigue life values in these tests were noticeably lower than that observed in isothermal tests at 538 C.

Review of specimen heating in mechanical tests at cryogenic temperatures

NASA Astrophysics Data System (ADS)

Ogata, T.; Yuri, T.; Ono, Y.

2014-01-01

At cryogenic temperatures near 4 K, a discontinuous deformation produces a large amount of specimen temperature rise that might bring significant changes in mechanical properties. The authors measured the specimen heating in tensile tests, fatigue test, and other tests in liquid helium for stainless steels and other materials. In this paper, we have measured the specimen temperature in high-cycle and low-cycle fatigue tests for stainless steels at various frequencies and stress levels and evaluated the testing conditions to keep the specimen at a specified temperature. We proposed maximum frequency in load-controlled fatigue tests for specified loading variables and a maximum strain rate in strain-controlled fatigue tests.

Rolling-element fatigue life with two synthetic cycloaliphatic traction fluids

NASA Technical Reports Server (NTRS)

Loewenthal, S. H.; Parker, R. J.

1976-01-01

The life potential of two synthetic cycloaliphatic hydrocarbon traction fluids in rolling element fatigue was evaluated in a five ball fatigue tester. Life comparisons with a MIL-L-23699 qualified tetraester oil showed that the traction test oils had good fatigue life performance, comparable to that of the tetraester oil. No statistically significant life differences between the traction fluids and the tetraester oil were exhibited under the accelerated fatigue test conditions. Erratic operating behavior was occasionally encountered during tests with the antiwear additive containing traction fluid for reasons thought to be related to excessive chemical activity under high contact pressure. This behavior occasionally resulted in premature test termination due to excessive surface distress and overheating.

Effects of Total SAT® Test Time on Performance and Fatigue. Research Notes. RN-37

ERIC Educational Resources Information Center

Ackerman, Phillip L.; Kanfer, Ruth; Wolman, Stacey D.

2005-01-01

The current study was designed to examine performance effects and fatigue effects associated with different total SAT testing times. In addition, the researchers examined personality, motivation, and other determinants of individual differences in examinee fatigue before, during, and after testing.

The role of fretting corrosion and fretting fatigue in aircraft rivet hole cracking

NASA Technical Reports Server (NTRS)

Elliott, Charles B., III; Moesser, Mark; Hoeppner, David W.

1994-01-01

Personnel in the Quality and Integrity Design Engineering Center (QIDEC) at the University of Utah are working under a two year grant from the FAA to better understand the role of fretting corrosion and fretting fatigue in aircraft rivet hole cracking. The current program follows a one year grant program which was completed in 1993. This paper provides a status report on the results of these grant programs. Recent effort has been focused on developing basic fretting fatigue models which consider variation in the coefficient of friction with time and location within the fretting interface. This is a very important characteristic of the QIDEC model because coefficient of friction varies significantly during the fretting fatigue process. Copies of QIDEC documents discussed in this paper can be obtained by contacting the authors.

Detailed Microstructural Characterization of the Disk Alloy ME3

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Garg, Anita; Ellis, David L.; O'Connor, Kenneth M.

2004-01-01

The advanced powder metallurgy disk alloy ME3 was designed using statistical screening and optimization of composition and processing variables in the NASA/General Electric/Pratt & Whitney HSR/EPM disk program to have extended durability for large disks at maximum temperatures of 600 to 700 C. Scaled-up disks of this alloy were then produced at the conclusion of that program to demonstrate these properties in realistic disk shapes. The objective of the present study was to assess the microstructural characteristics of these ME3 disks at two consistent locations, in order to enable estimation of the variations in microstructure across each disk and across several disks of this advanced alloy. Scaled-up disks processed in the HSR/EPM Compressor/Turbine Disk program had been sectioned, machined into specimens, and tested in tensile, creep, fatigue, and fatigue crack growth tests by NASA Glenn Research Center, in cooperation with General Electric Engine Company and Pratt & Whitney Aircraft Engines. For this study, microstructures of grip sections from tensile specimens in the bore and rim were evaluated from these disks. The major and minor phases were identified and quantified using transmission electron microscopy (TEM). Particular attention was directed to the .' precipitates, which along with grain size can predominantly control the mechanical properties of superalloy disks.

Ultrasonic Fatigue Endurance of Thin Carbon Fiber Sheets

NASA Astrophysics Data System (ADS)

Domínguez Almaraz, Gonzalo M.; Ruiz Vilchez, Julio A.; Dominguez, Aymeric; Meyer, Yann

2016-04-01

Ultrasonic fatigue tests were carried out on thin carbon fiber sheets (0.3 mm of thickness) to determine the fatigue endurance under very high-frequency loading (20 kHz). This material, called the gas diffusion layer (GDL), plays a major role in the overall performances of proton exchange membrane fuel cells (PEMFCs). The study of its physical-chemical properties is an on-going subject in the literature; nevertheless, no knowledge is available concerning the high-frequency fatigue endurance. A principal difficulty in carrying out ultrasonic fatigue tests on this material was to determine the dimensions of testing specimen to fit the resonance condition. This aspect was solved by modal numerical simulation: The testing specimen has been a combination of a low-strength steel frame (to facilitate the attachment to the ultrasonic machine and to increase the mass of the specimen), and the carbon fiber hourglass-shape profile. Under resonance condition, a stationary elastic wave is generated along the specimen that induces high stress at the neck section and high displacements at the ends. Results show that fatigue life was close to 3 × 108 cycles when the high Von Misses stress at the neck section was 170 MPa, whereas fatigue life attains the 4.5 × 109 cycles when stress decreases to 117 MPa. Crack initiation and propagation were analyzed, and conclusions were drawn concerning the fatigue endurance of these fiber carbon sheets under ultrasonic fatigue testing.

Fatigue analysis and testing of wind turbine blades

NASA Astrophysics Data System (ADS)

Greaves, Peter Robert

This thesis focuses on fatigue analysis and testing of large, multi MW wind turbine blades. The blades are one of the most expensive components of a wind turbine, and their mass has cost implications for the hub, nacelle, tower and foundations of the turbine so it is important that they are not unnecessarily strong. Fatigue is often an important design driver, but fatigue of composites is poorly understood and so large safety factors are often applied to the loads. This has implications for the weight of the blade. Full scale fatigue testing of blades is required by the design standards, and provides manufacturers with confidence that the blade will be able to survive its service life. This testing is usually performed by resonating the blade in the flapwise and edgewise directions separately, but in service these two loads occur at the same time.. A fatigue testing method developed at Narec (the National Renewable Energy Centre) in the UK in which the flapwise and edgewise directions are excited simultaneously has been evaluated by comparing the Palmgren-Miner damage sum around the blade cross section after testing with the damage distribution caused by the service life. A method to obtain the resonant test configuration that will result in the optimum mode shapes for the flapwise and edgewise directions was then developed, and simulation software was designed to allow the blade test to be simulated so that realistic comparisons between the damage distributions after different test types could be obtained. During the course of this work the shortcomings with conventional fatigue analysis methods became apparent, and a novel method of fatigue analysis based on multi-continuum theory and the kinetic theory of fracture was developed. This method was benchmarked using physical test data from the OPTIDAT database and was applied to the analysis of a complete blade. A full scale fatigue test method based on this new analysis approach is also discussed..

Resistance Spot Welding Characteristics and High Cycle Fatigue Behavior of DP 780 Steel Sheet

NASA Astrophysics Data System (ADS)

Pal, Tapan Kumar; Bhowmick, Kaushik

2012-02-01

Resistance spot welding characteristics of DP 780 steel was investigated using peel test, microhardness test, tensile shear test, and fatigue test. Tensile shear test provides better spot weld quality than conventional peel test and hardness is not a good indicator of the susceptibility to interfacial fracture. The results of high-cycle fatigue behavior of spot welded DP 780 steel under two different parameters show that at high load low cycle range a significant difference in the S- N curve and almost similar fatigue behavior of spot welds at low load high cycle range are obtained. However, when applied load was converted to stress intensity factor, the difference in the fatigue behavior between welds diminished. Furthermore, a transition in fracture mode, i.e., interfacial and plug and hole-type at about 50% of yield load is observed.

United States Air Force Summer Faculty Research Program for 1990. Program Management Report

DTIC Science & Technology

1991-06-05

propagation characteristics were extensively studied using pencil lead breaks in a center notch. For the fatigue studies center crack samples of 2024 - T351 ... aluminum specimens during fatigue cycling. The experimental procedure involved excitation of Rayleigh waves on the surface of each specimen and...Research Program (SFRP) provides opportunities for research in the physical sciences, engineering, and life sciences. The program has been effective

Synergistic Effects of Temperature, Oxidation and Stress Level on Fatigue Damage Evolution and Lifetime Prediction of Cross-Ply SiC/CAS Ceramic-Matrix Composites Through Hysteresis-Based Parameters

NASA Astrophysics Data System (ADS)

Li, Longbiao

2017-12-01

The damage development and cyclic fatigue lifetime of cross-ply SiC/CAS ceramic-matrix composites have been investigated at different testing temperatures in air atmosphere. The relationships between the fatigue hysteresis-based damage parameters, i.e., fatigue hysteresis dissipated energy, fatigue hysteresis modulus and fatigue peak strain and the damage mechanisms of matrix multicracking, fiber/matrix interface debonding, interface sliding and fibers failure, have been established. With the increase in the cycle number, the evolution of the fatigue hysteresis modulus, fatigue peak strain and fatigue hysteresis dissipated energy depends upon the fatigue peak stress levels, interface and fibers oxidation and testing temperature. The fatigue life S-N curves of cross-ply SiC/CAS composite at room and elevated temperatures have been predicted, and the fatigue limit stresses at room temperature, 750 and 850 °C, are 50, 36 and 30% of the tensile strength, respectively.

Stirling Space Engine Program. Volume 2; Appendixes A, B, C and D

NASA Technical Reports Server (NTRS)

Dhar, Manmohan

1999-01-01

The objective of this program was to develop the technology necessary for operating Stirling power converters in a space environment and to demonstrate this technology in full-scale engine tests. Volume 2 of the report includes the following appendices: Appendix A: Heater Head Development (Starfish Heater Head Program, 1/10th Segment and Full-Scale Heat Pipes, and Sodium Filling and Processing); Appendix B: Component Test Power Converter (CTPC) Component Development (High-temperature Organic Materials, Heat Exchanger Fabrication, Beryllium Issues, Sodium Issues, Wear Couple Tests, Pressure Boundary Penetrations, Heating System Heaters, and Cooler Flow Test); Appendix C: Udimet Testing (Selection of the Reference Material for the Space Stirling Engine Heater Head, Udimet 720LI Creep Test Result Update, Final Summary of Space Stirling Endurance Engine Udimet 720L1 Fatigue Testing Results, Udimet 720l1 Weld Development Summary, and Udimet 720L1 Creep Test Final Results Summary), and Appendix D: CTPC Component Development Photos.

Reliable high-power diode lasers: thermo-mechanical fatigue aspects

NASA Astrophysics Data System (ADS)

Klumel, Genady; Gridish, Yaakov; Szafranek, Igor; Karni, Yoram

2006-02-01

High power water-cooled diode lasers are finding increasing demand in biomedical, cosmetic and industrial applications, where repetitive cw (continuous wave) and pulsed cw operation modes are required. When operating in such modes, the lasers experience numerous complete thermal cycles between "cold" heat sink temperature and the "hot" temperature typical of thermally equilibrated cw operation. It is clearly demonstrated that the main failure mechanism directly linked to repetitive cw operation is thermo-mechanical fatigue of the solder joints adjacent to the laser bars, especially when "soft" solders are used. Analyses of the bonding interfaces were carried out using scanning electron microscopy. It was observed that intermetallic compounds, formed already during the bonding process, lead to the solders fatigue both on the p- and n-side of the laser bar. Fatigue failure of solder joints in repetitive cw operation reduces useful lifetime of the stacks to hundreds hours, in comparison with more than 10,000 hours lifetime typically demonstrated in commonly adopted non-stop cw reliability testing programs. It is shown, that proper selection of package materials and solders, careful design of fatigue sensitive parts and burn-in screening in the hard pulse operation mode allow considerable increase of lifetime and reliability, without compromising the device efficiency, optical power density and compactness.

14 CFR 35.37 - Fatigue limits and evaluation.

Code of Federal Regulations, 2014 CFR

2014-01-01

... AIRWORTHINESS STANDARDS: PROPELLERS Tests and Inspections § 35.37 Fatigue limits and evaluation. This section does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention...

14 CFR 35.37 - Fatigue limits and evaluation.

Code of Federal Regulations, 2012 CFR

2012-01-01

... AIRWORTHINESS STANDARDS: PROPELLERS Tests and Inspections § 35.37 Fatigue limits and evaluation. This section does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention...

14 CFR 35.37 - Fatigue limits and evaluation.

Code of Federal Regulations, 2013 CFR

2013-01-01

... AIRWORTHINESS STANDARDS: PROPELLERS Tests and Inspections § 35.37 Fatigue limits and evaluation. This section does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention...

14 CFR 35.37 - Fatigue limits and evaluation.

Code of Federal Regulations, 2011 CFR

2011-01-01

... AIRWORTHINESS STANDARDS: PROPELLERS Tests and Inspections § 35.37 Fatigue limits and evaluation. This section does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention...

Analytical and experimental investigation of fatigue in a sheet specimen with an interference-fit bolt

NASA Technical Reports Server (NTRS)

Crews, J. H., Jr.

1975-01-01

A fatigue analysis, based on finite-element calculations and fatigue tests, was conducted for an aluminum-alloy sheet specimen with a steel interference-fit bolt. The stress analysis of the region near the bolt hole showed that the beneficial effect of an interference-fit bolt can be interpreted as the combined result of two effects: (1) load transfer through the bolt and (2) the compressive interference stresses in the sheet. Results of the fatigue tests show that progressively higher interference levels produced longer fatigue lives. The tests also show that a high level of interference prevents fretting at the bolt-sheet interface and that interferences larger than this level produced little additional improvement in fatigue life.

Corrosion fatigue in nitrocarburized quenched and tempered steels

NASA Astrophysics Data System (ADS)

Khani, M. Karim; Dengel, D.

1996-05-01

In order to investigate the fatigue strength and fracture mechanism of salt bath nitrocarburized steels, specimens of the steels SAE 4135 and SAE 4140, in a quenched and tempered state, and additionally in a salt bath nitrocarburized and oxidizing cooled state as well as in a polished (after the oxidizing cooling) and renewed oxidized state, were subjected to comparative rotating bending fatigue tests in inert oil and 5 pct NaCl solution. In addition, some of the quenched and tempered specimens of SAE 4135 material were provided with an approximately 50-μm-thick electroless Ni-P layer, in order to compare corrosion fatigue behavior between the Ni-P layer and the nitride layers. Long-life corrosion fatigue tests of SAE 4135 material were carried out under small stresses in the long-life range up to 108 cycles with a test frequency of 100 Hz. Fatigue tests of SAE 4140 material were carried out in the range of finite life (low-cycle range) with a test frequency of 13 Hz. The results show that the 5 pct NaCl environment drastically reduced fatigue life, but nitrocarburizing plus oxidation treatment was found to improve the corrosion fatigue life over that of untreated and Ni-P coated specimens. The beneficial effect of nitrocarburizing followed by oxidation treatment on cor-rosion fatigue life results from the protection rendered by the compound layer by means of a well-sealed oxide layer, whereby the pores present in the compound layer fill up with oxides. The role of inclusions in initiating fatigue cracks was investigated. It was found that under corrosion fatigue conditions, the fatigue cracks started at cavities along the interfaces of MnS inclusions and matrix in the case of quenched and tempered specimens. The nitrocarburized specimens, however, showed a superposition of pitting corrosion and corrosion fatigue in which pores and nonmetallic inclusions in the compound layer play a predominant role concerning the formation of pits in the substrate.

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.

Results from recent NASA tire thermal studies

NASA Technical Reports Server (NTRS)

Mccarty, J. L.

1983-01-01

The testing technique and some results from an experimental study to determine tire temperature profiles to aid in defining the strength and fatigue limitations of the tire carcass structure are described. This effort is part of a program to explore analytically and through experiment the temperature distribution in an aircraft tire during free roll and braked and yawed rolling conditions.

Relationship of fatigue and exercise capacity with emotional and physical state in patients with coronary artery disease admitted for rehabilitation program.

PubMed

Bunevicius, Adomas; Stankus, Albinas; Brozaitiene, Julija; Girdler, Susan S; Bunevicius, Robertas

2011-08-01

The relationship between subjective fatigue, exercise capacity, and symptoms of depression and anxiety in patients with coronary artery disease (CAD) needs to be specified. In this cross-sectional study, a total of 1,470 (64% men; mean age 57 ± 11 years) consecutive CAD patients admitted for cardiac rehabilitation after treatment of acute cardiac events were evaluated for demographic characteristics, for past and current diagnosis and treatment, for New York Heart Association (NYHA) class, for symptoms of depression and for symptoms of anxiety using the Hospital Anxiety and Depression Scale, and for subjective fatigue using the Multidimensional Fatigue Inventory. On the next day, all patients underwent exercise capacity evaluation using a standard bicycle ergometer testing procedure. In univariate regression analyses, there was the strongest positive association between scores on all Multidimensional Fatigue Inventory subscales and scores on the Hospital Anxiety and Depression Scale depression and anxiety subscales and between exercise capacity and NYHA class. Multivariate regression analyses revealed that symptoms of depression were the strongest positive determinants of all dimensions of subjective fatigue and, together with other significant variables, accounted for 17% to 29% of the variance. However, neither depressive nor anxious symptoms were significant determinants of exercise capacity. The association between subjective fatigue and exercise capacity and vice versa was minimal. Subjective fatigue in CAD patients is strongly related to symptoms of depression and symptoms of anxiety. In contrast, exercise capacity in CAD patients is strongly related to NYHA functional class, with no relationship to symptoms of depression and anxiety. Copyright © 2011 Mosby, Inc. All rights reserved.

Statistical characterization of the fatigue behavior of composite lamina

NASA Technical Reports Server (NTRS)

Yang, J. N.; Jones, D. L.

1979-01-01

A theoretical model was developed to predict statistically the effects of constant and variable amplitude fatigue loadings on the residual strength and fatigue life of composite lamina. The parameters in the model were established from the results of a series of static tensile tests and a fatigue scan and a number of verification tests were performed. Abstracts for two other papers on the effect of load sequence on the statistical fatigue of composites are also presented.

The neural effects of positively and negatively re-experiencing mental fatigue sensation: a magnetoencephalography study.

PubMed

Ishii, Akira; Ishizuka, Takuya; Muta, Yuki; Tanaka, Masaaki; Yamano, Emi; Watanabe, Yasuyoshi

2018-06-01

Fatigue sensation is an essential biological alarm that urges us to take rest to avoid disrupting homeostasis and thus plays an important role in maintaining well-being. However, there are situations in which the anticipation of unpleasant fatigue sensation undesirably reduces motivation for activity. The aim of this study was to examine whether thinking positively about the fatigue sensation would increase motivation to accomplish the workload. Fourteen healthy male volunteers participated in this study and performed a two-back test for 30 min to induce mental fatigue sensation. After their subjective level of fatigue had recovered to the baseline level, they re-experienced the fatigue sensation experienced in the two-back test positively, negatively, and without any modification (i.e., re-experienced the fatigue sensation as it was). The level of motivation to perform another two-back test they felt during the re-experiencing was assessed. The neural activity related to the re-experiencing was recorded using magnetoencephalography. The level of the motivation to perform another two-back test was increased by positively re-experiencing the fatigue sensation. The increase in delta band power in Brodmann area 7 was positively associated with the increase in motivation. These results show that positive thinking about fatigue sensation can enhance motivation and suggest that this enhanced motivation may have some effects on visual attention system.

Learning to Live on a Mars Day: Fatigue Countermeasures during the Phoenix Mars Lander Mission

PubMed Central

Barger, Laura K.; Sullivan, Jason P.; Vincent, Andrea S.; Fiedler, Edna R.; McKenna, Laurence M.; Flynn-Evans, Erin E.; Gilliland, Kirby; Sipes, Walter E.; Smith, Peter H.; Brainard, George C.; Lockley, Steven W.

2012-01-01

Study Objectives: To interact with the robotic Phoenix Mars Lander (PML) spacecraft, mission personnel were required to work on a Mars day (24.65 h) for 78 days. This alien schedule presents a challenge to Earth-bound circadian physiology and a potential risk to workplace performance and safety. We evaluated the acceptability, feasibility, and effectiveness of a fatigue management program to facilitate synchronization with the Mars day and alleviate circadian misalignment, sleep loss, and fatigue. Design: Operational field study. Setting: PML Science Operations Center. Participants: Scientific and technical personnel supporting PML mission. Interventions: Sleep and fatigue education was offered to all support personnel. A subset (n = 19) were offered a short-wavelength (blue) light panel to aid alertness and mitigate/reduce circadian desynchrony. They were assessed using a daily sleep/work diary, continuous wrist actigraphy, and regular performance tests. Subjects also completed 48-h urine collections biweekly for assessment of the circadian 6-sulphatoxymelatonin rhythm. Measurements and Results: Most participants (87%) exhibited a circadian period consistent with adaptation to a Mars day. When synchronized, main sleep duration was 5.98 ± 0.94 h, but fell to 4.91 ± 1.22 h when misaligned (P < 0.001). Self-reported levels of fatigue and sleepiness also significantly increased when work was scheduled at an inappropriate circadian phase (P < 0.001). Prolonged wakefulness (≥ 21 h) was associated with a decline in performance and alertness (P < 0.03 and P < 0.0001, respectively). Conclusions: The ability of the participants to adapt successfully to the Mars day suggests that future missions should utilize a similar circadian rhythm and fatigue management program to reduce the risk of sleepiness-related errors that jeopardize personnel safety and health during critical missions. Citation: Barger LK; Sullivan JP; Vincent AS; Fiedler ER; McKenna LM; Flynn-Evans EE; Gilliland K; Sipes WE; Smith PH; Brainard GC; Lockley SW. Learning to live on a Mars day: fatigue countermeasures during the Phoenix Mars Lander mission. SLEEP 2012;35(10):1423-1435. PMID:23024441

Effects of sour crude oil on fatigue properties of steel plates for shipbuilding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ouchi, H.; Kobayashi, J.; Ishikawa, T.

1994-12-31

The concentration of diffusible hydrogen introduced into steel was measured, and fatigue crack growth tests and fatigue life tests were carried out in sour crude oil containing a high concentration of hydrogen sulfide and under electrolytic hydrogen-charging conditions in neutral solution, using a high strength steel produced by the thermo-mechanical control process (TMCP) and a mild steel which are steels for hull plates. Comparison of the results demonstrated that a very small amount of hydrogen such as that introduced into steel from sour crude oil under atmospheric pressure accelerated the fatigue crack growth in the high {Delta}K regime and shortenedmore » the fatigue life in the high stress range region, but did not shorten the fatigue life in the low stress region. The electrolytic hydrogen-charging condition appeared to be appropriate as a fatigue-crack-growth test environment to simulate sour crude oil. The deterioration of fatigue characteristics of the TMCP high strength steel was similar with that of the mild steel.« less

Fretting Fatigue Experiment and Analysis of AlSi9Cu2Mg Alloy

PubMed Central

Wang, Jun; Xu, Hong; Su, Tiexiong; Zhang, Yi; Guo, Zhen; Mao, Huping; Zhang, Yangang

2016-01-01

An investigation was carried out in order to study the fretting fatigue behavior of an AlSi9Cu2Mg aluminum alloy. The fretting fatigue tests of AlSi9Cu2Mg were performed using a specially designed testing machine. The failure mechanism of fretting fatigue was explored by studying the fracture surfaces, fretting scars, fretting debris, and micro-hardness of fretting fatigue specimens using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and micro Vickers hardness test techniques. The experimental results show that the fretting fatigue limit (42 MPa) is significantly reduced to approximately 47% of the plain fatigue limit (89 MPa) under 62.5 MPa contact pressure. Furthermore, the fretting fatigue life decreases with increasing alternating stress and increasing contact pressure. The examination results suggest that the stress concentrates induced by oxidation-assisted wear on the contact interface led to the earlier initiation and propagation of crack under the fretting condition. PMID:28774103

Fretting Fatigue Experiment and Analysis of AlSi9Cu2Mg Alloy.

PubMed

Wang, Jun; Xu, Hong; Su, Tiexiong; Zhang, Yi; Guo, Zhen; Mao, Huping; Zhang, Yangang

2016-12-05

An investigation was carried out in order to study the fretting fatigue behavior of an AlSi9Cu2Mg aluminum alloy. The fretting fatigue tests of AlSi9Cu2Mg were performed using a specially designed testing machine. The failure mechanism of fretting fatigue was explored by studying the fracture surfaces, fretting scars, fretting debris, and micro-hardness of fretting fatigue specimens using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and micro Vickers hardness test techniques. The experimental results show that the fretting fatigue limit (42 MPa) is significantly reduced to approximately 47% of the plain fatigue limit (89 MPa) under 62.5 MPa contact pressure. Furthermore, the fretting fatigue life decreases with increasing alternating stress and increasing contact pressure. The examination results suggest that the stress concentrates induced by oxidation-assisted wear on the contact interface led to the earlier initiation and propagation of crack under the fretting condition.

The fatigue experience for women with human immunodeficiency virus.

PubMed

Lee, K A; Portillo, C J; Miramontes, H

1999-01-01

To examine fatigue as a symptom experienced by women with human immunodeficiency virus (HIV). A convenience sample of 100 women with HIV. Independent sample t-tests were used to test for mean differences in fatigue related to variables in the women's sociocultural and home environment (ethnicity, employment, marital status, and parenting). Pearson product moment correlations were used to examine significant relationships between fatigue and physiologic variables (age, CD4 cell count, and sleep). Lower CD4 cell counts were related to more daytime sleep, higher evening fatigue, and higher morning fatigue. Morning fatigue was related to duration of wake episodes during the night, napping, and perception of sleep disturbance during the past week. The number of awakenings during the first night predicted the severity of fatigue the next evening. To understand the fatigue experienced by women with HIV, researchers and clinicians must focus on the relative contributions of sociocultural, home, and physiologic environments within which these women live. Additional research is ongoing to identify the strategies these women use to manage daily activities such that gender-relevant and culturally relevant interventions for alleviating fatigue can be tested in women with a variety of chronic illnesses, including HIV and acquired immune deficiency syndrome.

Thermomechanical and bithermal fatigue behavior of cast B1900 + Hf and wrought Haynes 188

NASA Technical Reports Server (NTRS)

Halford, G. R.; Verrilli, M. J.; Kalluri, S.; Ritzert, F. J.; Duckert, R. E.; Holland, F. A.

1992-01-01

A thermomechanical fatigue (TMF) high-temperature life prediction method has been evaluated using the experimental data. Bithermal fatigue (BTF), bithermal creep-fatigue (BTC-F), and TMF experiments were performed using two aerospace structural alloys, cast B1900 + Hf and wrought Haynes 188. The method which is based on the total strain version of strain range partitioning and unified cyclic constitutive modeling requires, as an input, information on the flow and failure behavior of the material of interest. Bithermal temperatures of 483 and 871 C were used for the cast B1900 + Hf nickel-base alloy and 316 and 760 C for the wrought Haynes 188 cobalt-base alloy. Maximum and minimum temperatures were also used in both TMF and BTF tests. Comparisons were made between the results of these tests and isothermal tensile and fatigue test data obtained previously. Qualitative correlations were observed between tensile and isothermal fatigue tests.

The direct-stress fatigue strength of 17S-T aluminum alloy throughout the range from 1/2 to 500,000,000 cycles of stress

NASA Technical Reports Server (NTRS)

Hartmann, E C; Stickley, G W

1942-01-01

Fatigue-test were conducted on six specimens made from 3/4-inch-diameter 17S-T rolled-and-drawn rod for the purpose of obtaining additional data on the fatigue life of the material at stresses up to the static strength. The specimens were tested in direct tension using a stress range from zero to a maximum in tension. A static testing machine was used to apply repeated loads in the case of the first three specimens; the other three specimens were tested in a direct tension-compression fatigue machine. The direct-stress fatigue curve obtained for the material indicates that, in the range of stresses above about two-thirds the tensile strength, the fatigue strength is higher than might be expected by simply extrapolating the ordinary curve of stress plotted against the number of cycles determined at lower stresses.

Novel Electrochemical Test Bench for Evaluating the Functional Fatigue Life of Biomedical Alloys

NASA Astrophysics Data System (ADS)

Ijaz, M. F.; Dubinskiy, S.; Zhukova, Y.; Korobkova, A.; Pustov, Y.; Brailovski, V.; Prokoshkin, S.

2017-08-01

The aim of the present work was first to develop and validate a test bench that simulates the in vitro conditions to which the biomedical implants will be actually subjected in vivo. For the preliminary application assessments, the strain-controlled fatigue tests of biomedically pure Ti and Ti-Nb-Zr alloy in simulated body fluid were undertaken. The in situ open-circuit potential measurements from the test bench demonstrated a strong dependence on the dynamic cycling and kind of material under testing. The results showed that during fatigue cycling, the passive oxide film formed on the surface of Ti-Nb-Zr alloy was more resistant to fatigue degradation when compared with pure Ti. The Ti-Nb-Zr alloy exhibited prolonged fatigue life when compared with pure Ti. The fractographic features of both materials were also characterized using scanning electron microscopy. The electrochemical results and the fractographic evidence confirmed that the prolonged functional fatigue life of the Ti-Nb-Zr alloy is apparently ascribable to the reversible martensitic phase transformation.

Initial Mechanical Testing of Superalloy Lattice Block Structures Conducted

NASA Technical Reports Server (NTRS)

Krause, David L.; Whittenberger, J. Daniel

2002-01-01

The first mechanical tests of superalloy lattice block structures produced promising results for this exciting new lightweight material system. The testing was performed in-house at NASA Glenn Research Center's Structural Benchmark Test Facility, where small subelement-sized compression and beam specimens were loaded to observe elastic and plastic behavior, component strength levels, and fatigue resistance for hundreds of thousands of load cycles. Current lattice block construction produces a flat panel composed of thin ligaments arranged in a three-dimensional triangulated trusslike structure. Investment casting of lattice block panels has been developed and greatly expands opportunities for using this unique architecture in today's high-performance structures. In addition, advances made in NASA's Ultra-Efficient Engine Technology Program have extended the lattice block concept to superalloy materials. After a series of casting iterations, the nickel-based superalloy Inconel 718 (IN 718, Inco Alloys International, Inc., Huntington, WV) was successfully cast into lattice block panels; this combination offers light weight combined with high strength, high stiffness, and elevated-temperature durability. For tests to evaluate casting quality and configuration merit, small structural compression and bend test specimens were machined from the 5- by 12- by 0.5-in. panels. Linear elastic finite element analyses were completed for several specimen layouts to predict material stresses and deflections under proposed test conditions. The structural specimens were then subjected to room-temperature static and cyclic loads in Glenn's Life Prediction Branch's material test machine. Surprisingly, the test results exceeded analytical predictions: plastic strains greater than 5 percent were obtained, and fatigue lives did not depreciate relative to the base material. These assets were due to the formation of plastic hinges and the redundancies inherent in lattice block construction, which were not considered in the simplified computer models. The fatigue testing proved the value of redundancies since specimen strength was maintained even after the fracture of one or two ligaments. This ongoing test program is planned to continue through high-temperature testing. Also scheduled for testing are IN 718 lattice block panels with integral face sheets, as well as specimens cast from a higher temperature alloy. The initial testing suggests the value of this technology for large panels under low and moderate pressure loadings and for high-risk, damage-tolerant structures. Potential aeropropulsion uses for lattice blocks include turbine-engine actuated panels, exhaust nozzle flaps, and side panel structures.

Taltirelin alleviates fatigue-like behavior in mouse models of cancer-related fatigue.

PubMed

Dougherty, John P; Wolff, Brian S; Cullen, Mary J; Saligan, Leorey N; Gershengorn, Marvin C

2017-10-01

Fatigue affects most cancer patients and has numerous potential causes, including cancer itself and cancer treatment. Cancer-related fatigue (CRF) is not relieved by rest, can decrease quality of life, and has no FDA-approved therapy. Thyrotropin-releasing hormone (TRH) has been proposed as a potential novel treatment for CRF, but its efficacy against CRF remains largely untested. Thus, we tested the TRH analog, taltirelin (TAL), in mouse models of CRF. To model fatigue, we used a mouse model of chemotherapy, a mouse model of radiation therapy, and mice bearing colon 26 carcinoma tumors. We used the treadmill fatigue test to assess fatigue-like behavior after treatment with TAL. Additionally, we used wild-type and TRH receptor knockout mice to determine which TRH receptor was necessary for the actions of TAL. Tumor-bearing mice displayed muscle wasting and all models caused fatigue-like behavior, with mice running a shorter distance in the treadmill fatigue test than controls. TAL reversed fatigue-like behavior in all three models and the mouse TRH 1 receptor was necessary for the effects of TAL. These data suggest that TAL may be useful in alleviating fatigue in all cancer patients and provide further support for evaluating TAL as a potential therapy for CRF in humans. Published by Elsevier Ltd.

The effect of matrix mechanical properties on (0)8 unidirectional SiC/Ti composite fatigue resistance

NASA Technical Reports Server (NTRS)

Gabb, T. P.; Gayda, J.; Lerch, B. A.; Halford, G. R.

1991-01-01

The relationship between constituent and MMC properties in fatigue loading is investigated with low-cycle fatigue-resistance testing of an alloy Ti-15-3 matrix reinforced with SiC SCS-6 fibers. The fabrication of the composite is described, and specimens are generated that are weak and ductile (WD), strong and moderately ductile (SM), or strong and brittle (SB). Strain is measured during MMC fatigue tests at a constant load amplitude with a load-controlled waveform and during matrix-alloy fatigue tests at a constant strain amplitude using a strain-controlled waveform. The fatigue resistance of the (0)8 SiC/Ti-15-3 composite is found to be slightly influenced by matrix mechanical properties, and the composite- and matrix-alloy fatigue lives are not correlated. This finding is suggested to relate to the different crack-initiation and -growth processes in MMCs and matrix alloys.

Room Temperature and Elevated Temperature Composite Sandwich Joint Testing

NASA Technical Reports Server (NTRS)

Walker, Sandra P.

1998-01-01

Testing of composite sandwich joint elements has been completed to verify the strength capacity of joints designed to carry specified running loads representative of a high speed civil transport wing. Static tension testing at both room and an elevated temperature of 350 F and fatigue testing at room temperature were conducted to determine strength capacity, fatigue life, and failure modes. Static tension test results yielded failure loads above the design loads for the room temperature tests, confirming the ability of the joint concepts tested to carry their design loads. However, strength reductions as large as 30% were observed at the elevated test temperature, where all failure loads were below the room temperature design loads for the specific joint designs tested. Fatigue testing resulted in lower than predicted fatigue lives.

Fatigue acceptance test limit criterion for larger diameter rolled thread fasteners

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kephart, A.R.

1997-05-01

This document describes a fatigue lifetime acceptance test criterion by which studs having rolled threads, larger than 1.0 inches in diameter, can be assured to meet minimum quality attributes associated with a controlled rolling process. This criterion is derived from a stress dependent, room temperature air fatigue database for test studs having a 0.625 inch diameter threads of Alloys X-750 HTH and direct aged 625. Anticipated fatigue lives of larger threads are based on thread root elastic stress concentration factors which increase with increasing thread diameters. Over the thread size range of interest, a 30% increase in notch stress ismore » equivalent to a factor of five (5X) reduction in fatigue life. The resulting diameter dependent fatigue acceptance criterion is normalized to the aerospace rolled thread acceptance standards for a 1.0 inch diameter, 0.125 inch pitch, Unified National thread with a controlled Root radius (UNR). Testing was conducted at a stress of 50% of the minimum specified material ultimate strength, 80 Ksi, and at a stress ratio (R) of 0.10. Limited test data for fastener diameters of 1.00 to 2.25 inches are compared to the acceptance criterion. Sensitivity of fatigue life of threads to test nut geometry variables was also shown to be dependent on notch stress conditions. Bearing surface concavity of the compression nuts and thread flank contact mismatch conditions can significantly affect the fastener fatigue life. Without improved controls these conditions could potentially provide misleading acceptance data. Alternate test nut geometry features are described and implemented in the rolled thread stud specification, MIL-DTL-24789(SH), to mitigate the potential effects on fatigue acceptance data.« less

Fatigue test results of the rotating steel blades of steam turbine K-25-0.6 GEO with ion-plasma coating

NASA Astrophysics Data System (ADS)

Kachalin, G. V.; Mednikov, A. F.; Tkhabisimov, A. B.; Arkad'ev, D. A.; Temkin, S. G.; Senina, N. A.

2016-12-01

Fatigue test results of the rotating steel blades of the fourth stage of the K-25-0.6 low pressure cylinder Geo steam turbine manufactured in the Kaluga Turbine Plant (hereinafter, KTP) with the ion-plasma coating were presented. Coating formation was carried out at the National Research University (MPEI) on the Gefest vacuum pilot plant by the magnetron sputtering method. Characteristics of the obtained coating were analyzed with the use of the scientific-research equipment of the National Research University (MPEI). Fatigue tests of the rotating blades and determination of the fatigue strength of the material with the ion-plasma coating were carried out on the electrodynamic vibration machines VEDS-400A in the KTP structural laboratory. The following characteristics were obtained after tests: Ti-TiN composition, 10-11 μm thickness, 1200 HV 0.05 microhardness. Fatigue tests showed that destruction, regardless of availability or nonavailability of the coating, took place by cross-section in the root zone both on the leading and trailing edges of the blade, i.e., in the most stressed zones. It was found out that the maximum stresses during tests were revealed in the root section along the trailing edge on the blade pressure side, and the less stresses were on the leading edge. Fatigue strength of the working blades after coating formation increased by 12% minimum. Results of the fatigue tests prove the previously obtained data concerning 10-12% increase of the fatigue strength of the blade steel with the ion-plasma coating and allow claiming that the process of their formation exerts the positive influence on the fatigue characteristics of the blade materials.

Study on Determination Method of Fatigue Testing Load for Wind Turbine Blade

NASA Astrophysics Data System (ADS)

Liao, Gaohua; Wu, Jianzhong

2017-07-01

In this paper, the load calculation method of the fatigue test was studied for the wind turbine blade under uniaxial loading. The characteristics of wind load and blade equivalent load were analyzed. The fatigue property and damage theory of blade material were studied. The fatigue load for 2MW blade was calculated by Bladed, and the stress calculated by ANSYS. Goodman modified exponential function S-N curve and linear cumulative damage rule were used to calculate the fatigue load of wind turbine blades. It lays the foundation for the design and experiment of wind turbine blade fatigue loading system.

A unified technology plan for fatigue and fracture design

NASA Technical Reports Server (NTRS)

Hardrath, H. F.

1973-01-01

An integrated research program is proposed that seeks to improve the technology of designing against fatigue and fracture and to develop a computerized capability for assessing the adequacy of a given design. Both fatigue life prediction and damage tolerance considerations are incorporated. The research for each of these considerations is organized to account for material behavior, the effect of structural configurations, the cumulative effects of the operating loadings, and for the effects of environment - temperature and corrosion. The goal is to achieve a viable fatigue and fracture design procedure for any practical problem. The overall program is outlined, assessments are made of the state of the art, subgoals are proposed, and means for achieving them are suggested.

High Speed Research Program Structural Acoustics Multi-Year Summary Report

NASA Technical Reports Server (NTRS)

Beier, Theodor H.; Bhat, Waman V.; Rizzi, Stephen A.; Silcox, Richard J.; Simpson, Myles A.

2005-01-01

This report summarizes the work conducted by the Structural Acoustics Integrated Technology Development (ITD) Team under NASA's High Speed Research (HSR) Phase II program from 1993 to 1999. It is intended to serve as a reference for future researchers by documenting the results of the interior noise and sonic fatigue technology development activities conducted during this period. For interior noise, these activities included excitation modeling, structural acoustic response modeling, development of passive treatments and active controls, and prediction of interior noise. For sonic fatigue, these activities included loads prediction, materials characterization, sonic fatigue code development, development of response reduction techniques, and generation of sonic fatigue design requirements. Also included are lessons learned and recommendations for future work.

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

NASA Astrophysics Data System (ADS)

Tahir, Fraaz

The Very High Temperature Reactor (VHTR) is one of six conceptual designs proposed for Generation IV nuclear reactors. Alloy 617, a solid solution strengthened Ni-base superalloy, is currently the primary candidate material for the tubing of the Intermediate Heat Exchanger (IHX) in the VHTR design. Steady-state operation of the nuclear power plant at elevated temperatures leads to creep deformation, whereas loading transients including startup and shutdown generate fatigue. A detailed understanding of the creep-fatigue interaction in Alloy 617 is necessary before it can be considered as a material for nuclear construction in ASME Boiler and Pressure Vessel Code. Current design codes for components undergoing creep-fatigue interaction at elevated temperatures require creep-fatigue testing data covering the entire range from fatigue-dominant to creep-dominant loading. Classical strain-controlled tests, which produce stress relaxation during the hold period, show a saturation in cycle life with increasing hold periods due to the rapid stress-relaxation of Alloy 617 at high temperatures. Therefore, applying longer hold time in these tests cannot generate creep-dominated failure. In this study, uniaxial isothermal creep-fatigue tests with non-traditional loading waveforms were designed and performed at 850 and 950°C, with an objective of generating test data in the creep-dominant regime. The new loading waveforms are hybrid strain-controlled and force-controlled testing which avoid stress relaxation during the creep hold. The experimental data showed varying proportions of creep and fatigue damage, and provided evidence for the inadequacy of the widely-used time fraction rule for estimating creep damage under creep-fatigue conditions. Micro-scale damage features in failed test specimens, such as fatigue cracks and creep voids, were quantified using a Scanning Electron Microscope (SEM) to find a correlation between creep and fatigue damage. Quantitative statistical imaging analysis showed that the microstructural damage features (cracks and voids) are correlated with a new mechanical driving force parameter. The results from this image-based damage analysis were used to develop a phenomenological life-prediction methodology called the effective time fraction approach. Finally, the constitutive creep-fatigue response of the material at 950°C was modeled using a unified viscoplastic model coupled with a damage accumulation model. The simulation results were used to validate an energy-based constitutive life-prediction model, as a mechanistic model for potential component and structure level creep-fatigue analysis.

Multiaxial Fatigue Life Prediction Based on Nonlinear Continuum Damage Mechanics and Critical Plane Method

NASA Astrophysics Data System (ADS)

Wu, Z. R.; Li, X.; Fang, L.; Song, Y. D.

2018-04-01

A new multiaxial fatigue life prediction model has been proposed in this paper. The concepts of nonlinear continuum damage mechanics and critical plane criteria were incorporated in the proposed model. The shear strain-based damage control parameter was chosen to account for multiaxial fatigue damage under constant amplitude loading. Fatigue tests were conducted on nickel-based superalloy GH4169 tubular specimens at the temperature of 400 °C under proportional and nonproportional loading. The proposed method was checked against the multiaxial fatigue test data of GH4169. Most of prediction results are within a factor of two scatter band of the test results.

Methods for structural design at elevated temperatures

NASA Technical Reports Server (NTRS)

Ellison, A. M.; Jones, W. E., Jr.; Leimbach, K. R.

1973-01-01

A procedure which can be used to design elevated temperature structures is discussed. The desired goal is to have the same confidence in the structural integrity at elevated temperature as the factor of safety gives on mechanical loads at room temperature. Methods of design and analysis for creep, creep rupture, and creep buckling are presented. Example problems are included to illustrate the analytical methods. Creep data for some common structural materials are presented. Appendix B is description, user's manual, and listing for the creep analysis program. The program predicts time to a given creep or to creep rupture for a material subjected to a specified stress-temperature-time spectrum. Fatigue at elevated temperature is discussed. Methods of analysis for high stress-low cycle fatigue, fatigue below the creep range, and fatigue in the creep range are included. The interaction of thermal fatigue and mechanical loads is considered, and a detailed approach to fatigue analysis is given for structures operating below the creep range.

Study of fatigue behavior of longitudinal welded pipes

NASA Astrophysics Data System (ADS)

Simion, P.; Dia, V.; Istrate, B.; Hrituleac, G.; Hrituleac, I.; Munteanu, C.

2016-08-01

During transport and storage of the various fluids, welded pipes are subjected to cyclic loading due to pressure fluctuations that often exceed the prescribed values for normal operation. These cyclic loading can significantly reduce the life of the pipes; as a result the design should be based on the fatigue strength not only on static resistance. In general the fatigue strength of pipes is dependent by strength, pipe geometry and surface quality. In case of the electric longitudinal welded pipes, the fatigue strength is significantly limited by concentration of residual stress and the size of existing defects in the weld seam. This paper presents the fatigue behaviour of the electric welded pipes by high frequency, under conditions that simulate real operating conditions pipes. Fatigue testing was performed on welded pipes made of micro alloyed carbon steels. Some of these pipes were previously subjected to a heat treatment of normalization, in order to also determine the influence of heat treatment on the fatigue strength of welded pipes. To determine and correlate the different factors affecting the fatigue strength, welded pipes were also subjected to various tests: tensile tests, impact tests, measurement of micro hardness, microstructural analysis by optical microscopy and scanning electron microscopy.

Indentation hardness: A simple test that correlates with the dissipated-energy predictor for fatigue-life in bovine pericardium membranes for bioprosthetic heart valves.

PubMed

Tobaruela, Almudena; Rojo, Francisco Javier; García Paez, José María; Bourges, Jean Yves; Herrero, Eduardo Jorge; Millán, Isabel; Alvarez, Lourdes; Cordon, Ángeles; Guinea, Gustavo V

2016-08-01

The aim of this study was to evaluate the variation of hardness with fatigue in calf pericardium, a biomaterial commonly used in bioprosthetic heart valves, and its relationship with the energy dissipated during the first fatigue cycle that has been shown to be a predictor of fatigue-life (García Páez et al., 2006, 2007; Rojo et al., 2010). Fatigue tests were performed in vitro on 24 pericardium specimens cut in a root-to-apex direction. The specimens were subjected to a maximum stress of 1MPa in blocks of 10, 25, 50, 100, 250, 500, 1000 and 1500 cycles. By means of a modified Shore A hardness test procedure, the hardness of the specimen was measured before and after fatigue tests. Results showed a significant correlation of such hardness with fatigue performance and with the energy dissipated in the first cycle of fatigue, a predictor of pericardium durability. The study showed indentation hardness as a simple and reliable indicator of mechanical performance, one which could be easily implemented in improving tissue selection. Copyright © 2016 Elsevier Ltd. All rights reserved.

Analysis of the Mechanical Behavior, Creep Resistance and Uniaxial Fatigue Strength of Martensitic Steel X46Cr13

PubMed Central

Brnic, Josip; Krscanski, Sanjin; Lanc, Domagoj; Brcic, Marino; Turkalj, Goran; Canadija, Marko; Niu, Jitai

2017-01-01

The article deals with the analysis of the mechanical behavior at different temperatures, uniaxial creep and uniaxial fatigue of martensitic steel X46Cr13 (1.4034, AISI 420). For the purpose of considering the aforementioned mechanical behavior, as well as determining the appropriate resistance to creep and fatigue strength levels, numerous uniaxial tests were carried out. Tests related to mechanical properties performed at different temperatures are presented in the form of engineering stress-strain diagrams. Short-time creep tests performed at different temperatures and different stress levels are presented in the form of creep curves. Fatigue tests carried out at stress ratios R=0.25 and R=−1 are shown in the form of S–N (fatigue) diagrams. The finite fatigue regime for each of the mentioned stress ratios is modeled by an inclined log line, while the infinite fatigue regime is modeled by a horizontal line, which represents the fatigue limit of the material and previously was calculated by the modified staircase method. Finally, the fracture toughness has been calculated based on the Charpy V-notch impact energy. PMID:28772749

Developing measures of fatigue using an alcohol comparison to validate the effects of fatigue on performance.

PubMed

Williamson, A M; Feyer, A M; Mattick, R P; Friswell, R; Finlay-Brown, S

2001-05-01

The effects of 28 h of sleep deprivation were compared with varying doses of alcohol up to 0.1% blood alcohol concentration (BAC) in the same subjects. The study was conducted in the laboratory. Twenty long-haul truck drivers and 19 people not employed as professional drivers acted as subjects. Tests were selected that were likely to be affected by fatigue, including simple reaction time, unstable tracking, dual task, Mackworth clock vigilance test, symbol digit coding, visual search, sequential spatial memory and logical reasoning. While performance effects were seen due to alcohol for all tests, sleep deprivation affected performance on most tests, but had no effect on performance on the visual search and logical reasoning tests. Some tests showed evidence of a circadian rhythm effect on performance, in particular, simple reaction time, dual task, Mackworth clock vigilance, and symbol digit coding, but only for response speed and not response accuracy. Drivers were slower but more accurate than controls on the symbol digit test, suggesting that they took a more conservative approach to performance of this test. This study demonstrated which tests are most sensitive to sleep deprivation and fatigue. The study therefore has established a set of tests that can be used in evaluations of fatigue and fatigue countermeasures.

Evaluating cyclic fatigue of sealants during outdoor testing

Treesearch

R. Sam Williams; Steven Lacher; Corey Halpin; Christopher White

2009-01-01

A computer-controlled test apparatus (CCTA) and other instrumentation for subjecting sealant specimens to cyclic fatigue during outdoor exposure was developed. The CCTA enables us to use weather-induced conditions to cyclic fatigue specimens and to conduct controlled tests in-situ during the outdoor exposure. Thermally induced dimensional changes of an aluminum bar...

A Full-Scale Fatigue Test of 9-m CX-100 Wind Turbine Blades

DTIC Science & Technology

2011-09-01

A Full-Scale Fatigue Test of 9-m CX-100 Wind Turbine Blades G. PARK, K. M. FARINHOLT, S. G. TAYLOR and C. R. FARRAR ABSTRACT This paper...presents the SHM result of a 9m CX-100 wind turbine blade under full- scale fatigue loads. The test was performed at the National Renewable Energy...surface of the blade. The blade underwent fatigue excitation at 1.8 Hz for defined intervals, and data from the sensors were collected between and

Method of Fatigue-Life Prediction for an Asphalt Mixture Based on the Plateau Value of Permanent Deformation Ratio.

PubMed

Sun, Yazhen; Fang, Chenze; Wang, Jinchang; Yuan, Xuezhong; Fan, Dong

2018-05-03

Laboratory predictions for the fatigue life of an asphalt mixture under cyclic loading based on the plateau value (PV) of the permanent deformation ratio (PDR) were carried out by three-point bending fatigue tests. The influence of test conditions on the recovery ratio of elastic deformation (RRED), the permanent deformation (PD) and PDR, and the trends of RRED, PD, and PDR were studied. The damage variable was defined by using PDR, and the relation of the fatigue life to PDR was determined by analyzing the damage evolution process. The fatigue equation was established based on the PV of PDR and the fatigue life was predicted by analyzing the relation of the fatigue life to the PV. The results show that the RRED decreases with the increase of the number of loading cycles, and the elastic recovery ability of the asphalt mixture gradually decreases. The two mathematical models proposed are based on the change laws of the RRED, and the PD can well describe the change laws. The RRED or the PD cannot well predict the fatigue life because they do not change monotonously with the fatigue life, and one part of the deformation causes the damage and the other part causes the viscoelastic deformation. The fatigue life decreases with the increase of the PDR. The average PDR in the second stage is taken as the PV, and the fatigue life decreases in a power law with the increase of the PV. The average relative error of the fatigue life predicted by the fatigue equation to the test fatigue life is 5.77%. The fatigue equation based on PV can well predict the fatigue life.

Inspection of aging aircraft: A manufacturer's perspective

NASA Technical Reports Server (NTRS)

Hagemaier, Donald J.

1992-01-01

Douglas, in conjunction with operators and regulators, has established interrelated programs to identify and address issues regarding inspection of aging aircraft. These inspection programs consist of the following: Supplemental Inspection Documents; Corrosion Prevention and Control Documents; Repair Assessment Documents; and Service Bulletin Compliance Documents. In addition, airframe manufacturers perform extended airframe fatigue tests to deal with potential problems before they can develop in the fleet. Lastly, nondestructive inspection (NDI) plays a role in all these programs through the detection of cracks, corrosion, and disbonds. However, improved and more cost effective NDI methods are needed. Some methods such as magneto-optic imaging, electronic shearography, Diffractor-Sight, and multi-parameter eddy current testing appear viable for near-term improvements in NDI of aging aircraft.

Application of powder metallurgy techniques to produce improved bearing elements for liquid rocket engines

NASA Technical Reports Server (NTRS)

Moracz, D. J.; Shipley, R. J.; Moxson, V. S.; Killman, R. J.; Munson, H. E.

1992-01-01

The objective was to apply powder metallurgy techniques for the production of improved bearing elements, specifically balls and races, for advanced cryogenic turbopump bearings. The materials and fabrication techniques evaluated were judged on the basis of their ability to improve fatigue life, wear resistance, and corrosion resistance of Space Shuttle Main Engine (SSME) propellant bearings over the currently used 440C. An extensive list of candidate bearing alloys in five different categories was considered: tool/die steels, through hardened stainless steels, cobalt-base alloys, and gear steels. Testing of alloys for final consideration included hardness, rolling contact fatigue, cross cylinder wear, elevated temperature wear, room and cryogenic fracture toughness, stress corrosion cracking, and five-ball (rolling-sliding element) testing. Results of the program indicated two alloys that showed promise for improved bearing elements. These alloys were MRC-2001 and X-405. 57mm bearings were fabricated from the MRC-2001 alloy for further actual hardware rig testing by NASA-MSFC.

Bell Helicopter Advanced Rotocraft Transmission (ART) program

NASA Technical Reports Server (NTRS)

Henry, Zachary S.

1995-01-01

Future rotorcraft transmissions require key emerging material and component technologies using advanced and innovative design practices in order to meet the requirements for a reduced weight to power ratio, a decreased noise level, and a substantially increased reliability. The specific goals for the future rotorcraft transmission when compared with a current state-of-the-art transmission (SOAT) are: (1) a 25 percent weight reduction; (2) a 10 dB reduction in the transmitted noise level; and (3) a system reliability of 5000 hours mean-time-between-removal (MTBR) for the transmission. This report summarizes the work conducted by Bell Helicopter Textron, Inc. to achieve these goals under the Advanced Rotorcraft Transmission (ART) program from 1988 to 1995. The reference aircraft selected by BHTI for the ART program was the Tactical Tiltrotor which is a 17,000 lb gross weight aircraft. A tradeoff study was conducted comparing the ART with a Selected SOAT. The results showed the ART to be 29 percent lighter and up to 13 dB quieter with a calculated MTBR in excess of 5000 hours. The results of the following high risk component and material tests are also presented: (1) sequential meshing high contact ratio planetary with cantilevered support posts; (2) thin dense chrome plated M50 NiL double row spherical roller planetary bearings; (3) reduced kinematic error and increased bending strength spiral bevel gears; (4) high temperature WE43 magnesium housing evaluation and coupon corrosion tests; (5) flexure fatigue tests of precision forged coupons simulating precision forged gear teeth; and (6) flexure fatigue tests of plasma carburized coupons simulating plasma carburized gear teeth.

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

NASA Astrophysics Data System (ADS)

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

2016-08-01

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

Advanced Gear Alloys for Ultra High Strength Applications

NASA Technical Reports Server (NTRS)

Shen, Tony; Krantz, Timothy; Sebastian, Jason

2011-01-01

Single tooth bending fatigue (STBF) test data of UHS Ferrium C61 and C64 alloys are presented in comparison with historical test data of conventional gear steels (9310 and Pyrowear 53) with comparable statistical analysis methods. Pitting and scoring tests of C61 and C64 are works in progress. Boeing statistical analysis of STBF test data for the four gear steels (C61, C64, 9310 and Pyrowear 53) indicates that the UHS grades exhibit increases in fatigue strength in the low cycle fatigue (LCF) regime. In the high cycle fatigue (HCF) regime, the UHS steels exhibit better mean fatigue strength endurance limit behavior (particularly as compared to Pyrowear 53). However, due to considerable scatter in the UHS test data, the anticipated overall benefits of the UHS grades in bending fatigue have not been fully demonstrated. Based on all the test data and on Boeing s analysis, C61 has been selected by Boeing as the gear steel for the final ERDS demonstrator test gearboxes. In terms of potential follow-up work, detailed physics-based, micromechanical analysis and modeling of the fatigue data would allow for a better understanding of the causes of the experimental scatter, and of the transition from high-stress LCF (surface-dominated) to low-stress HCF (subsurface-dominated) fatigue failure. Additional STBF test data and failure analysis work, particularly in the HCF regime and around the endurance limit stress, could allow for better statistical confidence and could reduce the observed effects of experimental test scatter. Finally, the need for further optimization of the residual compressive stress profiles of the UHS steels (resulting from carburization and peening) is noted, particularly for the case of the higher hardness C64 material.

Fatigue testing of energy storing prosthetic feet.

PubMed

Toh, S L; Goh, J C; Tan, P H; Tay, T E

1993-12-01

This paper describes a simple approach to the fatigue testing of prosthetic feet. A fatigue testing machine for prosthetic feet was designed as part of the programme to develop an energy storing prosthetic foot (ESPF). The fatigue tester does not simulate the loading pattern on the foot during normal walking. However, cyclic vertical loads are applied to the heel and forefoot during heel-strike and toe-off respectively, for 500,000 cycles. The maximum load applied was chosen to be 1.5 times that applied by the bodyweight of the amputee and the test frequency was chosen to be 2 Hz to shorten the test duration. Four prosthetic feet were tested: two Lambda feet (a newly developed ESPF), a Kingsley SACH foot and a Proteor SACH foot. It was found that the Lambda feet have very good fatigue properties. The Kingsley SACH foot performed better than the Proteor model, with no signs of wear at the heel. The results obtained using the simple approach was found to be comparable to the results from more complex fatigue machines which simulate the load pattern during normal walking. This suggests that simple load simulating machines, which are less costly and require less maintenance, are useful substitutes in studying the fatigue properties of prosthetic feet.

A comparison of fatigue life prediction methodologies for rotorcraft

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.

1990-01-01

Because of the current U.S. Army requirement that all new rotorcraft be designed to a 'six nines' reliability on fatigue life, this study was undertaken to assess the accuracy of the current safe life philosophy using the nominal stress Palmgrem-Miner linear cumulative damage rule to predict the fatigue life of rotorcraft dynamic components. It has been shown that this methodology can predict fatigue lives that differ from test lives by more than two orders of magnitude. A further objective of this work was to compare the accuracy of this methodology to another safe life method called the local strain approach as well as to a method which predicts fatigue life based solely on crack growth data. Spectrum fatigue tests were run on notched (k(sub t) = 3.2) specimens made of 4340 steel using the Felix/28 tests fairly well, being slightly on the unconservative side of the test data. The crack growth method, which is based on 'small crack' crack growth data and a crack-closure model, also predicted the fatigue lives very well with the predicted lives being slightly longer that the mean test lives but within the experimental scatter band. The crack growth model was also able to predict the change in test lives produced by the rainflow reconstructed spectra.

The J-2X Fuel Turbopump - Turbine Nozzle Low Cycle Fatigue Acceptance Rationale

NASA Technical Reports Server (NTRS)

Hawkins, Lakiesha V.; Duke, Gregory C.; Newman, Wesley R.; Reynolds, David C.

2011-01-01

The J-2X Fuel Turbopump (FTP) turbine, which drives the pump that feeds hydrogen to the J-2X engine for main combustion, is based on the J-2S design developed in the early 1970 s. Updated materials and manufacturing processes have been incorporated to meet current requirements. This paper addresses an analytical concern that the J-2X Fuel Turbine Nozzle Low Cycle Fatigue (LCF) analysis did not meet safety factor requirements per program structural assessment criteria. High strains in the nozzle airfoil during engine transients were predicted to be caused by thermally induced stresses between the vane hub, vane shroud, and airfoil. The heritage J-2 nozzle was of a similar design and experienced cracks in the same area where analysis predicted cracks in the J-2X design. Redesign options that did not significantly impact the overall turbine configuration were unsuccessful. An approach using component tests and displacement controlled fracture mechanics analysis to evaluate LCF crack initiation and growth rate was developed. The results of this testing and analysis were used to define the level of inspection on development engine test units. The programmatic impact of developing crack initiation/growth rate/arrest data was significant for the J-2X program. Final Design Certification Review acceptance logic will ultimately be developed utilizing this test and analytical data.

Testing the Shuttle heat-protection armor

NASA Technical Reports Server (NTRS)

Strouhal, G.; Tillian, D. J.

1976-01-01

The article deals with the thermal protection system (TPS) designed to keep Space Shuttle structures at 350 F ratings over a wide range of temperatures encountered in orbit, but also during prelaunch, launch, deorbit and re-entry, landing and turnaround. The structure, function, fabrication, and bonding of various types of reusable surface insulation and composite materials are described. Test programs are developed for insulation, seals, and adhesion bonds; leak tests and acoustic fatigue tests are mentioned. Test facilities include arc jets, radiant heaters, furnaces, and heated tunnels. The certification tests to demonstrate TPS reusability, structural integrity, thermal performance, and endurance will include full-scale assembly tests and initial orbital flight tests.

Prediction of in-season shoulder injury from preseason testing in division I collegiate football players.

PubMed

Pontillo, Marisa; Spinelli, Bryan A; Sennett, Brian J

2014-11-01

Collegiate football is a high-demand sport in which shoulder injuries are common. Research has described the incidence of these injuries, with little focus on causative factors or injury prevention. Football athletes who score lower on preseason strength and functional testing are more likely to sustain an in-season shoulder injury. Prospective, cohort study. Level 2. Twenty-six collegiate football players underwent preseason testing with a rotational profile for shoulder range of motion, isometric strength of the rotator cuff at 90° elevation and external rotation in the 90/90 position, fatigue testing (prone-Y, scaption, and standing cable press), and the Closed Kinetic Chain Upper Extremity Stability Test (CKCUEST). Data collected postseason included the type of shoulder injury and the side injured. Logistic regression was used to determine if the testing measures predicted injury, and a receiver operating characteristic curve was constructed to examine the relationship of CKCUEST to injury. Six athletes sustained shoulder injuries during the season. Predictor variables could significantly predict whether that player would sustain an injury during the season for both the right and left shoulders (P < 0.05). The variables that were significantly correlated with injury of the right side were forward elevation strength, prone-Y to fatigue, and the CKCUEST (P < 0.05); on the left, only the CKCUEST was significant (P < 0.05). The area under the receiver operating characteristic curve for the CKCUEST was 0.86 (ϵ = 0.87, P = 0.01). Using a score of 21 touches, the CKCUEST had a sensitivity of 0.83, a specificity of 0.79, and an odds ratio of 18.75 in determining whether a player sustained a shoulder injury. For this sample, the combination of preseason strength, fatigue, and functional testing was able to identify football players who would sustain a shoulder injury during the season. Using a battery of strength, fatigue, and functional testing may be helpful in identifying football players during preseason who are at a higher risk for sustaining a shoulder injury. This information can be used to optimize preseason testing and implementation of injury prevention programs.

Cyclic Axial-Torsional Deformation Behavior of a Cobalt-Base Superalloy

NASA Technical Reports Server (NTRS)

Bonacuse, Peter J.; Kalluri, Sreeramesh

1995-01-01

The cyclic, high-temperature deformation behavior of a wrought cobalt-base super-alloy, Haynes 188, is investigated under combined axial and torsional loads. This is accomplished through the examination of hysteresis loops generated from a biaxial fatigue test program. A high-temperature axial, torsional, and combined axial-torsional fatigue database has been generated on Haynes 188 at 760 C. Cyclic loading tests have been conducted on uniform gage section tubular specimens in a servohydraulic axial-torsional test rig. Test control and data acquisition were accomplished with a minicomputer. The fatigue behavior of Haynes 188 at 760 C under axial, torsional, and combined axial-torsional loads and the monotonic and cyclic deformation behaviors under axial and torsional loads have been previously reported. In this paper, the cyclic hardening characteristics and typical hysteresis loops in the axial stress versus axial strain, shear stress ,versus engineering shear strain, axial strain versus engineering shear strain. and axial stress versus shear stress spaces are presented for cyclic in-phase and out-of-phase axial-torsional tests. For in-phase tests, three different values of the proportionality constant lambda (the ratio of engineering shear strain amplitude to axial strain amplitude, are examined, viz. 0.86, 1.73, and 3.46. In the out-of-phase tests, three different values of the phase angle, phi (between the axial and engineering shear strain waveforms), are studied, viz., 30, 60, and 90 degrees with lambda equals 1.73. The cyclic hardening behaviors of all the tests conducted on Haynes 188 at 760 C are evaluated using the von Mises equivalent stress-strain and the maximum shear stress-maximum engineering shear strain (Tresca) curves. Comparisons are also made between the hardening behaviors of cyclic axial, torsional, and combined in-phase (lambda = 1.73 and phi = 0) and out-of-phase (lambda = 1.73 and phi = 90') axial-torsional fatigue tests. These comparisons are accomplished through simple Ramberg-Osgood type stress-strain functions for cyclic, axial stress-strain and shear stress-engineering shear strain curves.

Strength Training to Enhance Early Recovery after Hematopoietic Stem Cell Transplantation.

PubMed

Hacker, Eileen Danaher; Collins, Eileen; Park, Chang; Peters, Tara; Patel, Pritesh; Rondelli, Damiano

2017-04-01

Intensive cancer treatment followed by hematopoietic stem cell transplantation (HCT) results in moderate to severe fatigue and physical inactivity, leading to diminished functional ability. The purpose of this study was to determine the efficacy of an exercise intervention, strength training to enhance early recovery (STEER), on physical activity, fatigue, muscle strength, functional ability, and quality of life after HCT. This single-blind, randomized clinical trial compared strength training (n = 33) to usual care plus attention control with health education (UC + AC with HE) (n = 34). Subjects were stratified by type of transplantation and age. STEER consisted of a comprehensive program of progressive resistance introduced during hospitalization and continued for 6 weeks after hospital discharge. Fatigue, physical activity, muscle strength, functional ability, and quality of life were assessed before HCT hospital admission and after intervention completion. Data were analyzed using split-plot analysis of variance. Significant time × group interactions effects were noted for fatigue (P = .04). The STEER group reported improvement in fatigue from baseline to after intervention whereas the UC + AC with HE group reported worsened fatigue from baseline to after intervention. Time (P < .001) and group effects (P = .05) were observed for physical activity. Physical activity declined from baseline to 6 weeks after hospitalization. The STEER group was more physically active. Functional ability tests (timed stair climb and timed up and go) resulted in a significant interaction effect (P = .03 and P = .05, respectively). Subjects in the UC + AC with HE group were significantly slower on both tests baseline to after intervention, whereas the STEER group's time remained stable. The STEER group completed both tests faster than the UC + AC with HE group after intervention. Study findings support the use of STEER after intensive cancer treatment and HCT. Strength training demonstrated positive effects on fatigue, physical activity, muscle strength, and functional ability. The exact recovery patterns between groups and over time varied; the STEER group either improved or maintained their status from baseline to after intervention (6 weeks after hospital discharge) whereas the health education group generally declined over time or did not change. Copyright © 2017 The American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.

Alertness Management In Flight Operations: A NASA Education and Training Module

NASA Technical Reports Server (NTRS)

Rosekind, Mark R.; Lebacqz, Victor J.; Gander, Philippa H.; Co, Elizabeth L.; Weldon, Keri J.; Smith, Roy M.; Miller, Donna L.; Gregory, Kevin B.; Statler, Irving C. (Technical Monitor)

1994-01-01

Since 1980, the NASA Ames Fatigue Countermeasures Program has been conducting research on sleep, circadian rhythms, and fatigue in a variety of flight operations 1. An original goal of the program was to return the scientific and operational knowledge to the aviation industry. To meet this goal, the NASA Ames Fatigue Countermeasures Program has created an Education and Training Module entitled, "Strategies for Alertness Management in Flight Operations." The Module was designed to meet three objectives: 1) explain the current state of knowledge about the physiological mechanisms underlying fatigue, 2) demonstrate how this knowledge can be applied to improve flight crew sleep, performance, and alertness, and 3) offer countermeasure recommendations. The Module is composed of two components: 1) a 60-minute live presentation provided by a knowledgeable individual and 2) a NASA/FAA Technical Memorandum (TM) that contains the presentation materials and appendices with complementary information. The TM is provided to all individuals attending the live presentation. The Module content is divided into three parts: 1) basic information on sleep, sleepiness, circadian rhythms, fatigue, and how flight operations affect these physiological factors, 2) common misconceptions about sleep, sleepiness, and fatigue, and 3) alertness management strategies. The Module is intended for pilots, management personnel, schedulers, flight attendants, and the many other individuals involved in the aviation system.

Ultrasonic fatigue of SiC particle reinforced aluminum in the VHCF-regime

NASA Astrophysics Data System (ADS)

Wolf, M.; Wagner, G.; Eifler, D.

At the WKK ultrasonic testing facilities (UTF) are used to perform fatigue experiments in the VHCF regime with a frequency of 20 kHz. These systems allow an on-line characterization of the actual fatigue state by changes of different process parameters such as generator power, displacement, temperature or frequency-response characteristic. Moreover the experiments can be interrupted at user defined events in order to investigate variations of the surface microstructure or changes in the electrical resistance of the specimens. The fatigue tests were realized as load increase tests as well as constant amplitude tests.

Crack propagation analysis and fatigue life prediction for structural alloy steel based on metal magnetic memory testing

NASA Astrophysics Data System (ADS)

Ni, Chen; Hua, Lin; Wang, Xiaokai

2018-09-01

To monitor the crack propagation and predict the fatigue life of ferromagnetic material, the metal magnetic memory (MMM) testing was carried out to the single edge notched specimen made from structural alloy steel under three-point bending fatigue experiment in this paper. The variation of magnetic memory signal Hp (y) in process of fatigue crack propagation was investigated. The gradient K of Hp (y) was investigated and compared with the stress of specimen obtained by finite element analysis. It indicated that the gradient K can qualitatively reflect the distribution and variation of stress. The maximum gradient Kmax and crack size showed a good linear relationship, which indicated that the crack propagation can be estimated by MMM testing. Furthermore, the damage model represented by magnetic memory characteristic was created and a fatigue life prediction method was developed. The fatigue life can be evaluated by the relationship between damage parameter and normalized life. The method was also verified by another specimen. Because of MMM testing, it provided a new approach for predicting fatigue life.

Preliminary Study on Fatigue Strengths of Fretted Ti-48Al-2Cr-2Nb

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Lerch, Bradley A.; Draper, Susan L.

2002-01-01

The fatigue behavior (stress-life curve) of gamma titanium aluminide (Ti-48Al-2Cr-2Nb, atomic percent) was examined by conducting two tests: first, a fretting wear test with a fatigue specimen in contact with a typical nickel-based superalloy contact pad in air at temperatures of 296 and 823 K and second, a high-cycle fatigue test of the prefretted Ti-48Al-2Cr-2Nb fatigue specimen at 923 K. Reference high-cycle fatigue tests were also conducted with unfretted Ti-48Al-2Cr-2Nb specimens at 923 K. All Ti-48Al-2Cr-2Nb fatigue specimens were machined from cast slabs. The results indicate that the stress-life results for the fretted Ti-48Al-2Cr-2Nb specimens exhibited a behavior similar to those of the unfretted Ti-48Al-2Cr-2Nb specimens. The values of maximum stress and life for the fretted specimens were almost the same as those for the unfretted specimens. The resultant stress-life curve for the unfretted fatigue specimens was very flat. The flat appearance in the stress-life curve of the unfretted specimens is attributed to the presence of a high density of casting pores. The fatigue strengths of both the fretted and unfretted specimens can be significantly affected by the presence of this porosity, which can decrease the fatigue life of Ti-48Al-2Cr-2Nb. The presence of the porosity made discerning the effect of fretting damage on fatigue strength and life of the specimens difficult.

Analysis of the binder yield energy test as an indicator of fatigue behaviour of asphalt mixes

NASA Astrophysics Data System (ADS)

O'Connell, Johan; Mturi, Georges A. J.; Komba, Julius; Du Plessis, Louw

2017-09-01

Empirical binder testing has increasingly failed to predict pavement performance in South Africa, with fatigue cracking being one of the major forms of premature pavement distress. In response, it has become a national aspiration to incorporate a performance related fatigue test into the binder specifications for South Africa. The Binder Yield Energy Test (BYET) was the first in a series of tests analysed for its potential to predict the fatigue performance of the binder. The test is performed with the dynamic shear rheometer, giving two key parameters, namely, yield energy and shear strain at maximum shear stress (γτmax). The objective of the investigation was to perform a rudimentary evaluation of the BYET; followed by a more in-depth investigation should the initial BYET results prove promising. The paper discusses the results generated from the BYET under eight different conditions, using six different binders. The results are then correlated with four point bending beam fatigue test results obtained from asphalt mix samples that were manufactured from the same binders. Final results indicate that the BYET is not ideal as an indicator of fatigue performance.

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.

Removal Torque and Biofilm Accumulation at Two Dental Implant-Abutment Joints After Fatigue.

PubMed

Pereira, Jorge; Morsch, Carolina S; Henriques, Bruno; Nascimento, Rubens M; Benfatti, Cesar Am; Silva, Filipe S; López-López, José; Souza, Júlio Cm

2016-01-01

The aim of this study was to evaluate the removal torque and in vitro biofilm penetration at Morse taper and hexagonal implant-abutment joints after fatigue tests. Sixty dental implants were divided into two groups: (1) Morse taper and (2) external hexagon implant-abutment systems. Fatigue tests on the implant-abutment assemblies were performed at a normal force (FN) of 50 N at 1.2 Hz for 500,000 cycles in growth medium containing human saliva for 72 hours. Removal torque mean values (n = 10) were measured after fatigue tests. Abutments were then immersed in 1% protease solution in order to detach the biofilms for optical density and colony-forming unit (CFU/cm²) analyses. Groups of implant-abutment assemblies (n = 8) were cross-sectioned at 90 degrees relative to the plane of the implant-abutment joints for the microgap measurement by field-emission guns scanning electron microscopy. Mean values of removal torque on abutments were significantly lower for both Morse taper (22.1 ± 0.5 μm) and external hexagon (21.1 ± 0.7 μm) abutments after fatigue tests than those recorded without fatigue tests (respectively, 24 ± 0.5 μm and 24.8 ± 0.6 μm) in biofilm medium for 72 hours (P = .04). Mean values of microgap size for the Morse taper joints were statistically signicantly lower without fatigue tests (1.7 ± 0.4 μm) than those recorded after fatigue tests (3.2 ± 0.8 μm). Also, mean values of microgap size for external hexagon joints free of fatigue were statistically signicantly lower (1.5 ± 0.4 μm) than those recorded after fatigue tests (8.1 ± 1.7 μm) (P < .05). The optical density of biofilms and CFU mean values were lower on Morse taper abutments (Abs630nm at 0.06 and 2.9 × 10⁴ CFU/cm²) than that on external hexagon abutments (Abs630nm at 0.08 and 4.5 × 10⁴ CFU/cm²) (P = .01). The mean values of removal torque, microgap size, and biofilm density recorded at Morse taper joints were lower in comparison to those recorded at external hexagon implant-abutment joints after fatigue tests in a simulated oral environment for 72 hours.

Low cycle fatigue behavior of polycrystalline NiAl at 300 and 1000 K

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.; Noebe, Ronald D.

1993-01-01

The low cycle fatigue behavior of polycrystalline NiAl was determined at 300 and 1000 K - temperatures below and above the brittle- to-ductile transition temperature (BDTT). Fully reversed, plastic strain-controlled fatigue tests were conducted on two differently fabricated alloy samples: hot isostatically pressed (HIP'ed) prealloyed powder and hot extruded castings. HIP'ed powder (HP) samples were tested only at 1000 K, whereas the more ductile cast-and-extruded (C+E) NiAl samples were tested at both 1000 and 300 K. Plastic strain ranges of 0.06 to 0.2 percent were used. The C+E NiAl cyclically hardened until fracture, reaching stress levels approximately 60 percent greater than the ultimate tensile strength of the alloy. Compared on a strain basis, NiAl had a much longer fatigue life than other B2 ordered compounds in which fracture initiated at processing-related defects. These defects controlled fatigue life at 300 K, with fracture occurring rapidly once a critical stress level was reached. At 1000 K, above the BDTT, both the C+E and HP samples cyclically softened during most of the fatigue tests in air and were insensitive to processing defects. The processing method did not have a major effect on fatigue life; the lives of the HP samples were about a factor of three shorter than the C+E NiAl, but this was attributed to the lower stress response of the C+E material. The C+E NiAl underwent dynamic grain growth, whereas the HP material maintained a constant grain size during testing. In both materials, fatigue life was controlled by intergranular cavitation and creep processes, which led to fatigue crack growth that was primarily intergranular in nature. Final fracture by overload was transgranular in nature. Also, HP samples tested in vacuum had a life three times longer than their counterparts tested in air and, in contrast to those tested in air, hardened continuously over half of the sample life, thereby indicating an environmentally assisted fatigue damage mechanism. The C+E samples were tested only in air. At 1000 K, NiAl exhibited a superior fatigue life when compared to most superalloys on a plastic strain basis, but was inferior to most superalloys on a stress basis.

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

Treesearch

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

2015-01-01

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

Resistance training program for fatigue management in the workplace: exercise protocol in a cluster randomized controlled trial.

PubMed

Santos, Hélio Gustavo; Chiavegato, Luciana Dias; Valentim, Daniela Pereira; da Silva, Patricia Rodrigues; Padula, Rosimeire Simprini

2016-12-22

Fatigue is a multifactorial condition that leads to disease and loss in production, and it affects a large number of workers worldwide. This study aims to demonstrate a resistance exercise protocol that individuals will perform during the work schedule, and to evaluate the effectiveness of this exercises program for fatigue control. This is a cluster randomized controlled trial with two arms and is assessor blinded. A total of 352 workers of both sexes, aged 18-65 years, from a medium-sized dairy plant were enrolled in this study. Participants will be recruited from 13 production sectors according to the eligibility criteria and will be randomized by clusters to either the Progressive Resistance Exercise (PRE) intervention group or the Compensatory Workplace Exercise (CWE) comparative group. A resistance exercise program will be implemented for both groups. The groups will receive instructions on self-management, breaks, adjustments to workstations, and the benefits of physical exercise. The PRE group will perform resistance exercises with gradual loads in an exercise room, and the CWE group will perform exercise at their workstations using elastic bands. The exercise sessions will be held 3 times a week for 20 min. The primary outcome measures will be symptoms of physical and mental fatigue, and muscular fatigue based on a one-repetition maximum (1RM). The secondary outcome measures will be level of physical activity, musculoskeletal symptoms, physical condition, perceived exposure, and productivity. The workers will be assessed at baseline and after a 4-month program. A linear mixed model will be applied on an intention-to-treat basis. This intervention is expected to reduce symptoms of fatigue in the workers. The exercise program is indicating in the workplace, although there are few studies describing the effects of exercise on the control of fatigue in the workplace. Emphasis will be placed on adherence to the program, which may result in significant and clinically important reductions in fatigue. It is also expected that the findings of this study will contribute significantly to the decision-making capacity of professionals working in the field of occupational health. U.S. National Institutes of Health, ClinicalTrials.gov Identifier: NCT02172053 . Date registered 19 June 2014.

Fatigue in people with localized colorectal cancer who do and do not receive chemotherapy: a longitudinal prospective study

PubMed Central

Vardy, J. L.; Dhillon, H. M.; Pond, G. R.; Renton, C.; Dodd, A.; Zhang, H.; Clarke, S. J.; Tannock, I. F.

2016-01-01

Background Fatigue is associated with cancer and chemotherapy and may be sustained. Here, we describe a prospective longitudinal study evaluating fatigue and putative mechanisms in people with colorectal cancer (CRC). Patients and methods People with localized CRC completed the Functional Assessment of Cancer Treatment-Fatigue (FACT-F) questionnaire at baseline (before chemotherapy, if given), 6, 12, and 24 months. Healthy controls (HCs) were assessed at the first three time points. Fatigue was defined by standardized FACT-F scores ≤68/100. Quality-of-life (QoL, assessed by the FACT-G questionnaire), affective, and cognitive symptoms were evaluated. Associations were sought between fatigue, baseline factors, and blood tests (including hemoglobin, cytokines, and sex hormones). Regression analyses, Fisher's exact tests, and Wilcoxon rank-sum tests assessed levels of fatigue at each time point and change in fatigue from baseline. A repeated-measures analysis investigated prognostic factors of fatigue across all time points. Results A total of 289 subjects with localized CRC (173 received chemotherapy) and 72 HCs were assessed. More CRC patients had fatigue than HCs at baseline (52% versus 26%, P < 0.001). Fatigue was increased in the chemotherapy (CTh) group at 6 months [CTh+ 70% versus CTh− 31% (P < 0.001), HCs 22%] and remained more common at 12 [CTh+ 44% versus CTh− 31% (P = 0.079)] and 24 months [CTh+ 39% versus CTh− 24% (P = 0.047)]. There was no significant difference between those not receiving chemotherapy and HCs at follow-up assessments. Fatigue was associated with poor QoL, affective and cognitive symptoms, but not consistently with cytokine levels. Predictors for sustained fatigue were baseline fatigue, treatment group, cognitive and affective symptoms, poorer QoL, and comorbidities. Conclusions CRC patients have more fatigue than HCs at baseline. Fatigue peaks immediately after adjuvant chemotherapy, but remains common for 2 years in those who receive chemotherapy. Cognitive and affective symptoms, QoL, comorbidities, chemotherapy, and baseline fatigue predict for longer term fatigue. PMID:27443634

Cyclic fatigue behavior of nickel-titanium dental rotary files in clinical simulated root canals.

PubMed

Chi, Chih-Wen; Li, Chun-Chieh; Lin, Chun-Pin; Shin, Chow-Shing

2017-04-01

Dental rotary instruments can be applied in multiple conditions of canals, but unpredictable fatigue fracture may happen. This study evaluated the fatigue lives of two batches of nickel-titanium (NiTi) dental rotary files operating in clinically simulated root canals. Single-step cyclic fatigue tests were carried out to assess the performance of two batches of NiTi files (ProTaper and ProFile) in nine combinations of simulated canals (cylinder radii 5 mm, 7.5 mm, and 10 mm, and insertion angles 20°, 40°, and 60°). Two-step cyclic fatigue tests were carried out in simulated root canals with the same radius by using the following two sets of insertion angles: (20°, 40°), (20°, 60°), (40°, 20°), and (60°, 20°). Fracture surfaces were observed by scanning electron microscopy. The single-step cyclic fatigue results showed that cyclic fatigue lives of the files decreased with increasing insertion angles or decreasing cylinder radius. The ProFile #25 .04 file was more fatigue resistant than the ProTaper F2 file. In two-step cyclic fatigue tests, the total fatigue lives were usually more than 100% when the files operated at a lower strain and then at a higher strain. By scanning electron microscopy, a larger area of fatigue striation corresponded to a longer fatigue life. Cyclic fatigue life can be influenced by the strains and geometries of files. The fatigue life was prolonged when the files operated at a lower strain and then at a higher strain. However, the fatigue life was shortened if the loading sequence was reversed. Copyright © 2016. Published by Elsevier B.V.

Evaluation of materials during outdoor testing using a computer-controlled test apparatus

Treesearch

R. Sam Williams; Steven Lacher; Corey Halpin; Christopher White

2006-01-01

Ultraviolet radiation, moisture, heat, and cyclic fatigue are some of the stressors that cause materials to degrade outdoors. Considerable research has addressed the effects of ultraviolet radiation and moisture on the rate of this degradation. An often overlooked stressor on materials, during outdoor testing, is the cyclic fatigue. Cyclic fatigue is caused by self-...

75 FR 8479 - Airworthiness Directives; Airbus Model A340-541 and -642 Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2010-02-25

... A340-600 full scale fatigue test, cracks were found on left and right sides of the rear spar vertical... scale fatigue test, cracks were found on left and right sides of the rear spar vertical cruciform at... this full scale fatigue test completion, it has been determined that the current inspections values...

Crack Initiation and Growth Behavior at Corrosion Pit in 2024-T3 Aluminum Alloy

DTIC Science & Technology

2014-09-01

63 Figure B.1: The crack length vs. number of cycles during fatigue testing for the 2AI-01 specimen...number of cycles during fatigue testing for the the 2AI- 02 specimen...64 Figure B.3: The crack length vs. number of cycles during fatigue testing for the 2Sl-01 specimen

Relationship between functional electrical stimulation duty cycle and fatigue in wrist extensor muscles of patients with hemiparesis.

PubMed

Packman-Braun, R

1988-01-01

The purpose of this study was to investigate, in a sample of patients with hemiparesis secondary to cerebrovascular accident, the relationship between the ratio of stimulus on time to off time and muscle fatigue using a commercial electrical stimulation unit. An experimental model was used to test the hypothesis that the smaller the stimulus off time relative to stimulus on time, the greater will be the muscle fatigue over time. The wrist extensor muscles of 18 patients with hemiparesis were stimulated electrically, and isometric force output was recorded continuously using an adapted strain gauge-recorder apparatus. For each testing session, peak on time of the electrical stimulus was set at 5 seconds, and off time was set at 5, 15, or 25 seconds. Six randomly assigned treatment groups participated in three separate treatment sessions in a different order at 48-hour intervals. Treatment sessions were continued either until wrist extensor muscle force output decreased to 50% of its initial value or for a maximum of 30 minutes. Data analysis revealed that significant differences in muscle tension developed among all duty cycles (p less than .01). Duty-cycle ratios of 1:1, 1:3, and 1:5 were shown to be progressively less fatiguing. Within the limits of this investigation, the 1:5 duty-cycle ratio was determined to be the best suited for initial use in programs of prolonged stimulation to the wrist extensor muscles of patients with hemiparesis. The hypothesis was accepted that the smaller the stimulus off time (rest interval) with respect to the stimulus on time, the greater will be the muscle fatigue over time.

Effect of Creep and Oxidation on Reduced Creep-Fatigue life of Ni-based Alloy 617 at 850 C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A

Low cycle fatigue (LCF) and creep fatigue testing of Ni-based alloy 617 was carried out at 850 C. Compared with its LCF life, the material s creep fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep fatiguemore » tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material s fatigue life.« less

Effect of welding structure and δ-ferrite on fatigue properties for TIG welded austenitic stainless steels at cryogenic temperatures

NASA Astrophysics Data System (ADS)

Yuri, Tetsumi; Ogata, Toshio; Saito, Masahiro; Hirayama, Yoshiaki

2000-04-01

High-cycle and low-cycle fatigue properties of base and weld metals for SUS304L and SUS316L and the effects of welding structure and δ-ferrite on fatigue properties were investigated at cryogenic temperatures in order to evaluate the long-life reliability of the structural materials to be used in liquid hydrogen supertankers and storage tanks and to develop a welding process for these applications. The S-N curves of the base and weld metals shifted towards higher levels, i.e., the longer life side, with decreasing test temperatures. High-cycle fatigue tests demonstrated the ratios of fatigue strength at 10 6 cycles to tensile strength of the weld metals to be 0.35-0.7, falling below those of base metals with decreasing test temperatures. Fatigue crack initiation sites in SUS304L weld metals were mostly at blowholes with diameters of 200-700 μm, and those of SUS316L weld metals were at weld pass interface boundaries. Low-cycle fatigue tests revealed the fatigue lives of the weld metals to be somewhat lower than those of the base metals. Although δ-ferrite reduces the toughness of austenitic stainless steels at cryogenic temperatures, the effects of δ-ferrite on high-cycle and low-cycle fatigue properties are not clear or significant.

Investigation of fatigue by Australian general practice registrars: a cross-sectional study.

PubMed

Morgan, Simon; Henderson, Kim M; Tapley, Amanda; Thomson, Allison; Wilson, Jessica; Scott, John; Spike, Neil A; McArthur, Lawrie; van Driel, Mieke L; Magin, Parker J

2015-06-01

Fatigue is the most common undifferentiated problem presenting in general practice. Previous studies have shown that this presentation leads to multiple investigations. There is no published literature describing the management of patients with fatigue by general practice (GP) registrars. To document the investigation-ordering behaviour of GP registrars in managing patients with a new diagnosis of unexplained fatigue. This was a cross-sectional analysis of data from Registrar Clinical Encounters in Training (ReCEnT), an ongoing cohort study of GP registrars' consultations. We established the prevalence of new diagnoses of unexplained fatigue and associations with that diagnosis, the rate of test ordering and the number and types of investigations ordered. 644 registrars contributed data from 68 986 encounters. In 0.78% of patient encounters, a new diagnosis of unexplained fatigue was made. Pathology was ordered in 78.4% of these problems (versus 18.1% in non-fatigue problems), at a rate of 488 tests per 100 new fatigue problems. Our study suggests that unexplained fatigue elicits a non-rational approach to test ordering by registrars. These findings contribute to the understanding of GP registrar management of fatigue, and undifferentiated presentations more broadly, and suggest educational approaches to improve practice, including dealing with uncertainty.

Accelerated fatigue durability of a high performance composite

NASA Technical Reports Server (NTRS)

Rotem, A.

1982-01-01

The fatigue behavior of multidirectional graphite-epoxy laminates was analyzed theoretically and experimentally in an effort to establish an accelerated testing methodology. Analysis of the failure mechanism in fatigue of the laminates led to the determination of the failure mode governing fracture. The nonlinear, cyclic-dependent shear modulus was used to calculate the changing stress field in the laminate during the fatigue loading. Fatigue tests were performed at three different temperatures: 25 C, 74 C, and 114 C. The prediction of the S-N curves was made based on the artificial static strength artificial static strength at a reference temperature and the fatigue functions associated with them. The prediction of an S-N curve at other temperatures was performed using shifting factors determined for the specific failure mode. For multidirectional laminates, different S-N curves at different temperatures could be predicted using these shifting factors. Different S-N curves at different temperatures occur only when the fatigue failure mode is matrix dominated. It was found that whenever the fatigue failure mode is fiber dominated, temperature, over the range investigated, had no influence on the fatigue life. These results permit the prediction of long-time, low temperature fatigue behavior from data obtained in short time, high temperature testing, for laminates governed by a matrix failure mode.

Four-point-bending-fatigue behavior of the Zr-based Vitreloy 105 bulk metallic glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morrison, M. L.; Buchanan, R. A.; Liaw, Peter K

The purpose of this study was to make a direct comparison between four-point-bending and uniaxial fatigue tests with the Zr{sub 52.5}Cu{sub 17.9}Ni{sub 14.6}Al{sub 10.0}Ti{sub 5.0} (at.%) BMG alloy (Vitreloy 105). The fatigue lifetimes in four-point bending were found to be greater than those reported in uniaxial testing. However, the fatigue-endurance limit found in four-point bending was slightly less than that reported for uniaxial fatigue. Thus, the significant differences between fatigue studies in the literature are not likely due to this difference in testing geometry. On the contrary, the fatigue lifetimes were found to be highly dependent upon surface defects andmore » material quality. The four-point-bending-fatigue performance of the Vit 105 alloy was found to be greater than most BMGs and similar to the 300 M high-strength steel and other crystalline alloys in spite of not being 'perfectly amorphous.' Due to the detrimental effects of these inhomogeneities and wear at the supporting pins, this fatigue behavior can be assumed to be a conservative estimate of the potential fatigue performance of a perfectly amorphous and homogeneous BMG.« less

The effects of mental fatigue on cricket-relevant performance among elite players.

PubMed

Veness, Darren; Patterson, Stephen David; Jeffries, Owen; Waldron, Mark

2017-12-01

This study investigated the effects of a mentally fatiguing test on physical tasks among elite cricketers. In a cross-over design, 10 elite male cricket players from a professional club performed a cricket run-two test, a Batak Lite reaction time test and a Yo-Yo-Intermittent Recovery Level 1 (Yo-Yo-IR1) test, providing a rating of perceived exertion (RPE) after completing a 30-min Stroop test (mental fatigue condition) or 30-min control condition. Perceived fatigue was assessed before and after the two conditions and motivation was measured before testing. There were post-treatment differences in the perception of mental fatigue (P < 0.001; d = -7.82, 95% CIs = -9.05-6.66; most likely). Cricket run-two (P = 0.002; d = -0.51, 95% CIs = -0.72-0.30; very likely), Yo-Yo-IR1 distance (P = 0.023; d = 0.39, 95% CIs = 0.14-0.64; likely) and RPE (P = 0.001; d = -1.82, 95% CIs = -2.49-1.14; most likely) were negatively affected by mental fatigue. The Batak Lite test was not affected (P = 0.137), yet a moderate (d = 0.41, 95% CIs = -0.05-0.87) change was likely. Mental fatigue, induced by an app-based Stroop test, negatively affected cricket-relevant performance.

A novel evaluation strategy for fatigue reliability of flexible nanoscale films

NASA Astrophysics Data System (ADS)

Zheng, Si-Xue; Luo, Xue-Mei; Wang, Dong; Zhang, Guang-Ping

2018-03-01

In order to evaluate fatigue reliability of nanoscale metal films on flexible substrates, here we proposed an effective evaluation way to obtain critical fatigue cracking strain based on the direct observation of fatigue damage sites through conventional dynamic bending testing technique. By this method, fatigue properties and damage behaviors of 930 nm-thick Au films and 600 nm-thick Mo-W multilayers with individual layer thickness 100 nm on flexible polyimide substrates were investigated. Coffin-Manson relationship between the fatigue life and the applied strain range was obtained for the Au films and Mo-W multilayers. The characterization of fatigue damage behaviors verifies the feasibility of this method, which seems easier and more effective comparing with the other testing methods.

Evaluation of Giga-cycle Fatigue Properties of Austenitic Stainless Steels Using Ultrasonic Fatigue Test

NASA Astrophysics Data System (ADS)

Takahashi, Kyouhei; Ogawa, Takeshi

Ultrasonic fatigue tests have been performed in austenitic stainless steel, SUS316NG, in order to investigate giga-cycle fatigue strength of pre-strained materials, i.e. 5, 10 and 20% tensile pre-strains and -20% compressive pre-strain. The pre-strains were applied before specimen machining. The austenitic stainless steels are known to exhibit remarkable self-heating during the fatigue experiment. Therefore, heat radiation method was established by setting fatigue specimens in a low temperature chamber at about -100°C. The self-heating was controlled by intermittent loading condition, which enabled us to maintain the test section of the specimens at about room temperature. The results revealed that the fatigue strength increased with increasing pre-strain levels. Fish-eye fracture was observed for -20% pre-strained specimen fractured at 4.11×107 cycles, while the other specimens exhibited ordinary fatigue fracture surface originated from stage I facet on the specimen surface. The increase in fatigue limit was predicted by Vickers hardness, HV, which depended on the size of indented region. The prediction was successful using HV values obtained by the size of the indented region similar to those of the stage I facets.

a Study on the Fretting Fatigue Life of Zircaloy Alloys

NASA Astrophysics Data System (ADS)

Kwon, Jae-Do; Park, Dae-Kyu; Woo, Seung-Wan; Chai, Young-Suck

Studies on the strength and fatigue life of machines and structures have been conducted in accordance with the development of modern industries. In particular, fine and repetitive cyclic damage occurring in contact regions has been known to have an impact on fretting fatigue fractures. The main component of zircaloy alloy is Zr, and it possesses good mechanical characteristics at high temperatures. This alloy is used in the fuel rod material of nuclear power plants because of its excellent resistance. In this paper, the effect of the fretting damage on the fatigue behavior of the zircaloy alloy is studied. Further, various types of mechanical tests such as tension and plain fatigue tests are performed. Fretting fatigue tests are performed with a flat-flat contact configuration using a bridge-type contact pad and plate-type specimen. Through these experiments, it is found that the fretting fatigue strength decreases by about 80% as compared to the plain fatigue strength. Oblique cracks are observed in the initial stage of the fretting fatigue, in which damaged areas are found. These results can be used as the basic data for the structural integrity evaluation of corrosion-resisting alloys considering the fretting damages.

Effect of mental fatigue on the central nervous system: an electroencephalography study

PubMed Central

2012-01-01

Background Fatigue can be classified as mental and physical depending on its cause, and each type of fatigue has a multi-factorial nature. We examined the effect of mental fatigue on the central nervous system using electroencephalography (EEG) in eighteen healthy male volunteers. Methods After enrollment, subjects were randomly assigned to two groups in a single-blinded, crossover fashion to perform two types of mental fatigue-inducing experiments. Each experiment consisted of four 30-min fatigue-inducing 0- or 2-back test sessions and two evaluation sessions performed just before and after the fatigue-inducing sessions. During the evaluation session, the participants were assessed using EEG. Eleven electrodes were attached to the head skin, from positions F3, Fz, F4, C3, Cz, C4, P3, Pz, P4, O1, and O2. Results In the 2-back test, the beta power density on the Pz electrode and the alpha power densities on the P3 and O2 electrodes were decreased, and the theta power density on the Cz electrode was increased after the fatigue-inducing mental task sessions. In the 0-back test, no electrodes were altered after the fatigue-inducing sessions. Conclusions Different types of mental fatigue produced different kinds of alterations of the spontaneous EEG variables. Our findings provide new perspectives on the neural mechanisms underlying mental fatigue. PMID:22954020

Occupational therapists' experience of workplace fatigue: Issues and action.

PubMed

Brown, Cary A; Schell, Jennifer; Pashniak, Lisa M

2017-01-01

Occupational therapists (OTs) work in all areas of health and wellbeing. The work is physically and psychologically demanding, but OTs are often not diligent about recognizing and attending to the workplace health and safety issue of fatigue in their own work settings. The purpose of this paper is to determine current issues and the evidence-base as presented in the literature so as to develop awareness and best practice interventions for fatigue reduction and management in occupational therapists' workplace. A comprehensive search strategy was carried out by the medical librarian on the study team and themes were extracted from the relevant literature by the study team. The literature revealed little research directly addressing occupational therapy workplace fatigue and we expanded our review of the evidence-base across all healthcare workers to identify publications of particular relevance to occupational therapists. This background paper is an important first step to raising awareness among OTs, guide key stakeholders regarding contributing factors to, and consequences of, OTs' workplace fatigue, and set research direction. Knowing which factors influencing workplace fatigue are shared across healthcare professionals and which are unique to OTs can also help organizations develop more tailored workplace fatigue risk reduction programs. This review concludes with a list of existing guidelines and tools for developing workplace fatigue risk assessment and management programs relevant to occupational therapists.

NASA airframe structural integrity program

NASA Technical Reports Server (NTRS)

Harris, Charles E.

1991-01-01

NASA has initiated a research program with the long-term objective of supporting the aerospace industry in addressing issues related to the aging commercial transport fleet. The interdisciplinary program combines advanced fatigue crack growth prediction methodology with innovative nondestructive examination technology with the focus on multi-site damage (MSD) at riveted connections. A fracture mechanics evaluation of the concept of pressure proof testing the fuselage to screen for MSD has been completed. Also, a successful laboratory demonstration of the ability of the thermal flux method to detect disbonds at riveted lap splice joints has been conducted. All long-term program elements have been initiated and the plans for the methodology verification program are being coordinated with the airframe manufacturers.

NASA airframe structural integrity program

NASA Technical Reports Server (NTRS)

Harris, Charles E.

1990-01-01

NASA initiated a research program with the long-term objective of supporting the aerospace industry in addressing issues related to the aging of the commercial transport fleet. The program combines advanced fatigue crack growth prediction methodology with innovative nondestructive examination technology with the focus on multi-stage damage (MSD) at rivited connections. A fracture mechanics evaluation of the concept of pressure proof testing the fuselage to screen for MSD was completed. A successful laboratory demonstration of the ability of the thermal flux method to detect disbonds at rivited lap splice joints was conducted. All long-term program elements were initiated, and the plans for the methodology verification program are being coordinated with the airframe manufacturers.

Structural dynamic testing of composite propfan blades for a cruise missile wind tunnel model

NASA Technical Reports Server (NTRS)

Elgin, Stephen D.; Sutliff, Thomas J.

1993-01-01

The Naval Weapons Center at China Lake, California is currently evaluating a counter rotating propfan system as a means of propulsion for the next generation of cruise missiles. The details and results of a structural dynamic test program are presented for scale model graphite-epoxy composite propfan blades. These blades are intended for use on a cruise missile wind tunnel model. Both dynamic characteristics and strain operating limits of the blades are presented. Complications associated with high strain level fatigue testing methods are also discussed.

Investigation of Advanced Processed Single-Crystal Turbine Blade Alloys

NASA Technical Reports Server (NTRS)

Peters, B. J.; Biondo, C. M.; DeLuca, D. P.

1995-01-01

This investigation studied the influence of thermal processing and microstructure on the mechanical properties of the single-crystal, nickel-based superalloys PWA 1482 and PWA 1484. The objective of the program was to develop an improved single-crystal turbine blade alloy that is specifically tailored for use in hydrogen fueled rocket engine turbopumps. High-gradient casting, hot isostatic pressing (HIP), and alternate heat treatment (HT) processing parameters were developed to produce pore-free, eutectic-free microstructures with different (gamma)' precipitate morphologies. Test materials were cast in high thermal gradient solidification (greater than 30 C/cm (137 F/in.)) casting furnaces for reduced dendrite arm spacing, improved chemical homogeneity, and reduced interdendritic pore size. The HIP processing was conducted in 40 cm (15.7 in.) diameter production furnaces using a set of parameters selected from a trial matrix study. Metallography was conducted on test samples taken from each respective trial run to characterize the as-HIP microstructure. Post-HIP alternate HT processes were developed for each of the two alloys. The goal of the alternate HT processing was to fully solution the eutectic gamma/(gamma)' phase islands and to develop a series of modified (gamma)' morphologies for subsequent characterization testing. This was accomplished by slow cooling through the (gamma)' solvus at controlled rates to precipitate volume fractions of large (gamma)'. Post-solution alternate HT parameters were established for each alloy providing additional volume fractions of finer precipitates. Screening tests included tensile, high-cycle fatigue (HCF), smooth and notched low-cycle fatigue (LCF), creep, and fatigue crack growth evaluations performed in air and high pressure (34.5 MPa (5 ksi)) hydrogen at room and elevated temperature. Under the most severe embrittling conditions (HCF and smooth and notched LCF in 34.5 MPa (5 ksi) hydrogen at 20 C (68 F), screening test results showed increases in fatigue life typically on the order of 1OX, when compared to the current Space Shuttle Main Engine (SSME) Alternate Turbopump (AT) blade alloy (PWA 1480).

Modelling and Laboratory Studies on the Adhesion Fatigue Performance for Thin-Film Asphalt and Aggregate System

PubMed Central

Wang, Dongsheng; Feng, Decheng

2014-01-01

Adhesion between asphalt and aggregate plays an important role in the performance of asphalt mixtures. A low-frequency adhesion fatigue test was proposed in this paper to study the effect of environment on the asphalt-aggregate adhesion system. The stress-based fatigue model had been utilized to describe the fatigue behavior of thin-film asphalt and aggregate system. The factors influencing the adhesion fatigue performance were also investigated. Experiment results show that asphalt has more important effect on the adhesion performance comparing with aggregate. Basalt, which is regarded as hydrophobic aggregates with low silica content, has better adhesion performance to asphalt binder when compared with granite. The effects of aging on the adhesion fatigue performance are different for PG64-22 and rubber asphalt. Long-term aging is found to reduce the adhesion fatigue lives for rubber asphalt and aggregate system, while the effect of long-term aging for aggregate and PG64-22 binder system is positive. Generally the increased stress amplitude and test temperature could induce greater damage and lead to less fatigue lives for adhesion test system. PMID:25054187

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

PubMed

Wang, Dongsheng; Yi, Junyan; Feng, Decheng

2014-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hong; Lee, Sung Min; Wang, James L.

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

Assessment of physical fatigability and fatigue perception in myasthenia gravis.

PubMed

Jordan, Berit; Mehl, Theresa; Schweden, Tabea L K; Menge, Uwe; Zierz, Stephan

2017-05-01

Fatigue includes both performance fatigability and fatigue perception. In 32 stable patients with generalized myasthenia gravis (MG) and 17 controls, time-dependent physical performance was assessed by the arm movement test (AMT) and 6-minute walk test (6MWT). MG patients presented with low quantitative MG scores (mean 0.5, SD 0.5) and without pathologic decrement. Fatigability was based on calculation of linear trend (LT) reflecting dynamic performance within subsequent constant time intervals. Perception of physical fatigue was analyzed using fatigue questionnaires. MG patients showed a negative LT in both AMT and 6MWT, significantly differing from stable performance in controls. LT inversely correlated with elevation of acetylcholine receptor antibodies (r = -0.59, P < 0.005) but not with quantitative MG score and fatigue perception. LT allows quantification of fatigability as an objective measurement of decline in individual performance, even in patients without obvious neuromuscular deficits in routine testing. The missing correlation of experienced fatigue supports the multidimensional fatigue model. Muscle Nerve 55: 657-663, 2017. © 2016 Wiley Periodicals, Inc.

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

DOE PAGES

Wang, Hong; Lee, Sung Min; Wang, James L.; ...

2014-12-19

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

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.

Fatigue Behavior of AM60B Subjected to Variable Amplitude Loading

NASA Astrophysics Data System (ADS)

Kang, H.; Kari, K.; Khosrovaneh, A. K.; Nayaki, R.; Su, X.; Zhang, L.; Lee, Y.-L.

Magnesium alloys are considered as an alternative material to reduce vehicle weight due to their weight which are 33% lighter than aluminum alloys. There has been a significant expansion in the applications of magnesium alloys in automotives components in an effort to improve fuel efficiency through vehicle mass reduction. In this project, a simple front shock tower of passenger vehicle is constructed with various magnesium alloys. To predict the fatigue behavior of the structure, fatigue properties of the magnesium alloy (AM60B) were determined from strain controlled fatigue tests. Notched specimens were also tested with three different variable amplitude loading profiles obtained from the shock tower of the similar size of vehicle. The test results were compared with various fatigue prediction results. The effect of mean stress and fatigue prediction method were discussed.

P-8A Poseidon Multi Mission Maritime Aircraft (P-8A)

DTIC Science & Technology

2015-12-01

focus also includes procurement of depot and intermediate level maintenance capabilities, full scale fatigue testing, and continued integration and... Level Confidence Level of cost estimate for current APB: 50% The current APB cost estimate provided sufficient resources to execute the program under...normal conditions, encountering average levels of technical, schedule, and programmatic risk and external interference. It was consistent with

Hydrogen accelerated fatigue crack growth of friction stir welded X52 steel pipe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ronevich, Joseph Allen; Somerday, Brian P.; Feng, Zhili

Friction stir welded steel pipelines were tested in high pressure hydrogen gas to examine the effects of hydrogen accelerated fatigue crack growth. Fatigue crack growth rate (da/dN) vs. stress-intensity factor range (ΔK) relationships were measured for an X52 friction stir welded pipe tested in 21 MPa hydrogen gas at a frequency of 1 Hz and R = 0.5. Tests were performed on three regions: base metal (BM), center of friction stir weld (FSW), and 15 mm off-center of the weld. For all three material regions, tests in hydrogen exhibited accelerated fatigue crack growth rates that exceeded an order of magnitudemore » compared to companion tests in air. Among tests in hydrogen, fatigue crack growth rates were modestly higher in the FSW than the BM and 15 mm off-center tests. Select regions of the fracture surfaces associated with specified ΔK levels were examined which revealed intergranular fracture in the BM and 15 mm off-center specimens but an absence of intergranular features in the FSW specimens. In conclusion, the X52 friction stir weld and base metal tested in hydrogen exhibited fatigue crack growth rate relationships that are comparable to those for conventional arc welded steel pipeline of similar strength found in the literature.« less

Hydrogen accelerated fatigue crack growth of friction stir welded X52 steel pipe

DOE PAGES

Ronevich, Joseph Allen; Somerday, Brian P.; Feng, Zhili

2016-11-17

Friction stir welded steel pipelines were tested in high pressure hydrogen gas to examine the effects of hydrogen accelerated fatigue crack growth. Fatigue crack growth rate (da/dN) vs. stress-intensity factor range (ΔK) relationships were measured for an X52 friction stir welded pipe tested in 21 MPa hydrogen gas at a frequency of 1 Hz and R = 0.5. Tests were performed on three regions: base metal (BM), center of friction stir weld (FSW), and 15 mm off-center of the weld. For all three material regions, tests in hydrogen exhibited accelerated fatigue crack growth rates that exceeded an order of magnitudemore » compared to companion tests in air. Among tests in hydrogen, fatigue crack growth rates were modestly higher in the FSW than the BM and 15 mm off-center tests. Select regions of the fracture surfaces associated with specified ΔK levels were examined which revealed intergranular fracture in the BM and 15 mm off-center specimens but an absence of intergranular features in the FSW specimens. In conclusion, the X52 friction stir weld and base metal tested in hydrogen exhibited fatigue crack growth rate relationships that are comparable to those for conventional arc welded steel pipeline of similar strength found in the literature.« less

Advanced single crystal for SSME turbopumps

NASA Technical Reports Server (NTRS)

Fritzemeier, L. G.

1989-01-01

The objective of this program was to evaluate the influence of high thermal gradient casting, hot isostatic pressing (HIP) and alternate heat treatments on the microstructure and mechanical properties of a single crystal nickel base superalloy. The alloy chosen for the study was PWA 1480, a well characterized, commercial alloy which had previously been chosen as a candidate for the Space Shuttle Main Engine high pressure turbopump turbine blades. Microstructural characterization evaluated the influence of casting thermal gradient on dendrite arm spacing, casting porosity distribution and alloy homogeneity. Hot isostatic pressing was evaluated as a means of eliminating porosity as a preferred fatigue crack initiation site. The alternate heat treatment was chosen to improve hydrogen environment embrittlement resistance and for potential fatigue life improvement. Mechanical property evaluation was aimed primarily at determining improvements in low cycle and high cycle fatigue life due to the advanced processing methods. Statistically significant numbers of tests were conducted to quantitatively demonstrate life differences. High thermal gradient casting improves as-cast homogeneity, which facilitates solution heat treatment of PWA 1480 and provides a decrease in internal pore size, leading to increases in low cycle and high cycle fatigue lives.

Fatigue Crack Growth Behavior and Microstructural Mechanisms in Ti-6Al-4V Manufactured by Laser Engineered Net Shaping

DTIC Science & Technology

2015-12-01

hardening heat treatment were the controlling factors of the fatigue resistance, while testing directions have the least impact. Leuders et al. [16...radius. The microstructurally-small fatigue crack growth test was run under load control at constant stress ratio R=0.1 and a cyclic frequency of 20 Hz...not been thoroughly investigated. In this study, long fatigue crack growth tests were conducted at two stress ratios (R=0.1 and 0.8), using Ti-6Al

Several submaximal exercise tests are reliable, valid and acceptable in people with chronic pain, fibromyalgia or chronic fatigue: a systematic review.

PubMed

Ratter, Julia; Radlinger, Lorenz; Lucas, Cees

2014-09-01

Are submaximal and maximal exercise tests reliable, valid and acceptable in people with chronic pain, fibromyalgia and fatigue disorders? Systematic review of studies of the psychometric properties of exercise tests. People older than 18 years with chronic pain, fibromyalgia and chronic fatigue disorders. Studies of the measurement properties of tests of physical capacity in people with chronic pain, fibromyalgia or chronic fatigue disorders were included. Studies were required to report: reliability coefficients (intraclass correlation coefficient, alpha reliability coefficient, limits of agreements and Bland-Altman plots); validity coefficients (intraclass correlation coefficient, Spearman's correlation, Kendal T coefficient, Pearson's correlation); or dropout rates. Fourteen studies were eligible: none had low risk of bias, 10 had unclear risk of bias and four had high risk of bias. The included studies evaluated: Åstrand test; modified Åstrand test; Lean body mass-based Åstrand test; submaximal bicycle ergometer test following another protocol other than Åstrand test; 2-km walk test; 5-minute, 6-minute and 10-minute walk tests; shuttle walk test; and modified symptom-limited Bruce treadmill test. None of the studies assessed maximal exercise tests. Where they had been tested, reliability and validity were generally high. Dropout rates were generally acceptable. The 2-km walk test was not recommended in fibromyalgia. Moderate evidence was found for reliability, validity and acceptability of submaximal exercise tests in patients with chronic pain, fibromyalgia or chronic fatigue. There is no evidence about maximal exercise tests in patients with chronic pain, fibromyalgia and chronic fatigue. Copyright © 2014. Published by Elsevier B.V.

Relationship of fatigue to the tensile stiffness of asphaltic concrete : final report on phase 1, laboratory investigation.

DOT National Transportation Integrated Search

1972-01-01

The correlation between asphaltic concrete tensile stiffness and fatigue life was determined in the laboratory. Constant strain fatigue tests were utilized and indirect tensile tests were selected because of their simplicity and applicability. Four a...

PZT Active Frequency Based Wind Blade Fatigue to Failure Testing Results for Various Blade Designs

DTIC Science & Technology

2011-09-01

PZT Active Frequency Based Wind Blade Fatigue to Failure Testing Results for Various Blade Designs R. J. WERLINK...number. 1. REPORT DATE SEP 2011 2. REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE PZT Active Frequency Based Wind Blade Fatigue ...18 Abstract: This paper summarizes NASA PZT Health Monitoring System results previously reported for 9 meter blade Fatigue loading to failure

Nanosecond pulsed laser micromachining for experimental fatigue life study of Ti-3Al-2.5V tubes

NASA Astrophysics Data System (ADS)

Lin, Yaomin; Gupta, Mool C.; Taylor, Robert E.; Lei, Charles; Stone, William; Spidel, Tom; Yu, Michael; Williams, Reanne

2009-01-01

Defects on external surface of in-service hydraulic tubes can reduce total life cycles for operation. Evaluation of fatigue life of the tubes with damage is thus critical for safety reasons. A methodology of generating defects in the Ti-3Al-2.5V tube—a widely used pipeline in hydraulic systems of aircrafts—using nanosecond pulsed laser for experimental fatigue life study is described in this paper. Straight tubes of five different sizes were laser micromachined to generate notches of given length and depths on the outside surface. Approaches were developed to precisely control the notch dimensions. The laser-notched tubes were tested with cyclic internal impulse pressure and fatigue life was measured. The laser notches and fatigue cracks were characterized after the test. It is concluded that laser micromachining generated consistent notches, and the influence of notch depth on fatigue life of the tube is significant. Based on the experimental test results, the relationship between the fatigue life of the Ti-3Al-2.5V tube and the notch depth was revealed. The research demonstrated that laser micromachining is applicable for experimental fatigue life study of titanium tubes. The presented test data are useful for estimating the damage limits of the titanium tubes in service environment and for further theoretical studies.

Automated predesign of aircraft

NASA Technical Reports Server (NTRS)

Poe, C. C., Jr.; Kruse, G. S.; Tanner, C. J.; Wilson, P. J.

1978-01-01

Program uses multistation structural-synthesis to size and design box-beam structures for transport aircraft. Program optimizes static strength and scales up to satisfy fatigue and fracture criteria. It has multimaterial capability and library of materials properties, including advanced composites. Program can be used to evaluate impact on weight of variables such as materials, types of construction, structural configurations, minimum gage limits, applied loads, fatigue lives, crack-growth lives, initial crack sizes, and residual strengths.

Effect of Environment on Fatigue Behavior of a Nicalon(TM)/Si-N-C Ceramic Matrix Composite

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Ojard, Greg C.; Verrilli, Michael J.; Kiraly, Louis J. (Technical Monitor)

2002-01-01

The effect of environmental exposure on the fatigue life of Nicalon(TM) /Si-N-C composite was investigated in this study. Test specimens with arrays of 1.8 mm diameter holes and two different open areas, 25 and 35%, were machined. Three environmental conditions were studied: 1) continuous fatigue cycling in air, 2) fatigue cycling in air alternating with humidity exposure, and 3) fatigue cycling in air alternating with exposure to a salt-fog environment. All fatigue testing on specimens with holes was performed with a load ratio, R = 0.05, and at a temperature of 910 C. In general, fatigue lives were shortest for specimens subjected to salt-fog exposure and longest for specimens subjected to continuous fatigue cycling in air. The fatigue data generated on the specimens with holes were compared with fatigue data generated in air on specimens with no holes. Fatigue strength reduction factors for different environmental conditions and open areas investigated in the study were calculated for the Nicalon(TM) /Si-N-C composite.

Estimating the Contact Endurance of the AISI 321 Stainless Steel Under Contact Gigacycle Fatigue Tests

NASA Astrophysics Data System (ADS)

Savrai, R. A.; Makarov, A. V.; Osintseva, A. L.; Malygina, I. Yu.

2018-02-01

Mechanical testing of the AISI 321 corrosion resistant austenitic steel for contact gigacycle fatigue has been conducted with the application of a new method of contact fatigue testing with ultrasonic frequency of loading according to a pulsing impact "plane-to-plane" contact scheme. It has been found that the contact endurance (the ability to resist the fatigue spalling) of the AISI 321 steel under contact gigacycle fatigue loading is determined by its plasticity margin and the possibility of additional hardening under contact loading. It is demonstrated that the appearance of localized deep and long areas of spalling on a material surface can serve as a qualitative characteristic for the loss of the fatigue strength of the AISI 321 steel under impact contact fatigue loading. The value of surface microhardness measured within contact spots and the maximum depth of contact damages in the peripheral zone of contact spots can serve as quantitative criteria for that purpose.

The isothermal fatigue behavior of a unidirectional SiC/Ti composite and the Ti alloy matrix

NASA Technical Reports Server (NTRS)

Gayda, John, Jr.; Gabb, Timothy P.; Freed, Alan D.

1989-01-01

The high temperature fatigue behavior of a metal matrix composite (MMC) consisting of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced by 33 vol percent of continuous unidirectional SiC fibers was experimentally and analytically evaluated. Isothermal MMC fatigue tests with constant amplitude loading parallel to the fiber direction were performed at 300 and 550 C. Comparative fatigue tests of the Ti-15-3 matrix alloy were also conducted. Composite fatigue behavior and the in-situ stress state of the fiber and matrix were analyzed with a micromechanical model, the Concentric Cylinder Model (CCM). The cyclic stress-strain response of the composite was stable at 300 C. However, an increase in cyclic mean strain foreshortened MMC fatigue life at high strain ranges at 550 C. Fatigue tests of the matrix alloy and CCM analyses indicated this response was associated with stress relaxation of the matrix in the composite.

Health Monitoring for Airframe Structural Characterization

NASA Technical Reports Server (NTRS)

Munns, Thomas E.; Kent, Renee M.; Bartolini, Antony; Gause, Charles B.; Borinski, Jason W.; Dietz, Jason; Elster, Jennifer L.; Boyd, Clark; Vicari, Larry; Ray, Asok;

Nonlinear damage analysis: Postulate and evaluation

NASA Technical Reports Server (NTRS)

Leis, B. N.; Forte, T. P.

1983-01-01

The objective of this program is to assess the viability of a damage postulate which asserts that the fatigue resistance curve of a metal is history dependent due to inelastic action. The study focusses on OFE copper because this simple model material accentuates the inelastic action central to the damage postulate. Data relevant to damage evolution and crack initiation are developed via a study of surface topography. The effects of surface layer residual stresses are explored via comparative testing as were the effects in initial prestraining. The results of the study very clearly show the deformation history dependence of the fatigue resistance of OFE copper. Furthermore the concept of deformation history dependence is shown to qualitatively explain the fatigue resistance of all histories considered. Likewise quantitative predictions for block cycle histories are found to accurately track the observed results. In this respect the assertion that damage per cycle for a given level of the damage parameter is deformation history dependent appears to be physically justified.

Bending fatigue tests on SiC-Al tapes under alternating stress at room temperature

NASA Technical Reports Server (NTRS)

Herzog, J. A.

1981-01-01

The development of a testing method for fatigue tests on SiC-Al tapes containing a small amount of SiC filaments under alternating stress is reported. The fatigue strength curves resulting for this composite are discussed. They permit an estimate of its behavior under continuous stress and in combination with various other matrices, especially metal matrices.

Experiments of thermomechanical fatigue of SMAs

NASA Astrophysics Data System (ADS)

Lagoudas, Dimitris C.; Miller, David A.

1999-07-01

As SMA wires are gaining in popularity for use as actuators, one constitutive parameter that remain unknown is the thermomechanical fatigue life. Even though the effect of thermal cycles on the transformation characteristics of SMAs has been studied, these teste have not been extended to high number of cycles. In this study, a novel test frame developed to study the thermomechanical fatigue life of SMAs is described. Additionally, a testing protocol is discussed necessary to fully establish the fatigue characteristics of SMAs under various conditions. Initial results of the initial test show a substantial increase in the number of cycles to failure as the applied stress level reduces to approximately 100 MPa.

The effect of weld porosity on the cryogenic fatigue strength of ELI grade Ti-5Al-2.5Sn

NASA Technical Reports Server (NTRS)

Rogers, P. R.; Lambdin, R. C.; Fox, D. E.

1992-01-01

The effect of weld porosity on the fatigue strength of ELI grade Ti-5Al-2.5Sn at cryogenic temperature was determined. A series of high cycle fatigue (HCF) and tensile tests were performed at -320 F on specimens made from welded sheets of the material. All specimens were tested with weld beads intact and some amount of weld offset. Specimens containing porosity and control specimens containing no porosity were tested. Results indicate that for the weld configuration tested, the fatigue life of the material is not affected by the presence of spherical embedded pores.

Psychosocial correlates of fatigue in multiple sclerosis.

PubMed

Schwartz, C E; Coulthard-Morris, L; Zeng, Q

1996-02-01

To explore: (1) the interrelation among the neuropsychological, psychological, and psychosocial factors and fatigue as measured by the Multidimensional Assessment of Fatigue scale, and (2) the impact of fatigue on role performance. Clinical interview with neuropsychological testing and cross-sectional study by mail. Multiple sclerosis (MS) clinic registry of a large Boston teaching hospital. 139 MS patients representing a broad range of disability. The Multidimensional Assessment of Fatigue (MAF) scale, the Extended Disability Status Scale, the Sickness Impact Profile, Rao cognitive battery, the Trailmaking Test, depression, anxiety, and social activity limitations subscales from the Arthritis Impact Measurement Scales, and the Ryff Happiness Scale. Stepwise multiple regression analyses revealed that having a low sense of environmental mastery was the best psychosocial predictor of both global fatigue and fatigue-related distress, after adjusting for sociodemographic and medical factors. Further, people who reported being more depressed tended to report more severe fatigue. Neuropsychological performance was not associated with fatigue. Fatigue was found to limit social, work, and overall role performance, but not physical role performance. People who feel that they can choose or create environments suitable to their psychic or physical conditions report less global fatigue and less fatigue-related distress, and fatigue can have an important impact on role performance. The implications of these findings for designing fatigue management interventions are discussed.

Effect of stress ratio on the fatigue behaviour of glass/epoxy composite

NASA Astrophysics Data System (ADS)

Syayuthi, A. R. A.; Majid, M. S. Abdul; Ridzuan, M. J. M.; Basaruddin, K. S.; Peng, T. L.

2017-10-01

The effect of stress ratio on the fatigue behaviour of the GFRE composite has been investigated. The glass fibre reinforced epoxy (GFRE) composite plates were fabricated using vacuum infusion method. Static tensile was performed in accordance with the ASTM D5766 standard, and the cyclic test was conducted according to ASTM D3479 with three different stress ratio, R = 0, 0.5, -1. Static tensile tests were carried out to determine the ultimate strength of this composite. Subsequently, fatigue tests loads ranging from 30% to 90% of the ultimate load were applied to each specimen. The S-N curve of different stress ratio loading of fibreglass/epoxy composites was then established. The results show that the number of cycles to failure increases as the loading is decreased. The specimens for fatigue tests loads 30% at R = 0 and -1 recorded the highest number of cycles at 2 million cycles. The results obtained from this test indicated a significant life reduction for R = -1 compared with the tension-tension loading, with the life reduction for R = -1 being greatest. The fatigue behaviour of the GFRE composite materials is not only influenced by the percentage of fatigue tests load but with different of stress ratio.

Assessment of Proper Bonding Methods and Mechanical Characterization FPGA CQFPs

NASA Technical Reports Server (NTRS)

Davis, Milton C.

2008-01-01

This presentation discusses fractured leads on field-programmable gate array (FPGA) during flight vibration. Actions taken to determine root cause and resolution of the failure include finite element analysis (FEA) and vibration testing and scanning electron microscopy (with X-ray microanalysis) and energy dispersive spectrometry (SEM/EDS) failure assessment. Bonding methods for surface mount parts is assessed, including critical analysis and assessment of random fatigue damage. Regarding ceramic quad flat pack (CQFP) lead fracture, after disassembling the attitude control electronics (ACE) configuration, photographs showed six leads cracked on FPGA RTSX72SU-1 CQ208B package located on the RWIC card. An identical package (FPGA RTSX32SU-1 CQ208B) mounted on the RWIC did not results in cracked pins due to vibration. FPGA lead failure theories include workmanship issues in the lead-forming, material defect in the leads of the FPGA packages, and the insecure mounting of the board in the card guides, among other theories. Studies were conducted using simple calculations to determine the response and fatigue life of the package. Shorter packages exhibited more response when loaded by out-of-plane displacement of PCB while taller packages exhibit more response when loaded by in-plane acceleration of PCB. Additionally, under-fill did not contribute to reducing stress in leads due to out-of-plane PCB loading or from component twisting, as much as corner bonding. The combination of corner bond and under-fill is best to address mechanical and thermal S/C environment. Test results of bonded parts showed reduced (dampened) amplitude and slightly shifted peaks at the un-bonded natural frequency and an additional response at the bonded frequency. Stress due to PCBB out-of-plane loading was decreased on in the corners when only a corner bond was used. Future work may address CQFP fatigue assessment, including the investigation of discrepancy in predicted fatigue damage, as well as comparing fatigue life and fatigue damage cycle ration computed using FEA and Miner's rule to results from a fatigue assessment software program.

Prospective evaluation of a 12-week walking exercise program and its effect on fatigue in prostate cancer patients undergoing radical external beam radiotherapy.

PubMed

Truong, Pauline T; Gaul, Catherine A; McDonald, Rachel E; Petersen, Ross B; Jones, Stuart O; Alexander, Abraham S; Lim, Jan T W; Ludgate, Charles

2011-08-01

To evaluate tolerability and compliance to a walking exercise program and its effect on fatigue during and after radical external beam radiation therapy (EBRT) for prostate cancer. A total of 50 subjects with prostate cancer undergoing EBRT over 6 to 8 weeks were prospectively accrued to an exercise intervention group, matched for age and clinical characteristics to 30 subjects in a historical control group who underwent EBRT with no specific exercise intervention. Starting 1 week before EBRT, exercise participants performed moderate-intensity walking targeting 60% to 70% age-predicted maximum heart rate, at least 20 min/d, 3 d/wk over 12 weeks. The Brief Fatigue Inventory was administered at baseline, mid-EBRT (week 3-4), end-EBRT (week 6-8), and 6 months post-EBRT. Of 50, 42 (84%) of exercise participants completed the walking program. There were no cardiovascular complications, musculoskeletal injuries, or other adverse events. A total of 89% subjects reported "Good-Excellent" satisfaction during and up to 6 months post-EBRT. Fatigue in control subjects escalated from baseline to end-EBRT, remaining high at 6 months post-EBRT (P[r] = 0.03). In contrast, mean total fatigue scores in exercise subjects were stable from baseline up to 6 months post-EBRT (P = 0.52). Trends for higher fatigue interference with quality of life were observed in the control group as compared with the exercise group. Moderate-intensity walking exercise during radical EBRT is safe and feasible. The high convenience and satisfaction ratings, in conjunction with the observed fatigue trends, indicate that this activity has the potential to attenuate fatigue and improve quality of life for patients with localized prostate cancer undergoing curative therapy.

Surface fatigue life and failure characteristics of EX-53, CBS 1000M, and AISI 9310 gear materials

NASA Technical Reports Server (NTRS)

Townsend, D. P.

1985-01-01

Spur gear endurance tests and rolling-element surface fatigue tests are conducted to investigate EX-53 and CBS 1000M steels for use as advanced application gear materials, to determine their endurance characteristics, and to compare the results with the standard AISI 9310 gear material. The gear pitch diameter is 8.89 cm (3.50 in). Gear test conditions are an oil inlet temperature of 320 K (116 F), an oil outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. Bench-type rolling-element fatigue tests are conducted at ambient temperature with a bar specimen speed of 12,500 rpm and a maximum Hertz stress of 4.83 GPa (700 ksi). The EX-53 test gears have a surface fatigue life of twice that of the AISI 9310 spur gears. The CBS 1000M test gears have a surface fatigue life of more than twice that of the AISI 9310 spur gears. However, the CBS 1000M gears experience a 30-percent tooth fracture failure which limits its use as a gear material. The rolling-contact fatigue lines of RC bar specimens of EX-53 and ASISI 9310 are approximately equal. However, the CBS 1000M RC specimens have a surface fatigue life of about 50 percent that of the AISI 9310.

Pitting and Bending Fatigue Evaluations of a New Case-Carburized Gear Steel

NASA Technical Reports Server (NTRS)

Krantz, Timothy; Tufts, Brian

2007-01-01

The power density of a gearbox is an important consideration for many applications and is especially important for gearboxes used on aircraft. One approach to improving power density of gearing is to improve the steel properties by design of the alloy. The alloy tested in this work was designed to be case-carburized with surface hardness of Rockwell C66 after hardening. Test gear performance was evaluated using surface fatigue tests and single-tooth bending fatigue tests. The performance of gears made from the new alloy was compared to the performance of gears made from two alloys currently used for aviation gearing. The new alloy exhibited significantly better performance in surface fatigue testing, demonstrating the value of the improved properties in the case layer. However, the alloy exhibited lesser performance in single-tooth bending fatigue testing. The fracture toughness of the tested gears was insufficient for use in aircraft applications as judged by the behavior exhibited during the single tooth bending tests. This study quantified the performance of the new alloy and has provided guidance for the design and development of next generation gear steels.

Cognitive fatigue in patients with myasthenia gravis.

PubMed

Jordan, Berit; Schweden, Tabea L K; Mehl, Theresa; Menge, Uwe; Zierz, Stephan

2017-09-01

Cognitive fatigue has frequently been reported in myasthenia gravis (MG). However, objective assessment of cognitive fatigability has never been evaluated. Thirty-three MG patients with stable generalized disease and 17 healthy controls underwent a test battery including repeated testing of attention and concentration (d2-R) and Paced Auditory Serial Addition Test. Fatigability was based on calculation of linear trend (LT) reflecting dynamic performance within subsequent constant time intervals. Additionally, fatigue questionnaires were used. MG patients showed a negative LT in second d2-R testing, indicating cognitive fatigability. This finding significantly differed from stable cognitive performance in controls (P < 0.05). Results of Paced Auditory Serial Addition Test testing did not differ between groups. Self-assessed fatigue was significantly higher in MG patients compared with controls (P < 0.001), but did not correlate with LT. LT quantifies cognitive fatigability as an objective measurement of performance decline in MG patients. Self-assessed cognitive fatigue is not correlated with objective findings. Muscle Nerve 56: 449-457, 2017. © 2016 Wiley Periodicals, Inc.

The effect of hold-times on the fatigue behavior of type AISI 316L stainless steel under deuteron irradiation

NASA Astrophysics Data System (ADS)

Scholz, R.; Mueller, R.

1998-10-01

Strain controlled fatigue tests have been performed in torsion at 400°C on type 316L stainless steel samples in both 20% cold worked and annealed conditions during an irradiation with 19 MeV deuterons. A hold-time was imposed in the loading cycle. For the cold worked (cw) material, at shear strain ranges of 1.13% and 1.3%, irradiation creep induced stress relaxation led to the built up of a mean stress. The fatigue life was significantly reduced in comparison to thermal control tests. For the annealed (ann) material, tested under similar experimental conditions, irradiation creep effects were negligibly small compared to cyclic and irradiation hardening. The fatigue life was only slightly reduced. Continuous cycling tests conducted under irradiation conditions lay in the scatter band of the thermal control tests. The difference in fatigue life between continuous cycling and hold-time tests is attributed mainly to the observed difference in irradiation hardening.

Creep fatigue of low-cobalt superalloys: Waspalloy, PM U 700 and wrought U 700

NASA Technical Reports Server (NTRS)

Leis, B. N.; Rungta, R.; Hopper, A. T.

1983-01-01

The influence of cobalt content on the high temperature creep fatigue crack initiation resistance of three primary alloys was evaluated. These were Waspalloy, Powder U 700, and Cast U 700, with cobalt contents ranging from 0 up to 17 percent. Waspalloy was studied at 538 C whereas the U 700 was studied at 760 C. Constraints of the program required investigation at a single strain range using diametral strain control. The approach was phenomenological, using standard low cycle fatigue tests involving continuous cycling tension hold cycling, compression hold cycling, and symmetric hold cycling. Cycling in the absence of or between holds was done at 0.5 Hz, whereas holds when introduced lasted 1 minute. The plan was to allocate two specimens to the continuous cycling, and one specimen to each of the hold time conditions. Data was taken to document the nature of the cracking process, the deformation response, and the resistance to cyclic loading to the formation of small cracks and to specimen separation. The influence of cobalt content on creep fatigue resistance was not judged to be very significant based on the results generated. Specific conclusions were that the hold time history dependence of the resistance is as significant as the influence of cobalt content and increased cobalt content does not produce increased creep fatigue resistance on a one to one basis.

Microstructural and Material Quality Effects on Rolling Contact Fatigue of Highly Elastic Intermetallic Ball Bearings

NASA Technical Reports Server (NTRS)

DellaCorte, Christopher; Howard, S. Adam; Thomas, Fransua; Stanford, Malcolm K.

2016-01-01

Rolling element bearings made from highly-elastic intermetallic materials (HIM)s, such as 60NiTi, are under development for applications that require superior corrosion and shock resistance. Compared to steel, intermetallics have been shown to have much lower rolling contact fatigue (RCF) stress capability in simplified 3-ball on rod (ASTM STP 771) fatigue tests. In the 3-ball tests, poor material quality and microstructural flaws negatively affect fatigue life but such relationships have not been established for full-scale 60NiTi bearings. In this paper, 3-ball-on-rod fatigue behavior of two quality grades of 60NiTi are compared to the fatigue life of full-scale 50mm bore ball bearings made from the same materials. 60NiTi RCF rods with material or microstructural flaws suffered from infant mortality failures at all tested stress levels while high quality 60NiTi rods exhibited no failures at lower stress levels. Similarly, tests of full-scale bearings made from flawed materials exhibited early surface fatigue and through crack type failures while bearings made from high quality material did not fail even in long-term tests. Though the full-scale bearing test data is yet preliminary, the results suggest that the simplified RCF test is a good qualitative predictor of bearing performance. These results provide guidance for materials development and to establish minimum quality levels required for successful bearing operation and life.

Microstructural and Material Quality Effects on Rolling Contact Fatigue of Highly Elastic Intermetallic NiTi Ball Bearings

NASA Technical Reports Server (NTRS)

Dellacorte, Christopher; Howard, S. Adam; Thomas, Fransua; Stanford, Malcolm K.

2017-01-01

Rolling element bearings made from highly-elastic intermetallic materials (HIM)s, such as 60NiTi, are under development for applications that require superior corrosion and shock resistance. Compared to steel, intermetallics have been shown to have much lower rolling contact fatigue (RCF) stress capability in simplified 3-ball on rod (ASTM STP 771) fatigue tests. In the 3-ball tests, poor material quality and microstructural flaws negatively affect fatigue life but such relationships have not been established for full-scale 60NiTi bearings. In this paper, 3-ball-on-rod fatigue behavior of two quality grades of 60NiTi are compared to the fatigue life of full-scale 50mm bore ball bearings made from the same materials. 60NiTi RCF rods with material or microstructural flaws suffered from infant mortality failures at all tested stress levels while high quality 60NiTi rods exhibited no failures at lower stress levels. Similarly, tests of full-scale bearings made from flawed materials exhibited early surface fatigue and through crack type failures while bearings made from high quality material did not fail even in long-term tests. Though the full-scale bearing test data is yet preliminary, the results suggest that the simplified RCF test is a good qualitative predictor of bearing performance. These results provide guidance for materials development and to establish minimum quality levels required for successful bearing operation and life.

Load-Differential Features for Automated Detection of Fatigue Cracks Using Guided Waves (Preprint)

DTIC Science & Technology

2011-11-01

AFRL-RX-WP-TP-2011-4363 LOAD-DIFFERENTIAL FEATURES FOR AUTOMATED DETECTION OF FATIGUE CRACKS USING GUIDED WAVES (PREPRINT) Jennifer E...AUTOMATED DETECTION OF FATIGUE CRACKS USING GUIDED WAVES (PREPRINT) 5a. CONTRACT NUMBER FA8650-09-C-5206 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER...tensile loads open fatigue cracks and thus enhance their detectability using ultrasonic methods. Here we introduce a class of load-differential methods

Fatigue crack monitoring with coupled piezoelectric film acoustic emission sensors

NASA Astrophysics Data System (ADS)

Zhou, Changjiang

Fatigue-induced cracking is a commonly seen problem in civil infrastructures reaching their original design life. A number of high-profile accidents have been reported in the past that involved fatigue damage in structures. Such incidences often happen without prior warnings due to lack of proper crack monitoring technique. In order to detect and monitor the fatigue crack, acoustic emission (AE) technique, has been receiving growing interests recently. AE can provide continuous and real-time monitoring data on damage progression in structures. Piezoelectric film AE sensor measures stress-wave induced strain in ultrasonic frequency range and its feasibility for AE signal monitoring has been demonstrated recently. However, extensive work in AE monitoring system development based on piezoelectric film AE sensor and sensor characterization on full-scale structures with fatigue cracks, have not been done. A lack of theoretical formulations for understanding the AE signals also hinders the use of piezoelectric film AE sensors. Additionally, crack detection and source localization with AE signals is a very important area yet to be explored for this new type of AE sensor. This dissertation presents the results of both analytical and experimental study on the signal characteristics of surface stress-wave induced AE strain signals measured by piezoelectric film AE sensors in near-field and an AE source localization method based on sensor couple theory. Based on moment tensor theory, generalized expression for AE strain signal is formulated. A special case involving the response of piezoelectric film AE sensor to surface load is also studied, which could potentially be used for sensor calibration of this type of sensor. A new concept of sensor couple theory based AE source localization technique is proposed and validated with both simulated and experimental data from fatigue test and field monitoring. Two series of fatigue tests were conducted to perform fatigue crack monitoring on large-scale steel test specimens using piezoelectric film AE sensors. Continuous monitoring of fatigue crack growth in steel structures is demonstrated in these fatigue test specimens. The use of piezoelectric film AE sensor for field monitoring of existing fatigue crack is also demonstrated in a real steel I-girder bridge located in Maryland. The sensor couple theory based AE source localization is validated using a limited number of piezoelectric film AE sensor data from both fatigue test specimens and field monitoring bridge. Through both laboratory fatigue test and field monitoring of steel structures with active fatigue cracks, the signal characteristics of piezoelectric film AE sensor have been studied in real-world environment.

Effects of environment and frequency on the fatigue behavior of the spallation neutron source (SNS) target container material - 316 LN stainless steel

NASA Astrophysics Data System (ADS)

Tian, Hongbo

As the candidate target container material of the new Spallation Neutron Source (SNS) being designed and constructed at the Oak Ridge National Laboratory (ORNL), Type 316 low-carbon nitrogen-added (LN) stainless steel (SS) will operate in an aggressive environment, subjected to intense fluxes of high-energy protons and neutrons while exposed to liquid mercury. The current project is oriented toward materials studies regarding the effects of test environment and frequency on the fatigue behavior of 316 LN SS. In order to study the structural applications of this material and improve the fundamental understanding of the fatigue damage mechanisms, fatigue tests were performed in air and mercury environments at various frequencies and R ratios (R = sigma min/sigmamax, sigmamin and sigmamax are the applied minimum and maximum stresses, respectively). Fatigue data were developed for the structural design and engineering applications of this material. Specifically, high-cycle fatigue tests, fatigue crack-propagation tests, and ultrahigh cycle fatigue tests up to 10 9 cycles were conducted in air and mercury with test frequencies from 10 Hz to 700 Hz. Microstructure characterizations were performed using optical microscopy (OM), scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM). It was found that mercury doesn't seem to have a large impact on the crack-initiation behavior of 316 LN SS. However, the crack-propagation mechanisms in air and mercury are different in some test conditions. Transgranular cracks seem to be the main mechanism in air, and intergranular in mercury. A significant specimen self-heating effect was found during high-cycle faituge. Theoretical calculation was performed to predict temperature responses of the material subjected to cyclic deformation. The predicted cyclic temperature evolution seems to be in good agreement with the experimental results.

The effects of Nitinol phases on corrosion and fatigue behavior

NASA Astrophysics Data System (ADS)

Denton, Melissa

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

Near-threshold fatigue behavior of copper alloys in air and aqueous environments: A high cyclic frequency study

NASA Astrophysics Data System (ADS)

Ahmed, Tawfik M.

The near-threshold fatigue crack propagation behavior of alpha-phase copper alloys in desiccated air and several aqueous environments has been investigated. Three commercial alloys of nominal composition Cu-30Ni (Cu-Ni), Cu-30Zn (Cu-Zn) and 90Cu-7Al-3Fe (Cu-Al) were tested. Fatigue tests were conducted using standard prefatigued single edged notched (SEN) specimens loaded in tension at a high frequency of ˜100 Hz. Different R-ratios were employed, mostly at R-ratios of 0.5. Low loading levels were used that corresponded to the threshold and near-threshold regions where Delta Kth ≤ DeltaK ≤ 11 MPa√m. Fatigue tests in the aqueous solutions showed that the effect of different corrosive environments during high frequency testing (˜100 Hz) was not as pronounced as was expected when compared relative to air. Further testing revealed that environmental effects were present and fatigue crack growth rates were influenced by the fluid-induced closure effects which are generally reported in the fatigue literature to be operative only in viscous liquids, not in aqueous solutions. It was concluded that high frequency testing in aqueous environments consistently decreased crack growth rates in a manner similar to crack retardation effects in viscous fluids. Several theoretical models reported in the literature have underestimated, if not failed, to adequately predict the fluid induced closure in aqueous solutions. Results from the desiccated air tests confirmed that, under closure-free conditions (high R-ratios), both threshold values and fatigue crack growth rate of stage II can be related to Young's modulus, in agreement with results from the literature. The role of different mechanical and environmental variables on fatigue behavior becomes most visible in the low R -ratio regime, and contribute to various closure processes.

Effects of exercise on fatigue, sleep, and performance: a randomized trial.

PubMed

Coleman, Elizabeth Ann; Goodwin, Julia A; Kennedy, Robert; Coon, Sharon K; Richards, Kathy; Enderlin, Carol; Stewart, Carol B; McNatt, Paula; Lockhart, Kim; Anaissie, Elias J

2012-09-01

To compare usual care with a home-based individualized exercise program (HBIEP) in patients receiving intensive treatment for multiple myeloma (MM)and epoetin alfa therapy. Randomized trial with repeated measures of two groups (one experimental and one control) and an approximate 15-week experimental period. Outpatient setting of the Myeloma Institute for Research and Therapy at the Rockfellow Cancer Center at the University of Arkansas for Medical Sciences. 187 patients with newly diagnosed MM enrolled in a separate study evaluating effectiveness of the Total Therapy regimen, with or without thalidomide. Measurements included the Profile of Mood States fatigue scale, Functional Assessment of Cancer Therapy-Fatigue, ActiGraph® recordings, 6-Minute Walk Test, and hemoglobin levels at baseline and before and after stem cell collection. Descriptive statistics were used to compare demographics and treatment effects, and repeated measures analysis of variance was used to determine effects of HBIEP. Fatigue, nighttime sleep, performance (aerobic capacity) as dependent or outcome measures, and HBIEP combining strength building and aerobic exercise as the independent variable. Both groups were equivalent for age, gender, race, receipt of thalidomide, hemoglobin levels, and type of treatment regimen for MM. No statistically significant differences existed among the experimental and control groups for fatigue, sleep, or performance (aerobic capacity). Statistically significant differences (p < 0.05) were found in each of the study outcomes for all patients as treatment progressed and patients experienced more fatigue and poorer nighttime sleep and performance (aerobic capacity). The effect of exercise seemed to be minimal on decreasing fatigue, improving sleep, and improving performance (aerobic capacity). Exercise is safe and has physiologic benefits for patients undergoing MM treatment; exercise combined with epoetin alfa helped alleviate anemia.

Empathy and feelings of guilt experienced by nurses: A cross-sectional study of their role in burnout and compassion fatigue symptoms.

PubMed

Duarte, Joana; Pinto-Gouveia, José

2017-06-01

The main goal of this study was to explore the relationships between empathy, empathy-based pathogenic guilt and professional quality of life (burnout and compassion fatigue). We aim to test a model in which we hypothesize that when empathic feelings are related to pathogenic guilt, burnout and compassion fatigue symptoms may be increased. Empathy is at the core of nursing practice, and has been associated with positive outcomes not only for the healthcare provider but also for the patient. However, empathy is also at the core of guilt feelings that, when excessive and misdirected, can lead to pathogenic guilt beliefs. We focused on two types of empathy-based guilt characterized by excessive responsibility over others' well-being and how these can be related to professional quality of life. This study is a cross-sectional self-report survey. Data were collected during 2014 and 2015. Two hundred ninety-eight nurses from public hospitals in Portugal's north and center region were surveyed. Professional quality of life (burnout and compassion fatigue), empathy, and empathy-based guilt were measured using validated self-report measures. Correlation analyses showed that empathy-based guilt was positively associated with empathy, and with burnout and compassion fatigue. Results from multiple mediation models further indicated when empathy is associated with empathy-based guilt, this leads to greater levels of burnout and compassion fatigue. Given the nature of their work, nurses who experience pathogenic guilt feelings may have compromised well-being, and this should be addressed in training programs aiming at preventing or treating burnout and compassion fatigue. Copyright © 2017 Elsevier Inc. All rights reserved.

Energy efficient engine pin fin and ceramic composite segmented liner combustor sector rig test report

NASA Technical Reports Server (NTRS)

Dubiel, D. J.; Lohmann, R. P.; Tanrikut, S.; Morris, P. M.

1986-01-01

Under the NASA-sponsored Energy Efficient Engine program, Pratt and Whitney has successfully completed a comprehensive test program using a 90-degree sector combustor rig that featured an advanced two-stage combustor with a succession of advanced segmented liners. Building on the successful characteristics of the first generation counter-parallel Finwall cooled segmented liner, design features of an improved performance metallic segmented liner were substantiated through representative high pressure and temperature testing in a combustor atmosphere. This second generation liner was substantially lighter and lower in cost than the predecessor configuration. The final test in this series provided an evaluation of ceramic composite liner segments in a representative combustor environment. It was demonstrated that the unique properties of ceramic composites, low density, high fracture toughness, and thermal fatigue resistance can be advantageously exploited in high temperature components. Overall, this Combustor Section Rig Test program has provided a firm basis for the design of advanced combustor liners.

Program for establishing long-time flight service performance of composite materials in the center wing structure of C-130 aircraft. Phase 1: Advanced development

NASA Technical Reports Server (NTRS)

Harvill, W. E.; Kays, A. O.; Young, E. C.; Mcgee, W. M.

1972-01-01

Areas where selective reinforcement of conventional metallic structure can improve static strength/fatigue endurance at lower weight than would be possible if metal reinforcement were used are discussed. These advantages are now being demonstrated by design, fabrication, and tests of three boron-epoxy reinforced C-130E center wing boxes. This structural component was previously redesigned using an aluminum build-up to meet increased severity of fatigue loadings. Direct comparisons of relative structural weights, manufacturing costs, and producibility can therefore be obtained, and the long-time flight service performance of the composite reinforced structure can be evaluated against the wide background of metal reinforced structure.

All Fatigue is Not Created Equal: The Association of Fatigue and Its Subtypes on Pain Interference in Orofacial Pain.

PubMed

Boggero, Ian A; Rojas-Ramirez, Marcia V; Carlson, Charles R

2017-03-01

Fatigue is known to be a pathway through which depression, psychological distress, pain intensity, and sleep disturbance influence pain interference, but the independent effects of fatigue on pain interference after controlling for these variables remains unknown. In addition, no study to date has tested whether fatigue subtypes of general fatigue, mental fatigue, emotional fatigue, physical fatigue, or vigor differentially predict pain interference. The current study tested these associations using archival medical data of 2133 chronic orofacial pain patients, who completed a battery of psychological questionnaires at the time of their first appointment at an orofacial pain clinic. Hierarchical linear regression analysis revealed that after controlling for depression, psychological distress, sleep disturbance, pain intensity, and demographic variables, fatigue predicted higher pain interference (B=0.70, SE=0.17, P<0.001, η=0.01). Physical fatigue (B=1.70, SE=0.48, P<0.001, η=0.01) and vigor (B=-3.24, SE=0.47, P<0.001, η=0.03) were independently associated with pain interference after controlling for the aforementioned variables. The findings suggest that fatigue is an important independent predictor of pain interference and not merely a mediator. These findings also suggest that not all fatigue is created equal. Interventions aimed at reducing pain interference should target specific fatigue symptoms of physical fatigue and vigor. Future research investigating the independent associations of fatigue subtypes on pain outcomes may help clarify the nature of the interrelationships between pain and fatigue.

The effect of a virtual reality exercise program on physical fitness, body composition, and fatigue in hemodialysis patients.

PubMed

Cho, Hyeyoung; Sohng, Kyeong-Yae

2014-10-01

[Purpose] The aim of the present study was to investigate the effects of a virtual reality exercise program (VREP) on physical fitness, body composition, and fatigue in hemodialysis (HD) patients with end-stage renal failure. [Subjects and Methods] A nonequivalent control group pretest-posttest design was used. Forty-six HD patients were divided into exercise (n=23) and control groups (n=23); while waiting for their dialyses, the exercise group followed a VREP, and the control group received only their usual care. The VREP was accomplished using Nintendo's Wii Fit Plus for 40 minutes, 3 times a week for 8 weeks during the period of May 27 to July 19, 2013. Physical fitness (muscle strength, balance, flexibility), body composition (skeletal muscle mass, body fat rate, arm and leg muscle mass), and fatigue were measured at baseline and after the intervention. [Results] After the VREP, physical fitness and body composition significantly increased, and the level of fatigue significantly decreased in the exercise group. [Conclusion] These results suggest that a VREP improves physical fitness, body composition, and fatigue in HD patients. Based on the findings, VREPs should be used as a health promotion programs for HD patients.

The reliability and validity of fatigue measures during short-duration maximal-intensity intermittent cycling.

PubMed

Glaister, Mark; Stone, Michael H; Stewart, Andrew M; Hughes, Michael; Moir, Gavin L

2004-08-01

The purpose of the present study was to assess the reliability and validity of fatigue measures, as derived from 4 separate formulae, during tests of repeat sprint ability. On separate days over a 3-week period, 2 groups of 7 recreationally active men completed 6 trials of 1 of 2 maximal (20 x 5 seconds) intermittent cycling tests with contrasting recovery periods (10 or 30 seconds). All trials were conducted on a friction-braked cycle ergometer, and fatigue scores were derived from measures of mean power output for each sprint. Apart from formula 1, which calculated fatigue from the percentage difference in mean power output between the first and last sprint, all remaining formulae produced fatigue scores that showed a reasonably good level of test-retest reliability in both intermittent test protocols (intraclass correlation range: 0.78-0.86; 95% likely range of true values: 0.54-0.97). Although between-protocol differences in the magnitude of the fatigue scores suggested good construct validity, within-protocol differences highlighted limitations with each formula. Overall, the results support the use of the percentage decrement score as the most valid and reliable measure of fatigue during brief maximal intermittent work.

Sensitivity, reliability and the effects of diurnal variation on a test battery of field usable upper limb fatigue measures.

PubMed

Yung, Marcus; Wells, Richard P

2017-07-01

Fatigue has been linked to deficits in production quality and productivity and, if of long duration, work-related musculoskeletal disorders. It may thus be a useful risk indicator and design and evaluation tool. However, there is limited information on the test-retest reliability, the sensitivity and the effects of diurnal fluctuation on field usable fatigue measures. This study reports on an evaluation of 11 measurement tools and their 14 parameters. Eight measures were found to have test-retest ICC values greater than 0.8. Four measures were particularly responsive during an intermittent fatiguing condition. However, two responsive measures demonstrated rhythmic behaviour, with significant time effects from 08:00 to mid-afternoon and early evening. Action tremor, muscle mechanomyography and perceived fatigue were found to be most reliable and most responsive; but additional analytical considerations might be required when interpreting daylong responses of MMG and action tremor. Practitioner Summary: This paper presents findings from test-retest and daylong reliability and responsiveness evaluations of 11 fatigue measures. This paper suggests that action tremor, muscle mechanomyography and perceived fatigue were most reliable and most responsive. However, mechanomyography and action tremor may be susceptible to diurnal changes.

Fatigue of restorative materials.

PubMed

Baran, G; Boberick, K; McCool, J

2001-01-01

Failure due to fatigue manifests itself in dental prostheses and restorations as wear, fractured margins, delaminated coatings, and bulk fracture. Mechanisms responsible for fatigue-induced failure depend on material ductility: Brittle materials are susceptible to catastrophic failure, while ductile materials utilize their plasticity to reduce stress concentrations at the crack tip. Because of the expense associated with the replacement of failed restorations, there is a strong desire on the part of basic scientists and clinicians to evaluate the resistance of materials to fatigue in laboratory tests. Test variables include fatigue-loading mode and test environment, such as soaking in water. The outcome variable is typically fracture strength, and these data typically fit the Weibull distribution. Analysis of fatigue data permits predictive inferences to be made concerning the survival of structures fabricated from restorative materials under specified loading conditions. Although many dental-restorative materials are routinely evaluated, only limited use has been made of fatigue data collected in vitro: Wear of materials and the survival of porcelain restorations has been modeled by both fracture mechanics and probabilistic approaches. A need still exists for a clinical failure database and for the development of valid test methods for the evaluation of composite materials.

Microstructural examination of fatigue crack tip in high strength steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukuoka, C.; Yoshizawa, H.; Nakagawa, Y.G.

1993-10-01

Fatigue tests were performed to examine how microstructural conditioning influences crack initiation and propagation in SA508 class 3 low-carbon steel. A 3-mm-long crack was introduced in compact tension (CT) fatigue test specimens under four different loads in order to obtain crack tip plastic zones at different stress intensity factor ranges, [Delta]K = 18, 36, 54, and 72 MPa[radical]m. The microstructure of the plastic zones around the crack tip were examined by transmission electron microscopy (TEM) and selected area electron diffraction (SAD). Micro-orientation of the dislocation cells in the plastic zones of all of the CT samples increased to 4 degmore » from the level of an as-received sample. Four-point bending fatigue tests were performed for plate shape samples with a large cyclic strain range. The SAD value of the bending samples was also 4 deg in the damaged area where cracks already initiated at an early stage of the fatigue process. These test results indicate that the microstructural conditioning is a prerequisite for the fatigue crack initiation and propagation in SA508. These observations may lead to better understanding of how fatigue initiation processes transit to cracks.« less

Environmental Effects on Graphite-Epoxy Fatigue Properties

NASA Technical Reports Server (NTRS)

Sumsion, H. T.

1976-01-01

Effects of torsional and flexural fatigue on the long-time Integrity of advanced graphite-epoxy structural composites have been investigated. Torsional fatigue tests were run at stress ratios of R = 0 (zero to maximum, repeated) and R = -1 (zero mean stress) on unidirectional, angleply, and woven graphite fiber materials in air and water at room temperature and at 74 C. Flexural fatigue tests (four-point bending) with R = -1 were run in air and water at room temperature, and with R = 0 in air. Results show that, in torsional cycling, both water environment and higher test temperature contribute to significant degradation of torsional stiffness. The degradation of stiffness from torsional stress cycling was observed to be much greater with R = -1 than with simple R = 0 cycling. The effect of environment also is greater in the fully reversed cycling. Flexural fatigue results on +/- 30 deg material show a large fatigue effect, with fatigue limits of less than 50% and 30% of the static failure strength for specimens tested under stress ratios of R = 0 and R = -1, respectively. Compliance measurements indicate that the final failures are preceded by damage initiation and accumulation, which begins at about 1% of the specimen life.

Characterization of wear debris generated in accelerated rolling-element fatigue tests

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.; Parker, R. J.

1978-01-01

A ferrographic analysis was used to determine the types and quantities of wear debris generated during accelerated rolling contact fatigue tests. The five-ball rolling contact fatigue tester was used. Ball specimens were made of a corrosion resistant, high-temperature bearing steel. The lubricant was a superrefined naphthenic mineral oil. Conditions included a maximum Hertz stress of 5.52 10 to the 9th power Pa and a shaft speed of 10,000 rpm. Four types of wear debris were observed: (1) normal rubbing wear particles, (2) fatigue microspall particles, (3) spheres, and (4) friction polymer deposits. The characterization of wear debris as a function of time was of limited use in predicting fatigue failures in these accelerated tests.

Fatigue of immature baboon cortical bone.

PubMed

Keller, T S; Lovin, J D; Spengler, D M; Carter, D R

1985-01-01

Strain-controlled uniaxial fatigue and monotonic tensile tests were conducted on turned femoral cortical bone specimens obtained from baboons at various ages of maturity. Fatigue loading produced a progressive loss in stiffness and an increase in hysteresis prior to failure, indicating that immature primate cortical bone responds to repeated loading in a fashion similar to that previously observed for adult human cortical bone. Bone fatigue resistance under this strain controlled testing decreased during maturation. Maturation was also associated with an increase in bone dry density, ash fraction and elastic modulus. The higher elastic modulus of more mature bone meant that these specimens were subjected to higher stress levels during testing than more immature bone specimens. Anatomical regions along the femoral shaft exhibited differences in strength and fatigue resistance.

Influence of neutron irradiation at 430$deg;C on the fatigue properties of SA 316L steel

NASA Astrophysics Data System (ADS)

Vandermeulen, W.; Hendrix, W.; Massaut, V.; Van de Velde, J.

1988-07-01

Fatigue tests have been carried out at 430°C on hour-glass shaped specimens of the CEC reference heat of SA 316L stainless steel. The tests were performed under constant total axial strain control with a triangular fully reversed wave shape at frequencies of 0.5, 0.05 and 0.005 Hz. Specimens irradiated at 430°C to doses of 9-12 dpa and helium contents of 80 to 145 appm showed a fatigue life reduction by about a factor of two, compared to unirradiated specimens. The cyclic stress is found to be strongly increased by the irradiation. The test frequency influences the fatigue hardening slightly but it does not affect the fatigue life.

Machining of Aircraft Titanium with Abrasive-Waterjets for Fatigue Critical Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, H. T.; Hovanski, Yuri; Dahl, Michael E.

2010-10-04

Laboratory tests were conducted to determine the fatigue performance of AWJ-machined aircraft titanium. Dog-bone specimens machined with AWJs were prepared and tested with and without sanding and dry-grit blasting with Al2O3 as secondary processes. The secondary processes were applied to remove the visual appearance of AWJ-generated striations and to clean up the garnet embedment. The fatigue performance of AWJ-machined specimens was compared with baseline specimens machined with CNC milling. Fatigue test results not only confirmed the findings of the aluminum dog-bone specimens but also further enhance the fatigue performance. In addition, titanium is known to be notoriously difficult to cutmore » with contact tools while AWJs cut it 34% faster than stainless steel. AWJ cutting and dry-grit blasting are shown to be a preferred combination for processing aircraft titanium that is fatigue critical.« less

Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.; Ghosn, Louis J.; Kalluri, Sreeramesh

2004-01-01

The development of advanced high performance constant-volume-combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz) in conjunction with the mechanical fatigue loads (10 Hz). The mechanical high cycle fatigue (HCF) testing of some laser pre-exposed specimens has also been conducted under a frequency of 100 Hz to determine the laser surface damage effect. The test results have indicated that material surface oxidation and creep-enhanced fatigue is an important mechanism for the surface crack initiation and propagation under the simulated CVCCE engine conditions.

Rolling-Element Fatigue Testing and Data Analysis - A Tutorial

NASA Technical Reports Server (NTRS)

Vlcek, Brian L.; Zaretsky, Erwin V.

2011-01-01

In order to rank bearing materials, lubricants and other design variables using rolling-element bench type fatigue testing of bearing components and full-scale rolling-element bearing tests, the investigator needs to be cognizant of the variables that affect rolling-element fatigue life and be able to maintain and control them within an acceptable experimental tolerance. Once these variables are controlled, the number of tests and the test conditions must be specified to assure reasonable statistical certainty of the final results. There is a reasonable correlation between the results from elemental test rigs with those results obtained with full-scale bearings. Using the statistical methods of W. Weibull and L. Johnson, the minimum number of tests required can be determined. This paper brings together and discusses the technical aspects of rolling-element fatigue testing and data analysis as well as making recommendations to assure quality and reliable testing of rolling-element specimens and full-scale rolling-element bearings.

A study of fatigue and fracture in 7075-T6 aluminum alloy in vacuum and air environments

NASA Technical Reports Server (NTRS)

Hudson, C. M.

1973-01-01

Axial load fatigue life, fatigue-crack propagation, and fracture toughness experiments were conducted on sheet specimens made of 7075-T6 aluminum alloy. These experiments were conducted at pressures ranging from atmospheric to 5 x 10 to the minus 8th torr. Analysis of the results from the fatigue life experiments indicated that for a given stress level, lower air pressures produced longer fatigue lives. At a pressure of 5 x 10 to the minus 8th torr fatigue lives were 15 or more times as long as at atmospheric pressure. Analysis of the results from the fatigue crack propagation experiments indicated that for small stress intensity factor ranges the fatigue crack propagation rates were up to twice as high at atmospheric pressure as in vacuum. The fracture toughness of 7075-T6 was unaffected by the vacuum environment. Fractographic examination showed that specimens tested in both vacuum and air developed fatigue striations. Considerably more striations developed on specimens tested at atmospheric pressure, however.

Endurance and fatigue characteristics in the neck muscles during sub-maximal isometric test in patients with cervical radiculopathy.

PubMed

Halvorsen, Marie; Abbott, Allan; Peolsson, Anneli; Dedering, Åsa

2014-03-01

The aim of the study was to compare myoelectric manifestation in neck muscle endurance and fatigue characteristics during sub-maximal isometric endurance test in patients with cervical radiculopathy and asymptomatic subjects. An additional aim was to explore associations between primary neck muscle endurance, myoelectric fatigability, and self-rated levels of fatigue, pain and subjective health measurements in patients with cervical radiculopathy. Muscle fatigue in the ventral and dorsal neck muscles was assessed in patients with cervical radiculopathy and in an asymptomatic group during an isometric neck muscle endurance test in prone and supine. 46 patients and 34 asymptomatic subjects participated. Surface electromyography signals were recorded from the sternocleidomastoid, cervical paraspinal muscles and upper and middle trapezius bilaterally during the endurance test. Subjective health measurements were assessed with questionnaires. The results showed altered neck muscle endurance in several of the muscles investigated with greater negative median frequency slope, greater variability, side imbalance, lower endurance time and higher experience of fatigue among the cervical radiculopathy patients compared with healthy subjects. Endurance times were significantly lower in both prone and in supine positions between the patients compared to asymptomatic subjects. During the neck muscle endurance test, fatigues in the upper trapezius muscles during the prone test and in the sternocleidomastoid muscles during the supine test were of more importance than self-perceived pain, fatigue, disability and kinesiophobia in predicting neck muscle endurance (NME). NME testing in the primary neck muscles seems to be an important factor to take into consideration in rehabilitation.

Transverse Tension Fatigue Life Characterization Through Flexure Testing of Composite Materials

NASA Technical Reports Server (NTRS)

OBrien, T. Kevin; Chawan, Arun D.; Krueger, Ronald; Paris, Isabelle

2001-01-01

The transverse tension fatigue life of S2/8552 glass-epoxy and IM7/8552 carbon-epoxy was characterized using flexure tests of 90-degree laminates loaded in 3-point and 4-point bending. The influence of specimen polishing and specimen configuration on transverse tension fatigue life was examined using the glass-epoxy laminates. Results showed that 90-degree bend specimens with polished machined edges and polished tension-side surfaces, where bending failures where observed, had lower fatigue lives than unpolished specimens when cyclically loaded at equal stress levels. The influence of specimen thickness and the utility of a Weibull scaling law was examined using the carbon-epoxy laminates. The influence of test frequency on fatigue results was also documented for the 4-point bending configuration. A Weibull scaling law was used to predict the 4-point bending fatigue lives from the 3-point bending curve fit and vice-versa. Scaling was performed based on maximum cyclic stress level as well as fatigue life. The scaling laws based on stress level shifted the curve fit S-N characterizations in the desired direction, however, the magnitude of the shift was not adequate to accurately predict the fatigue lives. Furthermore, the scaling law based on fatigue life shifted the curve fit S-N characterizations in the opposite direction from measured values. Therefore, these scaling laws were not adequate for obtaining accurate predictions of the transverse tension fatigue lives.

Muscle contractile characteristics: relationship to high-intensity exercise.

PubMed

Morris, Martyn G; Dawes, Helen; Howells, Ken; Scott, Oona M; Cramp, Mary; Izadi, Hooshang

2010-09-01

We investigated the relationship between muscle contractile characteristics, collected using percutaneous electrical stimulation, and high-intensity exercise performance. Seventeen participants performed a muscle performance test for the calculation of rate of torque development (RTD), rate of relaxation (RR(1/2)), rate of fatigue and fatigue resistance. On a second visit the participants completed a Wingate cycle ergometer test with peak power, mean power, fatigue index and fatigue rate calculated. The muscle fatigue index related significantly to the WAnT fatigue index and fatigue rate (p < 0.01). The change in rate of torque development (%DeltaRTD) was also related significantly to the fatigue rate (W/s) during the WAnT. Subjects displaying the greatest reduction in RTD had the greatest fatigue rate during the WAnT and greater fatigue during the electrical stimulation protocol. There were no significant relationships between peak (r 0.36; p > 0.01) or mean power (r -0.11, p > 0.01) with any of the muscle performance measures. These findings demonstrate that muscle contractile characteristics, elicited during standardised in vivo electrical stimulation, relate to performance during a Wingate anaerobic test. They suggest that muscle contraction characteristics play an important role in high-intensity exercise performance and indicate that electrical stimulation protocols can be a useful additional tool to explore muscle contraction characteristics in relation to exercise performance and trainability.

Use of atomic force microscopy for characterizing damage evolution during fatigue

NASA Astrophysics Data System (ADS)

Cretegny, Laurent

2000-10-01

A study of the development of surface fatigue damage in PH 13-8 Mo stainless steel and copper by atomic force microscopy (AFM) was performed. AFM observations allow highly automated, quantitative characterization of surface deformation with a resolution of 5 nm or better, which is ideal for understanding fatigue damage evolution. A secondary objective was to establish a correlation between fatigue life exhausted and impedance spectroscopy. Strain controlled fatigue tests were conducted both in high and low cycle fatigue regimes, and interruptions of the fatigue tests allowed characterizing the evolution of the surface upset at various life-fractions. In the low strain amplitude tests on stainless steel (Deltaepsilonpl/2 = 0.0026%), surface damage occurred in the shape of narrow streaks at the interface between martensite laths where reverted austenite was present. The streaks eventually coalesced to form crack nuclei. In high strain amplitude tests (Deltaepsilon pl/2 = 0.049%), fatigue surface damage was essentially dominated by the formation of extrusions. In copper, both low (Deltaepsilonpl/2 = 0.061%) and high (Deltaepsilonpl/2 = 0.134%) strain amplitude tests showed the formation of slip bands (mainly extrusions) across entire grains. Protrusions were present only in copper specimens tested at the high strain amplitude. Crack nucleation in the low strain amplitude tests occurred in both materials at the interface between a region that sustained a high level of deformation and one with little evidence of surface upset. This commonality between these two materials that are otherwise very dissimilar in nature suggests a universal scheme for location of fatigue crack nucleation sites during HCF. A procedure was developed in this study to quantitatively characterize the amount of irreversible surface strain. The proposed formalism is applicable to any material, independently of the type of surface damage, and leads to a criterion for crack nucleation based on physical evidence of surface damage. A correlation between fatigue damage and impedance spectroscopy measurements was shown in copper, in particular during the primary cyclic hardening stage. The measurements were however less sensitive to the development of surface upset that occurred beyond that stage.

Effectiveness of a group-based self-management program for people with chronic fatigue syndrome: a randomized controlled trial.

PubMed

Pinxsterhuis, Irma; Sandvik, Leiv; Strand, Elin Bolle; Bautz-Holter, Erik; Sveen, Unni

2017-01-01

To evaluate the effectiveness of a group-based self-management program for people with chronic fatigue syndrome. A randomized controlled trial. Four mid-sized towns in southern Norway and two suburbs of Oslo. A total of 137 adults with chronic fatigue syndrome. A self-management program including eight biweekly meetings of 2.5 hours duration. The control group received usual care. Primary outcome measure: Medical Outcomes Study-Short Form-36 physical functioning subscale. Fatigue severity scale, self-efficacy scale, physical and mental component summary of the Short Form-36, and the illness cognition questionnaire (acceptance subscale). Assessments were performed at baseline, and at six-month and one-year follow-ups. At the six-month follow-up, a significant difference between the two groups was found concerning fatigue severity ( p = 0.039) in favor of the control group, and concerning self-efficacy in favor of the intervention group ( p = 0.039). These significant differences were not sustained at the one-year follow-up. No significant differences were found between the groups concerning physical functioning, acceptance, and health status at any of the measure points. The drop-out rate was 13.9% and the median number of sessions attended was seven (out of eight). The evaluated self-management program did not have any sustained effect, as compared with receiving usual care.

Reference values for fatigued versus non-fatigued limb symmetry index measured by a newly designed single-leg hop test battery in healthy subjects: a pilot study.

PubMed

Leister, Iris; Mattiassich, Georg; Kindermann, Harald; Ortmaier, Reinhold; Barthofer, Jürgen; Vasvary, Imre; Katzensteiner, Klaus; Stelzhammer, Christine; Kulnik, Stefan Tino

2018-01-01

There is sparse evidence for return to sport criteria after knee injury. Functional performance deficits, particularly in fatigued muscular condition, should be verified prior to the attempt to return to high-risk pivoting sports. The purpose of this study was to generate reference values for the limb symmetry index (LSI) of healthy subjects in fatigued and non-fatigued muscular condition in a newly designed test battery. Forty-two healthy subjects [22 females, 20 males; mean (SD) age 30.4 (6.6) years] were evaluated using a test battery consisting of an isometric strength test, a series of five single-leg hop tests and an integrated fatigue protocol. Subjective physical activity was assessed with the Tegner Activity Scale (TAS). The cut-off values for healthy subjects were calculated considering the fifth percentile as the minimum reference value for the LSI and single-leg hop distance. The mean (SD) overall LSI was 98.8% (4.6). No significant gender or age specific differences in limb symmetry were observed. The comparison of the non-fatigued LSI with the overall LSI revealed no clinically relevant change due to muscular fatigue. Repeated measures ANOVA revealed a significant within effect on fatigue/non-fatigue condition ( F (1,38)  = 18.000; p  < 0.001, η 2  = 0.321) on absolute single-leg hop distance. Moreover, a significant between effect on the TAS-parameter ( F (1,38)  = 5.928; p  = 0.020, η 2  = 0.135 between: TAS ≤ 5/TAS > 5) and on gender ( F (1,38)  = 23.956; p  < 0.001, η 2  = 0.387) could be detected. The absolute jumping distance in the single-leg hop for distance was significantly reduced due to fatigue. No clinically relevant effect of muscular fatigue was observed on limb symmetry in our study sample. Gender and physical activity are important factors to be considered when interpreting reference values.

The Relationships Between Microstructure, Tensile Properties and Fatigue Life in Ti-5Al-5V-5Mo-3Cr-0.4Fe (Ti-5553)

NASA Astrophysics Data System (ADS)

Foltz, John W., IV

beta-titanium alloys are being increasingly used in airframes as a way to decrease the weight of the aircraft. As a result of this movement, Ti-5Al-5V-5Mo-3Cr-0.4Fe (Timetal 555), a high-strength beta titanium alloy, is being used on the current generation of landing gear. This alloy features good combinations of strength, ductility, toughness and fatigue life in alpha+beta processed conditions, but little is known about beta-processed conditions. Recent work by the Center for the Accelerated Maturation of Materials (CAMM) research group at The Ohio State University has improved the tensile property knowledge base for beta-processed conditions in this alloy, and this thesis augments the aforementioned development with description of how microstructure affects fatigue life. In this work, beta-processed microstructures have been produced in a Gleeble(TM) thermomechanical simulator and subsequently characterized with a combination of electron and optical microscopy techniques. Four-point bending fatigue tests have been carried out on the material to characterize fatigue life. All the microstructural conditions have been fatigue tested with the maximum test stress equal to 90% of the measured yield strength. The subsequent results from tensile tests, fatigue tests, and microstructural quantification have been analyzed using Bayesian neural networks in an attempt to predict fatigue life using microstructural and tensile inputs. Good correlation has been developed between lifetime predictions and experimental results using microstructure and tensile inputs. Trained Bayesian neural networks have also been used in a predictive fashion to explore functional dependencies between these inputs and fatigue life. In this work, one section discusses the thermal treatments that led to the observed microstructures, and the possible sequence of precipitation that led to these microstructures. The thesis then describes the implications of microstructure on fatigue life and implications of tensile properties on fatigue life. Several additional experiments are then described that highlight possible causes for the observed dependence of microstructure on fatigue life, including fractographic evidence to provide support of microstructural dependencies.

Goals Set After Completing a Teleconference-Delivered Program for Managing Multiple Sclerosis Fatigue

PubMed Central

Asano, Miho; Preissner, Katharine; Duffy, Rose; Meixell, Maggie

2015-01-01

Setting goals can be a valuable skill to self-manage multiple sclerosis (MS) fatigue. A better understanding of the goals set by people with MS after completing a fatigue management program can assist health care professionals with tailoring interventions for clients. This study aimed to describe the focus of goals set by people with MS after a teleconference-delivered fatigue management program and to evaluate the extent to which participants were able to achieve their goals over time. In total, 485 goals were set by 81 participants. Over a follow-up period, 64 participants rated 284 goals regarding progress made toward goal achievement. Approximately 50% of the rated goals were considered achieved. The most common type of goal achieved was that of instrumental activities of daily living. Short-term goals were more likely to be achieved. This study highlights the need for and importance of promoting and teaching goal-setting skills to people with MS. PMID:25871602

Evaluating the Effectiveness of Fatigue Management Training to Improve Police Sleep Health and Wellness: A Pilot Study.

PubMed

James, Lois; Samuels, Charles H; Vincent, Fiona

2018-01-01

To evaluate the effectiveness of an intervention for improving sleep health in a sample of employees from the Royal Canadian Mounted Police (RCMP). Using a pre- and post-design we exposed 61 RCMP members to a fatigue-management training program. Pre- and post-intervention surveys included the Pittsburg Sleep Quality Index (PSQI), the World Health Organization Quality of Life (WHOQOL) instrument, and the six item index of psychological distress (Symptom Checklist-90). We found the training improved member satisfaction with sleep (Wald = 2.58; df = 1; P = 0.03) and reduced symptoms of insomnia (Wald = 5.5; df = 1; P = 0.02). Furthermore, the training reduced the incidence of headaches (Wald = 6.5; df = 1; P = 0.01). Our findings suggest that a fatigue management training program resulted in positive sleep health benefits for police. We stress the importance of continued evaluation to inform the large-scale implementation of fatigue-management programs.

Effect of lubricant extreme-pressure additives on surface fatigue life of AISI 9310 spur gears

NASA Technical Reports Server (NTRS)

Scibbe, H. W.; Townsend, D. P.; Aron, P. R.

1984-01-01

Surface fatigue tests were conducted with AISI 9310 spur gears using a formulated synthetic tetraester oil (conforming to MIL-L-23699 specifications) as the lubricant containing either sulfur or phosphorus as the EP additive. Four groups of gears were tested. One group of gears tested without an additive in the lubricant acted as the reference oil. In the other three groups either a 0.1 wt % sulfur or phosphorus additive was added to the tetraester oil to enhance gear surface fatigue life. Test conditions included a gear temperature of 334 K (160 F), a maximum Hertz stress of 1.71 GPa (248 000 psi), and a speed of 10,000 rpm. The gears tested with a 0.1 wt % phosphorus additive showed pitting fatigue life 2.6 times the life of gears tested with the reference tetraester based oil. Although fatigue lives of two groups of gears tested with the sulfur additive in the oil showed improvement over the control group gear life, the results, unlike those obtained with the phosphorus oil, were not considered to be statistically significant.

Effect of interlaminar normal stresses on the uniaxial zero-to-tension fatigue behavior of graphite/epoxy tubes

NASA Technical Reports Server (NTRS)

Krempl, Erhard; An, Deukman

1991-01-01

Fatigue tests conducted with and without internal pressure have been found to possess approximately the same fatigue life as (+/-45)s graphite/epoxy tubes for zero-to-tension axial load-controlled conditions on an axial torsion servohydraulic apparatus. These tests therefore cannot be considered as confirmations of the suspected detrimental effect of interlaminar tensile stresses on the fatigue performance of thin-walled tubes. The addition of 90-deg plies on both the inside and the outside is found to significantly improve the tubes' static and fatigue strengths.

Reliability improvement of wire bonds subjected to fatigue stresses.

NASA Technical Reports Server (NTRS)

Ravi, K. V.; Philofsky, E. M.

1972-01-01

The failure of wire bonds due to repeated flexure when semiconductor devices are operated in an on-off mode has been investigated. An accelerated fatigue testing apparatus was constructed and the major fatigue variables, aluminum alloy composition, and bonding mechanism, were tested. The data showed Al-1% Mg wires to exhibit superior fatigue characteristics compared to Al-1% Cu or Al-1% Si and ultrasonic bonding to be better than thermocompression bonding for fatigue resistance. Based on these results highly reliable devices were fabricated using Al-1% Mg wire with ultrasonic bonding which withstood 120,000 power cycles with no failures.

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.

Crack Initiation and Growth Behavior at Corrosion Pit in 7075-T6 Under Biaxial and Uniaxial Fatigue

DTIC Science & Technology

2014-06-19

al. examined the effect of biaxial loading on the fatigue crack growth [52]. They conducted their fatigue tests on SUS 304 stainless steel using a...specimens. Their experiments were carried out on cruciform test coupons using a digitally controlled four actuator biaxial testing system. Steel ...as shown in Figure 3.7. The test specimen was placed between two stainless steel chambers. These chambers were connected together using screws, and

Design and fabrication of prototype system for early warning of impending bearing failure

NASA Technical Reports Server (NTRS)

Meacher, J.; Chen, H. M.

1974-01-01

A test program was conducted with the objective of developing a method and equipment for on-line monitoring of installed ball bearings to detect deterioration or impending failure of the bearings. The program was directed at the spin-axis bearings of a control moment gyro. The bearings were tested at speeds of 6000 and 8000 rpm, thrust loads from 50 to 1000 pounds, with a wide range of lubrication conditions, with and without a simulated fatigue spall implanted in the inner race ball track. It was concluded that a bearing monitor system based on detection and analysis of modulations of a fault indicating bearing resonance frequency can provide a low threshold of sensitivity.

Overload and Underload Effects on the Fatigue Crack Growth Behavior of the 2024-T3 Aluminum Alloy

NASA Technical Reports Server (NTRS)

Dawicke, David S.

1997-01-01

Fatigue crack growth tests were conducted on 0.09 inch thick, 3.0 inch wide middle-crack tension specimens cut from sheets of 2024-T3 aluminum alloy. The tests were conducted using a load sequence that consisted of a single block of 2,500 cycles of constant amplitude loading followed by an overload/underload combination. The largest fatigue crack growth life occurred for the tests with the overload stress equal to 2 times the constant amplitude stress and the underload stress equal to the constant amplitude minimum stress. For the tests with compressive underloads, the fatigue crack growth life decreased with increasing compressive underload stress.

New method of determination of spot welding-adhesive joint fatigue life using full field strain evolution

NASA Astrophysics Data System (ADS)

Sadowski, T.; Kneć, M.

2016-04-01

Fatigue tests were conducted since more than two hundred years ago. Despite this long period, as fatigue phenomena are very complex, assessment of fatigue response of standard materials or composites still requires a long time. Quite precise way to estimate fatigue parameters is to test at least 30 standardized specimens for the analysed material and further statistical post processing is required. In case of structural elements analysis like hybrid joints (Figure 1), the situation is much more complex as more factors influence the fatigue load capacity due to much more complicated structure of the joint in comparison to standard materials specimen, i.e. occurrence of: welded hot spots or rivets, adhesive layers, local notches creating the stress concentrations, etc. In order to shorten testing time some rapid methods are known: Locati's method [1] - step by step load increments up to failure, Prot's method [2] - constant increase of the load amplitude up to failure; Lehr's method [2] - seeking for the point during regular fatigue loading when an increase of temperature or strains become non-linear. The present article proposes new method of the fatigue response assessment - combination of the Locati's and Lehr's method.

Postural Balance Following Aerobic Fatigue Tests: A Longitudinal Study Among Young Athletes.

PubMed

Steinberg, Nili; Eliakim, Alon; Zaav, Aviva; Pantanowitz, Michal; Halumi, Monder; Eisenstein, Tamir; Meckel, Yoav; Nemet, Dan

2016-01-01

General fatigue can cause aggravation of postural balance, with increased risk for injuries. The present longitudinal study aimed to evaluate the postural balance of young athletes following field aerobic tests throughout 1 year of training. Thirty children from a sports center in Nazareth, participating in a 3 times/week training program (specific to basketball, soccer, or athletic training), were assessed. Postural balance parameters were taken before, immediately after, and 10 min after a 20 m shuttle-run aerobic test, at 3 time points during 1 training year (Start/Y, Mid/Y, and End/Y). Fitness improved at the Mid/Y and End/Y compared to Start/Y. Postural balance significantly deteriorated immediately after the aerobic test and improved significantly in the 10-min testing in all 3 time points, with significant deterioration in the End/Y compared with the Start/Y. In conclusions, postural balance deteriorates immediately after aerobic exercises, and at the end of the year. To better practice drills related to postural balance and possibly to prevent injuries, it is best for young athletes to properly rest immediately following aerobic exercises and to practice postural balance mainly at the beginning and at the middle of the training year.

Development of an improved method of consolidating fatigue life data

NASA Technical Reports Server (NTRS)

Leis, B. N.; Sampath, S. G.

1978-01-01

A fatigue data consolidation model that incorporates recent advances in life prediction methodology was developed. A combined analytic and experimental study of fatigue of notched 2024-T3 aluminum alloy under constant amplitude loading was carried out. Because few systematic and complete data sets for 2024-T3 were available in the program generated data for fatigue crack initiation and separation failure for both zero and nonzero mean stresses. Consolidations of these data are presented.

Load-Differential Imaging for Detection and Localization of Fatigue Cracks Using Lamb Waves (Preprint)

DTIC Science & Technology

2012-03-01

AFRL-RX-WP-TP-2012-0278 LOAD-DIFFERENTIAL IMAGING FOR DETECTION AND LOCALIZATION OF FATIGUE CRACKS USING LAMB WAVES (PREPRINT) X. Chen...OF FATIGUE CRACKS USING LAMB WAVES (PREPRINT) 5a. CONTRACT NUMBER FA8650-09-C-5206 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 62102F 6...Jan 2012. Preprint journal article to be submitted to NDT & E. This document contains color. 14. ABSTRACT Fatigue cracks are common and

TS-SRP/PACK - COMPUTER PROGRAMS TO CHARACTERIZE ALLOYS AND PREDICT CYCLIC LIFE USING THE TOTAL STRAIN VERSION OF STRAINRANGE PARTITIONING

NASA Technical Reports Server (NTRS)

Saltsman, J. F.

1994-01-01

TS-SRP/PACK is a set of computer programs for characterizing and predicting fatigue and creep-fatigue resistance of metallic materials in the high-temperature, long-life regime for isothermal and nonisothermal fatigue. The programs use the total strain version of the Strainrange Partitioning (TS-SRP). The user should be thoroughly familiar with the TS-SRP method before attempting to use any of these programs. The document for this program includes a theory manual as well as a detailed user's manual with a tutorial to guide the user in the proper use of TS-SRP. An extensive database has also been developed in a parallel effort. This database is an excellent source of high-temperature, creep-fatigue test data and can be used with other life-prediction methods as well. Five programs are included in TS-SRP/PACK along with the alloy database. The TABLE program is used to print the datasets, which are in NAMELIST format, in a reader friendly format. INDATA is used to create new datasets or add to existing ones. The FAIL program is used to characterize the failure behavior of an alloy as given by the constants in the strainrange-life relations used by the total strain version of SRP (TS-SRP) and the inelastic strainrange-based version of SRP. The program FLOW is used to characterize the flow behavior (the constitutive response) of an alloy as given by the constants in the flow equations used by TS-SRP. Finally, LIFE is used to predict the life of a specified cycle, using the constants characterizing failure and flow behavior determined by FAIL and FLOW. LIFE is written in interpretive BASIC to avoid compiling and linking every time the equation constants are changed. Four out of five programs in this package are written in FORTRAN 77 for IBM PC series and compatible computers running MS-DOS and are designed to read data using the NAMELIST format statement. The fifth is written in BASIC version 3.0 for IBM PC series and compatible computers running MS-DOS version 3.10. The executables require at least 239K of memory and DOS 3.1 or higher. To compile the source, a Lahey FORTRAN compiler is required. Source code modifications will be necessary if the compiler to be used does not support NAMELIST input. Probably the easiest revision to make is to use a list-directed READ statement. The standard distribution medium for this program is a set of two 5.25 inch 360K MS-DOS format diskettes. The contents of the diskettes are compressed using the PKWARE archiving tools. The utility to unarchive the files, PKUNZIP.EXE, is included. TS-SRP/PACK was developed in 1992.

Exercise capacity, muscle strength and fatigue in sarcoidosis.

PubMed

Marcellis, R G J; Lenssen, A F; Elfferich, M D P; De Vries, J; Kassim, S; Foerster, K; Drent, M

2011-09-01

The aim of this case-control study was to investigate the prevalence of exercise intolerance, muscle weakness and fatigue in sarcoidosis patients. Additionally, we evaluated whether fatigue can be explained by exercise capacity, muscle strength or other clinical characteristics (lung function tests, radiographic stages, prednisone usage and inflammatory markers). 124 sarcoidosis patients (80 males) referred to the Maastricht University Medical Centre (Maastricht, the Netherlands) were included (mean age 46.6±10.2 yrs). Patients performed a 6-min walk test (6MWT) and handgrip force (HGF), elbow flexor muscle strength (EFMS), quadriceps peak torque (QPT) and hamstring peak torque (HPT) tests. Maximal inspiratory pressure (P(I,max)) was recorded. All patients completed the Fatigue Assessment Scale (FAS) questionnaire. The 6MWT was reduced in 45% of the population, while HGF, EFMS, QPT and HPT muscle strength were reduced in 15, 12, 27 and 18%, respectively. P(I,max) was reduced in 43% of the population. The majority of the patients (81%) reported fatigue (FAS ≥22). Patients with reduced peripheral muscle strength of the upper and/or lower extremities were more fatigued and demonstrated impaired lung functions, fat-free mass, P(I,max), 6MWT and quality of life. Fatigue was neither predicted by exercise capacity, nor by muscle strength. Besides fatigue, exercise intolerance and muscle weakness are frequent problems in sarcoidosis. We therefore recommend physical tests in the multidisciplinary management of sarcoidosis patients, even in nonfatigued patients.