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1

Mitigation Of Fretting Fatigue Damage In Blade And Disk Pressure Faces With Low Plasticity Burnishing  

Microsoft Academic Search

Low Plasticity Burnishing (LPB) is now established as a surface enhancement technology capable of introducing through-thickness compressive residual stresses in the edges of gas turbine engine blades and vanes to mitigate foreign object damage (FOD). The \\

Paul S. Prevéy; N. Jayaraman; Michael Shepard

2007-01-01

2

FATIGUE CHARACTERIZATION OF A VAWT BLADE MATERIAL  

Microsoft Academic Search

The fatigue analysis of Wind Energy Conversion System blades has been limited by the lack of fatigue data for typical blade materials, tncluding 6063 aluminum. an alloy commonly used for Vertical Axis Wind Turbine (VAWTI blades. This paper reports results to date of a testing program to establish a fatigue properties database for this alloy. TWO -s of fatigue response

J. A. Van; Den Avyle; H. J. Sutherland

3

Fatigue of fiberglass wind turbine blade materials.  

National Technical Information Service (NTIS)

Fatigue behavior for a variety of generic materials used in wind turbine blades has been explored. Coupon testing was carried out under constant amplitude tensile fatigue loading to beyond 10(sup 7) cycles for most materials. Unidirectional materials perf...

J. F. Mandell R. M. Reed D. D. Samborsky

1992-01-01

4

Simulation of fatigue failure in composite axial compressor blades  

Microsoft Academic Search

Centrifugal forces are generated by a spinning impeller, of magnitudes that create large stresses. Aerodynamic forces are also imparted on an impeller blade, which varies with time and position. These two forces play different roles during compressor events. Damage accumulated from these events results in the fatigue failure of impeller material and structure. Therefore, it is important to design an

Qubo Li; Janusz Piechna; Norbert Müeller

2011-01-01

5

Fatigue Evaluation of WTS-3 Wind Turbine Blade and Retention.  

National Technical Information Service (NTIS)

The WTS-3 wind turbine blade and retention computed stress levels are compared to material properties, and potentially fatigue critical areas are identified. For the blade, these are flatwise spar stresses, and blade shell flatwise stresses. It is not pos...

A. I. Gustavsson A. F. Blom

1987-01-01

6

Composite blade damaging under impact  

NASA Astrophysics Data System (ADS)

Composites materials are now being used in primary aircraft structures, and other domains because of numerous advantages. A part of a continuous in-flight operating costs, gas turbine engine manufacturers are always looking for ways to decrease engine weight. This is the case of compressor blades which have to satisfy, for example, the standard bird strike or debris in order to measure the crashworthiness. Bird strike impacts are actually among the most challenging loads that composite blades must accommodate. Thus for the further development of composite structures, it becomes important to have available predictive tools for simulating the response of composite structures under crash or impact loads, which will allow to evaluate damage state in the structure in function of time. A composites damage model, without mesh dependency, is presented, and allows to obtain agreement with impact experiment. Examples of finite element simulations for the impact response of blade based on this materials model are developped. These numerical results correspond to a bird strike on an equivalent composites blade, and insists on damage evolution in structure.

Menouillard, T.; Réthoré, J.; Bung, H.; Suffis, A.

2006-08-01

7

Simple method of estimating wind turbine blade fatigue at potential wind turbine sites.  

National Technical Information Service (NTIS)

This paper presents a technique of estimating blade fatigue damage at potential wind turbine sites. The cornerstone of this technique is a simple model for the blade's root flap bending moment. The model requires as input a simple set of wind measurements...

J. C. Barnard L. L. Wendell

1995-01-01

8

Approach to the fatigue analysis of vertical-axis wind-turbine blades  

SciTech Connect

A cursory analysis of the stress history of wind turbine blades indicates that a single stress level at each wind speed does not adequately describe the blade stress history. A statistical description is required. Blade stress data collected from the DOE/ALCOA Low Cost experimental turbines indicate that the Rayleigh probability density function adequately describes the distribution of vibratory stresses at each wind speed. The Rayleigh probability density function allows the distribution of vibratory stresses to be described by the RMS of the stress vs. time signal. With the RMS stress level described for all wind speeds, the complete stress history of the turbine blades is known. Miner's linear cumulative damage rule is used as a basis for summing the fatigue damage over all operating conditions. An analytical expression is derived to predict blade fatigue life.

Veers, P.S.

1981-09-01

9

Recrystallization and fatigue fracture of single crystal turbine blades  

Microsoft Academic Search

Two rotor blades in an aero-engine fractured during testing. The fracture mode and cause were analyzed on the basis of fracture surface observation, chemical analysis, and metallurgical structure examination. The results show that the two blades failed in the same mode – fatigue fracture caused by recrystallization. In order to find out the cause of recrystallization, simulation tests were carried

Y. H. He; X. Q. Hou; C. H. Tao; F. K. Han

2011-01-01

10

Application of the U.S. high cycle fatigue data base to wind turbine blade lifetime predictions  

SciTech Connect

This paper demonstrates a methodology for predicting the service lifetime of wind turbine blades using the high-cycle fatigue data base for typical U.S. blade materials developed by Mandell, et al. (1995). The first step in the analysis is to normalize the data base (composed primarily of data obtained from specialized, relatively small coupons) with fatigue data from typical industrial laminates to obtain a Goodman Diagram that is suitable for analyzing wind turbine blades. The LIFE2 fatigue analysis code for wind turbines is then used for the fatigue analysis of a typical turbine blade with a known load spectrum. In the analysis, a linear damage model, Miner`s Rule, is used to demonstrate the prediction of the service lifetime for a typical wind turbine blade under assumed operating strain ranges and stress concentration factors. In contrast to typical European data, the asymmetry in this data base predicts failures under typical loads to be compressive.

Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States); Mandell, J.F. [Montana State Univ., Bozeman, MT (United States)

1995-12-01

11

Effects of FOD on the fatigue crack initiation of ballistically impacted titanium-aluminum(6)-vanadium(4) simulated engine blades  

Microsoft Academic Search

Nicks and dents caused by foreign object damage (FOD) in leading edges of turbine engine blades often provide crack initiation sites that may grow under high cycle fatigue (HCF) conditions and lead to reduced life. Leading edge specimens simulating the geometry of these engine blades were fabricated from STOA Ti-6Al-4V. The leading edges were then ballistically impacted with small steel

Janine C. Birkbeck

2002-01-01

12

Full-scale fatigue tests of CX-100 wind turbine blades. Part II: analysis  

NASA Astrophysics Data System (ADS)

This paper presents the initial analysis results of several structural health monitoring (SHM) methods applied to two 9- meter CX-100 wind turbine blades subjected to fatigue loading at the National Renewable Energy Laboratory's (NREL) National Wind Technology Center (NWTC). The first blade was a pristine blade, manufactured to standard CX-100 design specifications. The second blade was manufactured for the University of Massachusetts, Lowell (UMass), with intentional simulated defects within the fabric layup. Each blade was instrumented with a variety of sensors on its surface. The blades were subject to harmonic excitation at their first natural frequency with steadily increasing loading until ultimately reaching failure. Data from the sensors were collected between and during fatigue loading sessions. The data were measured at multi-scale frequency ranges using a variety of data acquisition equipment, including off-the-shelf systems and prototype data acquisition hardware. The data were analyzed to identify fatigue damage initiation and to assess damage progression. Modal response, diffuse wave-field transfer functions in time and frequency domains, and wave propagation methods were applied to assess the condition of the turbine blade. The analysis methods implemented were evaluated in conjunction with hardware-specific performance for their efficacy in enabling the assessment of damage progression in the blade. The results of this assessment will inform the selection of specific data to be collected and analysis methods to be implemented for a CX-100 flight test to be conducted in collaboration with Sandia National Laboratory at the U.S. Department of Agriculture's (USDA) Conservation and Production Research Laboratory (CPRL) in Bushland, Texas.

Taylor, Stuart G.; Jeong, Hyomi; Jang, Jae Kyeong; Park, Gyuhae; Farinholt, Kevin M.; Todd, Michael D.; Ammerman, Curtt M.

2012-03-01

13

Acoustic emission monitoring of a wind turbine blade during a fatigue test  

SciTech Connect

A fatigue test of a wind turbine blade was conducted at the National Renewable Energy Laboratory in the fall of 1994. Acoustic emission monitoring of the test was performed, starting with the second loading level. The acoustic emission data indicated that this load exceeded the strength of the blade. From the first cycle at the new load, an oil can type of deformation occurred in two areas of the upper skin of the blade. One of these was near the blade root and the other was about the middle of the tested portion of the blade. The emission monitoring indicated that no damage was taking place in the area near the root, but in the deforming area near the middle of the blade, damage occurred from the first cycles at the higher load. The test was stopped after approximately one day and the blade was declared destroyed, although no gross damage had occurred. Several weeks later the test was resumed, to be continued until gross damage occurred. The upper skin tore approximately one half hour after the cycling was restarted.

Beattie, A.G.

1997-01-01

14

Helicopter rotor blade frequency evolution with damage growth and signal processing  

Microsoft Academic Search

Structural damage in materials evolves over time due to growth of fatigue cracks in homogenous materials and a complicated process of matrix cracking, delamination, fiber breakage and fiber matrix debonding in composite materials. In this study, a finite element model of the helicopter rotor blade is used to analyze the effect of damage growth on the modal frequencies in a

Niranjan Roy; Ranjan Ganguli

2005-01-01

15

Early Detection of Fatigue Damage.  

National Technical Information Service (NTIS)

The report describes the continuing effort to develop nondestructive test methods capable of determining the extent of fatigue damage and providing a means of predicting the future safe life of aerospace materials and structures. During the report period,...

D. S. Weinstein F. M. Coate J. F. Moore S. Hoenig S. Tsang

1970-01-01

16

Wind turbine blade fatigue tests: lessons learned and application to SHM system development  

SciTech Connect

This paper presents experimental results of several structural health monitoring (SHM) methods applied to a 9-meter CX-100 wind turbine blade that underwent fatigue loading. The blade was instrumented with piezoelectric transducers, accelerometers, acoustic emission sensors, and foil strain gauges. It underwent harmonic excitation at its first natural frequency using a hydraulically actuated resonant excitation system. The blade was initially excited at 25% of its design load, and then with steadily increasing loads until it failed. Various data were collected between and during fatigue loading sessions. The data were measured over multiple frequency ranges using a variety of acquisition equipment, including off-the-shelf systems and specially designed hardware developed by the authors. Modal response, diffuse wave-field transfer functions, and ultrasonic guided wave methods were applied to assess the condition of the wind turbine blade. The piezoelectric sensors themselves were also monitored using a sensor diagnostics procedure. This paper summarizes experimental procedures and results, focusing particularly on fatigue crack detection, and concludes with considerations for implementing such damage identification systems, which will be used as a guideline for future SHM system development for operating wind turbine blades.

Taylor, Stuart G. [Los Alamos National Laboratory; Farinholt, Kevin M. [Los Alamos National Laboratory; Jeong, Hyomi [Chonbuk National University, Korea; Jang, JaeKyung [Chonbuk National University, Korea; Park, Gyu Hae [Los Alamos National Laboratory; Todd, Michael D. [Los Alamos National Laboratory; Farrar, Charles R. [Los Alamos National Laboratory; Ammerman, Curtt N. [Los Alamos National Laboratory

2012-06-28

17

Early Detection of Fatigue Damage.  

National Technical Information Service (NTIS)

The report is the final technical report for a program directed at the development of nondestructive test (NDT) methods for the detection of early fatigue and fracture damage in metals and alloys. The program is based on an interdisciplinary approach desi...

G. Martin J. F. Mooer S. Tsang

1971-01-01

18

Microcrack growth behavior and life in high temperature low cycle fatigue of blade root and disc joint for turbines  

Microsoft Academic Search

Low cycle fatigue tests were carried out at a temperature of 600°C using a component specimen of 12%-Cr steel, which simulates a blade root and disc joint for turbines. The growth behavior of micro-cracks in the joint region of the specimens was investigated to clarify the damage mechanism of blade-root joints used in high temperature environments and to improve life

Nobuhiro Isobe; Shuhei Nogami

2009-01-01

19

High Frequency Fatigue of Turbine Blade Material.  

National Technical Information Service (NTIS)

This increased fatigue crack growth rate at elevated temperature due to high frequency loading is examined. The crack growth rate is found to depend upon major cycle stress intensity factor, hold-time and minor cycle frequency, and amplitude for a given t...

R. C. Goodman A. M. Brown

1982-01-01

20

Microstructural evaluation of cumulative fatigue damage below the fatigue limit  

SciTech Connect

The objective of this work is to evaluate the microstructural changes induced near and below the fatigue limit in a pressure vessel steel plate, SA508. Dislocation cell to cell misorientation differences, {theta}, which increase with fatigue damage accumulation, are measured by the Selected Area Diffraction (SAD) method. The misorientation difference, {theta}, of the sample failed just above the fatigue limit is about 4.0 degrees on the average, which is about the same as that for the failure conditions of low cycle fatigue at higher stresses. The {theta} value increases even below the fatigue limit, but it does not increase at stresses which are lower than 50% of the fatigue limit.

Fukuoka, C.; Nakagawa, Y.G. [IHI, Tokyo (Japan). Research Inst.

1996-05-01

21

Analysis of Fretting Fatigue Strength of Integral Shroud Blade for Steam Turbine  

NASA Astrophysics Data System (ADS)

To improve the reliability and the thermal efficiency of LP (Low Pressure) end blades of steam turbine, new standard series of LP end blades have been developed. The new LP end blades are characterized by the ISB (Integral Shroud Blade) structure. In the ISB structure, blades are continuously coupled by blade untwist due to centrifugal force when the blades rotate at high speed. One of the probable failure modes of the ISB structure seems to be fretting fatigue, because the ISB utilizes friction damping between adjacent shrouds and stubs. Therefore, in order to design a blade with high reliability, the design procedure for evaluating the fretting fatigue strength was established by the model test and the nonlinear contact analysis. This paper presents the practical design method for predicting the fretting fatigue strength of the ISB structure, and the some applications are explained.

Kaneko, Yasutomo; Tomii, Masayuki; Ohyama, Hiroharu; Kurimura, Takayuki

22

The influence of crystal orientations on fatigue life of single crystal cooled turbine blade  

Microsoft Academic Search

A method based on the orthotropic elastic finite element analysis (FEA) has been presented to analyze the fatigue life of cooled turbine blades made of nickel-based single crystal superalloy (SC). Special attention was put on the influence of the crystallographic orientations on the strength and fatigue life of SC cooled turbine blades. It is shown that, due to the influence

N. X. Hou; W. X. Gou; Z. X. Wen; Z. F. Yue

2008-01-01

23

ADVANCED COMPOSITE WIND TURBINE BLADE DESIGN BASED ON DURABILITY AND DAMAGE TOLERANCE  

SciTech Connect

The objective of the program was to demonstrate and verify Certification-by-Analysis (CBA) capability for wind turbine blades made from advanced lightweight composite materials. The approach integrated durability and damage tolerance analysis with robust design and virtual testing capabilities to deliver superior, durable, low weight, low cost, long life, and reliable wind blade design. The GENOA durability and life prediction software suite was be used as the primary simulation tool. First, a micromechanics-based computational approach was used to assess the durability of composite laminates with ply drop features commonly used in wind turbine applications. Ply drops occur in composite joints and closures of wind turbine blades to reduce skin thicknesses along the blade span. They increase localized stress concentration, which may cause premature delamination failure in composite and reduced fatigue service life. Durability and damage tolerance (D&DT) were evaluated utilizing a multi-scale micro-macro progressive failure analysis (PFA) technique. PFA is finite element based and is capable of detecting all stages of material damage including initiation and propagation of delamination. It assesses multiple failure criteria and includes the effects of manufacturing anomalies (i.e., void, fiber waviness). Two different approaches have been used within PFA. The first approach is Virtual Crack Closure Technique (VCCT) PFA while the second one is strength-based. Constituent stiffness and strength properties for glass and carbon based material systems were reverse engineered for use in D&DT evaluation of coupons with ply drops under static loading. Lamina and laminate properties calculated using manufacturing and composite architecture details matched closely published test data. Similarly, resin properties were determined for fatigue life calculation. The simulation not only reproduced static strength and fatigue life as observed in the test, it also showed composite damage and fracture modes that resemble those reported in the tests. The results show that computational simulation can be relied on to enhance the design of tapered composite structures such as the ones used in turbine wind blades. A computational simulation for durability, damage tolerance (D&DT) and reliability of composite wind turbine blade structures in presence of uncertainties in material properties was performed. A composite turbine blade was first assessed with finite element based multi-scale progressive failure analysis to determine failure modes and locations as well as the fracture load. D&DT analyses were then validated with static test performed at Sandia National Laboratories. The work was followed by detailed weight analysis to identify contribution of various materials to the overall weight of the blade. The methodology ensured that certain types of failure modes, such as delamination progression, are contained to reduce risk to the structure. Probabilistic analysis indicated that composite shear strength has a great influence on the blade ultimate load under static loading. Weight was reduced by 12% with robust design without loss in reliability or D&DT. Structural benefits obtained with the use of enhanced matrix properties through nanoparticles infusion were also assessed. Thin unidirectional fiberglass layers enriched with silica nanoparticles were applied to the outer surfaces of a wind blade to improve its overall structural performance and durability. The wind blade was a 9-meter prototype structure manufactured and tested subject to three saddle static loading at Sandia National Laboratory (SNL). The blade manufacturing did not include the use of any nano-material. With silica nanoparticles in glass composite applied to the exterior surfaces of the blade, the durability and damage tolerance (D&DT) results from multi-scale PFA showed an increase in ultimate load of the blade by 9.2% as compared to baseline structural performance (without nano). The use of nanoparticles lead to a delay in the onset of delamination. Load-displacement relati

Galib Abumeri; Frank Abdi (PhD)

2012-02-16

24

Cumulative fatigue damage in low cycle fatigue and gigacycle fatigue for low carbon–manganese steel  

Microsoft Academic Search

Typical tee and pipe components are subjected to thermal and mechanical loading histories which are variable and divided into two different regimes: low cycle fatigue and high cycle fatigue in steam generator vessel of nuclear power plants.Carbon–manganese steel A42 are often used in such applications. In order to investigate the cumulative damage of low cycle fatigue and gigacycle fatigue, the

Zhi Yong Huang; Danièle Wagner; Claude Bathias; Jean Louis Chaboche

2011-01-01

25

Fatigue and damage tolerance scatter models  

NASA Astrophysics Data System (ADS)

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

Raikher, Veniamin L.

1994-09-01

26

Thermal activation of fatigue damage  

Microsoft Academic Search

The effect of temperature on the fatigue of aluminum alloys results from a combination of thermally induced changes in the\\u000a microstructure and the intrinsic temperature dependence of the fatigue process. These two effects are separated for the first\\u000a time, and it is shown that the intrinsic fatigue process is thermally activated. Two distinct regimes are identified. For\\u000a fatigue lives 6

William J. Baxter; Donald R. Lesuer; Chol K. Syn

2000-01-01

27

Fatigue damage of human tendons  

Microsoft Academic Search

The study was designed to examine the effects of partial fatigue on specific mechanical parameters which characterise human tendons in vitro. Specimens prepared from 12 intact Extensor digitorum longus tendons of the foot were subjected to partial fatigue, equivalent to 25% of the median fatigue life, by a cyclic square tension–tension stress waveform at the physiological frequency of 4Hz. The

H. Schechtman; D. L. Bader

2002-01-01

28

Piezoelectric active sensing techniques for damage detection on wind turbine blades  

NASA Astrophysics Data System (ADS)

This paper presents the performance of a variety of structural health monitoring (SHM) techniques, based on the use of piezoelectric active sensors, to determine the structural integrity of a 9m CX-100 wind turbine blade (developed by Sandia National Laboratory). First, the dynamic characterization of a CX-100 blade is performed using piezoelectric transducers, where the results are compared to those by conventional accelerometers. Several SHM techniques, including Lamb wave propagations, frequency response functions, and time series based methods are then utilized to analyze the condition of the wind turbine blade. The main focus of this research is to assess and construct a performance matrix to compare the performance of each method in identifying incipient damage, with a special consideration given the issues related to field deployment. Experiments are conducted on a stationary, full length CX-100 wind turbine blade. This examination is a precursor for planned full-scale fatigue testing of the blade and subsequent tests to be performed on an operational CX-100 Rotor Blade to be flown in the field.

Park, Gyuhae; Farinholt, Kevin M.; Taylor, Stuart G.; Farrar, Charles R.

2011-03-01

29

Damage integral analysis of solder joint fatigue  

NASA Astrophysics Data System (ADS)

Thermal fatigue failures in the solder joints used in electronic packages are an important reliability concern. With electronic components moving through the development process quickly, it is practically impossible to test a given design's fatigue lifetime. Using a damage integral approach, however, accurate estimates of the fatigue lifetime can be generated. Such an approach extrapolates data from accelerated tests and integrates it to determine when failure will occur.

McGroarty, John; Subrahmanyan, Ravi; Li, Che-Yu

1991-06-01

30

Cumulative Fatigue Damage under Cyclic Strain Control.  

National Technical Information Service (NTIS)

Cyclic deformation resistance and fatigue damage accumulation are investigated using multiple level strain control. Data are reported for 2024-T4 and 7075-T6 aluminum alloys, aircraft quality SAE 4340 steel, and Titanium 811. Effects of cyclic strain leve...

T. H. Topper B. I. Sandor J. D. Morrow

1967-01-01

31

Ultrasonic evaluation of the effects of compressive residual stresses on aircraft engine turbine blades subjected to high cycle fatigue  

NASA Astrophysics Data System (ADS)

Experiments conducted on titanium (Ti-64) turbine blades with the LCR ultrasonic wave at 20 MHz showed significant differences in untreated blades and blades treated to increase the subsurface compressive residual stress. Group 1 showed significant differences in the treated and untreated areas, the top and bottom of the blades, high cycle fatigue and cracked and uncracked conditions. Group 2 blades showed significant difference between untreated and treated travel-times at probes located at the blade leading edge. .

Bray, Don E.; Suh, Ui; Hough, C. L. ``Mickey''

2002-05-01

32

CYCLIC FATIGUE CHARACTERISTICS OF 10%CR BLADE STEELS FOR ADVANCED STEAM TURBINE  

Microsoft Academic Search

Modified 9 ~ 12%Cr ferritic steels have been used extensively as the structural materials at the temperature up to 600oC in thermal power plants. And also the steels are excellent candidate materials for the advanced steam turbine blades in high pressure and temperature. In this paper, the low cycle fatigue (LCF) and high cycle fatigue (HCF) characteristics of the high

Jin-Ik Suk; Kuk-Cheol Kim; Byung-Hoon Kim; Jeong-Tae Kim

33

Thermal activation of fatigue damage  

SciTech Connect

The effect of temperature on the fatigue of aluminum alloys results from a combination of thermally induced changes in the microstructure and the intrinsic temperature dependence of the fatigue process. These two effects are separated for the first time, and it is shown that the intrinsic fatigue process is thermally activated. Two distinct regimes are identified. For fatigue lives < 3 x 16{sup 6} cycles, the activation energy is 86 kJ/mole in 339 aluminum/15 pct Kaowool composites and 120 kJ/mole in unreinforced 5086 aluminum, i.e., in the range reported for diffusion in aluminum. For fatigue lives > 2 x 10{sup 6} cycles, the activation energy is 240 kJ/mole. The magnitude of all three activation barriers decreases in direct proportion to the applied cyclic stress. These results are consistent with a dislocation model of job formation at low cyclic stresses and the diffusion-assisted motion of jogs at high cyclic stresses. The activation volumes correspond to dislocation loop lengths of 10 to 30 nm.

Baxter, W.J.; Lesuer, D.R.; Syn, C.K.

2000-01-01

34

Full-scale fatigue tests of CX-100 wind turbine blades. Part I: testing  

NASA Astrophysics Data System (ADS)

This paper overviews the test setup and experimental methods for structural health monitoring (SHM) of two 9-meter CX-100 wind turbine blades that underwent fatigue loading at the National Renewable Energy Laboratory's (NREL) National Wind Technology Center (NWTC). The first blade was a pristine blade, which was manufactured to standard specifications for the CX-100 design. The second blade was manufactured for the University of Massachusetts, Lowell with intentional simulated defects within the fabric layup. Each blade was instrumented with piezoelectric transducers, accelerometers, acoustic emission sensors, and foil strain gauges. The blades underwent harmonic excitation at their first natural frequency using the Universal Resonant Excitation (UREX) system at NREL. Blades were initially excited at 25% of their design load, and then with steadily increasing loads until each blade reached failure. Data from the sensors were collected between and during fatigue loading sessions. The data were measured over multi-scale frequency ranges using a variety of acquisition equipment, including off-the-shelf systems and specially designed hardware developed at Los Alamos National Laboratory (LANL). The hardware systems were evaluated for their aptness in data collection for effective application of SHM methods to the blades. The results of this assessment will inform the selection of acquisition hardware and sensor types to be deployed on a CX-100 flight test to be conducted in collaboration with Sandia National Laboratory at the U.S. Department of Agriculture's (USDA) Conservation and Production Research Laboratory (CPRL) in Bushland, Texas.

Farinholt, Kevin M.; Taylor, Stuart G.; Park, Gyuhae; Ammerman, Curtt M.

2012-03-01

35

Basic mechanisms of tendon fatigue damage.  

PubMed

Pathologic processes intrinsic and extrinsic to the tendons have been proposed as the underlying cause of rotator cuff disease, but the precise etiology is not known. Tear formation is, in part, attributable to the accumulation of subrupture tendon fatigue damage. We review the molecular, mechanical, and structural changes induced in tendons subjected to controlled amounts of fatigue loading in an animal model of early tendinopathy. The distinct tendon responses to low and moderate levels of loading, as opposed to high levels, provide insight into the potential mechanisms for the therapeutic benefits of exercise in the treatment of rotator cuff tendinopathy. The progression of damage accumulation leading to fiber rupture and eventual tendon tearing seen with higher loading illustrates the progression from tendinopathy to full-thickness tearing. We hope that this more realistic animal model of tendon fatigue damage will allow better assessment of biologic, mechanical, tissue-engineering, and rehabilitation strategies to improve repair success. PMID:22244058

Neviaser, Andrew; Andarawis-Puri, Nelly; Flatow, Evan

2012-02-01

36

Thermography detection on the fatigue damage  

NASA Astrophysics Data System (ADS)

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

Yang, Bing

37

Characterization of Widespread Fatigue Damage in Fuselage Structure.  

National Technical Information Service (NTIS)

The characteristics of widespread fatigue damage (WSFD) in fuselage riveted structure were established by detailed nondestructive and destructive examinations of fatigue damage contained in a full size fuselage test article. The objectives of this work we...

R. S. Piascik S. A. Willard M. Miller

1994-01-01

38

Evaluation of a threshold-based model of fatigue in gamma titanium aluminide following impact damage  

NASA Astrophysics Data System (ADS)

Recent interest in gamma titanium aluminide (gamma-TiAl) for use in gas turbine engine applications has centered on the low density and good elevated temperature strength retention of gamma-TiAl compared to current materials. However, the relatively low ductility and fracture toughness of gamma-TiAl leads to serious concerns regarding its ability to resist impact damage. Furthermore, the limited fatigue crack growth resistance of gamma-TiAl means that the potential for fatigue failures resulting from impact damage is real if a damage tolerant design approach is used. A threshold-based design approach may be required if fatigue crack growth from potential impact sites is to be avoided. The objective of the present research is to examine the feasibility of a threshold-based approach for the design of a gamma-TiAl low-pressure turbine blade subjected to both assembly-related impact damage and foreign object damage. Specimens of three different gamma-TiAl alloys were damaged in such a way as to simulate anticipated impact damage for a turbine blade. Step-loading fatigue tests were conducted at both room temperature and 600°C. In terms of the assembly-related impact damage, the results indicate that there is reasonably good agreement between the threshold-based predictions of the fatigue strength of damaged specimens and the measured data. However, some discrepancies do exist. In the case of very lightly damaged specimens, prediction of the resulting fatigue strength requires that a very conservative small-crack fatigue threshold be used. Consequently, the allowable design conditions are significantly reduced. For severely damaged specimens, an analytical approach found that the potential effects of residual stresses may be related to the discrepancies observed between the threshold-based model and measured fatigue strength data. In the case of foreign object damage, a good correlation was observed between impacts resulting in large cracks and a long-crack threshold-based approximation of the fatigue strength. However, in the case of smaller impact sites, a lower small-crack threshold appears to be more appropriate. In some cases, a complete perforation of the material, or blowout, would result from the impact. Prediction of the reduction in fatigue strength resulting from this form of damage required the use of a stress concentration factor, rather than a threshold-based prediction.

Harding, Trevor Scott

2000-10-01

39

Service load fatigue damage — a historical perspective  

Microsoft Academic Search

Although a general understanding of many aspects of fatigue crack growth behavior was established in the early 1960s, a specific ‘accumulation of damage model’ for computation of growth under a wide variety of service loads was lacking. The control of growth rates by K, the crack tip stress intensity factor and its reversing plastic zone, was well understood but somehow

Paul C Paris; Hiroshi Tada; J. Keith Donald

1999-01-01

40

Fatigue strength and life of compressor blades for marine gas turbine engines  

Microsoft Academic Search

An experimental procedure has been developed for the investigation of fatigue and crack growth resistance of materials and\\u000a real compressor blades. Methods for the determination of stress intensity factors in specimens and in blades with cracks have\\u000a been justified. Investigations have been performed on the influence of manufacturing residual stresses and surface defects\\u000a in the form of simulators of dents,

V. T. Troshchenko; A. V. Prokopenko

1999-01-01

41

Analysis of SNL/MSU/DOE fatigue database trends for wind turbine blade materials.  

SciTech Connect

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 infused 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.

Mandell, John F. (Montana State University, Bozeman, MT); Ashwill, Thomas D.; Wilson, Timothy J. (Montana State University, Bozeman, MT); Sears, Aaron T. (Montana State University, Bozeman, MT); Agastra, Pancasatya (Montana State University, Bozeman, MT); Laird, Daniel L.; Samborsky, Daniel D. (Montana State University, Bozeman, MT)

2010-12-01

42

Creep, creep-fatigue, and cavitation damage  

Microsoft Academic Search

Available creep and creep-fatigue data of type 304 stainless steel are re-examined in the light of some recently generated basic cavitation data on the same material. This basic study has shown creep damage to be a highly inhomogeneous phenomenon, both in space and in time. Thus a small fraction of boundaries are so intensely cavitated by about 10--25% of life

Majumdar

1986-01-01

43

A continuum Damage Approach of Asphalt Concrete Fatigue Tests  

Microsoft Academic Search

To forecast pavement fatigue cracking, fatigue performances of asphalt mixtures are assessed us- ing laboratory cyclic fatigue tests. A damage model is implemented to predict the behavior of asphalt mixtures during these tests. Under sinusoidal loading, the evolution of the complex modulus of the ma- terial is defined as the damage variable associated to a microcracking mechanism. Its evolution during

Didier Bodin; Gilles Pijaudier-Cabot; Chantal de La Roche; Jean-Michel Piau

44

Mean Stress and the Exhaustion of Fatigue-Damage Resistance.  

National Technical Information Service (NTIS)

Mean-stress effects on fatigue life are critical in isothermal and thermomechanically loaded materials and composites. Unfortunately, existing mean-stress life-prediction methods do not incorporate physical fatigue damage mechanisms. An objective is to ex...

A. Berkovits

1989-01-01

45

Prediction of transient engine loads and damage due to hollow fan blade-off  

Microsoft Academic Search

The loss of a fan blade causes serious damages on an engine and can endanger the aircraft integrity and the safety of passengers. Commercial aircraft engines must then meet the FAA (Federal Aviation Administration) and JAA (Joint Aviation Authorities) certification requirements concerning the fan blade containment. The certification is validated through a Fan Blade-Off (FBO) test on a whole engine.

Nicolas Cosmes; David Chevrolet; Jérôme Bonini; Bernard Peseux; Patrice Cartraud

2002-01-01

46

Estimation of fatigue damage and fatigue life of components under random loading  

Microsoft Academic Search

To examine the applicability of methods proposed in the estimation of fatigue damage and fatigue life of components under random loading, a batch of specimens made of 7075-T651 aluminium alloy has been studied and some of the results are reported in the present paper. The paper describes different methods and rules in the calculation of fatigue damage, especially when random

W. F. Wu; H. Y. Liou; H. C. Tse

1997-01-01

47

Experimental damage mechanics of microelectronic solder joints under fatigue loading  

Microsoft Academic Search

Fatigue damage is a progressive process of material degradation. The objective of this study is to experimentally qualify the damage mechanism in solder joints in electronic packaging under thermal fatigue loading. Another objective of this paper is to show that damage mechanism under thermal cycling and mechanical cycling is very different. Elastic modulus degradation under thermal cycling, which is considered

C. Basaran; H. Tang; S. Nie

2005-01-01

48

Experimental damage mechanics of microelectronic solder joints under fatigue loading  

Microsoft Academic Search

Fatigue damage is a progressive process of material degradation. The objective of this study is to experimentally qualify the damage mechanism in solder joints in electronic packaging under thermal fatigue loading. Another objective of this paper is to show that damage mechanism under thermal cycling and mechanical cycling are very different. Elastic modulus degradation under thermal cycling, which is considered

C. Basaran; H. Tang; S. Nie

2004-01-01

49

Blade fatigue life assessment with application to VAWTs  

Microsoft Academic Search

The possibility of satisfactory modeling of the vibratory stress level history of a vertical axis wind turbine (VAWT) is considered. Fatigue life prediction is expressed as a function of the vibratory stress level, the wind speed, and the wind speed distribution on-site. A statistical distribution of stress levels is asserted to more accurately simulate the stress level than determination of

P. S. Veers

1982-01-01

50

Effect of the flap and edgewise bending moment phase relationships on the fatigue loads of a typical HAWT blade.  

National Technical Information Service (NTIS)

The load spectrum unposed upon a horizontal-axis wind turbine blade is typically decomposed into two primary bending moments; flap and edgewise bending. The critical fatigue loads (stress cycles) imposed on the blade may not be on one of these axes, espec...

H. J. Sutherland

1992-01-01

51

Dislocation distribution and prediction of fatigue damage  

NASA Astrophysics Data System (ADS)

The dislocation density and distribution induced by tensile deformation in single crystals of silicon, aluminum and gold and by tension-compression cycling in aluminum single crystals and Al 2024-T3 alloys were studied by X-ray double-crystal diffractometry. The measurements of dislocation density were made at various depths from the surface by removing surface layers incrementally. In this way, a propensity for work hardening in the surface layers compared to the bulk material was demonstrated for both tensiledeformed and fatigue-cycled metals. Analysis of the cycled Al 2024 alloy as a function of the fraction of fatigue life showed that the dislocation density in the surface layer increased rapidly early in the fatigue life and maintained virtually a plateau value from 20 to 90 pct of the life. Beyond 90 pct the dislocation density increased rapidly again to a critical value at failure. Evaluation of the dislocation distribution in depth showed that the excess dislocation density in the bulk material increased more gradually during the life. Using deeply penetrating molybdenum K ? radiation, capable of analyzing grains representative of the bulk region, the accrued damage and the onset of fatigue failure could be predicted nondestructively for 2024 Al, cycled with constant stress as well as with variable stress amplitude. The dislocation structure produced in the bulk by prior cycling was unstable when the work-hardened surface layer was removed. It is proposed that the deformation response of the bulk material is controlled by the accumulation of dislocations and associated stresses in the surface layer.

Pangborn, R. N.; Weissmann, S.; Kramer, I. R.

1981-01-01

52

A study on fatigue damage modeling using neural networks  

Microsoft Academic Search

Fatigue crack growth and life have been estimated based on established empirical equations. In this paper, an alternative\\u000a method using artificial neural network (ANN) -based model developed to predict fatigue damages simultaneously. To learn and\\u000a generalize the ANN, fatigue crack growth rate and life data were built up using in-plane bending fatigue test results. Single\\u000a fracture mechanical parameter or nondestructive

Dong-Woo Lee; Soon-Hyeok Hong; Seok-Swoo Cho; Won-Sik Joo

2005-01-01

53

Conditioning monitoring by microstructural evaluation of cumulative fatigue damage  

SciTech Connect

The objective of this work is to evaluate the damage induced below and above the fatigue limit ({Delta}{sigma}{sub t} = 360 MPa) in pressure vessel steels, such as SA508. Fatigue damage was induced in samples taken from an SA508 steel plate by various loading histories in order to examine the influence of prior cyclic loading below the fatigue limit. Cell-to-cell misorientation differences were measured by the selected area diffraction (SAD) method. Surface cracking was also studied by the replication method. Small cracks were observed after precycling both below and above the fatigue limit. It was, however, found that fatigue test bars had a longer lifetime after precycling below the fatigue limit, while precycling above the fatigue limit caused other specimens to fail even when subsequently cycled below the fatigue limit. Cell-to-cell misorientation usually increases with accumulation of fatigue damage, but it was found that the misorientations measured after precycling below the fatigue limit decreased again at the beginning of the subsequent cycling above the fatigue limit. It should be noted that the misorientation at failure was always about 4 to 5 deg, regardless of loading histories. Misorientation showed good correlation with the fatigue lifetime of the samples.

Fukuoka, C.; Nakagawa, Y.G. [Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo (Japan). Research Labs.; Lance, J.J. [Electric Power Research Inst., Charlotte, NC (United States). O and M Cost Control Technology; Pangborn, R.N. [Pennsylvania State Univ., University Park, PA (United States). Coll. of Engineering

1996-12-01

54

Fatigue damage detection in 2024 aluminum alloy by optical correlation  

Microsoft Academic Search

The use of optical correlation techniques to monitor fatigue damage in 2024-T3 aluminum alloy is described. Topographical information from the surface of a sheet specimen is recorded holographically and compared with the actual surface by measuring correlation intensity as fatigue damage accumulates. The hologram is recorded on a thermoplastic - photoconductor device that can be developed and erased in situ,

W. L. Haworth; A. F. Hieber; R. K. Mueller

1977-01-01

55

Fatigue damage-fracture mechanics interaction in cortical bone  

Microsoft Academic Search

Fatigue loading causes accumulation of damage that may lead to the initiation of a macrocrack and result in a catastrophic failure of bone. The objective of this study was to examine the influence of fatigue damage on crack growth parameters in bovine cortical bone. Nineteen rectangular beam specimens (4 × 4 × 48 mm) were machined from bovine tibiae. The

Y. N Yeni; D. P Fyhrie

2002-01-01

56

Fatigue damage analysis on body shell of a passenger vehicle  

Microsoft Academic Search

A method for design durability qualification of a vehicle body shell is presented. Field test data were used to produce an accelerated durability test that retains all of the damaging real time load histories present in the original test cycle. Fatigue analysis methods are used to access and compare the fatigue damage imposed during durability test and laboratory (torsion) experiments.

E. S. Palma; F. A. C. Vidal

2002-01-01

57

14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.  

Code of Federal Regulations, 2013 CFR

...rate or no-growth of damage that may occur from fatigue, corrosion, manufacturing flaws or impact damage, under repeated loads...the probable locations and modes of damage due to fatigue, corrosion, or accidental damage. Damage at multiple sites...

2013-01-01

58

Fatigue strength and evaluation of creep damage during fatigue cycling of Inconel Alloy 625  

Microsoft Academic Search

Evaluation of high strain rate and corresponding low strain rate tests indicate no creep-fatigue interaction. For T greater than or equal to 900°C, creep damage predominates during the cyclic straining. For tests in which creep damage is largely suppressed - for example in high-frequency reverse bend fatigue tests - the cycles to fatigue failure were found to increase directly with

A. Purohit; U. Thiele; J. E. ODonnell

1983-01-01

59

Evaluation of service-induced damage and restoration of cast turbine blades  

SciTech Connect

Conventionally cast turbine blades of Inconel 713C, from a military gas turbine aircraft engine, have been investigated with regard to service-induced microstructural damage and residual creep life time. For cast turbine blades, service life is defined by statistical values. The statistical methods can prove to be uneconomical, because safe limits must be stated with regard to the statistical probability that some blades will have higher damage than normal. An alternative approach is to determine the service-induced microstructural damage on each blade, or a representative number of blades, to better optimize blade usage. Ways to use service-induced [gamma][prime] rafting and void formation as quantified microstructural damage parameters in a service lifetime prediction model are suggested. The damage parameters were quantified, in blades with different service exposure levels, and correlated to remaining creep life evaluated from creep test specimens taken from different positions of serviced blades. Results from tests with different rejuvenation treatments, including hot isostatic pressing and/or heat treatment, are discussed briefly.

Persson, C.; Persson, P.O. (Celsius Materialteknik, Linkoeping (Sweden))

1993-08-01

60

Behavior of gamma TiAl subjected to impact damage and elevated temperature fatigue  

SciTech Connect

Gamma titanium aluminide has received significant attention in recent years as a candidate material for use in aerospace and industrial gas turbine engine applications. It is well known that fatigue crack growth rates in {gamma}-TiAl alloys are very sensitive to stress intensity range and that there is a small difference between threshold stress intensity range and apparent fracture toughness in these materials. The result is limited damage tolerance and dramatic reductions in fatigue lifetime in the presence of extrinsic damage, such as that produced from an impact event. To apply a damage tolerance approach to this situation would require improved crack detection techniques and would increase the life cycle cost of the engine by decreasing the inspection interval. Using a threshold-based approach, on the other hand, would ensure that pre-existing or service indices cracks would not grow and that failure by fatigue would not occur. The present study investigates the feasibility of using a threshold calculation to estimate the fatigue strength reduction caused by impact damage at elevated temperatures (600 C). The results are part of a larger investigation into the feasibility of using {gamma}-TiAl for low-pressure turbine blades.

Harding, T.S.; Jones, J.W.

1999-12-31

61

Damage Tolerance Improvement of Ti-6-4 Fan Blades With Low Plasticity Burnishing.  

National Technical Information Service (NTIS)

Low plasticity burnishing (LPB) has been demonstrated to increase the damage tolerance of Ti- 6Al-4V fan blades by an order of magnitude. First stage Ti-6Al-4V fan blades were LPB processed using a conventional 4-axis CNC machine tool. LPB dramatically im...

P. S. Prevey D. J. Hornbach J. T. Cammett R. Ravindranath

2002-01-01

62

A fatigue damage model for the cement-bone interface.  

PubMed

Loss of fixation at the cement-bone interface can contribute to clinical loosening of cemented total hip replacements. In this study, the fatigue damage response was determined for cement-bone constructs subjected to shear fatigue loading. A typical three-phase fatigue response was observed with substantial early damage, followed by a long constant damage rate region and a final abrupt increase in damage to fracture. All of the damage resulted from creep (permanent) deformation during fatigue loading and there was no loss in cyclic stiffness. Using a Von Mises equivalent stress/strain concept, a general damage model was developed to describe the fatigue creep response of the cement-bone interface under either shear or tensile fatigue loading. Time to failure was highly correlated (r2=0.971) with equivalent creep strain rate and moderately related (r2=0.428) with equivalent initial strain for the two loading regimes. The equivalent creep strain at failure (0.052+/-0.018) was found to be independent of the applied equivalent stress. A combination of the creep damage model (to describe the damage process) with a constant final equivalent strain (as a failure criteria) could be used to assess the cement-bone failure response of cemented implant systems. PMID:15336925

Kim, Do-Gyoon; Miller, Mark A; Mann, Kenneth A

2004-10-01

63

The characterization of widespread fatigue damage in fuselage structure  

NASA Astrophysics Data System (ADS)

The characteristics of widespread fatigue damage (WSFD) in fuselage riveted structure were established by detailed nondestructive and destructive examinations of fatigue damage contained in a full size fuselage test article. The objectives of this work were to establish an experimental data base for validating emerging WSFD analytical prediction methodology and to identify first order effects that contribute to fatigue crack initiation and growth. Detailed examinations were performed on a test panel containing four bays of a riveted lap splice joint. The panel was removed from a full scale fuselage test article after receiving 60,000 full pressurization cycles. The results of in situ examinations document the progression of fuselage skin fatigue crack growth through crack linkup. Detailed tear down examinations and fractography of the lap splice joint region revealed fatigue crack initiation sites, crack morphology and crack linkup geometry. From this large data base, distributions of crack size and locations are presented and discussions of operative damage mechanisms are offered.

Piascik, Robert S.; Willard, Scott A.; Miller, Matthew

1994-09-01

64

Quantitative study of fretting fatigue damage in shot peened titanium-aluminum-vanadium  

NASA Astrophysics Data System (ADS)

Fretting fatigue damage has been known to be the origin of premature failure in some of the aerospace engine components. The blade/disk assemblies, for example have been particularly susceptible to fretting induced failure. Several nondestructive evaluation techniques are being used to detect the cracks due to fretting fatigue damage. Although partial success has been achieved in detection of cracks, research is lacking in the area of detection of precursors to the development of cracks due fretting fatigue damage. The goal of the research presented in this thesis is to develop a methodology based on x-ray diffraction residual stress measurements for quantitative nondestructive characterization of accumulated fretting fatigue damage. To achieve the goal a systematic experimental study of the characteristics of the residual stress due to surface treatments of shot peening (SP), Laser Shock Peening (LSP) and Low Plasticity Burnishing (LPB), used in the aerospace industry was conducted. The residual stress in LSP and LPB was found to be complex involving shear stress and spatial non-uniformity. On the other hand in shot peening it was found to be least complex. More over it is the most cost effective and hence often used surface treatment in the industry. In order to gain an understanding of the effect of shot peening parameters on the fretting fatigue life, experiments were conducted on samples with four different peening intensities (0, 4, 7 and 10 A) and two surface coverage (100% and 400%). It was observed that the fretting fatigue life increases with the increasing peening intensity, and increase in surface coverage beyond 100% has virtually no effect. Scanning Electron Microscopic (SEM) observation of fractured surface was utilized to identify crack initiation. On all of the fretting fatigued specimens relaxation of residual stress was observed and it increased with increasing number of cycles. A complete relaxation was observed before failure. To obtain an understanding of the mechanisms leading to the residual stress relaxation samples with varying number of fretting fatigue cycles were prepared and the microstructure of the damaged region was examined using SEM and White Light Intereference Microscopy (WLIM). The SEM images show formation of platelet like structures due to delamination at early stages. On further continuation of fretting the delaminated regions act as stress concentrators and generate micro-cracks. As the fretting fatigue damage is increased the micro-cracks appear to coalesce together to create a large crack to drive the sample to failure.

Martinez, Sonia A.

65

Continuum damage mechanics analysis of fatigue crack initiation  

Microsoft Academic Search

The crack initiation period in an originally defect-free component can be a significant portion of its total fatigue life. The initiation phase is generally believed to constitute the nucleation and growth of short cracks, but the threshold crack length at which initiation occurs lacks a uniform definition. Moreover, available methods for predicting fatigue damage growth usually require an existing flaw

Baidurya Bhattacharya; Bruce Ellingwood

1998-01-01

66

The treatment of fatigue and damage accumulation in composite design  

Microsoft Academic Search

Differences between the treatment of damage, damage accumulation, and fatigue for various types of advanced composite systems, for example, polymer matrix composites (PMCs), ceramic matrix composites (CMCs), and MMCs are discussed in general. The approach for PMCs from the aspect of damage mechanics is reviewed next and extended to a discussion of various aerospace certification approaches adopted for PMC structures.

K. T. Kedward; P. W. R. Beaumont

1992-01-01

67

Mean stress and the exhaustion of fatigue-damage resistance  

SciTech Connect

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

Berkovits, A.

1989-11-01

68

Comparative evaluation of environment induced cracking of conventional and advanced steam turbine blade steels. Part 2: Corrosion fatigue  

Microsoft Academic Search

Corrosion fatigue crack propagation rates have been determined for two steam turbine blade steels, PH13-8, a candidate steel for advanced turbines, and FV566, typical of conventional turbine blades. The testing was undertaken in simulated condensate environment, 300ppb Cl? and 300ppb SO42-, at 90°C using trapezoidal loading with a rise time of 20min to simulate two-shifting (switching on- and off-load on

A. Turnbull; S. Zhou

69

Fatigue damage analysis of unidirectional metal matrix composites  

Microsoft Academic Search

The paper deals with the non-linear analysis of industrial components subjected to strong thermo-mechanical cyclic loads. Two kinds of damages must be taken into account: the first one being a “constitutive damage” which will dominate the low cycle fatigue (LCF) regime and whose evolution law will be coupled to the elasto-viscoplastic model. The second one will be a “classical” fatigue

Serge Kruch; Nicolas Carrère; Jean-Louis Chaboche

2006-01-01

70

Fatigue damage detection in 2024 aluminum alloy by optical correlation  

Microsoft Academic Search

The use of optical correlation techniques to monitor fatigue damage in 2024-T3 aluminum alloy is described. Topographical\\u000a information from the surface of a sheet specimen is recorded holographically and compared with the actual surface by measuring\\u000a correlation intensity as fatigue damage accumulates. The hologram is recorded on a thermoplastic - photoconductor device that\\u000a can be developed and erasedin situ, so

W. L. Haworth; A. F. Hieber; R. K. Mueller

1977-01-01

71

Fatigue damage analysis on body shell of a passenger vehicle  

Microsoft Academic Search

A method for design durability qualification of a vehicle body shell is presented. Field test data were used to produce an\\u000a accelerated durability test that retains all of the damaging real time load histories present in the original test cycle.\\u000a Fatigue analysis methods are used to access and compare the fatigue damage imposed during durability test and laboratory (torsion)\\u000a experiments.

E. S. Palma; F. A. C. Vidal

2002-01-01

72

The effects of controls on fatigue loads in two-bladed teetered rotor wind turbines  

SciTech Connect

This paper presents a quantitative analysis of the fatigue loads in a down wind, yaw-controlled, fixed pitch, two-bladed teetered-rotor wind turbine using proportional-integral, full-state optimal, and fuzzy logic controllers. Time-domain simulation data is generated using the EASY5x/WT software developed at the University of Texas at El Paso. The simulation data reveal that the choice of controller type, or the controller dynamics, can play a very important role in the fatigue life of a wind turbine and should be considered early in the design process of the wind turbine. In summary, the fuzzy logic controller is the most robust controller under a wide regime of wind conditions. It provides the best overall performance in terms of power regulation capability and minimum fatigue loads. The optimal controller with a full-state Kalman filter observer provides a satisfactory performance in terms of power regulation capability and loads when the operating condition is close to the design point at which the controller was optimized. It fails to regulate the power output when the actual operating point deviated too far, about 30 percent in the computer simulations, from the designed operating point. The PI controller provided satisfactory performance in power regulation. However, it produced the worst fatigue loads to the wind turbine among the three controllers.

Wu, K.C.; Guardia, R. De La [Univ. of Texas, El Paso, TX (United States). Mechanical and Industrial Engineering Dept.

1996-11-01

73

Nonlinear Laser Ultrasonic Measurements of Localized Fatigue Damage  

NASA Astrophysics Data System (ADS)

A nonlinear laser ultrasonic system was developed and used to characterize the fatigue state of a fractured Ti-6Al-4V sample with high spatial-resolution and sensitivity. The measurement system is built around a scanning heterodyne interferometer, which allows detailed displacement field images to be created and visualized for propagating surface and bulk acoustic fields on a material surface. An assessment of the local fatigue damage of the material was made using nonlinear ultrasonic interaction principles, where the local amplitudes of the fundamental and second harmonic displacement fields are monitored simultaneously. This provides a means for evaluating the local acoustical nonlinearity parameter, ?, which can be related to the accumulation of fatigue damage in a material. A large increase in ? was observed between the unfatigued area (near the grip section) and the heavily fatigued area (gauge section) for a fractured dogbone specimen. The measurements show the potential for spatially-resolving the local fatigue state of a material using laser ultrasonics.

Blackshire, J. L.; Sathish, S.; Na, J.; Frouin, J.

2003-03-01

74

Detection and quantification of fatigue damage in aircraft structural components  

NASA Astrophysics Data System (ADS)

Retirement criteria for many structural components and particularly landing gear structural parts, are generally based on analytical fatigue methods because the current means of detecting actual component damage cannot detect sufficiently small levels of damage such that safe operation for a useful interval can be confidently determined; limiting the capability to apply damage tolerance methods. The testing completed in these projects demonstrated that Induced Positron Analysis (IPA) technologies are sensitive to the tensile plastic strain damage induced in aerospace material specimens and components. The IPA process has shown that IPA methods can reliably detect and quantify plastic strain and plastic deformation under simulated and operational conditions. A preliminary functional relationship between total strain and the normalized IPA S parameter has been developed for several aerospace materials. The fatigue testing has demonstrated the IPA technologies have potential to detect fatigue damage induced in specimens and operational components when the loads are large enough to cause plastic deformation.

Rideout, Curtis A.; Ritchie, Scott J.

2007-05-01

75

Detect, troubleshoot gas-turbine blade failures  

SciTech Connect

Approximately 40% of all gas-turbine failures stem from blading problems. This article describes state-of-the-art condition monitoring technologies that can help avoid or minimize the damage, and troubleshoot failures when they occur. In today`s gas-turbine (GT) fleet, predominant blade-failure mechanism and commonly affected components include: low-cycle fatigue--compressor and turbine disks; high-cycle fatigue--compressor and turbine blades and disks, compressor stator vanes; thermal fatigue--nozzles, combustors; environmental attack, such as oxidation, sulfidation, hot corrosion, and standby corrosion--hot-section blades and stators, transition pieces, and combustors; creep damage--hot-section nozzles and blades; erosion and wear; impact overload damage; thermal aging; combined failure mechanisms, such as creep/fatigue corrosion/fatigue, oxidation/erosion, and so on. Avoiding GT blade problems requires that two conditions be met: first, and most important, the basic design has to be sound, with adequate safety factors incorporates. Second, the proper operating regime must be maintained. Properly applied, condition monitoring can help maintain the operating regime and minimize blade distress. Should blade failures occur, data captured in a monitoring program may provide valuable clues to help identify the root causes. Reviewed here are the latest GT condition monitoring techniques, as well as several case histories that illustrate their importance.

Meher-Homji, C.B. [Boyce Engineering International Inc., Houston, TX (United States)

1995-12-01

76

Effects of Materials Parameters and Design Details on the Fatigue of Composite Materials for Wind Turbine Blades  

SciTech Connect

This paper presents an analysis of the results of nine years of fatigue testing represented in the USDOE/Montana State University (DOE/MSU) Composite Materials Fatigue Database. The focus of the program has been to explore a broad range of glass-fiber-based materials parameters encompassing over 4500 data points for 130 materials systems. Significant trends and transitions in fatigue resistance are shown as the fiber content and fabric architecture are varied. The effects of structural details including ply drops, bonded stiffeners, and other geometries that produce local variations in fiber packing and geometry are also described. Fatigue tests on composite beam structures are then discussed; these show generally good correlation with coupon fatigue data in the database. Goodman diagrams for fatigue design are presented, and their application to predicting the service lifetime of blades is described.

Mandell, J.F.; Samborsky, D.D.; Sutherland, H.J.

1999-03-04

77

Damage monitoring in fiber-reinforced composites under fatigue loading using carbon nanotube networks  

Microsoft Academic Search

The formation of carbon nanotube networks around the structural reinforcement in fiber composites has enabled in situ monitoring of matrix damage accumulation. Real-time monitoring of damage development under fatigue loading was studied. The electrical response of the fatigue specimens change synchronously with the applied fatigue loading and enable a quantitative measure of the damage state. The fatigue response of the

Limin Gao; Erik T. Thostenson; Zuoguang Zhang; Joon-Hyung Byun; Tsu-Wei Chou

2010-01-01

78

Study of fatigue damage in 7010 aluminum alloy  

Microsoft Academic Search

Microscopic mechanisms controlling the fatigue damage in 7010 aluminum alloy are analysed. Cracks are initiated by the fracture of second-phase particles. Particles located in grains with a twisted cubic texture have been observed as preferential damage sites. Cracks grow either along intergranular or transgranular paths both in recrystallized and unrecrystallized regions. The final rupture mechanism depends on the stress level:

G. Patton; C. Rinaldi; Y. Bréchet; G. Lormand; R. Fougères

1998-01-01

79

Investigation on fatigue-creep interaction damage model for solder  

Microsoft Academic Search

It is well known, reliability and workability are the more important issues in the field of chip size package (CSP). Creep and fatigue behaviors are the main loads of the solder joints, the reliability of which should take account of those two main loads. Based on the theory of continuum damage mechanics (CDM), this paper focuses on damage evolution of

Na Liu; Xiaoyan Li; Yongchang Yan

2008-01-01

80

Evaluation of service-induced damage and restoration of cast turbine blades  

Microsoft Academic Search

Conventionally cast turbine blades of Inconel 713C, from a military gas turbine aircraft engine, have been investigated with\\u000a regard to service-induced microstructural damage and residual creep life time. For cast turbine blades, service life is defined\\u000a by statistical values. The statistical methods can prove to be uneconomical, because safe limits must be stated with regard\\u000a to the statistical probability that

C. Persson; P.-O. Persson

1993-01-01

81

Creep–fatigue interaction damage model and its application in modified 9Cr–1Mo steel  

Microsoft Academic Search

Creep–fatigue interaction damage evolution of the nuclear engineering materials modified 9Cr–1Mo steel is studied with Continuum Damage Mechanics (CDM) theory. Based on the Norton creep damage and fatigue dissipate potential theory, an effective stress controlled creep–fatigue interaction damage model has been developed in this paper, in which the creep and fatigue damage function are both considered as nonlinear variables. The

Guodong Zhang; Yanfen Zhao; Fei Xue; Jinna Mei; Zhaoxi Wang; Changyu Zhou; Lu Zhang

82

Damage analysis in Al thin films fatigued at ultrahigh frequencies  

NASA Astrophysics Data System (ADS)

A quantitative damage analysis provides insight into the damage mechanisms and lifetimes of aluminum thin films fatigued at ultrahigh frequencies. Surface acoustic wave test devices were used to test continuous and patterned Al thin films up to more than 1014 cycles. The analysis revealed increasing extrusion and void formation concentrated at grain boundaries. This finding and the observed grain growth indicate a high material flux at the grain boundaries induced by the cyclic load. A correlation between device degradation and defect density is established which is explained by a theoretical model. For stress amplitudes as low as 14 MPa lifetime measurements showed no fatigue limit for 420 nm Al thin films.

Eberl, Christoph; Spolenak, Ralph; Kraft, Oliver; Kubat, Franz; Ruile, Werner; Arzt, Eduard

2006-06-01

83

Damage and fatigue in cross-linked rubbers  

NASA Astrophysics Data System (ADS)

Damage and fatigue of elastomers have not been fundamentally understood because of the complex nature of these materials. All currently existing models are completely phenomenological. Therefore two problems have been investigated in this research to address those fundamental issues. The first problem was creating an innovative concept with a mathematical modeling, which would be able to describe the damage using molecular characteristics of elastomers. The second problem is developing new approaches to study fatigue, and especially impact fatigue of elastomers. The following results have been obtained in this research. A theoretical model of damage has been developed which involves the basic molecular characteristics of cross-linked elastomers and takes into account the effects of viscoelasticity and stress-induced crystallization. This model was found very reliable and successful in description of numerous quasi-static simple extension experiments for monotonous and repeating loadings. It also roughly predicts in molecular terms the failure of elastomers with various degrees of cross-linking. Quasi-impact fatigue tests with different geometry of an indenter have also been performed. Some microscopic features of rubber damage have been investigated using optical microscopy and SEM. In particular, the accumulation of a completely de-vulcanized, liquid-like substance was observed under intense, multi-cycle impacts. All the findings discovered in quasi-impact experiments are consistent with the damage model predictions.

Melnikov, Alexei

84

Nondestructive evaluation of thick-composite fatigue damage  

NASA Astrophysics Data System (ADS)

This paper describes the results of the comparison of a variety of nondestructive evaluation techniques to monitor the development of fatigue damage in thick graphite/epoxy composites. Three inch long, one inch square cross-section test specimens were fatigue tested in compression. Most specimens incorporated stress (strain) concentration notches at their mid- section in order to localize the primary fatigue damage regions in an optimum location for nondestructive monitoring. The nondestructive techniques evaluated were ultrasonic B- and C- scan, ultrasonic velocity and attenuation, ultrasonic second harmonic generation, acoustic microscopy, acoustic emission, thermography, real-time high-speed digital/video laser speckle decorrelation, magnetic resonance imaging, radio-opaque penetrant enhanced x-radiography, and eddy current. Mechanical resonance spectroscopy was used to measure the second order (linear) elastic moduli. Optical and electron microscopy on cut and polished specimens were used to verify the results of the nondestructive tests.

Green, Robert E.

1995-06-01

85

Fatigue damage-fracture mechanics interaction in cortical bone.  

PubMed

Fatigue loading causes accumulation of damage that may lead to the initiation of a macrocrack and result in a catastrophic failure of bone. The objective of this study was to examine the influence of fatigue damage on crack growth parameters in bovine cortical bone. Nineteen rectangular beam specimens (4 x 4 x 48 mm) were machined from bovine tibiae. The long axis of the beams was aligned with the long axis of bones. Using a four-point bending fatigue setup, ten specimens were fatigue-damaged to different levels as indicated by stiffness loss. A through-thickness notch was machined at the center of each damaged and undamaged beam. The notched specimens were then monotonically loaded beyond failure using a three-point bending protocol. Critical stress intensity factor, K(I), and work to critical load, W(Q), were significantly lower in the damaged group than in the undamaged group (p < 0.03). When the undamaged specimens were assigned a percent stiffness loss of zero and pooled with the damaged group, significant negative correlations of percent stiffness loss with K(I) (R = 0.58, p < 0.01), W(Q) (R = 0.54, p < 0.02), maximum load, P(max) (R = 0.59, p < 0.008), deflection at maximum load, Delta(max) (R = 0.48, p < 0.04), structural stiffness, S(max) (R = 0.53, p < 0.02), W(max) (R = 0.55, p < 0.02), and load at 1.4 mm deflection (a value beyond failure but without complete fracture), P(1.4) (R = 0.47, p < 0.05), were found. Post hoc analysis revealed that the average load-deflection curve from the damaged group was transformable into that from the undamaged group through a special shift on the load-deflection plane. Fatigue damage reduces bone stiffness and resistance to crack initiation, maximum load-carrying capacity, and deflection before and after failure in cortical bone. The data suggest there is a single rule that governs the overall effect of fatigue damage on the fracture behavior of cortical bone. PMID:11882466

Yeni, Y N; Fyhrie, D P

2002-03-01

86

Accumulative damage near crack tip for welded bridge members: fatigue life determination  

Microsoft Academic Search

The behavior of crack growth for the fatigue damage accumulation near tip where damage is most severe is analyzed. Fatigue life is assessed for the welded members of bridges under traffic loading. Two parts are considered. They consist of the development of a fatigue damage accumulation model for welded bridge members and a method for calculating the stress intensity factor

Z. X. Li; T. H. T. Chan; T. Q. Zhou

2005-01-01

87

Statistical multi-site fatigue damage analysis model  

NASA Astrophysics Data System (ADS)

A statistical model has been developed to evaluate fatigue damage at multi-sites in complex joints based on coupon test data and fracture mechanics methods. The model is similar to the USAF model, but modified by introducing a failure criterion and a probability of fatal crack occurrence to account for the multiple site damage phenomenon. The involvement of NDI techniques has been included in the model which can be used to evaluate the structural reliability, the detectability of fatigue damage (cracks), and the risk of failure based on NDI results taken from samples. A practical example is provided for rivet fasteners and bolted fasteners. It is shown that the model can be used even if it is based on conventional S-N coupon experiments should further fractographic inspections be made for cracks on the broken surfaces of specimens.

Wang, G. S.

1995-02-01

88

Fatigue and creep-fatigue damage of austenitic stainless steels under multiaxial loading  

SciTech Connect

The objectives of the present study are to observe and model physical damage induced by cyclic multiaxial (tension-torsion) loading of 316L stainless steel both at room temperature and at elevated temperature. Four types of experiments were carried out on thin tubular specimens: (a) continuous pure fatigue (PF) tests; (b) PF sequential tests with different sequences of push-pull and torsional loading; (c) creep-fatigue (CF) tests with superimposed hold time at maximum tensile strain; and (d) sequential tests involving sequences of PF and CF loadings. Optical microscopy and scanning electron microscopy (SEM) were used to study quantitatively the damage, in particular, to determine the orientation of cracks and to measure the kinetics of crack nucleation and crack growth. It is shown that in PF at 600 C, the classical crack initiation stage one is bypassed due to a strong interaction between cyclic plasticity, oxidation, and cracking. Intense slip bands act as diffusional short circuits, leading to the formation of external and internal oxide scales. The orientation of the microcracks during initiation and propagation stages, which is strongly affected by oxidation effects, explains qualitatively the significant deviations observed in the sequential tests from the Miner linear damage cumulative rule. It is also shown that CF damage, which involves intergranular damage, is a complex process rather than a simple superposition of fatigue and creep damage. A stochastic model based on a Monte-Carlo simulation is developed. This model includes damage equations based on quantitative metallographical observations. Damage is modeled as the continuous nucleation of a population of growing cracks which eventually coalesce to lead to final fracture. It is shown that this simulation is able to reproduce with a good accuracy the fatigue lives measured under multiaxial continuous and sequential tests.

Weiss, J. (Dartmouth Coll., Hanover, NH (United States). Ice Research Lab.); Pineau, A. (Ecole des Mines, Evry (France). Centre des Materiaux)

1993-10-01

89

Thermography detection of damage initiation during fatigue tests  

NASA Astrophysics Data System (ADS)

The design of mechanical structures that are subject to repeated loads relies upon the knowledge of the fatigue limit of the constitutive materials. Conventional methods for the fatigue limit evaluation are lengthy and therefore expensive. We propose a new approach for this problem. It is based on the detection of a modification of the thermomechanical couplings occurring together with the damage onset. A specific synchronous demodulation thermography approach was devised which provides a map of the two first harmonics of temperature and a map of the temperature mean rise. Experiments performed on steel XC48, 316L and on Al 7010, Al 2024 show the high potential of this method.

Krapez, Jean-Claude; Pacou, Didier

2002-03-01

90

Inspecting for widespread fatigue damage: Is partial debonding the key?  

NASA Astrophysics Data System (ADS)

Experimental and analytical results indicate that cracks can initiate, grow, and coalesce more rapidly in fuselage lap joints that have experienced partial or complete debonding. Computational analysis in this paper shows that stress concentrations and stress intensity factors at the rivet holes are far less severe when the bond is intact. Debonding hastens the initiation of widespread fatigue cracks and significantly increases crack growth rate. Thus, debonded regions serve as "breeding grounds" for widespread fatigue damage. Therefore, the effectiveness of lap joint inspection programs may be enhanced if detailed inspections are focused on areas in which debonding has been detected.

Brewer, John

1994-09-01

91

Reduction in fiber damage thresholds due to static fatigue  

NASA Astrophysics Data System (ADS)

For a number of years we have been investigating laser-induced damage mechanisms that can occur during the transmission of Q-switched, Nd/YAG laser pulses through fused silica fibers. We have found that fiber end-face characteristics, laser characteristics, and aspects of the laser-to-fiber injection typically determine dominant damage mechanisms. However, an additional damage process has been observed occasionally at internal sites where fibers were experiencing significant local stresses due to fixturing or to bends in the fiber path. A transmission reduction prior to damage was typically not measureable at these sites. Damage would not always occur during initial testing, but sometimes occurred later in time at laser levels that previously had been transmitted without damage. In these cases the time at stress appeared to be more important than the number of transmitted shots prior to damage. A possible relation between internal damage thresholds at stressed sites and the total time under stress is suggested by the fact that silica fibers experience static fatigue processes. These processes involve the slow growth of local defects under tensile stress at rates that depend upon environmental conditions. Defects reaching sufficient size and having appropriate location could be sites for reduced laser-induced damage thresholds. This possibility could have important implications for high-power fiber transmission systems that must satisfy extended lifetime requirements. The needs of the telecommunications industry have motivated extensive studies into initial fiber defect characteristics and their likely growth mechanisms. The present work used the understanding developed in these studies to guide a preliminary experimental investigation into the possibility that static fatigue processes can affect damage thresholds. The experiments used a laser injection and fiber routing configuration that produced significantly elevated fluences within fiber core regions under tensile stress. In one set of experiments, internal damage thresholds were determined in available fiber samples that had been assembled in stress-imposing fixtures for periods up to 24 months. A decline in mean thresholds with time was observed, although measured values showed significant scatter. In order to establish initial strength and fatigue properties for these fibers, a number of additional samples were used to generate time-to-failure data at various stress levels. Based on these results, other fiber samples were subjected to conditions that greatly accelerated fatigue processes. Internal damage thresholds were then measured in these fibers and compared to thresholds measured in fresh fibers. Conclusive comparisons were frustrated by sample-to-sample and lot-to-lot variations in fiber defects.

Setchell, Robert E.

1995-07-01

92

Influence of porosity on fatigue cumulative damage of sintered iron  

NASA Astrophysics Data System (ADS)

Fatigue represents a common mechanical condition during service for materials used in structural components. This type of loading becomes particularly critical when alternating stress amplitude may be expected to vary, or change, in some way during the service life. Such variations and changes in load amplitude make the direct use of standard S-N curves inapplicable, because these curves are developed and presented for constant stress amplitude operation. In the present paper, results of cumulative damage under fatigue of porous materials are reported. The specimens used were produced by compacting and sintering iron powder. Their as-sintered porosity contents were P 0 = 4.1 and 12.4 %. Uniaxial fatigue tests (tensile-compression) were carried out at room temperature on a hydraulic testing machine.

Palma, E. S.

1997-10-01

93

Fiber-Optic Defect and Damage Locator System for Wind Turbine Blades  

SciTech Connect

IFOS in collaboration with Auburn University demonstrated the feasibility of a Fiber Bragg Grating (FBG) integrated sensor system capable of providing real time in-situ defect detection, localization and quantification of damage. In addition, the system is capable of validating wind turbine blade structural models, using recent advances in non-contact, non-destructive dynamic testing of composite structures. This new generation method makes it possible to analyze wind turbine blades not only non-destructively, but also without physically contacting or implanting intrusive electrical elements and transducers into the structure. Phase I successfully demonstrated the feasibility of the technology with the construction of a 1.5 kHz sensor interrogator and preliminary instrumentation and testing of both composite material coupons and a wind turbine blade.

Dr. Vahid Sotoudeh; Dr. Richard J. Black; Dr. Behzad Moslehi; Mr. Aleks Plavsic

2010-10-30

94

Continuum damage mechanics (CDM) modelling demonstrates that ligament fatigue damage accumulates by different mechanisms than creep damage.  

PubMed

Ligaments can be subjected to creep and fatigue damage when loaded to higher than normal stresses due to injury of a complementary joint restraint. Continuum damage mechanics (CDM) assumes that diffuse damage accumulates in a material, thereby reducing the effective cross-sectional area and leading to eventual rupture. The objective of this study was to apply CDM modelling to ligament creep and fatigue to reveal mechanisms of damage. Fatigue was modelled by cyclically varying the stress in the creep model. A few novel approaches were used. First, area reduction was not assumed equal to modulus reduction; thus, allowing damaged fibres to potentially contribute to load-bearing through the extracellular matrix. Modulus ratio was related to area reduction using residual strength. Second, damage rate was not assumed constant but rather was determined directly from the modulus ratio change with respect to time. Third, modulus ratio was normalized to maximum modulus to avoid artificial calculation of negative damage. With this approach, the creep time-to-rupture was predicted with -4% error at 60% UTS and -13% error at 30% UTS. At 15% UTS, no test was undertaken experimentally for a duration as long as the 24 days predicted theoretically. Oscillating the time-dependent damage in the creep model could not completely explain the fatigue behaviour because the fatigue time-to-rupture was predicted with over 1300% error at all stresses. These results suggest that a cycle-dependent damage mechanism, in addition to a time-dependent one, was responsible for fatigue rupture. Cycle-dependent damage may be an important consideration for rehabilitation activities following injury of a complementary ligament restraint. PMID:17582420

Schwab, Timothy D; Johnston, Clifton R; Oxland, Thomas R; Thornton, Gail M

2007-06-19

95

The treatment of fatigue and damage accumulation in composite design  

NASA Astrophysics Data System (ADS)

Differences between the treatment of damage, damage accumulation, and fatigue for various types of advanced composite systems, for example, polymer matrix composites (PMCs), ceramic matrix composites (CMCs), and MMCs are discussed in general. The approach for PMCs from the aspect of damage mechanics is reviewed next and extended to a discussion of various aerospace certification approaches adopted for PMC structures. Following this an explanation of the theoretical foundations for the 'wearout philosophy' in conjunction with related damage and fracture mechanics relationships is provided. This concludes with a survey of flaw, or more precisely, damage growth rate exponents for various matrix and/or interface-dominated failure mechanisms for PMCs and adhesively bonded joints.

Kedward, K. T.; Beaumont, P. W. R.

1992-09-01

96

A damage classification technique for impedance-based health monitoring of helicopter blades  

NASA Astrophysics Data System (ADS)

One of the most sensitive problems regarding the application of SHM (Structural Health Monitoring) is found in the aeronautical segment. This field presents the necessity of monitoring small structural changes representing damage, due both to economic aspects and safety. In this contribution two helicopter blade structures (pertaining to a civil and a military helicopter) are studied. In both cases, two types of damage are inserted, namely holes and cracks. Through the impedance-based structural health monitoring method, an identification procedure using cluster analysis techniques was performed aiming at distinguishing these two types of damage. Then, a meta-model based on a probabilistic neural network was built for fault position identification.

Moura, Jose R. V., Jr.; Steffen, Valder, Jr.; Inman, Daniel J.

2008-05-01

97

ACOUSTIC EMISSION MONITORING OF FATIGUE DAMAGE IN METALS  

Microsoft Academic Search

The objective of this study was to investigate and develop\\/adapt acoustic emission (AE) methods for detection and characterization of fatigue damage growth in metals. The materials investigated were 2024-T3 aluminum and 4340 steel. Edge-notch and compact tension specimens were tested under cyclic tensile loading. The investigation consisted of signal\\/noise discrimination, direct crack growth monitoring, acquisition of acoustic emission data, analysis

I. M. DANIEL; J.-J. LUO; C. G. SIFNIOTOPOULOS; H.-J. CHUN

1998-01-01

98

X-ray diffraction study of microstructural changes during fatigue damage initiation in steel pipes  

Microsoft Academic Search

Steel pipes used in the oil and gas industry undergo the action of cyclic loads that can cause their failure by fatigue. A consistent evaluation of the fatigue damage during the initiation phase should fundamentally be based on a nanoscale approach, i.e., at the scale of the dislocation network, in order to take into account the micromechanisms of fatigue damage

B. Pinheiro; J. Lesage; I. Pasqualino; N. Benseddiq; E. Bemporad

99

Detection of Pre-Crack Fatigue Damage in a U.S. Army MH47E Chinook Aft Rotor Shaft  

Microsoft Academic Search

Accumulated fatigue damage in flight critical helicopter dynamic components prior to crack initiation and detection is currently estimated by fatigue analysis based upon fatigue test results. To more accurately assess the operational fatigue damage and remaining useful life of a critical component prior to the initiation of a detectable crack, a non-destructive evaluation (NDE) process that directly measures accumulated fatigue

D. Granger; C. A. Rideout; S. Yano; D. J. White

2008-01-01

100

Surface damage accumulation in low-cycle fatigue: Physical analysis and numerical modeling  

SciTech Connect

The physical low-cycle fatigue damage of smooth 316 L stainless steel specimens is described at a mesoscopic scale (i.e. the grain size). More than 80% of the low-cycle fatigue lifetime consists of the development of multiple surface short cracks, the surface lengths of which are less than ten grain sizes. High densities of surface cracks lower than a grain size favor statistical aspects of their mutual interactions and their developments. This gives rise to an approach of low-cycle fatigue damage based on statistical physics. The fatigue damage description consists of accumulation of elementary independent damage events: the cracking of one grain. The statistical aspect of fatigue damage accumulation led to the development of numerical Monte Carlo type modeling. Principles of the modeling are presented. Low-cycle fatigue lifetime predictions concern in-air experiments and corrosion-fatigue experiments on 316 L stainless steel.

Bataille, A.; Magnin, T. (Univ. de Lille 1, Villeneuve D'Ascq (France). Lab. de Metallurgie Physique)

1994-11-01

101

Lamb wave assessment of fatigue damage in aluminum plates  

NASA Astrophysics Data System (ADS)

In this paper an experimental analysis of Lamb waves interaction with riveted aluminum plates representative of aircraft splice joints submitted to fatigue tests is given. In this joint evaluation technique Lamb waves are excited and received outside the joint area using piezoelectric transducers bonded onto the plates. Detected damages are cracks in joint resulting from fatigue loading. These cracks lead to waveform transformations. This phenomenon is studied in this paper by considering the first derivative of the envelope of the time domain signal. The position of the first derivative curve maximum during cyclical loading gives information about crack development. It suggests, that monitoring the change in the delay of this maximum may provide a means of sizing the defects. By using X-rays, it was possible to measure the size of the cracks and compare it with delay evolution. Results are obtained for two types of fatigue sequences. It is experimentally shown that the relative delay measured is very sensitive to crack development. With the continued progress in the field of damage assessment techniques such as methods relying on Lamb waves, the safety of such structures can be ensured.

Grondel, Sebastien; Moulin, Emmanuel; Delebarre, Christophe

1999-06-01

102

Damage mechanics characterization on fatigue behavior of a solder joint material  

SciTech Connect

This paper presents the first part of a comprehensive mechanics approach capable of predicting the integrity and reliability of solder joint material under fatigue loading without viscoplastic damage considerations. A separate report will be made to present a comprehensive damage model describing life prediction of the solder material under thermomechanical fatigue loading. The method is based on a theory of damage mechanics which makes possible a macroscopic description of the successive material deterioration caused by the presence of microcracks/voids in engineering materials. A damage mechanics model based on the thermodynamic theory of irreversible processes with internal state variables is proposed and used to provide a unified approach in characterizing the cyclic behavior of a typical solder material. With the introduction of a damage effect tensor, the constitutive equations are derived to enable the formulation of a fatigue damage dissipative potential function and a fatigue damage criterion. The fatigue evolution is subsequently developed based on the hypothesis that the overall damage is induced by the accumulation of fatigue and plastic damage. This damage mechanics approach offers a systematic and versatile means that is effective in modeling the entire process of material failure ranging from damage initiation and propagation leading eventually to macro-crack initiation and growth. As the model takes into account the load history effect and the interaction between plasticity damage and fatigue damage, with the aid of a modified general purpose finite element program, the method can readily be applied to estimate the fatigue life of solder joints under different loading conditions.

Chow, C.L.; Yang, F. [Univ. of Michigan, Dearborn, MI (United States). Dept. of Mechanical Engineering; Fang, H.E. [Sandia National Labs., Albuquerque, NM (United States). Computational Physics Dept.

1998-08-01

103

Periostin Deficiency Increases Bone Damage and Impairs Injury Response to Fatigue Loading in Adult Mice  

PubMed Central

Bone damage removal and callus formation in response to fatigue loading are essential to prevent fractures. Periostin (Postn) is a matricellular protein that mediates adaptive response of cortical bone to loading. Whether and how periostin influences damage and the injury response to fatigue remains unknown. We investigated the skeletal response of Postn-/- and Postn+/+ mice after fatigue stimulus by axial compression of their tibia. In Postn+/+ mice, cracks number and surface (CsNb, CsS) increased 1h after fatigue, with a decrease in strength compared to non-fatigued tibia. At 15 days, CsNb had started to decline, while CtTV and CtBV increased in fatigued vs non-fatigued tibia, reflecting a woven bone response that was present in 75% of the fatigued bones. Cortical porosity and remodelling also prominently increased in the fatigued tibia of Postn+/+ mice. At 30 days, paralleling a continuous removal of cortical damage, strength of the fatigued tibia was similar to the non-fatigue tibia. In Postn-/- mice, cracks were detectable even in the absence of fatigue, while the amount of collagen crosslinks and tissue hardness was decreased compared to Postn+/+. Fatigue significantly increased CsNb and CsS in Postn-/-, but was not associated with changes in CtTV and CtBV, as only 16% of the fatigued bones formed some woven bone. Cortical porosity and remodelling did not increase either after fatigue in Postn-/- , and the level of damage remained high even after 30 days. As a result, strength remained compromised in Postn-/- mice. Contrary to Postn+/+ , which osteocytic lacunae showed a change in the degree of anisotropy (DA) after fatigue, Postn-/- showed no DA change. Hence periostin appears to influence bone materials properties, damage accumulation and repair, including local modeling/remodeling processes in response to fatigue. These observations suggest that the level of periostin expression could influence the propensity to fatigue fractures.

Bonnet, Nicolas; Gineyts, Evelyne; Ammann, Patrick; Conway, Simon J.; Garnero, Patrick; Ferrari, Serge

2013-01-01

104

Numerical and experimental investigations into life assessment of blade–disc connections of gas turbines  

Microsoft Academic Search

The positively engaged connection between blade and disc of a gas turbine is highly stressed by fatigue and creep fatigue loadings. For this purpose, a new calculating method based on inelastic finite element analyses considering the main influences on damage was developed at MPA Stuttgart. Low cycle fatigue (LCF) tests with component-like specimens have been conducted for verification. Experimental data

Stephan Issler; Eberhard Roos

2003-01-01

105

Near-terminal creep damage does not substantially influence fatigue life under physiological loading.  

PubMed

Cortical bone specimens were damaged using repeated blocks of tensile creep loading until a near-terminal amount of creep damage was generated (corresponding to a reduction in elastic modulus of 15%). One group of cortical bone specimens was submitted to the near-terminal damage protocol and subsequently underwent fatigue loading in tension with a maximum strain of 2000 ?? (Damage Fatigue, n=5). A second group was submitted to cyclic fatigue loading but was not pre-damaged (Control Fatigue, n=5). All but one specimen (a damaged specimen) reached run-out (10 million cycles, 7.7 days). No significant differences in microscopic cracks or other tissue damage were observed between the two groups or between either group and additional, completely unloaded specimens. Our results suggest that damage in cortical bone allograft that is not obvious or associated with a stress riser may not substantially affect its fatigue life under physiologic loading. PMID:21592481

Stern, Lorraine C; Brinkman, Jennifer G; Furmanski, Jevan; Rimnac, Clare M; Hernandez, Christopher J

2011-05-18

106

Damage assessment in CFRP laminates exposed to impact fatigue loading  

NASA Astrophysics Data System (ADS)

Demand for advanced engineering composites in the aerospace industry is increasing continuously. Lately, carbon fibre reinforced polymers (CFRPs) became one of the most important structural materials in the industry due to a combination of characteristics such as: excellent stiffness, high strength-to-weight ratio, and ease of manufacture according to application. In service, aerospace composite components and structures are exposed to various transient loads, some of which can propagate in them as cyclic impacts. A typical example is an effect of the wind gusts during flight. This type of loading is known as impact fatigue (IF); it is a repetition of low-energy impacts. Such loads can cause various types of damage in composites: fibre breaking, transverse matrix cracking, de-bonding between fibres and matrix and delamination resulting in reduction of residual stiffness and loss of functionality. Furthermore, this damage is often sub-surface, which reinforces the need for more regular inspection. The effects of IF are of major importance due its detrimental effect on the structural integrity of components that can be generated after relatively few impacts at low force levels compared to those in a standard fatigue regime. This study utilises an innovative testing system with the capability of subjecting specimens to a series of repetitive impacts. The primary subject of this paper is to assess the damaging effect of IF on the behaviour of drilled CFRP specimens, exposed to such loading. A detailed damage analysis is implemented utilising an X-ray micro computed tomography system. The main findings suggested that at early stages of life damage is governed by o degree splits along the length of the specimens resulting in a 20% reduction of stiffness. The final failure damage scenario indicated that transverse crasks in the 90 degree plies are the main reason for complete delamination which can be translated to a 50% stiffness reduction.

Tsigkourakos, George; Silberschmidt, Vadim V.; Ashcroft, I. A.

2011-07-01

107

Influence of oxidation treatment on fatigue and fatigue-induced damage of commercially pure titanium.  

PubMed

In this investigation, the cyclic deformation behaviour of commercially pure titanium was characterized in axial stress controlled constant amplitude and load increase tests, as well as in rotating bending tests. The influence of different clinically relevant surface treatments (polishing, thermal and anodic oxidizing) on the fatigue behaviour was investigated. All tests were realized in oxygen-saturated Ringer's solution. The cyclic deformation behaviour was characterized by mechanical hysteresis measurements. In addition, the change of the free corrosion potential and the corrosion current during the fatigue tests in simulated physiological media indicated such types of surface damage as slip bands, microcracks and oxide film ablation. Microstructural changes on the specimen surfaces were examined by scanning electron microscopy. PMID:19394905

Leinenbach, C; Eifler, D

2009-03-31

108

Integration of structural health monitoring and fatigue damage prognosis  

NASA Astrophysics Data System (ADS)

This paper presents a Bayesian probabilistic methodology to integrate model-based fatigue damage prognosis (FDP) with online and offline structural health monitoring (SHM) data. The prognosis uses fracture mechanics-based fatigue crack growth modeling, along with quantification of various sources of uncertainty, including natural variability, data uncertainty and model errors. These uncertainty sources are connected using a Bayesian network and a probabilistic sensitivity analysis is performed to assess the uncertainty contributions from these sources. The cycle-by-cycle simulation of fatigue crack growth is expedited via the use of a surrogate modeling technique (Gaussian process model) to replace computationally expensive finite element analysis. Real-time monitoring data of external variable amplitude loading history is used to construct a Bayesian autoregressive integrated moving average (ARIMA) model to predict and update the loading. On-ground crack inspection data is used to quantify the uncertainty in the initial and current size of an existing crack, using the Bayesian approach. Three possible cases of inspection results are considered: (1) crack is not detected; (2) crack is detected but not measured; (3) crack is detected and measured. Different scenarios of data availability (load monitoring data and inspection data) are considered for the prognosis of an individual component in a fleet. A numerical example, surface cracking in a rotorcraft mast under service loading, is implemented to illustrate the proposed methodology. The results of prognosis are validated using Bayesian hypothesis testing.

Ling, You; Mahadevan, Sankaran

2012-04-01

109

Implementation of a Two-Axis Servo-Hydraulic System for Full-Scale Fatigue Testing of Wind Turbine Blades  

SciTech Connect

Recently, the blade fatigue testing capabilities at NREL were upgraded from single-axis to two-axis loading. To implement this, several practical challenges were addressed, as hardware complexity increased dramatically with two actuators applying the loads at right angles to each other. A custom bellcrank was designed and implemented to minimize the load angle errors and to prevent actuator side loading. The control system was upgraded to accept load and displacement feedback from two actuators. The inherent long strokes uniquely associated with wind turbine blade-tests required substantial real-time corrections for both the control and data systems. A custom data acquisition and control system was developed using a National Instruments LabVIEW platform that interfaces with proprietary servo-hydraulic software developed by MTS Corporation. Before testing, the program is run under quasi-static (slow speed) conditions and iterates to determine the correct operational control parameters for the controller, taking into consideration geometry, test speed, and phase angle errors between the two actuators. Comparisons are made between single-axis and two-axis test loads using actual test load data and load uncertainties are qualitatively described. To date, two fatigue tests have been completed and another is currently ongoing using NREL's two-axis capability.

Hughes, S. D.; Musial, W. D. [National Renewable Energy Lab., Golden, CO (US); Stensland, T. [Stensland Technologies (US)

1999-09-09

110

EXPERIMENTAL IDENTIFICATION OF FATIGUE DAMAGE MODEL FOR SHORT GLASS FIBRE REINFORCED THERMOPLASTIC COMPOSITES  

Microsoft Academic Search

A polycyclic fatigue damage model for short glass fibre reinforced thermoplastics is developed and implemented into ABAQUS FE code using UMAT subroutine. The MNL model is introduced here in terms of damage rates:

H. Nouri; H. Chalal; F. Meraghni; P. Lory

111

Determination of damage functions for the pitting of AISI type 403 blade alloy and ASTM A470\\/471 disk alloy  

Microsoft Academic Search

The prediction of pitting accumulation on turbine blades and disks is of particular importance to predict localized corrosion damages in low pressure (LP) steam turbines. Damage Function Analysis (DFA) and Deterministic Extreme Value Statistics (DEVS) have been employed to predict the pitting damage on AISI Type 403 stainless steel (SS) blade alloy and ASTM A470\\/471 disk steel in simulated LP

Yancheng Zhang

2005-01-01

112

A damage function used for prediction of low cyclic fatigue life  

Microsoft Academic Search

In this paper, the cyclic plastic strain energy is acted as damage variable and its mathematical model of transient response\\u000a is established. The nonlinear fatigue damage function is given by means of the damage mechanical method. The formula used\\u000a for prediction of low cyclic fatigue life is obtained from this damage function which takes into acount the cyclic relativity\\u000a of

Jiang Fengchun; Liu Ruitang; Liu Diankui

1999-01-01

113

Knee joint neuromuscular activation performance during muscle damage and superimposed fatigue  

Microsoft Academic Search

This study examined the concurrent effects of exercise-induced muscle damage and superimposed acute fatigue on the neuromuscular activation performance of the knee flexors of nine males (age: 26.7±6.1 years; height 1.81±0.05 m; body mass 81.2±11.7 kg [mean±s]). Measures were obtained during three experimental conditions: (i) ‘fatigue-muscle damage’, involving acute fatiguing exercise performed on each assessment occasion plus a single episode

Claire Minshull; Roger Eston; David Rees; Nigel Gleeson

2012-01-01

114

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

Microsoft Academic Search

Nonlinear ultrasonic (NLU) harmonic generation system was used to characterize the fatigue damage in a flat hour-glass, high strength Al-Cu-Zn-Mg alloy, AA7175-T7351 specimens. Experiments were carried out to introduce controlled levels of fatigue damage under constant amplitude loading to determine the NLU response using surface acoustic wave (or Rayleigh mode) at regular intervals of fatigue life. The NLU parameter (A2\\/A12)

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

2008-01-01

115

Characterisation of fatigue crack growth and related damage mechanisms in FRP–metal hybrid laminates  

Microsoft Academic Search

Fatigue crack growth and related damage mechanisms were investigated experimentally in a hybrid laminate consisting of carbon fibre-reinforced epoxy and an aluminium alloy. During the fatigue cycling, the strain within a defined area in the vicinity of the crack was measured directly using embedded fibre-optic Bragg grating sensors. The progress of delamination damage was monitored by means of an in

T. S. P. Austin; M. M. Singh; P. J. Gregson; P. M. Powell

2008-01-01

116

Evaluation of fatigue damage in an austenitic stainless steel (SUS304) using the eddy current probe  

Microsoft Academic Search

In order to prevent accidents, it is very important to evaluate fatigue damage in an austenitic stainless steel, which is widely used in structural components of industries. Some research groups have already proposed the evaluation method such as the residual magnetization method for this purpose. The residual magnetization method was effective to evaluate fatigue damage in austenitic stainless steels. However,

M. Oka; T. Yakushiji; Y. Tsuchida; M. Enokizono

2005-01-01

117

Stochastic Measure of Fatigue Crack Damage for Health Monitoring of Ductile Alloy Structures  

Microsoft Academic Search

This paper models a stochastic measure of fatigue crack damage in ductile alloys that are commonly encountered in structures and machinery components of complex mechanical systems such as land, air, ocean, and space vehicles. The constitutive equations of the damage measure are built upon the physics of fracture mechanics and are substantiated by Karhunen-Loeve decomposition of fatigue test data where

Asok Ray

2004-01-01

118

A thermo-mechanical fatigue damage model for variable temperature and loading amplitude conditions  

Microsoft Academic Search

A fatigue life prediction method for thermo-mechanical fatigue damage under variable temperature and loading amplitudes was proposed. In this approach, a rainflow cycle counting technique was used to extract cycle counts from the mechanical loading history. For each loading cycle, an equivalent damage temperature was determined. Once the equivalent temperature was used, the loop would be guaranteed closed. This approach

Hong Tae Kang; Yung-Li Lee; Jim Chen; David Fan

2007-01-01

119

Characterization of fretting fatigue damage using nondestructive approaches  

NASA Astrophysics Data System (ADS)

Ti-6Al-4V alloy specimens cut form a forged plate with a duplex microstructure, similar to the microstructure used in fan blades were tested under conditions of high-cycle fretting fatigue. The contact geometry, the normal stress, as well as the cyclic stress were selectee such that the mixed, slip-stick regime prevails during the experiments. Following testing, the specimens as well as the fretting pads were characterized by a variety of techniques including white light interference profilometry, scanning electron microscopy, ultrasonic force microscopy, microhardness testing, and electron dispersive spectroscopy (EDS). The results revealed that the surface roughness of the slip region increases compared to the roughness of the stick, and non-contact ones. In addition, at the higher spatial frequencies, the power spectral density (PSD) of the slip region increases compared to the PSD of the stick and non- contact regions, thus revealing that an increase of the population of the smaller size asperities occurs. The microstructure of the material below the slip zone was found to be transformed to a finer one; and the percentage of the transformed beta phase has been decreased substantially. The elastic property variation of this region was determined by ultrasonic force microscopy; the results revealed that in contrast to what found for the bulk of the material, there are significant local differences of the elastic properties inside the fretting-affected zone. In addition, the changes in the plastic behavior of the region below the slip zone, was determined using microhardness measurements. It was found that this transformed microstructure area, has also a higher hardness compared to the hardness of the bulk structure. Booth elastic and plastic property variations were attributed to the increased percent of alpha phase and the decreased amount of beta in the transformed zone, since the former phase exhibits higher elastic moduli as well as flow stresses.In addition, changes in the concentration of the oxygen at the specimen's surface as well as inside the transformed zone were examined by energy dispersive spectroscopy (EDS). The EDS analysis revealed a high concentration of oxygen on the specimen's surface only at the slip region of the two contacting materials. This finding indicates that elevated temperatures were developed during the fretting fatigue testing, which enable the diffusion of oxygen from the atmosphere to the alloy. However, within the transformed zone, no detectable differences in the oxygen concentration were revealed. This finding allowed us to assume that stress induced transformation is the most probable mechanism.

Matikas, Theodore E.; Shell, Eric B.; Nicolaou, Perikles D.

1999-02-01

120

Multiple-site-damage fatigue of riveted joints  

NASA Astrophysics Data System (ADS)

Results of fatigue tests in riveted lap joints, including fractographic observations, are presented and analyzed. They indicate that the load transmission in a riveted lap joint is a rather complex phenomenon, as confirmed by quite different crack initiation mechanisms. It may not be expected that fracture mechanics predicts early crack growth with a practically useful degree of accuracy. Most important, the fractographic analysis reveals, that if there are visible cracks in a riveted lap joint, there are many small cracks at most rivet holes in the same critical row of rivets. A multiple site damage situation is present. The conclusion also applies to fuselage lap joints. Scatter in laboratory tests in riveted lap joint specimens is relatively low. However, scatter of riveted joints in a fleet of aircraft may be larger for several reasons. Crack growth in riveted lap joints may be sufficiently slow to allow a timely detection in service. For aging aircraft this should be confirmed by full scale testing.

Schijve, J.

1992-04-01

121

A Damage Mechanics-Based Fatigue Life Prediction Model for Solder Joints  

Microsoft Academic Search

A thermomechanical fatigue life prediction model based on the theory of damage mechan- ics is presented. The damage evolution, corresponding to the material degradation under cyclic thermomechanical loading, is quantified thermodynamic framework. The damage, as an internal state variable, is coupled with unified viscoplastic constitutive model to characterize the response of solder alloys. The damage-coupled viscoplastic model with kinematic and

Hong Tang

2008-01-01

122

Modelling of damage and failure of glass\\/epoxy composite plates subject to impact fatigue  

Microsoft Academic Search

An investigation has been carried out to study the impact fatigue damage of glass\\/epoxy laminated composites. Accumulation of damage, such as matrix cracking, delamination and fibre breakage, with repeated impact of the composite material may reduce the overall stiffness. These damage modes have been combined in a very complicated way to describe damage growth and fracture. A model is proposed

K Azouaoui; S Rechak; Z Azari; S Benmedakhene; A Laksimi; G Pluvinage

2001-01-01

123

Fatigue analysis of cemented hip prosthesis: damage accumulation scenario and sensitivity analysis  

Microsoft Academic Search

This work is dedicated to the fatigue analysis of cemented total hip arthroplasty. In particular the damage evaluation scenario is simulated and a sensitivity analysis is performed. To this end, two different damage evaluation algorithms (the elasto-brittle and the continuous damage one) are proposed and implemented in the finite element code ABAQUS®. Some global damage criteria are introduced to quantify

P. Colombi

2002-01-01

124

Detecting fatigue damage in 2.25Cr-1Mo steel with scanning SQUID gradiometry  

NASA Astrophysics Data System (ADS)

In order to develop a new method for detecting fatigue damage nondestructively in 2.25Cr-1Mo steel, which is used in high temperature steam piping of fossil power plants and petroleum chemical facilities, fractured and interrupted samples in low-cycle fatigue (LCF) tests were investigated using scanning superconducting quantum interference device (SQUID) gradiometer. High temperature LCF experiments on 2.25Cr-1Mo steel were conducted to obtain various fatigue damage ratio, Df. Simultaneously, we also examined the fatigued samples by optical microscopy, electron back scatter diffraction pattern, magnetic force microscopy and hardness measurements to analyze the damage level. Except for a couple of samples, SQUID integrated intensity decreased with increasing Df, suggesting the potential of SQUID to evaluate fatigue damage in 2.25Cr-1Mo steel.

Isawa, K.; Hasegawa, S.; Miyaguchi, K.

2009-10-01

125

Advanced nondestructive examination technologies for measuring fatigue damage in nuclear power plant components  

SciTech Connect

This paper presents recent results from an ongoing project at the Idaho National Engineering Laboratory (INEL) to develop advanced nondestructive methods to characterize the aging degradation of nuclear power plant pressure boundary components. One of the advanced methods, positron annihilation, is being developed for in situ characterization of fatigue damage in nuclear power plant piping and other components. This technique can detect and correlate the microstructural changes that are precursors of fatigue cracking in austenitic stainless steel components. In fact, the initial INEL test results show that the method can detect fatigue damage in stainless steel ranging from a few percent of the fatigue life up to 40 percent.

MacDonald, P.E.; Shah, V.N.; Akers, D.W.

1995-12-01

126

Helicopter rotor blade frequency evolution withdamage growthand signal processing  

Microsoft Academic Search

Structural damage in materials evolves over time due to growthof fatigue cracks in h omogenous materials and a complicated process of matrix cracking, delamination, fiber breakage and fiber matrix debonding in composite materials. In this study, a finite element model of the helicopter rotor blade is used to analyze the effect of damage growth on the modal frequencies in a

Niranjan Roy; Ranjan Ganguli

127

Computational Fluid Dynamics Analysis of Blade Tip Clearances on Hemodynamic Performance and Blood Damage in a Centrifugal Ventricular Assist Device  

PubMed Central

An important challenge facing the design of turbodynamic ventricular assist devices (VADs) intended for long-term support is the optimization of the flow path geometry to maximize hydraulic performance while minimizing shear-stress-induced hemolysis and thrombosis. For unshrouded centrifugal, mixed-flow and axial-flow blood pumps, the complex flow patterns within the blade tip clearance between the lengthwise upper surface of the rotating impeller blades and the stationary pump housing have a dramatic effect on both the hydrodynamic performance and the blood damage production. Detailed computational fluid dynamics (CFD) analyses were performed in this study to investigate such flow behavior in blade tip clearance region for a centrifugal blood pump representing a scaled-up version of a prototype pediatric VAD. Nominal flow conditions were analyzed at a flow rate of 2.5 L/min and rotor speed of 3000 rpm with three blade tip clearances of 50, 100, and 200 ?m. CFD simulations predicted a decrease in the averaged tip leakage flow rate and an increase in pump head and axial thrust with decreasing blade tip clearances from 200 to 50 ?m. The predicted hemolysis, however, exhibited a unimodal relationship, having a minimum at 100 ?m compared to 50 ?m and 200 ?m. Experimental data corroborate these predictions. Detailed flow patterns observed in this study revealed interesting fluid dynamic features associated with the blade tip clearances, such as the generation and dissipation of tip leakage vortex and its interaction with the primary flow in the blade-blade passages. Quantitative calculations suggested the existence of an optimal blade tip clearance by which hydraulic efficiency can be maximized and hemolysis minimized.

Wu, Jingchun; Paden, Bradley E.; Borovetz, Harvey S.; Antaki, James F.

2011-01-01

128

Acoustography as a means of monitoring impact damage in composites under fatigue conditions  

NASA Astrophysics Data System (ADS)

Acoustography is a novel ultrasonic imaging technique in which the ultrasound that passes through a test piece from a broad sound source is imaged by a liquid crystal screen acousto-optic detector. Its advantage is that large area real-time ultrasonic images can be produced without the need for scanning. An acoustography system has been adapted to image defects in samples whilst they are subjected to fatigue in a dynamic mechanical testing machine. The samples studied are of aircraft carbon fiber composite which have been impact damaged at the ``barely visible impact damage'' (BVID) level. The aim of the work is to determine ``safe'' zero damage growth fatigue lives of the composites. The integration of the acoustography imaging system and the fatigue testing machine will be explained. The data taking and image analysis procedures developed to provide quantitative measures of damage size as a function of fatigue cycles will be outlined. Damage growth data will be presented. .

Chen, A. S.; Almond, D. P.; Harris, B.

2000-05-01

129

Damage Characteristics in Notched Carbon Fiber Composites Subjected to Fatigue Loading—Environmental Effects  

Microsoft Academic Search

Several destructive and non-destructive methods were used to study the effect of ab sorbed moisture and\\/or heat on the tension-compression fatigue properties of notched, 0°\\/±45°, carbon fiber reinforced plastic laminates. The main objective was the understanding of the nature of fatigue damage around notches (sharp slits and circular holes), under hot and\\/or wet conditions. The fatigue performance of the notched

J. Morton; S. Kellas; S. M. Bishop

1988-01-01

130

Simplified methods of creep-fatigue damage evaluations and the application to life extension  

Microsoft Academic Search

A simplified method for creep-fatigue damage evaluations is presented. The material requirements include the standard tensile, creep-rupture and fatigue data over temperature ranges and special creep-fatigue test data. From the average data of these tests the average cyclic constitutive relationships are determined without any reduction factors. These constitutive equations are used in the analyses of the design loadings to obtain

Manjoine

1994-01-01

131

Fatigue is more damaging than creep in ligament revealed by modulus reduction and residual strength.  

PubMed

Following injury of a complementary joint restraint, ligaments can be subjected to higher than normal stresses. Normal ligaments are exposed to static (creep) and cyclic (fatigue) loading from which damage can accumulate at these higher than normal stresses. This study tracked damage accumulation during creep and fatigue loading of normal rabbit medial collateral ligaments (MCLs) over a range of stresses, using modulus reduction as a marker of damage. Creep tests were interrupted occasionally with unloading/reloading cycles to measure modulus. Test stresses were normalized to ultimate tensile strength (UTS): 60%, 30%, and 15% UTS. Not all creep and fatigues tests progressed until rupture but were stopped and followed by an assessment of the residual strength of that partially damaged ligament using a monotonic failure test. Fatigue loading caused earlier modulus reduction than creep. Modulus reduction occurred at lower increases in strain (strain relative to initial strain) for fatigue than creep. In other words, at the same time or increase in strain, fatigue is more damaging than creep because the modulus ratio reduction is greater. These findings suggest that creep and fatigue have different strain and damage mechanisms. Ligaments exposed to creep or fatigue loading which produced a modulus reduction had decreased residual strength and increased toe-region strain in a subsequent monotonic failure test. This finding confirmed that modulus reduction during creep and fatigue is a suitable marker of partial damage in ligament. Cyclic loading caused damage earlier than static loading, likely an important consideration when ligaments are loaded to higher than normal magnitudes following injury of a complementary joint restraint. PMID:17629791

Thornton, Gail M; Schwab, Timothy D; Oxland, Thomas R

2007-07-14

132

A study on coating class damage degree by use cycle of gas turbine blade coating  

NASA Astrophysics Data System (ADS)

The component of the hot gas path in gas turbines can survive to very high temperatures because they are protected by ceramic Thermal Barrier Coating(TBC); the failure of such coating can dramatically reduce the component life. A reliable assessment of the Coating integrity and/or an Incipient TBC Damage Detection can help both in optimizing the inspection intervals and in finding the appropriate remedial actions. In this paper the potential of NDT techniques applicable to the metallo/ceramic coating hot parts are discussed in the light of both results obtained on laboratory aged specimens and in field measurements on operated components. An investigation of the NDTs capability to detect damage evolution was performed on thermal-cycled specimens coated with TBC by pulsed thermography. The observation of metallogaphy sections of the thermal cycled specimens allowed to give the right the interpretation to the results of NDT methodology and enlightened its specific characteristics and potentiality. Moreover in field applicability is discussed for each technique. Finally it is shown how an integrated approach of suitable coating evolution models and complimentary NDT techniques can provide an interesting assessment of the damage level of the metallo/ceramic coating of operated rotating blade

Choi, Choul Jun; Kim, Jae Yeol

2007-10-01

133

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

134

Use of Eddy Current Technology to Assist in the Evaluation of the Fatigue Damage of Electrical Conductors  

Microsoft Academic Search

The article deals with the evaluation of fatigue damage on overhead conductors which have been in service for a period exceeding 50 years. Under wind excitation, electrical transmission lines are subjected to aeolian vibrations that may induce wire fatigue of conductor at the exit of supporting equipment. This fatigue phenomenon is a fretting fatigue problem which is located at contact

C. Dalpe; S. Goudreau; L. Cloutier; A. Cardou

2008-01-01

135

Stacking Sequence Effects on Fatigue Intra-laminar Damage Progression in Composite Joints  

NASA Astrophysics Data System (ADS)

In this paper the effects of the stacking sequence on the fatigue intra-laminar damage accumulation in pinned composite joints is investigated. A fatigue damage propagation numerical model based on gradual material degradation rules and Hashin fatigue failure criteria is formulated, implemented in a finite element platform and then used to simulate the intra-laminar fatigue damage evolution in the analysed composite joints. The model has been preliminary validated against literature experimental data in terms of s-n curves providing confirmation of its effectiveness in predicting the joints fatigue life. Different stacking sequences: zero-dominated, quasi-isotropic, cross-ply with different 0 ° and 90 ° plies distributions, have been considered when investigating the influence of the stacking sequence on the fatigue behaviour of the joints. The simulation of the joints' fatigue life provided detailed information on the intra-laminar damage mechanisms on-set and evolution related to fatigue gradual degradation of material stiffness and strength for different values of the applied maximum stresses.

Riccio, A.; Mozzillo, G.; Scaramuzzino, F.

2013-06-01

136

Fatigue Damage in CFRP Woven Fabric Composites through Dynamic Modulus Measurements  

SciTech Connect

Advanced fiber reinforced composite materials offer substantial advantages over metallic materials for the structural applications subjected to fatigue loading. With the increasing use of these composites, it is required to understand their mechanical response to cyclic loading (1)-(4). Our major concern in this work is to macroscopically evaluate the damage development in composites during fatigue loading. For this purpose, we examine what effect the fatigue damage may have on the material properties and how they can be related mathematically to each other. In general, as the damage initiates in composite materials and grows during cyclic loading, material properties such as modulus, residual strength and strain would vary and, in many cases, they may be significantly reduced because of the progressive accumulation of cracks. Therefore, the damage can be characterized by the change in material properties, which is expected to be available for non-destructive evaluation of the fatigue damage development in composites. Here, the tension-tension fatigue tests are firstly conducted on the plain woven fabric carbon fiber composites for different loading levels. In the fatigue tests, the dynamic elastic moduli are measured on real-time, which will decrease with an increasing number of cycles due to the degradation of stiffness. Then, the damage function presenting the damage development during fatigue loading is determined from the dynamic elastic moduli thus obtained, from which the damage function is formulated in terms of a number of cycles and an applied loading level. Finally, the damage function is shown to be applied for predicting the remaining lifetime of the CFRP composites subjected to two-stress level fatigue loading.

Chiaki Miyasaka; K. L. Telschow

2004-07-01

137

Root damage analysis of aircraft engine blade subject to ice impact  

Microsoft Academic Search

The blade root response due to ice impact on an engine blade is simulated using the NASA in-house code BLASIM. The ice piece is modeled as an equivalent spherical object impacting on the leading edge of the blade and has the velocity opposite to that of the aircraft with direction parallel to the engine axis. The effect of ice impact

E. S. Reddy; G. H. Abumeri; C. C. Chamis; P. L. N. Murthy

1992-01-01

138

Damage Mechanics Based Fatigue Life Prediction for 63Sn-37Pb Solder Materials.  

National Technical Information Service (NTIS)

This paper presents a method of TMF analysis based on the theory of damage mechanics to examine the fatigue damage accumulation in 63 Sn-37Pb solder. The method is developed by extending a viscoplastic damage model proposed earlier by the authors (Wei, et...

Y. Wei C. L. Chow M. K. Neilsen H. E. Fang

2000-01-01

139

Acoustic emission energy as a fatigue damage parameter for CFRP composites  

Microsoft Academic Search

Carbon fibre reinforced plastic composite laminates have been tested under static and fatigue loading with acoustic emission (AE) as the main damage monitoring method. AE energy results were found to correlate with damage indicated by ultrasonic C-scanning and microscopic inspection in terms of type, location and accumulation of damage and to provide indications of effective failure states before catastrophic failure.

M. Bourchak; I. R. Farrow; I. P. Bond; C. W. Rowland; F. Menan

2007-01-01

140

Fatigue evaluation of wood laminates for the design of 100M diameter wind turbine blades.  

National Technical Information Service (NTIS)

The fatigue properties of wood laminates have been evaluated in axial tension, compression and shear. A complete constant life diagram has been constructed for Khaya ivorensis (African mahogany) from S-N curves at various R ratios. The form of S-N curves ...

P. W. Bonfield M. P. Ansell

1991-01-01

141

Analytical Methodology for Predicting the Onset of Widespread Fatigue Damage in Fuselage Structure.  

National Technical Information Service (NTIS)

NASA has developed a comprehensive analytical methodology for predicting the onset of widespread fatigue damage in fuselage structure. The determination of the number of flights and operational hours of aircraft service life that are related to the onset ...

C. E. Harris J. C. Newman R. S. Piascik J. H. Starnes

1996-01-01

142

Fatigue-induced damage in zr-based bulk metallic glasses.  

PubMed

In the present work, we investigate the effect of "fatigue" on the fatigue behavior and atomic structure of Zr-based BMGs. Fatigue experiments on the failed-by-fatigue samples indicate that the remnants generally have similar or longer fatigue life than the as-cast samples. Meanwhile, the pair-distribution-function (PDF) analysis of the as-cast and post-fatigue samples showed very small changes of local atomic structures. These observations suggest that the fatigue life of the 6-mm in-diameter Zr-based BMG is dominated by the number of pre-existing crack-initiation sites in the sample. Once the crack initiates in the specimen, the fatigue-induced damage is accumulated locally on these initiated sites, while the rest of the region deforms elastically. The results suggest that the fatigue failure of BMGs under compression-compression fatigue experiments is a defect-controlled process. The present work indicates the significance of the improved fatigue resistance with decreasing the sample size. PMID:23999496

Chuang, Chih-Pin; Yuan, Tao; Dmowski, Wojciech; Wang, Gong-Yao; Freels, Matt; Liaw, Peter K; Li, Ran; Zhang, Tao

2013-09-01

143

Damage development in pultruded composites for optical telecommunications cables under tensile and flexural fatigue  

Microsoft Academic Search

This paper investigates the long-term behaviour of pultruded glass-fibre composites, which are used as load-bearing components in optical telecommunications cables. Both flexural and tensile fatigue tests were conducted using the materials in their commercial product forms. Fatigue damage progression was monitored on-line by the acoustic emission technique. Damage accumulation was quantified by the stiffness loss evaluated from the change of

S. N. Kukureka; C. Y. Wei

2003-01-01

144

Effect of fatigue damage on the dynamic response frequency of spot-welded joints  

Microsoft Academic Search

The effect of fatigue damage on the dynamic natural frequency response was studied over the entire fatigue life process for tensile-shear spot-welded joints. The results of the experimental study showed that the changes to the specimens’ natural frequency varied non-linearly with the cycle ratio or damage fraction, and that relatively large changes in the natural frequency could be measured near

De-Guang Shang; Mark E. Barkey; Yi Wang; Teik C. Lim

2003-01-01

145

A continuum damage modeling of quasi-static fatigue strength of plain concrete  

Microsoft Academic Search

A three-dimensional phenomenological model is developed to describe the fatigue behavior of concrete. The approach is based on the framework of continuum damage mechanics where the fatigue model is derived by means of Marigo’s formulation where the yield concept is replaced by a loading–unloading irreversibility concept allowing to account for damage accumulation even for loading levels below the yield surface.

S. H. Mai; F. Le-Corre; G. Foret; B. Nedjar

146

Application of a Nonlinear Creep-Fatigue Damage Model to 2 1/4Cr-1Mo Steel  

NASA Astrophysics Data System (ADS)

A nonlinear damage model, previously developed for creep-fatigue life evaluation of Mod. 9Cr-1Mo steel and 316FR stainless steel in a high vacuum environment was applied to 2 1/4Cr-1Mo steel. In the damage model, the damage accumulation process is considered to be composed of three basic processes: fatigue, creep and creep-fatigue. The fatigue damage process consists of a crack initiation period and a crack growth period. The creep damage process consists of nucleation of creep cavities. Damage interaction is fatigue cracks propagate from creep cavities. Application of this damage model to creep-fatigue tests under complex waveforms and complex strain histories showed a good correlation with the experimental results within a factor of 2.

Jirapong, Kasivitamnuay; Nakamura, Toshiya; Asada, Yasuhide

147

Damage behaviour of composite systems under biaxial fatigue loading  

Microsoft Academic Search

I. INTRODUCTION In the industrial sectors where strength, stiffness and weight are often decisive, the criteria for fatigue and durability are of- ten key drivers. Therefore, fundamental studies, both experi- mentally and theoretically, of the fatigue behaviour and life ex- pectancy of composites are essential to increase their market share in engineering applications. Yet, current research shows a number of

Ebrahim Lamkanfi

148

Acoustic emission for fatigue damage characterization in metal plates  

Microsoft Academic Search

Acoustic emission (AE) supplies information on the fracturing behavior of different materials. In this study, AE activity was recorded during fatigue experiments in metal coupons. The plates were characterized by a symmetric V-shape notch and were loaded in tension–tension fatigue until final failure with concurrent AE activity monitoring. The relatively broad bandwidth of the sensors enabled the recording of a

D. G. Aggelis; E. Z. Kordatos; T. E. Matikas

2011-01-01

149

Crystallographic life model for single crystal turbine blade and validation by the miniature specimens cut from the turbine blades  

Microsoft Academic Search

Purpose – The purpose of this paper is to found a life model for the single crystal (SC) turbine blade based on the rate-dependent crystallographic plasticity theory. Design\\/methodology\\/approach – This life model has taken into consideration the creep and fatigue damages by the linear accumulation theory. A SC blade was taken from an aero-engine, which had worked for 1,000 hours,

Zhixun Wen; Naixian Hou; Baizhi Wang; Zhufeng Yue

2010-01-01

150

Assessment of material fatigue damage using nonlinear vibro-modulation technique  

NASA Astrophysics Data System (ADS)

Heavy periodic loads exerted on structural materials often lead to fatigue damage (material degradation at microscale) which may finally trigger irreversible fracture process. Conventional NDT techniques detect only the latter, and there is an increasing need for new tools to assess fatigue damage at the earliest possible stage, i.e., before fracture. This paper presents experimental results of early damage characterization using an innovative nonlinear vibro-modulation technique (VMT) [Donskoy et al., NDT&E Int. 34 (2001)]. In the experiments, fatigue damage was initiated in steel, aluminum, and carbon-carbon composite specimens during strain-controlled three-point bending high-cycling fatigue tests. The damage progress was independently monitored using dataflow from the testing machine and the real-time nonlinear vibro-modulation measurements. The tests demonstrated that the reduction in the specimens' stiffness (direct indication of damage accumulation) correlates well with the increase in the VMT's nonlinear damage index. These results confirm that VMT could offer new opportunities for early damage detection and remaining life prediction. [Work supported by NAVAIR.

Zagrai, Andrei; Donskoy, Dimitri; Chudnovsky, Alexander; Wu, Hudson

2001-05-01

151

Linear and nonlinear acoustic control of accumulated fatigue damage in steel  

NASA Astrophysics Data System (ADS)

We present results of linear and nonlinear acoustic testing of steel samples with different levels of fatigue damage. The steel specimens were tested under programed cyclic loading on a fatigue testing machine and accumulated different levels of fatigue damage. No visible surface-crack formations during fatigue cycling were observed. In other words, the emphasis was placed on the characterization of continued but physically invisible in service life conditions damage in different materials and structures. Both linear and nonlinear acoustic techniques were used to assess damage accumulation. (1) Impulse resonant acoustic spectroscopy (IRAS) is based on analysis of the free-sample vibration after impact excitation. It demonstrated the increasing of the resonance frequencies and Q factor with damage accumulation. (2) Nonlinear resonant acoustic spectroscopy (NRAS) is based on measurement of the resonance response for different levels of acoustic excitation. The amplitude-dependent frequency shift for damaged steel was observed to increased with damage accumulation. (3) Nonlinear wave modulation spectroscopy (NWMS) implies the modulation of ultrasound wave by lower frequency vibration. High level of the side-band components for damaged samples were observed. The comparison of different methods is given.

Sutin, Alexander; Kin, Yulian; Johnson, Paul

2001-05-01

152

Fatigue analysis of multiple site damage at a row of holes in a wide panel  

Microsoft Academic Search

This paper is concerned with predicting the fatigue life of unstiffened panels which contain multiple site damage (MSD). The initial damage consists of through-the-thickness cracks emanating from a row of holes in the center of a finite width panel. A fracture mechanics analysis has been developed to predict the growth, interaction, and coalescence of the various cracks which propagate in

Kimberley Buhler; Alten F. Grandt Jr.; E. J. Moukawsher

1994-01-01

153

Effect of Preloading on Fatigue Damage in Composite Structures: Part 1.  

National Technical Information Service (NTIS)

The effect of preload on damage development in unnotched graphite/epoxy laminates is studied. Two types of tension-tension fatigue tests were conducted on quasi-isotropic (0/45/-45/90)53, AS-4/3501-6 laminates, and damage was measured in the form of ply c...

H. T. Hahn J. L. Timmer J. Bartley-Cho S. Lee S. G. Lim

1996-01-01

154

Nondestructive Evaluation of Creep-Fatigue Damage: An Interim Report.  

National Technical Information Service (NTIS)

In view of the uncertainties involved in designing against creep-fatigue failure and the consequences of such failures in Class 1 nuclear components that operate at elevated temperature, the possibility of intermittent or even continuous non-destructive e...

R. E. Nickell

1977-01-01

155

Standardization of fretting fatigue test methods and equipment  

SciTech Connect

Papers contained in this book are grouped under the topics of the fundamental aspects of fretting fatigue testing (conceptual framework and mechanics of contact), methods and equipment for fretting fatigue testing, environmental and surface conditions, and nonconventional materials and test methods. Papers are presented on the problems of fretting fatigue testing, a critical appraisal of testing methods in fretting fatigue, the determination and control of contact pressure distribution in fretting fatigue, and fretting fatigue analysis of strength improvement models with grooving or knurling on a contact surface. Other papers include a critical review of fretting fatigue investigations at the Royal Aerospace Establishment, techniques for the characterization of fretting fatigue damage, improving fretting fatigue strength at elevated temperatures by shot peening in steam turbine steel, the fretting fatigue properties of a blade steel in air and vapor environments, and fretting fatigue of carbon-fiber-reinforced epoxy laminates.

Attia, M.H.; Waterhouse, R.B.

1992-01-01

156

Fatigue crack initiation and damage evolution of unnotched titanium matrix composites  

NASA Astrophysics Data System (ADS)

Fatigue crack initiation, multiplication, matrix crack density evolution, and stiffness reduction of several unnotched SCS-6 silicon carbide fiber-reinforced titanium and titanium aluminide matrix composites have been investigated experimentally and analytically. The effects of the thickness of the interfacial reaction layer and fiber coating on fatigue crack initiation life, crack growth rate, and fatigue damage evolution of the composites were examined. Growth behavior of small fatigue cracks in TMCs was also studied carefully. It was found that fatigue crack initiation and multiplication of TMCs are strongly influenced by the thickness of the interfacial reaction layer. Fatigue crack will not develop from the micro-notches in the interfacial reaction layer until the thickness of the reaction layer exceeds a critical value. Matrix crack growth rate is affected by the applied stress level, however, it appears to be independent of the matrix material and heat treatment. The combined effects of fatigue crack multiplication and propagation result in stiffness degradation of the composites. The Ag/Ta duplex fiber coating significantly improves the transverse tensile and flexural creep resistance of the SCS-6/Ti-25-10 composite. However, the Ag/Ta-coated composite exhibits a shorter crack initiation life, higher number of matrix cracks, and higher crack growth rate than the uncoated composite. The embrittlement of the residual Ag/Ta layer suggests that Ag is not an effective diffusion barrier to prevent the interdiffusion of atomic species across the interface. The high interfacial cracking density and high interfacial bond strength in the Ag/Ta-coated SCS-6/Tisb3Al composite are believed to be responsible for its poor fatigue damage tolerance. For titanium alloys, the threshold intensity factor range, Delta Ksbth, for small fatigue cracks in the matrix alloys of TMCs has been determined to be between 0.9 ˜ 1.0 MPa*msp{1/2} which is much lower than that for long fatigue cracks which is ˜5 MPa*msp{1/2}. The crack growth rate fluctuates widely while the cracks are short, and converges gradually with crack growth. The transition from short fatigue crack to long fatigue crack in the SCS-6/Ti-15-3 composite has been found to occur when the crack length is in the range of 400 to 1000 mum. Finally, an interface-controlled fatigue cracking model incorporating a modified shear-lag model, the strain-life equation, and a fiber bridging model is developed to predict the fatigue crack initiation life, matrix crack growth rate, saturated matrix crack spacing, normalized matrix crack density, and residual stiffness of the composites. The predicted fatigue properties correlate well with experimental results.

Her, Yung-Chiun

157

Measurement and analysis of damping factor in engineering materials to assess fatigue damage  

NASA Astrophysics Data System (ADS)

Metallic materials are used in many applications because of their economy, strength and endurance limit. Fatigue damage may increase the risk of failure under cyclic load. Energy dissipation, termed damping, occurs in engineering metals as a function of the cyclic loading history. Damping behavior of materials has been estimated using many different experimental techniques, and parameters i.e., the loss factor versus strain amplitude, frequency range, etc. However, micro-structural changes (fatigue damage) are also major contributors of failure or fracture in engineering materials. In order to measure energy dissipation, a damping monitoring method, which estimates the damping factor by vibration excitation, has been developed. Under a constant cyclic load, the effects of the number of fatigue cycles on the damping factor were studied for five different engineering metals. Experimental results show that the damping factor changes with the number of fatigue cycles. In addition, cyclic hardening, cyclic softening, and catastrophic failure effect the damping factor.

Colakoglu, Mehmet

158

An intelligent sensor system for monitoring fatigue damage in welded steel components  

Microsoft Academic Search

A sensor and data storage system that monitors fatigue damage in load-bearing steel components is described. The sensor is a thin steel sheet measuring 50 × 20 mm, with a pre-crack in its centre. It is fixed next to a welded joint on the component under test. It follows the component's flexions in service and begins to fatigue, thereby lengthening its crack. Crack

Bosco Fernandes; Patrick Gaydecki; F. Michael Burdekin

2006-01-01

159

Damage of low-alloy high temperature steels loaded by low-cycle fatigue and creep  

Microsoft Academic Search

Present-day models used for calculations of life at combinations of low-cycle fatigue loading and creep mostly work with experimental curves of life at constant amplitude of deformation. However, during such a type of loading, a relative proportion of damage caused by low-cycle fatigue and creep is changed.On the basis of large-extension experimental measurement made on low-alloy CrNiMoV and CrMoV steels,

Miroslav Kneifl; Ivo ?erný; Vladim??r B??na

2001-01-01

160

Nondestructive evaluation of creep-fatigue damage: an interim report. [LMFBR  

Microsoft Academic Search

In view of the uncertainties involved in designing against creep-fatigue failure and the consequences of such failures in Class 1 nuclear components that operate at elevated temperature, the possibility of intermittent or even continuous non-destructive examination of these components has been considered. In this interim report some preliminary results on magnetic force and ultrasonic evaluation of creep-fatigue damage in an

Nickell

1977-01-01

161

Fatigue-damage evaluation in aluminum heat-transfer tubes by measuring dislocation cell-wall thickness  

Microsoft Academic Search

Evolution of dislocation structure during low cycle fatigue in 3003 aluminum alloy was investigated for the purpose of finding a possible parameter to indicate fatigue damage prior to crack initiation. In low cycle fatigue, it is observed that by increasing the number of cycles, the dislocation structure develops to random cells, then changes to clear cells and finally to sub-grains.

H Yaguchi; H Mitani; K Nagano; T Fujii; M Kato

2001-01-01

162

Improving fatigue damage resistance of alumina through surface grading.  

PubMed

Porcelain-veneered alumina crown restorations often fail from bulk fracture resulting from radial cracks that initiate at the cementation surface with repeated flexure of the stiffer crown layers on the soft dentin support. We hypothesized that bulk fracture may be substantially mitigated by grading the elastic modulus at the crown surfaces. In this study, we fabricated graded structures by infiltrating glass into dense alumina plates, resulting in a diminished modulus at the surface layers. The plates were then bonded to polycarbonate substrates and subjected to fatigue loading in water. Tests were terminated when fracture occurred at the cementation tensile surface or at the fatigue endurance limit (1 million cycles). Infiltrated specimens showed a significant increase in fatigue fracture loads over non-infiltrated controls. Our results indicate that controlled elastic gradients at the surface could be highly beneficial in the design of fracture-resistant alumina crowns. PMID:21555776

Ren, L; Liu, L; Bhowmick, S; Gerbig, Y B; Janal, M N; Thompson, V P; Zhang, Y

2011-05-09

163

Improving Fatigue Damage Resistance of Alumina through Surface Grading  

PubMed Central

Porcelain-veneered alumina crown restorations often fail from bulk fracture resulting from radial cracks that initiate at the cementation surface with repeated flexure of the stiffer crown layers on the soft dentin support. We hypothesized that bulk fracture may be substantially mitigated by grading the elastic modulus at the crown surfaces. In this study, we fabricated graded structures by infiltrating glass into dense alumina plates, resulting in a diminished modulus at the surface layers. The plates were then bonded to polycarbonate substrates and subjected to fatigue loading in water. Tests were terminated when fracture occurred at the cementation tensile surface or at the fatigue endurance limit (1 million cycles). Infiltrated specimens showed a significant increase in fatigue fracture loads over non-infiltrated controls. Our results indicate that controlled elastic gradients at the surface could be highly beneficial in the design of fracture-resistant alumina crowns.

Ren, L.; Liu, L.; Bhowmick, S.; Gerbig, Y.B.; Janal, M.N.; Thompson, V.P.; Zhang, Y.

2011-01-01

164

Use of atomic force microscopy for characterizing damage evolution during fatigue  

NASA Astrophysics Data System (ADS)

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.

Cretegny, Laurent

2000-10-01

165

Multiaxial low-cycle fatigue damage evaluation using a. c. potential method for alloy 738LC superalloy  

SciTech Connect

This paper studies tension/torsion multiaxial low-cycle fatigue lives and creep-fatigue damage evaluation for Alloy 738LC superalloy. Tension/torsion creep-fatigue tests were carried out using hollow cylinder specimens and multiaxial creep-fatigue lives were obtained. The Mises' equivalent strain correlated the multiaxial low cycle fatigue lives within a factor of two scatter band. An a.c. potential method is developed to detect the creep-fatigue damage associated with crack nucleation and extension. A.c. potentials at high frequencies accurately detect the creep-fatigue damage from the early stage of life while those at low frequencies detect that in the final stage of life. A.c. potentials at high frequencies detect the crack density, defined as the total crack length per unit area, and maximum crack length more sensitivity than those at low frequencies.

Isono, Yoshitada; Sakane, Masao; Ohnami, Masateru (Ritsumeikan Univ., Kyoto (Japan). Dept. of Mechanical Engineering); Fujiyama, Kazunari (Toshiba Corp., Yokohama (Japan). Heavy Apparatus Engineering Lab.)

1994-10-01

166

Micro-Damage Evaluation and Remaining Fatigue Life Assessment with Nonlinear Vibro-Modulation Technique  

NASA Astrophysics Data System (ADS)

Assessment of structural deterioration due to in-service and environmental loads is an essential element in ensuring safety, operability and long life of various structures and structural components. We applied vibro-acoustic modulation technique to monitor material degradation at the micro/meso scale before the onset of the macro-scale fracture. The technique explores nonlinear acoustic interaction of high frequency ultrasound and low frequency structural vibration at the site of the incipient damage. It is shown that micro/meso scale degradation increases the material nonlinearity leading to modulation of the high frequency ultrasonic signal by low frequency vibration, quantified by the nonlinear acoustic Damage Index (DI). Numerous tests with hundreds of test coupons proved high sensitivity of the developed technique to micro/meso scale fatigue damage accumulation. The study further demonstrated that the remaining life of the fatigued material can be predicted using phenomenological damage accumulation rule expressed through measured Damage Index.

Donskoy, Dimitri; Chudnovsky, Alexander; Zagrai, Andrei; Golovin, Edward

2008-06-01

167

Multiple-site-damage fatigue of riveted joints  

Microsoft Academic Search

Results of fatigue tests in riveted lap joints, including fractographic observations, are presented and analyzed. They indicate that the load transmission in a riveted lap joint is a rather complex phenomenon, as confirmed by quite different crack initiation mechanisms. It may not be expected that fracture mechanics predicts early crack growth with a practically useful degree of accuracy. Most important,

J. Schijve

1992-01-01

168

Fatigue crack propagation damaging micromechanisms in ductile cast irons  

Microsoft Academic Search

Ductile iron discovery in 1948 gave a new lease on life to the cast iron family. In fact, these cast irons are characterized both by a high castability and by high toughness values, combining cast irons and steel good properties. Ductile cast irons are also characterized by high fatigue crack propagation resistance, although this property is still not widely investigated.In

M. Cavallini; O. Di Bartolomeo; F. Iacoviello

2008-01-01

169

Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model  

Microsoft Academic Search

The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. As part of a NAVAIR High Strength Steel Corrosion–Fatigue Assessment Program, methods were studied to predict the impact that corrosion-induced surface roughness has on the fatigue life of high-strength steel aircraft components. In order to adequately capture the corrosion damage features that cause fatigue

D. T. Rusk; W. Hoppe

2009-01-01

170

Development of a new fatigue damage growth model for polymer matrix composites  

NASA Astrophysics Data System (ADS)

The objective of this research is to develop a new fatigue crack growth model for fiber reinforced polymer composites. This new model takes into account the progressive damage that occurs at each load increment in fatigue cycling through a weighted average stress intensity factor. The fatigue crack growth rate is modeled using a power law equation; however, the fatigue damage controlling parameters used in this equation are the stress intensity range as well as the weighted stress intensity factor. The model was developed and verified using three different polymer matrix composites, namely, a randomly oriented short carbon fiber reinforced thermoplastic (PEEK), a polyester sheet molding compound composite containing randomly oriented short glass fibers and a plain weave glass fabric reinforced epoxy. Fatigue crack growth experiments were conducted using either a compact tension specimen or a double cantilever beam specimen. The stress intensity approach is used for the first two composites. The strain energy release rate approach is used for the woven fabric reinforced epoxy matrix composite since delamination growth was the primary mode of fatigue failure in these laminates and delamination growth can be better modeled using the strain energy release rate. In all cases, it was observed that the proposed model given by the following equation can represent the fatigue crack growth rate at different load ratio in a unified equation${da/ dN}=B(Ksbsp{average}{gamma}.Delta Ksp{1-gamma})sp {p}where, B, gamma$ and p are the model constants determined from the fatigue crack growth rate data. The fatigue crack growth rate predicted with this single power law equation for each load ratio gives a close agreement with the experimental data for all three composites under study.

Atodaria, Devrajsinh R.

171

Fatigue  

MedlinePLUS

... sense, fatigue is defined as a lack of energy, a subjective feeling of being tired. Fatigue also ... muscular dystrophies as muscles weaken and require greater energy to perform the same activities. Types of fatigue ...

172

Fatigue  

MedlinePLUS

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

173

Characterization of low cycle fatigue damage in 9Cr–1Mo ferritic steel using X-ray diffraction technique  

Microsoft Academic Search

X-ray diffraction (XRD) technique has been used to characterize the low cycle fatigue (LCF) damage in 9Cr–1Mo ferritic steel. In this study, full-width at half-maximum (FWHM) of the XRD peak has been measured for assessing the fatigue damage. Fully reversed total-axial-strain controlled fatigue tests have been performed at ambient temperature (300K) at strain amplitudes of ±0.25%, ±0.50% and ±0.75%. FWHM

Sanjay Rai; B. K Choudhary; T Jayakumar; K. Bhanu Sankara Rao; Baldev Raj

1999-01-01

174

Fatigue analysis of multiple site damage at a row of holes in a wide panel  

NASA Astrophysics Data System (ADS)

This paper is concerned with predicting the fatigue life of unstiffened panels which contain multiple site damage (MSD). The initial damage consists of through-the-thickness cracks emanating from a row of holes in the center of a finite width panel. A fracture mechanics analysis has been developed to predict the growth, interaction, and coalescence of the various cracks which propagate in the panel. A strain-life analysis incorporating Neuber's rule for notches, and Miner's rule for cumulative damage, is also employed to predict crack initiation for holes without initial cracking. This analysis is compared with the results of a series of fatigue tests on 2024-T3 aluminum panels, and is shown to do an excellent job of predicting the influence of MSD on the fatigue life of nine inch wide specimens. Having established confidence in the ability to analyze the influence of MSD on fatigue life, a parametric study is conducted to examine the influence of various MSD scenarios in an unstiffened panel. The numerical study considered 135 cases in all, with the parametric variables being the applied cyclic stress level, the lead crack geometry, and the number and location of MSD cracks. The numerical analysis provides details for the manner in which lead cracks and MSD cracks grow and coalesce leading to final failure. The results indicate that MSD located adjacent to lead cracks is the most damaging configuration, while for cases without lead cracks, MSD clusters which are not separated by uncracked holes are most damaging.

Buhler, Kimberley; Grandt, Alten F., Jr.; Moukawsher, E. J.

1994-09-01

175

A Stiffness Degradation Based Fatigue Damage Model for FRP Composites of (0/ ?) Laminate Systems  

NASA Astrophysics Data System (ADS)

The present study develops a stiffness reduction—based model to characterize fatigue damage in unidirectional 0? and ?° plies and (0/?) laminates of fiber-reinforced polymer (FRP) composites. The proposed damage model was constructed based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding stiffness reduction of unidirectional composite laminates as the number of cycles progresses. The proposed model enabled damage assessment of FRP (0/?) composite laminates by integrating the fatigue damage values of 0? and ?° plies. A weighting factor ? was introduced to partition the efficiency of load carrying plies of 0° and ?° in the (0/?) composite lamina. The fatigue damage curves of unidirectional FRP composite samples with off-axis angles of 0?, 30?, 45?, and 90? and composite laminate systems of (0?/30?), (0?/45?) and (0?/90?) predicted based on the proposed damage model were found in good agreement with experimental data reported at various cyclic stress levels and stress ratios in the literature.

Shirazi, Alireza; Varvani-Farahani, A.

2010-04-01

176

Fatigue damage in centrally notched GR/EP laminates  

SciTech Connect

An investigation is presented of the fatigue properties of graphite/epoxy T300/5208 composite laminates of 16 plies with a central circular hole subjected to tension-tension constant-stress amplitudes at low humidity and room temperature. Four types of notched laminates, classified as unidirectional, off-axis, orthotropic shear, and quasi-isotropic, are studied. Some of the laminates were precracked to initiate and guide the crack growth transversely. Experimentally measured S-N curves, crack lengths, and their corresponding growth directions, failure surfaces, delamination areas, and transverse delamination lengths for these composites are evaluated. It is concluded that the precracked specimens have shorter fatigue life and the crack-growth rate predicted by the Paris law can be modified to apply to the effective transverse delamination length. 24 refs.

Jen, M.H.R.; Hsu, J.M.; Lee, C.H. (National Sun Yat-Sen University, Kaohsiung (China))

1990-12-01

177

Dependence of microelastic-plastic nonlinearity of martensitic stainless steel on fatigue damage accumulation  

NASA Astrophysics Data System (ADS)

Self-organized substructural arrangements of dislocations formed during cyclic stress-induced fatigue of metals produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter ? extracted from acoustic harmonic generation measurements. The contributions to ? from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell model [Proc. R. Soc. London, Ser. A 460, 757 (2004)] as a function of percent full fatigue life to fracture. A wave interaction factor fWI is introduced into the model to account experimentally for the relative volume of fatigue damage included in the total volume of material swept out by an interrogating acoustic wave. For cyclic stress-controlled loading at 551 MPa and fWI=0.013 the model predicts a monotonic increase in ? from dislocation substructures of almost 100% from the virgin state to roughly 95% full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, during the last 5% of fatigue life the model predicts a rapid monotonic increase of ? by several thousand percent that is dominated by crack growth. The theoretical predictions are in good agreement with experimental measurements of 410Cb stainless steel samples fatigued in uniaxial, stress-controlled cyclic loading at 551 MPa from zero to full tensile load with a measured fWI of 0.013.

Cantrell, John H.

2006-09-01

178

Monitoring of fatigue damage in metal plates by acoustic emission and thermography  

NASA Astrophysics Data System (ADS)

Acoustic Emission (AE) supplies information on the fracturing behavior of different materials. In this study, AE activity was recorded during fatigue experiments in metal CT specimens with a V-shape notch which were loaded in fatigue until final failure. AE parameters exhibit a sharp increase approximately 1000 cycles before than final failure. Therefore, the use of acoustic emission parameters is discussed both in terms of characterization of the damage mechanisms, as well as a tool for the prediction of ultimate life of the material under fatigue. Additionally, an innovative nondestructive methodology based on lock-in thermography is developed to determine the crack growth rate using thermographic mapping of the material undergoing fatigue. The thermographic results on the crack growth rate of aluminium alloys were then correlated with measurements obtained by the conventional compliance method, and found to be in agreement.

Kordatos, E. Z.; Aggelis, D. G.; Matikas, T. E.

2011-03-01

179

Thermographic detection of fatigue damage of pressure vessel steels at 1,000 Hz and 20 Hz  

SciTech Connect

Fatigue behavior is strongly affected by the environment, materials, and loading conditions. The process of fatigue can be categorized into three stages: crack initiation, growth, and final fracture. Nondestruction evaluation (NDE) of fatigue damage is of critical importance for life assessments and structural integrity evaluations. Several NDE methods, including ultrasonics, acoustic emission, and thermography, have been used to monitor fatigue damage. However, relatively little work has been conducted to assess fatigue characteristics using thermographic infrared techniques. In this paper, a thermographic infrared imaging system was used to detect the heat conditions of fatigued pressure vessel steels at 1,000 Hz and 20 Hz. Moreover, the fatigue behavior has been investigated at 1,000 Hz using an advanced electrohydraulic machine.

Liaw, P.K.; Wang, H.; Jiang, L.; Yang, B.; Huang, J.Y.; Kuo, R.C.; Huang, J.G.

2000-01-31

180

Damage characterisation of glass\\/polyester composite plates subjected to low-energy impact fatigue  

Microsoft Academic Search

This work reports and discusses an experimental method for characterising the damage behaviour of glass\\/polyester laminated composite plates at low-energy impact fatigue. Experimental tests are performed under increasing impact energy and increasing number of impacts conditions. The investigated energies are in the range of 3.5–7J in order to describe the internal damage behaviour at different levels of incident impact energy.

K. Azouaoui; N. Ouali; Y. Ouroua; A. Mesbah; T. Boukharouba

2007-01-01

181

Influence of Fatigue Damage in Dynamic Tensile Properties of AISI 4140T Steel  

Microsoft Academic Search

Usually material properties are determined from damage free materials, but is unknown if these properties can vary with respect\\u000a to previous fatigue damage. In different engineering applications such as automobile and train crashes, the high speed impact\\u000a of debris as well as the high speed manufacturing processes, makes it necessary to have deep understanding of the dynamic\\u000a behavior of materials

U. Sánchez-Santana; C. Rubio-González; G. Mesmacque; A. Amrouche

182

Fatigue damage accumulation in steel 45 under loading regimes involving low-cycle overloads  

NASA Astrophysics Data System (ADS)

The paper presents the results of experimental investigations into the regularities of fatigue damage accumulation in steel 45 under block loading involving elastoplastic (low-cycle) overloads. The experiments were carried out using the methods of the factorial design theory. Mathematical models are developed for damage accumulation depending on the variation of the parameters (factors) investigated: the level of the main (elastic) strain, the relative level of overloads, and their relative number.

Shlyushenkov, A. P.; Tatarintsev, V. A.

1994-05-01

183

Advanced nondestructive examination technologies for measuring fatigue damage in nuclear power plant components  

Microsoft Academic Search

This paper presents recent results from an ongoing project at the Idaho National Engineering Laboratory (INEL) to develop advanced nondestructive methods to characterize the aging degradation of nuclear power plant pressure boundary components. One of the advanced methods, positron annihilation, is being developed for in situ characterization of fatigue damage in nuclear power plant piping and other components. This technique

P. E. MacDonald; V. N. Shah; D. W. Akers

1995-01-01

184

Prevention of fluttering fatigue damage in a tilting pad journal bearing  

Microsoft Academic Search

Tilting pad journal bearings have been widely used to support high-pressure\\/fast rotating turbine rotors owing to their inherent dynamic stability characteristics. However, fatigue damage in the upper unloaded pads and the break of locking pins by pad fluttering continuously take place in actual steam turbines. The purpose of this paper is to develop a bearing model that can prevent bearing

Seongheon Yang; Chaesil Kim; Wonchang Lee

2009-01-01

185

Numerical study on fatigue damage properties of cavitation erosion for rigid metal materials  

Microsoft Academic Search

Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology. The loading spectrum used was generated by a spark-discharged electrode. Initiation crack life and true stress amplitude was used to explain the cavitation failure period and damage mechanism. The computational results indicated

Guogang Wang; Guang Ma; Dongbai Sun; Hongying Yu; Huimin Meng

2008-01-01

186

Damage Development During Low Cycle Fatigue of Carbon-Black Loaded SBR.  

National Technical Information Service (NTIS)

Fatigue of elastomers is a subject that has received considerable study over the years. This paper explores the problem of damage accumulation in a series of styrene butadiene rubber (SBR) based compounds containing 0, 15, 25, and 35 wt % carbon-black und...

D. Lesuer A. Goldberg D. Hiromoto J. Patt

1984-01-01

187

Evaluation of fatigue damage in reinforced concrete slab by acoustic emission  

Microsoft Academic Search

The applicability of acoustic emission (AE) technique for evaluation of fatigue damage in reinforced concrete (RC) slabs under cyclic loadings in both laboratory and as a structure in service is studied. The fundamental test performed in laboratory shows that the cracking process can be practically monitored by the measurement of AE signals. Analysis of the relationship between loading phase and

S Yuyama; Z.-W Li; M Yoshizawa; T Tomokiyo; T Uomoto

2001-01-01

188

Response of sub-surface fatigue damage under sonic load – a computational study  

Microsoft Academic Search

Graphite\\/epoxy composite samples with a center hole were subjected to fatigue loading, and were tested for damage using the sonic infrared (sonic IR) imaging technique. The technique revealed the presence of semi-elliptical delaminations near the circular notch. In the sonic IR technique, a short pulse of sound infuses into the material and results in frictional heating at the delamination surfaces.

Ahsan Mian; Golam Newaz; Xiaoyan Han; Tonfiz Mahmood; Chinmoy Saha

2004-01-01

189

Microstructural factors of low cycle fatigue damage in two phase Al–Si alloys  

Microsoft Academic Search

Low cycle fatigue (LCF) tests in air have been carried out on smooth specimens of several model binary Al–Si alloys with microstructures characterised by a high degree of homogeneity and the absence of casting defects, owing to the processing involving directed solidification. The elementary damage events, namely short crack nucleation at Al–Si interfaces and propagation across microstructural barriers (layers of

Jacques Stolarz; Olivier Madelaine-Dupuich; Thierry Magnin

2001-01-01

190

Influence of wear damage on the fretting fatigue life prediction of an Al7175 alloy  

Microsoft Academic Search

This paper proposes a modification on both the Smith–Watson–Topper and the Morrow parameters concerning the prediction on fretting fatigue life, in order to take into account the wear damage. It is proposed that, besides the principal stresses involved in fretting contact (axial, normal and tangential stresses), a new parameter that is the stress concentration factor, Kt, due to the “fretting

M. Buciumeanu; I. Crudu; L. Palaghian; A. S. Miranda; F. S. Silva

2009-01-01

191

Fatigue Life Prediction of Steel Bridges for Extreme Loading Using a New Damage Indicator  

NASA Astrophysics Data System (ADS)

High cycle fatigue (HCF) damage caused by normal traffic loading is one of the major modes of failures in steel bridges. During bridge service life, there are extreme loading situations such as typhoons, earthquakes which cause higher amplitude loading than normal traffic loading. Due to this reason, critical members could undergo overstress cycles in the plastic range. Therefore, such members are subjected to low cycle fatigue (LCF) during these situations while subjecting to HCF in serviceable condition. Bridges, which are not seriously damaged, generally continue to be functioned after these extreme loading situations and fatigue life estimation is required to ensure their safety. Therefore, this paper presents a new damage indicator based fatigue model to predict life of steel bridges due to combined effect of extreme and normal traffic loadings. It consists of a modified strain life curve and a strain based damage indicator. Both the strain life curve and the damage indicator are newly proposed in the study. Modified strain life curve consists of Coffin Manson relation in the LCF regime and a new strain life curve in the HCF regime. Damage variable is based on von Mises equivalent strain and modified by factors to consider effects of loading non proportionality and loading path in multiaxial stress state. The new damage indicator can capture the loading sequence effect. The proposed model is verified with experimental test results of combined HCF and LCF of three materials; S304L stainless steel, Haynes 188 (a Cobolt superalloy) and S45C steel obtained from the literature. The verification of experimental results confirms the validity of the proposed model.

Karunananda, Pallaha Athawudagedara Kamal; Ohga, Mitao; Dissanayake, Punchi Bandage Ranjith; Siriwardane, Siriwardane Arachchilage Sudath Chaminda

192

Non-Destructive Evaluation of Fatigue Damage for SUS316 by Using Electromagnetic Methods  

NASA Astrophysics Data System (ADS)

There are some fatigue damage estimation methods for an austenitic stainless steel that uses martensitic transformation. For instance, those are the remanent magnetization method, the excitation method using the differential pick-up coil, and so on. We are researching also those two methods in our laboratory now. In the remanent magnetization method, it is well known that the relationship between fatigue damage and the remanent magnetization is simple, clear, and reproducible. In addition, the excitation method can be easily used at the job site because the special magnetizer is unnecessary. But, these methods have some disadvantages shown as follows. For instance, the former needs a special magnetizer and the latter's output signal is small. On the other hand, it is well known that the inductance of a pancake type coil put on the metallic specimen changes according to the electromagnetic properties of the metallic specimen. In this paper, the assessment method of fatigue of an austenitic stainless steel (SUS316) that uses the change by fatigue of the inductance of the pancake type coil measured with the LCR meter is shown. In addition, the fatigue evaluation performance of this method is described.

Oka, M.; Tsuchida, Y.; Yakushiji, T.; Enokizono, M.

2009-03-01

193

System and method for predicting material fatigue and damage  

US Patent & Trademark Office Database

A method and system for determining damage prediction of a component. The component may be critical component used in an aircraft or other vehicle experiencing cyclic loading. The method and system determines the .DELTA.K, K.sub.max and K.sub.internal values for the component and utilizes these values in order to predict damage and/or failure of the component.

Vasudevan; Asuri K. (Reston, VA); Sadananda; Kuntimaddi (Springfield, VA); Glinka; Grzegorz (Petersburg, CA); Kujawski; Daniel (Portage, MI)

2011-02-15

194

Characterization of microstructural damage due to low-cycle fatigue by EBSD observation  

SciTech Connect

Electron backscatter diffraction (EBSD) in conjunction with scanning electron microscopy was used to assess the damage due to cyclic or uniform strain. Samples of Type 316 stainless steel after fatigue and tensile tests were prepared for EBSD observation and the misorientation angle between neighboring points (local misorientation) was evaluated. It was shown that the local misorientation developed due to the cyclic and uniform strain and that its spatial distribution was not uniform. In fatigue samples, the area of large local misorientation tended to form clusters, whereas it localized to the grain boundaries in the tensile samples, and the magnitude of local misorientation and the degree of the localization increased with the strain amplitude. The degree of localization was quantified via statistical processing of the measured data. It was also shown that the source of damage (cyclic or uniform strain) and the loading direction could be deduced from the EBSD observations of the damaged sample.

Kamaya, Masayuki, E-mail: kamaya@inss.co.jp [Institute of Nuclear Safety System, Inc., 64 Sata, Mihama-cho, Mikata-gun, Fukui 919-1205 (Japan)

2009-12-15

195

Estimation of Fatigue Damage for AN Austenitic Stainless Steel (SUS304) Using a Pancake Type Coil  

NASA Astrophysics Data System (ADS)

There are some fatigue damage estimation methods of an austenitic stainless steel that uses martensitic transformation. For instance, those are the remanent magnetization method, the excitation method, and so on. Those two methods are researched also in our laboratory now. In the remanent magnetization method, it is well known that the relationship between fatigue damage and the remanent magnetization is simple, clear, and reproducible. However, this method has the disadvantage to need a special magnetizer. Then, this method cannot be easily used at the job site such as the factory. On the other hand, as the special magnetizer is unnecessary, the excitation method can be easily used at the job site. But, this method has some disadvantages shown as follows. For instance, the output signal of this method is small. And the surface state of the specimen strongly influences the noise component of the output signal. It is well known that the inductance of a pancake type coil put on the metallic specimen changes according to the electromagnetic properties of the metallic specimen. In this paper, the method of evaluation of fatigue damage of an austenitic stainless steel (SUS304) by using a change of an inductance of a pancake type coil is shown. In addition, the fatigue evaluation performance of this method is described.

Oka, M.; Tsuchida, Y.; Nagato, S.; Yakushiji, T.; Enokizono, M.

2008-02-01

196

The effect of cement creep and cement fatigue damage on the micromechanics of the cement-bone interface.  

PubMed

The cement-bone interface provides fixation for the cement mantle within the bone. The cement-bone interface is affected by fatigue loading in terms of fatigue damage or microcracks and creep, both mostly in the cement. This study investigates how fatigue damage and cement creep separately affect the mechanical response of the cement-bone interface at various load levels in terms of plastic displacement and crack formation. Two FEA models were created, which were based on micro-computed tomography data of two physical cement-bone interface specimens. These models were subjected to tensile fatigue loads with four different magnitudes. Three deformation modes of the cement were considered: 'only creep', 'only damage' or 'creep and damage'. The interfacial plastic deformation, the crack reduction as a result of creep and the interfacial stresses in the bone were monitored. The results demonstrate that, although some models failed early, the majority of plastic displacement was caused by fatigue damage, rather than cement creep. However, cement creep does decrease the crack formation in the cement up to 20%. Finally, while cement creep hardly influences the stress levels in the bone, fatigue damage of the cement considerably increases the stress levels in the bone. We conclude that at low load levels the plastic displacement is mainly caused by creep. At moderate to high load levels, however, the plastic displacement is dominated by fatigue damage and is hardly affected by creep, although creep reduced the number of cracks in moderate to high load region. PMID:20692663

Waanders, Daan; Janssen, Dennis; Mann, Kenneth A; Verdonschot, Nico

2010-08-07

197

Fretting fatigue of Ti–6Al–4V under flat-on-flat contact  

Microsoft Academic Search

A fretting fatigue test system has been developed to simulate the fretting fatigue damage that occurs in turbine engine blade attachments. The test system employs a flat-on-flat contact with blending radii, which reproduces the nominal levels of normal and internal shear stresses present in dovetails. These stress states are achieved through the application of the normal loads required to grip

Alisha L. Hutson; Ted Nicholas; Rick Goodman

1999-01-01

198

Damage accumulation, fatigue and creep behaviour of vacuum mixed bone cement.  

PubMed

The behaviour of bone cement under fatigue loading is of interest to assess the long-term in vivo performance. In this study, uniaxial tensile fatigue tests were performed on CMW-1 bone cement. Acoustic emission sensors and an extensometer were attached to monitor damage accumulation and creep deformation respectively. The S-N data exhibited the scatter synonymous with bone cement fatigue, with large pores generally responsible for premature failure; at 20 MPa specimens failed between 2 x 10(3) and 2 x 10(4) load cycles, while at 7 MPa specimens failed from 3 x 10(5) load cycles but others were still intact after 3 x 10(6) load cycles. Acoustic emission data revealed a non-linear accumulation of damage with respect to time, with increasing non-linearity at higher stress levels. The damage accumulation process was not continuous, but occurred in bursts separated by periods of inactivity. Damage in the specimen was located by acoustic emissions, and allowed the failure site to be predicted. Acoustic emission data were also used to predict when failure was not imminent. When this was the case at 3 million load cycles, the tests were terminated. Creep strain was plotted against the number of load cycles and a linear relationship was found when a double logarithmic scale was employed. This is the first time a brand of cement has been characterised in such detail, i.e. fatigue life, creep and damage accumulation. Results are presented in a manner that allows direct comparison with published data for other cements. The data can also be used to characterise CMW-1 in computational simulations of the damage accumulation process. Further evidence is provided for the condition-monitoring capabilities of the acoustic emission technique in orthopaedic applications. PMID:15860209

Jeffers, Jonathan R T; Browne, Martin; Taylor, Mark

2005-09-01

199

Ultrasonic detection of fatigue damage in glass-epoxy composites  

SciTech Connect

Energy storage flywheels fabricated of S2 glass-epoxy composite were studied to determine the behavior of the ultrasonic properties as a function of strain history and to identify possible predictors of incipient failure. Tensile specimens of the flywheel material were loaded uniaxially, and the ultrasonic properties (i.e., the shear and longitudinal wave velocities and the attenuation) were measured as a function of strain. Finished flywheels were similarly tested at various stages during cyclic spin testing; in addition, the polar backscattering intensity as a function of fatigue cycle was recorded. The velocities are excellent indicators of the maximum strain incurred at each point of the flywheel, and the attenuation delineates the region in which the stress is high enough to initiate microcracking in the matrix.

Simpson, W.A. Jr.; McClung, R.W.

1990-01-01

200

Fatigue damage at room temperature in aluminium single crystals. 4: Secondary slip  

SciTech Connect

Two Al single crystals were fatigued in push-pull in air at room temperature, at a constant shear stress amplitude of 4 MPa, zero mean stress and frequency of 20 Hz. Secondary slip lines were observed in the matrix, macrobands and PSBs (mainly in extrusions and intrusions) on the side-surfaces of the two specimens. At the later stage of the fatigue test (after 5 {times} 10{sup 6} cycles), in addition to extrusions and intrusions which were probably formed by local persistent secondary slip in PSBs, short cracks were also usually observed on the side-surfaces mainly along the interface between the matrix and the extrusions in the PSBs. It is suggested that an internal stress at each slip offset (caused by net irreversible secondary slip in the extrusions within PSBs due to lattice rotation on the side-surface), is mainly responsible for crack initiation in the extrusions. Secondary slip takes place commonly to assist lattice rotation during fatigue, and plays a significant role in fatigue damage at room temperature, especially in the later stage of fatigue, in Al single crystals.

Zhai, T.; Briggs, G.A.D.; Martin, J.W. [Univ. of Oxford (United Kingdom). Dept. of Materials

1996-09-01

201

a Study on Fatigue Damage of Shape Memory Alloy Composite Using Nde Technique  

NASA Astrophysics Data System (ADS)

TiNi shape memory alloy was used to recover the shape of transformed objects using its shape memory effect. This shape memory effect plays an important role inside metal matrix composite. A composite using shape memory alloy has a large advantage that can control crack initiation and propagation, when compared with other composites due to the shape memory effect of shape memory alloy under high temperature. In this study, TiNi/Al6061 and TiNi/2024 shape memory composites were fabricated by the hot press method, and a fatigue test was performed to evaluate the fatigue damage for the shape memory composites under room temperature and high temperature. The relationship of the crack growth rate and the stress intensity factor for these shape memory composites were clarified at both temperature conditions. The delay effect of crack propagation due to shape memory alloy was also evaluated under high temperature. In addition, an acoustic emission technique was used to evaluate the crack initiation and the control of crack propagation by shape memory effect under fatigue test nondestructively. The relationship between AE parameter and the degree of fatigue damage of the shape memory composites was discussed.

Park, Young-Chul; Lee, Jin-Kyung; Lee, Sang-Pill; Lee, Gyu-Chang; Lee, Joon-Hyun; Cho, Youn-Ho; Lee, Jong-Back

202

Effect of in situ material properties on fatigue damage modes in titanium matrix composites  

SciTech Connect

Titanium matrix composites (TMC) and their behavior under mechanical fatigue loads was the subject of this research. The primary objective was to explain fatigue damage modes in center-notched TMC specimens. Two modes of damage have been observed in continuously reinforced, zero-degree unidirectional, SCS-6/Ti-15V-3Cr-3Al-3Sn (SCS-6/Ti-15-3) laminates. The fatigue specimens were destructively analyzed using optical microscopy to determine where cracks originated and how they grew throughout the specimen. A micromechanical model was developed to explain the fatigue crack patterns observed in the interface region surrounding the fibers of the woven and acrylic-binder TMC material systems. A two-dimensional (2-D) model of a longitudinal lamina with a center hole was used to obtain a set of displacement boundary conditions for an element near the notch, yet within the net section where the spiral crack patterns were observed. These boundary conditions were then used on a three-dimensional (3-D) unit cell model of the fiber, matrix, and interface.

Harmon, D. [Boeing Co., St. Louis, MO (United States); Jerina, K.L. [Washington Univ., St. Louis, MO (United States). Materials Science and Engineering Program

1999-02-01

203

LCF (Low Cycle Fatigue) and Crack Growth Rate of Turbine Blade Alloys in Hydrogen and Hydrogen/Steam Environments.  

National Technical Information Service (NTIS)

The low cycle fatigue (LCF) and fatigue crack growth testing of MAR-M246+Hf and PWA 1480 in high pressure hydrogen and hydrogen enriched steam at elevated temperatures are described. The PWA 1480 single crystal exhibited the best properties overall, compa...

B. A. Cowles D. P. Deluca J. R. Warren F. K. Haake

1986-01-01

204

Experimental and theoretical quantification of the development of damage in fatigue tests of bone and antler.  

PubMed

This study concerns the development of damage (as measured by a reduction in elastic modulus) in two kinds of bones differing considerably in their degrees of mineralisation: laminar bone from bovine femur and osteonal bone from red deer antler. Antler bone is much tougher than 'ordinary' bone and its failure properties have been investigated in: (i) monotonic tensile tests and (ii) creep rupture experiments. Tensile fatigue is another way of examining how damage develops in bone. The development of damage in the present fatigue tests was non-linear with the cycle number, the degree of non-linearity was dependent on the level of stress and followed a clearly different course for bone and antler. Antler was a more damage-tolerant material, being able to achieve a reduction in the final modulus of elasticity, just prior to failure, three times greater than 'ordinary' bone. The evolution of damage is quantified by an empirical and a graphical method and by the use of Continuum Damage Mechanics (CDM) expressions. The CDM method shows important conditions, found in antler, but not in bone, that seen necessary for achieving stable fractures and consequently producing very tough materials. PMID:8817365

Zioupos, P; Wang, X T; Currey, J D

1996-08-01

205

The molecular response of the patellar tendon to fatigue loading explained in the context of the initial induced damage and number of fatigue loading cycles  

PubMed Central

Accumulation of sub-rupture fatigue damage has been implicated in the development of tendinopathy. We previously developed an in vivo model of damage accumulation using the rat patellar tendon. Our model allows us to control the input loading parameters to induce fatigue damage in the tendon. Despite this precise control, the resulting induced damage could vary among animals because of differences in size or strength among their patellar tendons. In this study, we used number of applied cycles and initial (day-0) parameters that are indicative of induced damage to assess the molecular response 7 days after fatigue loading. We hypothesized that day-0 hysteresis, elongation, and stiffness of the loading and unloading load-displacement curves would be predictive of the 7-day molecular response. Results showed correlations between the 7-day molecular response and both day-0 elongation and unloading stiffness. Additionally, loading resulted in upregulation of several extracellular matrix genes that suggest adaptation; however, several of these genes (Col-I, -XII, MMP 2, and TIMP 3) shut down after a high level of damage was induced. We showed that evaluating the 7-day molecular profile in light of day-0 elongation provides important insight that is lost from comparing number of fatigue loading cycles only. Our data showed that loading generally results in an adaptive response. However, the tendon's ability to effectively respond deteriorates as greater damage is induced.

Andarawis-Puri, Nelly; Sereysky, Jedd B.; Sun, Hui B.; Jepsen, Karl J.; Flatow, Evan L.

2013-01-01

206

High-temperature ultra-high cycle fatigue damage of notched single crystal superalloys at high mean stresses  

Microsoft Academic Search

Blade nickel superalloy CMSX-4 widely used in the aero industry and its potential low cost alternative, superalloy CM186LC intended for use in the industrial gas turbines, were subjected to ultra-high-cycle fatigue at high mean stresses to model the effect of vibrations superimposed on sustained load. Circumferentially notched cylindrical specimens of single crystals with the axis orientation of [001] were tested

P. Lukáš; L. Kunz; M. Svoboda

2005-01-01

207

Experimental study on fatigue performance and damage model of aluminum alloy welding joints for high-speed train car body  

NASA Astrophysics Data System (ADS)

In order to realize lightweight, security and comfort, the aluminum alloy profile becomes the first choice of the high speed train carbody. The fatigue experiments are carried on the typical welding joins such as butt, fillet, cruciform and lap joins. The fatigue limits and P-S-N curves are obtained. The non-linearity cumulative damage model is proposed taking loading sequences for consideration and the two-level loading experiments on butt and fillet joints are studied to verify the feasibility of the damage model. The fatigue life of carbody is predicted based on the proposed damage model and the online dynamic stress test results. The results show that the fatigue life calculated by non-linearity damage model is close to that by modified Miner law and 22% less than that by Miner law.

Wang, Wenjing; Li, Qiang; Liu, Zhiming; Wang, Binjie

2009-12-01

208

Fatigue crack growth in damage tolerant Al-Li sheet alloys  

NASA Astrophysics Data System (ADS)

The fatigue crack growth properties of two candidate damage tolerant Al-Li sheet alloys, 2091 and 8090 are compared with those of the conventional and widely used 2024 alloy. There were three load histories: constant amplitude, gust spectrum, and constant amplitude with occasional peak loads. The results are interpreted with the aid of fractographic observations and measurements of fracture surface roughness. The practical significance of the results is assessed, and recommendations are made for further evaluations.

Wanhill, R. J. H.

1990-03-01

209

Simulation of thermal fatigue damage in a 316L model pipe component  

Microsoft Academic Search

To contribute to the development of improved methods for assessing possible thermal fatigue damage in nuclear plant piping systems, a unique set of crack growth data has been generated for tubular test pieces in 316L(N) stainless steel subjected to cyclic thermal loads in a specially designed rig. By accurate modelling of the thermal loads and non-linear material behaviour using the

E. Paffumi; K.-F. Nilsson; N. G. Taylor

2008-01-01

210

Nondestructive evaluation of fatigue damage in aluminum 2024 by x-ray diffraction  

Microsoft Academic Search

Aluminum alloys are widely used in the automobile and aerospace industries. This is due to their attractive low density-high modulus and low density-high strength characteristics. Unfortunately, cyclic stress-strain deformations alter the microstructure of aluminum alloys when they are placed into service. These structural changes can lead to fatigue damage and ultimately service failure. Since x-ray diffraction analysis is known to

Milton W. Ferguson

1994-01-01

211

Fatigue-damage evaluation for mild steel incorporating mean stress and overload effects  

Microsoft Academic Search

Successful estimation of the service life of a structure or component which is subjected to a complex history of loading,\\u000a depends on a suitable cumulative-damage summation technique. A general technique must be capable of predicting the effects\\u000a on fatigue life of geometry, mean stress or strain, occasional overloads or overstrains, frequency of cycling and environment.\\u000a As a contribution towards the

P. Watson; T. H. Topper

1972-01-01

212

Estimation of Fatigue life of Cortical Bone Considering Viscoelastic Properties and Damage Mechanics  

Microsoft Academic Search

\\u000a Recently, the Osteoporosis victims increase in the senior citizen. Therefore, the danger of the stress fracture due to the\\u000a decrease in bone strength is pointed out. Especially, the damage accumulation behavior of the bone in the cyclic load becomes\\u000a a problem for the fatigue of the bone. Moreover, it is necessary to consider the viscoelastic property for the prediction\\u000a of

Takenobu Sakai; Keita Yasui; Shuichi Wakayama

213

Effect of the strength of railroad rails on the formation of contact-fatigue damage under service conditions  

Microsoft Academic Search

Conclusions 1.One of the main causes of contact-fatigue damage in rails (chips and fragments on the lateral surface of the head) is the severe work-hardening of the peripheral layers of the metal and the development of considerable stresses at the boundary between the hardened and unhardened layers.2.With increasing degree of work-hardening the tendency of the rails toward contact-fatigue damage increases.

V. V. Lempitskii; D. S. Kazarnovskii; L. Ya. Shnaperman

1975-01-01

214

SHM of wind turbine blades using piezoelectric active-sensors  

SciTech Connect

This paper presents a variety of structural health monitoring (SHM) techniques, based on the use of piezoelectric active-sensors, used to determine the structural integrity of wind turbine blades. Specifically, Lamb wave propagations, frequency response functions, and time series based methods are utilized to estimate the condition of wind turbine blades. For experiments, a 1m section of a 9m CX100 blade is used. Overall, these three methods yielded a sufficient damage detection capability to warrant further investigation into field deployment. A full-scale fatigue test of a CX-100 wind turbine blade is also conducted. This paper summarizes considerations needed to design such SHM systems, experimental procedures and results, and practical implementation issues that can be used as guidelines for future investigations.

Park, Gyuhae [Los Alamos National Laboratory; Taylor, Stuart G [Los Alamos National Laboratory; Farinholt, Kevin M [Los Alamos National Laboratory; Farrar, Charles R [Los Alamos National Laboratory

2010-01-01

215

Fatigue  

Microsoft Academic Search

Fatigue is a highly prevalent, complex and poorly delineated symptom, which occurs before, during and after treatment for\\u000a cancer. Difficulties in establishing a case definition of cancer-related fatigue have resulted in an absence of reliable and\\u000a valid epidemiological data, and confound investigation into the etiology and pathogenesis of this problem. Among the possible\\u000a predisposing and perpetuating factors underlying fatigue are

Michael J. Fisch

216

Fatigue  

Microsoft Academic Search

Fatigue is a common complaint in patients with Parkinson’s disease (PD). More than half of all patients with PD rank fatigue\\u000a among their three worst symptoms. Fatigue has been variously hypothesized to be caused by dysfunction of the striato-thalamo-cortical\\u000a loop, abnormalities in the hypothalamic-pituitary-adrenal axis, inflammatory processes, and neurotransmitter abnormalities\\u000a within the central nervous system. However, there is no firm

Carol Ewing Garber; Joseph H. Friedman

217

Study of frequency effects and damage accumulation during the fatigue of graphite/epoxy and glass/epoxy composite materials  

SciTech Connect

The objective of this research is to understand the frequency effect on the fatigue behavior of graphite/epoxy and glass/epoxy composite materials. Fatigue tests were conducted on (+/-45)/sub (2s)/ layups using 0.05, 0.5, and 5 Hz frequencies. Basically, the fatigue life increased as the loading frequency increased. Experimental results showed that the initial dynamic modulus of the composites is larger for glass/epoxy and graphite/epoxy composite laminates at high frequency. A nonlinear damage accumulation model is developed to describe the material properties degradation and predict the fatigue life at different stresses and frequencies. The frequency does not enter the model explicitly but only through the frequency effect on the initial modulus. The behavior of the dynamic strain and cyclic creep strain were tested as measures of fatigue damage.

Tsai, G.C.

1984-01-01

218

High-temperature, high-frequency fretting fatigue of a single crystal nickel alloy  

Microsoft Academic Search

Fretting is a structural damage mechanism arising from a combination of wear, corrosion, and fatigue between two nominally clamped surfaces subjected to an oscillatory loading. A critical location for fretting induced damage has been identified at the blade\\/disk and blade\\/damper interfaces of gas turbine engine turbomachinery and space propulsion components. The high-temperature, high-frequency loading environment seen by these components lead

John Frederick Matlik

2004-01-01

219

Systematic Error in Mechanical Measures of Damage During Four-Point Bending Fatigue of Cortical Bone  

PubMed Central

Accumulation of fatigue microdamage in cortical bone specimens is commonly measured by a modulus or stiffness degradation after normalizing tissue heterogeneity by the initial modulus or stiffness of each specimen measured during a preloading step. In the first experiment, the initial specimen modulus defined using linear elastic beam theory (LEBT) was shown to be nonlinearly dependent on the preload level, which subsequently caused systematic error in the amount and rate of damage accumulation measured by the LEBT modulus degradation. Therefore, the secant modulus is recommended for measurements of the initial specimen modulus during preloading. In the second experiment, different measures of mechanical degradation were directly compared and shown to result in widely varying estimates of damage accumulation during fatigue. After loading to 400,000 cycles, the normalized LEBT modulus decreased by 26% and the creep strain ratio decreased by 58%, but the normalized secant modulus experienced no degradation and histology revealed no significant differences in microcrack density. The LEBT modulus was shown to include the combined effect of both elastic (recovered) and creep (accumulated) strain. Therefore, at minimum, both the secant modulus and creep should be measured throughout a test to most accurately indicate damage accumulation and account for different damage mechanisms. Histology further revealed indentation of tissue adjacent to roller supports, with significant sub-surface damage beneath large indentations, accounting for 22% of the creep strain on average. The indentation of roller supports resulted in inflated measures of the LEBT modulus degradation and creep. The results of this study suggest that investigations of fatigue microdamage in cortical bone should avoid the use of four-point bending unless no other option is possible.

Landrigan, Matthew D.; Roeder, Ryan K.

2009-01-01

220

Fatigue damage estimate comparisons for northern European and US wind farm loading environments  

NASA Astrophysics Data System (ADS)

Typical loading histories associated with wind turbine service environments in northern Europe and within a large wind farm in the continental US were recently compared by Kelley using the WISPER (Ten Have) loading standard and its development protocol. In this study, an equivalent load spectrum for a US wind farm was developed by applying the WISPER development protocol to representative service load histories collected from two adjacent turbines operating within a large wind farm in San Gorgonio Pass, California. The results of this study showed that turbines operating in the California wind farm experience many more loading cycles with larger peak-to-peak values for the same mean wind speed classification than their European counterparts. In this paper, the impact of the two WISPER-protocol fatigue-load spectra on service lifetime predictions are used to compare and contrast the impact of the two loading environments with one another. The service lifetime predictions are made using the LIFE2 Fatigue Analysis Code (Sutherland and Schluter), with the fatigue properties of typical fiber glass composite blade materials. Additional analyses, based on rainflow counted time histories from the San Gorgonio turbines, are also used in the comparisons. In general, these results indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a US wind farm site; i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a US wind farm site. The authors conclude that there are fundamental differences in the two service environments.

Sutherland, H. J.; Kelley, N. D.

221

Blade Manufacturing Improvement: Remote Blade Manufacturing Demonstration  

SciTech Connect

The objective of this program was to investigate manufacturing improvements for wind turbine blades. The program included a series of test activities to evaluate the strength, deflection, performance, and loading characteristics of the prototype blades. The original contract was extended in order to continue development of several key blade technologies identified in the project. The objective of the remote build task was to demonstrate the concept of manufacturing wind turbine blades at a temporary manufacturing facility in a rural environment. TPI Composites successfully completed a remote manufacturing demonstration in which four blades were fabricated. The remote demonstration used a manufacturing approach which relied upon material ''kits'' that were organized in the factory and shipped to the site. Manufacturing blades at the wind plant site presents serious logistics difficulties and does not appear to be the best approach. A better method appears to be regional manufacturing facilities, which will eliminate most of the transportation cost, without incurring the logistical problems associated with fabrication directly onsite. With this approach the remote facilities would use commonly available industrial infrastructure such as enclosed workbays, overhead cranes, and paved staging areas. Additional fatigue testing of the M20 root stud design was completed with good results. This design provides adhesive bond strength under fatigue loading that exceeds that of the fastener. A new thru-stud bonding concept was developed for the M30 stud design. This approach offers several manufacturing advantages; however, the test results were inconclusive.

ASHWILL, THOMAS D.

2003-05-01

222

Impact damage prediction and failure analysis of heavily loaded, blade-stiffened composite wing panels  

Microsoft Academic Search

Within the framework of a European research programme to develop design methodology for the improvement of damage tolerance within composite materials, two heavily loaded, stiffened composite wing panels were designed, fabricated and tested. The panels were impacted at the vulnerable stiffener edges and the failure modes and mechanisms related to the infliction of impact damage and the subsequent compression after

J. F. M. Wiggenraad; X. Zhang; G. A. O. Davies

1999-01-01

223

Transition from dislocation glide to creep controlled damage in fatigued thin Cu films  

NASA Astrophysics Data System (ADS)

The ultra-high cycle fatigue behavior of supported Cu films with thicknesses between 40 and 360 nm has been investigated using a novel atomic force microscope (AFM)-based resonance method. The damage created under strain controlled fatigue loading is investigated as a function of applied strain, film thickness, and cycle numbers up to 5 × 1010. For films thicker than 100 nm, extrusions and boundary cracks limit the fatigue performance but only appear above a threshold in the applied strain amplitude which scales inversely with the square root of the film thickness. The extrusion formation is attributed to dislocation activation. The grain boundary cracks are replaced by grain boundary grooves in films of 100 nm and thinner. The grooves are believed to form by diffusion mediated creep processes, similar to observations at higher temperatures but here driven by cyclic stresses and capillarity, and become detectable once the accumulated plastic strain exceeds a critical value. These results indicate that due to creep processes, thinner films can be less resistant to fatigue than thicker films, particularly for large cycle numbers.

Trinks, C.; Volkert, C. A.

2013-09-01

224

Structural health monitoring of composite wind blades by fiber bragg grating  

NASA Astrophysics Data System (ADS)

The wind turbine industry is the fastest growing market area for the use of composite materials. Fiber Bragg grating sensor can be used to monitor the mechanical behavior of composite wind blade. The internal strain of composite wind blade during a constant stress amplitude fatigue testing process was monitored with fiber Bragg gratings sensors. FBG sensors can not only be embedded in composite structures to detect fatigue damage, but also have excellent durability compared with other sensors such as electric strain gauges. After 1 million cycles, the FBG sensors can still keep good sensibility. FBGs as a fatigue indicator are a novel sensor to monitor, evaluate and give crash alert for the health state of composite wind blades during their whole service life.

Guo, Zhan-Sheng; Zhang, Junqian; Hu, Hongjiu; Guo, Xingming

2007-10-01

225

Damage repair in CMSX-4 alloy without fatigue life reduction penalty  

NASA Astrophysics Data System (ADS)

The microstructural changes in a single-crystal Ni-base superalloy, CMSX-4, that might occur during the processes of repair and recoating of hot section components for advanced gas turbines were studied. It is shown that the cellular ?/?? microstructure is formed when the material is subjected to local plastic straining, followed by the reheat treatments during the course of damage recovery. The formation of cellular microstructure in the material led to the remarkably reduced fatigue strength. In order to reduce or prevent the preceding undesirable effect resulting from cellular microstructure, a new method based on applying overlay coating technique was developed. The method is based on an idea that the alloying elements that are depleted in base alloys could be supplemented via the overlay coating. An X alloy, which contains grain boundary strengthening elements, was selected and coated on the CMSX-4 with the cellular microstructure by low-pressure plasma spraying. The fatigue tests on the coated CMSX-4 specimens demonstrated the effectiveness of the method. The observations of the crack initiation site, the fatigue fracture mode, the crack density in the cellular transformed area, and the crack propagation morphologies near the prior interface strongly supported the validity of this approach. The method is expected to build a road to a so-called damage cure (or recovery) coating.

Okazaki, Masakazu; Ohtera, Issei; Harada, Yoshio

2004-02-01

226

Performance optimization of a diagnostic system based upon a simulated strain field for fatigue damage characterization  

NASA Astrophysics Data System (ADS)

The work presented hereafter is about the development of a diagnostic system for crack damage detection, localization and quantification on a typical metallic aeronautical structure (skin stiffened through riveted stringers). Crack detection and characterization are based upon strain field sensitivity to damage. The structural diagnosis is carried out by a dedicated smart algorithm (Artificial Neural Network) which is trained on a database of Finite Element simulations relative to damaged and undamaged conditions, providing the system with an accurate predictor at low overall cost. The algorithm, trained on numerical damage experience, is used in a simulated environment to provide reliable preliminary information concerning the algorithm performances for damage diagnosis, thus further reducing the experimental costs and efforts associated with the development and optimization of such systems. The same algorithm has been tested on real experimental strain patterns acquired during real fatigue crack propagation, thus verifying the capability of the numerically trained algorithm for anomaly detection, damage assessment and localization on a real complex structure. The load variability, the discrepancy between the Finite Element Model and the real structure, and the uncertainty in the algorithm training process have been addressed in order to enhance the robustness of the system inference process. Some further algorithm training strategies are discussed, aimed at minimizing the risk for false alarms while maintaining a high probability of damage detection.

Sbarufatti, C.; Manes, A.; Giglio, M.

2013-11-01

227

An experimental investigation of homogeneous fatigue damage in a random short-fiber composite under combined tension-torsion loading  

SciTech Connect

An experimental study is conducted to examine the effects of the state of stress on the fundamental nature of distributed fatigue damage in a random short fiber composite. The project consists of two different tasks: first, to develop a new experimental method, for conducting combined shear and axial fatigue damage in composites which are difficult to fabricate in axisymmetric configurations; and second, to study the evolution of the multiaxial fatigue damage in the material. A sandwich specimen, consisting of SMC composite skins bonded to an aluminum honeycomb core, is proposed. Anisotropic finite element analyses are used to obtained detailed stress and deformation fields in the composite facing and in the core of specimens with optimum geometry. The macroscopic fatigue damage is defined and measured as the relative change in the elastic stiffness tensor of the composite. Multiaxial extensometry is developed for strain measurements, and an approximate analytical technique is evolved for online prediction of the multiaxial stress state in the damaged material. Measurements of residual modulus are conducted, after multiaxial fatiguing, to provide additional information on the residual stiffness of the composite. The magnitude and rate of stiffness degradation are found to depend not only on the level of stress but also on the state of stress. Combined stress states are found to be particularly detrimental to the degradation rate of shear modulus. Microscopic damage parameters such as crack length distribution and crack orientation distribution are monitored through non-destructive replication and subsequent quantitative microscopy techniques.

Dasgupta, A.

1989-01-01

228

Muscle Damage and Its Relationship with Muscle Fatigue During a Half-Iron Triathlon  

PubMed Central

Background To investigate the cause/s of muscle fatigue experienced during a half-iron distance triathlon. Methodology/Principal Findings We recruited 25 trained triathletes (36±7 yr; 75.1±9.8 kg) for the study. Before and just after the race, jump height and leg muscle power output were measured during a countermovement jump on a force platform to determine leg muscle fatigue. Body weight, handgrip maximal force and blood and urine samples were also obtained before and after the race. Blood myoglobin and creatine kinase concentrations were determined as markers of muscle damage. Results Jump height (from 30.3±5.0 to 23.4±6.4 cm; P<0.05) and leg power output (from 25.6±2.9 to 20.7±4.6 W · kg?1; P<0.05) were significantly reduced after the race. However, handgrip maximal force was unaffected by the race (430±59 to 430±62 N). Mean dehydration after the race was 2.3±1.2% with high inter-individual variability in the responses. Blood myoglobin and creatine kinase concentration increased to 516±248 µg · L?1 and 442±204 U · L?1, respectively (P<0.05) after the race. Pre- to post-race jump change did not correlate with dehydration (r?=?0.16; P>0.05) but significantly correlated with myoglobin concentration (r?=?0.65; P<0.001) and creatine kinase concentration (r?=?0.54; P<0.001). Conclusions/significance During a half-iron distance triathlon, the capacity of leg muscles to produce force was notably diminished while arm muscle force output remained unaffected. Leg muscle fatigue was correlated with blood markers of muscle damage suggesting that muscle breakdown is one of the most relevant sources of muscle fatigue during a triathlon.

Coso, Juan Del; Gonzalez-Millan, Cristina; Salinero, Juan Jose; Abian-Vicen, Javier; Soriano, Lidon; Garde, Sergio; Perez-Gonzalez, Benito

2012-01-01

229

Study of the Applicability of Eddy Current NDT for Fatigue Damage Evaluation in Aluminum Alloy 2024-T3  

Microsoft Academic Search

Mechanical components are generally expected to be damaged by fatigue processes along their lifetime. Since the maximum allowable stress value is reached, some irrecoverable and cumulative damage appears in materials. That process is related with the nucleation of superficial or volumetric discontinuities (micro-cracks or micro-cavities) and begins when any localized stress is greater than the material yield stress. For components

Tanius R. Mansur; Nelson N. Atanázio Filho; Paulo T. V. Gomes; Denis H. B. Scaldaferr; Vlamir C. E. Almeida; Antônio E. Aguiar; Geraldo A. Scoralick; André L. Nogueira; Donizete A. Alencar

230

Corrosion fatigue of steam turbine-blading alloys in operational environments. Final report. [Ti-6Al-4V  

SciTech Connect

The corrosion fatigue strengths of Type 403 and 17-4 PH stainless steel and several processing variations of Ti-6Al-4V were determined in various steam turbine environments. Steam and turbine deposits were analyzed to establish test environments. Pure 80/sup 0/C water base line data was determined and compared to saturated aqueous solutions of NaCl, Na/sub 2/SO/sub 4/, Na/sub 3/PO/sub 4/, Na/sub 2/SiO/sub 3/ and some mixtures of these. The pH and oxygen content were also varied. Fatigue strengths at 20 kHz and 100 Hz were established for 10/sup 9/ and 10/sup 7/ cycles, respectively. The corrosion fatigue effect of notches, shot peening and mean stress were measured. Acidic, high oxygen 22% NaCl solutions were found to be extremely aggressive, causing Type 403 to lose 87% of its pure water fatigue strength; more basic solutions and other chemical species were less severe. The Ti-6Al-4V alloys were only mildly affected in most environments although NaOH plus SiO/sub 2/ was found to dissolve this alloy. The effect of the environments on 17-4 PH was intermediate between Type 403 and Ti-6Al-4V.

Cunningham, J.W.; Dowling, N.E.; Heymann, F.J.; Jonas, O.; Kunsman, L.D.; Pebler, A.R.; Swaminathan, V.P.; Willertz, L.E.; Rust, T.M.

1984-09-01

231

Fatigue  

MedlinePLUS

... 20-40% in the short term. Trials using modafinil in MS fatigue have involved small numbers and ... studies are recommended to ascertain the effect of modafinil in the longer term and the appropriate dose. ...

232

A study on coating class damage degree by use cycle of gas turbine blade coating  

Microsoft Academic Search

The component of the hot gas path in gas turbines can survive to very high temperatures because they are protected by ceramic Thermal Barrier Coating(TBC); the failure of such coating can dramatically reduce the component life. A reliable assessment of the Coating integrity and\\/or an Incipient TBC Damage Detection can help both in optimizing the inspection intervals and in finding

Choul Jun Choi; Jae Yeol Kim

2007-01-01

233

The generation of deformation damage during fatigue loading in Al-Cu alloy studied by the Doppler Broadening technique  

NASA Astrophysics Data System (ADS)

We have investigated the evolution of damage during fatigue loading in Al-Cu 2024-T3 alloys using the positron annihilation Doppler Broadening (DB) technique. This technique enables us to monitor in a non destructive way, at the atomic and vacancy level, the formation of deformation defects and their interaction with solute atoms at selected stages of fatigue testing. The changes in the S and W Doppler Broadening parameters are linked to the changes in fatigue behavior at lower stress levels. The material was tested under constant amplitude fatigue loading at four different stress levels and DB tests were conducted at selected stages of fatigue lifetime. The results are compared to those obtained during static tensile tests.

Ruiz-Ripoll, M. L.; Schut, H.; Van Dijk, N. H.; Alderliesten, R. C.; Van Der Zwaag, S.; Benedictus, R.

2011-01-01

234

Life assessment and repair of fatigue damaged high strength aluminium alloy structure using a peening rework method  

Microsoft Academic Search

This paper discusses a holistic assessment and rework\\/repair process for fatigue damaged structure based on estimating the depth of any potential cracking, its removal and subsequently improving the fatigue resistance of the region by peening the area using tightly controlled conditions. The process was developed to be generally applicable to parts of the F\\/A-18 aircraft’s aluminium alloy 7050 centre barrel

L. Molent; S. Barter; B. Main

2008-01-01

235

Finite element modeling of thermal fatigue and damage of solder joints in a ceramic ball grid array package  

Microsoft Academic Search

A nonlinear finite element model is presented for analyzing the cyclic and thermal fatigue loading and for viscoplastic damage\\u000a characterization of the lead-tin (Pb-Sn) solder joints in a ceramic ball grid array (CBGA) surface mount package. An approach\\u000a using a ? ?\\u000a eq\\u000a in\\u000a -modified Coffin-Manson equation is proposed to estimate the fatigue life of the solder joints. The ?

Bor Zen Hong

1997-01-01

236

Nondestructive evaluation of fatigue damage in aluminum 2024 by x-ray diffraction  

NASA Astrophysics Data System (ADS)

Aluminum alloys are widely used in the automobile and aerospace industries. This is due to their attractive low density-high modulus and low density-high strength characteristics. Unfortunately, cyclic stress-strain deformations alter the microstructure of aluminum alloys when they are placed into service. These structural changes can lead to fatigue damage and ultimately service failure. Since x-ray diffraction analysis is known to be a sensitive nondestructive indicator of structural changes due to deformations, this technique is being used to evaluate changes in the microstructure of cycled aluminum 2024 commercial alloys. Line shapes, widths, and positions in an x-ray diffraction pattern depend on microstructural properties such as grain size, grain orientation, residual stress, microstrain, etc. Changes in the microstructure due to fatigue will appear as changes in the diffraction pattern. One parameter used to characterize a reflection in a diffraction pattern is the full width at half maximum (FWHM). Preliminary x-ray diffraction results on cycled Al 2024 indicate that the (111) and (222) reflections of the matrix phase do not show any variations in the FWHM due to an increase in the fatigue cycles. However, the FWHM of the (200) and (400) reflections of the same phase unexpectedly showed a dramatic decrease. These results can be interpreted as due to the relaxation of some initial nonuniform residual stresses in the matrix phase lattice. Further work is in progress to evaluate the FWHM of the second phase of the cycled alloys.

Ferguson, Milton W.

1994-12-01

237

Micro/meso scale fatigue damage accumulation monitoring using nonlinear acoustic vibro-modulation measurements  

NASA Astrophysics Data System (ADS)

Monitoring the incipient damage at the earliest possible stage is essential for predicting structural performance and remaining life of structural components. Existing prognostic methodologies incorporate conventional SHM and NDE techniques responsive to cracks and delaminations resulted from the irreversible material fracture and disintegration at the macro-scale. There is an increasing need for technologies that could allow for monitoring material degradation at the micro/meso scale before the onset of the macro-scale fracture. In this contribution, we report results of the real-time monitoring of the material micro/meso scale degradation using the nonlinear acoustic vibro-modulation technique. The technique explores nonlinear acoustic interaction of high frequency ultrasound and low frequency structural vibration at the site of the incipient damage. The indicator of the damage severity, nonlinear acoustic damage index (DI), was measured in real time during the strain-controlled three-point bending fatigue test of aluminum and steel specimens. Nondestructively, degradation of the specimen was revealed through the increase in the DI, which correlated well with the respective decrease in the specimen's stiffness. Destructive SEM examination confirmed sensitivity of the DI to the incipient micro/meso scale damage and advocated for utilizing the vibro-modulation approach for assessment of material degradation before fracture.

Zagrai, Andrei; Donskoy, Dimitri; Chudnovsky, Alexander; Golovin, Edward; Agarwala, Vinod S.

2006-04-01

238

Towards Glare: The Development of a Fatigue Insensitive and Damage Tolerant Aircraft Material.  

National Technical Information Service (NTIS)

The constant amplitude fatigue behavior of ARALL is investigated. The fatigue crack growth rates in ARALL 2 increase considerably when failure of the crack bridging fiber layers occurs. This fiber failure behavior was studied. The influences of fatigue lo...

G. H. J. J. Roebroeks

1991-01-01

239

Infrared thermal wave nondestructive testing for rotor blades in wind turbine generators non-destructive evaluation and damage monitoring  

Microsoft Academic Search

The rotor blades are key components in wind turbine generators. A visual inspection of the laminated shells for delaminations, air pockets, missing\\/disoriented fabric etc. is in most cases also not possible due to the manufacturing process, so Non-destructive testing and evaluation (NDT & E) techniques for assessing the integrity of rotor blades structure are essential to both reduce manufacturing costs

Shi Bin Zhao; Cun-Lin Zhang; Nai-Ming Wu; Yu-Xia Duan; Hao Li

2009-01-01

240

Effect of microstructure on pitting and corrosion fatigue of 17-4 PH turbine blade steel in chloride environments  

SciTech Connect

Depending on its heat treatment, 17-4 PH stainless steel may contain significant levels of reformed austenite and untempered martensite in a matrix of tempered martensite. Shot peening can cause changes in the microstructure of the surface layers by transforming the austenite to untempered martensite. The effect of these microstructural varations on the resistance of 17-4 PH stainless steel to pitting and corrosion fatigue has been determined in simulated steam turbine environments. The results of two electrochemical tests (large amplitude cyclic voltammetry and the pit propagation rate (PPR) test) indicate that tempering temperature and shot peening have only minor effects on resistance to pit initiation and propagation in any one of three aqueous chloride environments. However, the susceptibility of this stainless steel to corrosion fatigue in one of these environments (6 wt % FeCl/sub 3/) was reduced by increasing the tempering temperature from 538/sup 0/C (1000/sup 0/F) to 649/sup 0/C (1200/sup 0/F).

Syrett, B.C.; Viswanathan, R.

1982-02-01

241

Creep-fatigue Damage Evaluation of the 316SS Y-junction Structure in a Liquid Metal Reactor  

SciTech Connect

The Liquid Metal Reactor (LMR) structures are subjected to a high temperature and creep-fatigue damage is one of the principal concerns to be dealt with for the structural integrity. This paper deals with the creep-fatigue damage evaluation of a typical geometrical discontinuity structure made of 316SS subjected to both tensile loading and high temperature loading with a hold time. The creep-fatigue structural test of a cylindrical structure welded to a conical shell has been carried out with the 1MN IST actuator and 50 kW induction heater with a 1 hour hold time at 550 deg. C. Two penetration defects and another two surface defects have been prepared and their behaviors have been investigated. Also, the high temperature structural analysis program (NONSTA-VP) by implementing Chaboche's unified visco-plasticity model into ABAQUS, developed to analyze the creep-fatigue behavior, has been used to evaluate creep-fatigue damage and the result has been compared with those of the structural test and elastic rules. (authors)

Kim, J.B.; Lee, H.Y.; Park, C.G.; Jeon, G.P.; Lee, J.H. [Korea Atomic Energy Research Institute, 150 Dukjin-dong, Yusong-gu, Daejeon 305-353 (Korea, Republic of)

2004-07-01

242

Fatigue damage evolution and property degradation of a SCS-6/Ti-22Al-23Nb orthorhombic titanium aluminide composite  

SciTech Connect

The fatigue damage evolution and property degradation of a SCS-6/Ti-22Al-23Nb orthorhombic titanium aluminide composite under low cycle fatigue loading at room temperature was investigated. The fatigue test was conducted under a load-controlled mode with a load ratio (R) of 0.1, a frequency of 10 Hz, and a maximum applied stress ranging from 600 to 945 MPa. The stiffness reduction as well as the evolution of microstructural damage which includes matrix crack length, matrix crack density and interfacial debonding length as a function of fatigue cycles, and applied stresses were measured. An analytical model and a computer simulation were also developed to predict the residual stiffness and the post-fatigued tensile strength as a function of microstructural damage. Finally, a steady-state crack growth model proposed by Marshall et al. was used to predict the interfacial frictional stress and the critical crack length. Correlation between the theoretical predictions and experimental results were also discussed.

Wang, P.C.; Jeng, S.M.; Yang, J.M. [Univ. of California, Los Angeles, CA (United States). Dept. of Materials Science and Engineering; Russ, S.M. [Wright Lab., Wright-Patterson AFB, OH (United States). Materials Directorate

1996-08-01

243

Influence of the loading frequency on the fatigue damage sensor readings  

NASA Astrophysics Data System (ADS)

The influence of loading frequency f on the dependence of the change in the electrical resistivity of a fatigue damage sensor, on the amplitude of the cyclic strain, and on the number of loading cycles N and the sensor's resistance to fatigue is studied. The influence of f on the sensor characteristics is estimated by determining the dependence of the relative change in the sensor electrical resistivity on N for different values of f in the 36-780 Hz range and a fixed amplitude of the cyclic strain equal to 0.0016. In the 36-310 Hz range, the sensor characteristics do not vary; over the 310-620 Hz range, the rate of change in Delta R/R does not vary; over the 310-620 Hz range, this rate diminishes while the number of loading cycles needed to achieve identical values of Delta R/R increases by eight to ten times. For f = 620-780 Hz, the sensor characteristics stabilize again. This regularity is valid also for other values of the cyclic strain.

Boiko, V. I.; Orlov, S. G.

1986-04-01

244

Damage development of Al\\/SiC metal matrix composite under fatigue, creep and monotonic loading conditions  

Microsoft Academic Search

A consolidation of powders using the KOBO method at elevated temperature was elaborated for production of Al\\/SiC metal matrix composite (MMC). The observations of the mean strain and inelastic strain range during the force controlled high cycle fatigue (HCF) tests identified the ratcheting mechanism combined with mechanism characterized by cyclic plasticity. Damage parameters were calculated on the basis of strain

A. Rutecka; Z. L. Kowalewski; K. Pietrzak; L. Dietrich; K. Makowska; J. Wo?niak; M. Kostecki; W. Bochniak; A. Olszyna

2011-01-01

245

Fatigue crack growth behaviour of Inconel 718 – the concept of a damaged zone caused by high temperature hold times  

Microsoft Academic Search

Fatigue crack growth testing of Inconel 718 has been carried out at the temperatures 550°C and 650°C. The tests were conducted using a mix of hold times and pure cyclic loading, referred to as block tests. From the test results, the existence of an embrittled volume or damaged zone in the vicinity of the crack tip has been revealed. It

David Gustafsson; Johan Moverare; Kjell Simonsson; Sten Johansson; Magnus Hörnqvist; Tomas Månsson; Sören Sjöström

2011-01-01

246

Restoring Fatigue Performance Of Corrosion Damaged Aa7075-T6 and Fretting in 4340 Steel with Low Plasticity Burnishing  

Microsoft Academic Search

Corrosion related fatigue in aluminum structural alloys and fretting damage in high strength steels are primary failure mechanisms that reduce the structural integrity of aging aircraft. A chemically active environment, susceptible material and static and\\/or alternating tensile stresses are all required for failure. Conventional approaches to mitigate corrosion and fretting related failure mechanisms address either elimination of the corrosive environment

John T. Cammett

247

PREDICTION OF FATIGUE LIFE OF COLD FORGING TOOLS BY FE SIMULATION AND COMPARISON OF APPLICABILITY OF DIFFERENT DAMAGE MODELS  

Microsoft Academic Search

Tools for cold forging mainly fail due to cyclic fatigue. Tool costs can reach a significant portion of production costs and therefore meth ods to improve tool life are of high interest. However, tools are still main ly designed and optimized by the trial and error method. The purpose of the work presented is to implement damage models in a

M. Meidert; C. Walter

248

A time-dependent damage operator approach to thermo-mechanical fatigue of Niresist D-5S  

Microsoft Academic Search

The damage operator approach is extended to time dependent viscoplasticity and creep. The oxidation is taken into account indirectly. Time efficient viscoplastic approximation based on the nonlinear Maxwell model and the corresponding lifetime prediction is presented. Both thermo-mechanical fatigue tests on the specimens and the thermal shock tests on turbine housings of a turbocharger subject to a complex change of

Marko Nagode; Frank Längler; Michael Hack

2011-01-01

249

Fatigue and damage to the masseter muscle by prolonged low-frequency stimulation in the rat.  

PubMed

This study aimed to examine peripheral fatigue and the resultant damage to the masseter muscle due to prolonged low-frequency stimulation. Thirty male rats were divided into S1, S2, S4, Dantr and Sham groups. The left masseters were used as experimental muscles. A pair of stimulation electrodes was placed on the left masseter. A stimulating session included rectangular electric pulses of 18 Hz (5 mA, approximately 18 V, 0.7 ms) for 2 h with a 3 min rest period between sessions. One session was given to the S1 group, two sessions to the S2 group and four sessions to the S4 group. Four sessions were given to the Dantr group with administration of dantrolene to determine any artifacts of the electrical current. No electric stimulation was given to both side masseters in the Sham group or to the control (right) masseters in the other groups. In each session, jaw-closing force increased to a peak within 1 min and attenuated to the steady force. The peak force decreased as the session advanced in each group. Both side masseters were dissected after the stimulations and examined histologically. The experimental masseter was significantly heavier than that of the controls in the S1, S2 and S4 groups, and the muscle fibres showed irregularity of size and shape with enlargement of interstitial space and infiltration of mononuclear cells into the fibres. However, no such histological change was observed in the Dantr and Sham groups. It was confirmed that fatigue and damage to muscle fibres could be induced in masticatory muscles by prolonged low-frequency stimulation. PMID:15949787

Yamasaki, Konosuke; Harada, Shuitsu; Higuchi, Itsuro; Osame, Mitsuhiro; Ito, Gakuji

2005-06-08

250

Overview of Low Plasticity Burnishing for Mitigation of Fatigue Damage Mechanisms.  

National Technical Information Service (NTIS)

Surface enhancement technologies such as shot peening (SP), laser shock peening (LSP), and low plasticity burnishing (LPB) can provide substantial fatigue life improvement. However, to be effective, the compressive residual stresses that increase fatigue ...

P. S. Prevey N. Jayaraman J. Cammett

2005-01-01

251

Effects of Foreign Object Damage From Small Hard Particles on the High- Cycle Fatigue Life of Ti-6Al-4V.  

National Technical Information Service (NTIS)

Thin rectangular samples of Ti-6Al-4V were damaged by four methods to represent foreign object damage found in turbine engine blades: 1) impact with 2 mm and 5 mm diameter glass spheres at 305 m/s, 2) impact with 2 mm and 4 mm diameter steel spheres at 30...

J. L. Hamrick

1999-01-01

252

Thermal fatigue life prediction for solder joints with the consideration of damage evolution  

Microsoft Academic Search

Thermal fatigue of solder joints is critical to electronic package performance and service life. It is well known that the fatigue life is rather difficult to estimate because of the complex interaction between creep and fatigue of solder materials. Conventional life prediction methods such as the Coffin-Manson relation or its modifications may give erroneous results at the low strain range.

X. Zhang; S.-W. R. Lee

1998-01-01

253

A damage parameter based on fracture surface for fatigue life prediction of CSP solder joints  

Microsoft Academic Search

FEM simulation for the fatigue life of CSP solder joints with various geometries and array types under thermal cycling condition is studied. Coffin-Manson law with inelastic strain range is used to estimate the fatigue life of CSP solder joints. Therefore, the two unknown material parameters in the fatigue life model need to be determined first. Actually, the two parameters are

Lianxi Shen; Sung Yi; Jo Caers; Xiujuan Zhao; K. Zhang

2001-01-01

254

Ultrasonic detection of fretting fatigue damage at bolt joints of aluminum alloy plates  

Microsoft Academic Search

The fatigue failure evaluation was carried out to determine the effect of the tightening torque of the bolt on the failure mode and the fatigue life of bolted joints of aluminum alloy plates 2024-T3 at different levels of the stress amplitude. These results were shown in the tightening torque and fatigue life diagram. Regardless the stress amplitude, when the tightening

Sanat Wagle; Hiroshi Kato

2009-01-01

255

Acoustic harmonic generation due to fatigue damage in high-strength aluminum  

Microsoft Academic Search

It is shown that acoustic second harmonic generation is a useful tool for studying surface microcrack development during fatigue of a high-strength aluminum alloy. A fundamental (5 MHz) surface acoustic wave (SAW) was transmitted across the gauge section of flexural fatigue specimens of Al 7075-T6. The second harmonic amplitude was determined after several increments of fatigue, as a function of

W. L. Morris; O. Buck; R. V. Inman

1979-01-01

256

Application of piezoelectric active-sensors for SHM of wind turbine blades  

SciTech Connect

The goal of this study is to characterize the dynamic response of a CX-100 wind blade and the design parameters of SHM techniques as they apply to wind turbine blades, and to investigate the performance of high-frequency active-sensing SHM techniques, including lamb wave and frequency response functions, as a way to monitor the health of a wind turbine blade. The results of the dynamic characterization will be used to validate a numerical model and understand the effect of structural damage on the performance of the blades. The focus of SHM study is to assess and compare the performance of each method in identifying incipient damage, with a special consideration given to field deployability. For experiments, a 9-m CX-100 blade was used. Overall, the methods yielded sufficient damage detection to warrant further investigation into field deployment. This paper also summarizes the SHM results of a full-scale fatigue test of 9-m CX-100 blade using piezoelectric active-sensors.

Park, Gyuhae [Los Alamos National Laboratory; Taylor, Stuart G. [Los Alamos National Laboratory; Farinholt, Kevin M [Los Alamos National Laboratory; Farrar, Charles R [Los Alamos National Laboratory

2010-10-04

257

Critical plane-energy based approach for assessment of biaxial fatigue damage where the stress-time axes are at different frequencies  

Microsoft Academic Search

A new fatigue parameter has been developed to assess the fatigue lives under in-phase and out-of-phase biaxial constant amplitude fatigue stressing where the stresses are at different frequencies. In this parameter, the normal and shear stress and strain ranges have been calculated from the largest stress and strain Mohr's circles. The total damage accumulation in a block loading history has

A. Varvani-Farahani

2003-01-01

258

A combined finite element method and continuum damage mechanics approach to simulate the in vitro fatigue behavior of human cortical bone  

Microsoft Academic Search

The fatigue of bone, in particular the associated modulus degradation and accumulation of permanent strain, has been implicated as the cause of femoral neck fractures and the migration of total joint replacements. The objective of this study was to develop a technique to simulate the tensile fatigue behavior of human cortical bone. A combined continuum damage mechanics (CDM) and finite

M. Taylor; NJJ Verdonschot; R. Huiskes; P. Zioupos

1999-01-01

259

Stochastic propagation of an array of parallel cracks: Exploratory work on matrix fatigue damage in composite laminates  

SciTech Connect

Transverse cracking of polymeric matrix materials is an important fatigue damage mechanism in continuous-fiber composite laminates. The propagation of an array of these cracks is a stochastic problem usually treated by Monte Carlo methods. However, this exploratory work proposes an alternative approach wherein the Monte Carlo method is replaced by a more closed-form recursion relation based on fractional Brownian motion.'' A fractal scaling equation is also proposed as a substitute for the more empirical Paris equation describing individual crack growth in this approach. Preliminary calculations indicate that the new recursion relation is capable of reproducing the primary features of transverse matrix fatigue cracking behavior. Although not yet fully tested or verified, this cursion relation may eventually be useful for real-time applications such as monitoring damage in aircraft structures.

Williford, R.E.

1989-09-01

260

Application of microcomputer to automatizing fatigue testing  

NASA Astrophysics Data System (ADS)

This paper describes how a microcomputer is applied to a blade fatigue testing system. Automatic checking and controlling of blade fatigue testing in the system are implemented with the aid of a nest-form of assembly language and high-level language. The system can also be used for fatigue testing of fuel or oil tubes.

Yang, Daman; Zhuang, Zhongliang; Lu, Qixin

1989-01-01

261

Incipient Crack Detection in Composite Wind Turbine Blades  

SciTech Connect

This paper presents some analysis results for incipient crack detection in a 9-meter CX-100 wind turbine blade that underwent fatigue loading to failure. The blade was manufactured to standard specifications, and it underwent harmonic excitation at its first resonance using a hydraulically-actuated excitation system until reaching catastrophic failure. This work investigates the ability of an ultrasonic guided wave approach to detect incipient damage prior to the surfacing of a visible, catastrophic crack. The blade was instrumented with piezoelectric transducers, which were used in an active, pitchcatch mode with guided waves over a range of excitation frequencies. The performance results in detecting incipient crack formation in the fiberglass skin of the blade is assessed over the range of frequencies in order to determine the point at which the incipient crack became detectable. Higher excitation frequencies provide consistent results for paths along the rotor blade's carbon fiber spar cap, but performance falls off with increasing excitation frequencies for paths off of the spar cap. Lower excitation frequencies provide more consistent performance across all sensor paths.

Taylor, Stuart G. [Los Alamos National Laboratory; Choi, Mijin [Chonbuk National University, Korea; Jeong, Hyomi [Chonbuk National University, Korea; Jang, Jae Kyeong [Chonbuk National University, Korea; Park, Gyuhae [Chonnam National University, Korea; Farinholt, Kevin [Commonwealth Center for Advanced Manufacturing, VA; Farrar, Charles R. [Los Alamos National Laboratory; Ammerman, Curtt N. [Los Alamos National Laboratory; Todd, Michael D. [Los Alamos National Laboratory; Lee, Jung-Ryul [Chonbuk National University, Korea

2012-08-28

262

Characteristics of the formation of chronic fatigue syndrome and approaches to its treatment in young patients with focal brain damage  

Microsoft Academic Search

Chronic fatigue is among the manifestations of focal brain lesions. It is most often encountered in multiple sclerosis (MS)\\u000a and patients with the sequelae of traumatic, inflammatory, and vascular brain damage (encephalopathies). The aim of the present\\u000a work was to study the mechanisms of formation of this syndrome in 50 patients with focal brain lesions of different origins\\u000a (in the

A. N. Boiko; T. T. Batysheva; O. V. Matvievskaya; T. M. Manevich; E. I. Gusev

2007-01-01

263

On the temperature dependence of the fatigue and damage behaviour of a particulate-reinforced metal-matrix composite  

Microsoft Academic Search

The fatigue and damage behaviour of the particulate-reinforced aluminum-matrix composite AA6061-Al2O3-20p was investigated at temperatures between T=?100 and 300°C. Experiments performed at the highest temperature are characterized by pronounced cyclic softening which can clearly be explained by overaging (coarsening) of the precipitate structure in the matrix. A completely different behaviour was found at low and ambient temperature, where, at larger

Horst Biermann; Mathias Kemnitzer; Oliver Hartmann

2001-01-01

264

Fatigue damage coupled constitutive model for 63Sn37Pb solder under proportional and non-proportional loading  

Microsoft Academic Search

In this paper, a series of low cycle fatigue tests under multiaxial non-proportional loading at constant room temperature is carried out. It is observed that 63Sn37Pb solder exhibits non-additional cyclic hardening effect under non-proportional loading compared with proportional loading. A damage coupled Ohno–Wang constitutive model is implemented to simulate stress strain loops of solder over a wide range of loading

Gang Chen; Xu Chen

2007-01-01

265

Influence of residual stresses on high cycle fatigue strength of Ti–6Al–4V subjected to foreign object damage  

Microsoft Academic Search

The role of residual stresses in the high cycle fatigue (HCF) strength of Ti–6Al–4V subjected to foreign object damage (FOD) was evaluated on simulated airfoil and rectangular geometries. Both real and simulated impacts were conducted using spherical projectiles launched at 300 m\\/s and quasi-static chisel indentation, respectively. The spheres used were 1 mm diameter glass beads while the quasi-static indentor

Steven R. Thompson; John J. Ruschau; Theodore Nicholas

2001-01-01

266

An assessment of low cycle fatigue damage using magnetic Barkhausen emission in 9Cr–1Mo ferritic steel  

Microsoft Academic Search

A non-destructive, magnetic Barkhausen emission (MBE) technique has been used to assess various stages of low cycle fatigue (LCF) damage in 9Cr–1Mo ferritic steel. The initial decrease in the MBE peak height in the early stage of LCF cycling indicates the cyclic hardening stage, in which the formation of dislocation tangles reduces the mean free path of the domain wall

V. Moorthy; B. K. Choudhary; S. Vaidyanathan; T. Jayakumar; K. Bhanu Sankara Rao; Baldev Raj

1999-01-01

267

On the application of the Kitagawa–Takahashi diagram to foreign-object damage and high-cycle fatigue  

Microsoft Academic Search

The role of foreign-object damage (FOD) and its effect on high-cycle fatigue (HGF) failures in a turbine engine Ti–6Al–4V alloy is examined in the context of the use of the Kitagawa–Takahashi diagram to describe the limiting conditions for such failures. Experimentally, FOD is simulated by firing 1 and 3.2 mm diameter steel spheres onto the flat specimen surface of tensile

J. O. Peters; B. L. Boyce; X. Chen; J. M. McNaney; J. W. Hutchinson; R. O. Ritchie

2002-01-01

268

Finite element modeling of thermal fatigue and damage of solder joints in a ceramic ball grid array package  

NASA Astrophysics Data System (ADS)

A nonlinear finite element model is presented for analyzing the cyclic and thermal fatigue loading and for viscoplastic damage characterization of the lead-tin (Pb-Sn) solder joints in a ceramic ball grid array (CBGA) surface mount package. An approach using a ? ?{eq/in}-modified Coffin-Manson equation is proposed to estimate the fatigue life of the solder joints. The ? ?{eq/in} represents a saturated equivalent inelastic strain range as determined by the finite element model. The present study shows that the predictied fatigue life and the associated damage mechanism of the solder joint agree reasonably well with the test data for the 18,25, and 32 mm CBGA packages run at a cyclic temperature load of 0°C/100°C with a frequency of 1.5 cycles per hour. Analysis also shows that a preferred failure site is expected to occur in and around the Pb37-Sn63 solder attachment of the solder joint. A time-dependent (creep induced) damage mechanism is found to be more pronounced than the time-independent (plastic deformation) mechanism.

Hong, Bor Zen

1997-07-01

269

Competing damage mechanisms in the thermo-mechanical fatigue of AISI 304L stainless steel  

Microsoft Academic Search

Thermo-mechanical fatigue (TMF) in AISI 304L stainless steel is investigated in two temperature ranges using four phase differences between the mechanical loading and the temperature. In the temperature range from 450°C to 700°C, the fatigue life was lowest in the in-phase condition. However, in the temperature range from 400°C to 650°C, the minimum fatigue life occurs in the counter-clockwise-diamond condition.

Keun-Ho Bae; Hyun-Ho Kim; Soon-Bok Lee

2011-01-01

270

Infrared thermal wave nondestructive testing for rotor blades in wind turbine generators non-destructive evaluation and damage monitoring  

NASA Astrophysics Data System (ADS)

The rotor blades are key components in wind turbine generators. A visual inspection of the laminated shells for delaminations, air pockets, missing/disoriented fabric etc. is in most cases also not possible due to the manufacturing process, so Non-destructive testing and evaluation (NDT & E) techniques for assessing the integrity of rotor blades structure are essential to both reduce manufacturing costs and out of service time of wind turbine generators due to maintenance. Nowadays, Infrared Thermal Wave Nondestructive Testing (Pulsed thermography) is commonly used for assessing composites. This research work utilizes Infrared Thermal Wave Nondestructive Testing system (EchoTherm, Thermal Wave Imaging, Inc.) to inspect a specimen with embedded defects (i.e. foreign matter and air inclusions) in different depth which is a part of rotor blades in wind turbine generators, we have successfully identified defects including foreign matter and air inclusions, and discovered a defective workmanship. The system software allows us to simultaneously view and analyze the results for an entire transition.

Zhao, Shi Bin; Zhang, Cun-Lin; Wu, Nai-Ming; Duan, Yu-Xia; Li, Hao

2009-07-01

271

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

SciTech Connect

Lightweight and miniaturized weapon systems are driving the use of new materials in design such as microscale materials and ultra low-density metallic materials. Reliable design of future weapon components and systems demands a thorough understanding of the deformation modes in these materials that comprise the components and a robust methodology to predict their performance during service or storage. Traditional continuum models of material deformation and failure are not easily extended to these new materials unless microstructural characteristics are included in the formulation. For example, in LIGA Ni and Al-Si thin films, the physical size is on the order of microns, a scale approaching key microstructural features. For a new potential structural material, cast Mg offers a high stiffness-to-weight ratio, but the microstructural heterogeneity at various scales requires a structure-property continuum model. Processes occurring at the nanoscale and microscale develop certain structures that drive material behavior. The objective of the work presented in this report was to understand material characteristics in relation to mechanical properties at the nanoscale and microscale in these promising new material systems. Research was conducted primarily at the University of Colorado at Boulder to employ tightly coupled experimentation and simulation to study damage at various material size scales under monotonic and cyclic loading conditions. Experimental characterization of nano/micro damage will be accomplished by novel techniques such as in-situ environmental scanning electron microscopy (ESEM), 1 MeV transmission electron microscopy (TEM), and atomic force microscopy (AFM). New simulations to support experimental efforts will include modified embedded atom method (MEAM) atomistic simulations at the nanoscale and single crystal micromechanical finite element simulations. This report summarizes the major research and development accomplishments for the LDRD project titled 'Atomistic Modeling of Nanowires, Small-scale Fatigue Damage in Cast Magnesium, and Materials for MEMS'. This project supported a strategic partnership between Sandia National Laboratories and the University of Colorado at Boulder by providing funding for the lead author, Ken Gall, and his students, while he was a member of the University of Colorado faculty.

Dunn, Martin L. (University of Colorado, Boulder, CO); Talmage, Mellisa J. (University of Colorado, Boulder, CO); McDowell, David L., 1956- (,-Georgia Institute of Technology, Atlanta, GA); West, Neil (University of Colorado, Boulder, CO); Gullett, Philip Michael (Mississippi State University , MS); Miller, David C. (University of Colorado, Boulder, CO); Spark, Kevin (University of Colorado, Boulder, CO); Diao, Jiankuai (University of Colorado, Boulder, CO); Horstemeyer, Mark F. (Mississippi State University , MS); Zimmerman, Jonathan A.; Gall, K (Georgia Institute of Technology, Atlanta, GA)

2006-10-01

272

Role of brain macrophages on IL-1beta and fatigue following eccentric exercise-induced muscle damage.  

PubMed

Fatigue associated with recovery from muscle damage has recently been linked to increases in brain and muscle proinflammatory cytokines. However, little is known regarding the origin of these cytokines. Since macrophage-like cells in the brain are a primary source of cytokines, we used a brain specific macrophage depletion technique involving liposome encapsulated clodronate (CLD) to examine the role of macrophages on brain IL-1beta and fatigue following eccentric exercise-induced muscle damage. Mice were assigned to six groups: Downhill saline (DWNSAL), downhill clodronate (DWNCLD), uphill saline (UPSAL), uphill clodronate (UPCLD), non-running saline (CONSAL) or non-running clodronate (CONCLD). Mice were given intracerebroventricular (ICV) (10 microL) injections of clodronate-filled liposomes (CLD) to deplete macrophages, or saline-filled liposomes (SAL) and run on a treadmill at 22m/min and -14% (DWN) or 14% (UP) grade for 150 min. A subset of uphill and downhill running mice (n=40) was then run to fatigue on a treadmill at 36m/min, 8% grade at 24h after the uphill and downhill runs. A second subset of uphill, downhill, and control mice (n=30) was sacrificed 24h after the run for analysis of brain IL-1beta concentration. Histological examination confirmed previous reports that CLD administration reduced perivascular and meningeal macrophage subsets in the brain. CLD reduced IL-1beta concentration in the cortex of DWN mice (P<0.05), which was associated with enhanced treadmill performance 24h after both uphill and downhill runs (P<0.05) although the magnitude was greater following the downhill run. These results suggest that brain macrophages can contribute to the increase in brain IL-1beta and fatigue that are associated with recovery from exercise-induced muscle damage. PMID:20051263

Carmichael, Martin D; Davis, J Mark; Murphy, E Angela; Carson, James A; Van Rooijen, N; Mayer, Eugene; Ghaffar, Abdul

2010-01-04

273

Self-sealing of thermal fatigue and mechanical damage in fiber-reinforced composite materials  

NASA Astrophysics Data System (ADS)

Fiber reinforced composite tanks provide a promising method of storage for liquid oxygen and hydrogen for aerospace applications. The inherent thermal fatigue of these vessels leads to the formation of microcracks, which allow gas phase leakage across the tank walls. In this dissertation, self-healing functionality is imparted to a structural composite to effectively seal microcracks induced by both mechanical and thermal loading cycles. Two different microencapsulated healing chemistries are investigated in woven glass fiber/epoxy and uni-weave carbon fiber/epoxy composites. Self-healing of mechanically induced damage was first studied in a room temperature cured plain weave E-glass/epoxy composite with encapsulated dicyclopentadiene (DCPD) monomer and wax protected Grubbs' catalyst healing components. A controlled amount of microcracking was introduced through cyclic indentation of opposing surfaces of the composite. The resulting damage zone was proportional to the indentation load. Healing was assessed through the use of a pressure cell apparatus to detect nitrogen flow through the thickness direction of the damaged composite. Successful healing resulted in a perfect seal, with no measurable gas flow. The effect of DCPD microcapsule size (51 microm and 18 microm) and concentration (0--12.2 wt%) on the self-sealing ability was investigated. Composite specimens with 6.5 wt% 51 microm capsules sealed 67% of the time, compared to 13% for the control panels without healing components. A thermally stable, dual microcapsule healing chemistry comprised of silanol terminated poly(dimethyl siloxane) plus a crosslinking agent and a tin catalyst was employed to allow higher composite processing temperatures. The microcapsules were incorporated into a satin weave E-glass fiber/epoxy composite processed at 120°C to yield a glass transition temperature of 127°C. Self-sealing ability after mechanical damage was assessed for different microcapsule sizees (25 microm and 42 microm) and concentrations (0--11 vol%). Incorporating 9 vol% 42 microm capsules or 11 vol% 25 microm capsules into the composite matrix leads to 100% of the samples sealing. The effect of microcapsule concentration on the short beam strength, storage modulus, and glass transition temperature of the composite specimens was also investigated. The thermally stable tin catalyzed poly(dimethyl siloxane) healing chemistry was then integrated into a [0/90]s uniweave carbon fiber/epoxy composite. Thermal cycling (-196°C to 35°C) of these specimens lead to the formation of microcracks, over time, formed a percolating crack network from one side of the composite to the other, resulting in a gas permeable specimen. Crack damage accumulation and sample permeability was monitored with number of cycles for both self-healing and traditional non-healing composites. Crack accumulation occurred at a similar rate for all sample types tested. A 63% increase in lifetime extension was achieved for the self-healing specimens over traditional non-healing composites.

Moll, Jericho L.

274

Optimizing Material Use in Blade Design by Improving Failure Prediction Methodology and Introducing Damage Tolerant Concepts in FRP Composites  

Microsoft Academic Search

Preliminary results are presented in this work, concerning the validation of a reliable FEM tool under development, featuring damage tolerant concepts, to enhance design capabilities and optimize material use in large composite structures. User defined material constitutive equations concerning anisotropic non- linearity and material stiffness degradation as a result of damage accumulation, are implemented to model inherent damage tolerance of

A. E. Antoniou; T. P. Philippidis

275

Application of FIB technique to study of early fatigue damage in polycrystals  

NASA Astrophysics Data System (ADS)

Focused ion beam (FIB) technique together with other advanced microscopic techniques were applied to study early microstructural changes leading to crack initiation in fatigued polycrystals. Dislocation structures of persistent slip bands (PSBs) and surrounding matrix were revealed in the bulk of surface grains by electron channelling contrast imaging (ECCI) technique on the FIB cross-sections. True shape of extrusions, intrusions and the path of initiated fatigue cracks were assessed in three dimensions by serial FIB cross-sectioning (FIB tomography). Advantageous potential of FIB technique and its other possible utilization in fatigue crack initiation studies in polycrystals are highlighted.

Man, J.; Weidner, A.; Kub?na, I.; Vystav?l, T.; Skrotzki, W.; Polák, J.

2010-07-01

276

Thermomechanical fatigue damage/failure mechanisms in SCS-6/Timetal 21S (0/90)s composite. Final report  

SciTech Connect

The thermomechanical fatigue (TMF) deformation, damage, and life behaviors of SCS6/Timetal 21S (0/90)s were investigated under zero-tension conditions. In-phase (IP) and out-of-phase (OP) loadings were investigated with a temperature cycle from 150 to 650 deg C. An advanced TMF test technique was used to quantify mechanically damage progression. The technique incorporated explicit measurements of the macroscopic (1) isothermal static moduli at the temperature extremes of the TMF cycle and (2) coefficient of thermal expansion (CTE) as functions of the TMF cycles. The importance of thermal property degradation and its relevance to accurate post-test data analysis and interpretation is briefly addressed. Extensive fractography and metallography were conducted on specimens from failed and interrupted tests to characterize the extent of damage at the microstructure level. Fatigue life results indicated trends analogous to those established for similar unidirectional(0) reinforced titanium matrix composite systems. High stress IP and mid to low stress OP loading conditions were life-limiting in comparison to maximum temperature isothermal conditions. Dominant damage mechanisms changed with cycle type. Damage resulting from IP TMF conditions produced measurable decreases in static moduli but only minimal changes in the CTE. Metallography on interrupted and failed specimens revealed extensive (0) fiber cracking with sparse matrix damage. No surface initiated matrix cracks were present. Comparable OP TMF conditions initiated environment enhanced surface cracking and matrix cracking initiated at (90) fiber/matrix (F/M) interfaces. Notable static moduli and CTE degradations were measured. Fractography and metallography revealed that the transverse cracks originating from the surface and (90) F/M interfaces tended to converge and coalesce at the (0) fibers.

Castelli, M.G.

1994-06-01

277

14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.  

Code of Federal Regulations, 2010 CFR

...withstood: (i) Critical limit flight loads...must be determined by analysis, tests, or both...on each production article that will apply the critical limit design load...fatigue tests, or analysis supported by...

2009-01-01

278

14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.  

Code of Federal Regulations, 2010 CFR

...withstood: (i) Critical limit flight loads...must be determined by analysis, tests, or both...on each production article that will apply the critical limit design load...fatigue tests, or analysis supported by...

2010-01-01

279

Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics  

NASA Astrophysics Data System (ADS)

Safe-life and damage-tolerant design philosophies of high performance structures have driven the development of various methods to evaluate nondestructively the accumulation of damage in such structures resulting from cyclic loading. Although many techniques have proven useful, none has been able to provide an unambiguous, quantitative assessment of damage accumulation at each stage of fatigue from the virgin state to fracture. A method based on nonlinear acoustics is shown to provide such a means to assess the state of metal fatigue. The salient features of an analytical model are presented of the microelastic-plastic nonlinearities resulting from the interaction of an acoustic wave with fatigue-generated dislocation substructures and cracks that predictably evolve during the metal fatigue process. The interaction is quantified by the material (acoustic) nonlinearity parameter ? extracted from acoustic harmonic generation measurements. The ? parameters typically increase monotonically by several hundred percent over the fatigue life of the metal, thus providing a unique measure of the state of fatigue. Application of the model to aluminum alloy 2024-T4 and 410 Cb stainless steel specimens fatigued using different loading conditions yields good agreement between theory and experiment. Application of the model and measurement technique to the on-site inspection of steam turbine blades is discussed.

Cantrell, John H.

2009-03-01

280

Muscle Damage and Its Relationship with Muscle Fatigue During a Half-Iron Triathlon  

Microsoft Academic Search

BackgroundTo investigate the cause\\/s of muscle fatigue experienced during a half-iron distance triathlon.Methodology\\/Principal FindingsWe recruited 25 trained triathletes (36±7 yr; 75.1±9.8 kg) for the study. Before and just after the race, jump height and leg muscle power output were measured during a countermovement jump on a force platform to determine leg muscle fatigue. Body weight, handgrip maximal force and blood

Juan Del Coso; Cristina González-Millán; Juan José Salinero; Javier Abián-Vicén; Lidón Soriano; Sergio Garde; Benito Pérez-González

2012-01-01

281

Microstructure-dependent fatigue damage process zone and notch sensitivity index  

Microsoft Academic Search

The development of simulation methods for calculating notch root parameters for purposes of estimating the fatigue life of\\u000a notched components is a critical aspect of designing against fatigue failures. At present, however, treatment of the notch\\u000a root stress and plastic strain field gradients, coupled with intrinsic length scales of grains or other material attributes,\\u000a has yet to be developed. Ultimately,

Gbadebo Owolabi; Benedict Egboiyi; Li Shi; Horace Whitworth

282

On the cumulative fatigue damage in short carbon fiber reinforced poly-ether-ether-ketone  

Microsoft Academic Search

The actual load for mechanical structures is not always a constant stress amplitude. Therefore, in order to predict the fatigue life under various stress amplitudes, it is important to investigate whether Miner's rule is applicable or not. In this paper, rotating-bending fatigue tests under two-step loading for short carbon fiber reinforced poly-ether-ether-ketone, CFRPEEK, were carried out in order to investigate

Hiroshi Noguchi; Yun-Hae Kim; Hironobu Nisitani

1995-01-01

283

Scanning electron microscope fractography of induced fatigue-damaged saline breast implants.  

PubMed

Breast implant strength and durability is presently an important topic in biomaterials science. Research studies are being conducted to determine the mechanisms and rates of failure in order to assess the in vivo performance of breast implants. Fatigue life is a measure of breast implant durability since fatigue failure is a potential in vivo failure mechanism. This study describes the characterization of the fracture surface morphology of breast implant shell regions that have failed due to cyclic fatigue. Saline breast implants were fatigue tested to failure using a laboratory apparatus in which flat plates cyclically compressed the implants. The implants were unimplanted control devices of both textured and smooth saline implants. The failure surfaces of the fatigued shells were examined using scanning electron microscopy (SEM). The morphological features of the failure surfaces are described for implants with short and long fatigue lifetimes. The details of both the inside and outside surfaces of the shell at the failure location are described. Two different modes of failure were observed in both the textured and smooth shells. These modes depend on the magnitude of the cyclic load and corresponding number of fatigue cycles at failure. The first mode is a tear in the shell of about 18 mm in length, and the second mode is a pinhole approximately 1 mm in diameter. Details of the surface morphology for these two types of failure modes and shell thickness data are presented herein. There was no significant change in the crosslink density of the shell as a result of fatigue. PMID:16566747

Brandon, H J; Jerina, K L; Savoy, T L; Wolf, C J

2006-01-01

284

Dependence of microelastic-plastic nonlinearity of martensitic stainless steel on fatigue damage accumulation  

Microsoft Academic Search

Self-organized substructural arrangements of dislocations formed during cyclic stress-induced fatigue of metals produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter beta extracted from acoustic harmonic generation measurements. The contributions to beta from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell

John H. Cantrell; John H

2006-01-01

285

Dependence of microelastic-plastic nonlinearity of martensitic stainless steel on fatigue damage accumulation  

Microsoft Academic Search

Self-organized substructural arrangements of dislocations formed during cyclic stress-induced fatigue of metals produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter ? extracted from acoustic harmonic generation measurements. The contributions to ? from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell

John H. Cantrell

2006-01-01

286

Distrubance Tracking and Blade Load Control of Wind Turbines in Variable-Speed Operation: Preprint  

SciTech Connect

A composite state-space controller was developed for a multi-objective problem in the variable-speed operation of wind turbines. Disturbance Tracking Control theory was applied to the design of a torque controller to optimize energy capture under the influence of persistent wind disturbances. A limitation in the theory for common multi-state models is described, which led to the design of a complementary pitch controller. The goal of the independent blade pitch design was to minimize blade root fatigue loads. Simulation results indicate an 11% reduction in fatigue damage using the proposed controllers, compared to a conventional torque-only design. Meanwhile, energy capture is almost identical, partly because of nonlinear effects.

Stol, K. A.

2003-01-01

287

Nondestructive Measurement of Fatigue Damage of Thermally Sprayed Al 2 O 3 \\/NiCr Using ESPI Method Under High Temperature  

Microsoft Academic Search

High-temperature fatigue (R = 0) damage and deformation behaviors of SUS304 steel thermally sprayed with an Al2O3\\/NiCr coating were investigated using a servopulse fatigue-testing machine, SEM, and an electronic speckle pattern interferometry (ESPI) method. The relation between crack\\/delamination and strain variation is discussed. Surface cracks occurred at the outer Al2O3 coating but stopped at the inner NiCr coating after one

Rongguang Wang; Mitsuo Kido

2002-01-01

288

FOD Simulation for Ceramic Turbine Blades  

Microsoft Academic Search

Foreign object impact damage is a serious problem for ceramic gas turbines. In this paper, a series of finite element analyses with an elastic assumption was made to estimate the plausible damage behavior of axial and radial ceramic blades. Foreign objects were assumed to impact the leading part of the blade suction surface. The present analysis showed that the stress

Hiro Yoshida; Yinsheng Li

2006-01-01

289

Analysis of the effects of controlled shot peening on fatigue damage of high strength aluminium alloys  

Microsoft Academic Search

The use of two micro-mechanical models for notch sensitivity and fatigue life allowed the development of boundary conditions that would evaluate potential life improvement after controlled shot peening (CSP) in high strength aluminium alloys. The boundary conditions describe the state of equal weight between surface roughening and residual stresses and the implication of material and loading parameters. From the boundary

S. Curtis; E. R. de los Rios; C. A. Rodopoulos; A. Levers

2003-01-01

290

Theory Relating the Woehler Equation to Cumulative Damage in the Distribution Fatigue Life.  

National Technical Information Service (NTIS)

A theoretical model which is able to encompass the observed fatigue growth phenomena of crack acceleration or crack deceleration, crack arrest, and crack jump at a change of load level, is proposed for the expected incremental crack growth rate under prog...

S. C. Saunders

1974-01-01

291

Influence of ambient temperature on the fatigue damage of welded bridge decks  

Microsoft Academic Search

Fatigue life assessment of critical bridge members using online monitoring data has been investigated in recent years. To make an efficient evaluation, a representative block of cycles is usually defined. However, relatively small amount of data in the representative block sometimes fail to cover the change caused by temperature and increasing traffic flow, which are proved by this paper to

Tong Guo; Aiqun Li; Hao Wang

2008-01-01

292

Systematic error in mechanical measures of damage during four-point bending fatigue of cortical bone  

Microsoft Academic Search

Accumulation of fatigue microdamage in cortical bone specimens is commonly measured by a modulus or stiffness degradation after normalizing tissue heterogeneity by the initial modulus or stiffness of each specimen measured during a preloading step. In the first experiment, the initial specimen modulus defined using linear elastic beam theory (LEBT) was shown to be nonlinearly dependent on the preload level,

Matthew D. Landrigan; Ryan K. Roeder

2009-01-01

293

Nonlocalized fatigue damage of metals and alloys. Part 3. Strain and energy criteria  

Microsoft Academic Search

The paper considers methods of accelerated determination of endurance limits of metals and alloys based on the analysis of\\u000a regularities in their inelastic deformation, strain and energy criteria of fatigue fracture, and methods for life prediction\\u000a with the use of those criteria.

V. T. Troshchenko

2006-01-01

294

Diagnostics of corrosion fatigue damage in components of equipment of thermal electric power stations  

Microsoft Academic Search

The complicated service conditions of components of steam boilers operating at moderate temperatures (bends of nonheated boiler pipes, drums, etc.) lead in some cases to premature damage in these components. The identification of this damage in metallographic and fractographic investigations is a complicated problem because this type of damage is caused by the combined effect of a number of factors.

M. B. Balakhovskaya; Yu. V. Balashov; L. V. Nadtsyna; L. N. Davlyatova

1988-01-01

295

Use of Residual Compression in Design to Improve Damage Tolerance in Ti- 6AI-4V Aero Engine Blade Dovetails.  

National Technical Information Service (NTIS)

The deep stable layer of compressive residual stress produced by low plasticity burnishing (LPB) has been demonstrated to improve the damage tolerance in engine alloys IN718, Ti-6Al-4V, and 17-4PH. This paper describes the application of LPB to the doveta...

P. S. Prevey N. Jayaraman R. A. Ravindranath

2005-01-01

296

The DF-4 fuel damage experiment in ACRR (Annual Core Research Reactor) with a BWR (Boiling Water Reactor) control blade and channel box  

SciTech Connect

The DF-4 test was an experimental investigation into the melt progression behavior of boiling water reactor (BWR) core components under high temperature severe core damage conditions. In this study 14 zircaloy clad UO{sub 2} fuel rods, and representations of the zircaloy fuel canister and stainless steel/B{sub 4}C control blade were assembled into a 0.5 m long test bundle. The test bundle was fission heated in a flowing steam environment, using the Annular Core Research Reactor at Sandia Laboratories, simulating the environmental conditions of an uncovered BWR core experiencing high temperature damage as a result residual fission product decay heating. The experimental results provide information on the thermal response of the test bundle components, the rapid exothermic oxidation of the zircaloy fuel cladding and canister, the production of hydrogen from metal-steam oxidation, and the failure behavior of the progressively melting bundle components. This information is provided in the form of thermocouple data, steam and hydrogen flow rate data, test bundle fission power data and visual observation of the damage progression. In addition to BWR background information, this document contains a description of the experimental hardware with details on how the experiment was instrumented and diagnosed, a description of the test progression, and a presentation of the on-line measurements. Also in this report are the results of a thermal analysis of the fueled test section of the fueled test section of the experiment demonstrating an overall consistency in the measurable quantities from the test. A discussion of the results is provided. 38 refs., 72 figs., 7 tabs.

Gauntt, R.O.; Gasser, R.D.; Ott, L.J. (Sandia National Labs., Albuquerque, NM (USA))

1989-11-01

297

Damage development during low cycle fatigue of carbon-black loaded SBR. [Styrene butadiene rubber containing 0, 15, 25, and 35 wt % carbon black  

SciTech Connect

Fatigue of elastomers is a subject that has received considerable study over the years. This paper explores the problem of damage accumulation in a series of styrene butadiene rubber (SBR) based compounds containing 0, 15, 25, and 35 wt % carbon-black under conditions in which a limited number of higher stress cycles have been applied to the material (referred to here as low cycle fatigue). Damage development in elastomers can take many forms. Generally speaking, one can classify the degradation as mechanical or chemical in origin. The most obvious form of mechanical damage is flaw or cut growth, while typical examples of chemical damage include chain scission or thermal oxidation. The fatigue crack growth relationship given in Equation 1 obviously only applies to flaw growth. However, it does an excellent job of following the data and exhibits the threshold behavior observed in both SBR and SBR-35 at room temperature. At higher temperatures, the damaged material shows an increasing deviation from threshold behavior. The obvious implication is that some thermally activated damage mechanism is degrading the material. In previous work, carbon-black loaded SBR subjected to a high temperature, high stress environment was shown to undergo a thermal-mechanical oxidation process. Certainly, this process is a candidate for a damage mechanism in these studies. 6 references, 14 figures, 1 table.

Lesuer, D.; Goldberg, A.; Hiromoto, D.; Patt, J.

1984-06-18

298

Detection of Fatigue Damage Prior to Crack Initiation withScanning SQUID Microscopy  

SciTech Connect

The remanence fields of fatigued ferritic steel specimens were measured using a scanning microscope based on a high transition temperature Superconducting Quantum Interference Device (SQUID). The results show an overall increase of remanence until dislocation density saturates and an additional local remanence increase after saturation during cyclic loading. Because of the combined magnetic and spatial resolution of the SQUID microscope, these local changes of dislocation structures can be detected before a crack actually initiates, and identify the sites where crack nucleation will occur.

Lee, Tae-Kyu; Morris Jr., J.W.; Lee, Seungkyun; Clarke, John

2005-11-07

299

Effect of Fatigue Damage in Woven Composites on ThermoMechanical Properties and Residual Compressive Strength  

Microsoft Academic Search

The long term mechanical and thermal fatigue of a Celion G30-500\\/PMR-15 woven composite system is investigated to study the interrelationship between thermo-mechanical properties, namely the thermal expansion coefficent (TEC) and the compressive strength. Qualitative trends in the experimental data generated by either thermal or mechanical loadings are shown to be similar to properties predicted by a shear lag based model.

Milan Mitrovic; Greg P. Carman

1996-01-01

300

Fatigue damage at room temperature in aluminium single crystals. 2: TEM  

SciTech Connect

Dislocation structures in aluminium single crystals fatigued at room temperature have been studied by TEM and compared with those reported for copper crystals. The fatigue tests were performed in push-pull at a stress amplitude 4 MPa, R = {minus}1 and frequency of 20 Hz. A band structure was observed in thin foils with planes parallel to the stress axis and the Burgers vector. Some parts of the bands were similar in appearance and dimensions to the ladder-like pattern formed in the same sample by several microcracks in a PSB on the surface containing b. This suggests that the microcracks are associated with dislocation walls in the PSBs. In the matrix, the dislocation arrangement was a cell structure, but areas of a high dislocation density which might be a vein structure were also seen. Dislocation walls in PSBs might be described as two sets of entangled edge dislocations, one set being the primaries and the other being large jogs in primary screw dislocations lying on the cross-slip planes. A large number of dislocation loops were observed, suggesting that their formation was a significant form of irreversible deformation in single crystal Al fatigue. Three types of dislocation loops were identified.

Zhai, T.; Martin, J.W.; Briggs, G.A.D. [Univ. of Oxford (United Kingdom). Dept. of Materials

1996-05-01

301

An elastic-plastic finite element alternating method for analyzing wide-spread fatigue damage in aircraft structures  

NASA Astrophysics Data System (ADS)

In this paper, a new analytical technique to study the effect of wide-spread fatigue damage in ductile panels is presented. The main purpose of the study is to develop an efficient methodology to predict the maximum load carrying capacity of panels with cracks. The problem arises especially in the fuselage skin of aging airplanes, in which cracks initiate from a row of rivet holes. This problem is known as Multi Site Damage (MSD) in aging aircraft. It is very important to estimate the load carrying capacity. Usually, the approach based on elastic fracture mechanics may overestimate the load capacity. It is very important for the aircraft structure with MSD to estimate the load carrying capacity of such damaged structures. Approaches based on elastic fracture mechanics often lead to a considerable error. In this paper, the Elastic Finite Element Alternating Method (EFEAM) has been extended to the case of elastic-plastic fracture of panels with MSD cracks. In EFEAM, analytical solutions to crack problems in an infinite plate are employed. In this study, we adopted an analytical solution for a row of cracks in an infinite panel. Furthermore, the plastic deformation is accounted for, by using the initial stress algorithm. The T {inf?/sup*}integral is employed for the fracture criterion. The methodology developed in the present study can be called as Elastic-Plastic Finite Element Alternating Method (EPFEAM) for MSD problems. A series of studies on the maximum load capacity of panels with a row of cracks has been conducted.

Pyo, C. R.; Okada, H.; Atluri, S. N.

1995-04-01

302

Damage development during low cycle fatigue of carbon-black loaded SBR. [Styrene butadiene rubber containing 0, 15, 25, and 35 wt % carbon black  

Microsoft Academic Search

Fatigue of elastomers is a subject that has received considerable study over the years. This paper explores the problem of damage accumulation in a series of styrene butadiene rubber (SBR) based compounds containing 0, 15, 25, and 35 wt % carbon-black under conditions in which a limited number of higher stress cycles have been applied to the material (referred to

D. Lesuer; A. Goldberg; D. Hiromoto; J. Patt

1984-01-01

303

Panel resonant behavior of wind turbine blades.  

SciTech Connect

The principal design drivers in the certification of wind turbine blades are ultimate strength, fatigue resistance, adequate tip-tower clearance, and buckling resistance. Buckling resistance is typically strongly correlated to both ultimate strength and fatigue resistance. A composite shell with spar caps forms the airfoil shape of a blade and reinforcing shear webs are placed inside the blade to stiffen the blade in the flap-wise direction. The spar caps are dimensioned and the shear webs are placed so as to add stiffness to unsupported panel regions and reduce their length. The panels are not the major flap-wise load carrying element of a blade; however, they must be designed carefully to avoid buckling while minimizing blade weight. Typically, buckling resistance is evaluated by consideration of the load-deflection behavior of a blade using finite element analysis (FEA) or full-scale static testing of blades under a simulated extreme loading condition. The focus of this paper is on the use of experimental modal analysis to measure localized resonances of the blade panels. It can be shown that the resonant behavior of these panels can also provide a means to evaluate buckling resistance by means of analytical or experimental modal analysis. Further, panel resonances have use in structural health monitoring by observing changes in modal parameters associated with panel resonances, and use in improving panel laminate model parameters by correlation with test data. In recent modal testing of wind turbine blades, a set of panel modes were measured. This paper will report on the findings of these tests and accompanying numerical and analytical modeling efforts aimed at investigating the potential uses of panel resonances for blade evaluation, health monitoring, and design.

Paquette, Joshua A.; Griffith, Daniel Todd

2010-03-01

304

The prediction of creep damage in Type 347 weld metal: part II creep fatigue tests  

Microsoft Academic Search

Calculations of creep damage under conditions of strain control are often carried out using either a time fraction approach or a ductility exhaustion approach. In part I of this paper the rupture strength and creep ductility data for a Type 347 weld metal were fitted to provide the material properties that are used to calculate creep damage. Part II of

M. W. Spindler

2005-01-01

305

Parametric study of blade tip clearance, flow rate, and impeller speed on blood damage in rotary blood pump.  

PubMed

Phenomenological studies on mechanical hemolysis in rotary blood pumps have provided empirical relationships that predict hemoglobin release as an exponential function of shear rate and time. However, these relations are not universally valid in all flow circumstances, particularly in small gap clearances. The experiments in this study were conducted at multiple operating points based on flow rate, impeller speed, and tip gap clearance. Fresh bovine red blood cells were resuspended in phosphate-buffered saline at about 30% hematocrit, and circulated for 30 min in a centrifugal blood pump with a variable tip gap, designed specifically for these studies. Blood damage indices were found to increase with increased impeller speed or decreased flow rate. The hemolysis index for 50-microm tip gap was found to be less than 200-microm gap, despite increased shear rate. This is explained by a cell screening effect that prevents cells from entering the smaller gap. It is suggested that these parameters should be reflected in the hemolysis model not only for the design, but for the practical use of rotary blood pumps, and that further investigation is needed to explore other possible factors contributing to hemolysis. PMID:19473143

Kim, Nahn Ju; Diao, Chenguang; Ahn, Kyung Hyun; Lee, Seung Jong; Kameneva, Marina V; Antaki, James F

2009-06-01

306

Influence of grain orientations on the initiation of fatigue damage in an Al-Li alloy.  

PubMed

The variation in microstructure and texture in a rectangular bar extruded from a billet of spray-cast 8090 Al-Li alloy has been examined. The fine grain size of the as sprayed billet and the moderate extrusion ratio ( approximately 25 : 1) were seen to cause geometric dynamic recrystallization (GDR) in regions of higher strain towards the edge of the bar. The grain morphology varied from the expected elongated grains at the centre of the bar to equiaxed grains where GDR occurred at the bar edges. A <111> + <100> double fibre texture, significantly distorted towards rolling components and varying through the bar thickness, was found using electron backscatter diffraction. Fatigue resulted in a high density of short secondary cracks, many of which had arrested at grain boundaries. The cracks preferentially nucleated in grains from the <100> fibre texture corresponding to high Schmid factors. PMID:10460690

Taylor; Zhai; Wilkinson; Martin

1999-09-01

307

Comprehensive testing of Nedwind 12-Meter wind turbine blades at NREL  

SciTech Connect

This paper describes the structural testing of two NedWind 25 12-m blades at the National Renewable Energy Laboratory (NREL). The tests were conducted under the Standards, Measurement and Testing (SMT) Program in conjunction with tests conducted by four European laboratories to develop a common database of blade testing methods. All of the laboratories tested duplicate copies of blades taken from series production. Blade properties, including weight, center of gravity, natural frequencies, stiffness, and damping, were determined. Static load tests were performed at 110% of the extreme design load for strain verification. NREL performed single-axis and two-axis fatigue tests using business-as-usual testing practices. The single-axis test combined equivalent life loading for the edge and flap spectra into a single resultant load. The two-axis test applied the edge and flap components independently at a phase angle of 90{degree}. Damage areas were observed at (1) the trailing edge, which cracked near the maximum chord; (2) between the steel root collar and the composite, where circumferential cracking was noted; and (3) along the top of the spar between the 2,500-mm and 4,200-mm stations, where a notable increase in acoustic emissions was detected. NREL observed that the onset of damage occurred earlier in the single-axis test.

Larwood, S.; Musial, W.

2000-03-13

308

Predicting sequence effects and cumulative damage in fatigue using a unified model for crack initiation and growth  

Microsoft Academic Search

A new unified fatigue model which covers both crack initiation and crack growth has been used to predict load sequence effects in fatigue failure of 7075-T6 aluminum subjected to two-level loading histories. Dubbed ''FATIGMOD,'' the model simulates fatigue as the successive failure of elements within, and on the surface of, a material; failure of each element occurs when the local

1983-01-01

309

Fatigue Damage in Notched Composite Laminates under Tension-Tension Cyclic Loads.  

National Technical Information Service (NTIS)

The results are given of an investigation to determine the damage states which develop in graphite epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of ...

E. G. Henneke G. R. Kress K. L. Reifsnider W. W. Stinchcomb

1985-01-01

310

14 CFR 27.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.  

Code of Federal Regulations, 2013 CFR

...Each applicant must evaluate parts that include PSEs of the airframe...mountings, landing gear, other parts, detail design points, and...service; (iii) The loading spectra as severe as those expected...repair or replacement of damaged parts before a catastrophic...

2013-01-01

311

Characterisation of Microstructures, Deformation, and Fatigue Damage in Different Steels Using Magnetic Barkhausen Emission Technique  

Microsoft Academic Search

The characterization of microstructures, mechanical properties, deformation, damage initiation, and growth by Non-Destructive Evaluation (NDE) techniques is assuming a vital role in various industries because of the growing awareness of the benefits that can be derived by using NDE techniques for assessing the performance of various components. NDE is widely applied for assessment of material degradation, where investment in new

R. Baldev; T. Jayakumar; V. Moorthy; S. Vaidyanathan

2001-01-01

312

Fatigue damage editing for accelerated durability testing using strain range and SWT parameter criteria  

Microsoft Academic Search

The objective of this research was to determine if conventional strain range editing and a new SWT parameter editing technique can be used to accurately edit a variable amplitude strain history to predetermined damage levels. A variable amplitude strain history containing 62 672 reversals was scaled to various peak strain levels and used as full length histories. These histories were

R. I. Stephens; P. M. Dindinger; J. E. Gunger

1997-01-01

313

Study of Damage and Fracture Toughness Due to Influence of Creep and Fatigue of Commercially Pure Copper by Monotonic and Cyclic Indentation  

NASA Astrophysics Data System (ADS)

Fracture toughness is the ability of a component containing a flow to resist fracture. In the current study, the Ball indentation (BI) test technique, which is well acknowledged as an alternative approach to evaluate mechanical properties of materials due to its semi-nondestructive, fast, and high accurate qualities is used to estimate damage and the fracture toughness for copper samples subjected to varying levels of creep and fatigue. The indentation fracture toughness shows the degradation of Cu samples when they are subjected to different creep conditions. Axial fatigue cycling increases the strength at the mid-gauge section compared to other regions of the samples due to initial strain hardening. The advancement of indentation depth with indentation fatigue cycles experiences transient stage, i.e., jump in indentation depth has been observed, which may be an indication of failure and followed by a steady state with almost constant depth propagation with indentation cycles.

Ghosh, Sabita; Prakash, Raghu V.

2013-01-01

314

Fatigue damage in aluminium single crystals. 1: On the surface containing the slip Burgers vector  

SciTech Connect

An aluminum single crystal with the axial direction of [25{bar 1}] was fatigued in push-pull at the constant resolved shear stress amplitude 4 MPa, frequency 20 Hz and room temperature. Microcracks, microvoids, macrobands, extrusions and intrusions were observed on the side-surface containing the Burgers vector b. Most microcracks were opened, and were within, but approximately perpendicular to, PSBs. Slip steps were found in the extrusions and intrusions. There was net irreversible slip in one direction in most PSBs. Some short cracks along the PSBs on the side-surface were also observed at 5 {times} 10{sup 6} cycles. These observations indicate that, without the aid of the surface roughness of PSBs, cracks can still be nucleated, and that, apart from the notch effect of a PSB, there are other factors controlling crack initiation in single crystal aluminum. There may be an internal tensile stress existing in a PSB in the direction of b, and a shear stress applied by the specimen grips in the specimens due to the irreversible slip in one direction in PSBs. These stresses and the applied stress are responsible for the formation of microcracks, microvoids, extrusions, intrusions and macrobands on the side-surface.

Zhai, T.; Martin, J.W.; Briggs, G.A.D. [Univ. of Oxford (United Kingdom). Dept. of Materials

1995-10-01

315

Continuum damage evolution in Pb-free solder joint under shear fatigue loadings  

Microsoft Academic Search

Progressive materials damage process in solder joint under cyclic shear deformation is examined in this study. A 3-D finite element model of a single reflowed SAC405 solder specimen is developed for this purpose. Cyclic relative displacement cycles between zero and 1.0 mm at displacement ramp rate of 2.0 mm\\/sec. is applied in the direction parallel to the solder\\/pad interface. Strain

N. M. Shaffiar; W. K. Loh; N. Kamsah; M. N. Tamin

2010-01-01

316

Smart structure for small wind turbine blade  

NASA Astrophysics Data System (ADS)

Wind energy is seen as a viable alternative energy option for future energy demand. The blades of wind turbines are generally regarded as the most critical component of the wind turbine system. Ultimately, the blades act as the prime mover of the whole system which interacts with the wind flow during the production of energy. During wind turbine operation the wind loading cause the deflection of the wind turbine blade which can be significant and affect the turbine efficiency. Such a deflection in wind blade not only will result in lower performance in electrical power generation but also increase of material degradation due high fatigue life and can significantly shorten the longevity for the wind turbine material. In harnessing stiffness of the blade will contribute massive weight factor and consequently excessive bending moment. To overcome this excessive deflection due to wind loading on the blade, it is feasible to use shape memory alloy (SMA) wires which has ability take the blade back to its optimal operational shape. This paper details analytical and experimental work being carried out to minimize blade flapping deflection using SMA.

Supeni, E. E.; Epaarachchi, J. A.; Islam, M. M.; Lau, K. T.

2013-08-01

317

Damage development under compression-compression fatigue loading in a stitched uniwoven graphite/epoxy composite material. Interim Report No. 86  

SciTech Connect

Damage initiation and growth under compression-compression fatigue loading were investigated for a stitched uniweave material system with an underlying AS4/3501-6 quasi-isotropic layup. Performance of unnotched specimens having stitch rows at either 0 degree or 90 degrees to the loading direction was compared. Special attention was given to the effects of stitching related manufacturing defects. Damage evaluation techniques included edge replication, stiffness monitoring, x-ray radiography, residual compressive strength, and laminate sectioning. It was found that the manufacturing defect of inclined stitches had the greatest adverse effect on material performance. Zero degree and 90 degree specimen performances were generally the same. While the stitches were the source of damage initiation, they also slowed damage propagation both along the length and across the width and affected through-the-thickness damage growth. A pinched layer zone formed by the stitches particularly affected damage initiation and growth. The compressive failure mode was transverse shear for all specimens, both in static compression and fatigue cycling effects.

Vandermey, N.E.; Morris, D.H.; Masters, J.E.

1991-07-01

318

Thermal-Barrier-Coated Turbine Blade Study.  

National Technical Information Service (NTIS)

The effects of coating TBC on a CF6-50 stage 2 high-pressure turbine blade were analyzed with respect to changes in the mean bulk temperature, cooling air requirements, and high-cycle fatigue. Localized spallation was found to have a possible deleterious ...

P. A. Siemers W. B. Hillig

1981-01-01

319

Fatigue Life and Short Crack Behavior in Ti6Al4V Alloy; Interactions of Foreign Object Damage, Stress, and Temperature  

Microsoft Academic Search

High-cycle fatigue (HCF) failures associated with foreign object damage (FOD) in turbine engines of military aircrafts have\\u000a been of major concern for the aeronautic industry in recent years. The present work is focused on characterizing the effects\\u000a of FOD on crack initiation and small crack growth of a Ti-6Al-4V alloy at ambient and also elevated temperatures. Results\\u000a show that the

Behzad Majidi

2008-01-01

320

Ceramic blade attachment system  

DOEpatents

A retainer ring is arranged to mount turbine blades to a turbine disk so that aerodynamic forces produced by a gas turbine engine are transferred from the turbine blades to the turbine disk to cause the turbine blades and turbine disk to rotate, but so that centrifugal forces of the turbine blades resulting from the rotation of the turbine blades and turbine disk are not transferred from the turbine blades to the turbine disk.

Boyd, Gary L. (Alpine, CA)

1995-01-01

321

Ceramic blade attachment system  

DOEpatents

A retainer ring is arranged to mount turbine blades to a turbine disk so that aerodynamic forces produced by a gas turbine engine are transferred from the turbine blades to the turbine disk to cause the turbine blades and turbine disk to rotate, but so that centrifugal forces of the turbine blades resulting from the rotation of the turbine blades and turbine disk are not transferred from the turbine blades to the turbine disk. 6 figures.

Boyd, G.L.

1995-04-11

322

FOD Simulation for Ceramic Turbine Blades  

NASA Astrophysics Data System (ADS)

Foreign object impact damage is a serious problem for ceramic gas turbines. In this paper, a series of finite element analyses with an elastic assumption was made to estimate the plausible damage behavior of axial and radial ceramic blades. Foreign objects were assumed to impact the leading part of the blade suction surface. The present analysis showed that the stress peaking process is strongly influenced by the interaction of various stress waves, leading to structural damage. The locations of the peak principal tensile stress (peak stress) in the axial blade corresponded well with the damaged parts of the blade observed experimentally. The maximum peak stress appeared in the suction surface and the averaged peak stress value in this surface was roughly double that in the pressure surface. Unlike the axial blade, the radial blade reached maximum peak stress in the pressure surface. The value was much larger than the initial impact stress due to the wave interactions. For the effect of the rotation, centrifugal force did not change the basic distribution of peak stresses, but it caused additional stress peaks near the hub in the pressure surface. Moreover, the centrifugal force caused appreciable differences in the averaged peak stresses in the suction and the pressure surfaces. The present finite element analysis with elastic assumption seems useful for understanding structural fracture behavior, when designing ceramic blades.

Yoshida, Hiro; Li, Yinsheng

323

Cumulative damage theory in multiaxial fatigue of graphite/epoxy (+/-45)s composites and weight function theory for a rectilinear anisotropic body  

SciTech Connect

The phenomenological evolution laws of damage based on residual life and residual strength were critically examined. The failure of a specimen can be defined immediately before or after fracture. The former is called failure defined by approach II and the latter failure defined by approach I. Usually at failure there is discontinuity of forcing variables and, because of this, damage at failure is discontinuous. Therefore, the values of damage at failure by two different approaches are not the same. Based on this idea the sequence effects of the phenomenological evolution law of damage were studied. A multiaxial growth law of damage was proposed based on experimental data of axial, torsional, combined axial and torsional inphase, and step-loading fatigue in thin-walled graphite epoxy tubes consisting of four layers of (+-45)/sub s/ laminates. Interlaminar normal stress effect on the fatigue behavior of a tubular specimen was studied experimentally. In the second part of this thesis, Bueckner's weight function theory is extended to rectilinear anisotropic bodies for two-dimensional loading systems

An, D.M.

1986-01-01

324

Aluminum-blade development for the Mod-0A 200-kilowatt wind turbine  

SciTech Connect

This report documents the operating experience with two aluminum blades used on the DOE/NASA Mod-0A 200-kilowatt wind turbine located at Clayton, New Mexico. Each Mod-0A aluminum blade is 59.9 feet long and weighs 2360 pounds. The aluminum Mod-0A blade design requirements, the selected design, fabrication procedures, and the blade analyses are discussed. A detailed chronology is presented on the operating experience of the Mod-0A aluminum blades used at Clayton, New Mexico. Blade structural damage was experienced. Inspection and damage assessment were required. Structural modifications that were incorporated to the blades successfully extended the useful operating life of the blades. The aluminum blades completed the planned 2 years of operation of the Clayton wind turbine. The blades were removed from service in August 1980 to allow testing of advanced technology wood composite blades.

Linscott, B.S.; Shaltens, R.K.; Eggers, A.G.

1981-12-01

325

Feasibility study of pultruded blades for wind turbine rotors  

SciTech Connect

In work performed under subcontract to the National Renewable Energy Laboratory (NREL), a preliminary design study and proof-of-concept field test were conducted to evaluate the feasibility of using pultruded blades for wind turbine rotors. A 400 kW turbine was selected for the design study, and a scaled 80 kW rotor was fabricated and tested as a demonstration of the concept. To examine the feasibility of pultruded blades, several issues were addressed, including power performance, tower strikes, yaw stability, stall flutter, fatigue, and rotor cost. Results showed that with proper design, rotors using pultruded blades demonstrate acceptable fatigue life and stable yaw behavior without tower strikes. Furthermore, blades using this technology may be manufactured for approximately half the cost of conventional blades. Field tests of the scaled rotor provided experimental data on power performance and loads while verifying stable yaw operation.

Migliore, P.G.; Cheney, M.C.

2000-02-28

326

A Failure Analysis Conducted on a Fractured AISI 5160 Steel Blade Which Separated from an Agricultural Rotary Cutter  

NASA Astrophysics Data System (ADS)

One of the six blades of an agricultural rotary cutter used for cutting down small trees and bushes broke into two pieces while the blades were rotating. One piece was hurled from the cutter and struck a young farmer, who had been operating the machine, causing a near fatal leg injury. In the ensuing litigation against the manufacturers and marketer of the machine each litigant retained a metallurgist and other experts. The metallurgists jointly directed laboratory work on the broken blade conducted at an independent laboratory according to a protocol which they developed and which was approved by the court. As a result of the laboratory work the present authors, working for the Plaintiffs, concluded that failure of the blade occurred because it contained quench cracks introduced when it was manufactured. The Defendants' metallurgists concluded that the blade had been misassembled onto the machine and, as a result, had failed by fatigue. Eventually, the case was set for a jury trial in a Circuit Court in rural Kentucky. The jury found for the Plaintiffs and awarded them $5.9 million in damages. Part of this judgement was later reversed by the Kentucky Court of Appeals and the case was then settled without a second trial under terms which were not revealed.

Johnson, Alan A.; Storey, Randall J.

2011-07-01

327

Performance of twist-coupled blades on variable speed rotors  

SciTech Connect

The load mitigation and energy capture characteristics of twist-coupled HAWT blades that are mounted on a variable speed rotor are investigated in this paper. These blades are designed to twist toward feather as they bend with pretwist set to achieve a desirable twist distribution at rated power. For this investigation, the ADAMS-WT software has been modified to include blade models with bending-twist coupling. Using twist-coupled and uncoupled models, the ADAMS software is exercised for steady wind environments to generate C{sub p} curves at a number of operating speeds to compare the efficiencies of the two models. The ADAMS software is also used to generate the response of a twist-coupled variable speed rotor to a spectrum of stochastic wind time series. This spectrum contains time series with two mean wind speeds at two turbulence levels. Power control is achieved by imposing a reactive torque on the low speed shaft proportional to the RPM squared with the coefficient specified so that the rotor operates at peak efficiency in the linear aerodynamic range, and by limiting the maximum RPM to take advantage of the stall controlled nature of the rotor. Fatigue calculations are done for the generated load histories using a range of material exponents that represent materials from welded steel to aluminum to composites, and results are compared with the damage computed for the rotor without twist-coupling. Results indicate that significant reductions in damage are achieved across the spectrum of applied wind loading without any degradation in power production.

Lobitz, D.W.; Veers, P.S.; Laino, D.J.

1999-12-07

328

Characterization and fatigue damage of plasma sprayed HAp top coat with Ti and HAp/Ti bond coat layers on commercially pure titanium substrate.  

PubMed

The surface of commercially pure Ti (cp-Ti) substrate was grit-blasted with Al(2)O(3) powders and then wet-blasted with HAp/Ti mixed powders at room temperature. Then plasma spraying with Ti powders or HAp/Ti mixed powders on the blasted surface was carried out to form a bond coat layer, denoted as T50 and T100 bond coat for the former and HT100 bond coat for the later. The HAp top coat was subsequently sprayed with 100 mum thickness. The XRD patterns showed that the as-sprayed HT100 bond coat layer was mainly composed of HAp with minor components of Ti and TiO(2). EDS analysis also showed there co-existed HAp and Ti without reaction in the HT100 bond coat layer. Some cracks were observed in the bond coat and the top coat layers after compression-compression and tension-tension fatigue tests. The HT100 bond coat specimen produced less AE signal and a small amount of debonding and cracking in compression-compression fatigue test. The HT100 specimen could survive up to 10 million cycles at stress amplitude of 200 MPa, which is high enough compared to the maximum stress in bones: the order of 100 MPa. The degree of damage (debonding and cracking) in tension-tension fatigue test was more severe than that in compression-compression fatigue testing. PMID:19627850

Rakngarm, Achariya; Mutoh, Yoshiharu

2008-11-20

329

Influence of Creep Damage on the Low Cycle Thermal-Mechanical Fatigue Behavior of Two Tantalum Base Alloys.  

National Technical Information Service (NTIS)

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 iso...

G. S. Doble K. D. Sheffler

1972-01-01

330

Three-dimensional modeling and aeroelastic coupling analysis for the wind turbine blade  

Microsoft Academic Search

In order to study damage problems of the wind turbine blade under complicated offshore working conditions (damaging winds), the nonlinear aeroelastic analysis was achieved for the blade with flexible high aspect ratio. The three-dimensional solid model of the wind turbine blade was established and the appropriate computational domain was fixed. Finite element equations were deduced under the coupling effects between

Jian-Ping Zhang; Ling-ling Pan

2009-01-01

331

Decision Making of Aircraft Engine Blades Condition Based on Bispectral Analysis of the Vibroacoustical Signal  

NASA Astrophysics Data System (ADS)

In this paper the simulation of vibroacoustical signals radiated by the engine turbine at the stationary vibration excitation is carried out for situations when all turbine blades have no defects and one blade has a small fatigue crack. Bispectral analysis is used for diagnostic information processing. It demonstrates that appearance and evolution of the fatigue crack in a blade change intensity of global and local extremums of bispectral modules. The results of bispectral processing and Probability Neural Network (PNN) are used to recognize of the turbine blades condition. The efficiency factor is used for precision analysis.

Bouraou, N. I.; Protasov, A. G.; Sopilka, Yu. V.; Zazhitsky, O. V.

2005-04-01

332

Elevated temperature fretting fatigue of nickel based alloys  

NASA Astrophysics Data System (ADS)

This document details the high temperature fretting fatigue of high temperature nickel based alloys common to turbine disk and blade applications. The research consists of three area of focus: Experiments are conducted to determine quantitatively the fretting fatigue lives of advanced nickel based alloys; Analytical tools are developed and used to investigate the fretting fatigue response of the material; Fractographic analysis of the experimental results is used to improve the analytical models employed in the analysis of the experiments. Sixty three fretting fatigue experiments were conducted at 649 °C using a polycrystalline Nickel specimen in contact with directionally solidified and single crystal Nickel pads. Various influences on the fretting fatigue life are investigated. Shot peened Rene' 95 had better fretting fatigue life compared to shot peened Rene' 88. Shot peening produced a 2x increase in life for Rene' 95, but only a marginal improvement in the fretting fatigue life for Rene' 88. Minor cycles in variable amplitude loading produces significant damage to the specimen. Addition of occasional overpeaks in load produces improvements in fretting fatigue life. Contact tractions and stresses are obtained through a variety of available tools. The contact tractions can be efficiently obtained for limited geometries, while FEM can provide the contact tractions for a broader class of problems, but with the cost of increased CPU requirements. Similarly, the subsurface contact stresses can be obtained using the contact tractions as a boundary condition with either a semi-analytical FFT method or FEM. It is found that to calculate contact stresses the FFT was only marginally faster than FEM. The experimental results are combined with the analysis to produce tools that are used to design against fretting fatigue. Fractographic analysis of the fracture surface indicates the nature of the fretting fatigue crack behavior. Interrupted tests were performed to analyze the crack at intermediate lives. Fretting fatigue cracks were found to have formed in less than 10% of total fretting fatigue life. In addition to the formation of the individual fretting fatigue cracks, by 10% of the total expected fretting fatigue life, the individual fretting fatigue cracks have linked together to form a through the thickness edge crack. At some point in the experiment in between 20% to 50% of total expected fretting fatigue life, the edge crack growth retards or a corner crack accelerates. The result is a corner crack forms out of the edge crack. In many experiments this corner crack is the primary crack that leads to failure. The experimental results are combined with the analytic tools to generate usefull tools for the analysis of the fretting fatigue behavior of nickel based alloys at high temperature. This analysis tool is helpfull in the design of gas turbine engines which use nickel based alloys for the turbine blades and disks.

Gean, Matthew C.

333

Thermal Imaging of Medical Saw Blades and Guides  

SciTech Connect

Better Than New, LLC., has developed a surface treatment to reduce the friction and wear of orthopedic saw blades and guides. The medical saw blades were thermally imaged while sawing through fresh animal bone and an IR camera was used to measure the blade temperature as it exited the bone. The thermal performance of as-manufactured saw blades was compared to surface-treated blades, and a freshly used blade was used for temperature calibration purposes in order to account for any emissivity changes due to organic transfer layers. Thermal imaging indicates that the treated saw blades cut faster and cooler than untreated blades. In orthopedic surgery, saw guides are used to perfectly size the bone to accept a prosthesis. However, binding can occur between the blade and guide because of misalignment. This condition increases the saw blade temperature and may result in tissue damage. Both treated ad untreated saw guides were also studied. The treated saw guide operated at a significantly lower temperature than untreated guide. Saw blades and guides that operate at a cooler temperature are expected to reduce the amount of tissue damage (thermal necrosis) and may reduce the number of post-operative complications.

Dinwiddie, Ralph Barton [ORNL; Steffner, Thomas E [ORNL

2007-01-01

334

Fatigue life prediction and failure mechanisms of composite materials  

Microsoft Academic Search

Fatigue life prediction and failure mechanisms of composite materials are studied based on the fatigue modulus concept and experimental results. Single-stress level fatigue life is predicted using generalized fatigue modulus degradation model and resultant strain failure criterion. Cumulative damage models defined by fatigue modulus and resultant strains are derived as functions of fatigue cycle and applied stress. This approach can

K. S. Han; W. Hwang

1992-01-01

335

High and low cycle fatigue life estimation of welding steel under constant amplitude loading: Analysis of different multiaxial damage models and in-phase and out-of-phase loading effects  

Microsoft Academic Search

The objective of the present work is to estimate the high and low cycle fatigue life of a type of welding steel used for construction (S355 J2 according to UNE EN 10025-2: 2006), subject to in-phase and out-of-phase multiaxial loading, by means of different classical multiaxial fatigue damage models. A complete cyclic characterization of the material is obtained, including new

C. Gómez; M. Canales; S. Calvo; R. Rivera; J. R. Valdés; J. L. Núñez

2011-01-01

336

Evaluation of the durability of composite tidal turbine blades.  

PubMed

The long-term reliability of tidal turbines is critical if these structures are to be cost effective. Optimized design requires a combination of material durability models and structural analyses. Composites are a natural choice for turbine blades, but there are few data available to predict material behaviour under coupled environmental and cycling loading. The present study addresses this problem, by introducing a multi-level framework for turbine blade qualification. At the material scale, static and cyclic tests have been performed, both in air and in sea water. The influence of ageing in sea water on fatigue performance is then quantified, and much lower fatigue lives are measured after ageing. At a higher level, flume tank tests have been performed on three-blade tidal turbines. Strain gauging of blades has provided data to compare with numerical models. PMID:23319705

Davies, Peter; Germain, Grégory; Gaurier, Benoît; Boisseau, Amélie; Perreux, Dominique

2013-01-14

337

Advanced turbofan blade refurbishment technique  

SciTech Connect

The purpose of the work reported here is to investigate whether the lessons learned from the work of Suder et al. can be used to reduce the in-service performance deterioration of a fan on a high bypass ratio turbofan engine. To this end, a back-to-back test was done on the fan of an RB211-22B engine with the cooperation of Delta Airlines. The fan and engine were first overhauled per normal airline practice and cell-tested to establish that the engine performance met flight acceptance standards. This test, which the engine passed, also established a performance baseline for the overhauled engine. At this point the fan blade leading edge had not been filed or scraped and the blade surfaces had not been polished because the leading edge damage and blade surface roughness fell within the acceptable limits specified by the manufacturer for normal overhaul practice. After the cell test, the fan was removed from the engine and sent to Sermatech International where the following additional operations were performed: (1) the blade surfaces were polished to a finish of 20 rms {micro}in; (2) leading edge roughness due to particle impact damage was removed and the leading edge was polished to a finish of 20 rms {micro}in; (3) the leading edge shape was rounded and the leading edge thickness was reduced over the first 5--10% of chord. Test results indicated a 0.7% drop in thrust specific fuel consumption (lb fuel/lb thrust/hr) relative to the baseline engine after the enhanced fan overhaul. Based on the results of Suder et al. (1995) it appears that 70--80% of this performance gain is due to the thin smooth leading edge and the remainder to the highly polished finish of the blade.

Roberts, W.B. [Flow Application Research and Sermatech International Inc., Fremont, CA (United States)

1995-10-01

338

Investigation of the fatigue and short-term mechanical properties of 13% chromium steel and titanium alloys after welding or treatment with high-frequency currents as applied to steam-turbine blades  

NASA Astrophysics Data System (ADS)

We present the results of a study on comparing the structural strength of rotor blades made of stainless 13% chromium steels for their design versions in which wear-resistant straps made of cast VZK stellite are soldered or welded on the blade inlet edges. It is shown that treatment of VT6 alloy with high-frequency currents increases the endurance limit of the zone subjected to strengthening and makes the alloy more resistant to erosion. The worn blades of a 48-T4 titanium alloy repaired with the use of welding technologies have operational characteristics at least as good as those of newly manufactured ones.

Gonserovskii, F. G.; Nikitin, V. I.; Silevich, V. M.; Simin, O. N.

2008-02-01

339

Laser thermal shock and fatigue testing system  

NASA Astrophysics Data System (ADS)

Thermal fatigue consists in repeatedly cycling the temperature of a specimen under test without any other constraint and stopping the test when predefined damage aspects. The result is a lifetime in terms of number of cycles. The parameters of the thermal cycle are the following: minimum and maximum temperature, time of heating, of cooling and time at high or at low temperature. When the temperature jump is very big and fast, phenomena of thermal shock can be induced. Among the numerous techniques used to perform these tests, the laser thermal fatigue cycling is very effective when fast heating of small and localized zones is required. That's the case of test performed to compare new and repaired blades of turbogas machines or components of combustion chambers of energy power plants. In order to perform these tests a thermal fatigue system, based on 1 kW Nd-YAG laser as source of heating, has been developed. The diameter of the heated zone of the specimen irradiated by the laser is in the range 0.5 - 20 mm. The temperatures can be chosen between 200 degree(s)C and 1500 degree(s)C and the piece can be maintained at high and/or low temperature from 0 s to 300 s. Temperature are measured by two sensors: a pyrometer for the high range (550 - 1500 degree(s)C) and a contactless thermocouple for the low range (200 - 550 degree(s)C). Two different gases can be blown on the specimen in the irradiated spot or in sample backside to speed up cooling phase. A PC-based control unit with a specially developed software performs PID control of the temperature cycle by fast laser power modulation. A high resolution vision system of suitable magnification is connected to the control unit to detect surface damages on the specimen, allowing real time monitoring of the tested zone as well as recording and reviewing the images of the sample during the test. Preliminary thermal fatigue tests on flat specimens of INCONEL 738 and HAYNES 230 are presented. IN738 samples, laser cladded by powder of the same material to simulate the refurbishing of a damaged turbine blade after long-term operation, are compared to the parents. Lifetimes are decreasing when high temperature of the cycle is increased and shorter lifetimes of repaired pieces have been found. Laser and TIG welding on HY230 specimens are compared to the parent. Parent and repaired samples have no evidence of cracks after 1500 thermal cycles between 650 and 1000 degree(s)C.

Fantini, Vincenzo; Serri, Laura; Bianchi, P.

1997-08-01

340

Analysis and Tests of Pultruded Blades for Wind Turbine Rotors  

SciTech Connect

PS Enterprises, Inc. investigated a flexible, downwind, free-yaw, five-blade rotor system employing pultruded blades. A rotor was designed, manufactured and tested in the field. A preliminary design study and proof of concept test were conducted to assess the feasibility of using pultruded blades for wind turbine rotors. A 400 kW turbine was selected for the design study and a scaled 80 kW rotor was fabricated and field tested as a demonstration of the concept. The design studies continued to support the premise that pultruded blades offer the potential for significant reductions in rotor weight and cost. The field test provided experimental performance and loads data that compared well with predictions using the FLEXDYNE aeroelastic analysis. The field test also demonstrated stable yaw behavior and the absence of stall flutter over the wind conditions tested. During the final year of the contract, several studies were conducted by a number of independent consultants to address specific technical issues related to pultruded blades that could impact the commercial viability of turbines using this technology. The issues included performance, tower strikes, yaw stability, stall flutter, fatigue, and costs. While the performance of straight pultruded blades was projected to suffer a penalty of about 13% over fully twisted and tapered blades, the study showed that an aerodynamic fairing over the inner 40% could recover 85% of that loss while still keeping the blade cost well below that of conventional blades. Other results of the study showed that with proper design, rotors using pultruded blades could operate without aeroelastic problems, have acceptable fatigue life, and cost less than half that of rotors employing conventionally manufactured blades.

Cheney, M. C. (PS Enterprises, Glastonbury, Connecticut); Olsen, T.; Quandt, G.; Archidiacono, P.

1999-07-19

341

Characterization of the fatigue behavior of the medial collateral ligament utilizing traditional and novel mechanical variables for the assessment of damage accumulation.  

PubMed

Ligaments are regularly subjected to repetitive loading in vivo. Typically, mechanical studies focus on repetitive loading protocols of short duration, while those characterizing damage accumulation over a longer duration (i.e., fatigue studies) are lacking. The aims of this study were as follows: (a) to demonstrate that damage does accumulate in ligament tissue subjected to repetitive loading and (b) to evaluate existing and new methods for characterizing fatigue damage accumulation. It was hypothesized that ligaments would accumulate damage with repetitive loading as evidenced by failure at stresses well below ultimate tensile strength, creep curve discontinuities, and by reductions in stiffness during loading. Eight normal medial collateral ligaments from female New Zealand white rabbits were cycled in tension, between 0 MPa and 28 MPa, to failure or until 259,200 cycles, whichever came first. Medial collateral ligaments that did not fail were subsequently loaded to failure. Displacement rates (dl(max)/dt) as well as primary, secondary, and tertiary creeps were monitored as indices of damage accumulation and impending mechanical failure. Additionally, the relative utilities of tangent, secant, and chord stiffness parameters were critically evaluated. Finally, new uses for the second derivative of force-displacement data were explored. Three out of eight ligaments failed during testing, demonstrating that ligaments can fail in fatigue under moderate tensile stress in vitro. The evaluation of displacement rates (dl(max)/dt), as well as primary through tertiary creep patterns, were not well suited to predicting failure in normal ligaments until rupture was all but imminent. Tangent stiffness, which was calculated from a mathematically defined start of the "linear region," was surprisingly constant throughout testing. Secant stiffness dropped in a predictable fashion, providing a global indicator of tissue stiffness, but did not provide any insight into fiber mechanics. Chord stiffness, on the other hand, appeared to be sensitive to fiber recruitment patterns. The second derivative of force-displacement data proved to be a useful means of (a) objectively defining the start of the linear region and (b) inferring changes in fiber recruitment patterns within ligament tissue. Tangent, secant, and chord stiffnesses highlight different attributes of ligament responses to loading; hence these parameters cannot be used interchangeably. Additionally, the second derivative of the force-displacement curve was introduced as a useful descriptive and analytical tool. PMID:20524739

Zec, Michelle L; Thistlethwaite, Paul; Frank, Cyril B; Shrive, Nigel G

2010-01-01

342

Impingement Cooled Turbine Blade.  

National Technical Information Service (NTIS)

The patent application relates to an impingement cooled turbine blade to be used with a hollow turbine shaft, using a female dovetail and having an easily removable insert for guiding and directing the cooling fluid through the hollow blade.

H. H. Ernst

1973-01-01

343

Residual Stresses in Fatigue.  

National Technical Information Service (NTIS)

The effects of residual stress on the fatigue life of a machine component or structure are reviewed. The residual stress effect on the crack initiation, usually estimated by using the fatigue damage and notch stress-strain concepts, is analyzed quantitati...

G. Glinka

1990-01-01

344

Controllable Camber Windmill Blades.  

National Technical Information Service (NTIS)

The present invention relates to a windmill power generation system which includes at least two variable camber blades fastened to a rotatable hub, which blades are driven by a fluid such as wind. Each of the variable camber blades has embedded shape memo...

C. H. Beauchamp W. H. Nedderman

2001-01-01

345

Blade hub air scoop  

Microsoft Academic Search

This patent describes a gas turbine engine with a variable pitch rotatable propulsor blade, including means for varying the pitch of the blade, air control means comprising: a platform fixedly attached to a radially inner end of the blade. The platform is generally positioned in a first opening in a rotatable annular surface, and the platform and surface define outer

G. C. Wollenweber; W. Y. Tseng; T. J. Sullivan

1988-01-01

346

Hydrodynamic blade guide  

DOEpatents

A saw having a self-pumped hydrodynamic blade guide or bearing for retaining the saw blade in a centered position in the saw kerf (width of cut made by the saw). The hydrodynamic blade guide or bearing utilizes pockets or grooves incorporated into the sides of the blade. The saw kerf in the workpiece provides the guide or bearing stator surface. Both sides of the blade entrain cutting fluid as the blade enters the kerf in the workpiece, and the trapped fluid provides pressure between the blade and the workpiece as an inverse function of the gap between the blade surface and the workpiece surface. If the blade wanders from the center of the kerf, then one gap will increase and one gap will decrease and the consequent pressure difference between the two sides of the blade will cause the blade to re-center itself in the kerf. Saws using the hydrodynamic blade guide or bearing have particular application in slicing slabs from boules of single crystal materials, for example, as well as for cutting other difficult to saw materials such as ceramics, glass, and brittle composite materials.

Blaedel, Kenneth L. (Dublin, CA); Davis, Pete J. (Pleasanton, CA); Landram, Charles S. (Livermore, CA)

2000-01-01

347

Overview of Elevated Temperature Damage Mechanisms and Fatigue Behavior of a Unidirectional Scs-6/Ti-15-3 Composite.  

National Technical Information Service (NTIS)

The fatigue behavior of a unidirectionally reinforced titanium matrix composite (TMC), SiC/Ti-15-3, was thoroughly characterized to support life prediction modeling of advanced TMC disks designed for gas turbine engine applications. The results of this co...

M. G. Castelli J. Gayda

1993-01-01

348

Fatigue Crack Propagation and Fracture Studies of a Pressure Vessel Steel Temper Embrittled to Simulate Irradiation Damage.  

National Technical Information Service (NTIS)

Fatigue crack propagation tests were conducted using plate bend specimens machined from shell material of the PM-2A half-scale model pressure vessel. The material is a Cr-Mo-V rotor steel, temper embrittled to represent the irradiated shell of the PM-2A r...

T. W. Crooker L. A. Cooley E. A. Lange

1967-01-01

349

Experimental Verification of a Progressive Damage Model for IM7/5260 Laminates Subjected to Tension-Tension Fatigue.  

National Technical Information Service (NTIS)

The durability and damage tolerance of laminated composites are critical design considerations for airframe composite structures. Therefore, the ability to model damage initiation and growth and predict the life of laminated composites is necessary to ach...

T. W. Coats C. E. Harris

1995-01-01

350

Failure analysis of J85 Engine turbine blades  

Microsoft Academic Search

This paper analyzes the cause of the engine damage due to the fracture of the J85 Engine first stage turbine blades. Discoloration due to thermal effect and fine multi-cracks as well as necking at 1\\/3 of the way down from the tip on the entire first stage turbine blade concave side surface have been noted. Of the first stage blades,

Seon-gab Kim; Young-ha Hwang; Tae-gu Kim; Chang-min Shu

2008-01-01

351

Experimental Verification of a Progressive Damage Model for IM7\\/5260 Laminates Subjected to Tension-Tension Fatigue  

Microsoft Academic Search

The durability and damage tolerance of laminated composites are critical design considerations for airframe composite structures. Therefore, the ability to model damage initiation and growth and predict the life of laminated composites is necessary to achieve structurally efficient and economical designs. The purpose of this research is to experimentally verify the application of a continuum damage model to predict progressive

Timothy W. Coats; Charles E. Harris

1995-01-01

352

Composite fan blade  

SciTech Connect

A composite fan blade is described for a prop fan engine comprising: a support disk having a plurality of hinge lugs formed therein, the disk being connected to an engine drive means; a bushing element; a fan blade formed from a first set of radially oriented unidirectional layers of fibers, the first set of layers of fibers being wrapped around the bushing element to form an elongated front side, an elongated back side, and a portion encompassing the bushing element; a blade platform formed from a second set of unidirectional layers of fibers having a first and a second end which are both wrapped around respective resin filler elements to form resin filled support pockets, the second set of unidirectional layers of fibers being wrapped around the portion of the fan blade encompassing the bushing element to place the resin filled support pockets against the portion of the fan blade encompassing the bushing element, wherein the fan blade and the blade platform form a fan blade assembly, the fan blade assembly having a plurality of hinge slots formed therein; and a pin element extending through the hinge formed by the plurality of hinge lugs in the support disk and the plurality of hinge slots in the fan blade assembly for attaching the fan blade assembly to the support disk.

Farr, J.D.

1993-08-31

353

Damage Interaction in Composites.  

National Technical Information Service (NTIS)

The purpose of the experimental study was to investigate the effects of foreign object damage (FOD) on the bending fatigue characteristics of a composite material, unidirectional boron/aluminum-6061. Fatigue curves were generated for a control group and e...

T. D. Gray

1973-01-01

354

Casting defects induced fatigue damage in aircraft frames of ZL205A aluminum alloy – A failure analysis  

Microsoft Academic Search

Two different types of aircraft frame components, which had collapsed respectively in their former vibration-fatigue performance tests, were submitted for failure analysis. The two failed frames were both made of aerial material ZL205A, a high-strength cast Al–Cu–Mn–Ti alloy. According to a series of experimental procedures including visual observations, X-ray detections, fractography inspections, microstructure examinations, mechanical tensile tests, hardness measurements and

Bo Li; Yifu Shen; Weiye Hu

2011-01-01

355

Fatigue monitoring by laser speckle  

NASA Astrophysics Data System (ADS)

A non-contact, non-destructive remote fatigue damage monitoring technique is described. This technique employs a laser beam that illuminates the surface of a cyclically loaded specimen, and an image processing system that extracts fatigue-damage-related information in the speckle pattern scattered from the surface. The spectrum width extracted from the laser speckle pattern increases as a function of the number of loading cycles, indicating the possibility that it may be utilized for monitoring fatigue damage development. The numerical process for obtaining the spectrum width is discussed in detail followed by an experimental demonstration on a tension-tension fatigue study of the aluminum alloy 6061-T6.

Dai, Y. Z.; Chiang, F. P.; Kato, A.

1991-05-01

356

Fatigue: environment and temperature effects  

SciTech Connect

An overview of temperature and environmental effects of fatigue is provided and room temperature environmental effects are examined, taking into account corrosion fatigue crack propagation, surface reactions and fatigue crack growth, and the determination of prefracture damage and failure prediction in corrosion-fatigued Al-2024-T4 by X-ray diffraction methods. Room temperature environmental effects are considered along with materials, and design engineering applications. High temperature and environmental effects are explored, giving attention to the effect of microstructure on the fatigue behavior of Ni base superalloys, creep crack growth, the temperature dependent deformation mechanisms of alloy 718 in low cycle fatigue, deformation induced microstructural changes in austenitic stainless steels, fatigue and fracture resistance of stainless steel weld deposits after elevated temperature irradiation, high-temperature static fatigue in ceramics, and environment, frequency, and temperature effects on fatigue in engineering plastics.

Burke, J.J.; Weiss, V.

1983-01-01

357

Failure analysis of two sets of aircraft blades  

Microsoft Academic Search

This paper describes the methodology employed for the failure analysis of aircraft blades and its application to two premature failed sets. The first one corresponds to the high pressure compressor manufactured in a 718 nickel base superalloy. The failure analysis carried out on this blade points towards foreign object damage (FOD). The second set belongs to the high pressure turbine

E. Silveira; G. Atxaga; A. M. Irisarri

2010-01-01

358

Length Scale Considerations in the Formation of Attachment Fatigue Cracks.  

National Technical Information Service (NTIS)

Fretting fatigue is often the root cause of nucleation of high cycle fatigue (HCF) cracks in clamped components. Fretting fatigue damage accumulation occurs within depths of only a few grains at the interface between contacting components. Therefore, more...

R. W. Neu D. L. McDowell

2004-01-01

359

Effect of variables on the fatigue behavior of Ti-6Al-4V  

SciTech Connect

Ti-6Al-4V, a titanium alloy widely used for aircraft jet engine compressor blades, is currently being tested for use in steam turbine low-pressure blades, where fatigue strength is the most important design parameter. This study summarized the extensive aerospace data base on the fatigue strength of Ti-6Al-4V.

Wood, R.A.

1984-10-01

360

Mechanisms of fretting-fatigue of titanium alloys  

Microsoft Academic Search

The effect of continuous fretting in air at 20°C on fatigue performance has been studied for Ti-17 and T1-6Al-4V, high strength titanium alloys used for gas-turbine fan and compressor disks and blades, respectively. The effect of fretting was to reduce the fatigue stress limit from 700 MPa for plain fatigue to 200 MPa for fretting-fatigue. A number of models, supported

R. A. Antoniou; T. C. Radtke

1997-01-01

361

On the Fatigue Analysis of Wind Turbines  

SciTech Connect

Modern wind turbines are fatigue critical machines that are typically used to produce electrical power from the wind. Operational experiences with these large rotating machines indicated that their components (primarily blades and blade joints) were failing at unexpectedly high rates, which led the wind turbine community to develop fatigue analysis capabilities for wind turbines. Our ability to analyze the fatigue behavior of wind turbine components has matured to the point that the prediction of service lifetime is becoming an essential part of the design process. In this review paper, I summarize the technology and describe the ''best practices'' for the fatigue analysis of a wind turbine component. The paper focuses on U.S. technology, but cites European references that provide important insights into the fatigue analysis of wind turbines.

Sutherland, Herbert J.

1999-06-01

362

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine disc having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade and forms a turbine assembly. The turbine blade has a root portion defining a pair of sides having a pair of grooves therein. The turbine assembly includes a pair of flanges between which the turbine blades are positioned. Each of the pair of flanges has a plurality of grooves defined therein. The grooves within the pair of flanges are aligned with the grooves in the blades and have a space formed therebetween. A plurality of spherical balls are positioned within the space. The plurality of spherical balls has a preestablished rate of thermal expansion being equal to the preestablished rate of thermal expansion of the turbine blade.

Shaffer, James E. (Maitland, FL)

1995-01-01

363

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine disc having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade and forms a turbine assembly. The turbine blade has a root portion defining a pair of sides having a pair of grooves therein. The turbine assembly includes a pair of flanges between which the turbine blades are positioned. Each of the pair of flanges has a plurality of grooves defined therein. The grooves within the pair of flanges are aligned with the grooves in the blades and have a space formed therebetween. A plurality of spherical balls are positioned within the space. The plurality of spherical balls has a preestablished rate of thermal expansion being equal to the preestablished rate of thermal expansion of the turbine blade. 4 figs.

Shaffer, J.E.

1995-07-11

364

14 CFR 35.37 - Fatigue limits and evaluation.  

Code of Federal Regulations, 2013 CFR

...AIRCRAFT AIRWORTHINESS STANDARDS: PROPELLERS Tests and Inspections § 35.37...does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue...tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades....

2013-01-01

365

On the inverse power laws for accelerated random fatigue testing  

Microsoft Academic Search

This paper addresses the usage of inverse power laws in accelerated fatigue testing under wide-band Gaussian random loading. The aim is not at predicting an ab- solute value of fatigue life but assessing the fatigue damage relative accumulation. The widely accepted inverse power scaling laws in fatigue damage assessment is discussed, reviewing the engineering standards and pointing out their inherent

G. Allegri; X. Zhang

2009-01-01

366

Application of BSTRAIN software for wind turbine blade testing  

SciTech Connect

NREL currently operates the largest structural testing facility in US for testing wind turbine blades. A data acquisition system was developed to measure blade response and monitor test status; it is called BSTRAIN (Blade Structural Test Real-time Acquisition Interface Network). Software objectives were to develop a robust, easy-to-use computer program that could automatically collect data from static and fatigue blade tests without missing any significant events or overloading the computer with excess data. The program currently accepts inputs from up to 32 channels but can be expanded to over 1000 channels. In order to reduce the large amount of data collected during long fatigue tests, options for real-time data processing were developed including peak-valley series collection, peak-valley decimation, block decimation, and continuous recording of all data. Other BSTRAIN features include automated blade stiffness checks, remote terminal access to blade test status, and automated VCR control for continuous test recording. Results from tests conducted with the software revealed areas for improvement including test accuracy, post-processing analysis, and further data reduction.

Musial, W D; Clark, M E [National Renewable Energy Lab., Golden, CO (United States); Stensland, T [Stensland (T.), Lakewood, CO (United States)

1996-07-01

367

Progressive damage in Sn4Ag0.5Cu solder joints during flexural fatigue of a BGA package  

Microsoft Academic Search

This study examines evolution characteristics of inelastic strains and materials damage in Sn-4Ag-0.5Cu (SAC405) solder joints of a BGA package under cyclic mechanical stressing. For this purpose, a finite element model of the assembly under four-point bend test set-up is employed. Strain rate-dependent response of the solder is represented by Anand model. Progressive damage in the solder joint is described

N. M. Shaffiar; W. K. Loh; N. Kamsah; M. N. Tamin

2010-01-01

368

Analysis of Fatigue Crack Growth Mechanism and Oxidation and Fatigue Life at Elevated Temperatures.  

National Technical Information Service (NTIS)

Two quantitative models based on experimentally observed fatigue damage processes have been made: (1) a model of low cycle fatigue life based on fatigue crack growth under general-yielding cyclic loading; and (2) a model of accelerated fatigue crack growt...

H. W. Liu

1988-01-01

369

Influence of different wind profiles due to varying atmospheric stability on the fatigue life of wind turbines  

NASA Astrophysics Data System (ADS)

Offshore wind energy is being developed on a very large scale in the European seas. The objective of developing wind energy offshore is to capture greater wind speeds than are encountered onshore and as a result more energy. With this also come more challenges in the design of wind turbines due to the hostile offshore environment. Currently the standards for offshore wind turbines prescribe a site specific design for the support structures and the design for the rotor nacelle assembly according to onshore standards. Wind turbines are designed to withstand fatigue and ultimate loads. For the fatigue loading several input conditions have been prescribed, amongst which wind profile is one of them. Wind profile is represented by power law or logarithmic law as given in the standards. A neutral stability of the atmosphere is considered while obtaining the wind profile using the logarithmic law. In this paper the atmospheric stability is varied in order to estimate different wind profiles and simulations are run in Bladed to check its influence on the fatigue damage at the blade root. The variations in the atmospheric stability has been taken into account by using some typical values of Obukhov length. From steady state simulations it has been found that atmospheric stability is important for fatigue damage. The analysis showed that variation in the distribution of atmospheric stability causes large variations in the fatigue damage for different sites. Thus, it is worthwhile to carry out a full scale study using the turbulent winds and real data for wind turbine and environmental conditions.

Sathe, Ameya; Bierbooms, Wim

2007-07-01

370

Impedance-based structural health monitoring of wind turbine blades  

NASA Astrophysics Data System (ADS)

Wind power is a fast-growing source of non-polluting, renewable energy with vast potential. However, current wind turbine technology must be improved before the potential of wind power can be fully realized. Wind turbine blades are one of the key components in improving this technology. Blade failure is very costly because it can damage other blades, the wind turbine itself, and possibly other wind turbines. A successful damage detection system incorporated into wind turbines could extend blade life and allow for less conservative designs. A damage detection method which has shown promise on a wide variety of structures is impedance-based structural health monitoring. The technique utilizes small piezoceramic (PZT) patches attached to a structure as self-sensing actuators to both excite the structure with high-frequency excitations, and monitor any changes in structural mechanical impedance. By monitoring the electrical impedance of the PZT, assessments can be made about the integrity of the mechanical structure. Recently, advances in hardware systems with onboard computing, including actuation and sensing, computational algorithms, and wireless telemetry, have improved the accessibility of the impedance method for in-field measurements. This paper investigates the feasibility of implementing such an onboard system inside of turbine blades as an in-field method of damage detection. Viability of onboard detection is accomplished by running a series of tests to verify the capability of the method on an actual wind turbine blade section from an experimental carbon/glass/balsa composite blade developed at Sandia National Laboratories.

Pitchford, Corey; Grisso, Benjamin L.; Inman, Daniel J.

2007-05-01

371

Fatigue crack initiation life prediction of railroad  

NASA Astrophysics Data System (ADS)

Study of multiaxial high-cycle fatigue initiation life prediction for railroad is done in this paper. Using ANSYS 11.0 software three dimensional elasto-plastic finite element model of rail/wheel contact is constructed and fine mesh technique in contact region is used to achieve both computational efficiency and accuracy. Stress analysis is performed and fatigue damage in railroad is evaluated numerically using multiaxial fatigue crack initiation model. Using the stress history during one loading cycle and fatigue damage model, the effects of vertical loading, material hardness material fatigue properties and wheel/rail contact situation on fatigue crack initiation life are investigated.

Tehrani, P. Hosseini; Saket, M.

2009-08-01

372

Composite Cooled Rotor Blade.  

National Technical Information Service (NTIS)

A description is given of a composite cooled blade, for example for a gas or steam turbine rotor, consisting of a detachable root with a coolant chamber and a blade section with profiled ducts. To increase static and vibration strength and operational rel...

N. Y. Litvinov V. S. Lyubinetskii

1970-01-01

373

Blade pitch varying mechanism  

Microsoft Academic Search

A gas turbine engine is described comprising: (a) a stationary member; (b) first and second rotating structures coaxially disposed about the stationary member; (c) an annular gas flowpath coaxial with the first and second rotating structures; (d) first and second rotor blades attached to the first and second rotating structures; (e) forward and aft rows of variable pitch propulsor blades

1988-01-01

374

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a first groove and a second groove therein. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings has a first groove and a second groove therein. The space or void formed between the first grooves and the second grooves has a plurality of spherical balls positioned therein. The plurality of spherical balls has a preestablished rate of thermal expansion being equal to the preestablished rate of thermal expansion of the turbine blade.

Shaffer, James E. (Maitland, FL)

1995-01-01

375

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a first groove and a second groove therein. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings has a first groove and a second groove therein. The space or void formed between the first grooves and the second grooves has a plurality of spherical balls positioned therein. The plurality of spherical balls has a preestablished rate of thermal expansion being equal to the preestablished rate of thermal expansion of the turbine blade. 4 figures.

Shaffer, J.E.

1995-01-10

376

Condition monitoring techniques for composite wind turbine blades  

NASA Astrophysics Data System (ADS)

The range of possible NDT techniques that might be applied to wind turbine blades is reviewed. Thermal techniques are selected and implemented in various active and passive modes. Theoretical modeling of 3D thermal interactions is performed using a finite difference model. Several thermal condition monitoring methods are evaluated experimentally on both composites and composite wood blades. The relative detectability of various effects using the active heating approach is shown. Internal generation of heat was detected during a full-size wood laminate blade fatigue test. Temperature differences of over 1 C were measured at the surface above the underlying butt joint some 12 hr before failure occurred at the point. The hot spot was identified as early as at two-thirds of the final blade life.

Bond, Leonard J.; Aftab, Nadeem; Clayton, Brian R.; Dutton, A. G.; Irving, Andrew D.; Lipman, Norman H.

377

Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model. Part II: Model development and results  

Microsoft Academic Search

The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. However, there have historically been no analytical methods to quantify the specific fatigue life reduction of individual unfailed corroded components with any reasonable degree of confidence. As part of a NAVAIR high-strength steel corrosion–fatigue assessment program, methods were studied to predict the impact that

D. T. Rusk; W. Hoppe; W. Braisted; N. Powar

2009-01-01

378

Behavior of nickel-base superalloy single crystals under thermal-mechanical fatigue  

NASA Astrophysics Data System (ADS)

The thermal-mechanical fatigue behavior of AM1 nickel-base superalloy single crystals is studied using a cycle from 600 °C to 1100 °C. It is found to be strongly dependent on crystallo-graphic orientation, which leads to different shapes of the stress-strain hysteresis loops. The cyclic stress-strain response is influenced by variation in Young’s modulus, flow stress, and cyclic hardening with temperature for every crystallographic orientation. The thermalmechanical fatigue life is mainly spent in crack growth. Two main crack-initiation mechanisms occur, depending on the mechanical strain range. Oxidation-induced cracking is the dominant damage mechanism in the lifetime of interest for turbine blades.

Fleury, E.; Rémy, L.

1994-12-01

379

Structural health monitoring of wind turbine blade using fiber Bragg grating sensors and fiber optic rotary joint  

NASA Astrophysics Data System (ADS)

Wind energy utilization as a reliable energy source has become a large industry in the last 20 years. Nowadays, wind turbines can generate megawatts of power and have rotor diameters that are on the order of 100 meters in diameter. One of the key components in a wind turbine is the blade which could be damaged by moisture absorption, fatigue, wind gusts or lighting strikes. The wind turbine blades should be routinely monitored to improve safety, minimize downtime, lower the risk of sudden breakdowns and associated huge maintenance and logistics costs, and provide reliable power generation. In this paper, a real-time wind turbine blade monitoring system using fiber Bragg grating (FBG) sensors with the fiber optic rotary joint (FORJ) is proposed, and applied to monitor the structural responses of a 600 W small scale wind turbine. The feasibility and effectiveness of the FORJ is validated by continuously transmitting the optical signals between the FBG interrogator at the stationary side and the FBG sensors on the rotating part. A comparison study between the measured data from the proposed system and those from an IMote2-based wireless strain measurement system is conducted.

Chen, Y.; Ni, Y. Q.; Ye, X. W.; Yang, H. X.; Zhu, S.

2012-03-01

380

Very high cycle fatigue behavior of nickel-based superalloy Rene 88 DT  

Microsoft Academic Search

The fatigue behavior of the polycrystalline nickel-based superalloy Rene 88 DT has been investigated at 593°C up to the very high cycle fatigue regime using ultrasonic fatigue techniques. Conventional damage tolerant methods failed to predict the fatigue life nor the large fatigue life viability of two orders of magnitude observed in the very high cycle regime. Fatigue crack initiation rather

Jiashi Miao

2010-01-01

381

Vibrodiagnostic parameters of fatigue damage in rectangular plates. Part 3. Through-the-thickness and surface semi-elliptical cracks  

Microsoft Academic Search

The paper addresses the analytical determination of vibrodiagnostic parameters that describe the presence of normal-rupture\\u000a flat through-the-thickness and surface semi-elliptical central cracks in a rectangular homogeneous plate of constant thickness\\u000a for various plate fixing conditions and vibration modes. It is shown that the most sensitive vibrodiagnostic damage parameter\\u000a of a plate is the variation of the logarithmic decrement in the

V. V. Matveev; O. E. Boginich

2006-01-01

382

Efficiency of the method of spectral vibrodiagnostics for fatigue damage of structural elements. Part 1. Longitudinal vibrations, analytical solution  

Microsoft Academic Search

On the basis of an analysis of the asymptotics of higher approximations to solutions of a differential equation of longitudinal\\u000a vibrations of a macroelastic body whose nonlinearity is explained by the hysteresis and “breathing” of the damaged material\\u000a in the process of its cyclic deformation under conditions of tension-compression, we estimate the applicability of the spectral\\u000a characteristics of strain cycles

V. V. Matveev

1997-01-01

383

Dynamic stall on wind turbine blades  

SciTech Connect

Dynamic loads must be predicted accurately in order to estimate the fatigue life of wind turbines operating in turbulent environments. Dynamic stall contributes to increased dynamic loads during normal operation of all types of horizontal-axis wind turbine (HAWTs). This report illustrates how dynamic stall varies throughout the blade span of a 10 m HAWT during yawed and unyawed operating conditions. Lift, drag, and pitching moment coefficients during dynamics stall are discussed. Resulting dynamic loads are presented, and the effects of dynamic stall on yaw loads are demonstrated using a yaw loads dynamic analysis (YAWDYN). 12 refs., 22 figs., 1 tab.

Butterfield, C.P.; Simms, D.; Scott, G. (National Renewable Energy Lab., Golden, CO (United States)); Hansen, A.C. (Utah Univ., Salt Lake City, UT (United States))

1991-12-01

384

Heat generation by two different saw blades used for tibial plateau leveling osteotomies.  

PubMed

During tibial plateau leveling osteotomy (TPLO) the saw blade produces frictional heat. The purpose of this study was to evaluate and compare heat generated by two TPLO blade designs (Slocum Enterprises [SE] and New Generation Devices [NDG]), with or without irrigation, on cadaveric canine tibias. Thirty-six paired tibias were used to continuously measure bone temperatures during osteotomy through both cortices (i.e., the cis and trans cortices). Each pair was assigned to either an irrigation or nonirrigation group during osteotomy, and each tibia within a pair was osteotomized using a different saw blade design. Saw blade temperatures were recorded and temperatures were compared for all combinations of blade type, cortex, and irrigation. In the cis cortex group, the SE blade generated more bone heat than the NGD blade (P=0.0258). Significant differences in temperature generation between saw blade types were seen only when the osteotomy site was not irrigated (P=0.0156). For all variables measured, bone and saw blade temperature generation was lower with irrigation (P<0.05). None of the osteotomies performed with either saw blade produced a critical duration of damaging temperature ranges in this study. Although saw blade design and irrigation influence heat generation during the TPLO, the potential for bone thermal damage during TPLO is low. The use of the NGD blade with irrigation is recommended. PMID:22267171

Bachelez, Andreas; Martinez, Steven A

2012-01-19

385

Instrumented composite turbine blade for health monitoring  

NASA Astrophysics Data System (ADS)

A health monitoring approach is investigated for hydrokinetic turbine blade applications. In-service monitoring is critical due to the difficult environment for blade inspection and the cost of inspection downtime. Composite blade designs have advantages that include long life in marine environments and great control over mechanical properties. Experimental strain characteristics are determined for static loads and free-vibration loads. These experiments are designed to simulate the dynamic characteristics of hydrokinetic turbine blades. Carbon/epoxy symmetric composite laminates are manufactured using an autoclave process. Four-layer composite beams, eight-layer composite beams, and two-dimensional eight-layer composite blades are instrumented for strain. Experimental results for strain measurements from electrical resistance gages are validated with theoretical characteristics obtained from in-house finite-element analysis for all sample cases. These preliminary tests on the composite samples show good correlation between experimental and finite-element strain results. A health monitoring system is proposed in which damage to a composite structure, e.g. delamination and fiber breakage, causes changes in the strain signature behavior. The system is based on embedded strain sensors and embedded motes in which strain information is demodulated for wireless transmission.

Robison, Kevin E.; Watkins, Steve E.; Nicholas, James; Chandrashekhara, K.; Rovey, Joshua L.

2012-03-01

386

Characterization of a nine-meter sensor-equipped wind turbine blade using a laser measuring device  

Technology Transfer Automated Retrieval System (TEKTRAN)

A nine-meter turbine blade was prepared for an experiment to examine the movement and fatigue patterns during operation on a 115 kW turbine. The blade, equipped with surface mounted fiber optic strain gauges, foil strain gauges, single, and triple axis accelerometers was placed on a calibration fixt...

387

Fatigue loading parameter identification of a wind turbine operating in complex terrain  

Microsoft Academic Search

An analytic tool is introduced for the evaluation of the fatigue loading of a wind turbine operating in complex terrain, from large scale experimental data. The fatigue loading magnitudes quantified by the equivalent load ranges of the different wind turbine components, namely blade, main shaft and tower, are modelled using multiple regression analysis in order to identify the fatigue inducing

F Mouzakis; E Morfiadakis; P Dellaportas

1999-01-01

388

Observation, analysis and prediction of fretting fatigue in 2024-T351 aluminum alloy  

Microsoft Academic Search

Fretting is associated with microslip at the interface of contacts experiencing oscillatory loads. One consequence of fretting is the formation and subsequent growth of cracks at the edge of contact, a phenomenon known as fretting fatigue. Fretting fatigue is an important fatigue failure mechanism in aircraft structural lap joints and turbine blade\\/disk contacts. A well-characterized, integrated fretting test system has

Matthew P. Szolwinski; Thomas N. Farris

1998-01-01

389

Saw Blades and Resonance  

NASA Astrophysics Data System (ADS)

This paper describes an inexpensive, classroom experiment that allows students to quantitatively investigate resonance using a hacksaw blade. The blade clamped to the edge of a table forms a cantilever that may vibrate at any of a number of preferred frequencies. A small cylindrical magnet is fixed to the saw blade. An electromagnetic coil powered by a frequency generator causes large-amplitude vibrations of the saw blade at the resonant frequencies. Vibrations of a similar system, a vibrating car antenna, have been discussed by Newburgh and Newburgh.1 The dramatic increases in the oscillation amplitude are both instructive and fascinating. Analogies may be drawn to systems ranging from a child on a swing to the Tacoma Narrows bridge.

Liebl, Michael

2005-05-01

390

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a pair of recessed portions thereon. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings have a pair of grooves therein in which are positioned a pair of pins having a generally rectangular cross-section and a reaction surface thereon. A pair of cylindrical rollers interposed respective ones of the pair of reaction surfaces and the pair of recessed portions. The attachment system or turbine assembly provides an economical, reliable and effective attachment of a component having a preestablished rate of thermal expansion to a component having a greater preestablished rate of thermal expansion. 3 figures.

Boyd, G.L.

1994-12-13

391

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a pair of recessed portions thereon. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings have a pair of grooves therein in which are positioned a pair of pins having a generally rectangular cross-section and a reaction surface thereon. A pair of cylindrical rollers interposed respective ones of the pair of reaction surfaces and the pair of recessed portions. The attachment system or turbine assembly provides an economical, reliable and effective attachment of a component having a preestablished rate of thermal expansion to a component having a greater preestablished rate of thermal expansion.

Boyd, Gary L. (Alpine, CA)

1994-01-01

392

Underbody Truck Blade.  

National Technical Information Service (NTIS)

Based on existing data from the Equipment Management Information System, experience with individual forests, and observations of different operations and conditions, a forest road maintenance concept involving the use of underbody truck blades is outlined...

J. McDermott J. Bassel

1985-01-01

393

Damage mechanisms under thermal-Mechanical fatigue in a unidirectionally reinforced SiC-titanium metal matrix composite for advanced jet engine components  

Microsoft Academic Search

The thermal-mechanical fatigue behaviour of a titanium composite reinforced by continuous SiC fibres, the SM 1140+\\/Ti-6242, was investigated for uniaxial loading, under conditions which simulate service loading in a compressor disc during a flight. The thermal-mechanical tests (100–500°C) give rise to a reduction of fatigue lives compared to isothermal tests (550°C). The fatigue crack growth behaviour for isothermal and non-isothermal

S. Hertz-Clemens; C. Aumont; L. Remy

2002-01-01

394

The critical role of environment in fatigue damage accumulation in deep-reactive ion-etched single-crystal silicon structural films  

Microsoft Academic Search

The importance of service environment to the fatigue resistance of n+-type, 10 ?m thick, deep-reactive ion-etched (DRIE) silicon structural films used in microelectromechanical systems (MEMS) was characterized by testing of electrostatically actuated resonators (natural frequency, f0, ?40 kHz) in controlled atmospheres. Stress-life (S-N) fatigue tests conducted in 30°C, 50% relative humidity (R.H.) air demonstrated the fatigue susceptibility of silicon films.

Olivier N. Pierron; Christopher L. Muhlstein

2006-01-01

395

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine flange having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine flange includes a first upstanding flange and a second upstanding flange having a groove formed between them. The turbine flange further includes a recess. Each of the first and second upstanding flanges have a plurality of bores therein. A turbine blade has a first member and a second member positioned in one of the groove and the recess. Each of the first member and the second member have a plurality of bores therein. A pin is positioned in respective ones of the plurality of bores in the first and second upstanding members and the first and second members and attach the blade to the turbine flange. The pin has a preestablished rate of thermal expansion being substantially equal to the rate of thermal expansion of the blade. 4 figs.

Frey, G.A.; Jimenez, O.D.

1996-12-03

396

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine flange having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine flange includes a first upstanding flange and a second upstanding flange having a groove formed therebetween. The turbine flange further includes a recess. Each of the first and second upstanding flanges have a plurality of bores therein. A turbine blade has a first member and a second member positioned in one of the groove and the recess. Each of the first member and the second member have a plurality of bores therein. And, a pin is positioned in respective ones of the plurality of bores in the first and second upstanding members and the first and second members and attach the blade to the turbine flange. The pin has a preestablished rate of thermal expansion being substantially equal to the rate of thermal expansion of the blade.

Frey, deceased, Gary A. (late of Poway, CA); Jimenez, Oscar D. (Escondia, CA)

1996-01-01

397

A model for the formation of fatigue striations and its relationship with small fatigue crack growth in an aluminum alloy  

Microsoft Academic Search

The fatigue crack growth process involves damage accumulation and crack extension. The two sub-processes that lead to fatigue crack extension were quantified separately in a recent model for small fatigue crack growth applicable to engineering alloys. Here, we report the results of an experimental investigation to assess the assumptions of that model. The fatigue striation formation in an aluminum alloy

Amit Shyam; Edgar Lara-Curzio

2010-01-01

398

Fluid blade disablement tool  

SciTech Connect

A fluid blade disablement (FBD) tool that forms both a focused fluid projectile that resembles a blade, which can provide precision penetration of a barrier wall, and a broad fluid projectile that functions substantially like a hammer, which can produce general disruption of structures behind the barrier wall. Embodiments of the FBD tool comprise a container capable of holding fluid, an explosive assembly which is positioned within the container and which comprises an explosive holder and explosive, and a means for detonating. The container has a concavity on the side adjacent to the exposed surface of the explosive. The position of the concavity relative to the explosive and its construction of materials with thicknesses that facilitate inversion and/or rupture of the concavity wall enable the formation of a sharp and coherent blade of fluid advancing ahead of the detonation gases.

Jakaboski, Juan-Carlos (Albuquerque, NM); Hughs, Chance G. (Albuquerque, NM); Todd, Steven N. (Rio Rancho, NM)

2012-01-10

399

A weight function-critical plane approach for low-cycle fatigue under variable amplitude multiaxial loading  

Microsoft Academic Search

Low-cycle fatigue data of type 304 stainless steel obtained under axial-torsional loading of variable amplitudes are analyzed using four multiaxial fatigue parameters: SWT, KBM, FS and LKN. Rainflow cycle counting and Morrow's plastic work interaction rule are used to calculate fatigue damage. The performance of a fatigue model is dependent on the fatigue parameter, the critical plane and the damage

X. C HEN; D. J IN; K. S. KIM

2006-01-01

400

Nondestructive evaluation of fatigue in titanium alloys  

SciTech Connect

Dissipated heat has been measured by thermographic technique during fatigue experiments on Ti-6Al-4V. Surface temperature of the specimen was found sensitive to the amount of fatigue damage accumulated in the material. An increased heat dissipation due to fatigue can be related to continuous change in the microstructure (increased dislocation density, stacking faults, etc.) of the material. A method based on passive thermography can be proposed to monitor damage accumulation in Ti-6Al-4V due to cyclic loading.

Roesner, H.; Meyendorf, N.; Sathish, S.; Matikas, T.E.

2000-07-01

401

Individual blade control for vibration reduction of a helicopter with dissimilar blades  

NASA Astrophysics Data System (ADS)

A control method is proposed to reduce vibrations in helicopters using active trailing-edge flaps on the rotor blades. The novelty of the method is that each blade is controlled independently, taking into account possible blade dissimilarities. This is different from previous control approaches that assumed blades were identical and generated a single control input which is applied with adequate phase shift to each blade. The controller is developed in discrete time, with the control inputs updated every rotor revolution. The method consists of performing simultaneous system identification (using Kalman filtering technique) and closed loop control (using a deterministic control law) at each time step. For the system identification, different inputs are applied to each blade, and the relationship between the individual blade inputs and the resulting loads in the fixed frame is estimated on-line, assuming a linear-time-periodic model of the helicopter. A comprehensive rotor analysis, including all blade degrees of freedom and a free wake model for computing the inflow across the rotor disk, was used to investigate the controller performance in detail. The rotor model is based on a modern bearingless rotor that includes detailed modeling of trailing edge flap effects. The controller performance was tested at advance ratios from mu = 0.10 to mu = 0.40, both for a baseline rotor with identical blades and a damaged rotor with dissimilar blades. In the case of the dissimilar rotor, comprehensive analysis predicts that allowing independent control inputs for each blade dramatically improves the vibration reduction compared to restricting the control inputs to be specific phase shifted versions of each other. For example, at mu = 0.30, the vibration index is reduced by over 90% using individual inputs, compared to only 45% using phase-shifted inputs, for both structural and aerodynamic blade dissimilarities. Required flap deflections are similar for both methods, around +/-2.5°. In forward flight, the controller could simultaneously reduce the baseline 4/rev fixed frame vibration as well other harmonics of vibration such as 1/rev and 3/rev arising from blade dissimilarities. It was also possible to minimize vibration in the fixed frame for several loads simultaneously. However, for most control tests, increases in other loads (not included in the control objective) were observed. During most closed loop tests, the maximum allowable input to the actuators was reached. It was found that the method used to account for actuator saturation and maintain actuator input within acceptable limits had an important effect on controller performance. The best controller performance was obtained when control inputs are computed by solving the constrained minimization problem. However, this procedure is very time consuming and could not be implemented in real-time with the available computer. It can be concluded that accounting for blade dissimilarities using individual inputs for each blade results in improved vibration reduction. However, to maximize the benefits of this control scheme, an efficient, practical method to limit control inputs needs to be devised. (Abstract shortened by UMI.)

Roget, Beatrice

402

Operating factors can reduce drill pipe fatigue on floating vessel  

Microsoft Academic Search

In offshore drilling from a floating vessel, fatigue damage to drill pipe is determined mainly by the pipe tension and inclination angle of the marine riser. This article identifies the operating conditions (i.e., tension, angle, revolutions per minute, drilling rate, etc.) which may alleviate fatigue damage and prevent fatigue failure. When drilling in deep water, especially in high current areas,

Zeren

1986-01-01

403

Modal analysis and SHM investigation of CX-100 wind turbine blade  

SciTech Connect

This paper presents the dynamic characterization of a CX-100 wind turbine blade using modal testing. Obtaining a thorough dynamic characterization of turbine blades is important because they are complex structures, making them very difficult to accurately model without supplementing with experimental data. The results of this dynamic characterization can be used to validate a numerical model and understand the effect of structural damage on the performance of the blades. Also covered is an exploration into Structural Health Monitoring (SHM) techniques employed on the blade surface to detect changes in the blade dynamic properties. SHM design parameters such as traveling distance of the wave were examined . Results obtained during modal and SHM testing will provide a baseline for future work in blade damage detection and mitigation.

Deines, Krystal E [Los Alamos National Laboratory; Marinone, Timothy [Los Alamos National Laboratory; Schultz, Ryan A [Los Alamos National Laboratory; Farinholt, Kevin R [Los Alamos National Laboratory; Park, Gyuhae [Los Alamos National Laboratory

2010-11-08

404

Non-Destructive Evaluation of Wind Turbine Blades Using an Infrared Camera  

SciTech Connect

The use of a digital infrared as a non-destructive evaluation thermography camera (NDE) tool was ex- plored in two separate wind turbine blade fatigue tests. The fwst test was a fatigue test of part of a 13.1 meter wood-epoxy-composite blade. The second test was on a 4.25 meter pultruded fiber glass blade section driven at several mechanical resonant frequencies. The digital infrared camera can produce images of either the static temperature distribution on the surface of the specimen, or the dynamic temperature distribution that is in phase with a specific frequency on a vibrating specimen. The dynamic temperature distribution (due to thermoplastic effects) gives a measure of the sum of the principal stresses at each point on the surface. In the wood- epoxy-composite blade fatigue test, the point of ultimate failure was detected long before failure occurred. The mode shapes obtained with the digital infrared camera, from the resonant blade tests, were in very good agree- ment with the finite-element calculations. In addition, the static temperature images of the resonating blade showed two areas that contained cracks. Close-up dy- namic inf%red images of these areas showed the crack structure that agreed with subsequent dye-penetrant analysis.

Beattie, A.G.; Rumsey, M.

1998-12-17

405

Cooled Turbine Blade Tip Closure.  

National Technical Information Service (NTIS)

An improved high pressure turbine rotor blade and tip cap structure therefor is provided, which comprises, a plurality of metallic layers bonded to the tip end of the blade, each layer having peripheral shape conforming to the camber of the blade, the lay...

R. L. Horvath R. W. Harris

1983-01-01

406

Single wire fretting fatigue tests for electrical conductor bending fatigue evaluation  

Microsoft Academic Search

Overhead electrical conductors are often subjected to aeolian vibrations which may induce fretting fatigue damage of individual aluminium wires in suspension clamp regions. Many bending fatigue tests have been performed on electrical conductors. Depending on the test conditions, wire fracture may be found to occur in the external as well as internal layers. Individual wire fretting fatigue is very difficult

Z. R. Zhou; S. Goudreau; M. Fiset; A. Cardou

1995-01-01

407

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

SciTech Connect

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.

Carek, G.A.

1987-04-01

408

Postdialysis fatigue  

Microsoft Academic Search

To clarify the demographic and clinicolaboratory features of postdialysis fatigue (PDF), we enrolled 85 patients on maintenance hemodialysis in a cross-sectional study using validated questionnaires and chart review. Forty-three patients complained of fatigue after dialysis. On formal testing using the Kidney Disease Questionnaire, the PDF group had statistically greater severity of fatigue and somatic complaints than the group of patients

Allan H. Sklar; Lee Ann Riesenberg; Avi K. Silber; Waqar Ahmed; Amir Ali

1996-01-01

409

Postoperative fatigue  

Microsoft Academic Search

Uncomplicated major surgery is followed by a pronounced increased feeling of fatigue extending throughout the first month in about one-third of patients. Postoperative fatigue correlates with the degree of surgical trauma but is not related to duration of general anesthesia and surgery or to preoperative nutritional status, age, or sex. Fatigue also correlates with postoperative deterioration in nutritional parameters and

Tom Christensen; Henrik Kehlet

1993-01-01

410

Nonscratching Windshield Wiper Blade.  

National Technical Information Service (NTIS)

The program was undertaken to assess the possible utilization of low friction and/or porous materials in making wiper blades for helicopter plastic windshields. It was, therefore, directed to a search for new materials in current use. A literature search ...

J. W. Woestman

1974-01-01

411

Razor Blades to Computers.  

ERIC Educational Resources Information Center

Stages in developing editing equipment and processes for videotape are described. In 1956, when the first broadcast videotape recorders were installed, a splicing block, consisting of an aluminum block, steel ruler, and sharp razor blade, was used. Gradually, technicians developed more sophisticated methods. At present, two very advanced methods…

Schneider, Arthur

412

Effect of Electrochemical Treatment on the Fatigue Strength of Vanes Made of MA-2 Alloy.  

National Technical Information Service (NTIS)

Electrochemical finishing of fan blades of an engine was performed and compared with mechanical polishing. Stress distribution diagrams are given. Grain boundaries of the surface were found to corrode, and fatigue strength was found to be inferior. (Autho...

N. M. Mitrokhin

1973-01-01

413

Fatigue life prediction for wind turbines: A case study on loading spectra and parameter sensitivity  

SciTech Connect

Wind turbines are fatigue-critical machines used to produce electrical energy from the wind. These rotating machines are subjected to environmental loadings that are highly irregular in nature. Historical examples of fatigue problems in both research and commercial wind turbine development are presented. Some example data on wind turbine environments, loadings and material properties are also shown. Before a description of how the authors have chosen to attack the cumulative damage assessment, questions are presented for the reader's reflection. The solution technique used by the authors is then presented, followed by a case study applying the procedures to an actual wind turbine blade joint. The wind turbine is the 34-meter diameter vertical axis wind turbine (VAWT) erected by Sandia National Laboratories near Bushland, Texas. The case study examines parameter sensitivities for realistic uncertainties in inputs defining the turbine environment, stress response and material properties. The fatigue lifetimes are calculated using a fatigue analysis program, called LIFE2, which was developed at Sandia. The LIFE2 code, described in some detail in an appendix, is a PC-based, menu-driven package that leads the user through the steps required to characterize the loading and material properties, then uses Miner's rule or a linear crack propagation rule to numerically calculate the time to failure. Only S-n based cumulative damage applications are illustrated here. The LIFE2 code is available to educational institutions for use as a case study in describing complicated loading histories and for use by students in examining, hands on, parameter sensitivity of fatigue life analysis.

Sutherland, H.J.; Veers, P.S.; Ashwill, T.D.

1992-01-01

414

The effect of seismic loading on the fatigue strength of welded joints  

Microsoft Academic Search

Earthquakes sometimes damage steel structures. Structures which are not seriously damaged are still used after earthquakes but their fatigue strength may have been reduced by the large cyclic loadings imposed by the earthquakes. In order to clarify the effect of seismic loading on the fatigue strength of welded joints, high cycle fatigue and variable amplitude fatigue tests after a number

Y. Kondo; K. Okuya

2007-01-01

415

Mechanistic approach for creep-fatigue evaluation of 9Cr-1Mo-V-Nb steel  

SciTech Connect

A mechanistic model was developed to describe the creep-fatigue interaction of 9Cr-1Mo-V-Nb steel based on a damage mechanics approach. The model assumes that each of the fatigue and creep damage consists of basic damages with a size and density. The mechanism of the creep-fatigue interaction is considered to be an early growth of a size of fatigue basic damage from a creep basic damage formed prior to fatigue loading. The model interprets well the experimental creep-fatigue life under complex strain histories.

Asada, Yasuhide; Yaguchi, Masatsugu [Univ. of Tokyo (Japan). Dept. of Mechanical Engineering

1995-10-01

416

Flight Test of a Composite Multi-tubular Spar Main Rotor Blade on the AH-1G Helicopter, Volume I. Materials, Design and Test.  

National Technical Information Service (NTIS)

The objectives of this program were to design a composite main rotor blade in the multi-tubular spar configuration to be directly interchangeable (in pairs) with the production metal (540) blades on the AH-1G helicopter, have increased fatigue life, invul...

R. E. Head

1977-01-01

417

Flight Test of a Composite Multi-Tubular Spar Main Rotor Blade on the AH-1G Helicopter. Volume II. Cost Estimates and Process Specifications.  

National Technical Information Service (NTIS)

The objectives of this program were to design a composite main rotor blade in the multi-tubular spar configuration to be directly interchangeable (in pairs) with the production metal (540) blades on the AH-1G helicopter, have increased fatigue life, invul...

R. E. Head

1977-01-01

418

The mechanics and tribology of fretting fatigue with application to riveted lap joints  

NASA Astrophysics Data System (ADS)

Fretting is the synergistic combination of wear, corrosion, and fatigue damage mechanisms driven by the partial slip of contacting surfaces. The surface microslip and near-surface contact stresses associated with fretting can lead to severe reduction in service lifetimes of contacting components as diversified as bearings, turbine blades and mechanically-fastened joints, both structural and biological. This tribologically induced degradation has come under close scrutiny by those responsible for maintaining aging fleets of both commercial and military aircraft. Thus a critical need exists for predicting fretting crack nucleation in riveted aluminum. aircraft joints. Fulfilling this need requires characterizing both the near-surface mechanics and intimately-related tribology of fretting. To this end, a well characterized experimental setup has been developed to generate carefully controlled and monitored fretting contacts to investigate the nature of the near-surface conditions. Included in this investigation were in-situ observations of the fretting contact stress field via a non-invasive thermal imaging technique and a characterization of the evolution of friction under partial slip conditions. With specific qualitative and quantitative understanding of these near-surface conditions, a series of fretting fatigue experiments have been conducted to validate a mechanics-based model for predicting fretting fatigue crack nucleation. Finally, efforts have been directed toward extending this understanding of fretting crack nucleation to riveted aircraft structure through modeling of the riveting process and a related experimental program designed to link riveting process parameters and fretting damage in single-lap joint structures. This work focuses specifically on determination of the residual stresses induced during rivet installation and the morphological characterization of fretting fatigue damage in the riveted test specimens manufactured under controlled conditions.

Szolwinski, Matthew Paul

419

Erosion behaviour of turbine rotor blades installed in the Krsko nuclear power plant  

Microsoft Academic Search

Turbines installed in nuclear power plants operate with wet steam. The flow of wet steam causes the erosion of the last stage rotor blades, and can cause a considerable damage to the condensing steam turbines. This paper reviews the results of many years of monitoring and researching of the behaviour of the erosion process and its mechanism for rotor blades

B. Staniša; Z. Schauperl; K. Grilec

2003-01-01

420

The Microstructural Analysis of the Effect of Fic on Gas Turbine Blades  

Microsoft Academic Search

Advancements in superalloys permit hot gas path components to operate for many thousands of hours under severe centrifugal, thermal and vibratory stresses. The blade of a gas turbine must withstand the most severe combination of temperature, stress, and environment. After a certain period of operation, the blade is damaged by the turbine operation mode. To recover the similar initial mechanical

Hyung-Ick Kim; Yong Huh; Hong-Sun Park; Chang-Sung Seok; Moon-Young Kim

2006-01-01

421

Field monitoring of the ice load of an icebreaker propeller blade using fiber optic strain gauges  

Microsoft Academic Search

Navigation in polar waters presents a formidable challenge to ships' propulsion systems as large ice pieces impinging on their propeller blades sometimes result in stresses exceeding the yield strength of the blade material. Damage to propellers is costly and can also spell disaster if a ship becomes disabled in a remote area. To prevent such situations, design practice must be

Andre Morin; Serge Caron; Richard van Neste; Merv H. Edgecombe

1996-01-01

422

Fixed blade turbulence generator  

SciTech Connect

A device and method for installing a device for improving the fuel/air mixture in internal combustion engines with or without a fuel injection system. An intermediate member operatively dispositioned between the engine intake manifold and the intake port comprises at least two helically twisted blades attached to the inner bore of an intake port opening in the intermediate member; these blades are angled in relation to the fuel/air flow path and twisted so as to impart a swirling to the fuel/air mixture. In fuel injected systems, the swirl is imparted to the air flow just prior to encountering the umbrella mist injected to the intake port by the fuel injector. The swirl mixing of the fuel/air improves engine performance, reduces pollutants, and increases gas mileage. Further, in fuel injection systems, the device reduces or eliminates the common occurrence of a burned intake valve caused by a clogged injector.

Lyssy, N.G.

1982-11-23

423

Constructal blade shape in nanofluids  

NASA Astrophysics Data System (ADS)

Blade configuration of nanofluids has been proven to perform much better than dispersed configuration for some heat conduction systems. The analytical analysis and numerical calculation are made for the cylinder--shaped and regular-rectangular-prism--shaped building blocks of the blade-configured heat conduction systems (using nanofluids as the heat conduction media) to find the optimal cross-sectional shape for the nanoparticle blade under the same composing materials, composition ratio, volumetric heat generation rate, and total building block volume. The regular-triangular-prism--shaped blade has been proven to perform better than all the other three kinds of blades, namely, the regular-rectangular-prism--shaped blade, the regular-hexagonal-prism--shaped blade, and the cylinder--shaped blade. Thus, the regular-triangular-prism--shaped blade is selected as the optimally shaped blade for the two kinds of building blocks that are considered in this study. It is also proven that the constructal cylinder--regular-triangular-prism building block performs better than the constructal regular-rectangular-prism--regular-triangular-prism building block.

Bai, Chao; Wang, Liqiu

2011-12-01

424

Hysteresis and fatigue  

SciTech Connect

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

Erber, T. (Univ. of California, Los Angeles (United States)); Guralnick, S.A.; Michels, S.C. (Illinois Institute of Technology, Chicago (United States))

1993-06-01

425

Fracture mechanics evaluation of progressive fatigue damage in a circular-hole-notched GRP composite under combined tension/torsion loading  

NASA Astrophysics Data System (ADS)

Progressive failure from a circular hole in glass-fiber-reinforced plastics (GRP) under combined tension/torsion cyclic loading has been investigated. Thin-walled tubular specimens were used. The composition of the specimens was the same as in previous work. As pseudo-crack growth was observed under fatigue loading leading to the final failure, fracture mechanics methods were applied to characterize the fatigue failure process. The energy release rate was used as a parameter for progressive failure. Fatigue life under combined cyclic loading was estimated on the basis of the relationship between pseudo-crack-growth rate and energy release rate. The prediced S/N lines agree with the experimental results in all except a few cases.

Takemura, Kenichi; Fujii, Toru

426

Snubber assembly for turbine blades  

DOEpatents

A snubber associated with a rotatable turbine blade in a turbine engine, the turbine blade including a pressure sidewall and a suction sidewall opposed from the pressure wall. The snubber assembly includes a first snubber structure associated with the pressure sidewall of the turbine blade, a second snubber structure associated with the suction sidewall of the turbine blade, and a support structure. The support structure extends through the blade and is rigidly coupled at a first end portion thereof to the first snubber structure and at a second end portion thereof to the second snubber structure. Centrifugal loads exerted by the first and second snubber structures caused by rotation thereof during operation of the engine are at least partially transferred to the support structure, such that centrifugal loads exerted on the pressure and suctions sidewalls of the turbine blade by the first and second snubber structures are reduced.

Marra, John J

2013-09-03

427

Creep and fatigue research efforts on advanced materials  

SciTech Connect

Two of the more important materials problems encountered in turbine blades of aircraft engines are creep and fatigue. To withstand these high-temperature phenomena modern engines utilize single-crystal, nickel-based superalloys as the material of choice in critical applications. Recent research activities at Lewis on single-crystal blading material as well as future research initiatives on metal matrix composites related to creep and fatigue are discussed. The goal of these research efforts is improving the understanding of microstructure-property relationships and thereby guide material development.

Gayda, J.

1987-11-01

428

Fabrication of low-cost Mod-OA wood composite wind turbine blades  

NASA Astrophysics Data System (ADS)

The wood composite blades were fabricated by using epoxy resin-bonded laminates of Douglas fir veneers for the leading edge spar sections and honeycomb-cored birch plywood panels for the blade trailing edge or afterbody sections. The blade was joined to the wind turbine hub assembly by epoxy resin-bonded steel load take-off studs. The wood composite blades were installed in the Mod-OA wind turbine test facility at Kahuku, Hawaii. The wood composite blades have successfully completed high power (average of 150 kW) operations for an eighteen month period (nearly 8,000 hr) before replacement with another set of wood composite blades. The original set of blades was taken out of service because of the failure of the shank on one stud. An inspection of the blades at NASA-Lewis showed that the shank failure was caused by a high stress concentration at a corrosion pit on the shank fillet radius which resulted in fatigue stresses in excess of the endurance limit.

Lark, R. F.; Gougeon, M.; Thomas, G.; Zuteck, M.

1983-02-01

429

A study on fretting fatigue behaviors in 2024-T351 aluminum alloy  

Microsoft Academic Search

Fretting fatigue is an important fatigue failure mechanism in aircraft structures, such as mechanically fastened lap joint components. It is well known that multiple site fatigue cracking was originated from fretting damages especially in aging aircrafts and these premature crackings due to the fretting threaten aircraft safety which was certified by the damage tolerant fail safe concept. Fretting damages are

Kyung-Jung Hwang; Won-Ung Cho; Jung-Ho Kwon

2005-01-01

430

Development of the Smart Spring for Active Vibration Control of Helicopter Blades  

Microsoft Academic Search

Significant structural vibration is an undesirable characteristic in helicopter flight that leads to structural fatigue, poor ride quality for passengers and high acoustic signature for the vehicle. Previous Individual Blade Control (IBC) techniques based on piezoelectric actuator schemes to reduce these effects have been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an active tunable vibration absorber

C. Yong; D. G. Zimcik; V. K. Wickramasinghe; F. Nitzsche

2004-01-01

431

Axial-thrust responses due to a gas turbine's rotor blade distortions  

Microsoft Academic Search

The axial thrust imposed on the shaft of a gas turbine depends upon its rotor blade inlet inclination to the turbine's axial direction: this inclination can change due to the distortions resulting from fouling, aging, tip rubbing, erosion, thermal-fatigue cracks, and corrosion. Relevant influential parameters for an operational gas turbine were measured. Theoretical predictions for the behavior of the same

B. T. Lebele-Alawa

2010-01-01

432

Ceramic blade with tip seal  

DOEpatents

The present gas turbine engine includes a disc assembly defining a disc having a plurality of blades attached thereto. The disc has a preestablished rate of thermal expansion and the plurality of blades have a preestablished rate of thermal expansion being less than the preestablished rate of thermal expansion of the disc. A shroud assembly is attached to the gas turbine engine and is spaced from the plurality of blades a preestablished distance forming an interface there between. Positioned in the interface is a seal having a preestablished rate of thermal expansion being generally equal to the rate of thermal expansion of the plurality of blades. 4 figs.

Glezer, B.; Bhardwaj, N.K.; Jones, R.B.

1997-08-05

433

A shape adaptive airfoil for a wind turbine blade  

NASA Astrophysics Data System (ADS)

The loads on wind turbine components are primarily from the blades. It is important to control these blade loads in order to avoid damaging the wind turbine. Rotor control technology is currently limited to controlling the rotor speed and the pitch of the blades. As blades increase in length it becomes less desirable to pitch the entire blade as a single rigid body, but instead there is a requirement to control loads more precisely along the length of the blade. This can be achieved with aerodynamic control devices such as flaps. Morphing technologies are good candidates for wind turbine flaps because they have the potential to create structures that have the conflicting abilities of being load carrying, light-weight and shape adaptive. A morphing flap design with a highly anisotropic cellular structure is presented which is able to undergo large deflections and high strains without a large actuation penalty. An aeroelastic analysis couples the work done by aerodynamic loads on the flap, the flap strain energy and the required actuation work to change shape. The morphing flap is experimentally validated with a manufactured demonstrator and shown to have reduced actuation requirements compared to a conventional hinged flap.

Daynes, Stephen; Weaver, Paul M.

2011-03-01

434

Dynamically Reconfigurable Wind Turbine Blade Assembly.  

National Technical Information Service (NTIS)

A dynamically reconfigurable wind turbine blade assembly includes a plurality of reconfigurable blades mounted on a hub, an actuator fixed to each of the blades and adapted to effect the reconfiguration thereof, and an actuator power regulator for regulat...

C. H. Beauchamp S. A. Huyer S. J. Plunkett

2002-01-01

435

Fatigue behavior of 6063 aluminum alloy extrusions for wind-turbine applications  

SciTech Connect

The fatigue behavior of a 6063 aluminum alloy used in the Vertical Axis Wind Turbine (VAWT) blade extrusions was investigated under a variety of cyclic loading conditions and with different specimen geometries in order to examine the mechanisms of fatigue crack initiation and crack growth, and to provide fatigue data for use in life prediction models. The effect of open holes on fatigue crack initiation and crack growth, and on the S-N curves were investigated with plate bending. Fatigue life in plane bending was controlled by crack propagation. Hole preparation by drilling, or drilling and reaming were found to produce equivalent crack initiation behavior, and overall fatigue lives. Fatigue crack growth rates, including near-threshold behavior, were measured under LEFM conditions with compact tension specimens as a function of: heat treatment, crack plane orientation with respect to the extrusion direction, and R ratio. Low-cycle fatigue behavior and cyclic material properties were examined, and compared on the basis of material condition for extruded VAWT blade material, re-heat treated blade material and commercial 6063-T5 extruded rod. Low cyclic ductility values were observed in the extruded blade material.

Warren, A.S.

1990-01-01

436

Creep-fatigue interaction in aircraft gas turbine components by simulation and testing at scaled temperatures  

Microsoft Academic Search

Advanced gas turbine engines, which use hot section airfoil cooling, present a wide range of design problems. The frequencies of applied loads and the natural frequencies of the blade also are important since they have significant effects on failure of the component due to fatigue phenomenon. Due to high temperature environment the thermal creep and fatigue are quite severe. One-dimensional

Mohammad Hossein Sabour

2005-01-01

437

Development of a Fatigue-Life Methodology for Composite Structures Subjected to out-of-Plane Load Components.  

National Technical Information Service (NTIS)

The efforts to identify and implement a fatigue life methodology applicable to demonstrate delamination failures for use in certifying composite rotor blades are presented. The RSRA/X-Wing vehicle was a proof-of-concept stopped rotor aircraft configuratio...

M. Sumich K. T. Kedward

1991-01-01

438

Fatigue properties of 316 stainless steel and its failure due to internal cracks in low-cycle and extremely low-cycle fatigue regimes  

Microsoft Academic Search

It is important to know residual fatigue strength of materials in the extremely low-cycle fatigue (ELCF) regime in order to assess structural integrity after large cyclic strain caused by an earthquake. In the ELCF regime, it was pointed out that not only surface cracking but also additional bulk damage reduces the fatigue life. In this study, the fatigue strength of

Masayuki Kamaya

2010-01-01

439

Justification of the use of strain criteria for multicycle fatigue failure of metals. Communication 2. A new approach  

SciTech Connect

On the basis of analyzing available results for studying features of inelastic strain and fatigue damage of various materials the possibility is considered of determining the end of the stage of dispersed fatigue damage or fatigue crack generation from the overall accumulated inelastic strain, and also construction of the corresponding fatigue curve. An example is given for steel 45.

Matveev, V.V. [Institute of Strength Problems, Kiev (Russian Federation)

1995-11-01

440

SERI advanced wind turbine blades  

SciTech Connect

The primary goal of the Solar Energy Research Institute's (SERI) advanced wind turbine blades is to convert the kinetic energy in the wind into mechanical energy in an inexpensive and efficient manner. To accomplish this goal, advanced wind turbine blades have been developed by SERI that utilize unique airfoil technology. Performance characteristics of the advanced blades were verified through atmospheric testing on fixed-pitch, stall-regulated horizontal-axis wind turbines (HAWTs). Of the various wind turbine configurations, the stall-regulated HAWT dominates the market because of its simplicity and low cost. Results of the atmospheric tests show that the SERI advanced blades produce 10% to 30% more energy than conventional blades. 6 refs.

Tangler, J.; Smith, B.; Jager, D.

1992-02-01

441

SERI advanced wind turbine blades  

SciTech Connect

The primary goal of the Solar Energy Research Institute`s (SERI) advanced wind turbine blades is to convert the kinetic energy in the wind into mechanical energy in an inexpensive and efficient manner. To accomplish this goal, advanced wind turbine blades have been developed by SERI that utilize unique airfoil technology. Performance characteristics of the advanced blades were verified through atmospheric testing on fixed-pitch, stall-regulated horizontal-axis wind turbines (HAWTs). Of the various wind turbine configurations, the stall-regulated HAWT dominates the market because of its simplicity and low cost. Results of the atmospheric tests show that the SERI advanced blades produce 10% to 30% more energy than conventional blades. 6 refs.

Tangler, J.; Smith, B.; Jager, D.

1992-02-01

442

Measuring the performance of underplatform dampers for turbine blades by rotating laser Doppler Vibrometer  

NASA Astrophysics Data System (ADS)

Underplatform friction dampers are commonly used to control the vibration level of turbine blades in order to prevent high-cycle fatigue failures. Experimental validation of highly non-linear response predictions obtained from FEM bladed disk models incorporating underplatform dampers models has proved to be very difficult so as the assessment of the performance of a chosen design. In this paper, the effect of wedge-shaped underplatform dampers on the dynamics of a simple bladed disk under rotating conditions is measured and the effect of the excitation level on the UPDs performances is investigated at different number of the engine order excitation nearby resonance frequencies of the 1st blade bending modes of the system. The measurements are performed with an improved configuration of a rotating test rig, designed with a non-contact magnetic excitation and a non-contact rotating SLDV measurement system.

Zucca, S.; Di Maio, D.; Ewins, D. J.

2012-10-01

443

Fatigue life prediction of welded ship details  

Microsoft Academic Search

Ship structures are submitted to variable cyclic loading during navigation. The cyclic motion of waves induces variable and complex loadings in the structure, which could generate fatigue damage. Moreover, most of these metallic structures are welded assemblies. This technique generates local stress concentrations at the weld toe, which becomes a critical area regarding fatigue. In previous works, a methodology to

Carole Erny; David Thevenet; Jean-Yves Cognard; Manuel Körner

444

Modeling Thermal Fatigue in CPV Cell Assemblies  

Microsoft Academic Search

A finite-element (FEM) model has been created to quantify the thermal fatigue damage of the concentrating photovoltaic (CPV) die attach. Simulations are used to compare the results of empirical thermal fatigue equations that have originally been developed for accelerated chamber cycling. While the empirical equations show promise when extrapolated to the lower temperature cycles characteristic of weather-induced temperature changes in

Nick Bosco; Timothy J. Silverman; Sarah Kurtz

2011-01-01

445

CROSSWIND RESPONSE INDUCED FATIGUE OF SLENDER STRUCTURES  

Microsoft Academic Search

Gust-excited vibrations of slender structures can induce fatigue damage and cause structural failure under actions lower than design loads. The growing importance of the problem is coupled with an evident lack of simple calculation criteria. Working in this field, the authors of this paper have recently proposed a mathematical model of the fatigue behavior of slender structures subjected to gust-excited

M. P. Repetto; G. Solari

2000-01-01

446

Effect of Low Temperature on Fatigue Crack Formation and Microstructure-Scale Growth from Corrosion Damage in Al-Zn-Mg-Cu  

NASA Astrophysics Data System (ADS)

The strong effect of cold temperature on the fatigue resistance of 7075-T651 is established. As temperature decreases from 296 K to 183 K (23 °C to -90 °C), the formation life for cracking about pit and EXCO corrosion perimeters increases, microstructure scale crack growth rates decrease in the range from 20 to 500 ?m beyond the corrosion topography, and long crack growth rates similarly decline. Fatigue crack surface features correlate with reduced hydrogen embrittlement with decreasing temperature fed by localized H produced during precorrosion for pit and EXCO-proximate cracks, as well as by crack tip H produced by water vapor reaction during stressing for all crack sizes. The importance of the former H source increases with decreasing temperature for cracks sized below 200 ?m. Decreasing temperature to 223 K (-50 °C) eliminates the contribution of environmental H through interaction of reduced water vapor pressure in equilibrium with ice and reduced H diffusion. The Knudsen flow model and exposure parameter, P_{{{{H}}2 {{O}}}}/f , enables improved modeling of temperature dependent crack propagation, but does not fully describe low temperature fatigue behavior due to possible rate limitation by H diffusion. Further decreases in MSC da/dN to 183 K (-90 °C) are related to reduced mobility of the corrosion-precharged H which may associate with vacancies from dissolution. Crack formation, and growth rates correlate with either elastic stress intensity range or cyclic crack tip opening displacement, and are available to predict corrosion effects on airframe fatigue for the important low temperature regime.

Burns, James T.; Gangloff, Richard P.

2013-05-01

447

Extending the Fatigue Life of Riveted Coped Stringer Connections  

Microsoft Academic Search

Fatigue cracking occurs at the copes of stringer-floorbeam connections of older, riveted steel bridges. Some cracks are quite long and raise serious questions regarding the remaining fatigue life of the subject bridges. Damage limitation methods (DLMs) have been used to increase the fatigue life of these stringers, but the effectiveness of the DLMs for these riveted connections had never been

Charles W. Roeder; Gregory MacRae; Amy Leland

2005-01-01

448

Fatigue crack initatiin in high-purity titanium crystals  

Microsoft Academic Search

Fatigue crack initation has been studied in high-purity titanium monocrystals, bicrystals and polycrystals. Concerning persistent slip bands (PSBs), two fatigue damage modes were identified: holes and cavities along the bands, and microcracks perpendicular to the bands. The interactions of grain boundaries with slip bands or cyclic twins were observed to induce fatigue cracks. In addition to the twin-matrix interfaces, impinging

Tan Xiaoli; Gu Haicheng

1996-01-01

449

Prediction of residual fatigue life using nonlinear ultrasound  

Microsoft Academic Search

Prediction of fatigue life of components during service is an on-going and unsolved challenge for the NDT and structural health monitoring community. It has been demonstrated by a number of researchers that nonlinear guided waves or the acoustic nonlinear signature of fatigued cracked material provides clear signs of the progressive fatigue damage in the material, unlike linear guided waves. However,

Mikael Amura; Michele Meo

2012-01-01

450

Fatigue Resistance Criteria for Laminated Composite Structures.  

National Technical Information Service (NTIS)

This work investigated criteria for prevention of fatigue damage in metal matrix composite laminates. The approach was based on an earlier observation that, in as-fabricated unidirectional composites with elastic-brittle fibers and soft elastic-plastic ma...

G. J. Dvorak

1978-01-01

451

Modelling low-cycle fatigue life of particulate-reinforced metal-matrix composites  

Microsoft Academic Search

A low-cycle fatigue life prediction model for particulate-reinforced metal-matrix composites (MMCs) is presented. The low-cycle fatigue behaviour of particulate-reinforced MMCs is treated as a localised damage development phenomenon activated by applied cyclic loading. The localised cyclic stress and strain concentration and fatigue damage evolution of microstructural elements within the fatigue damaged zone ahead of the crack tip are considered to

H.-Z Ding; O Hartmann; H Biermann; H Mughrabi

2002-01-01

452

A zero torsional stiffness twist morphing blade as a wind turbine load alleviation device  

NASA Astrophysics Data System (ADS)

This paper presents the design, analysis and realization of a zero stiffness twist morphing wind turbine blade. The morphing blade is designed to actively twist as a means of alleviating the gust loads which reduce the fatigue life of wind turbine blades. The morphing structure exploits an elastic strain energy balance within the blade to enable large twisting deformations with modest actuation requirements. While twist is introduced using the warping of the blade skin, internal pre-stressed members ensure that a constant strain energy balance is achieved throughout the deformation, resulting in a zero torsional stiffness structure. The torsional stability of the morphing blade is characterized by analysing the elastic strain energy in the device. Analytical models of the skin, the pre-stressed components and the complete blade are compared to their respective finite element models as well as experimental results. The load alleviation potential of the adaptive structure is quantified using a two-dimensional steady flow aerodynamic model which is experimentally validated with wind tunnel measurements.

Lachenal, X.; Daynes, S.; Weaver, P. M.

2013-06-01

453

Multiple piece turbine blade  

SciTech Connect

A turbine rotor blade with a spar and shell construction, the spar including an internal cooling supply channel extending from an inlet end on a root section and ending near the tip end, and a plurality of external cooling channels formed on both side of the spar, where a middle external cooling channel is connected to the internal cooling supply channels through a row of holes located at a middle section of the channels. The spar and the shell are held together by hooks that define serpentine flow passages for the cooling air and include an upper serpentine flow circuit and a lower serpentine flow circuit. the serpentine flow circuits all discharge into a leading edge passage or a trailing edge passage.

Kimmel, Keith D (Jupiter, FL)

2012-05-29

454

Turbine blade cooling  

DOEpatents

A turbine rotor blade comprises a shank portion, a tip portion and an airfoil. The airfoil has a pressure side wall and a suction side wall that are interconnected by a plurality of partition sidewalls, defining an internal cooling passageway within the airfoil. The internal cooling passageway includes at least one radial outflow passageway to direct a cooling medium flow from the shank portion towards the tip portion and at least one radial inflow passageway to direct a cooling medium flow from the tip portion towards the shank portion. A number of mixing ribs are disposed on the partition sidewalls within the radial outflow passageways so as to enhance the thermal mixing of the cooling medium flow, thereby producing improved heat transfer over a broad range of the Buoyancy number. 13 figs.

Staub, F.W.; Willett, F.T.

1999-07-20

455

Cam assisted blade folding system  

SciTech Connect

In a rotor system of a helicopter including a rotor hub, at least two pitch housings mounted to the rotor hub and a rotor blade attached to each pitch housing, each rotor blade including a blade spar, the attachment of the rotor blade to the pitch housing defining a vertical pin lag hinge axis, a blade folding system, is described comprising: a lead-lag damper mounted to the rotor blade-spar, centered at the vertical pin lag hinge axis and extending partly about the vertical pin lag hinge axis; an actuator mounted to the pitch housing; a lead-lag damper linkage assembly connected to the actuator, the pitch housing and the lead-lag damper; a pitch lock pin connected to the actuator and engageable with the rotor hub; and a cam pivotably mounted to the pitch housing for sequential engagement with the actuator and the lead-lag damper. The rotor blade is folded by actuation of the actuator to engage the pitch lock pin with the rotor hub, by initiating displacement of the lead-lag damper linkage assembly in the direction of the actuator and by initiating the sequential engagement of the cam with the actuator and the lead-lag damper.

Cavanaugh, T.J.

1988-04-19

456

A two parameter driving force for fatigue crack growth analysis  

Microsoft Academic Search

A model for fatigue crack growth (FCG) analysis based on the elastic–plastic crack tip stress–strain history was proposed. The fatigue crack growth was predicted by simulating the stress–strain response in the material volume adjacent to the crack tip and estimating the accumulated fatigue damage. The fatigue crack growth was regarded as a process of successive crack re-initiation in the crack

A. H. Noroozi; G. Glinka; S. Lambert

2005-01-01

457

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

Microsoft Academic Search

A life prediction model is developed for crack nucleation and early crack growth based on fatigue, environment (oxidation),\\u000a and creep damage. The model handles different strain-temperature phasings(i.e., in-phase and out-of-phase thermomechanical fatigue, isothermal fatigue, and others, including nonproportional phasings).\\u000a Fatigue life predictions compare favorably with experiments in 1070 steel for a wide range of test conditions and strain-temperature\\u000a phasings. An

R. W. Neu; Huseyin Sehitoglu

1989-01-01

458

Apparatus for loading a band saw blade  

DOEpatents

A band saw blade is loaded between pairs of guide wheels upon tensioning the blade by guiding the blade between pairs of spaced guide plates which define converging slots that converge toward the guide wheels. The approach is particularly useful in loading blades on underwater band saw machines used to cut radioactive materials.

Reeves, Steven R. (49 Williams Ave., West Valley, NY 14171)

1990-01-01

459

Aerodynamic tests of Darrieus wind turbine blades  

Microsoft Academic Search

An indoor facility for the aerodynamic testing of Darrieus turbine blades was developed. Lift, drag, and moment coefficients were measured for