These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Mitigation of FOD and Corrosion Fatigue Damage in 17-4 PH Stainless Steel Compressor Blades with Surface Treatment  

Microsoft Academic Search

Compressor blades of a military aircraft turbine engine made of 17 -4 PH stainless steel have been reported to have blade edge foreign object damage (FOD), corrosion pitting, and erosion damage that reduce fatigue life. This paper reports the findings of a comprehensive investigation of the effect of residual compressive stresses, imparted by various surface treatments, to improve leading edge

Paul S. Prevéy; N. Jayaraman; Ravi Ravindranath

2

Research on fatigue damage detection for wind turbine blade based on high-spatial-resolution DPP-BOTDA  

NASA Astrophysics Data System (ADS)

In this paper, a fatigue damage detection system used for wind turbine blade is successfully developed by using highspatial- resolution differential pulse-width pair Brillouin optical time-domain analysis (DPP-BOTDA) sensing system. A piece of polarization-maintaining optical fiber is bonded on the blade surface to form the distributed sensing network. A DPP-BOTDA system, with a spatial resolution of 20cm and sampling interval of 1cm, is adopted to measuring distributed strain and detecting fatigue damage of wind turbine blade during fatigue test using the differential pulse pair of 39.5ns/41.5ns. Strain and the Brillouin gain spectra changes from undamaged state to fatigue failure are experimentally presented. The experimental results reveal that fatigue damage changes the strain distribution especially around the high strain area, and the width, amplitude and central frequency of the Brillouin gain spectra are sensitive to fatigue damage as the stiffness degradation and accumulated cracks change local strain gradient. As the damage becomes larger, the width of the Brillouin gain spectra becomes broader. Consequently, location and size of fatigue damage could be estimated. The developed system shows its potentiality for developing highly reliable wind turbine monitoring system as the effectiveness of damage detection and distributed sensing.

Xu, Jinlong; Dong, Yongkang; Li, Hui

2014-03-01

3

Damage tolerance based life prediction in gas turbine engine blades under vibratory high cycle fatigue  

SciTech Connect

A novel fracture mechanics approach has been used to predict crack propagation lives in gas turbine engine blades subjected to vibratory high cycle fatigue (HCF). The vibratory loading included both a resonant mode and a nonresonant mode, with one blade subjected to only the nonresonant mode and another blade to both modes. A life prediction algorithm was utilized to predict HCF propagation lives for each case. The life prediction system incorporates a boundary integral element (BIE) derived hybrid stress intensity solution, which accounts for the transition from a surface crack to corner crack to edge crack. It also includes a derivation of threshold crack length from threshold stress intensity factors to give crack size limits for no propagation. The stress intensity solution was calibrated for crack aspect ratios measured directly from the fracture surfaces. The model demonstrates the ability to correlate predicted missions to failure with values deduced from fractographic analysis. This analysis helps to validate the use of fracture mechanics approaches for assessing damage tolerance in gas turbine engine components subjected to combined steady and vibratory stresses.

Walls, D.P.; deLaneuville, R.E.; Cunningham, S.E. [United Technologies Pratt and Whitney, West Palm Beach, FL (United States)

1997-01-01

4

Fatigue analysis and testing of wind turbine blades  

NASA Astrophysics Data System (ADS)

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

Greaves, Peter Robert

5

Fatigue of Wind Blade Laminates:Fatigue of Wind Blade Laminates: Effects of Resin and Fabric Structure  

E-print Network

Fatigue of Wind Blade Laminates:Fatigue of Wind Blade Laminates: Effects of Resin and Fabric University MCARE 2012 #12;Outline · Overview of MSU Fatigue Program on Wind Blade MaterialsWind Blade for Infused Laminates · Comparison of Fatigue Trends for Various· Comparison of Fatigue Trends for Various

6

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

7

Damage and fatigue Continuum damage mechanics modeling  

E-print Network

Damage and fatigue Continuum damage mechanics modeling for fatigue of materials and structures Cachan Cedex, France desmorat@lmt.ens-cachan.fr ABSTRACT. Application of damage mechanics to fatigue is addressed in the present paper. The ability of Lemaitre's damage law to describe low and high cycle fatigue

8

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

9

Probabilistic Evaluation of Blade Impact Damage  

NASA Technical Reports Server (NTRS)

The response to high velocity impact of a composite blade is probabilistically evaluated. The evaluation is focused on quantifying probabilistically the effects of uncertainties (scatter) in the variables that describe the impact, the blade make-up (geometry and material), the blade response (displacements, strains, stresses, frequencies), the blade residual strength after impact, and the blade damage tolerance. The results of probabilistic evaluations results are in terms of probability cumulative distribution functions and probabilistic sensitivities. Results show that the blade has relatively low damage tolerance at 0.999 probability of structural failure and substantial at 0.01 probability.

Chamis, C. C.; Abumeri, G. H.

2003-01-01

10

A simple method of estimating wind turbine blade fatigue at potential wind turbine sites  

SciTech Connect

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 which may be obtained as part of a routine site characterization study. By using the model to simulate a time series of the root flap bending moment, fatigue damage rates may be estimated. The technique is evaluated by comparing these estimates with damage estimates derived from actual bending moment data; the agreement between the two is quite good. The simple connection between wind measurements and fatigue provided by the model now allows one to readily discriminate between damaging and more benign wind environments.

Barnard, J.C.; Wendell, L.L.

1995-06-01

11

Probabilistic Fatigue Damage Program (FATIG)  

NASA Technical Reports Server (NTRS)

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

Michalopoulos, Constantine

2012-01-01

12

Fatigue and creep-fatigue damage of  

NASA Astrophysics Data System (ADS)

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 (600 °C). 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 pure fatigue at 600 °C, the classical crack initiation stage I 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 (Fe2O3) and internal ((FeCr)3O4) 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 creep-fatigue 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, which accounts very well for the situations in which crack initiation and crack propagation are coplanar, 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.; Pineau, A.

1993-10-01

13

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

14

Structural fatigue test results for large wind turbine blade sections  

NASA Technical Reports Server (NTRS)

In order to provide quantitative information on the operating life capabilities of wind turbine rotor blade concepts for root-end load transfer, a series of cantilever beam fatigue tests was conducted. Fatigue tests were conducted on a laminated wood blade with bonded steel studs, a low cost steel spar (utility pole) with a welded flange, a utility pole with additional root-end thickness provided by a swaged collar, fiberglass spars with both bonded and nonbonded fittings, and, finally, an aluminum blade with a bolted steel fitting (Lockheed Mod-0 blade). Photographs, data, and conclusions for each of these tests are presented. In addition, the aluminum blade test results are compared to field failure information; these results provide evidence that the cantilever beam type of fatigue test is a satisfactory method for obtaining qualitative data on blade life expectancy and for identifying structurally underdesigned areas (hot spots).

Faddoul, J. R.; Sullivan, T. L.

1982-01-01

15

Loading Analysis of Composite Wind Turbine Blade for Fatigue Life Prediction of Adhesively Bonded Root Joint  

NASA Astrophysics Data System (ADS)

Nowadays wind energy is widely used as a non-polluting cost-effective renewable energy resource. During the lifetime of a composite wind turbine which is about 20 years, the rotor blades are subjected to different cyclic loads such as aerodynamics, centrifugal and gravitational forces. These loading conditions, cause to fatigue failure of the blade at the adhesively bonded root joint, where the highest bending moments will occur and consequently, is the most critical zone of the blade. So it is important to estimate the fatigue life of the root joint. The cohesive zone model is one of the best methods for prediction of initiation and propagation of debonding at the root joint. The advantage of this method is the possibility of modeling the debonding without any requirement to the remeshing. However in order to use this approach, it is necessary to analyze the cyclic loading condition at the root joint. For this purpose after implementing a cohesive interface element in the Ansys finite element software, one blade of a horizontal axis wind turbine with 46 m rotor diameter was modelled in full scale. Then after applying loads on the blade under different condition of the blade in a full rotation, the critical condition of the blade is obtained based on the delamination index and also the load ratio on the root joint in fatigue cycles is calculated. These data are the inputs for fatigue damage growth analysis of the root joint by using CZM approach that will be investigated in future work.

Salimi-Majd, Davood; Azimzadeh, Vahid; Mohammadi, Bijan

2014-07-01

16

Fatigue damage mapping  

NASA Technical Reports Server (NTRS)

Observations of fatigue crack nucleation and early growth are presented. The state of stress/strain was shown to play a significant role in this process. Early growth occurs on planes experiencing the largest range of shear strain (Mode 2) or normal strain (Mode 1) depending on the stress state, strain amplitude, and microstructure. These observations were summarized in a fatigue map for each material. These maps provide regions where one fatigue failure mode dominates the behavior. Each failure mechanism results in a different failure mode. Once the expected failure mode is identified, bulk deformation models based on the cyclic stresses and strains can be used to obtain reliable estimates of fatigue lives for complex loading situations.

Socie, Darrell

1988-01-01

17

Analysis of aeroelastic loads and their contributions to fatigue damage  

NASA Astrophysics Data System (ADS)

The paper presents an analysis of the aeroelastic loads on a wind turbine in normal operation. The characteristic of the loads causing the highest fatigue damage are identified, so to provide indications to the development of active load alleviation systems for smart- rotor applications. Fatigue analysis is performed using rain-flow counting and Palmgren-Miner linear damage assumption; the contribution to life-time fatigue damage from deterministic load variations is quantified, as well as the contributions from operation at different mean wind speeds. A method is proposed to retrieve an estimation of the load frequencies yielding the highest fatigue contributions from the bending moment spectra. The results are in good agreement with rain-flow counting analysis on filtered time series, and, for the blade loads, show dominant contributions from frequencies close to the rotational one; negligible fatigue contributions are reported for loads with frequencies above 2 Hz.

Bergami, L.; Gaunaa, M.

2014-12-01

18

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.

2012-04-01

19

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

20

Widespread Fatigue Damage Assessment Approach  

Microsoft Academic Search

A methodology to assess the development of widespread fatigue damage (WFD) and its effect on the residual strength of aircraft structure has been developed. The three major components of the methodology are crack initiation, crack growth and linkup, and residual strength. The crack initiation methodology uses experimentally generated equivalent initial flaw size (EIFS) data and an analytical closure model to

Paul W. Tan; Catherine A. Bigelow; John G. Bakuckas

21

Fatigue Failure Analysis of Small Wooden Wind Turbine Blade  

E-print Network

Advances in engineering technology in recent years have brought demands for reliable wind turbine blade which can operate at different climatic condition and speeds. When failures occur they are expensive, not only in terms of the cost of replacement or repair, but also the costs associated with the down-time of the system of which they are part. Reliability is thus a critical economic factor and for designers to produce wind turbine blade with a high reliability they need to be able to accurately predict the stresses experienced by the different load condition. A wooden 1.5m wind turbine blade was tested by means of a mechanically operated test rig for fatigue failure. The rig uses a crank eccentric mechanism by variable load for each load cycle. The stress distribution in fatigue critical areas of the blade during testing was found to be similar to the expected stress distribution under normal operational condition

Maldhure S. S; Dr. Kharde Y. R

22

Fatigue Failure of Space Shuttle Main Engine Turbine Blades  

NASA Technical Reports Server (NTRS)

Experimental validation of finite element modeling of single crystal turbine blades is presented. Experimental results from uniaxial high cycle fatigue (HCF) test specimens and full scale Space Shuttle Main Engine test firings with the High Pressure Fuel Turbopump Alternate Turbopump (HPFTP/AT) provide the data used for the validation. The conclusions show the significant contribution of the crystal orientation within the blade on the resulting life of the component, that the analysis can predict this variation, and that experimental testing demonstrates it.

Swanson, Gregrory R.; Arakere, Nagaraj K.

2000-01-01

23

Structural damage identification in wind turbine blades using piezoelectric active sensing with ultrasonic validation  

SciTech Connect

This paper gives a brief overview of a new project at LANL in structural damage identification for wind turbines. This project makes use of modeling capabilities and sensing technology to understand realistic blade loading on large turbine blades, with the goal of developing the technology needed to automatically detect early damage. Several structural health monitoring (SHM) techniques using piezoelectric active materials are being investigated for the development of wireless, low power sensors that interrogate sections of the wind turbine blade using Lamb wave propagation data, frequency response functions (FRFs), and time-series analysis methods. The modeling and sensor research will be compared with extensive experimental testing, including wind tunnel experiments, load and fatigue tests, and ultrasonic scans - on small- to mid-scale turbine blades. Furthermore, this study will investigate the effect of local damage on the global response of the blade by monitoring low-frequency response changes.

Claytor, Thomas N [Los Alamos National Laboratory; Ammerman, Curtt N [Los Alamos National Laboratory; Park, Gyu Hae [Los Alamos National Laboratory; Farinholt, Kevin M [Los Alamos National Laboratory; Farrar, Charles R [Los Alamos National Laboratory; Atterbury, Marie K [Los Alamos National Laboratory

2010-01-01

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

High-cycle fatigue design evolution and experience of free-standing combustion turbine blades  

Microsoft Academic Search

This paper presents the evolution of the combustion turbine blade high cycle fatigue design criteria for free-standing blades. It also presents the analysis and corrective actions taken to resolve several unique combustion turbine blade fatigue problems, all encountered over a 35-year period. Included are high-cycle fatigue problems due to cooling air leakage, seal pin friction, and combustion temperature maldistribution, as

A. J. Scalzo

1992-01-01

26

Fatigue failure analysis of holding U-bolts of a cooling fan blade  

Microsoft Academic Search

Fatigue failure of holding U-bolt of a cooling fan blade is analyzed. Fractography of the fracture surface reveals the characteristics of a fatigue fracture. Finite element modeling is used for stress analyzing. Analysis of the loading conditions indicates that the bolts are under multiaxial fatigue. Effective alternating and mean stresses are obtained based on the multiaxial fatigue criteria. By using

M. Reihanian; K. Sherafatnia; M. Sajjadnejad

2011-01-01

27

Novelty detection applied to vibration data from a CX-100 wind turbine blade under fatigue loading  

NASA Astrophysics Data System (ADS)

The remarkable evolution of new generation wind turbines has led to a dramatic increase of wind turbine blade size. In turn, a reliable structural health monitoring (SHM) system will be a key factor for the successful implementation of such systems. Detection of damage at an early stage is a crucial issue as blade failure would be a catastrophic result for the entire wind turbine. In this study the SHM analysis will be based on experimental measurements of Frequency Response Functions (FRFs) extracted by using an input/output acquisition technique under a fatigue loading of a 9m CX-100 blade at the National Renewable Energy Laboratory (NREL) and National Wind Technology Center (NWTC) performed in the Los Alamos National Laboratory. The blade was harmonically excited at its first natural frequency using a Universal Resonant Excitation (UREX) system. For analysis, the Auto-Associative Neural Network (AANN) is a non-parametric method where a set of damage sensitive features gathered from the measured structure are used to train a network that acts as a novelty detector. This traditionally has a highly complex "bottleneck" structure with five layers in the AANN. In the current paper, a new attempt is also exploited based on an AANN with one hidden layer in order to reduce the theoretical and computational difficulties. Damage detection of composite bodies of blades is a "grand challenge" due to varying aerodynamic and gravitational loads and environmental conditions. A study of the noise tolerant capability of the AANN which is associated to its generalisation capacity is addressed. It will be shown that vibration response data combined with AANNs is a robust and powerful tool, offering novelty detection even when operational and environmental variations are present. The AANN is a method which has not yet been widely used in the structural health monitoring of composite blades.

Dervilis, N.; Choi, M.; Antoniadou, I.; Farinholt, K. M.; Taylor, S. G.; Barthorpe, R. J.; Park, G.; Worden, K.; Farrar, C. R.

2012-08-01

28

Blade reliability collaborative : collection of defect, damage and repair data.  

SciTech Connect

The Blade Reliability Collaborative (BRC) was started by the Wind Energy Technologies Department of Sandia National Laboratories and DOE in 2010 with the goal of gaining insight into planned and unplanned O&M issues associated with wind turbine blades. A significant part of BRC is the Blade Defect, Damage and Repair Survey task, which will gather data from blade manufacturers, service companies, operators and prior studies to determine details about the largest sources of blade unreliability. This report summarizes the initial findings from this work.

Ashwill, Thomas D.; Ogilvie, Alistair B.; Paquette, Joshua A.

2013-04-01

29

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

30

Effects of Glass Fabric and Laminate Construction on the Fatigue of Resin Infused Blade Materials  

E-print Network

Effects of Glass Fabric and Laminate Construction on the Fatigue of Resin Infused Blade Materials are presented for infusion molded laminates, providing a comparison of several commercial E-glass reinforcing reinforcing fabrics used in blade infusion processes. II. Background The fatigue behavior of laminates based

31

The relationship between observed fatigue damage and life estimation models  

NASA Technical Reports Server (NTRS)

Observations of the surface of laboratory specimens subjected to axial and torsional fatigue loadings has resulted in the identification of three damage fatigue phenomena: crack nucleation, shear crack growth, and tensile crack growth. Material, microstructure, state of stress/strain, and loading amplitude all influence which of the three types of fatigue damage occurs during a dominant fatigue life fraction. Fatigue damage maps are employed to summarize the experimental observations. Appropriate bulk stress/strain damage parameters are suggested to model fatigue damage for the dominant fatigue life fraction. Extension of the damage map concept to more complex loadings is presented.

Kurath, Peter; Socie, Darrell F.

1988-01-01

32

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

33

Damage detection in turbine wind blades by vibration based methods  

NASA Astrophysics Data System (ADS)

The paper describes results of numerical simulation for damage localization in the composite coat of a wind turbine blade using modal parameters and a modern damage detection method (wavelet transform). The presented results were obtained in the first period of research on the diagnostic method, which is aimed at detecting damage in the blades of large wind turbines during normal operation. A blade-modelling process including the geometry, loads and failures has been introduced in the paper. A series of simulations has been carried out for different localizations and size of damage for finding the method's limits. To verify the results of numeric simulations a subscale blade has been built which has geometric features and mechanical properties similar to the computer model.

Doli?ski, L.; Krawczuk, M.

2009-08-01

34

Mixed Mode Static and Fatigue Crack Growth in Wind Blade Paste Adhesives  

E-print Network

several mm thick. Blades are subjected to high cycle fatigue conditions under complex loading in service performance must be predictable under the broad range of static and fatigue loading conditions experienced. Test results are presented for static and fatigue crack growth rates, the latter under tension

35

Combined wind turbine fatigue and ultimate load reduction by individual blade control  

NASA Astrophysics Data System (ADS)

If each blade of the wind turbine has individual pitch actuator, there is possibility of employing the pitch system to mitigate structural loads through advanced control methods. Previously, considerable reduction of blade lifetime equivalent fatigue loads has been achieved by Individual Blade Control (IBC) and in addition, it has also been shown the potential in blade ultimate loads reduction. However, both fatigue and ultimate loads impact on the design and life of wind turbine blades. In this paper, the design and application of IBC that concurrently reduce both blade fatigue and ultimate loads is investigated. The contributions of blade load spectral components, which are 1P, 2P and edgewise mode from blade in-plane and/or out-of-plane bending moments, are firstly explored. Four different control options for reducing various combinations of these load components are compared. In response to the different spectral peaks of both fatigue and ultimate loads, the controller has been designed so that it can act on different frequency components which vary with wind speed. The performance of the IBC controller on fatigue and ultimate load reduction is assessed by simulating a 5MW exemplar wind turbine. Simulation results show that with a proper selection of controlling inputs at different wind speed, the use of a single combined IBC can achieve satisfactory reduction on both fatigue and ultimate loads.

Han, Y.; Leithead, W. E.

2014-06-01

36

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.

2011-04-01

37

Brittleness Effect on Rock Fatigue Damage Evolution  

NASA Astrophysics Data System (ADS)

The damage evolution mechanism of rocks is one of the most important aspects in studying of rock fatigue behavior. Fatigue damage evolution of three rock types (onyx marble, sandstone and soft limestone) with different brittleness were considered in the present study. Intensive experimental tests were conducted on the chosen rock samples and acoustic emission (AE) sensors were used in some of them to monitor the fracturing process. Experimental tests indicated that brittleness strongly influences damage evolution of rocks in the course of static and dynamic loading. AE monitoring revealed that micro-crack density induced by the applied loads during different stages of the failure processes increases as rock brittleness increases. Also, results of fatigue tests on the three rock types indicated that the rock with the most induced micro-cracks during loading cycles has the least fatigue life. Furthermore, the condition of failure surfaces of the studied rocks samples, subjected to dynamic and static loading, were evaluated and it was concluded that the roughness of failure surfaces is influenced by loading types and rock brittleness. Dynamic failure surfaces were rougher than static ones and low brittle rock demonstrate a smoother failure surface compared to high brittle rock.

Nejati, Hamid Reza; Ghazvinian, Abdolhadi

2014-09-01

38

Fatigue life variability and reliability analysis of a wind turbine blade  

NASA Astrophysics Data System (ADS)

Wind turbines must withstand harsh environments that induce many stress cycles into their components. A numerical analysis package is used to illustrate the sobering variability in predicted fatigue life with relatively small changes in inputs. The variability of the input parameters is modeled to obtain estimates of the fatigue reliability of the turbine blades.

Veers, P. S.; Sutherland, H. J.; Ashwill, T. D.

39

Use of the WEST-1 wind turbine simulator to predict blade fatigue load distribution  

NASA Technical Reports Server (NTRS)

To test the ability of WEST-1 to predict blade fatigue load distribution, actual wind signals were fed into the simulator and the response data were recorded and processed in the same manner as actual wind turbine data. The WEST-1 simulator was operated in a stable, unattended mode for six hours. The probability distribution of the cyclic flatwise bending moment for the blade was comparable to that for an actual wind turbine in winds with low turbulence. The input from a stationary anemometer was found to be inadequate for use in the prediction of fatigue load distribution for blade design purposes and modifications are necessary.

Janetzke, D. C.

1983-01-01

40

CHARACTERIZATION OF A MOBILE OSCILLATORY FATIGUE OPERATOR FOR WIND TURBINE BLADE TESTING  

SciTech Connect

Laboratory testing of wind turbine blades is required to meet wind turbine design standards, reduce machine cost, and reduce the technical and fi nancial risks of deploying mass-produced wind turbine models. Fatigue testing at the National Wind Technology Center (NWTC) is currently conducted using Universal Resonance Excitation (UREX) technology. In a UREX test, the blade is mounted to a rigid stand and hydraulic exciters mounted to the blade are used to excite the blade to its resonant frequency. A drawback to UREX technology is that mounting hydraulic systems to the blade is diffi cult and requires a relatively long set-up period. An alternative testing technology called the Mobile Oscillatory Fatigue Operator (MOFO) has been analyzed. The MOFO uses an oscillating blade test-stand rather than a rigid stand, avoiding the need to place hydraulic systems on the blade. The MOFO will be demonstrated by converting an existing test-stand at the NWTC to an oscillating stand that can test blades up to 25 m in length. To obtain the loads necessary to design the MOFO, the system motion is modeled using rigid body and lumped mass dynamics models. Preliminary modeling indicates the existing stand can be converted to a MOFO relatively easily. However, the blade dynamic models suggest that blade bending moment distributions are signifi cantly different for UREX and MOFO testing; more sophisticated models are required to assess the implication of this difference on the accuracy of the test.

Donohoo, P.E.; Cotrell, J.

2008-01-01

41

Blade fatigue life assessment with application to VAWTs  

NASA Astrophysics Data System (ADS)

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 the stress levels at each wind speed. Miner's cumulative damage rule is examined as a tool to generate a vibratory stress level distribution in terms of peak vibrations in a narrow-band Gaussian process. Examples are given for 30-40 sec intervals on the 17 m VAWT at Sandia Laboratories. A threshold was set beneath which no vibrations were recorded, yielding a Rayleigh distribution at the 0.5 significance level. It is concluded that a Rayleigh distribution from test data produces a cycle to failure versus wind speed curve which is superior to constant amplitude fatigue life data such as appropriate to Miner's Rule.

Veers, P. S.

1982-05-01

42

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.

2012-04-01

43

Modeling Fatigue Damage in Long-Fiber Thermoplastics  

Microsoft Academic Search

This paper applies a fatigue damage model recently developed for injection-molded long-fiber thermoplastics (LFTs) to predict the modulus reduction and fatigue lifetime of glass\\/polyamide 6,6 (PA6,6) specimens. The fatigue model uses a multiscale mechanistic approach to describe fatigue damage accumulation in these materials subjected to cyclic loading. Micromechanical modeling using a modified Eshelby-Mori-Tanaka approach combined with averaging techniques for fiber

Ba Nghiep Nguyen; Vlastimil Kunc; Satish K. Bapanapalli

2009-01-01

44

Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys  

NASA Technical Reports Server (NTRS)

High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine engines is a pervasive problem affecting a wide range of components and materials. HCF is currently the primary cause of component failures in gas turbine aircraft engines. Turbine blades in high performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys. Single-crystal Nickel-base superalloys were developed to provide superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys previously used in the production of turbine blades and vanes. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. PWA1493, identical to PWA1480, but with tighter chemical constituent control, is used in the NASA SSME (Space Shuttle Main Engine) alternate turbopump, a liquid hydrogen fueled rocket engine. Objectives for this paper are motivated by the need for developing failure criteria and fatigue life evaluation procedures for high temperature single crystal components, using available fatigue data and finite element modeling of turbine blades. Using the FE (finite element) stress analysis results and the fatigue life relations developed, the effect of variation of primary and secondary crystal orientations on life is determined, at critical blade locations. The most advantageous crystal orientation for a given blade design is determined. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to optimize blade design by increasing its resistance to fatigue crack growth without adding additional weight or cost.

Arakere, Nagaraj K.; Swanson, Gregory R.

2000-01-01

45

Reliability evaluation of chloride diffusion in fatigue damaged concrete  

Microsoft Academic Search

Chloride diffusion is widely used to evaluate the durability of concrete structures. For civil concrete structures, millions of cycles of repeated loads are expected during their intended life. Those fatigue loads may lead to progressive damage of concrete. The objective of this paper is to study the time-variant reliability of chloride diffusion in fatigue damaged concrete structures through integrating damage

Tianyu Xiang; Renda Zhao

2007-01-01

46

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

47

Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys  

NASA Technical Reports Server (NTRS)

High cycle fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Single crystal nickel turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493, PWA 1484, RENE' N-5 and CMSX-4. These alloys play an important role in commercial, military and space propulsion systems. Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades are complicated to predict due to the material orthotropy and variations in crystal orientations. Fatigue life estimation of single crystal turbine blades represents an important aspect of durability assessment. It is therefore of practical interest to develop effective fatigue failure criteria for single crystal nickel alloys and to investigate the effects of variation of primary and secondary crystal orientation on fatigue life. A fatigue failure criterion based on the maximum shear stress amplitude /Delta(sub tau)(sub max))] on the 24 octahedral and 6 cube slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criterion reduces the scatter in uniaxial LCF test data considerably for PWA 1493 at 1200 F in air. Additionally, single crystal turbine blades used in the alternate advanced high-pressure fuel turbopump (AHPFTP/AT) are modeled using a large-scale three-dimensional finite element model. This finite element model is capable of accounting for material orthotrophy and variation in primary and secondary crystal orientation. Effects of variation in crystal orientation on blade stress response are studied based on 297 finite element model runs. Fatigue lives at critical points in the blade are computed using finite element stress results and the failure criterion developed. Stress analysis results in the blade attachment region are also presented. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to significantly increase a component S resistance to fatigue crack growth with- out adding additional weight or cost. [DOI: 10.1115/1.1413767

Arakere, N. K.; Swanson, G.

2002-01-01

48

Implementation of a Biaxial Resonant Fatigue Test Method on a Large Wind Turbine Blade  

SciTech Connect

A biaxial resonant test method was utilized to simultaneously fatigue test a wind turbine blade in the flap and edge (lead-lag) direction. Biaxial resonant blade fatigue testing is an accelerated life test method utilizing oscillating masses on the blade; each mass is independently oscillated at the respective flap and edge blade resonant frequency. The flap and edge resonant frequency were not controlled, nor were they constant for this demonstrated test method. This biaxial resonant test method presented surmountable challenges in test setup simulation, control and data processing. Biaxial resonant testing has the potential to complete test projects faster than single-axis testing. The load modulation during a biaxial resonant test may necessitate periodic load application above targets or higher applied test cycles.

Snowberg, D.; Dana, S.; Hughes, S.; Berling, P.

2014-09-01

49

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

50

Modeling Fatigue Damage in Long-Fiber Thermoplastics  

SciTech Connect

This paper applies a fatigue damage model recently developed for injection-molded long-fiber thermoplastics (LFTs) to predict the modulus reduction and fatigue lifetime of glass/polyamide 6,6 (PA6,6) specimens. The fatigue model uses a multiscale mechanistic approach to describe fatigue damage accumulation in these materials subjected to cyclic loading. Micromechanical modeling using a modified Eshelby-Mori-Tanaka approach combined with averaging techniques for fiber length and orientation distributions is performed to establish the stiffness reduction relation for the composite as a function of the microcrack volume fraction. Next, continuum damage mechanics and a thermodynamic formulation are used to derive the constitutive relations and the damage evolution law. The fatigue damage model has been implemented in the ABAQUS finite element code and has been applied to analyze fatigue of the studied glass/PA6,6 specimens. The predictions agree well with the experimental results.

Nguyen, Ba Nghiep; Kunc, Vlastimil; Bapanapalli, Satish K.

2009-10-30

51

FATIGUE LIFE AND RESIDUAL STRESSES IN COLD ROLLED PROPELLER BLADES  

Microsoft Academic Search

This paper introduces a quantitative concept developed jointly by WR-ALC, the FAA, and the Technology for Energy Corporation to ensure the structural integrity of aluminum alloy propeller blades used on numerous military and civil aircraft. The propeller assembly of a turboprop engine is a highly energetic rotating assembly--that a catastrophic, single point failure in a propeller blade can cause catastrophic

T. Yentzer; B. Stillman; M. Fisher; B. Pardue; TN D. Krafsur; Knoxville TN T. Khaled

52

Fatigue Damage Evolution in Silicon Films for Micromechanical Applications  

E-print Network

"! \\' Fatigue Damage Evolution in Silicon Films for Micromechanical Applications by P. Shrotriya, S microelectromechanical systems (MEMS) structures. The surface topography evolu- tion that occurs during cyclic fatigue and Si layers. Finally, the implications of the results are discussed for the prediction of fatigue

Suo, Zhigang

53

Reexamination of Cumulative Fatigue Damage Laws  

NASA Technical Reports Server (NTRS)

Treatment of accumulated fatigue damage in materials and structures subjected to a history of nonsimple repetitive loadings has received a large amount of attention in recent years. A method used for the treatment of complex loading is known as linear damage rule. It was recognized that, this method could result in unconservative predictions of material and structural behavior. An intense flurry of activity followed in the pursuit of alternative methods of analysis that would predict behavior more accurately. So many methods were introduced that it became necessary periodically to prepare review papers placing all the new methods into perspective. The current integrated view regarding the state of the art as it applies to this effort is discussed. The more recently proposed cumulative damage life prediction methods are reviewed. The double linear damage rule (DLDR), which has evolved over the past 20 years, is reexamined with the intent of improving its accuracy and applicability to engineering problems. Modifications are introduced to the analytical formulation to achieve greater compatibility between the DLDR and the so-called damage curve approach, which is an alternative continuous representation of the DLDR.

Halford, G. R.; Manson, S. S.

1985-01-01

54

Aspect of cumulative fatigue damage under multiaxial strain cycling.  

NASA Technical Reports Server (NTRS)

The concept of order of loading and its effect on cumulative fatigue damage under multiaxial strain cyclings was investigated. The effect is illustrated through nonlinear relationships between biaxial fatigue damage and cycle-ratio diagrams. Uniaxial theories such as Miner's method, the convergence method, and the double linear damage rule in its special and generalized form, were examined and extended to the biaxial case through the octahedral shear strain theory. The generalized double linear damage rule was found more applicable to biaxial cumulative fatigue damage.

Zamrik, S. Y.; Tang, P. Y.

1972-01-01

55

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

56

77 FR 55105 - Aging Airplane Program: Widespread Fatigue Damage; Correction  

Federal Register 2010, 2011, 2012, 2013

...FAA-2006-24281; Amendment Nos. 121-360A, 129-51A] RIN 2120-AI05 Aging Airplane Program: Widespread Fatigue Damage; Correction AGENCY...amendment to a final rule. The technical amendment is entitled ``Aging Airplane Program: Widespread Fatigue Damage'' (77 FR...

2012-09-07

57

77 FR 4890 - Damage Tolerance and Fatigue Evaluation for Composite Rotorcraft Structures, and Damage Tolerance...  

Federal Register 2010, 2011, 2012, 2013

...Fatigue Evaluation for Composite Rotorcraft Structures...75435). In the ``Composite Rotorcraft Structures...static strength of composite rotorcraft structures...fatigue substantiation technology for metallic structures...damage occur during manufacturing or within the...

2012-02-01

58

Thermomechanics of damage and fatigue by a phase field model  

E-print Network

In the paper we present an isothermal model for describing damage and fatigue by the use of the Ginzburg-Landau (G-L) equation. Fatigue produces progressive damage, which is related with a variation of the internal structure of the material. The G-L equation studies the evolution of the order parameter, which describes the constitutive arrangement of the system and, in this framework, the evolution of damage. The thermodynamic coherence of the model is proved. In the last part of the work, we extend the results of the paper to a non-isothermal system, where fatigue contains thermal effects, which increase the damage of materials.

Giovambattista Amendola; Mauro Fabrizio

2014-10-26

59

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

60

Active sensing of fatigue damage using embedded ultrasonics  

NASA Astrophysics Data System (ADS)

Dynamic measurements are widely used for structural condition assessment and damage detection. A wide range of studies are available on vibration-based detection and identification of fatigue cracks in simple and complex structures. This research explores the application of the electromechanical impedance method and nonlinear resonance measurements to high frequency detection of incipient fatigue damage in aluminum alloy specimens. The electromechanical impedance method relies on the coupling between the mechanical properties of a structure and the electrical properties of attached piezoelectric wafer active sensors (PWAS). This coupling allows structural properties to be inferred from the electrical impedance signature of the sensor. In this study, the electromechanical impedance method is utilized for assessment of material deterioration under cyclic fatigue loads. Aluminum specimens were subjected to increasing fatigue cycles at stress amplitudes below the yield point, and electromechanical impedance signatures were taken at discrete levels of fatigue damage. Linear and nonlinear features of the impedance signatures were compared for different damage conditions. The results show a downward frequency shift of impedance peaks with increasing fatigue load. This frequency shift is observed before visible crack development and fracture. Nonlinear resonance tests were applied to fatigued aluminum samples. PWAS were utilized for transmission and reception of elastic waves at increasing amplitude levels. Variations in structural dynamic characteristics were considered for different excitation conditions and increasing damage severity. This paper discusses damage detection capabilities of each method and provides perspectives for utilizing information on incipient damage for predicting structural performance under known operational loads.

Kruse, Walter A.; Zagrai, Andrei; Gigineishvili, Vlasi

2010-03-01

61

QUANTITATIVE DAMAGE ASSESSMENT OF HYBRID COMPOSITE WIND TURBINE BLADES BY ENERGY BASED ACOUSTIC EMISSION SOURCE  

E-print Network

QUANTITATIVE DAMAGE ASSESSMENT OF HYBRID COMPOSITE WIND TURBINE BLADES BY ENERGY BASED ACOUSTIC energy with higher efficiency and cost-effective considerations, the size of the wind turbine blade has in the wind turbine blade. It was tried to apply a new source location method, which has a developed algorithm

Boyer, Edmond

62

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

SciTech Connect

Evaluation of high strain rate and corresponding low strain rate tests indicate no creep-fatigue interaction. For T greater than or equal to 900/sup 0/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 the degree of suppression of creep damage. However, a practical limit exists for suppression of creep damage at 1100/sup 0/C; at that temperature, even for the high frequency reverse bend tests (approx. 1000 rpm with ..sigma.. = 12.3% s/sup -1/), the creep damage predominated over the fatigue damage.

Purohit, A.; Thiele, U.; O'Donnell, J.E.

1983-06-01

63

Resolution of tower shadow models for downwind mounted rotors and its effects on the blade fatigue  

NASA Astrophysics Data System (ADS)

A simulation study on the wind field resolution in computer load simulations has been conducted, both in transversal/vertical and longitudinal direction, to determine the effect on blade fatigue loading. Increasing the transversal/vertical resolution decreased the loading significantly, while only small changes to the load, at very low frequencies were found for increased longitudinal resolution. Next the influence of the tower shadow for a downwind mounted rotor was investigated, with respect to blade fatigue loading. The influence of different components to the total tower shadow effect was studied, both for a monopile and a truss tower, latter at inclination 0 and 22.5 degrees with respect to the incoming wind direction. Four components were considered, both individually and in combinations: mean wind speed, mean velocity deficit, unsteady motions from vortex shedding, and turbulence. The mean velocity deficit and turbulence were the main contributors to blade fatigue loading, and the unsteady motions can be neglected for the truss tower. For the monopile, neglecting the unsteady motions resulted in an underestimation of fatigue loading in the order of 3 percent.

Reiso, M.; Muskulus, M.

2014-12-01

64

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.  

... false Metallic damage tolerance and fatigue evaluation of commuter category airplanes...COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category...

2014-01-01

65

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.  

Code of Federal Regulations, 2010 CFR

... false Metallic damage tolerance and fatigue evaluation of commuter category airplanes...COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category...

2010-01-01

66

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.  

Code of Federal Regulations, 2012 CFR

... false Metallic damage tolerance and fatigue evaluation of commuter category airplanes...COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category...

2012-01-01

67

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.  

Code of Federal Regulations, 2013 CFR

... false Metallic damage tolerance and fatigue evaluation of commuter category airplanes...COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category...

2013-01-01

68

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.  

Code of Federal Regulations, 2011 CFR

... false Metallic damage tolerance and fatigue evaluation of commuter category airplanes...COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category...

2011-01-01

69

The characterization of widespread fatigue damage in fuselage structure  

NASA Technical Reports Server (NTRS)

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 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

1994-01-01

70

Lamb wave assessment of fatigue damage in aluminum plates  

Microsoft Academic Search

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

Sebastien Grondel; Emmanuel Moulin; Christophe Delebarre

1999-01-01

71

NONLINEAR ULTRASONIC DAMAGE DETECTION FOR FATIGUE CRACK USING SUBHARMONIC COMPONENT  

E-print Network

NONLINEAR ULTRASONIC DAMAGE DETECTION FOR FATIGUE CRACK USING SUBHARMONIC COMPONENT Zhi Wang 1 of this paper is to demonstrate the application of nonlinear ultrasonic subharmonic method for detecting fatigue amplitude and frequency subharmonic resonance range. Two surface-bonded piezoelectric transducers are used

Boyer, Edmond

72

Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage  

Microsoft Academic Search

Simple procedures are presented for treating cumulative fatigue damage under complex loading history using either the Damage Curve concept or the Double Linear Damage Rule. A single equation is provided for use with the Damage Curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the Double

S. S. Manson; G. R. Halford

1981-01-01

73

Deformation and fatigue behavior of SSME turbopump blade materials  

NASA Technical Reports Server (NTRS)

Directionally solidified and single crystal superalloys which are intended for use as turbopump blade materials are anisotropic both elastically and plastically. Therefore, isotropic constitutive models must be modified. Several models which are now being developed are based on metallurgical theories of deformation in these types of alloys. However, these theories have not been fully justified, and the temperature and strain regimes over which they may be valid are poorly defined. The objective of this work is to study the deformation behavior of the alloys, in order to determine the validity of these models and to thereby support the ongoing research efforts in solid mechanics.

Milligan, Walter W.; Antolovich, Stephen D.

1987-01-01

74

DAMAGE DETECTION METHODS ON WIND TURBINE BLADE TESTING WITH WIRED AND WIRELESS ACCELEROMETER SENSORS  

E-print Network

degrees of damage. Excitation was performed in two ways: near the delamination zone involve determining loading on wind turbine blades, either for danger of impact, as in the case of ice forming on the blade surface, and/or damage to the structure incurred by otherthananticipated loadings. 7

Paris-Sud XI, Université de

75

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

76

Effects of geometry and materials on low cycle fatigue life of turbine blades in LOX/hydrogen rocket engines  

NASA Technical Reports Server (NTRS)

This paper presents the results of an advanced turbine blade test program aimed at improving turbine blade low cycle fatigue (LCF) life. A total of 21 blades were tested in a blade thermal tester. The blades were made of MAR-M-246(Hf)DS and PWA-1480SC in six different geometries. The test results show that the PWA-1480SC material improved life by a factor of 1.7 to 3.0 over the current MAR-M-246(Hf)DS. The geometry changes yielded life improvements as high as 20 times the baseline blade made of PWA-1480SC and 34 times the baseline MAR-M-246DS blade.

Ryan, R. M.; Gross, L. A.

1986-01-01

77

Impact Damage Detection for Fiberglass Composite Rotor Blade  

Microsoft Academic Search

In this paper, a method is introduced for impact identification in operational composite helicopter rotor blades. By applying modal impact testing to simplified fiberglass rotor blades, a frequency response function model is developed relating impact response data from the hub of a four bladed rotor to impact force data in the frequency domain. A sum of least squares method is

Carson Budde; Nathanael Yoder; Douglas Adams; Peter Meckl; Dave Koester

2009-01-01

78

Multiaxial and thermomechanical fatigue considerations in damage tolerant design  

NASA Technical Reports Server (NTRS)

In considering damage tolerant design concepts for gas turbine hot section components, several challenging concerns arise: Complex multiaxial loading situations are encountered; Thermomechanical fatigue loading involving very wide temperature ranges is imposed on components; Some hot section materials are extremely anisotropic; and coatings and environmental interactions play an important role in crack propagation. The effects of multiaxiality and thermomechanical fatigue are considered from the standpoint of their impact on damage tolerant design concepts. Recently obtained research results as well as results from the open literature are examined and their implications for damage tolerant design are discussed. Three important needs required to advance analytical capabilities in support of damage tolerant design become readily apparent: (1) a theoretical basis to account for the effect of nonproportional loading (mechanical and mechanical/thermal); (2) the development of practical crack growth parameters that are applicable to thermomechanical fatigue situations; and (3) the development of crack growth models that address multiple crack failures.

Leese, G. E.; Bill, R. C.

1985-01-01

79

Inuence of foreign-object damage on crack initiation and early crack growth during high-cycle fatigue of Ti6Al4V  

E-print Network

In¯uence of foreign-object damage on crack initiation and early crack growth during high of small surface fatigue cracks in a Ti±6Al±4V alloy, processed for typical turbine blade applications to earlier crack ini- tiation. Premature crack initiation and subsequent near-threshold crack growth

Ritchie, Robert

80

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

NASA Astrophysics Data System (ADS)

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 us-age. Ways to use service-induced ? rafting and void formation as quantified microstructural damage pa-rameters 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 andJor heat treatment, are discussed briefly.

Persson, C.; Persson, P.-O.

1993-08-01

81

Fatigue damage initiation in Waspaloy under complex cyclic loading  

Microsoft Academic Search

The low-cycle fatigue damage initiation i n Waspaloy under complex cyclic loading (out-of-phase) is studied from experimental and theoretical viewpoints. Special emphasis is put on the transgranular damage development and results are compared to those reproduced in the literature. A physico-phenomenological model based on slip theory is used to predict the damage initiation lives as well as the directional aspect

A. Abdul-Latif; V. Ferney; K. Saanouni

1999-01-01

82

Blasim: A computational tool to assess ice impact damage on engine blades  

Microsoft Academic Search

A portable computer called BLASIM was developed at NASA LeRC to assess ice impact damage on aircraft engine blades. In addition to ice impact analyses, the code also contains static, dynamic, resonance margin, and supersonic flutter analysis capabilities. Solid, hollow, superhybrid, and composite blades are supported. An optional preprocessor (input generator) was also developed to interactively generate input for BLASIM.

E. S. Reddy; G. H. Abumeri; C. C. Chamis

1993-01-01

83

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

Microsoft Academic Search

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

Galib Abumeri; Frank Abdi

2012-01-01

84

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

85

Active sensing of fatigue damage using embedded ultrasonics  

NASA Astrophysics Data System (ADS)

Embedded ultrasonics has demonstrated considerable utility in structural health monitoring of aeronautical vehicle. This active sensing approach has been widely used to detect and monitor cracks, delaminations, and disbonds in a broad spectrum of metallic and composite structures. However, application of the embedded ultrasonics for active sensing of incipient damage before fracture has received limited attention. The aim of this study was to investigate the suitability of embedded ultrasonics and nonlinear acoustic signatures for monitoring pre-crack fatigue damage in aerospace structural material. A harmonic load was applied to structural specimens in order to induce fatigue damage accumulation and growth. Specimens of simple geometry were considered and piezoelectric active sensors were employed for generation and reception of elastic waves. The elastic wave signatures were analyzed in the frequency domain using nonlinear impedance and nonlinear resonance methods. A relationship between fatigue severity and linear as well as nonlinear acoustic signatures was investigated and considered in the damage classification procedure. Practical aspects of the active sensing of the fatigue damage before fracture were discussed and prospective avenues for future research were suggested.

Zagrai, Andrei; Kruse, Walter A.; Gigineishvili, Vlasi

2009-03-01

86

Detection of wind turbine blades damage by spectrum-recognition using gaussian wavelet-entropy  

Microsoft Academic Search

In this paper, a complex continuous wavelet transform (CWT)-based entropy method is proposed to enhance the damage-detection capability of wind turbine blades. By embedding the time-frequency localization features in wavelets, wavelet entropy of acquired signals can be readily computed. This approach can form a quantitative index systematically to detect the damage of blades, anticipating formulating a forewarning mechanism for wind

C. S. Tsai; C. T. Hsieh; K. L. Lew

2009-01-01

87

Stochastic Fatigue Damage Accumulation Due to Nonlinear Ship Loads  

Microsoft Academic Search

Efficient methods are described here to predict the stochastic accumulation offatigue damage due to nonlinear ship loads that are produced in random seas. The stochastic analysis method, which may be applied both to overload and fatigue limit states, is based on a relatively new concept: the \\

Alok K. Jha; Steven R. Winterstein

2000-01-01

88

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

89

Fatigue Damage Mechanisms in Advanced Hybrid Titanium Composite Laminates  

NASA Technical Reports Server (NTRS)

Hybrid Titanium Composite Laminates (HTCL) are a type of hybrid composite laminate with promise for high-speed aerospace applications, specifically designed for improved damage tolerance and strength at high-temperature (350 F, 177 C). However, in previous testing, HTCL demonstrated a propensity to excessive delamination at the titanium/PMC interface following titanium cracking. An advanced HTCL has been constructed with an emphasis on strengthening this interface, combining a PETI-5/IM7 PMC with Ti-15-3 foils prepared with an alkaline-perborate surface treatment. This paper discusses how the fatigue capabilities of the "advanced" HTCL compare to the first generation HTCL which was not modified for interface optimization, in both tension-tension (R = 0.1) and tension-compression (R=-0.2). The advanced HTCL under did not demonstrate a significant improvement in fatigue life, in either tension-tension or tension-compression loading. However, the advanced HTCL proved much more damage tolerant. The R = 0.1 tests revealed the advanced HTCL to increase the fatigue life following initial titanium ply damage up to 10X that of the initial HTCL at certain stress levels. The damage progression following the initial ply damage demonstrated the effect of the strengthened PMC/titanium interface. Acetate film replication of the advanced HTCL edges showed a propensity for some fibers in the adjacent PMC layers to fail at the point of titanium crack formation, suppressing delamination at the Ti/PMC interface. The inspection of failure surfaces validated these findings, revealing PMC fibers bonded to the majority of the titanium surfaces. Tension compression fatigue (R = -0.2) demonstrated the same trends in cycles between initial damage and failure, damage progression, and failure surfaces. Moreover, in possessing a higher resistance to delamination, the advanced HTCL did not exhibit buckling following initial titanium ply cracking under compression unlike the initial HTCL.

Johnson, W. Steven; Rhymer, Donald W.; St.Clair, Terry L. (Technical Monitor)

2000-01-01

90

Investigation of Spur Gear Fatigue Damage Using Wear Debris  

NASA Technical Reports Server (NTRS)

A new diagnostic tool for detecting and assess- ing su$ace fatigue damage to spur gears was developed. This diagnostic tool was evaluated by analyzing metallic oil wear debris generated during fatigue tests that were performed using a spur gearbox rig. During each test, readings from an on-line oil debris sensor were monitored and recorded for assessment of gear pitting damage. The debris measured by the oil debris sensor was used to identify "membership functions" to build a simple fuzzy logic model. Using fuzzy logic techniques on the oil debris data, threshold limits were defined that discriminated between different stages of pitting wear. Results showed that oil wear debris data combined with fuzzy logic analysis techniques was a good predictor of pitting damage on spur gears.

Dempsey, Paula J.; Morales, Wilfredo; Afjeh, Abdollah A.

2003-01-01

91

Continuum Fatigue Damage Modeling for Use in Life Extending Control  

NASA Technical Reports Server (NTRS)

This paper develops a simplified continuum (continuous wrp to time, stress, etc.) fatigue damage model for use in Life Extending Controls (LEC) studies. The work is based on zero mean stress local strain cyclic damage modeling. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modeling. Stress based continuum models are derived. Extension to plastic strain-strain rate models are also presented. Application of these models to LEC applications is considered. Progress toward a nonzero mean stress based continuum model is presented. Also, new nonlinear explicit equation forms in terms of stress amplitude are also derived for this case.

Lorenzo, Carl F.

1994-01-01

92

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

93

Recovery of Fatigue Damage and Life Prediction by Laser Irradiation Healing Treatment for Copper Film  

NASA Astrophysics Data System (ADS)

A fatigue life prediction method was investigated after healing fatigue damage by excimer laser irradiation treatment for the damaged copper film. First, the variations of residual fatigue life and strain range for the damaged specimens after laser irradiation healing treatment were analyzed. The results showed that the fatigue damage can be effectively healed by laser irradiation for copper film. The presented healing phenomenon during laser irradiation process showed that the recovery of fatigue damage can result in the improvement in fatigue life for the damaged copper film. Then, based on the fact that the strain concentration factor of copper film had not been changed before and after laser irradiation treatment, a residual fatigue life prediction method was proposed by the local stress transformation. The predicted residual fatigue lives by the proposed method agreed well with the experimental results for copper film after laser irradiation treatment.

Guo, Yu-Bo; Shang, De-Guang; Liu, Xiao-Dong; Ren, Chong-Gang; Liu, Feng-Zhu; Zhang, Li-Hong; Sun, Yu-Juan

2015-01-01

94

Recovery of Fatigue Damage and Life Prediction by Laser Irradiation Healing Treatment for Copper Film  

NASA Astrophysics Data System (ADS)

A fatigue life prediction method was investigated after healing fatigue damage by excimer laser irradiation treatment for the damaged copper film. First, the variations of residual fatigue life and strain range for the damaged specimens after laser irradiation healing treatment were analyzed. The results showed that the fatigue damage can be effectively healed by laser irradiation for copper film. The presented healing phenomenon during laser irradiation process showed that the recovery of fatigue damage can result in the improvement in fatigue life for the damaged copper film. Then, based on the fact that the strain concentration factor of copper film had not been changed before and after laser irradiation treatment, a residual fatigue life prediction method was proposed by the local stress transformation. The predicted residual fatigue lives by the proposed method agreed well with the experimental results for copper film after laser irradiation treatment.

Guo, Yu-Bo; Shang, De-Guang; Liu, Xiao-Dong; Ren, Chong-Gang; Liu, Feng-Zhu; Zhang, Li-Hong; Sun, Yu-Juan

2014-11-01

95

Static and Fatigue Analysis of Wind Turbine Blades Subject to Cold Weather Conditions Using Finite Element Analysis  

E-print Network

simulate boundary conditions, applied loading and thermal stresses for a 1.5 MW wind turbine. It is shownStatic and Fatigue Analysis of Wind Turbine Blades Subject to Cold Weather Conditions Using Finite experienced in candi- date Canadian wind turbine deployment locations. The thesis then narrows its focus

Victoria, University of

96

FATIGUE RESISTANT FIBERGLASS LAMINATES FOR WIND TURBINE BLADES (published for Wind Energy 1996, ASME, pp. 46-51)  

E-print Network

/MSU database to lifetime prediction as described in Ref. [1]. INTRODUCTION Most U.S. fiberglass wind turbineFATIGUE RESISTANT FIBERGLASS LAMINATES FOR WIND TURBINE BLADES (published for Wind Energy 1996 strands, which occurs at lower strains than does fiber failure, will produce significant stress

97

Fatigue damage initiation in Waspaloy under complex cyclic loading  

SciTech Connect

The low-cycle fatigue damage initiation i n Waspaloy under complex cyclic loading (out-of-phase) is studied from experimental and theoretical viewpoints. Special emphasis is put on the transgranular damage development and results are compared to those reproduced in the literature. A physico-phenomenological model based on slip theory is used to predict the damage initiation lives as well as the directional aspect of the damage distribution. In this model, the micro-damage is supposed to initiate and then evolve on the activated crystallographic slip systems. The theoretical results are compared to both the experimental ones concerning the same material (Waspaloy) as well as other experimental results extracted from the literature.

Abdul-Latif, A. [IUT de Tremblay (France); Ferney, V.; Saanouni, K. [Univ. de Technologie de Troyes (France)

1999-07-01

98

BLASIM - A computational tool to assess ice impact damage on engine blades  

NASA Technical Reports Server (NTRS)

A portable computer code called BLASIM is developed at NASA LeRC to assess the ice impact damage on aircraft engine blades. In addition to the ice impact analyses, the code is also capable of carrying out static, dynamic, resonance margin and flutter analyses. The blade can be solid, hollow, superhybrid or composite material. An optional preprocessor (input generator) is also developed to generate input to the code through interactive process. The blade geometry can be defined either by a series of airfoils at discrete input stations or by a finite element grid. The code employs a coarse fixed finite element mesh with triangular plate finite elements and has quick turnaround time. The ice piece is modeled as an equivalent spherical object and has the velocity opposite to that of the aircraft with direction parallel to the engine axis. For the local impact damage assessment, the impact force is considered as a distributed load acting over a region around the impact point and the average radial strain of the finite elements along the leading edge is taken as a measure of the local damage. To estimate the damage at the blade root, the impact is considered to be an impulse and a combined stress failure criteria is employed. Parametric studies for local and root ice impact damage, and post-impact dynamics are discussed for solid and composite blades.

Reddy, E. S.; Abumeri, G. H.; Chamis, C. C.

1993-01-01

99

Blasim: A computational tool to assess ice impact damage on engine blades  

NASA Technical Reports Server (NTRS)

A portable computer called BLASIM was developed at NASA LeRC to assess ice impact damage on aircraft engine blades. In addition to ice impact analyses, the code also contains static, dynamic, resonance margin, and supersonic flutter analysis capabilities. Solid, hollow, superhybrid, and composite blades are supported. An optional preprocessor (input generator) was also developed to interactively generate input for BLASIM. The blade geometry can be defined using a series of airfoils at discrete input stations or by a finite element grid. The code employs a coarse, fixed finite element mesh containing triangular plate finite elements to minimize program execution time. Ice piece is modeled using an equivalent spherical objective that has a high velocity opposite that of the aircraft and parallel to the engine axis. For local impact damage assessment, the impact load is considered as a distributed force acting over a region around the impact point. The average radial strain of the finite elements along the leading edge is used as a measure of the local damage. To estimate damage at the blade root, the impact is treated as an impulse and a combined stress failure criteria is employed. Parametric studies of local and root ice impact damage, and post-impact dynamics are discussed for solid and composite blades.

Reddy, E. S.; Abumeri, G. H.; Chamis, C. C.

1993-01-01

100

Fatigue damage assessment in 7075 and 7050 aluminum alloys at low cyclic stresses  

Microsoft Academic Search

Dynamic loads from buffeting, shock waves, and separated flow cause aircraft structural fatigue. Increases in aircraft performance cause sonic high cycle fatigue (HCF) in structural components. The accuracy of HCF damage predictions and fracture mechanics analysis has been limited in the past by the maximum cyclic rate of fatigue test equipment. Constant load amplitude axial fatigue data has previously been

Mary Kathryn Malast

2000-01-01

101

Lamb Wave Assessment of Fatigue and Thermal Damage in Composites  

NASA Technical Reports Server (NTRS)

Among the various techniques available, ultrasonic Lamb waves offer a convenient method of evaluating composite materials. Since the Lamb wave velocity depends on the elastic properties of a structure, an effective tool exists to monitor damage in composites by measuring the velocity of these waves. Lamb wave measurements can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper describes two studies which monitor fatigue damage and two studies which monitor thermal damage in composites using Lamb waves. In the fatigue studies, the Lamb wave velocity is compared to modulus measurements obtained using strain gage measurements in the first experiment and the velocity is monitored along with the crack density in the second. In the thermal damage studies, one examines samples which were exposed to varying temperatures for a three minute duration and the second includes rapid thermal damage in composites by intense laser beams. In all studies, the Lamb wave velocity is demonstrated to be an excellent method to monitor damage in composites.

Seale, Michael D.; Smith, Barry T.; Prosser, W. H.

2004-01-01

102

Use of atomic force microscopy for characterizing damage evolution during fatigue  

Microsoft Academic Search

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

Laurent Cretegny

2000-01-01

103

A stress invariant based criterion to estimate fatigue damage under multiaxial loading  

Microsoft Academic Search

This paper summarises an attempt to propose a novel stress invariant based approach suitable for estimating fatigue damage in the presence of complex multiaxial fatigue loadings. In more detail, according to the devised method, fatigue damage is evaluated by studying the components of the deviator path projected along the axes of a convenient frame of reference, whose orientation univocally depends

A. Cristofori; L. Susmel; R. Tovo

2008-01-01

104

Fatigue life prediction under variable loading based on a new damage model  

Microsoft Academic Search

To examine the performance of nonlinear models proposed in the estimation of fatigue damage and fatigue life of components under random loading, a batch of specimens made of 6082 T 6 aluminium alloy has been studied and some of the results are reported in the present paper. The paper describes an algorithm and suggests a fatigue cumulative damage model, especially

A. Aid; A. Amrouche; B. Bachir Bouiadjra; M. Benguediab; G. Mesmacque

2011-01-01

105

High cycle fatigue damage mechanisms in cast aluminium subject to complex loads  

E-print Network

behaviour, and more specifically the fatigue damage mechanisms observed under complex loading conditionsHigh cycle fatigue damage mechanisms in cast aluminium subject to complex loads Imade Koutiria in "International Journal of Fatigue 47 (2013) 44-57" DOI : 10.1016/j.ijfatigue.2012.07.008 #12;loading conditions

Paris-Sud XI, Université de

106

77 FR 30877 - Aging Airplane Program: Widespread Fatigue Damage; Technical Amendment  

Federal Register 2010, 2011, 2012, 2013

...121-360, 129-51] RIN 2120-AI05 Aging Airplane Program: Widespread Fatigue Damage...FAA published a final rule entitled, ``Aging Airplane Program: Widespread Fatigue Damage...the preamble of the rule entitled, ``Aging Airplane Program: Widespread Fatigue...

2012-05-24

107

Fatigue and damage tolerance evaluation of an aircraft spoiler  

NASA Astrophysics Data System (ADS)

The spoilers on an aircraft are responsible for several tasks, including execution of roll maneuvers, lift dumping (aerodynamic "spoiling"), and braking. The examined spoiler is manufactured from carbon fiber reinforced composite material and is attached to the wing by four bearing hinges and one actuator hinge. Correct spoiler design involves knowledge of the loads acting on the spoiler, calculation of stresses and strains, and examination of possible failures. Additionally, the fatigue and damage tolerance evaluation of such a spoiler has to follow established certification protocols. This study defines a load cycle based on in-service loadings, including aerodynamic loading, wing bending, inertial loading, and actuator loading. A finite element model of the spoiler is used to calculate the reaction forces in the hinges and the strain in the carbon fiber components occurring during the load cycle. The Miner Rule is used to calculate the fatigue life of the hinges based on the computed stress. A damage tolerance evaluation is then performed assuming that different hinges have failed. Finally, a certification test for fatigue and damage tolerance evaluation of a spoiler is discussed.

Hurlebaus, Stefan; Gaul, Lothar

2005-05-01

108

USE OF COMPOSITE MATERIALS TO REPAIR STEEL STRUCTURES VULNERABLE TO FATIGUE DAMAGE  

E-print Network

This study investigates mainly two different topics related to the use of CFRP's for strengthening and repair of steel bridges: the use of CFRP's to prevent damage in fatigue vulnerable welded connections prior to fatigue-crack initiation...

Alemdar, Fatih

2010-01-01

109

Fatigue damage estimation of metal roof cladding subject to wind loading  

Microsoft Academic Search

This paper introduces a procedure for estimating wind-induced fatigue damage to metal roof cladding. Fatigue loading on roof cladding is determined using a rainflow count method and considering long-term wind climate. Linear or bilinear S-N curves on a log-log plot are derived based on fatigue tests of three types of commonly used light gauge steel roofing sheets. Fatigue damage indexes

Y. L. Xu

1997-01-01

110

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

111

Model-Trained Neural Networks and Electronic Holography Demonstrated to Detect Damage in Blades  

NASA Technical Reports Server (NTRS)

Detect Damage in Blades Electronic holography can show damaged regions in fan blades at 30 frames/sec. The electronic holograms are transformed by finite-element-model-trained artificial neural networks to visualize the damage. The trained neural networks are linked with video and graphics to visualize the bending-induced strain distribution, which is very sensitive to damage. By contrast, it is very difficult to detect damage by viewing the raw, speckled, characteristic fringe patterns. For neural-network visualization of damage, 2 frames or 2 fields are used, rather than the 12 frames normally used to compute the displacement distribution from electronic holograms. At the NASA Lewis Research Center, finite element models are used to compute displacement and strain distributions for the vibration modes of undamaged and cracked blades. A model of electronic time-averaged holography is used to transform the displacement distributions into finite-element-resolution characteristic fringe patterns. Then, a feedforward neural network is trained with the fringe-pattern/strain-pattern pairs, and the neural network, electronic holography, and video are implemented on a workstation. Now that the neural networks have been tested successfully at 30 frames/sec on undamaged and cracked cantilevers, the electronic holography and neural-network processing are being adapted for onsite damage inspection of twisted fan blades and rotormounted blades. Our conclusion is that model-trained neural nets are effective when they are trained with good models whose application is well understood. This work supports the aeromechanical testing portion of the Advanced Subsonic Technology Project.

Decker, Arthur J.; Fite, E. Brian; Mehmed, Oral; Thorp, Scott A.

1998-01-01

112

Cumulative fatigue damage and life prediction theories: a survey of the state of the art for homogeneous materials  

Microsoft Academic Search

Fatigue damage increases with applied load cycles in a cumulative manner. Cumulative fatigue damage analysis plays a key role in life prediction of components and structures subjected to field load histories. Since the introduction of damage accumulation concept by Palmgren about 70 years ago and ‘linear damage rule’ by Miner about 50 years ago, the treatment of cumulative fatigue damage

A. Fatemi; L. Yang

1998-01-01

113

Periostin deficiency increases bone damage and impairs injury response to fatigue loading in adult mice.  

PubMed

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. PMID:24167618

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

2013-01-01

114

Cycle distribution and fatigue damage under broad-band random loading  

Microsoft Academic Search

Fatigue damage under broad-band loading is analysed by summarizing and reviewing available analytical solutions. Relationships between fatigue damage assessment and counting methods are investigated by establishing when, in frequency domain analysis, analytical solutions of expected damage are connected with a counting procedure assumption and how this is related to the rainflow counting procedure. A new approach is also proposed for

Roberto Tovo

2002-01-01

115

REAL-TIME FATIGUE DAMAGE MONITORING VIA IN SITU ULTRASONIC SENSING  

Microsoft Academic Search

Estimation of structural damage and quantification of structural integrity are crit- ical for safe and reliable operation of human-engineered complex systems. Fatigue damage is one of the most commonly encountered sources of structural degradation in mechanical systems. Detection of incipient fatigue damage is essential for averting widespread crack growth that leads to catastrophic failures. This chapter presents online in situ

Shalabh Guptayand; Asok Rayz

116

The effect of yield strength and ductility to fatigue damage  

NASA Technical Reports Server (NTRS)

The cumulative damage of aluminium alloys with different yield strength and various ductility due to seismic loads was studied. The responses of an idealized beam with a centered mass at one end and fixed at the other end to El Centro's and Taft's earthquakes are computed by assuming that the alloys are perfectly elastoplastic materials and by using numerical technique. Consequently, the corresponding residual plastic strain can be obtained from the stress-strain relationship. The revised Palmgren-Miner cumulative damage theorem is utilized to calculate the fatigue damage. The numerical results show that in certain cases, the high ductility materials are more resistant to seismic loads than the high yield strength materials. The results also show that if a structure collapse during the earthquake, the collapse always occurs in the very early stage.

Yeh, H. Y.

1973-01-01

117

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

118

Online fatigue damage monitoring by ultrasonic measurements: A symbolic dynamics approach  

Microsoft Academic Search

The paper presents an analytical tool for early detection and online monitoring of fatigue damage in polycrystalline alloys that are commonly used in mechanical structures of human-engineered complex systems. Real-time fatigue damage monitoring algorithms rely on time series analysis of ultrasonic signals that are sensitive to micro-structural changes occurring inside the material during the early stages of fatigue damage; the

Shalabh Gupta; Asok Ray; Eric Keller

2007-01-01

119

Structural and Damage Assessment of Multi-Section Modular Hybrid Composite Wind Turbine Blade  

E-print Network

the size of wind turbines to generate higher power output. Typically, the larger/longer blade designs rely on hybrid material systems such as carbon and/or glass fiber (CF/GF) reinforced polymers to improve specific stiffness/strength and damage tolerance...

Nanami, Norimichi

2014-07-25

120

Damage evolution in metal matrix composites subjected to thermomechanical fatigue  

SciTech Connect

A thermomechanical analysis of unidirectional continuous fiber metal matrix composites is presented. The analysis includes the effects of processing induced residual thermal stresses, interface cracking, and inelastic matrix behavior on damage evolution. Due to the complexity of the nonlinear effects, the analysis is performed computationally using the finite element method. The interface fracture is modeled by a nonlinear constitutive model. The problem formulation is summarized and results are presented for a four-ply unidirectional SCS-6/{beta}21S titanium composite under high temperature isothermal mechanical fatigue.

Allen, D.H. [Texas A and M Univ., College Station, TX (United States). Center for Mechanics of Composites; Hurtado, L.D.; Helms, K.L.E. [Sandia National Labs., Albuquerque, NM (United States)

1995-05-01

121

Fatigue crack growth spectrum simplification: Facilitation of on-board damage prognosis systems  

Microsoft Academic Search

Better lifetime predictions of systems subjected to fatigue loading are needed in support of the optimization of the costs of life-cycle engineering. In particular, the climate is especially encouraging for the development of safer aircraft. One issue is that aircraft experience complex fatigue loading and current methods for the prediction of fatigue damage accumulation rely on intensive computational tools that

Matthew Adam Adler

2009-01-01

122

Online fatigue damage monitoring by ultrasonic measurements: A symbolic dynamics approach q  

E-print Network

proposed in recent literature [10­12]. The capabilities of electrochemical sensors [13] and thermal imaging.elsevier.com/locate/ijfatigue International Journal of Fatigue 29 (2007) 1100­1114 International Journalof Fatigue #12;using acoustic emissionOnline fatigue damage monitoring by ultrasonic measurements: A symbolic dynamics approach q Shalabh

Ray, Asok

123

A continuous low cycle fatigue damage model and its application in engineering materials  

Microsoft Academic Search

In this study, the low cycle fatigue (LCF) damage evolution of the engineering materials is studied by use of continuum damage mechanics (CDM) theory. Based on thermodynamics, on a continuum damage variable, D, and on the effective stress concept, a continuum damage model of isotropic LCF is derived and is used to analyze the strain-controlled LCF damage evolution of steam

Xiaohua Yang; Nian Li; Zhihao Jin; Tiejun Wang

1997-01-01

124

A study of cumulative fatigue damage in titanium 6Al-4V alloy  

NASA Technical Reports Server (NTRS)

Experimental data were obtained using titanium 6Al-4V alloy under stress ratios of -1, 0, and negative infinity. A study of cumulative fatigue damage using Miner's (1945) and Kramer's (1974) equations for stress ratios of -1 and 0 for low-high, low-high mixed, high-low, and high-low mixed stress sequences has revealed close agreement between the theoretical and experimental values of fatigue damage and fatigue life. Kramer's equation predicts less conservative and more realistic cumulative fatigue damage than does the popularly used Miner's rule.

Jeelani, S.; Ghebremedhin, S.; Musial, M.

1986-01-01

125

Investigation of Gear and Bearing Fatigue Damage Using Debris Particle Distributions  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

126

Variance of the fatigue damage due to a Gaussian narrowband process  

Microsoft Academic Search

The fatigue life of a structure is inherently random when the loading is irregular. There is a vast body of literature on the analysis of the mean fatigue damage, but very few studies have been devoted to the variance. This paper presents an improved method for analyzing the variance of the damage for any narrowband Gaussian process. The field of

Y. M. Low

2011-01-01

127

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

128

Finite element approach for modelling fatigue damage in fibre-reinforced composite materials  

Microsoft Academic Search

Today, a lot of research is dedicated to the fatigue behaviour of fibre-reinforced composite materials due to their increasing use in all sorts of applications. These materials have a quite good rating as regards to lifetime in fatigue, but the same does not apply to the number of cycles to initial damage, or to the evolution of damage. Composite materials

W. Van Paepegem; J. Degrieck; P. De Baets

2001-01-01

129

Numerical modelling of cyclic plasticity and fatigue damage in cold-forging tools  

Microsoft Academic Search

Industrial cold-forging tools with complex geometry are very likely to be exposed to local plastic deformation near stress concentrating details. The accumulation of plastic deformation resulting from the cyclic loading conditions leads to fatigue damage and eventually to generation of a crack in the surface of the die. To study the effect of die prestressing on fatigue damage development, a

Thomas Ørts Pedersen

2000-01-01

130

Numerical Modeling of Fatigue Damage and Fissure Propagation under Cyclic Loadings  

Microsoft Academic Search

The purpose of this work is to develop a numerical simulation procedure in order to predict the evolution of the fatigue damage and rupture in mechanical parts (such as rolling bearings and gears) under cyclic loadings. The study of the fatigue damage evolution, from the first defect appearance until the part's failure, is primordial in view of the preventive maintenance.

F. Bogard; P. Lestriez; Y. Q. Guo

2008-01-01

131

C. R. Acad. Sci. Paris, t. 332, Serie II b, p. 1??, 2001 -PXPPxxxxx.TEX -Endommagement, fatigue, rupture/Damage, fatigue, rupture  

E-print Network

C. R. Acad. Sci. Paris, t. 332, S´erie II b, p. 1­??, 2001 - PXPPxxxxx.TEX - Endommagement, fatigue, rupture/Damage, fatigue, rupture Identification of the scatter in high cycle fatigue from temperature´emie des sciences/´Editions scientifiques et m´edicales Elsevier SAS Fatigue/ Microplasticity/ Poisson

132

Estimation of spallation life of thermal barrier coating of gas turbine blade by thermal fatigue test  

Microsoft Academic Search

Plasma-sprayed thermal barrier coatings (TBCs) are applied to protect the blades of a gas turbine system from high-temperature gas and to lower the surface temperature of the blades. The failure of TBC is directly connected to the failure of the blades because the spallation of a ceramic layer leads to the acceleration of local corrosion and oxidation at the location

In-Hwan Shin; Jae-Mean Koo; Chang-Sung Seok; Sung-Ho Yang; Tack-Woon Lee; Bum-Soo Kim

2011-01-01

133

Improved Damage Tolerance in Titanium Alloy Fan Blades with Low Plasticity Burnishing  

Microsoft Academic Search

Low Plasticity Burnishing (LPB) has been applied to produce a layer of deep high magnitude compressive residual stress in the leading edge of Ti -6Al-4V first stage fan blades. The goal was to improve damage tolerance from 0.13 to 0.5 mm (0.005 to 0.02 in.). LPB processing of the airfoil surface was performed on a conventional four-axis CNC mill. The

P. S. Prevéy; D. J. Hornbach; T. L. Jacobs; R. Ravindranath

134

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

135

Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage  

NASA Technical Reports Server (NTRS)

Simple procedures are presented for treating cumulative fatigue damage under complex loading history using either the damage curve concept or the double linear damage rule. A single equation is provided for use with the damage curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the double linear damage rule, analytical expressions are provided for determining the two phases of life. The procedure involves two steps, each similar to the conventional application of the commonly used linear damage rule. When the sum of cycle ratios based on phase 1 lives reaches unity, phase 1 is presumed complete, and further loadings are summed as cycle ratios on phase 2 lives. When the phase 2 sum reaches unity, failure is presumed to occur. No other physical properties or material constants than those normally used in a conventional linear damage rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons of both methods are discussed.

Manson, S. S.; Halford, G. R.

1980-01-01

136

Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage  

NASA Technical Reports Server (NTRS)

Simple procedures are given for treating cumulative fatigue damage under complex loading history using either the damage curve concept or the double linear damage rule. A single equation is given for use with the damage curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the double linear damage rule, analytical expressions are given for determining the two phases of life. The procedure comprises two steps, each similar to the conventional application of the commonly used linear damage rule. Once the sum of cycle ratios based on Phase I lives reaches unity, Phase I is presumed complete, and further loadings are summed as cycle ratios based on Phase II lives. When the Phase II sum attains unity, failure is presumed to occur. It is noted that no physical properties or material constants other than those normally used in a conventional linear damage rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons are discussed for both methods.

Manson, S. S.; Halford, G. R.

1981-01-01

137

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

138

Fatigue damage in cross-ply titanium metal matrix composites containing center holes  

NASA Technical Reports Server (NTRS)

The development of fatigue damage in (0/90) sub SCS-6/TI-15-3 laminates containing center holes was studied. Stress levels required for crack initiation in the matrix were predicted using an effective strain parameter and compared to experimental results. Damage progression was monitored at various stages of fatigue loading. In general, a saturated state of damage consisting of matrix cracks and fiber matrix debonding was obtained which reduced the composite modulus. Matrix cracks were bridged by the 0 deg fibers. The fatigue limit (stress causing catastrophic fracture of the laminates) was also determined. The static and post fatigue residual strengths were accurately predicted using a three dimensional elastic-plastic finite element analysis. The matrix damage that occurred during fatigue loading significantly reduced the notched strength.

Bakuckas, J. G., Jr.; Johnson, W. S.; Bigelow, C. A.

1992-01-01

139

Effect of notch-root radius on fatigue damage of notched FRP plates  

NASA Astrophysics Data System (ADS)

Fatigue tests under plane bending and pulsating tension were carried out on notched FRP plates for a wide range of notch-root radii and stress amplitudes, with focus on the fatigue damage development near the notch root. The luminance at the limited spot near the notch root was measured during fatigue tests to evaluate the fatigue damage. Observation by means of a scanning electron microscope revealed that the initiation of microcracks at the notch root was accompanied with a decrease in luminance near the notch root. The experiment shows that the number of cycles to fatigue damage initiation is determined by both the maximum elastic stress at the notch root and the notch-root radius. On the basis of the concept of linear notch mechanics, the experimental results can be clearly elucidated and a criterion of fatigue damage initiation is determined in terms of a combination of the maximum elastic stress, sigma(max), notch-root radius, rho, and the number of cycles to fatigue damage initiation Nd. The criterion is expressed as: (sigma)max x (Nd) exp m = C(rho), where m is the material constant. The parameter C is the material constant which is governed by the notch-root radius only and is independent of other notch geometries and specimen size. By applying the criterion derived, it is possible to make an accurate estimate of the fatigue life for notched FRP plates.

Hyakutake, Hiizu; Yamamoto, Toshihiro

1993-06-01

140

Cumulative creep-fatigue damage evolution in an austenitic stainless steel  

NASA Technical Reports Server (NTRS)

A model of cumulative creep-fatigue damage has been developed which is based on the use of damage curve equations to describe the evolution of creep-fatigue damage for four basic creep-fatigue cycle types. These cycle types correspond to the four fundamental cycles of the Strain Range Partitioning Life Prediction approach of Manson, Halford, and Hirschberg. A concept referred to as Damage Coupling is introduced to analytically account for the differences in the nature of the damage introduced by each cycle type. For application of this model, the cumulative creep-fatigue damage behavior of type 316 stainless steel at 816 C has been experimentally established for the two-level loading cases involving fatigue and creep-fatigue, in various permutations. The tests were conducted such that the lower life (high strain) cycling was applied first, for a controlled number of cycles, and the higher life (lower strain) cycling was conducted at the second level, to failure. The proposed model correlated the majority of the observed cumulative creep-fatigue data.

Mcgaw, Michael A.

1992-01-01

141

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

NASA Technical Reports Server (NTRS)

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 of widespread fatigue damage includes analyses for crack initiation, fatigue crack growth, and residual strength. Therefore, the computational capability required to predict analytically the onset of widespread fatigue damage must be able to represent a wide range of crack sizes from the material (microscale) level to the global structural-scale level. NASA studies indicate that the fatigue crack behavior in aircraft structure can be represented conveniently by the following three analysis scales: small three-dimensional cracks at the microscale level, through-the-thickness two-dimensional cracks at the local structural level, and long cracks at the global structural level. The computational requirements for each of these three analysis scales are described in this paper.

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

1996-01-01

142

Mitigation of fatigue damage in self-healing vascular materials A.R. Hamilton a,b,1  

E-print Network

Mitigation of fatigue damage in self-healing vascular materials A.R. Hamilton a,b,1 , N.R. Sottos b: Self-healing Fatigue Vascular network a b s t r a c t The fatigue response of an epoxy matrix. Fatigue is particularly problematic because it occurs at stress levels below the critical fracture stress

Sottos, Nancy R.

143

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

144

Fatigue damage assessment of high-usage in-service aircraft fuselage structure  

Microsoft Academic Search

As the commercial and military aircraft fleets continue to age, there is a growing concern that multiple-site damage (MSD) can compromise structural integrity. Multiple site damage is the simultaneous occurrence of many small cracks at independent structural locations, and is the natural result of fatigue, corrosion, fretting and other possible damage mechanisms. These MSD cracks may linkup and form a

Bao Rasebolai Mosinyi

2007-01-01

145

New Techniques for Detecting Early Fatigue Damage Accumulation in Aircraft Structural Components  

Microsoft Academic Search

The remaining safe operational life of flight critical aircraft structural components prior to crack initiation and detection is currently estimated by fatigue and fracture models supplemented by destructive testing. To more accurately assess the remaining life of a structural component prior to the initiation of a detectable crack, a non-destructive inspection process that measures fatigue damage accumulation is required. Induced

Curtis A. Rideout; Scott J. Ritchie

2007-01-01

146

Risk assessment of Cumberland unit 2 L-O blades  

SciTech Connect

Concern about the reliability of the 1,300 mw Cumberland steam turbine units after an unexpected blade tip failure in the fall of 1995 caused TVA to conduct an investigation into the current reliability of the L-O blades. A probabilistic model based on the measured frequencies, damping and material fatigue data was generated. The influence of significant erosion damage on the blade natural frequencies and on the local stresses was estimated. A probabilistic model of the local fatigue limit was generated based on test data. Monte Carlo simulation was employed to estimate the probability of blade failure by comparing the dynamic stress with the fatigue limit. Risk assessment of the blade failure is presented.

Lam, T.C.T. [Stress Technology Inc., Rochester, NY (United States); Puri, A. [Tennessee Valley Authority, Chattanooga, TN (United States)

1996-12-31

147

Fatigue-Induced Damage in Zr-Based Bulk Metallic Glasses  

PubMed Central

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

2013-01-01

148

Investigation of closed-form solutions to estimate fatigue damage on a building  

Microsoft Academic Search

If a stress process is wide-band, it is not obvious what constitutes a cycle and how cycles should be counted so that the Miner's rule can be employed. If a stress process is non-Gaussian, the stress process may cause accelerated fatigue damage. In this study, high-cycle fatigue damage for fasteners of curtain walls on a side face of a square

Nag-Ho Ko; Young-Moon Kim

2007-01-01

149

Microstructure: Property correlation. [multiaxial fatigue damage evolution in waspaloy  

NASA Technical Reports Server (NTRS)

Strain controlled torsional and biaxial (tension-torsion) low cycle fatigue behavior of Waspaloy was studied at room temperature as a function of heat treatment. Biaxial tests were conducted under proportional (when the axial and torsional strain cycles are in-phase) and non-proportional (when the axial and torsional strain cycles are 90 deg out-of-phase) cyclic conditions. The deformation behavior under these different cyclic conditions were evaluated by slip trace analysis. For this, a Schmidt-type factor was defined for multiaxial loading conditions and it was shown that when the slip deformation is predominant, non-proportional cycles are more damaging than proportional or pure axial or torsional cycles. This was attributed to the fact that under non-proportional cyclic conditions, deformation was through multiple slip as opposed single slip for other loading conditions, which gave rise to increased hardening. The total life for a given test condition was found to be independent of heat treatment. This was interpreted as being due to the differences in the cycles to initiation and propagation of cracks.

Jayaraman, N.

1990-01-01

150

Fatigue damage evaluation of plain woven carbon fiber reinforced plastic (CFRP) modified with MFC (micro-fibrillated cellulose) by thermo-elastic damage analysis (TDA)  

NASA Astrophysics Data System (ADS)

The aim of this study is to investigate characteristics of fatigue damage of CFRP modified with MFC by TDA under tensile cyclic loading. In this paper, fatigue life of CFRP modified with MFC was investigated under cyclic loading. Characteristics of fatigue damage of CFRP modified with MFC were evaluated by thermo-elastic damage analysis. Maximum improvement in fatigue life was also obtained under cyclic loading when epoxy matrix was enhanced with 0.3wt% of MFC as well as under static loading. Result of TDA showed same tendency as the result of fatigue test, and the result of TDA well expressed the fatigue damage behavior of plain woven CFRP plate. Eventually, TDA was effective for clear understanding the degree of fatigue damage progression of CFRP modified with MFC.

Aoyama, Ryohei; Okubo, Kazuya; Fujii, Toru

2013-04-01

151

Fatigue damage prognosis of a cruciform structure under biaxial random and flight profile loading  

NASA Astrophysics Data System (ADS)

The accurate estimation of fatigue life of metallic structural components in service environments is still a challenge for the aircraft designer or fleet manager. Majority of the current available fatigue life prediction models has deficiency to accurately predict damage under random or flight profile service loads. The inherent accuracy is due to the stochastic nature of crack propagation in metallic structure. In addition, currently no generic prediction model available accounting the load interaction effects due to variable loading. In the present paper we discus the use of a Generic Bayesian framework based Gaussian process approach to probabilistically predict the fatigue damage under complex random and flight profile loading.

Mohanty, Subhasish; Chattopadhyay, Aditi; Peralta, Pedro; Quech, Dan

2010-04-01

152

Characterization of fatigue damage in A36 steel specimens using nonlinear rayleigh surface waves  

NASA Astrophysics Data System (ADS)

This research uses nonlinear Rayleigh surface waves to characterize damage in A36 steel specimens caused by monotonic tension and low cycle fatigue. Fatigue damage produces the increased acoustic nonlinearity that leads to the generation of measurable higher harmonics in the initially monochromatic Rayleigh wave. Tone burst Rayleigh wave signals are generated and detected using a pair of wedge transducers. The experimental results show an increase of acoustic nonlinearity in the early stage of fatigue life and a close relationship between the acoustic nonlinearity and cumulative plastic deformation.

Walker, Simon V.; Kim, Jin-Yeon; Jacobs, Laurence J.; Qu, Jianmin

2012-05-01

153

Methodology for Predicting the Onset of Widespread Fatigue Damage in Lap-Splice Joints  

E-print Network

NASA has conducted an Airframe Structural Integrity Program to develop the methodology to predict the onset of widespread fatigue damage in lap-splice joints of fuselage structures. Several stress analysis codes have been developed or enhanced to analyze the lap-splice-joint configuration. Fatigue lives in lap-splicejoint specimens and fatigue-crack growth in a structural fatigue test article agreed well with calculations from small-crack theory and fatigue-crack-growth analyses with the FASTRAN code. Residual-strength analyses of laboratory specimens and wide stiffened panels were predicted quite well from the critical crack-tip-opening angle (CTOA) fracture criterion and elastic-plastic finite-element analyses (two- or three-dimensional codes and the STAGS shell code). INTRODUCTION In the past decade, NASA in collaboration with the Federal Aviation Administration (FAA) and aircraft industry has conducted a program to develop the methodology to predict the onset of widespread fatigu...

Newman Jr Harris; J. C. Newman; C. E. Harris; R. S. Piascik; D. S. Dawicke

1998-01-01

154

A coupled/uncoupled deformation and fatigue damage algorithm utilizing the finite element method  

NASA Technical Reports Server (NTRS)

A fatigue damage computational algorithm utilizing a multiaxial, isothermal, continuum based fatigue damage model for unidirectional metal matrix composites has been implemented into the commercial finite element code MARC using MARC user subroutines. Damage is introduced into the finite element solution through the concept of effective stress which fully couples the fatigue damage calculations with the finite element deformation solution. An axisymmetric stress analysis was performed on a circumferentially reinforced ring, wherein both the matrix cladding and the composite core were assumed to behave elastic-perfectly plastic. The composite core behavior was represented using Hill's anisotropic continuum based plasticity model, and similarly, the matrix cladding was represented by an isotropic plasticity model. Results are presented in the form of S-N curves and damage distribution plots.

Wilt, Thomas E.; Arnold, Steven M.

1994-01-01

155

The octahedral shear strain theory and its relation to biaxial cumulative fatigue damage.  

NASA Technical Reports Server (NTRS)

The octahedral shear strain range concept is used in analyzing multiaxial fatigue damage. Limited test data from a two-step loading sequence show that the loading effect is still pronounced in the multiaxial case and that the relation between damage and cycle ratio is nonlinear. Among uniaxial cumulative damage concepts, the modified multiaxial double linear damage rule seems to show the most favorable experimental results.

Zamrik, S. Y.

1972-01-01

156

Differential continuum damage mechanics models for creep and fatigue of unidirectional metal matrix composites  

NASA Technical Reports Server (NTRS)

Three multiaxial isothermal continuum damage mechanics models for creep, fatigue, and creep/fatigue interaction of a unidirectional metal matrix composite volume element are presented, only one of which will be discussed in depth. Each model is phenomenological and stress based, with varying degrees of complexity to accurately predict the initiation and propagation of intergranular and transgranular defects over a wide range of loading conditions. The development of these models is founded on the definition of an initially transversely isotropic fatigue limit surface, static fracture surface, normalized stress amplitude function and isochronous creep damage failure surface, from which both fatigue and creep damage evolutionary laws can be obtained. The anisotropy of each model is defined through physically meaningful invariants reflecting the local stress and material orientation. All three transversely isotropic models have been shown, when taken to their isotropic limit, to directly simplify to previously developed and validated creep and fatigue continuum damage theories. Results of a nondimensional parametric study illustrate (1) the flexibility of the present formulation when attempting to characterize a large class of composite materials, and (2) its ability to predict anticipated qualitative trends in the fatigue behavior of unidirectional metal matrix composites. Additionally, the potential for the inclusion of various micromechanical effects (e.g., fiber/matrix bond strength, fiber volume fraction, etc.), into the phenomenological anisotropic parameters is noted, as well as a detailed discussion regarding the necessary exploratory and characterization experiments needed to utilize the featured damage theories.

Arnold, S. M.; Kruch, S.

1991-01-01

157

Structural health monitoring and condition based fatigue damage prognosis of complex metallic structures  

NASA Astrophysics Data System (ADS)

Current practice in fatigue life prediction is based on assumed initial structural flaws regardless of whether these assumed flaws actually occur in service. Furthermore, the model parameters are often estimated empirically based on previous coupon test results. Small deviations of the initial conditions and model parameters may generate large errors in the expected dynamical behavior of fatigue damage growth. Consequently, a large degree of conservatism is incorporated into structural designs due to these expected uncertainties. The current research in the area of Structural Health Monitoring (SHM) and probabilistic fatigue modeling can help in improved fatigue damage modeling and remaining useful life estimation (RULE) techniques. This thesis discusses an integrated approach of SHM and adaptive prognosis model that not only estimates the current health, but can also forecast the future health and calculate RULE of an aerospace structural component with high level of confidence. The approach does not assume any fixed initial condition and model parameters. This dissertation include the following novel contributions. 1) A Bayesian based off-line Gaussian Process (GP) model is developed, which is the core of the present condition based prognosis approach. 2) Different passive and active SHM approaches are used for on-line damage state estimation. Applications of passive sensing are shown to estimate the time-series fatigue damage states both under constant and random fatigue loading. It is found that there is a good correlation between estimated damage states and optically measured damage states. In addition, applications for both narrow and broadband active sensing approaches are presented to estimate smaller incipient damage. It is demonstrated that the active sensing techniques not only can identify smaller incipient damage but also can quantify fatigue damage during all the three stages (stages I, II, and III) of fatigue life. 3) An integrated on-line SHM and off-line GP predictive model is developed for real-time condition based damage state estimation of complex Aluminum structures under fatigue loading. It is found that the proposed technique can forecast the future damage states well before the final failure.

Mohanty, Subhasish

158

Damage mechanisms in bithermal and thermomechanical fatigue of Haynes 188  

NASA Technical Reports Server (NTRS)

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

Kalluri, Sreeramesh; Halford, Gary R.

1992-01-01

159

Foreign object damage and fatigue crack threshold: Cracking outside shallow indents  

Microsoft Academic Search

Foreign Object Damage (FOD) usually happens when objects are ingested into jet engines powering military or civil aircraft. Under extreme conditions, FOD can lead to severe structural damage. More commonly it produces local impacted sites of the fan and compressor airfoils, lowering fatigue life of these components. FOD is a prime cause for maintenance and repair in aircraft engines. In

Xi Chen; John W. Hutchinson

2001-01-01

160

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

161

Characterization of fretting fatigue damage of PVD TiN coated biomedical titanium alloys  

Microsoft Academic Search

Fretting fatigue is a form of adhesive wear damage due to small oscillatory movement between two contacting bodies under the action of uniform or non-uniform cyclic loads. Cyclic loads may be experienced due to vibration of one or both the bodies eventually leading to failure at the contact area. Fretting damage is also experienced by load bearing implants within the

Aravind Vadiraj; M. Kamaraj

2006-01-01

162

Fatigue life performance comparisons of tapered roller bearings with debris-damaged raceways{copyright}  

SciTech Connect

Debris-contaminated lubrication environments is inherent in many equipment applications and requires mechanical components that, as much as possible, are resistant to the potential effects of debris particles. Bearing fatigue life performance comparisons were made for various bearing materials and manufacturer origin, in order to assess the variability in performance of debris-damaged raceways. The evaluation was conducted using a repeatable debris-damaging process prior to fatigue testing of each group of bearings. The performance results reveal wide variations in the impact that debris damage can have on various bearing products and materials. 11 refs., 4 figs., 4 tabs.

Nixon, H.P.; Zantopulos, H. [Timken Company, Canton, OH (United States)

1995-09-01

163

Dynamics and Fatigue Damage of Wind Turbine Rotors  

E-print Network

. The model avoids computer si- mulation and succeeding rainflow counting and yields an analyti- cal solution; FATIGUE; FINITE-ELEMENT METHOD; MECHANICAL VIBRATIONS; PEAK LOAD; R CODES; ROTORS; SERVICE LIFE

164

Fatigue damage of stainless steel diffusion-bonded joints  

Microsoft Academic Search

Vacuum diffusion bonding was carried out on 316L stainless steel. Metallographic inspections and micro-hardness testing were conducted near the interface of diffusion-bonded joints. Fatigue tests were performed to investigate the mechanical performance of diffusion-bonded joints under cyclic loading. Results indicate that, although the static strength of joints closes to that of base metal, fatigue life of the diffusion-bonded joint is

Shu-Xin Li; Fu-Zhen Xuan; Shan-Tung Tu

2008-01-01

165

Swept Blade Aero-Elastic Model for a Small Wind Turbine (Presentation)  

SciTech Connect

A preprocessor for analyzing preswept wind turbines using the in-house aero-elastic tool coupled with a multibody dynamic simulator was developed. A baseline 10-kW small wind turbine with straight blades and various configurations that featured bend-torsion coupling via blade-tip sweep were investigated to study their impact on ultimate loads and fatigue damage equivalent loads.

Damiani, R.; Lee, S.; Larwood, S.

2014-07-01

166

Drilling induced fatigue damage in titanium aluminum vanadate  

NASA Astrophysics Data System (ADS)

The objective of this work is to develop an understanding of the relationship between hole drilling processes and the fatigue performance of the resulting part in Ti-6Al-4V. This problem is significant, as on the order of one-hundred thousand to a million holes are created in a typical large aircraft, and the limiting performance criterion is usually the fatigue lifetime. The path between the drilling process parameters and the fatigue performance has two main steps: characterization of the thermo-mechanical drill process and assessment of the relationship between the hole integrity left by the drill process and the fatigue performance. Development has been limited by the robustness of previously available thermal characterization systems, poor correlation between drill processes and physical observations of metallic effects, and limited success identifying the key hole integrity characteristics. This work develops robust novel thermal methods which enable integration into current drill process development techniques. The key integrity drivers in the hole wall are identified, characterized, and a system to assess is presented. The thermal and hole integrity trends are presented as guidance for drill process development providing significant opportunities to optimize processes. Thus, this work advances knowledge of the process to fatigue lifetime relationship by correlating the thermo-mechanical drill process to fatigue life in Ti-6Al-4V.

Castle, James B.

167

Role of Brain IL1? on Fatigue Following Exercise-Induced Muscle Damage  

Microsoft Academic Search

ABSTRACT Brain cytokines, induced by various inflammatory challenges have been linked to sickness behaviors, including fatigue. However, the relationship between brain cytokines and fatigue following exercise is not well understood. Delayed recovery of running performance,following muscle-damaging,downhill running is associated with increased brain IL-1?concentration as compared to uphill running. However, there has been no systematic evaluation of the direct effect of

Martin D. Carmichael; J. Mark Davis; E. Angela Murphy; Adrienne S. Brown; James A. Carson; Eugene P. Mayer; Abdul Ghaffar

2006-01-01

168

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

169

Fatigue damage growth mechanisms in continuous fiber reinforced titanium matrix composites  

NASA Technical Reports Server (NTRS)

The role of fiber/matrix interface strength, residual thermal stresses, and fiber and matrix properties on fatigue damage accumulation in continuous fiber metal matrix composites (MMC) is discussed. Results from titanium matrix silicon carbide fiber composites is the primary topic of discussion. Results were obtained from both notched and unnotched specimens at room and elevated temperatures. The stress in the 0 deg fibers was identified as the controlling factor in fatigue life. Fatigue of the notched specimens indicated that cracks can grow in the matrix materials without breaking fibers.

Johnson, W. S.; Naik, R. A.; Pollock, W. D.

1990-01-01

170

Fatigue damage evaluation of austenitic stainless steel using nonlinear ultrasonic waves in low cycle regime  

SciTech Connect

The interrupted low cycle fatigue test of austenitic stainless steel was conducted and the dislocation structure and fatigue damage was evaluated subsequently by using both transmission electron microscope and nonlinear ultrasonic wave techniques. A “mountain shape” correlation between the nonlinear acoustic parameter and the fatigue life fraction was achieved. This was ascribed to the generation and evolution of planar dislocation structure and nonplanar dislocation structure such as veins, walls, and cells. The “mountain shape” correlation was interpreted successfully by the combined contribution of dislocation monopole and dipole with an internal-stress dependent term of acoustic nonlinearity.

Zhang, Jianfeng; Xuan, Fu-Zhen, E-mail: fzxuan@ecust.edu.cn [MOE Key Laboratory of Pressurized System and Safety, School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237 (China)

2014-05-28

171

Fatigue damage localization using time-domain features extracted from nonlinear Lamb waves  

NASA Astrophysics Data System (ADS)

Nonlinear guided waves are sensitive to small-scale fatigue damage that may hardly be identified by traditional techniques. A characterization method for fatigue damage is established based on nonlinear Lamb waves in conjunction with the use of a piezoelectric sensor network. Theories on nonlinear Lamb waves for damage detection are first introduced briefly. Then, the ineffectiveness of using pure frequency-domain information of nonlinear wave signals for locating damage is discussed. With a revisit to traditional gross-damage localization techniques based on the time of flight, the idea of using temporal signal features of nonlinear Lamb waves to locate fatigue damage is introduced. This process involves a time-frequency analysis that enables the damage-induced nonlinear signal features, which are either undiscernible in the original time history or uninformative in the frequency spectrum, to be revealed. Subsequently, a finite element modeling technique is employed, accounting for various sources of nonlinearities in a fatigued medium. A piezoelectric sensor network is configured to actively generate and acquire probing Lamb waves that involve damageinduced nonlinear features. A probability-based diagnostic imaging algorithm is further proposed, presenting results in diagnostic images intuitively. The approach is experimentally verified on a fatigue-damaged aluminum plate, showing reasonably good accuracy. Compared to existing nonlinear ultrasonics-based inspection techniques, this approach uses a permanently attached sensor network that well accommodates automated online health monitoring; more significantly, it utilizes time-domain information of higher-order harmonics from time-frequency analysis, and demonstrates a great potential for quantitative characterization of small-scale damage with improved localization accuracy.

Hong, Ming; Su, Zhongqing; Lu, Ye; Cheng, Li

2014-03-01

172

Computer simulation of variable amplitude fatigue crack initiation behaviour using a new strain-based cumulative damage model  

Microsoft Academic Search

Computer software for the prediction of fatigue crack initiation has been developed. Based on a model derived from the closure behaviour of microcracks and the intrinsic resistance of metals and alloys to fatigue damage, this software allows predictions to be readily applied to quickly provide fatigue crack initiation life predictions for a wide range of alloys based on inputs of

A. K. Lynn; D. L. DuQuesnay

2002-01-01

173

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

2007-07-01

174

Damage detection in carbon composite material typical of wind turbine blades using auto-associative neural networks  

NASA Astrophysics Data System (ADS)

The structure of a wind turbine blade plays a vital role in the mechanical and structural operation of the turbine. As new generations of offshore wind turbines are trying to achieve a leading role in the energy market, key challenges such as a reliable Structural Health Monitoring (SHM) of the blades is significant for the economic and structural efficiency of the wind energy. Fault diagnosis of wind turbine blades is a "grand challenge" due to their composite nature, weight and length. The damage detection procedure involves additional difficulties focused on aerodynamic loads, environmental conditions and gravitational loads. It will be shown that vibration dynamic response data combined with AANNs is a robust and powerful tool, offering on-line and real time damage prediction. In this study the features used for SHM are Frequency Response Functions (FRFs) acquired via experimental methods based on an LMS system by which identification of mode shapes and natural frequencies is accomplished. The methods used are statistical outlier analysis which allows a diagnosis of deviation from normality and an Auto-Associative Neural Network (AANN). Both of these techniques are trained by adopting the FRF data for normal and damage condition. The AANN is a method which has not yet been widely used in the condition monitoring of composite materials of blades. This paper is trying to introduce a new scheme for damage detection, localisation and severity assessment by adopting simple measurements such as FRFs and exploiting multilayer neural networks and outlier novelty detection.

Dervilis, N.; Barthorpe, R. J.; Antoniadou, I.; Staszewski, W. J.; Worden, K.

2012-04-01

175

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

176

Fatigue and Damage in Structural Materials Studied by X-Ray Tomography  

NASA Astrophysics Data System (ADS)

This paper reviews progress using X-ray computed tomography to study damage accumulation. Since its introduction, X-ray microtomography has been used to diagnose the presence of damage. In this review, a wide range of damage-accumulation mechanisms are covered including cavitation, fracture, microcracking, fatigue cracking, and stress corrosion cracking. In this regard, the advantages of attenuation and phase contrast imaging are discussed. This review includes both measurements of damage accumulation, taken postmortem, and the incremental monitoring of damage-accumulation processes during life (sometimes termed four-dimensional tomography). In addition to the qualitative diagnostic studies, the quantitative analysis of tomography images to extract key failure parameters is examined.

Withers, Philip J.; Preuss, Michael

2012-08-01

177

Isothermal Fatigue, Damage Accumulation, and Life Prediction of a Woven PMC  

NASA Technical Reports Server (NTRS)

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

Gyekenyesi, Andrew L.

1998-01-01

178

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.

179

Fatigue damage criteria - Matrix, fibers and interfaces of continuous fiber reinforced metal matrix composites  

NASA Technical Reports Server (NTRS)

Continuous fiber reinforced metal matrix composites (MMC) are projected for use in high temperature, stiffness critical parts that will be subjected to cyclic loadings. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four catagories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage are discussed and illustrated by examples. The emphasis is on the fatigue of unnotched laminates.

Johnson, W. S.

1988-01-01

180

Experimental and numerical investigation of fatigue damage due to wave-induced vibrations in a containership in head seas  

Microsoft Academic Search

Fatigue cracks have been known to occur in welded ships for several decades. For large ocean-going ships wave-induced vibrations\\u000a can, depending on trade and design, cause up to 50% of the fatigue damage. The vibrations may be due to springing and whipping\\u000a effects. In this paper, we address the fatigue damage caused by wave-induced vibrations in a containership of newer

Ingo Drummen; Gaute Storhaug; Torgeir Moan

2008-01-01

181

On the application of the KitagawaTakahashi diagram to foreign-object damage and high-cycle fatigue  

E-print Network

-cycle fatigue J.O. Peters a,1 , B.L. Boyce a,2 , X. Chen b , J.M. McNaney a , J.W. Hutchinson b , R.O. Ritchie a-object damage (FOD) and its effect on high-cycle fatigue (HGF) failures in a turbine engine Ti­ 6Al­4V alloy specimen surface of tensile fatigue specimens at velocities of 200 and 300 m/s. Such damage was found

Hutchinson, John W.

182

Fatigue life prediction of rotor blade composites: Validation of constant amplitude formulations with variable amplitude experiments  

NASA Astrophysics Data System (ADS)

The effect of Constant Life Diagram (CLD) formulation on the fatigue life prediction under variable amplitude (VA) loading was investigated based on variable amplitude tests using three different load spectra representative for wind turbine loading. Next to the Wisper and WisperX spectra, the recently developed NewWisper2 spectrum was used. Based on these variable amplitude fatigue results the prediction accuracy of 4 CLD formulations is investigated. In the study a piecewise linear CLD based on the S-N curves for 9 load ratios compares favourably in terms of prediction accuracy and conservativeness. For the specific laminate used in this study Boerstra's Multislope model provides a good alternative at reduced test effort.

Westphal, T.; Nijssen, R. P. L.

2014-12-01

183

Fatigue Life of Damaged Bridge Deck Panels Strengthened With Carbon Fiber Hongseob Oh, Jongsung Sim, and Christian Meyer  

E-print Network

1 Fatigue Life of Damaged Bridge Deck Panels Strengthened With Carbon Fiber Sheets Hongseob Oh was applied to test panels, which were then reinforced with carbon fiber sheets (CFS) using two different for bridge decks, based on cumulative damage theory. Keywords: bridge deck slab, carbon fiber sheets, fatigue

Meyer, Christian

184

Cumulative damage and the response of human bone in two-step loading fatigue.  

PubMed

It has already been shown that in fatigue tests in vitro human cortical bone accumulates damage in the form of microcracks and that the total number of microcracks generated prior to the creation of the fatal macrocrack, and their effect (softening) on the material properties, depends on the level of applied stress. At each stress level the amount of accumulated damage has also been shown to be a non-linear function of the cycle number (Zioupos et al., 1996a, b; Pattin et al., 1996). The theoretical implications of the previous findings and two possible models for cumulative damage were put to the test here by performing tensile fatigue tests in two-step level (high/low or low/high) loading on human cortical bone specimens. The results indicate that the accumulation of damage in-vitro is highly dependent on the level of stress and the stress history. Usual linear expressions for fatigue lifetime predictions, like the Palmgren-Miner rule, substantially over or underestimate the outcome depending on whether the stress was applied in a high/low or a low/high sequence, respectively. In view of these discrepancies we conclude that predicting the fatigue lifetime of any bone in vivo under variable loading and complex history regimes is an extremely difficult task to which the study of accumulation of damage can offer a significant but, perhaps, still limited contribution. PMID:9802783

Zioupos, P; Casinos, A

1998-09-01

185

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

NASA Technical Reports Server (NTRS)

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.

1994-01-01

186

Modeling nonlinearities of ultrasonic waves for fatigue damage characterization: theory, simulation, and experimental validation.  

PubMed

A dedicated modeling technique for comprehending nonlinear characteristics of ultrasonic waves traversing in a fatigued medium was developed, based on a retrofitted constitutive relation of the medium by considering the nonlinearities originated from material, fatigue damage, as well as the "breathing" motion of fatigue cracks. Piezoelectric wafers, for exciting and acquiring ultrasonic waves, were integrated in the model. The extracted nonlinearities were calibrated by virtue of an acoustic nonlinearity parameter. The modeling technique was validated experimentally, and the results showed satisfactory consistency in between, both revealing: the developed modeling approach is able to faithfully simulate fatigue crack-incurred nonlinearities manifested in ultrasonic waves; a cumulative growth of the acoustic nonlinearity parameter with increasing wave propagation distance exists; such a parameter acquired via a sensing path is nonlinearly related to the offset distance from the fatigue crack to that sensing path; and neither the incidence angle of the probing wave nor the length of the sensing path impacts on the parameter significantly. This study has yielded a quantitative characterization strategy for fatigue cracks using embeddable piezoelectric sensor networks, facilitating deployment of structural health monitoring which is capable of identifying small-scale damage at an embryo stage and surveilling its growth continuously. PMID:24156928

Hong, Ming; Su, Zhongqing; Wang, Qiang; Cheng, Li; Qing, Xinlin

2014-03-01

187

Observations of fatigue crack initiation and damage growth in notched titanium matrix composites  

NASA Technical Reports Server (NTRS)

The purpose was to characterize damage initiation and growth in notched titanium matrix composites at room temperature. Double edge notched or center open hole SCS-6/Ti-15-3 specimens containing 0 deg plies or containing both 0 and 90 deg plies were fatigued. The specimens were tested in the as-fabricated (ASF) and in heat-treated conditions. A local strain criterion using unnotched specimen fatigue data was successful in predicting fatigue damage initiation. The initiation stress level was accurately predicted for both a double edge notched unidirectional specimen and a cross-plied center hole specimen. The fatigue produced long multiple cracks growing from the notches. These fatigue cracks were only in the matrix material and did not break the fibers in their path. The combination of matrix cracking and fiber/matrix debonding appears to greatly reduce the stress concentration around the notches. The laminates that were heat treated showed a different crack growth pattern. In the ASF specimens, matrix cracks had a more tortuous path and showed considerable more crack branching. For the same specimen geometry and cyclic stress, the (0/90/0) laminate with a hole had far superior fatigue resistance than the matrix only specimen with a hole.

Naik, R. A.; Johnson, W. S.

1990-01-01

188

Observations of fatigue crack initiation and damage growth in notched titanium matrix composites  

NASA Technical Reports Server (NTRS)

The purpose was to characterize damage initiation and growth in notched titanium matrix composites at room temperature. Double edge notched or center open hole SCS-6/Ti-15-3 specimens containing 0 deg plies or containing both 0 and 90 deg plies were fatigued. The specimens were tested in the as-fabricated (ASF) and in heat-treated conditions. A local strain criterion using unnotched specimen fatigue data was successful in predicting fatigue damage initiation. The initiation stress level was accurately predicted for both a double edge notched unidirectional specimen and a cross-plied center hole specimen. The fatigue produced long multiple cracks growing from the notches. These fatigue cracks were only in the matrix material and did not break the fibers in their path. The combination of matrix cracking and fiber/matrix debonding appears to greatly reduce the stress concentration around the notches. The laminates that were heat treated showed a different crack growth pattern. In the ASF specimens, matrix cracks had a more tortuous path and showed considerable more crack branching. For the same specimen geometry and cyclic stress, the (0/90/0) laminate with a hole had far superior fatigue resistance than the matrix only specimen with a hole.

Naik, Rajiv A.; Johnson, W. S.

1991-01-01

189

Fatigue  

MedlinePLUS

... this page It's been added to your dashboard . Fatigue Fatigue is when you feel very tired or exhausted. ... prepare for the hard work ahead. Causes of fatigue During early pregnancy, your body makes more of ...

190

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, ...

191

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

192

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

NASA Technical Reports Server (NTRS)

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

Jones, David J.; Kurath, Peter

1988-01-01

193

Dependence of Microelastic-plastic Nonlinearity of Martensitic Stainless Steel on Fatigue Damage Accumulation  

NASA Technical Reports Server (NTRS)

Self-organized substructural arrangements of dislocations formed in wavy slip metals during cyclic stress-induced fatigue 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 model as a function of percent full fatigue life to fracture. A wave interaction factor f(sub WI) is introduced into the model to account experimentally for the relative volume of material fatigue damage included in the volume of material swept out by an interrogating acoustic wave. For cyclic stress-controlled loading at 551 MPa and f(sub WI) = 0.013 the model predicts a monotonic increase in Beta from dislocation substructures of almost 100 percent from the virgin state to roughly 95 percent full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, over the last five percent of fatigue life the model predicts a rapid monotonic increase of Beta 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 f(sub WI) of 0.013.

Cantrell, John H.

2006-01-01

194

Evidence of Fatigue Damage in the Local Structure of Zr-based Bulk Metallic Glasses  

NASA Astrophysics Data System (ADS)

Bulk metallic glasses (BMG) are particularly vulnerable to fatigue damage, where catastrophic failure may occur without observable macroscopic changes. The local atomic structure of two BMGs with compositions of Zr50Cu40Al10 and Zr60Cu30Al10 was investigated by synchrotron X-ray and neutron diffraction via the pair density function analysis. Under a load of 1600 MPa, the number of compression cycles ranged from 0 -- 10^7 at 10 Hz. At room temperature, a subtle but irreversible change is observed in the local structure due to fatigue. Upon cooling down to 10 K, however, a significant structural re-organization is observed especially in the short range that is proportional to the number of fatigue cycles. The effect becomes more pronounced with increasing the number of loading cycles. The changes are beyond the usual narrowing from reducing thermal vibrations. The results indicate that hardening occurs after fatigue.

Louca, Despina; Tong, Peng; Liaw, Peter; Wang, Gongyao; Yokoyama, Yoshihiko; Llobet, Anna; Spence, Rick

2011-03-01

195

Thermography Inspection for Early Detection of Composite Damage in Structures During Fatigue Loading  

NASA Technical Reports Server (NTRS)

Advanced composite structures are commonly tested under controlled loading. Understanding the initiation and progression of composite damage under load is critical for validating design concepts and structural analysis tools. Thermal nondestructive evaluation (NDE) is used to detect and characterize damage in composite structures during fatigue loading. A difference image processing algorithm is demonstrated to enhance damage detection and characterization by removing thermal variations not associated with defects. In addition, a one-dimensional multilayered thermal model is used to characterize damage. Lastly, the thermography results are compared to other inspections such as non-immersion ultrasonic inspections and computed tomography X-ray.

Zalameda, Joseph N.; Burke, Eric R.; Parker, F. Raymond; Seebo, Jeffrey P.; Wright, Christopher W.; Bly, James B.

2012-01-01

196

Subsurface damage development during fretting fatigue of high strength steel  

Microsoft Academic Search

The results of fretting fatigue experiments performed on two high-strength structural steels, PH 13-8 Mo stainless steel and quenched and tempered 4340 steel, are evaluated. Observations regarding the subsurface deformation and cracking behavior of the steels are compared and contrasted. It was found that the fretting stresses influenced early crack growth to a greater depth in PH 13-8 Mo stainless

J. A. Pape; R. W. Neu

2007-01-01

197

Fatigue Damage Mechanism of Oil Film Bearing Sleeve  

Microsoft Academic Search

With the rapid development of the steel industry, to keep pace with the current trend of high speed, continuous, and large-scale production that focuses on automation and high levels of efficiency, many state-owned steel companies are being equipped with oil film bearings. Through long-term on-spot inspection and research on the fatigue failure of oil film bearing, three segments of annulated

Qing-xue HUANG; Jian-mei WANG; Li-feng MA; Chun-Jiang ZHAO

2007-01-01

198

Imaging of Fatigue Damage in CFRP Composite Laminates Using Nonlinear Harmonic Generation  

NASA Astrophysics Data System (ADS)

In this paper, experimental evidence is presented that suggests a strong nonlinear interaction between acoustic wave and micro-structural damage before the onset of delaminations in fatigued CFRP samples. Sample used were 32 plies quasi-isotropic graphite/epoxy laminate fatigued with a four point bending fatigue. First harmonic images were constructed from the amplitude of the first harmonic normalized by the amplitude of the fundamental. Harmonic imaging technique (HIT) shows a much higher sensitivity to micro-damage than amplitude C-scan. Correlations are established between the image zone where the nonlinear parameter is high and the region where a high density of micro-delamination and matrix cracks is observed.

Mattei, Christophe; Marty, Pierre

2003-03-01

199

In-situ fatigue damage monitoring using symbolic dynamic filtering of ultrasonic signals  

Microsoft Academic Search

This article presents a data-driven method of pattern identification forin-situ monitor- ing of fatigue damage in polycrystalline alloys that are commonly used in aerospace structures. The concept is built upon analytic signal space partitioning of ultrasonic data sequences for sym- bolic dynamic filtering of the underlying information. The statistical patterns of evolving damage are generated for real-time monitoring of the

D S Singh; S Gupta; A Ray

2009-01-01

200

Fatigue Damage Evaluation through Stiffness Measurements in Boron-Epoxy Laminates  

Microsoft Academic Search

Stiffness reductions, resulting from fatigue damage, were measured for unnotched [±45]s, [0\\/90] s, and [0\\/90\\/ ±45 ] s boron\\/epoxy laminates. Deg radation in the various in-plane stiffnesses (Exx, Byy, Gxy) were measured using a combination of uniaxial tension, rail shear, and flexure tests. An attempt was made to predict stiffness loss at failure from a secant modulus criterion. Damage growth

T. Kevin OBrien; Kenneth L. Reifsnider

1981-01-01

201

The Characteristics of Fatigue Damage in the Fuselage Riveted Lap Splice Joint  

NASA Technical Reports Server (NTRS)

An extensive data base has been developed to form the physical basis for new analytical methodology to predict the onset of widespread fatigue damage in the fuselage lap splice joint. The results of detailed destructive examinations have been cataloged to describe the physical nature of MSD in the lap splice joint. ne catalog includes a detailed description, e.g., crack initiation, growth rates, size, location, and fracture morphology, of fatigue damage in the fuselage lap splice joint structure. Detailed examinations were conducted on a lap splice joint panel removed from a full scale fuselage test article after completing a 60,000 cycle pressure test. The panel contained a four bay region that exhibited visible outer skin cracks and regions of crack link-up along the upper rivet row. Destructive examinations revealed undetected fatigue damage in the outer skin, inner skin, and tear strap regions. Outer skin fatigue cracks were found to initiate by fretting damage along the faying surface. The cracks grew along the faying surface to a length equivalent to two to three skin thicknesses before penetrating the outboard surface of the outer skin. Analysis of fracture surface marker bands produced during full scale testing revealed that all upper rivet row fatigue cracks contained in a dim bay region grow at similar rates; this important result suggests that fracture mechanics based methods can be used to predict the growth of outer skin fatigue cracks in lap splice structure. Results are presented showing the affects of MSD and out-of-plane pressure loads on outer skin crack link-up.

Piascik, Robert S.; Willard, Scott A.

1997-01-01

202

A method for accurate estimation of the fatigue damage induced by bimodal processes  

Microsoft Academic Search

This paper presents a method for calculating the fatigue damage from a stochastic bimodal process, in which the high frequency (HF) and low frequency (LF) components are narrowband Gaussian processes. Rainflow cycle counting identifies the following: small but numerous cycles, and large but fewer ones. In existing methods, the small-cycle amplitudes are assumed to be identical to that of the

Y. M. Low

2010-01-01

203

Role of brain macrophages on IL1? and fatigue following eccentric exercise-induced muscle damage  

Microsoft Academic Search

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

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

2010-01-01

204

Stochastic Measure of Fatigue Crack Damage for Health Monitoring of Ductile  

E-print Network

modeling Á fatigue crack growth Á damage measure Á risk analysis Á life prediction 1 Introduction Decision represent the material degradation aspects of critical plant components [11]. The reason is that traditional should be addressed. E-mail: axr2@psu.edu Copyright � 2004 Sage Publications, Vol 3(3): 0245­263 [1475

Ray, Asok

205

A modified nonlinear damage accumulation model for fatigue life prediction considering load interaction effects.  

PubMed

Many structures are subjected to variable amplitude loading in engineering practice. The foundation of fatigue life prediction under variable amplitude loading is how to deal with the fatigue damage accumulation. A nonlinear fatigue damage accumulation model to consider the effects of load sequences was proposed in earlier literature, but the model cannot consider the load interaction effects, and sometimes it makes a major error. A modified nonlinear damage accumulation model is proposed in this paper to account for the load interaction effects. Experimental data of two metallic materials are used to validate the proposed model. The agreement between the model prediction and experimental data is observed, and the predictions by proposed model are more possibly in accordance with experimental data than that by primary model and Miner's rule. Comparison between the predicted cumulative damage by the proposed model and an existing model shows that the proposed model predictions can meet the accuracy requirement of the engineering project and it can be used to predict the fatigue life of welded aluminum alloy joint of Electric Multiple Units (EMU); meanwhile, the accuracy of approximation can be obtained from the proposed model though more simple computing process and less material parameters calling for extensive testing than the existing model. PMID:24574866

Gao, Huiying; Huang, Hong-Zhong; Zhu, Shun-Peng; Li, Yan-Feng; Yuan, Rong

2014-01-01

206

Probabilistic assessment of weld fatigue damage for a nonlinear combination of correlated stress components  

Microsoft Academic Search

Estimation of fatigue damage for welds which are subjected to multiple stress components is addressed. Each component is represented by a separate stress cycle distribution of the Weibull type, and the effect of correlation between the different components is addressed. Three different types of bivariate Weibull distributions are considered. These are of the following categories: (i) The Nataf model (ii)

Bernt J. Leira

2011-01-01

207

A Modified Nonlinear Damage Accumulation Model for Fatigue Life Prediction Considering Load Interaction Effects  

PubMed Central

Many structures are subjected to variable amplitude loading in engineering practice. The foundation of fatigue life prediction under variable amplitude loading is how to deal with the fatigue damage accumulation. A nonlinear fatigue damage accumulation model to consider the effects of load sequences was proposed in earlier literature, but the model cannot consider the load interaction effects, and sometimes it makes a major error. A modified nonlinear damage accumulation model is proposed in this paper to account for the load interaction effects. Experimental data of two metallic materials are used to validate the proposed model. The agreement between the model prediction and experimental data is observed, and the predictions by proposed model are more possibly in accordance with experimental data than that by primary model and Miner's rule. Comparison between the predicted cumulative damage by the proposed model and an existing model shows that the proposed model predictions can meet the accuracy requirement of the engineering project and it can be used to predict the fatigue life of welded aluminum alloy joint of Electric Multiple Units (EMU); meanwhile, the accuracy of approximation can be obtained from the proposed model though more simple computing process and less material parameters calling for extensive testing than the existing model. PMID:24574866

Huang, Hong-Zhong; Yuan, Rong

2014-01-01

208

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

NASA Astrophysics Data System (ADS)

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

Colin, Julie

209

A Coupled/Uncoupled Computational Scheme for Deformation and Fatigue Damage Analysis of Unidirectional Metal-Matrix Composites  

NASA Technical Reports Server (NTRS)

A fatigue damage computational algorithm utilizing a multiaxial, isothermal, continuum-based fatigue damage model for unidirectional metal-matrix composites has been implemented into the commercial finite element code MARC using MARC user subroutines. Damage is introduced into the finite element solution through the concept of effective stress that fully couples the fatigue damage calculations with the finite element deformation solution. Two applications using the fatigue damage algorithm are presented. First, an axisymmetric stress analysis of a circumferentially reinforced ring, wherein both the matrix cladding and the composite core were assumed to behave elastic-perfectly plastic. Second, a micromechanics analysis of a fiber/matrix unit cell using both the finite element method and the generalized method of cells (GMC). Results are presented in the form of S-N curves and damage distribution plots.

Wilt, Thomas E.; Arnold, Steven M.; Saleeb, Atef F.

1997-01-01

210

Fatigue damage in superalloys determined using Doppler broadening positron annihilation  

NASA Technical Reports Server (NTRS)

Axial fatigue specimens of three superalloys, Inconel 718, Incoloy 903 and Haynes 188, were machined from solution-heat-treated material and artificially aged. They were subjected to cyclic loading for a selected number of cycles after which the S parameter was determined using Doppler broadening positron annihilation. Initially, the S parameter decreased, followed by a large increase and a subsequent decline leading to fracture. This has been interpreted as the removal of residual vacancies, the introduction of new defects by cyclic loading, and, finally, a clustering of the defects as microcracks which grow to cause failure.

Hoeckelman, Donald; Leighly, H. P., Jr.

1990-01-01

211

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

212

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

PubMed Central

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 micro cracks, 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

2010-01-01

213

A model for predicting damage induced fatigue life of laminated composite structural components  

NASA Technical Reports Server (NTRS)

This paper presents a model for predicting the life of laminated composite structural components subjected to fatigue induced microstructural damage. The model uses the concept of continuum damage mechanics, wherein the effects of microcracks are incorporated into a damage dependent lamination theory instead of treating each crack as an internal boundary. Internal variables are formulated to account for the effects of both matrix cracks and internal delaminations. Evolution laws for determining the damage variables as functions of ply stresses are proposed, and comparisons of predicted damage evolution are made to experiment. In addition, predicted stiffness losses, as well as ply stresses are shown as functions of damage state for a variety of stacking sequences.

Allen, David H.; Lo, David C.; Georgiou, Ioannis T.; Harris, Charles E.

1990-01-01

214

A Multiscale Modeling Approach to Fatigue Damage in Discontinuous Fiber Polymer Composites  

SciTech Connect

The damage process in composite materials occurs at different length scales, ranging from the scale of the constituents and defects (microscale) to that of a composite structure (macroscale). This paper develops a multiscale mechanistic approach to fatigue damage in discontinuous-fiber polymer composites. The approach accounts for the damage mechanisms in addition to the constituents’ properties and characteristics. It links these micro-features to the behavior of the composite structure through a series of scale transitions using computational techniques that are based on micromechanical modeling, a thermodynamics-based formulation and finite element analysis.

Nguyen, Ba Nghiep; Tucker, Brian J.; Khaleel, Mohammad A.

2005-06-14

215

The Growth of Multi-Site Fatigue Damage in Fuselage Lap Joints  

NASA Technical Reports Server (NTRS)

Destructive examinations were performed to document the progression of multi-site damage (MSD) in three lap joint panels that were removed from a full scale fuselage test article that was tested to 60,000 full pressurization cycles. Similar fatigue crack growth characteristics were observed for small cracks (50 microns to 10 mm) emanating from counter bore rivets, straight shank rivets, and 100 deg counter sink rivets. Good correlation of the fatigue crack growth data base obtained in this study and FASTRAN Code predictions show that the growth of MSD in the fuselage lap joint structure can be predicted by fracture mechanics based methods.

Piascik, Robert S.; Willard, Scott A.

1999-01-01

216

Nondestructive indication of fatigue damage and residual lifetime in ferromagnetic construction materials  

NASA Astrophysics Data System (ADS)

A new revolutionary attitude toward investigation of fatigue damage in cyclically loaded steel samples is reported. The measurement is based on the method of magnetic adaptive testing, which--in contrast to traditional magnetic hysteresis investigations--picks up the relevant information from systematic measurement and evaluation of whole minor magnetic hysteresis loops and their derivatives. Satisfactory correlations between nondestructively measured magnetic descriptors and actual lifetime of the fatigued material were found. The presented method is able to serve as a powerful tool for indication of changes, which occur in the structure of the inspected objects during their industrial service lifetime, as long as they are manufactured from ferromagnetic materials.

Tomáš, Ivan; Ková?ík, Ond?ej; Vértesy, Gábor; Kadlecová, Jana

2014-06-01

217

Temporal Effect of In Vivo Tendon Fatigue Loading on the Apoptotic Response Explained in the Context of Number of Fatigue Loading Cycles and Initial Damage Parameters  

PubMed Central

Accumulation of damage is a leading factor in the development of tendinopathy. Apoptosis has been implicated in tendinopathy, but the biological mechanisms responsible for initiation and progression of these injuries are poorly understood. We assessed the relationship between initial induced damage and apoptotic activity 3 and 7 days after fatigue loading. We hypothesized that greater apoptotic activity (i) will be associated with greater induced damage and higher number of fatigue loading cycles, and (ii) will be higher at 7 than at 3 days after loading. Left patellar tendons were fatigue loaded for either 100 or 7,200 cycles. Diagnostic tests were applied before and after fatigue loading to determine the effect of fatigue loading on hysteresis, elongation, and loading and unloading stiffness (damage parameters). Cleaved Caspase-3 staining was used to identify and calculate the percent apoptosis in the patellar tendon. While no difference in apoptotic activity occurred between the 100 and 7,200 cycle groups, greater apoptotic activity was associated with greater induced damage. Apoptotic activity was higher at 7 than 3 days after loading. We expect that the decreasing number of healthy cells that can repair the induced damage in the tendon predispose it to further injury. PMID:24838769

Andarawis-Puri, Nelly; Philip, Anaya; Laudier, Damien; Schaffler, Mitchell B.; Flatow, Evan L.

2014-01-01

218

Bone formation after damaging in vivo fatigue loading results in recovery of whole-bone monotonic strength and increased fatigue life.  

PubMed

Bone has a remarkable capacity for self-repair. We previously reported a woven bone response after damaging in vivo fatigue loading of the rat ulna that led to a rapid recovery of whole-bone strength. In the current study we asked: does the bone response in the 12 days after damaging fatigue loading result in a bone that has normal fatigue properties? The right forelimbs of 52 adult rats were subjected to a single bout of in vivo fatigue loading. Nonloaded left forelimbs were used as controls. Ulnar geometric properties were assessed by peripheral quantitative computed tomography (pQCT) and ex vivo mechanical properties were assessed by three-point bending. On day 0, ulnae from loaded forelimbs had a 15-20% reduction in stiffness and ultimate force versus controls (p < 0.10), indicative of structural damage. On day 12, bone area at the midshaft was increased by 27% (p < 0.001) and microCT scans revealed periosteal woven bone at this site. This bone response led to a recovery of the monotonic properties of loaded ulnae at day 12 versus control (stiffness, p = 0.73; ultimate force, p = 0.96). Importantly, fatigue testing ex vivo at day 12 demonstrated significantly greater fatigue life in in vivo loaded ulnae versus controls (p < 0.001). Additionally, the slope of the fatigue-life curve was significantly less in loaded versus control ulnae (p < 0.002). We conclude that woven bone "repair" of a bone damaged by fatigue loading restores whole-bone strength and enhances resistance to further damage by repetitive loading. PMID:17106875

Silva, Matthew J; Touhey, Daniel C

2007-02-01

219

Prevention of dental damage and improvement of difficult intubation using a paraglossal technique with a straight Miller blade.  

PubMed

Patients with diseased teeth, or those who are difficult to intubate, have a higher risk of dental injury during laryngoscopy. We report 3 cases of smooth endotracheal intubation using a paraglossal technique with a straight Miller blade in patients with poor dentition. Three patients with poor dentition were scheduled to undergo surgery under general anesthesia. All patients presented with extremely loose upper central incisors and had lost the other right upper teeth, while micrognathia and prominent, loose upper incisors were noted in 1 case. We elected to use a straight Miller blade using a paraglossal approach. A nasopharyngeal airway was inserted after induction of general anesthesia to facilitate mask ventilation and prevent air leakage from the mask. The Miller blade was then inserted from the right corner of the mouth, avoiding contact with the vulnerable incisors, and advanced along the groove between the tongue and tonsil. The endotracheal tube was subsequently smoothly inserted after obtaining a grade 1 Cormack and Lehane view without dental trauma in all 3 cases. Direct laryngoscopy using the paraglossal straight blade technique avoids dental damage in patients with mobile upper incisors and no right maxillary molars. It is a practical alternative method that differs from the traditional Macintosh laryngoscope in patients with a high risk of dental injury during the procedure. This technique, which provides an improved view of the larynx, might also be helpful with patients in whom intubation is difficult. PMID:21051035

Huang, Yu-Feng; Ting, Chien-Kun; Chang, Wen-Kuei; Chan, Kwok-Hon; Chen, Pin-Tarng

2010-10-01

220

Damage mechanisms in alloy 800H under creep-fatigue conditions  

NASA Astrophysics Data System (ADS)

The interaction between fatigue damage (i.e., fatigue crack propagation) and internal grain boundary damage (i.e., cavity formation at grain boundaries) has been studied for the Alloy 800H at 750 C for constant plastic strain ranges but different experimental conditions. Most experiments were performed at constant ranges of alternating tensile/compression stresses. Symmetrical as well as asymmetrical tests (with larger compression stresses) were performed. In comparison to the former tests, asymmetrical tests led to shorter cyclic lifetimes mainly due to cavity formation which was not observed for symmetrical tests. It could be shown that a fast compressive and a slow tensile half cycle (at large compressive and low tensile stresses) are ideal conditions for the nucleation and growth of cavities. Based on quantitative measurements of the cavity density from interrupted fatigue tests, a physical model is presented which can predict the number of cycles to failure. This cycle number is determined only by fatigue crack growth which is controlled by (1) athermal plastic deformation, (2) creep deformation and (3) rate enhancement by cavitation.

Mu, Z.; Bothe, K.; Gerold, V.

1994-05-01

221

Simulated Fatigue Damage Index on Mooring Lines of a Gulf of Mexico Truss Spar Determined from Recorded Field Data  

E-print Network

. The platform is equipped with an Environmental Platform Response Monitoring System (EPRMS) which records real-time motions, environmental parameters and loads. These measurements were used to hind-cast the platform mooring tensions and estimate fatigue damage...

Kiecke, Adam Fuller

2012-07-16

222

Coordinate Regulation of IL1? and MMP-13 in Rat Tendons Following Subrupture Fatigue Damage  

Microsoft Academic Search

Mechanical overloading is a major causative factor of tendinopathy; however, its underlying mechanisms are unclear. We hypothesized\\u000a mechanical overloading would damage tendons and alter genes associated with tendinopathy in a load-dependent manner. To test\\u000a this hypothesis, we fatigue loaded rat patellar tendons in vivo and measured expression of the matrix-degrading enzyme MMP-13\\u000a and the inflammatory cytokine IL-1?. We also examined these

Hui B. Sun; Yonghui Li; David T. Fung; Robert J. Majeska; Mitchell B. Schaffler; Evan L. Flatow

2008-01-01

223

Interfaces and fatigue damage in a metastable beta titanium matrix composite  

Microsoft Academic Search

The results of a systematic study of the effects of interfacial microstructure on fatigue damage in a metastable ? Ti?15V?3Cr?3Al?3Sn\\/SiC (SCS-9) composite are presented. Interfacial microstructure is controlled by heat treatment in the ? phase field of the matrix, which promotes coarsening of the fiber-matrix interface without significant changes in the metastable ? matrix microstructure (grain size). The effects of

W. O Soboyejo; B. M Rabeeh; P Kantzos

1995-01-01

224

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

225

Self-monitoring of fatigue damage and dynamic strain in carbon fiber polymer-matrix composite  

Microsoft Academic Search

Self-monitoring of static\\/fatigue damage and dynamic strain in a continuous crossply [0\\/90] carbon fiber polymer-matrix composite by electrical resistance (R) measurement was achieved. With a static\\/cyclic tensile stress along the 0° direction, R in this direction and R perpendicular to the fiber layers were measured. Upon static tension to failure, R in the 0° direction first decreased (due to increase

Xiaojun Wang; D. D. L. Chung

1998-01-01

226

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

227

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

228

Estimation of the damaging energy under creep-fatigue interaction conditions in 1Cr-Mo-V steel  

SciTech Connect

1Cr-Mo-V steel is widely used in power-generating plants for components which operate at high temperatures. Since many components used in power plants are subjected to complex loading cycles at high temperatures, high temperature low-cycle fatigue (LCF) experiments with hold time can be very meaningful tests for understanding the creep-fatigue interaction phenomenon under complex loading conditions. Therefore, in the study of creep-fatigue interaction, a damage formation mechanism is important in understanding a prediction for fatigue lives. In this study an estimation of the damaging energy is tried by using the power law relation between the fatigue life and the hysteresis loop energy, and the quantitative values of it are compared with the fractured area per cycle, with a scanning electron microscope (SEM) analysis.

Jeong, C.Y.; Nam, S.W. [Korea Advanced Inst. of Science and Technology, Taejon (Korea, Republic of). Dept. of Materials Science and Engineering] [Korea Advanced Inst. of Science and Technology, Taejon (Korea, Republic of). Dept. of Materials Science and Engineering

1999-02-05

229

On the Use of Infrared Thermography for Analysis of Fatigue Damage in Ti6Al4V-Welded Joints  

NASA Astrophysics Data System (ADS)

The present work is aimed at comparatively studying fatigue damage evolution of a pulsed Nd:YAG laser beam-welded (LBW) joint and the base metal (BM) of Ti6Al4V alloy subjected to cyclic loading. To reveal crack nucleation and propagation during the fatigue process, in situ fatigue was generated using infrared measurement methods. The results indicate that the rate of damage accumulated in the LBW joint was higher than in the BM specimens during a fatigue test, which decreased the fatigue life of the LBW joint. This observation is attributable to the LBW joint fusion zone microstructure, which has a higher void nucleation and growth rate compared with the BM microstructure.

Liu, Jing; Gao, Xiao-Long; Zhang, Lin-Jie; Zhang, Jian-Xun

2014-08-01

230

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

231

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

232

Coordinate Regulation of IL-1? and MMP-13 in Rat Tendons Following Subrupture Fatigue Damage  

PubMed Central

Mechanical overloading is a major causative factor of tendinopathy; however, its underlying mechanisms are unclear. We hypothesized mechanical overloading would damage tendons and alter genes associated with tendinopathy in a load-dependent manner. To test this hypothesis, we fatigue loaded rat patellar tendons in vivo and measured expression of the matrix-degrading enzyme MMP-13 and the inflammatory cytokine IL-1?. We also examined these responses in cultured tenocytes exposed to intermittent hydrostatic pressure in vitro. Additionally, we hypothesized load-induced changes in tenocyte MMP-13 expression would be dependent on expression of IL-1?. In vivo fatigue loading at 1.7% strain caused overt microstructural damage and upregulated expression of MMP-13 and IL-1?, while 0.6% strain produced only minor changes in matrix microstructure and downregulated expression of both MMP-13 and IL-1?. Loading of cultured tenocytes at 2.5 and 7.5 MPa produced comparable changes in expression to those of in vivo tendon loading. Blocking IL-1? expression with siRNA suppressed load-induced both MMP-13 mRNA expression and activity. The data suggest fatigue loading alters expression of MMP-13 and IL-1? in tendons in vivo and tenocytes in vitro in a load-dependent manner. The data also suggest MMP-13 is regulated by both IL-1?-dependent and IL-1?-independent pathways. PMID:18470577

Sun, Hui B.; Li, Yonghui; Fung, David T.; Majeska, Robert J.; Schaffler, Mitchell B.

2008-01-01

233

Coordinate regulation of IL-1beta and MMP-13 in rat tendons following subrupture fatigue damage.  

PubMed

Mechanical overloading is a major causative factor of tendinopathy; however, its underlying mechanisms are unclear. We hypothesized mechanical overloading would damage tendons and alter genes associated with tendinopathy in a load-dependent manner. To test this hypothesis, we fatigue loaded rat patellar tendons in vivo and measured expression of the matrix-degrading enzyme MMP-13 and the inflammatory cytokine IL-1beta. We also examined these responses in cultured tenocytes exposed to intermittent hydrostatic pressure in vitro. Additionally, we hypothesized load-induced changes in tenocyte MMP-13 expression would be dependent on expression of IL-1beta. In vivo fatigue loading at 1.7% strain caused overt microstructural damage and upregulated expression of MMP-13 and IL-1beta, while 0.6% strain produced only minor changes in matrix microstructure and downregulated expression of both MMP-13 and IL-1beta. Loading of cultured tenocytes at 2.5 and 7.5 MPa produced comparable changes in expression to those of in vivo tendon loading. Blocking IL-1beta expression with siRNA suppressed load-induced both MMP-13 mRNA expression and activity. The data suggest fatigue loading alters expression of MMP-13 and IL-1beta in tendons in vivo and tenocytes in vitro in a load-dependent manner. The data also suggest MMP-13 is regulated by both IL-1beta-dependent and IL-1beta-independent pathways. PMID:18470577

Sun, Hui B; Li, Yonghui; Fung, David T; Majeska, Robert J; Schaffler, Mitchell B; Flatow, Evan L

2008-07-01

234

Investigation of Bearing Fatigue Damage Life Prediction Using Oil Debris Monitoring  

NASA Technical Reports Server (NTRS)

Research was performed to determine if a diagnostic tool for detecting fatigue damage of helicopter tapered roller bearings can be used to determine remaining useful life (RUL). The taper roller bearings under study were installed on the tail gearbox (TGB) output shaft of UH- 60M helicopters, removed from the helicopters and subsequently installed in a bearing spall propagation test rig. The diagnostic tool was developed and evaluated experimentally by collecting oil debris data during spall progression tests on four bearings. During each test, data from an on-line, in-line, inductance type oil debris sensor was monitored and recorded for the occurrence of pitting damage. Results from the four bearings tested indicate that measuring the debris generated when a bearing outer race begins to spall can be used to indicate bearing damage progression and remaining bearing life.

Dempsey, Paula J.; Bolander, Nathan; Haynes, Chris; Toms, Allison M.

2011-01-01

235

Continuum Fatigue Damage Modeling for Critical Design, Control, and Fault Prognosis  

NASA Technical Reports Server (NTRS)

This paper develops a simplified continuum (continuous with respect to time, stress, etc.) fatigue damage model for use in critical design, Life Extending Control and fault prognosis. The work is based on the local strain cyclic damage modeling method. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modelling. Stress based continuum models are derived. Extension to plastic strain-strain rate models is also presented. Progress toward a non-zero mean stress based is presented. Also new nonlinear explicit equation forms in terms of stress amplitude are derived for this case. Application of the various models to design, control, and fault prognosis is considered.

Lorenzo, Carl F.

1996-01-01

236

Gear Fault Detection Effectiveness as Applied to Tooth Surface Pitting Fatigue Damage  

NASA Technical Reports Server (NTRS)

A study was performed to evaluate fault detection effectiveness as applied to gear tooth pitting fatigue damage. Vibration and oil-debris monitoring (ODM) data were gathered from 24 sets of spur pinion and face gears run during a previous endurance evaluation study. Three common condition indicators (RMS, FM4, and NA4) were deduced from the time-averaged vibration data and used with the ODM to evaluate their performance for gear fault detection. The NA4 parameter showed to be a very good condition indicator for the detection of gear tooth surface pitting failures. The FM4 and RMS parameters performed average to below average in detection of gear tooth surface pitting failures. The ODM sensor was successful in detecting a significant amount of debris from all the gear tooth pitting fatigue failures. Excluding outliers, the average cumulative mass at the end of a test was 40 mg.

Lewicki, David G.; Dempsey, Paula J.; Heath, Gregory F.; Shanthakumaran, Perumal

2009-01-01

237

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

238

A comparative study of fatigue damage sensing in aluminum alloys using electrical impedance and laser ultrasonic methods  

NASA Astrophysics Data System (ADS)

Fatigue damage sensing and measurement in aluminum alloys is critical to estimating the residual useful lifetime of a range of aircraft structural components. In this work, we present electrical impedance and ultrasonic measurements in aluminum alloy 2024 that has been fatigued under high cycle conditions. While ultrasonic measurements can indicate fatigue-induced damage through changes in stiffness, the primary indicator is ultrasonic attenuation. We have used laser ultrasonic methods to investigate changes in ultrasonic attenuation since simultaneous measurement of longitudinal and shear properties provides opportunities to develop classification algorithms that can estimate the degree of damage. Electrical impedance measurements are sensitive to changes in the conductivity and permittivity of materials - both are affected by the microstructural damage processes related to fatigue. By employing spectral analysis of impedance over a range of frequencies, resonance peaks can be identified that directly reflect the damage state in the material. In order to compare the impedance and ultrasonic measurements for samples subjected to tension testing, we use processing and classification tools that are matched to the time-varying spectral nature of the measurements. Specifically, we process the measurements to extract time-frequency features and estimate stochastic variation properties to be used in robust classification algorithms. Results are presented for fatigue damage identification in aluminum lug joint specimens.

Channels, Lindsey; Chakraborty, Debejyo; Butrym, Brad; Kovvali, Narayan; Spicer, James; Papandreou-Suppappola, Antonia; Afshari, Mana; Inman, Daniel; Chattopadhyay, Aditi

2009-03-01

239

Estimating the strength of turbine rotor blades taking into account operational damage  

Microsoft Academic Search

Conclusions 1.The law of equality of the action of opposite forces was used as the basis for determining the ratio of residual surface compressive stresses to subsurface tensile stresses in a hardened compressor rotor blade for the case of thin and thick cross sections.2.Equations were derived which relate components of the stress state due to service loads to components of

V. T. Kozyrev

1977-01-01

240

An investigation of rolling-sliding contact fatigue damage of carburized gear steels  

NASA Astrophysics Data System (ADS)

The goal of this study was to evaluate the differences in RSCF performance between vacuum and gas carburized steels as well as to investigate the evolution of damage (wear and microstructure changes) leading to pitting. Vacuum and gas carburizing was performed on two gear steels (4120 and 4320) at 1010°C. The carburized specimens were tested in the as-carburized condition using a RSCF machine designed and built at the Colorado School of Mines. The tests were conducted at 3.2 GPa nominal Hertzian contact stress, based on pure rolling, 100°C, and using a negative twenty percent slide ratio. Tests were conducted to pitting failure for each condition for a comparison of the average fatigue lives. Pure rolling tests were also conducted, and were suspended at the same number of cycles as the average RSCF life for a comparison of fatigue damage developed by RCF and RSCF. Incremental tests were suspended at 1,000, 10,000, 100,000, and 200,000 cycles for the vacuum carburized steels to evaluate the wear and damage developed during the initial cycles of RSCF testing and to relate the wear and damage to pitting resistance. Incremental damage was not investigated for gas carburizing due to the limited number of available specimens. The vacuum carburized samples showed a decreased pitting fatigue resistance over the gas carburized samples, possibly due to the presence of bainite in the vacuum carburized cases. Pitting was observed to initiate from surface micropitting and microcracking. A microstructural change induced by contact fatigue, butterflies, was shown to contribute to micropitting and microcracking. Incremental testing revealed that the formation of a microcrack preceded and was necessary for the formation of the butterfly features, and that the butterfly features developed between 10,000 and 100,000 cycles. The orientation and depth of butterfly formation was shown to be dependent upon the application of traction stresses from sliding. RSCF butterflies formed nearly parallel to the rolling direction at a large range of depths. RCF butterflies formed at about 45° to the rolling direction in a more narrow range of depths. The surface roughness and surface profile were observed to change quickly in the first several thousand cycles of RSCF testing leading to a reduction in contact stress and increase in lambda ratio (ratio of lubricant fluid film thickness to composite surface roughness). The ability of a carburized sample wear track to reach and maintain a steady state morphology (run-in condition) during testing is postulated to translate to increased RSCF resistance.

Kramer, Patrick C.

241

Fatigue routing of container ships–assessment of contributions to fatigue damage from wave-induced torsion and horizontal and vertical bending  

Microsoft Academic Search

The traditional method for assessing fatigue damage of ship structures assumes moderate wave amplitudes and linear responses. This method can be questioned when applied to container ships which are characterised by large deck openings that cause low torsion rigidity of the structure. Depending on the heading of the vessel in relation to the wave encounter direction, container ships can therefore

Zhiyuan Li; Jonas W. Ringsberg

2012-01-01

242

Fatigue routing of container ships–assessment of contributions to fatigue damage from wave-induced torsion and horizontal and vertical bending  

Microsoft Academic Search

The traditional method for assessing fatigue damage of ship structures assumes moderate wave amplitudes and linear responses. This method can be questioned when applied to container ships which are characterised by large deck openings that cause low torsion rigidity of the structure. Depending on the heading of the vessel in relation to the wave encounter direction, container ships can therefore

Zhiyuan Li; Jonas W. Ringsberg

2011-01-01

243

Fatigue damage assessment of high-usage in-service aircraft fuselage structure  

NASA Astrophysics Data System (ADS)

As the commercial and military aircraft fleets continue to age, there is a growing concern that multiple-site damage (MSD) can compromise structural integrity. Multiple site damage is the simultaneous occurrence of many small cracks at independent structural locations, and is the natural result of fatigue, corrosion, fretting and other possible damage mechanisms. These MSD cracks may linkup and form a fatigue lead crack of critical length. The presence of MSD also reduces the structure's ability to withstand longer cracks. The objective of the current study is to assess, both experimentally and analytically, MSD formation and growth in the lap joint of curved panels removed from a retired aircraft. A Boeing 727-232 airplane owned and operated by Delta Air Lines, and retired at its design service goal, was selected for the study. Two panels removed from the left-hand side of the fuselage crown, near stringer 4L, were subjected to extended fatigue testing using the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration (FAA) William J. Hughes Technical Center. The state of MSD was continuously assessed using several nondestructive inspection (NDI) methods. Damage to the load attachment points of the first panel resulted in termination of the fatigue test at 43,500 fatigue cycles, before cracks had developed in the lap joint. The fatigue test for the second panel was initially conducted under simulated in-service loading conditions for 120,000 cycles, and no cracks were detected in the skin of the panel test section. Artificial damage was then introduced into the panel at selected rivets in the critical (lower) rivet row, and the fatigue loads were increased. Visually detectable crack growth from the artificial notches was first seen after 133,000 cycles. The resulting lead crack grew along the lower rivet row, eventually forming an 11.8" long unstable crack after 141,771 cycles, at which point the test was terminated. Posttest fractograpic examinations of the crack surfaces were conducted, revealing the presence of subsurface MSD at the critical rivet row of the lap joint. Special attention was also given to the stringer clips that attach the fuselage frames to the stringers, since they also experienced cracking during the fatigue tests. The performance of the different conventional and emerging NDI methods was also assessed, and some of the emerging NDI methods were quite effective in detecting and measuring the length of subsurface cracks. Delta Air Lines conducted a separate destructive investigation on the state of damage along the right-hand side of the fuselage, near stringer 4R. A comparison of these two studies showed that the lap joint on the left hand-side of the aircraft, along stringer 4L, had better fatigue life than the one on the opposite side, along stringer 4R. The cause of the difference in fatigue life was investigated by close examination of the rivet installation qualities, and was found to be a result of better rivet installation along the lap joint at stringer 4L. Finite element models for both the skin and substructures of the panels were developed and geometrically nonlinear finite element analyses were conducted to verify the loading conditions and to determine near-field parameters governing MSD initiation and growth. Fatigue crack growth predictions based on the NASGRO equation were in good agreement with the experimental crack growth data for through-the-thickness cracks. For subsurface cracks, simulation of crack growth was found to correlate better with fractography data when an empirical crack growth model was used. The results of the study contribute to the understanding of the initiation and growth of MSD in the inner skin layer of a lap joint, and provide valuable data for the evaluation and validation of analytical methodologies to predict MSD initiation and growth and a better understanding on the effect of manufacturing quality on damage accumulation along the lap joint.

Mosinyi, Bao Rasebolai

244

Noncontact acousto-thermal evaluation of evolving fatigue damage in polycrystalline Ti-6Al-4V  

NASA Astrophysics Data System (ADS)

Non-Contact Acousto-Thermal Signature (NCATS) analysis uses conversion of acoustic energy to heat to characterize evolving damage in materials. In the past, the observed temperature changes were interpreted using phenomenological approaches. This paper presents details of the mechanisms and the theoretical models to predict the temperature change due to conversion of acoustic energy to heat. NCATS experimental measurements performed using 20 kHz high amplitude acoustic waves on as received and fatigued polycrystalline Ti-6Al-4V are compared with theoretical calculations based on the mechanisms of transverse thermal currents, inter-crystalline thermal currents, and dislocation density changes. In the as received samples, the transverse thermal currents contribution has been found to be negligible compared with inter-crystalline thermal currents contribution. The experimentally measured maximum temperature change in the as received sample has been found to be 0.5 °C, and the theoretical prediction based on inter-crystalline thermal currents is 0.08 °C. In the fatigue damaged samples, the maximum temperature change increases with increasing damage that can be attributed to the increasing dislocation density. The theoretical prediction of the maximum temperature attained by a sample that is near failure based on dislocation contribution is 2.0 °C, while the experimental measurements have been found to be 0.95 °C. The differences between the theoretical and the experimental measurements are discussed in the context of the uncertainties in several physical parameters used in the theoretical calculations.

Sathish, S.; Welter, J. T.; Schehl, N.; Jata, K. V.

2014-05-01

245

Characterization of Fatigue Damage for Bonded Composite Skin/Stringer Configurations  

NASA Technical Reports Server (NTRS)

The fatigue damage was characterized in specimens which consisted of a tapered composite flange bonded onto a composite skin. Quasi-static tension tests were performed first to determine the failure load. Subsequently, tension fatigue tests were performed at 40%, 50%, 60% and 70% of the failure load to evaluate the debonding mechanisms. For four specimens, the cycling loading was stopped at intervals. Photographs of the polished specimen edges were taken under a light microscope to document the damage. At two diagonally opposite corners of the flange, a delamination appeared to initiate at the flange tip from a matrix crack in the top 45deg skin ply and propagated at the top 45deg/-45deg skin ply interface. At the other two diagonally opposite corners, a delamination running in the bondline initiated from a matrix crack in the adhesive pocket. In addition, two specimens were cut longitudinally into several sections. Micrographs revealed a more complex pattern inside the specimen where the two delamination patterns observed at the edges are present simultaneously across most of the width of the specimen. The observations suggest that a more sophisticated nondestructive evaluation technique is required to capture the complex damage pattern of matrix cracking and multi-level delaminations.

Paris, Isabelle; Cvitkovich, Michael; Krueger, Ronald

2008-01-01

246

Fatigue  

MedlinePLUS

... make greater demands than your muscles can handle. MDA Research Development Director Sharon Hesterlee says muscle fatigue ... physically or even mentally. According to Margaret Wahl, MDA Medical and Science Editor, “If people are underoccupied ...

247

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

248

An overview of elevated temperature damage mechanisms and fatigue behavior of a unidirectional SCS-6/Ti-15-3 composite  

NASA Technical Reports Server (NTRS)

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 coupon-level experimental investigation are reviewed. On a stress basis, the isothermal fatigue behavior of the (0 deg) TMC revealed significant improvements over the unreinforced matrix. In contrast, the (90 deg) TMC exhibited degraded properties and lives for similar comparisons. This was attributed to the weak fiber/matrix interfacial bond. Encasing the (0 deg) TMC with a Ti-15-3 case did not affect isothermal fatigue lives at higher strain levels. However, at lower strain levels, rapid initiation and propagation of large fatigue cracks in the case degraded the fatigue lives. Thermomechanical fatigue (TMF) lives were significantly reduced for the (0 deg) TMC when compared to isothermal lives. At high strains, in-phase TMF produced extremely short lives. This degradation was attributed to fiber overload failures brought about by stress relaxation in the matrix. At low strains, out-of-phase TMF conditions became life limiting. Environment-assisted surface cracking was found to accelerate fatigue failure. This produced extensive matrix damage with minimal fiber damage. For the (90 deg) TMC, TMF conditions did not promote an additional degradation in cyclic life beyond that observed under isothermal conditions.

Castelli, Michael G.; Gayda, John

1993-01-01

249

Experiments on a wind turbine blade testing an indication for damage using the causal and anti-causal Green's function reconstructed from a diffuse field  

NASA Astrophysics Data System (ADS)

The increasing demand for renewable and clean power generation has resulted in increasing sizes of rotor blades in wind turbine systems. The demanding and variable operational environments have introduced the need for structural health monitoring systems in the blades in order to prevent unexpected downtime events in the operation of the power plant. Many non-destructive evaluation methods used for structural health monitoring purposes need external excitation sources. However, several systems already accepted in the wind turbine industry are passive. Here we present a new approach to health monitoring of a wind turbine blade using only passive sensors and the existing noise created on the blade during operation. This is achieved using a known method to reconstruct the causal and anticausal time-domain Green's function between any two points in an array of passive sensors placed in a diffuse field. Damage is indicated when the similarity between the causal and anticausal signals decrease due to nonlinearities introduced from structural damage. This method was studied experimentally using a CX-100 wind turbine test blade located at the UCSD's Powell Structural Laboratories where a diffuse field was approximated by exciting the skin of the blade with a random signal at several locations.

Tippmann, Jeffery D.; Lanza di Scalea, Francesco

2014-03-01

250

Micromechanics Fatigue Damage Analysis Modeling for Fabric Reinforced Ceramic Matrix Composites  

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

251

Fatigue crack growth spectrum simplification: Facilitation of on-board damage prognosis systems  

NASA Astrophysics Data System (ADS)

Better lifetime predictions of systems subjected to fatigue loading are needed in support of the optimization of the costs of life-cycle engineering. In particular, the climate is especially encouraging for the development of safer aircraft. One issue is that aircraft experience complex fatigue loading and current methods for the prediction of fatigue damage accumulation rely on intensive computational tools that are not currently carried onboard during flight. These tools rely on complex models that are made more difficult by the complicated load spectra themselves. This presents an overhead burden as offline analysis must be performed at an offsite facility. This architecture is thus unable to provide online, timely information for on-board use. The direct objective of this research was to facilitate the real-time fatigue damage assessments of on-board systems with a particular emphasis on aging aircraft. To achieve the objective, the goal of this research was to simplify flight spectra. Variable-amplitude spectra, in which the load changes on a cycle-by-cycle basis, cannot readily be supported by an onboard system because the models required to predict fatigue crack growth during variable-amplitude loading are too complicated. They are too complicated because variable-amplitude fatigue crack growth analysis must be performed on a cycle-by-cycle basis as no closed-form solution exists. This makes these calculations too time-consuming and requires impractical, heavy onboard systems or offsite facilities. The hypothesis is to replace a variable-amplitude spectrum with an equivalent constant-amplitude spectrum. The advantage is a dramatic reduction in the complexity of the problem so that damage predictions can be made onboard by simple, fast calculations in real-time without the need to add additional weight to the aircraft. The intent is to reduce the computational burden and facilitate on-board projection of damage evolution and prediction for the accurate monitoring and management of aircraft. A spectrum reduction method was proposed and experimentally validated that reduces a variable-amplitude spectrum to a constant-amplitude equivalent. The reduction from a variable-amplitude (VA) spectrum to a constant-amplitude equivalent (CAE) was proposed as a two-part process. Preliminary spectrum reduction is first performed by elimination of those loading events shown to be too negligible to significantly contribute to fatigue crack growth. This is accomplished by rainflow counting. The next step is to calculate the appropriate, equivalent maximum and minimum loads by means of a root-mean-square average. This reduced spectrum defines the CAE and replaces the original spectrum. The simplified model was experimentally shown to provide the approximately same fatigue crack growth as the original spectrum. Fatigue crack growth experiments for two dissimilar aircraft spectra across a wide-range of stress-intensity levels validated the proposed spectrum reduction procedure. Irrespective of the initial K-level, the constant-amplitude equivalent spectra were always conservative in crack growth rate, and were so by an average of 50% over the full range tested. This corresponds to a maximum 15% overestimation in driving force Delta K. Given other typical sources of scatter that occur during fatigue crack growth, a consistent 50% conservative prediction on crack growth rate is very satisfying. This is especially attractive given the reduction in cost gained by the simplification. We now have a seamless system that gives an acceptably good approximation of damage occurring in the aircraft. This contribution is significant because in a very simple way we now have given a path to bypass the current infrastructure and ground-support requirements. The decision-making is now a lot simpler. In managing an entire fleet we now have a workable system where the strength is in no need for a massive, isolated computational center. The fidelity of the model gives credence because experimental data show that the approximate spectrum model captures the

Adler, Matthew Adam

2009-12-01

252

77 FR 50576 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures; OMB Approval of...  

Federal Register 2010, 2011, 2012, 2013

...Fatigue Evaluation of Composite Rotorcraft Structures; OMB Approval of Information Collection...Fatigue Evaluation of Composite Rotorcraft Structures,'' which was published on December...Fatigue Evaluation of Composite Rotorcraft Structures,'' published in the Federal...

2012-08-22

253

Fatigue  

MedlinePLUS

... discuss your eating habits. For some people, vitamin B12 supplements or better nutrition can eliminate fatigue. Anemia ( ... health care provider will determine what is causing anemia. It could be due to ... medications or vitamin deficiencies, or by a low level of the hormone ...

254

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

255

Re-examination of cumulative fatigue damage analysis - An engineering perspective  

NASA Technical Reports Server (NTRS)

A method which has evolved in the laboratories for the past 20 yr is re-examined with the intent of improving its accuracy and simplicity of application to engineering problems. Several modifications are introduced both to the analytical formulation of the Damage Curve Approach, and to the procedure for modifying this approach to achieve a Double Linear Damage Rule formulation which immensely simplifies the calculation. Improvements are also introduced in the treatment of mean stress for determining fatigue life of the individual events that enter into a complex loading history. While the procedure is completely consistent with the results of numerous two level tests that have been conducted on many materials, it is still necessary to verify applicability to complex loading histories. Caution is expressed that certain phenomenon can also influence the applicability - for example, unusual deformation and fracture modes inherent in complex loading especially if stresses are multiaxial. Residual stresses at crack tips, and metallurgical factors are also important in creating departures from the cumulative damage theories; examples of departures are provided.

Manson, S. S.; Halford, G. R.

1986-01-01

256

Re-examination of cumulative fatigue damage analysis: An engineering perspective  

NASA Technical Reports Server (NTRS)

A method which has evolved in our laboratories for the past 20 yr is re-examined with the intent of improving its accuracy and simplicity of application to engineering problems. Several modifications are introduced both to the analytical formulation of the Damage Curve Approach, and to the procedure for modifying this approach to achieve a Double Linear Damage Rule formulation which immensely simplifies the calculation. Improvements are also introduced in the treatment of mean stress for determining fatigue life of the individual events that enter into a complex loading history. While the procedure is completely consistent with the results of numerous two level tests that have been conducted on many materials, it is still necessary to verify applicability to complex loading histories. Caution is expressed that certain phenomena can also influence the applicability - for example, unusual deformation and fracture modes inherent in complex loading - especially if stresses are multiaxial. Residual stresses at crack tips, and metallurgical factors are also important in creating departures from the cumulative damage theories; examples of departures are provided.

Manson, S. S.; Halford, G. R.

1986-01-01

257

Gear Fault Detection Effectiveness as Applied to Tooth Surface Pitting Fatigue Damage  

NASA Technical Reports Server (NTRS)

A study was performed to evaluate fault detection effectiveness as applied to gear-tooth-pitting-fatigue damage. Vibration and oil-debris monitoring (ODM) data were gathered from 24 sets of spur pinion and face gears run during a previous endurance evaluation study. Three common condition indicators (RMS, FM4, and NA4 [Ed. 's note: See Appendix A-Definitions D were deduced from the time-averaged vibration data and used with the ODM to evaluate their performance for gear fault detection. The NA4 parameter showed to be a very good condition indicator for the detection of gear tooth surface pitting failures. The FM4 and RMS parameters perfomu:d average to below average in detection of gear tooth surface pitting failures. The ODM sensor was successful in detecting a significant 8lDOunt of debris from all the gear tooth pitting fatigue failures. Excluding outliers, the average cumulative mass at the end of a test was 40 mg.

Lewicki, David G.; Dempsey, Paula J.; Heath, Gregory F.; Shanthakumaran, Perumal

2010-01-01

258

Multidisciplinary design optimization of a fighter aircraft with damage tolerance constraints and a probabilistic model of the fatigue environment  

NASA Astrophysics Data System (ADS)

Damage tolerance analysis (DTA) was considered in the global design optimization of an aircraft wing structure. Residual strength and fatigue life requirements, based on the damage tolerance philosophy, were investigated as new design constraints. In general, accurate fatigue prediction is difficult if the load environment is not known with a high degree of certainty. To address this issue, a probabilistic approach was used to describe the uncertain load environment. Probabilistic load spectra models were developed from flight recorder data. The global/local finite element approach allowed local fatigue requirements to be considered in the global design optimization. AFGROW fatigue crack growth analysis provided a new strength criterion for satisfying damage tolerance requirements within a global optimization environment. Initial research with the ASTROS program used the probabilistic load model and this damage tolerance constraint to optimize cracked skin panels on the lower wing of a fighter/attack aircraft. For an aerodynamic and structural model similar to an F-16, ASTROS simulated symmetric and asymmetric maneuvers during the optimization. Symmetric maneuvers, without underwing stores, produced the highest stresses and drove the optimization of the inboard lower wing skin. Asymmetric maneuvers, with underwing stores, affected the optimum thickness of the outboard hard points. Subsequent design optimizations included von Mises stress, aileron effectiveness, and lift effectiveness constraints simultaneously. This optimization was driven by the DTA and von Mises stress constraints and, therefore, DTA requirements can have an active role to play in preliminary aircraft design.

Arrieta, Albert Joseph

2001-07-01

259

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

260

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

261

Helicopter rotor blade design for minimum vibration  

NASA Technical Reports Server (NTRS)

The importance of blade design parameters in rotor vibratory response and the design of a minimum vibration blade based upon this understanding are examined. Various design approaches are examined for a 4 bladed articulated rotor operating at a high speed flight condition. Blade modal shaping, frequency placement, structural and aerodynamic coupling, and intermodal cancellation are investigated to systematically identify and evaluate blade design parameters that influence blade airloads, blade modal response, hub loads, and fuselage vibration. The relative contributions of the various components of blade force excitation and response to the vibratory hub loads transmitted to the fuselage are determined in order to isolate primary candidates for vibration alleviation. A blade design is achieved which reduces the predicted fuselage vibration from the baseline blade by approximately one half. Blade designs are developed that offer significant reductions in vibration (and fatigue stresses) without resorting to special vibration alleviation devices, radical blade geometries, or weight penalties.

Taylor, R. B.

1984-01-01

262

Prediction of damage evolution in continuous fiber metal matrix composites subjected to fatigue loading  

SciTech Connect

A life prediction model is being developed by the authors for application to metal matrix composites (MMC`s). The systems under study are continuous silicon carbide fibers imbedded in titanium matrix. The model utilizes a computationally based framework based on thermodynamics and continuum mechanics, and accounts for matrix inelasticity, damage evolution, and environmental degradation due to oxidation. The computational model utilizes the finite element method, and an evolutionary analysis of a unit cell is accomplished via a time stepping algorithm. The computational scheme accounts for damage growth such as fiber-matrix debonding, surface cracking, and matrix cracking via the inclusion of cohesive zone elements in the unit cell. These elements are located based on experimental evidence also obtained by the authors. The current paper outlines the formulation utilized by the authors to solve this problem, and recent results are discussed. Specifically, results are given for a four-ply unidirectional composite subjected to cyclic fatigue loading at 650{degrees}C both in air and inert gas. The effects of oxidation on the life of the composite are predicted with the model, and the results are compared to limited experimental results.

Allen, D.; Helms, K.; Lagoudas, D. [Texas A& M Univ., College Station, TX (United States)] [and others

1995-08-01

263

Tungsten fiber reinforced FeCralY: A first generation composite turbine blade material  

NASA Technical Reports Server (NTRS)

Tungsten-fiber/FeCrAlY (W/FeCrAlY) was identified as a promising aircraft engine, first generation, turbine blade composite material. Based on available data, W/FeCrAlY should have the stress-rupture, creep, tensile, fatigue, and impact strengths required for turbine blades operating from 1250 to 1370 K. It should also have adequate oxidation, hot corrosion, and thermal cycling damage resistance as well as high thermal conductivity. Concepts for potentially low cost blade fabrication were developed. These concepts were used to design a first stage JT9D convection cooled turbine blade having a calculated 50 K use-temperature advantage over the directionally solidified superalloy blade.

Petrasek, D. W.; Winsa, E. A.; Westfall, L. J.; Signorelli, R. A.

1979-01-01

264

Fatigue creep damage at the cement-bone interface: an experimental and a micro-mechanical finite element study  

PubMed Central

The goal of this study was to quantify the micromechanics of the cement-bone interface under tensile fatigue loading using finite element analysis (FEA) and to understand the underlying mechanisms that play a role in the fatigue behavior of this interface. Laboratory cement-bone specimens were subjected to a tensile fatigue load, while local displacements and crack growth on the specimen's surface were monitored. FEA models were created from these specimens based upon micro-computed tomography data. To accurately model interfacial gaps at the interface between the bone and cement, a custom-written erosion algorithm was applied to the bone model. A fatigue load was simulated in the FEA models while monitoring the local displacements and crack propagation. The results showed the FEA models were able to capture the general experimental creep damage behavior and creep stages of the interface. Consistent with the experiments, the majority of the deformation took place at the contact interface. Additionally, the FEA models predicted fatigue crack patterns similar to experimental findings. Experimental surface cracks correlated moderately with FEA surface cracks (r2=0.43), but did not correlate with the simulated crack volume fraction (r2=0.06). Although there was no relationship between experimental surface cracks and experimental creep damage displacement (r2=0.07), there was a strong relationship between the FEA crack volume fraction and the FEA creep damage displacement (r2=0.76). This study shows the additional value of FEA of the cement-bone interface relative to experimental studies and can therefore be used to optimize its mechanical properties. PMID:19682690

Waanders, Daan; Janssen, Dennis; Miller, Mark A.; Mann, Kenneth A.; Verdonschot, Nico

2009-01-01

265

Damage development under compression-compression fatigue loading in a stitched uniwoven graphite/epoxy composite material  

NASA Technical Reports Server (NTRS)

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, Nancy E.; Morris, Don H.; Masters, John E.

1991-01-01

266

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

267

Mechanistically-Based Acoustic Emission Models for the Prediction of Fatigue Damage in a Titanium Matrix Composite  

Microsoft Academic Search

This paper presents the results of a detailed study of the micromechanisms of room-temperature fatigue damage in a metastable beta Ti-15V-3Cr-3Al-3Sn composite reinforced with SiC (SCS-6) fibers. Mechanistically based fracture mechanics\\/acoustic emission models are then applied to the prediction of the total number of AE counts to failure. The predicted number of AE counts to failure are in good agreement

W. O. Soboyejo; B. Rabeeh; Y. Li; S. Rokhlin

1998-01-01

268

EFFECTS OF SUCCESSIVE JUDO MATCHES ON FATIGUE AND MUSCLE DAMAGE MARKERS.  

PubMed

This study aimed to investigate the acute effects of simulated judo matches on fatigue and muscle damage markers. Twenty male judo athletes participated in this study. The athletes performed three 5-minute judo matches separated by 15 minutes of passive rest between each match. The following measurements were performed before and after each match: shoulder external/internal rotation isokinetic torque and countermovement jump (CMJ). Blood samples were taken before the first match and after the third match for serum creatine kinase (CK) and lactate dehydrogenase (LDH) analysis. T-tests for dependent samples and analysis of variance for repeated measures were used to compare the variables over the time; the level of significance was set at 0.05. An overall effect of the successive matches on shoulder internal (PTIN) and external (PTEX) rotation peak torque and CMJ performance was observed. PTIN and PTEX showed significant decreases in post-match 2 and post-match 3 when compared to the baseline (p<0.01). Also, CMJ height declined in post-match 2 and post-match 3 (p<0.01) when compared to the baseline. Serum CK and LDH activity increased significantly after the third match (p<0.01). It was concluded that three successive judo matches induced a decline of peak torque and muscle power in the upper and lower limbs, respectively, and also provoked an increase of muscle damage markers. These findings may provide important knowledge for coaches and physical trainers in order to improve judo-specific strength training in both the upper and lower limbs. PMID:25426512

Detanico, Daniele; Pupo, Juliano Dal; Franchini, Emerson; Dos Santos, Saray G

2014-11-25

269

X-ray Diffraction Based Residual Stress Measurements for Assessment of Fatigue Damage and Rejuvenation Process for Undercarriages of Aircrafts  

Microsoft Academic Search

Assessment of fatigue damage during the service life of any component is important to ensure its continued integrity and predict\\u000a the remnant life of the component. This is important to reduce the overall life cycle cost of the components. A component\\u000a undergoing fluctuating stresses experiences fatigue damage and this is one of the major causes of failure of engineering components.

Baldev Raj; T. Jayakumar; S. Mahadevan; Sanjay K. Rai

2009-01-01

270

The Effect of Ballistic Impacts on the High Cycle Fatigue Properties of Ti-48Al-2Nb-2Cr (at.%)  

NASA Technical Reports Server (NTRS)

The ability of gamma - TiAl to withstand potential foreign and/or domestic object damage is a technical risk to the implementation of gamma - TiAl in low pressure turbine (LPT) blade applications. The overall purpose of the present study was to determine the influence of ballistic impact damage on the high cycle fatigue strength of gamma - TiAl simulated LPT blades. Impact and specimen variables included ballistic impact energy, projectile hardness, impact temperature, impact location, and leading edge thickness. The level of damage induced by the ballistic impacting was studied and quantified on both the impact (front) and backside of the specimens. Multiple linear regression was used to model the cracking and fatigue response as a function of the impact variables. Of the impact variables studied, impact energy had the largest influence on the response of gamma - TiAl to ballistic impacting. Backside crack length was the best predictor of remnant fatigue strength for low energy impacts (<0.74J) whereas Hertzian crack length (impact side damage) was the best predictor for higher energy impacts. The impacted gamma - TiAl samples displayed a classical mean stress dependence on the fatigue strength. For the fatigue design stresses of a 6th stage LPT blade in a GE90 engine, a Ti-48Al-2Nb-2Cr LPT blade would survive an impact of normal service conditions.

Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Austin, C. M.; Erdman, O.

2000-01-01

271

Fatigue assessment of multi-loading suspension bridges using continuum damage model  

Microsoft Academic Search

Long-span steel suspension bridges carrying both highway and railway\\u000a have been built in wind-prone regions. The fatigue assessment of such\\u000a bridges under the combined action of railway, highway, and wind loading\\u000a represents a challenging task in consideration of uncertainties in both\\u000a fatigue loading and fatigue resistance. This paper presents a framework\\u000a for fatigue assessment of a long-span suspension bridge under

You-Lin Xu; Zhi-Wei Chen; Yong Xia

2012-01-01

272

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

273

Space Shuttle main engine powerhead structural modeling, stress and fatigue life analysis. Volume 2: Dynamics of blades and nozzles SSME HPFTP and HPOTP  

NASA Technical Reports Server (NTRS)

Normal modes of the blades and nozzles of the HPFTP and HPOTP are defined and potential driving forces for the blades are identified. The computer models used in blade analyses are described, with results. Similar information is given for the nozzles.

Hammett, J. C.; Hayes, C. H.; Price, J. M.; Robinson, J. K.; Teal, G. A.; Thomson, J. M.; Tilley, D. M.; Welch, C. T.

1983-01-01

274

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.

275

Mechanics of elevated temperature fatigue damage in fiber-reinforced ceramics. Final report, 1 December 1990-30 November 1992  

SciTech Connect

The focus of the research conducted under Grant No. 91-0106 (a two year effort) was to identifying the fundamental mechanisms of fatigue damage that occur in fiber-reinforced ceramics. Several new findings were made during the research effort: (1) the fatigue life of fiber-reinforced ceramics decreased markedly during high frequency fatigue loading, (2) fiber-reinforced ceramics undergo significant internal heating during cyclic loading, (3) because of frictional wear along the fiber-matrix interface, the frictional shear stress in fiber-reinforced ceramics decreases sharply under cyclic loading. Based upon insight gained from the analytical and experimental parts of the investigation, we developed a novel approach to estimate the level of frictional shear stress that exists along the fiber-matrix interface during fatigue. Since this technique allows confirmation of other techniques for estimating frictional shear stress (e.g., fiber pushout technique developed by Marshall at Rockwell Science Center). Moreover, it is the only approach that allows determination of the in-situ change in frictional shear stress during cyclic loading (note that the level of frictional shear stress controls many mechanical properties such as strength, toughness and mechanical damping as well as thermophysical properties such as thermal diffusivity). The analysis that was developed to estimate frictional shear stress can also be used to understand the relationship between composite microstructure and cyclic energy dissipation in fiber-reinforced ceramics.

Holmes, J.W.

1993-01-01

276

Probabilistic fatigue methodology and wind turbine reliability  

SciTech Connect

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

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

1996-05-01

277

Thermomechanical Fatigue Damage/Failure Mechanisms in SCS-6/Timetal 21S [0/90](Sub S) Composite  

NASA Technical Reports Server (NTRS)

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, Michael G.

1994-01-01

278

Materials Science and Engineering A319321 (2001) 597601 Foreign-object damage and high-cycle fatigue of Ti6Al4V  

E-print Network

, very high mean stress levels [1,2]. Foreign-object damage (FOD), from hard body im- pacts of simulated high velocity FOD in affecting the initiation and early growth of small surface fatigue cracks factors: (i) the presence of small microcracks in the damaged zone; (ii) the stress concentration

Ritchie, Robert

279

Peripheral and central fatigue after muscle-damaging exercise is muscle length dependent and inversely related.  

PubMed

Healthy untrained men performed 10 series of 12 knee eccentric extension repetitions (EE) at 160 degrees /s. The maximal voluntary isometric contraction force of the quadriceps muscle, the maximal rate of electrically induced torque development (RTD) and relaxation (RTR), isokinetic concentric torque at 30 degrees /s, the electrostimulation-induced torque at 20 and 100Hz frequencies were established before and after EE at shorter and longer muscle lengths. Besides, voluntary activation (VA) index and central activation ratio (CAR) were tested. There was more peripheral fatigue than central after EE. We established more central fatigue as well as low frequency fatigue at a shorter muscle length compared to the longer muscle length. Relative RTD as well as relative RTR, improved after EE and did not depend on the muscle length. Finally, central fatigue is inversely significantly related with the eccentric torque reduction during eccentric exercise and with the changes in muscle torque induced by low frequency stimulation. PMID:20347333

Skurvydas, Albertas; Brazaitis, Marius; Kamandulis, Sigitas; Sipaviciene, Saule

2010-08-01

280

THE DEVELOPMENT OF MICROSTRUCTURAL DAMAGE DURING HIGH TEMPERATURE CREEP-FATIGUE OF A NICKEL ALLOY  

SciTech Connect

Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include hold times up to 9000 s at maximum tensile strain were conducted at 950 degrees C. The fatigue resistance decreased when a hold time was added at peak tensile strain, owing to the mechanisms resulting in a change in fracture mode from transgranular in pure fatigue to intergranular in creep–fatigue. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep–fatigue resistance. An analysis of the evolving failure modes was facilitated by interrupting tests during cycling for ex situ microstructural investigation.

L.J. Carroll; M.C. Carroll; C. Cabet; R.N. Wright

2013-02-01

281

Development of criteria for fatigue repairs in bridge girders damaged by out-of-plane distortion  

E-print Network

Numerous highway bridge girders across the United States have experienced fatigue cracking due to repetitive out-of-plane distortion at unstiffened web gaps caused by poorly designed diaphragm connection details. Due to the widespread nature...

Wilson, Scott David

1994-01-01

282

Stochastic Damage Evolution under Static and Fatigue Loading in Composites with Manufacturing Defects  

E-print Network

defects, the initiation and multiplication of cracks evolve in a stochastic way. The experimental study on the in-plane shear stress finds the detrimental effect of the shear stress on the fatigue performance of composite laminates. Combined...

Huang, Yongxin

2012-07-16

283

Fatigue and Damage Tolerance Analysis of a Hybrid Composite Tapered Flexbeam  

NASA Technical Reports Server (NTRS)

The behavior of nonlinear tapered composite flexbeams under combined axial tension and cyclic bending loading was studied using coupon test specimens and finite element (FE) analyses. The flexbeams used a hybrid material system of graphite/epoxy and glass/epoxy and had internal dropped plies, dropped in an overlapping stepwise pattern. Two material configurations, differing only in the use of glass or graphite plies in the continuous plies near the midplane, were studied. Test specimens were cut from a full-size helicopter tail-rotor flexbeam and were tested in a hydraulic load frame under combined constant axialtension load and transverse cyclic bending loads. The first determination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group in the tapered region of the flexbeam, near the thick end. Delaminations grew slowly and stably, toward the thick end of the flexbeam, at the interfaces above and below the dropped-ply region. A 2D finite element model of the flexbeam was developed. The model was analyzed using a geometrically non-linear analysis with both the ANSYS and ABAQUS FE codes. The global responses of each analysis agreed well with the test results. The ANSYS model was used to calculate strain energy release rates (G) for delaminations initiating at two different ply-ending locations. The results showed that delaminations were more inclined to grow at the locations where they were observed in the test specimens. Both ANSYS and ABAQUS were used to calculate G values associated with delamination initiating at the observed location but growing in different interfaces, either above or below the ply-ending group toward the thick end, or toward the thin end from the tip of the resin pocket. The different analysis codes generated the same trends and comparable peak values, within 5-11 % for each delamination path. Both codes showed that delamination toward the thick region was largely mode II, and toward the thin region was predominantly mode I. The calculated peak G-values from either analysis predict delamination is most likely to occur along the same interface where it was observed in the test specimens. Calculated peak G values were used with material characterization data to calculate a curve relating the fatigue life of the specimens, N, to the applied transverse load, V, for a given constant axial load.

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

2001-01-01

284

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

285

Investigation of the effect of bending twisting coupling on the loads in wind turbines with superelement blade definition  

NASA Astrophysics Data System (ADS)

Bending-twisting coupling in the composite blades is exploited for load alleviation in the whole turbine system. For the purpose of the study, inverse design of a reference blade is performed such that sectional beam properties of the 3D blade design approximately match the sectional beam properties of NREL's 5MW turbine blade. In order to appropriately account for the bending-twisting coupling effect, dynamic superelement of the blade is created and introduced into the multi-body dynamic model of the wind turbine system. Initially, a comparative study is conducted on the performance of wind turbines which have blades defined as superelements and geometrically nonlinear beams, and conclusions are inferred with regard to the appropriateness of the use of superelement blade definition in the transient analysis of the 5MW wind turbine system that is set up in the present study. Multi-body dynamic simulations of the wind turbine system are performed for the power production load case with the constant wind and the normal turbulence model as external wind loadings. For the internal loads, fatigue damage equivalent load is used as the metric to assess the effect of bending-twisting coupling on the load alleviation in the whole wind turbine system. Results show that in the overall, through the bending-twisting coupling induced with the use of off-axis plies in the main spar caps of the blade, damage equivalent loads associated with the critical load components can be reduced in the wind turbine system.

Gözcü, M. O.; Kayran, A.

2014-06-01

286

Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics  

NASA Technical Reports Server (NTRS)

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, 410Cb stainless steel, and IN100 nickel-base superalloy 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., Jr.

2008-01-01

287

Characterization of Damage Progression in SCS-6/timetal 21S (0)4 Under Thermomechanical Fatigue Loadings  

NASA Technical Reports Server (NTRS)

A detailed experimental investigation was performed at a single maximum cyclic stress (sigma max) level to physically characterize the progression of thermomechanical fatigue (lW) damage in continuously reinforced (0 deg) SCS-6/Timetal 21S, a titanium matrix composite. In-phase (IP) and out of-phase (OP) loadings were investigated at sigma max = 1000 MPa with a temperature cycle from 150 to 6500 C. Damage progression, in terms of macroscopic property degradation, was experimentally quantified through an advanced TMF test methodology which incorporates explicit measurements of the isothermal static moduli at the TMF temperature extremes and the coefficient of thermal expansion (CTE) as functions of the TMF cycles. Detailed characterization of the physical damage progression at the microstructural level was performed by interrupting multiple TMF tests at various stages of mechanical property degradation and analyzing the microstructure through extensive destructive metallography. Further, the extent of damage was also quantified through residual static strength measurements. Results indicated that damage initiation occurred very early in cyclic life (N less than 0.1Nf) for both the IP and OP TMF loadings. IP TMF damage was found to be dominated by fiber breakage with a physical damage progression in the microstructure which was difficult to quantify. OP TMF loadings produced matrix cracking exclusively associated with surface initiations. Here, damage progression was easily distinguished in terms of both the number of cracks and their relative inward progressions toward the outer fiber rows with increased cycling. The point at which the leading cracks reached the outer fiber rows (when localized fiber/matrix de-bonding and matrix crack bridging occurred) appeared to be reflected in the macroscopic property degradation curves.

Castelli, Michael G.

1994-01-01

288

Successful Solutions to SSME/AT Development Turbine Blade Distress  

NASA Technical Reports Server (NTRS)

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

Montgomery, Stuart K.

1999-01-01

289

High cycles fatigue damage of CFRP plates clamped by bolts for axial coupling joint with off-set angle during rotation  

NASA Astrophysics Data System (ADS)

This study discussed the change of residual fracture torque and the fatigue damage process of thin CFRP plates clamped by bolts for axial coupling joint, in which flexible deformation was allowed in the direction of off-set angle by the deflection of the CFRP plates while effective stiffness was obtained in rotational direction. Mechanically laminated 4 layers of the CFRP plates were repeatedly deflected during the rotation of axial coupling, when two axes were jointed with 3 degree of off-set angle, in which number of revolution was 1,800 rpm (30Hz of loading frequency). At first, the fracture morphology of specimen and the residual fracture torque was investigated after 1.0×107 cycles of repeated revolutions. The reduction ratio of spring constant was also determined by simple bending test after the fatigue. The residual fracture torque of the joint was determined on the rotational test machine after 1.0×107 cycles of fatigue. After rotations of cyclic fatigue, fiber breaking and wear of matrix were observed around the fixed parts compressed by washers for setting bolts. The reduction of spring constant of the CFRP plates was caused by the initiation of cyclic fatigue damages around the fixed parts, when the axial coupling joint was rotated with off-set angle. It was found that residual fracture torque of the joint was related with the specific fatigue damage of the CFRP observed in this study.

Ooka, Kazuaki; Okubo, Kazuya; Fujii, Toru; Umeda, Shinichi; Fujii, Masayuki; Sugiyama, Tetsuya

2014-03-01

290

Characterization and fatigue damage of TiO2 layer on spark-anodized titanium before and after hot water treatment  

NASA Astrophysics Data System (ADS)

Spark anodizing of titanium in phosphoric acid solution produced porous TiO2 layer on its surface, and subsequent hot water treatment was performed to modify the surface characteristics of resultant oxide layer. Results show that water treatment not only transformed the original amorphous TiO2 into crystalline anatase, but also resulted in a nanostructured surface. Also, the influence of spark anodizing treatment on fatigue behavior of titanium and the fatigue damage of TiO2 layer before and after water treatment was investigated. Results show that the present spark anodizing at 200 V had no significant influence on the fatigue life of titanium. However, significant fatigue damage was induced in the TiO2 layer. Before water treatment, tensile fatigue loading first caused transverse cracking to occur in the TiO2 layer, and then inclined spallation of oxide layer driven by slip bands in the titanium substrate was observed at a maximum cyclic stress of 140 MPa. In comparison, after water treatment, TiO2 layer exhibited severer fatigue damage, and extensive cracking and delamination of TiO2 layer occurred at a lower maximum cyclic stress of 120 MPa.

Chen, Z. X.; Wang, W. X.; Takao, Y.; Matsubara, T.; Ren, L. M.

2012-12-01

291

Development of the Non-Destructive Evaluation System Using an Eddy Current Probe for Detection of Fatigue Damage in a Stainless Steel  

SciTech Connect

The non-destructive evaluation system which is developed using an eddy current probe to evaluate fatigue damage in an austenitic stainless steel is reported in this paper. This probe is composed of the ferrite core and two pick-up coils connected differentially. The eddy current induced by the excitation coil is disarranged by nonuniform distribution of electromagnetic characteristics due to fatigue damage. The structural function of the eddy current probe proposed, enable to detect the eddy current disarrangement by fatigue damage. This probe detects the change of electromagnetic characteristics in the direction of X. In this paper, SUS304, a austenitic stainless steel was used as the sample. The experimental results show that the output voltage of the probe clearly depends on the number of stress cycles.

Oka, M. [Department of Computer and Control Engineering, Oita National College of Technology, 1666 Maki, Oita, 870-0152 (Japan); Yakushiji, T. [Department of Mechanical Engineering, Oita National College of Technology, 1666 Maki, Oita, 870-0152 (Japan); Tsuchida, Y.; Enokizono, M. [Faculty of Engineering, Oita University, 700 Dannoharu, Oita, 870-1192 (Japan)

2006-03-06

292

LOW PLASTICITY BURNISHING (LPB) TREATMENT TO MITIGATE FOD AND CORROSION FATIGUE DAMAGE IN 17-4 PH STAINLESS STEEL  

Microsoft Academic Search

The benefits of applying low plasticity burnishing (LPB) to 17-4PH Stainless Steel (H1100) on both the fatigue and corrosion fatigue performance were compared with the shot peened (SP) and low stress ground (LSG) conditions. LPB treatment dramatically improved both the high cycle fatigue (HCF) performance and fatigue strength. The baseline LSG and SP treatments showed similar fatigue strengths of about

Paul S. Prevéy; N. Jayaraman

293

A non-uniformly under-sampled blade tip-timing signal reconstruction method for blade vibration monitoring.  

PubMed

High-speed blades are often prone to fatigue due to severe blade vibrations. In particular, synchronous vibrations can cause irreversible damages to the blade. Blade tip-timing methods (BTT) have become a promising way to monitor blade vibrations. However, synchronous vibrations are unsuitably monitored by uniform BTT sampling. Therefore, non-equally mounted probes have been used, which will result in the non-uniformity of the sampling signal. Since under-sampling is an intrinsic drawback of BTT methods, how to analyze non-uniformly under-sampled BTT signals is a big challenge. In this paper, a novel reconstruction method for non-uniformly under-sampled BTT data is presented. The method is based on the periodically non-uniform sampling theorem. Firstly, a mathematical model of a non-uniform BTT sampling process is built. It can be treated as the sum of certain uniform sample streams. For each stream, an interpolating function is required to prevent aliasing in the reconstructed signal. Secondly, simultaneous equations of all interpolating functions in each sub-band are built and corresponding solutions are ultimately derived to remove unwanted replicas of the original signal caused by the sampling, which may overlay the original signal. In the end, numerical simulations and experiments are carried out to validate the feasibility of the proposed method. The results demonstrate the accuracy of the reconstructed signal depends on the sampling frequency, the blade vibration frequency, the blade vibration bandwidth, the probe static offset and the number of samples. In practice, both types of blade vibration signals can be particularly reconstructed by non-uniform BTT data acquired from only two probes. PMID:25621612

Hu, Zheng; Lin, Jun; Chen, Zhong-Sheng; Yang, Yong-Min; Li, Xue-Jun

2015-01-01

294

TEM observations of fatigue damage accumulation at the surface of the near-{alpha} titanium alloy IMI 834  

SciTech Connect

A high performance near-{alpha} titanium alloy (IMI 834) was cyclically fatigued to failure under load controlled four point bend testing with an R ratio of 0.1 to a maximum stress of 80--100% of the 0.2% proof stress. Detailed transmission electron microscope (TEM) characterization of the damage accumulation was performed as a function of depth below the surface on samples from two orthogonal orientations. The slip band type and density was determined as a function of the resolved shear stress acting on the slip planes and their proximity to the surface. In the primary-{alpha}, fatigue damage accumulation occurred primarily by slip on basal planes. Evidence of and prism slip was also found, but only where the resolved shear stress on the basal planes was low. Significantly, basal slip was identified on planes on which the resolved shear stress was low. In the transformed-{beta} phase strain accumulation was substantially greater and was accommodated approximately equally on both basal and prism planes. In all cases, strain was a maximum in the surface grains and decreased with depth at a greater rate than the applied stress. Direct TEM evidence of crack nuclei was found. Cracks formed subsurface at stress concentrations on basal planes and grew along the basal plane towards the surface. The crack initiation mechanism is discussed in relation to strain discontinuities, resolved shear and tensile stresses, chemical composition and slip band length.

Baxter, G.J.; Rainforth, W.M. [Univ. of Sheffield (United Kingdom). Dept. of Engineering Materials] [Univ. of Sheffield (United Kingdom). Dept. of Engineering Materials; Grabowski, L. [Rolls-Royce and Associates, Derby (United Kingdom)] [Rolls-Royce and Associates, Derby (United Kingdom)

1996-09-01

295

Fatigue damage accumulation and property degradation in flat versus cylindrical specimens  

E-print Network

Results 66 66 66 68 70 70 70 76 76 77 77 VI COMPRESSION-COMPRESSION FATIGUE RESPONSE . . 79 6. 1 6. 2 6. 3 6. 4 6. 5 Introduction . . Flat [+45/90/0), Coupons 6. 2. I Experimental Procedure 6. 2. 2 Experimental Results . Flat [+45... for 1-F-QSC-02. . . . . . . 74 Table 15. Modulus reduction ratio for flat coupons subjected to quasi-static compressive loading 76 Table 16. Modified test matrix. 80 Page Table 17. Fatigue results for [+45/90/0], flat coupons cycled at 5 hz...

Andrews, Kristine Bachtel

1992-01-01

296

Acoustic Emission and Damage Monitoring During Fatigue of C-SiC Composites at Room Temperature  

NASA Technical Reports Server (NTRS)

Fatigue experiments were performed at room temperature for C-fiber reinforced chemical vapor infiltrated (CVI Sic) matrix and melt-infiltrated (MI) matrix composites. The goal was to associate some nondestructive parameter or acoustic emission characteristic with the processes that lead to fatigue failure. Failure only occurred at loads very close to the ultimate. However, correlations between the acoustic data and the eventual failure of the composites could be made. These will be presented with respect to health monitoring of these types of composites.

Morscher, Gregory N.; Deemer, Chris; Cuneo, Jacques; Smith, Aron; Koenig, John

2003-01-01

297

Health monitoring and prognostics of blades and disks with blade tip sensors  

Microsoft Academic Search

Blade tip sensors embedded in the engine case have been used for decades to measure blade tip clearance and blade vibration. Many sensing technologies have been used: capacitive, inductive, optical, microwave, infrared, eddy-current, pressure and acoustic. This paper outlines the technology of blade and disk health monitoring with such sensors. The basic measurement techniques are reviewed, along with damage signatures

Andreas von Flotow; Mathieu Mercadal; Peter Tappert

2000-01-01

298

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

NASA Astrophysics Data System (ADS)

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 steam turbine environments within the phase transition zone. The passivity properties of Type 403 SS and A470/471 steel in the passive regions, including defect type, defect concentration in the barrier film, barrier film thickness, and the steady-state current density, agree with the predictions of the Point Defect Model (PDM) for an n-type semiconductor. Optimization of the PDM based impedance model on the experimental electrochemical impedance data has yielded a set of parameter values that can be used to predict the barrier film growth on Type 403 SS in deaerated borate buffer solution ( pH = 8.2) at ambient temperature. Experimental relationships between the breakdown potential and chloride activity, pH, temperature, and potential scan rate have demonstrated the applicability of the PDM for describing passivity breakdown on Type 403 SS and A470/471 steel. The obtained parameter values were used to calculate the breakdown potential, induction time, and their distributions, via the PDM, which represents the first quantitative characterization of the passivity breakdown behavior on Type 403 SS. Pitting damage functions for Type 403 SS have been experimentally determined for the first time. However, low pit density on A470/471 steel led to insufficient pit numbers on the 1.27 cm2 surface for the effective determination of damage functions. DEVS has been demonstrated by predicting the average maximum pit depth for 750 hours from short-term (24 hours and 240 hours) maximum pit depth data on Type 403 SS in deaerated buffer solution with 0.10 M NaCl at an applied potential of 0.090 VSCE and on A470/471 steel in the solution with 0.028 M NaCl at 0.058 VSCE. To the author's knowledge, the work reported in this dissertation represents the first instance in which DEVS has been used to predict the accumulation of pitting damage on LP steam turbine alloys, thereby heralding a new era in the prediction of corrosion damage in these systems.

Zhang, Yancheng

299

Fatigue design 2011 November 23 & 24 Cetim, Senlis -France MECHANICAL BEHAVIOR AND DAMAGE OF TRIDIMENSIONAL  

E-print Network

in width). Most important, it has to be designed to operate under large thermal loading amplitude. The mainFatigue design 2011 ­ November 23 & 24 ­ Cetim, Senlis - France 1 of 8 MECHANICAL BEHAVIOR dissipation in operating conditions due to the Joule effect. In addition, the complexity of the geometry

300

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

Microsoft Academic Search

Fatigue loading seldom involves constant amplitude loading. This is especially true in the cooling systems of nuclear power plants, typically made of stainless steel, where thermal fluctuations and water turbulent flow create variable amplitude loads, with presence of mean stresses and overloads. These complex loading sequences lead to the formation of networks of microcracks (crazing) that can propagate. As stainless

Julie Colin

2010-01-01

301

Quantitative Assessment of Fatigue Damage Accumulation in Wavy Slip Metals from Acoustic Harmonic Generation  

NASA Technical Reports Server (NTRS)

A comprehensive, analytical treatment is presented of the microelastic-plastic nonlinearities resulting from the interaction of a stress perturbation with dislocation substructures (veins and persistent slip bands) and cracks that evolve during high-cycle fatigue of wavy slip metals. The nonlinear interaction is quantified by a material (acoustic) nonlinearity parameter beta extracted from acoustic harmonic generation measurements. The contribution to beta from the substructures is obtained from the analysis of Cantrell [Cantrell, J. H., 2004, Proc. R. Soc. London A, 460, 757]. The contribution to beta from cracks is obtained by applying the Paris law for crack propagation to the Nazarov-Sutin crack nonlinearity equation [Nazarov, V. E., and Sutin, A. M., 1997, J. Acoust. Soc. Am. 102, 3349]. The nonlinearity parameter resulting from the two contributions is predicted to increase monotonically by hundreds of percent during fatigue from the virgin state to fracture. The increase in beta during the first 80-90 percent of fatigue life is dominated by the evolution of dislocation substructures, while the last 10-20 percent is dominated by crack growth. The model is applied to the fatigue of aluminium alloy 2024-T4 in stress-controlled loading at 276MPa for which experimental data are reported. The agreement between theory and experiment is excellent.

Cantrell, John H.

2006-01-01

302

Effect of BCAA intake during endurance exercises on fatigue substances, muscle damage substances, and energy metabolism substances  

PubMed Central

The increase rate of utilization of branched-chain amino acids (BCAA) by muscle is reduced to its plasma concentration during prolonged exercise leading to glycogen. BCAA supplementation would reduce the serum activities of intramuscular enzymes associated with muscle damage. To examine the effects of BCAA administration on fatigue substances (serotonin, ammonia and lactate), muscle damage substances (CK and LDH) and energy metabolism substances (FFA and glucose) after endurance exercise. Subjects (n = 26, college-aged males) were randomly divided into an experimental (n = 13, EXP) and a placebo (n = 13, CON) group. Subjects both EXP and CON performed a bout of cycle training (70% VO2max intensity) to exhaustion. Subject in the EXP were administrated BCAA (78ml/kg·w) prior to the bout of cycle exercise. Fatigue substances, muscle damage substances and energy metabolism substances were measured before ingesting BCAAs and placebos, 10 min before exercise, 30 min into exercise, immediately after exercise, and 30 min after exercise. Data were analyzed by two-way repeated measure ANCOVA, correlation and statistical significance was set at p < 0.05. The following results were obtained from this study; 1. In the change of fatigue substances : Serotonin in the EXP tended to decreased at the 10 min before exercise, 30 min into exercise, post exercise, and recovery 30 min. Serotonin in the CON was significantly greater than the EXP at the10 min before exercise and recovery 30. Ammonia in the EXP was increased at the 10 min before exercise, 30 min into exercise, and post exercise, but significantly decreased at the recovery 30min (p < 0.05). Ammonia in the CON was significantly lower than the EXP at the 10 min before exercise, 30 min into exercise, and post exercise (p < 0.05). Lactate in the EXP was significantly increased at the 30 min into exercise and significantly decreased at the post exercise and recovery 30 min. Lactate in the CON was significantly lower than the EXP at the post exercise (p < 0.05). 2. In the change of muscle damage substances : CK in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. CK in the CON was greater than the EXP. LDH in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. LDH in the CON was higher than the EXP. 3. In the change of energy metabolism substances :Glucose in the EXP tended to decrease at the 10 min before exercise, 30 min into exercise, post exercise and recovery 30 min. Glucose in the CON was significantly greater than the EXP at the recovery 30 min (p < .05). FFA in both EXP and CON was increased at the post exercise and recovery 30 min. % increase for FFA in the EXP was greater than the CON at the post exercise and recovery 30 min. 4. The relationship of the fatigue substances, muscle damage substances and energy metabolism substances after endurance exercise indicated strongly a positive relationship between LDH and ammonia and a negative relationship between LDH and FFA in the EXP. Also, there were a strong negative relationship between glucose and FFA and a positive relationship between glucose and serotonin in the EXP. There was a strong positive relationship between CK and LDH and a strong negative relationship between FFA and glucose in the CON. These results indicate that supplementary BCAA decreased serum concentrations of the intramuscular enzymes as CK and LDH following exhaustive exercise. This observation suggests that BCAA supplementation may reduce the muscle damage associated with endurance exercise.

Kim, Dong-Hee; Kim, Seok-Hwan; Jeong, Woo-Seok; Lee, Ha-Yan

2013-01-01

303

Effect of BCAA intake during endurance exercises on fatigue substances, muscle damage substances, and energy metabolism substances.  

PubMed

The increase rate of utilization of branched-chain amino acids (BCAA) by muscle is reduced to its plasma concentration during prolonged exercise leading to glycogen. BCAA supplementation would reduce the serum activities of intramuscular enzymes associated with muscle damage. To examine the effects of BCAA administration on fatigue substances (serotonin, ammonia and lactate), muscle damage substances (CK and LDH) and energy metabolism substances (FFA and glucose) after endurance exercise. Subjects (n = 26, college-aged males) were randomly divided into an experimental (n = 13, EXP) and a placebo (n = 13, CON) group. Subjects both EXP and CON performed a bout of cycle training (70% VO2max intensity) to exhaustion. Subject in the EXP were administrated BCAA (78ml/kg·w) prior to the bout of cycle exercise. Fatigue substances, muscle damage substances and energy metabolism substances were measured before ingesting BCAAs and placebos, 10 min before exercise, 30 min into exercise, immediately after exercise, and 30 min after exercise. Data were analyzed by two-way repeated measure ANCOVA, correlation and statistical significance was set at p < 0.05. The following results were obtained from this study; 1. In the change of fatigue substances : Serotonin in the EXP tended to decreased at the 10 min before exercise, 30 min into exercise, post exercise, and recovery 30 min. Serotonin in the CON was significantly greater than the EXP at the10 min before exercise and recovery 30. Ammonia in the EXP was increased at the 10 min before exercise, 30 min into exercise, and post exercise, but significantly decreased at the recovery 30min (p < 0.05). Ammonia in the CON was significantly lower than the EXP at the 10 min before exercise, 30 min into exercise, and post exercise (p < 0.05). Lactate in the EXP was significantly increased at the 30 min into exercise and significantly decreased at the post exercise and recovery 30 min. Lactate in the CON was significantly lower than the EXP at the post exercise (p < 0.05). 2. In the change of muscle damage substances : CK in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. CK in the CON was greater than the EXP. LDH in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. LDH in the CON was higher than the EXP. 3. In the change of energy metabolism substances :Glucose in the EXP tended to decrease at the 10 min before exercise, 30 min into exercise, post exercise and recovery 30 min. Glucose in the CON was significantly greater than the EXP at the recovery 30 min (p < .05). FFA in both EXP and CON was increased at the post exercise and recovery 30 min. % increase for FFA in the EXP was greater than the CON at the post exercise and recovery 30 min. 4. The relationship of the fatigue substances, muscle damage substances and energy metabolism substances after endurance exercise indicated strongly a positive relationship between LDH and ammonia and a negative relationship between LDH and FFA in the EXP. Also, there were a strong negative relationship between glucose and FFA and a positive relationship between glucose and serotonin in the EXP. There was a strong positive relationship between CK and LDH and a strong negative relationship between FFA and glucose in the CON. These results indicate that supplementary BCAA decreased serum concentrations of the intramuscular enzymes as CK and LDH following exhaustive exercise. This observation suggests that BCAA supplementation may reduce the muscle damage associated with endurance exercise. PMID:25566428

Kim, Dong-Hee; Kim, Seok-Hwan; Jeong, Woo-Seok; Lee, Ha-Yan

2013-12-01

304

Influence of Prior Fatigue Damage on Tensile Properties of 316L(N) Stainless Steel and Modified 9Cr-1Mo Steel  

NASA Astrophysics Data System (ADS)

In the current study, the effect of prior low-cycle fatigue (LCF) damage on the tensile properties of 316L(N) stainless steel (SS) and modified 9Cr-1Mo steel were systematically investigated. The LCF tests were interrupted at 5, 10, 30, and 50 pct of the total fatigue life followed by tensile tests on the same specimens at the same strain rate (3 × 10-3 s-1) and temperatures of 300 K, 823 K, and 873 K (27 °C, 550 °C, and 600 °C). Prior strain cycling at elevated temperatures had remarkable effect on the tensile properties of both cyclically hardening and cyclically softening materials. An exponential relationship between the yield stress and the amount of pre-strain cycles is obtained for both the materials. The initial drastic change in the yield strength values up to 10 pct of fatigue life may be due to the microstructural changes that lead to hardening or softening in 316L(N) SS and modified 9Cr-1Mo steel, respectively. Saturation in the yield strength values beyond 10 pct of fatigue life has practical importance for remnant fatigue life assessment. Evolution of fatigue damage in both the 316L(N) SS and modified 9Cr-1Mo steel was analyzed using the surface replica technique.

Mariappan, K.; Shankar, Vani; Sandhya, R.; Mathew, M. D.; Bhaduri, A. K.

2014-12-01

305

Influence of Prior Fatigue Damage on Tensile Properties of 316L(N) Stainless Steel and Modified 9Cr-1Mo Steel  

NASA Astrophysics Data System (ADS)

In the current study, the effect of prior low-cycle fatigue (LCF) damage on the tensile properties of 316L(N) stainless steel (SS) and modified 9Cr-1Mo steel were systematically investigated. The LCF tests were interrupted at 5, 10, 30, and 50 pct of the total fatigue life followed by tensile tests on the same specimens at the same strain rate (3 × 10-3 s-1) and temperatures of 300 K, 823 K, and 873 K (27 °C, 550 °C, and 600 °C). Prior strain cycling at elevated temperatures had remarkable effect on the tensile properties of both cyclically hardening and cyclically softening materials. An exponential relationship between the yield stress and the amount of pre-strain cycles is obtained for both the materials. The initial drastic change in the yield strength values up to 10 pct of fatigue life may be due to the microstructural changes that lead to hardening or softening in 316L(N) SS and modified 9Cr-1Mo steel, respectively. Saturation in the yield strength values beyond 10 pct of fatigue life has practical importance for remnant fatigue life assessment. Evolution of fatigue damage in both the 316L(N) SS and modified 9Cr-1Mo steel was analyzed using the surface replica technique.

Mariappan, K.; Shankar, Vani; Sandhya, R.; Mathew, M. D.; Bhaduri, A. K.

2015-02-01

306

Monte Carlo simulation for system damage prediction: an example from thermo-mechanical fatigue (TMF) damage for a turbine engine  

Microsoft Academic Search

For high performance\\/high cost systems like aircraft systems, there is a need to achieve real-time, and continual assessment of engine condition, and possibly, to extend the life of operation. A turbine engine component life is varied depending on its operating environments. It is almost impossible to predict a damage of component correctly since operating conditions might be different. The challenge

C. L. Philip Chen; Jinwoo Kim; Ten-Huei Guo

2006-01-01

307

Utilizing Fiber-Reinforced Polymers to Retrofit Steel Bridge Girders Damaged by Fatigue Loading.  

E-print Network

’s metal surface. Numerous theoretical and experimental analyses have been conducted on the use of FRP adhesively bonded to steel beams as a retrofit to extend fatigue life. As reported by Tavakkolizadeh and Saadatmanesh (2003), beams in aged steel... requires removal of a portion of the concrete deck); a hybrid connection including both welding and bolting the angle to the flange; utilizing adhesives to connect the angle to the flange; and nailing the angle to the flange (Dexter, R and Ocel, J. 2013...

Bonet, Eric

2014-08-31

308

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

309

Detection of Fatigue Damage Prior Crack Initiation with Scanning 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, J. W. Jr. [Department of Materials Science and Engineering, University of California, Berkeley, CA 94720 (United States); Lee, Seungkyun; Clarke, John [Department of Physics, University of California, Berkeley, CA 94720 (United States); Materials Science Division, Lawrence Berkeley, National Laboratory, Berkeley, CA 94720 (United States)

2006-03-06

310

Monitoring Thermal Fatigue Damage In Nuclear Power Plant Materials Using Acoustic Emission  

SciTech Connect

Proactive aging management of nuclear power plant passive components requires technologies to enable monitoring and accurate quantification of material condition at early stages of degradation (i.e., pre-macrocrack). Acoustic emission (AE) is well-suited to continuous monitoring of component degradation and is proposed as a method to monitor degradation during accelerated thermal fatigue tests. A key consideration is the ability to separate degradation responses from external sources such as water spray induced during thermal fatigue testing. Water spray provides a significant background of acoustic signals, which can overwhelm AE signals caused by degradation. Analysis of AE signal frequency and energy is proposed in this work as a means for separating degradation signals from background sources. Encouraging results were obtained by applying both frequency and energy filters to preliminary data. The analysis of signals filtered using frequency and energy provides signatures exhibiting several characteristics that are consistent with degradation accumulation in materials. Future work is planned to enable verification of the efficacy of AE for thermal fatigue crack initiation detection. While the emphasis has been placed on the use of AE for crack initiation detection during accelerated aging tests, this work also has implications with respect to the use of AE as a primary tool for early degradation monitoring in nuclear power plant materials. The development of NDE tools for characterization of aging in materials can also benefit from the use of a technology such as AE which can continuously monitor and detect crack initiation during accelerated aging tests.

Meyer, Ryan M.; Ramuhalli, Pradeep; Watson, Bruce E.; Pitman, Stan G.; Roosendaal, Timothy J.; Bond, Leonard J.

2012-04-26

311

DETECTION, ESTIMATION, AND CHARACTERIZATION OF FATIGUE DAMAGE IN POLYCRYSTALLINE-ALLOY STRUCTURES.  

E-print Network

??Quantifying damage in complex electromechanical systems under uncertain loading conditions becomes a difficult task due to the absence of a reliable mathematical model. Therefore, sensor-based… (more)

Singh, Dheeraj

2011-01-01

312

Fatigue Damage in Notched Composite Laminates Under Tension-Tension Cyclic Loads  

NASA Technical Reports Server (NTRS)

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 damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Two quasi-isotropic laminates were selected to give different distributions of interlaminar stresses around the hole. The laminates were tested under cyclic loads (R=0.1, 10 Hz) at maximum stresses ranging between 60 and 95 percent of the notched tensile strength.

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

1985-01-01

313

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

314

Structural tailoring of engine blades (STAEBL) user's manual  

NASA Technical Reports Server (NTRS)

This User's Manual contains instructions and demonstration case to prepare input data, run, and modify the Structural Tailoring of Engine Blades (STAEBL) computer code. STAEBL was developed to perform engine fan and compressor blade numerical optimizations. This blade optimization seeks a minimum weight or cost design that satisfies realistic blade design constraints, by tuning one to twenty design variables. The STAEBL constraint analyses include blade stresses, vibratory response, flutter, and foreign object damage. Blade design variables include airfoil thickness at several locations, blade chord, and construction variables: hole size for hollow blades, and composite material layup for composite blades.

Brown, K. W.

1985-01-01

315

Structural tailoring of engine blades (STAEBL) theoretical manual  

NASA Technical Reports Server (NTRS)

This Theoretical Manual includes the theories included in the Structural Tailoring of Engine Blades (STAEBL) computer program which was developed to perform engine fan and compressor blade numerical optimizations. These blade optimizations seek a minimum weight or cost design that satisfies practical blade design constraints, by controlling one to twenty design variables. The STAEBL constraint analyses include blade stresses, vibratory response, flutter, and foreign object damage. Blade design variables include airfoil thickness at several locations, blade chord, and construction variables: hole size for hollow blades, and composite material layup for composite blades.

Brown, K. W.

1985-01-01

316

Stress analysis and life prediction of gas turbine blade  

NASA Technical Reports Server (NTRS)

A stress analysis procedure is presented for a redesign of the Space Shuttle Main Engine high pressure fuel turbopump turbine blades. The analysis consists of the one-dimensional scoping analysis to support the design layout and the follow-on three-dimensional finite element analysis to confirm the blade design at operating loading conditions. Blade life is evaluated based on high-cycle fatigue and low-cycle fatigue.

Hsiung, H. C.; Dunn, A. J.; Woodling, D. R.; Loh, D. L.

1988-01-01

317

An advanced method for tracking the evolution of fatigue damage in reusable space propulsion systems  

NASA Astrophysics Data System (ADS)

NASA-Lewis is actively involved in the general effort to research, develop, test, and evaluate advanced theoretical, analytical, experimental, and probabilistic analysis concepts required for life prediction of liquid rocket engines at the subcomponent, component, and engine system levels. The models developed are oriented toward use in advanced health monitoring systems of space propulsion systems. It is planned to demonstrate the methodology considering a representative set of three components such as a main injector element, a combustion chamber liner, and a turbopump blade. This paper describes the initial development and application of this method to a specific location in the main injector element of the SSME. Further enhancements and various elements of the framework will be completed as the work proceeds in subsequent years.

Rajagopal, K. R.; Orient, G.; Newell, J. F.; McGaw, M.

318

The LIFE computer code: Fatigue life prediction for vertical axis wind turbine components  

NASA Astrophysics Data System (ADS)

The LIFE computer code was originally written by Veers to analyze the fatigue life of a vertical axis wind turbine (VAWT) blade. The basic assumptions built into this analysis tool are: the fatigue life of a blade component is independent of the mean stress; the frequency distribution of the vibratory stresses may be described adequately by a Rayleigh probability density function; and damage accumulates linearly (Miner's Rule). Further, the yearly distribution of wind is assumed to follow a Rayleigh distribution. The original program has been updated to run in an interactive mode on a personal computer with a BASIC interpreter and 256K RAM. Additional capabilities included in this update include: the generalization of the Rayleigh function for the wind speed distribution to a Weibull function; the addition of two constitutive rules for the evaluation of the effects of mean stress on fatigue life; interactive data input; and the inclusion of a stress concentration factor into the analysis.

Sutherland, H. J.; Ashwill, T. D.; Slack, N.

1987-08-01

319

Early stage fatigue damage occurs in bovine tendon fascicles in the absence of changes in mechanics at either the gross or micro-structural level  

PubMed Central

Many tendon injuries are believed to result from repetitive motion or overuse, leading to the accumulation of micro-damage over time. In vitro fatigue loading can be used to characterise damage during repeated use and investigate how this may relate to the aetiology of tendinopathy. This study considered the effect of fatigue loading on fascicles from two functionally distinct bovine tendons: the digital extensor and deep digital flexor. Micro-scale extension mechanisms were investigated in fascicles before or after a period of cyclic creep loading, comparing two different measurement techniques – the displacement of a photo-bleached grid and the use of nuclei as fiducial markers. Whilst visual damage was clearly identified after only 300 cycles of creep loading, these visual changes did not affect either gross fascicle mechanics or fascicle microstructural extension mechanisms over the 900 fatigue cycles investigated. However, significantly greater fibre sliding was measured when observing grid deformation rather than the analysis of nuclei movement. Measurement of microstructural extension with both techniques was localised and this may explain the absence of change in microstructural deformation in response to fatigue loading. Alternatively, the data may demonstrate that fascicles can withstand a degree of matrix disruption with no impact on mechanics. Whilst use of a photo-bleached grid to directly measure the collagen is the best indicator of matrix deformation, nuclei tracking may provide a better measure of the strain perceived directly by the cells. PMID:25001495

Shepherd, Jennifer H.; Riley, Graham P.; Screen, Hazel R.C.

2014-01-01

320

Structural health and prognostics management for offshore wind turbines : case studies of rotor fault and blade damage with initial O&M cost modeling.  

SciTech Connect

Operations and maintenance costs for offshore wind plants are significantly higher than the current costs for land-based (onshore) wind plants. One way to reduce these costs would be to implement a structural health and prognostic management (SHPM) system as part of a condition based maintenance paradigm with smart load management and utilize a state-based cost model to assess the economics associated with use of the SHPM system. To facilitate the development of such a system a multi-scale modeling approach developed in prior work is used to identify how the underlying physics of the system are affected by the presence of damage and faults, and how these changes manifest themselves in the operational response of a full turbine. This methodology was used to investigate two case studies: (1) the effects of rotor imbalance due to pitch error (aerodynamic imbalance) and mass imbalance and (2) disbond of the shear web; both on a 5-MW offshore wind turbine in the present report. Based on simulations of damage in the turbine model, the operational measurements that demonstrated the highest sensitivity to the damage/faults were the blade tip accelerations and local pitching moments for both imbalance and shear web disbond. The initial cost model provided a great deal of insight into the estimated savings in operations and maintenance costs due to the implementation of an effective SHPM system. The integration of the health monitoring information and O&M cost versus damage/fault severity information provides the initial steps to identify processes to reduce operations and maintenance costs for an offshore wind farm while increasing turbine availability, revenue, and overall profit.

Myrent, Noah J. [Purdue Center for Systems Integrity, Lafayette, IN; Kusnick, Joshua F. [Purdue Center for Systems Integrity, Lafayette, IN; Barrett, Natalie C. [Purdue Center for Systems Integrity, Lafayette, IN; Adams, Douglas E. [Purdue Center for Systems Integrity, Lafayette, IN; Griffith, Daniel Todd

2013-04-01

321

Quantitative damage detection and sparse sensor array optimization of carbon fiber reinforced resin composite laminates for wind turbine blade structural health monitoring.  

PubMed

The active structural health monitoring (SHM) approach for the complex composite laminate structures of wind turbine blades (WTBs), addresses the important and complicated problem of signal noise. After illustrating the wind energy industry's development perspectives and its crucial requirement for SHM, an improved redundant second generation wavelet transform (IRSGWT) pre-processing algorithm based on neighboring coefficients is introduced for feeble signal denoising. The method can avoid the drawbacks of conventional wavelet methods that lose information in transforms and the shortcomings of redundant second generation wavelet (RSGWT) denoising that can lead to error propagation. For large scale WTB composites, how to minimize the number of sensors while ensuring accuracy is also a key issue. A sparse sensor array optimization of composites for WTB applications is proposed that can reduce the number of transducers that must be used. Compared to a full sixteen transducer array, the optimized eight transducer configuration displays better accuracy in identifying the correct position of simulated damage (mass of load) on composite laminates with anisotropic characteristics than a non-optimized array. It can help to guarantee more flexible and qualified monitoring of the areas that more frequently suffer damage. The proposed methods are verified experimentally on specimens of carbon fiber reinforced resin composite laminates. PMID:24763210

Li, Xiang; Yang, Zhibo; Chen, Xuefeng

2014-01-01

322

Quantitative Damage Detection and Sparse Sensor Array Optimization of Carbon Fiber Reinforced Resin Composite Laminates for Wind Turbine Blade Structural Health Monitoring  

PubMed Central

The active structural health monitoring (SHM) approach for the complex composite laminate structures of wind turbine blades (WTBs), addresses the important and complicated problem of signal noise. After illustrating the wind energy industry's development perspectives and its crucial requirement for SHM, an improved redundant second generation wavelet transform (IRSGWT) pre-processing algorithm based on neighboring coefficients is introduced for feeble signal denoising. The method can avoid the drawbacks of conventional wavelet methods that lose information in transforms and the shortcomings of redundant second generation wavelet (RSGWT) denoising that can lead to error propagation. For large scale WTB composites, how to minimize the number of sensors while ensuring accuracy is also a key issue. A sparse sensor array optimization of composites for WTB applications is proposed that can reduce the number of transducers that must be used. Compared to a full sixteen transducer array, the optimized eight transducer configuration displays better accuracy in identifying the correct position of simulated damage (mass of load) on composite laminates with anisotropic characteristics than a non-optimized array. It can help to guarantee more flexible and qualified monitoring of the areas that more frequently suffer damage. The proposed methods are verified experimentally on specimens of carbon fiber reinforced resin composite laminates. PMID:24763210

Li, Xiang; Yang, Zhibo; Chen, Xuefeng

2014-01-01

323

Effect of machining damage on low cycle fatigue crack initiation life in drilled holes in UdimetRTM 720  

NASA Astrophysics Data System (ADS)

White layer is a generic term for a light etching surface layer on metal alloys that can result under extreme deformation conditions in wear, sliding or machining. While there has been some characterization of white layer due to abusive machining, the specific effect on fatigue crack initiation life has not been well documented. This study aimed to establish a relationship between the presence of white layer due to abusive machining and fatigue crack initiation life in a wrought nickel based superalloy (Udimet ® 720). Low cycle fatigue testing was conducted on large specimens containing through holes drilled with parameters aimed at creating holes with and without white layer. Initially, Acoustic Emission monitoring technologies were used to monitor for acoustic events associated with crack initiation, however, this technology was deemed unreliable for this testing. Instead, cycles to crack initiation was determined using striation density measurements on each fracture surface to estimate the number of cycles of crack propagation, which was subtracted from the total number of cycles for the specimen. A total of sixteen specimens were tested in this manner. The results suggested that the crack initiation lives of holes machined with good machining parameters were statistically longer than crack initiation lives of holes machined with poor machining parameters. The mean initiation life of the poorly machined specimens was a factor of approximately 2 times shorter than the mean initiation life of the well machined specimens. The holes machined with good machining parameters exhibited subsurface initiations which suggested that no anomalies affected crack initiation for these specimens. It was also shown that some of the poorly machined holes exhibited subsurface initiations rather than initiations at white layer damage. These holes had better surface finish than the poorly machined specimens that did fail at white layer. The mean initiation life of the poorly machined holes with subsurface initiation was 7 times longer than the mean initiation life of the holes that exhibited white layer at the crack origins. Lastly, no apparent correlation between white layer thickness and initiation life was demonstrated in this study.

Magadanz, Christine M.

324

Isothermal Damage and Fatigue Behavior of SCS-6/Timetal 21S [0/90](Sub S) Composite at 650 Deg C  

NASA Technical Reports Server (NTRS)

The isothermal fatigue damage and life behaviors of SCS-6/Timetal 21S (0/90)s were investigated at 650 C. Strain ratcheting and degradation of the composite's static elastic modulus were carefully monitored as functions of cycles to indicate damage progression. Extensive fractographic and metallographic analyses were conducted to determine damage/failure mechanisms. Resulting fatigue lives show considerable reductions in comparison to (0) reinforced titanium matrix composites subjected to comparable conditions. Notable stiffness degradations were found to occur after the first cycle of loading, even at relatively low maximum stress levels, where cyclic lives are greater than 25,000 cycles. This was attributed to the extremely weak fiber/matrix bond which fails under relatively low transverse loads. Stiffness degradations incurred on first cycle loadings and degradations thereafter were found to increase with increasing maximum stress. Environmental effects associated with oxidation of the (90) fiber interfaces clearly played a role in the damage mechanisms as fracture surfaces revealed environment assisted matrix cracking along the (90) fibers. Metallographic analysis indicated that all observable matrix fatigue cracks initiated at the (90) fiber/matrix interfaces. Global de-bonding in the loading direction was found along the (90) fibers. No surface initiated cracks were evident and minimal if any (0) fiber cracking was visible.

Castelli, Michael G.

1994-01-01

325

A thermodynamics based damage mechanics framework for fatigue analysis of microelectronics solder joints with size effects  

NASA Astrophysics Data System (ADS)

Experimental observations of an increase in resistance with decreasing specimen size and under the presence of non-uniform plastic deformation fields have pushed the development for small scale plasticity theories since the early 90's. The observed phenomenon has been explained in terms of an accumulation of a density of geometrically necessary dislocations, which is required in order to accommodate nonuniform plastic deformation fields. This extra density of dislocations, contributes to the additional hardening observed in small scale specimens under imposed non-uniform plastic deformations. The density of geometrically necessary dislocations has been related to the gradients of plastic strain which are imposed either by the loading conditions or the geometry of the specimen. The proposed set of theories has promoted the idea that there is an additional material parameter, namely a plastic length scale. Within these theories when the material is under the presence of a non-uniform plastic deformation field and once typical structural dimensions approaches the material length scale there is an increase in resistance. Such a class of mathematical framework is currently known as strain gradient plasticity (SGP) theory. On the other hand, the current trend towards miniaturization in the microelectronics industry has raised questions about the true behavior of small structural systems. In this dissertation we address such a problem but from the perspective of eutectic solder alloys. Eutectic solder alloys as frequently used in the microelectronics industry exhibit considerable rate dependent response even at room temperature. Moreover for this type of material, the problem of interest is the response under cyclic loadings induced by thermomechanical fatigue leading to the classical case of creep-fatigue interaction. Several experimental and theoretical studies have been developed in order to generate robust constitutive descriptions for this class of applications. For a structure whose size is close to a 100mum or larger several and relatively simple to implement constitutive models are now available in the literature, and it can be generally stated that the level of understanding has reached a mature level. However, the same problem when the size of the structure is below this characteristic dimension has not been studied before. In other words, the available constitutive models completely neglect the incidence of size effects when evaluating the true behavior of the material at small scales. (Abstract shortened by UMI.)

Gomez, Juan

326

Application of aluminum foil for ``strain sensing'' at fatigue damage evaluation of carbon fiber composite  

NASA Astrophysics Data System (ADS)

Surface layer of a loaded solid is an individual structural level of deformation that was shown numerously within concept of physical mesomechanics. This gives rise to advance in its deformation development under loading as well as allows using this phenomenon to sense the strain induced structure changes. It is of specific importance for composite materials since they are highly heterogeneous while estimating their mechanical state is a topical applied problem. Fatigue tests of carbon fiber composite specimens were carried out for cyclic deformation estimation with the use of strain sensors made of thin (80 ?m) aluminum foil glued to the specimen's surface. The surface images were captured by DSLR camera mounted onto an optical microscope. Strain relief to form during cyclic loading was numerically estimated using different parameters: dispersion, mean square error, universal image quality index, fractal dimension and energy of Fourier spectrum. The results are discussed in view of deformation mismatch in thin foil and bulk specimen and are offered to be applied for the development of Structural Health Monitoring (SHM) approach.

Panin, Sergey; Burkov, Mikhail; Lyubutin, Pavel; Altukhov, Yurii

2014-01-01

327

Reducing fatigue damage for ships in transit through structured decision making  

USGS Publications Warehouse

Research in structural monitoring has focused primarily on drawing inference about the health of a structure from the structure’s response to ambient or applied excitation. Knowledge of the current state can then be used to predict structural integrity at a future time and, in principle, allows one to take action to improve safety, minimize ownership costs, and/or increase the operating envelope. While much time and effort has been devoted toward data collection and system identification, research to-date has largely avoided the question of how to choose an optimal maintenance plan. This work describes a structured decision making (SDM) process for taking available information (loading data, model output, etc.) and producing a plan of action for maintaining the structure. SDM allows the practitioner to specify his/her objectives and then solves for the decision that is optimal in the sense that it maximizes those objectives. To demonstrate, we consider the problem of a Naval vessel transiting a fixed distance in varying sea-state conditions. The physics of this problem are such that minimizing transit time increases the probability of fatigue failure in the structural supports. It is shown how SDM produces the optimal trip plan in the sense that it minimizes both transit time and probability of failure in the manner of our choosing (i.e., through a user-defined cost function). The example illustrates the benefit of SDM over heuristic approaches to maintaining the vessel.

Nichols, J.M.; Fackler, P.L.; Pacifici, K.; Murphy, K.D.; Nichols, J.D.

2014-01-01

328

Mechanisms of microstructural damage during rolling contact fatigue of bearing steels  

E-print Network

position of the upper stage during the repetitive push test XC C mol fraction XkC C mol fraction in the precipitate X?,fC C mol fraction in the matrix after carbide dissolution X?,iC C mol fraction in the matrix before carbide dissolution xi Instantaneous... . Some images are adopted from [5, 6]. 3 during RCF are studied. A literature survey is presented in Chapter 2 to illustrate how the damage is related to the important microstructural changes (carbide coarsening and dissolution) and the test conditions...

Kang, JeeHyun

2014-04-08

329

Dynamic characteristics of single crystal SSME blades  

NASA Technical Reports Server (NTRS)

The Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump (HPFTP) blades are currently manufactured using a directionally solidified (DS) material, MAR-M-246+Hf. However, a necessity to reduce the occurrence of fatigue cracking within the DS blades has lead to an interest in the use of a single crystal (SC) material, PWA-1480. A study was initiated to determine the dynamic characteristics of the HPFTP blades made of SC material and find possible critical engine order excitations. This study examined both the first and second stage drive turbine blades of the HPFTP. The dynamic characterization was done analytically as well as experimentally. The analytical study examined the SC first stage HPFTP blade dynamic characteristics under typical operating conditions. The blades were analyzed using MSC/NASTRAN and a finite element model. Two operating conditions, 27500 RPM and 35000 RPM, were investigated.

Moss, L. A.; Smith, T. E.

1987-01-01

330

Piezoelectric Vibration Damping Study for Rotating Composite Fan Blades  

NASA Technical Reports Server (NTRS)

Resonant vibrations of aircraft engine blades cause blade fatigue problems in engines, which can lead to thicker and aerodynamically lower performing blade designs, increasing engine weight, fuel burn, and maintenance costs. In order to mitigate undesirable blade vibration levels, active piezoelectric vibration control has been investigated, potentially enabling thinner blade designs for higher performing blades and minimizing blade fatigue problems. While the piezoelectric damping idea has been investigated by other researchers over the years, very little study has been done including rotational effects. The present study attempts to fill this void. The particular objectives of this study were: (a) to develop and analyze a multiphysics piezoelectric finite element composite blade model for harmonic forced vibration response analysis coupled with a tuned RLC circuit for rotating engine blade conditions, (b) to validate a numerical model with experimental test data, and (c) to achieve a cost-effective numerical modeling capability which enables simulation of rotating blades within the NASA Glenn Research Center (GRC) Dynamic Spin Rig Facility. A numerical and experimental study for rotating piezoelectric composite subscale fan blades was performed. It was also proved that the proposed numerical method is feasible and effective when applied to the rotating blade base excitation model. The experimental test and multiphysics finite element modeling technique described in this paper show that piezoelectric vibration damping can significantly reduce vibrations of aircraft engine composite fan blades.

Min, James B.; Duffy, Kirsten P.; Choi, Benjamin B.; Provenza, Andrew J.; Kray, Nicholas

2012-01-01

331

Damage Assessment of Heat Resistant Steels through Electron BackScatter Diffraction Strain Analysis under Creep and Creep-Fatigue Conditions  

NASA Astrophysics Data System (ADS)

EBSD(Electron BackScatter Diffraction) analyses were conducted for studying the quantitative microstructural metrics of creep and creep-fatigue damage for austenitic SUS304HTB boiler tube steel and ferritic Mod.9Cr piping steel. KAM(Kernel Average Misorientation) maps and GOS(Grain Orientation Spread) maps were obtained for these samples and the area averaged values KAMave and GOSave were obtained. While the increasing trends of these misorientation metrics were observed for SUS304HTB steel, the decreasing trends were observed for damaged Mod.9Cr steel with extensive recovery of subgrain structure. To establish more universal parameter representing the accumulation of damage to compensate these opposite trends, the EBSD strain parameters were introduced for converting the misorientation changes into the quantities representing accumulated permanent strains during creep and creep-fatigue damage process. As KAM values were dependent on the pixel size (inversely proportional to the observation magnification) and the permanent strain could be expressed as the shear strain which was the product of dislocation density, Burgers vector and dislocation movement distance, two KAM strain parameters M?KAMnet and M??KAMave were introduced as the sum of product of the noise subtracted KAMnet and the absolute change from initial value ?KAMave with dislocation movement distance divided by pixel size. M??KAMave parameter showed better relationship both with creep strain in creep tests and accumulated creep strain range in creep-fatigue tests. This parameter can be used as the strain-based damage evaluation and detector of final failure.

Fujiyama, Kazunari; Kimachi, Hirohisa; Tsuboi, Toshiki; Hagiwara, Hiroyuki; Ogino, Shotaro; Mizutani, Yoshiki

332

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

2009-10-01

333

Bimodal processing of titanium steam turbine blades  

Microsoft Academic Search

A study was undertaken to determine the properties of Ti-6A1-4V steam turbine blades produced by a special bimodal process. The bimodal process consists of special thermomechanical treatments used in the bar stock production and blade forging to yield a fine-grained microstructure consisting of about 40 percent primary alpha imbedded in a fine lamellar alpha-plus-beta matrix which exhibits high fatigue strength

Rust

1985-01-01

334

A real time neural net estimator of fatigue life  

NASA Technical Reports Server (NTRS)

A neural net architecture is proposed to estimate, in real-time, the fatigue life of mechanical components, as part of the Intelligent Control System for Reusable Rocket Engines. Arbitrary component loading values were used as input to train a two hidden-layer feedforward neural net to estimate component fatigue damage. The ability of the net to learn, based on a local strain approach, the mapping between load sequence and fatigue damage has been demonstrated for a uniaxial specimen. Because of its demonstrated performance, the neural computation may be extended to complex cases where the loads are biaxial or triaxial, and the geometry of the component is complex (e.g., turbopump blades). The generality of the approach is such that load/damage mappings can be directly extracted from experimental data without requiring any knowledge of the stress/strain profile of the component. In addition, the parallel network architecture allows real-time life calculations even for high frequency vibrations. Owing to its distributed nature, the neural implementation will be robust and reliable, enabling its use in hostile environments such as rocket engines. This neural net estimator of fatigue life is seen as the enabling technology to achieve component life prognosis, and therefore would be an important part of life extending control for reusable rocket engines.

Troudet, T.; Merrill, W.

1990-01-01

335

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

336

Estimation of the damaging energy under creep-fatigue interaction conditions in 1Cr-Mo-V steel  

Microsoft Academic Search

1Cr-Mo-V steel is widely used in power-generating plants for components which operate at high temperatures. Since many components used in power plants are subjected to complex loading cycles at high temperatures, high temperature low-cycle fatigue (LCF) experiments with hold time can be very meaningful tests for understanding the creep-fatigue interaction phenomenon under complex loading conditions. Therefore, in the study of

Chang Yeol Jeong; Soo Woo Nam

1999-01-01

337

Test evaluation of a laminated wood wind turbine blade concept  

NASA Technical Reports Server (NTRS)

A series of tests conducted on a root end section of a laminated wood wind turbine blade are reported. The blade to hub transition of the wood blade uses steel studs cast into the wood D spar with a filled epoxy. Both individual studs and a full scale, short length, root section were tested. Results indicate that the bonded stud concept is more than adequate for both the 30 year life fatigue loads and for the high wind or hurricane gust loads.

Faddoul, J. R.

1981-01-01

338

PREDICTION OF DELAM INATION IN WIND TURBINE BLADE STRUCTURAL DETAILS John F. Mandell, Douglas S. Cairns  

E-print Network

materials structures such as wind turbine blades. Design methodologies to prevent such failures have1 PREDICTION OF DELAM INATION IN WIND TURBINE BLADE STRUCTURAL DETAILS John F. Mandell, Douglas S static and fatigue loading. INTRODUCTION Composite material structures such as wind turbine blades

339

Development of fatigue loading spectra  

SciTech Connect

The present work on fatigue-loading spectra encompasses the current status of standardized stress-time histories, European approaches to standard loading spectrum development, transport aircraft airframe fatigue test spectra, the TURBISTAN fatigue-loading standard for fighter-aircraft engine disks, an automated procedure for the creation of flight-by-flight spectra, and the development of a wave-action standard history for fatigue testing relevant to tubular structures in the North Sea. Also treated is the use of the TURBISTAN mission spectra to evaluate fatigue crack growth in a rotating disk, fatigue-spectra development for airborne stores, a simplified analysis of fatigue-loading spectra, variable-amplitude load models for fatigue-damage crack growth, the tracking time service histories for multiaxis fatigue problems, and the compilation of procedures for fatigue crack propagation testing under complex load sequences.

Potter, J.M.; Watanabe, R.T.

1989-01-01

340

Turbine blade root design concept promises superior alignment  

NASA Technical Reports Server (NTRS)

Blade-to-hub mounting concept assures excellent alignment integrity and results in elimination of some welding problems associated with designs. With this design, if rework is required, blade removal and replacement may be readily accomplished without damage to blade positioning media on the wheel hub.

King, O. D.

1966-01-01

341

Boron/aluminum fan blades for SCAR engines  

NASA Technical Reports Server (NTRS)

Processing procedures were developed to enhance boron/aluminum bond behavior and foreign object damage (FOD) tolerance. Design and analysis indicated that the J101 Stage 1 fan blade meets the required frequencies without a midspan shroud. The fabricability of full size J101 blades was assessed, while six blades were fabricated and finished machined.

Stabrylla, R. G.; Carlson, R. G.

1977-01-01

342

Bimodal processing of titanium steam turbine blades  

SciTech Connect

A study was undertaken to determine the properties of Ti-6A1-4V steam turbine blades produced by a special bimodal process. The bimodal process consists of special thermomechanical treatments used in the bar stock production and blade forging to yield a fine-grained microstructure consisting of about 40 percent primary alpha imbedded in a fine lamellar alpha-plus-beta matrix which exhibits high fatigue strength and consistent dynamic modulus properties as a result of crystallographic texture control. The bimodal process showed an excellent combination of tensile, fatigue and modulus properties. However, there was no clearcut superiority of the bimodal process in tensile and fatigue properties over conventional alpha-plus-beta forging procedures. The primary advantage of bimodal processing over conventional processing appears to be in the control of dynamic modulus. Bimodal processing produces a fully annealed structure, without residual cold work, which can be expected to show more consistent properties from blade to blade and from lot to lot. Bimodal processing also results in the same microstructure in the thin airfoil section of the blade as in the larger section root, a condition generally not achieved in conventional forging. 11 refs., 16 figs., 9 tabs.

Rust, T.M.

1985-10-01

343

Thermal-barrier-coated turbine blade study  

NASA Technical Reports Server (NTRS)

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 effect on low-cycle fatigue life. New blade design concepts were developed to take optimum advantage of TBCs. Process and material development work and rig evaluations were undertaken which identified the most promising combination as ZrO2 containing 8 w/o Y2O3 applied by air plasma spray onto a Ni22Cr-10Al-1Y bond layer. The bond layer was applied by a low-pressure, high-velocity plasma spray process onto the base alloy. During the initial startup cycles the blades experienced localized leading edge spallation caused by foreign objects.

Siemers, P. A.; Hillig, W. B.

1981-01-01

344

Fiber composite fan blade impact improvement  

NASA Technical Reports Server (NTRS)

The improved foreign object damage resistance of a metal matrix advanced composite fan blade was demonstrated. The fabrication, whirl impact test and subsequent evaluation of nine advanced composite fan blades of the "QCSEE" type design were performed. The blades were designed to operate at a tip speed of 282 m/sec. The blade design was the spar/shell type, consisting of a titanium spar and boron/aluminum composite airfoils. The blade retention was designed to rock on impact with large birds, thereby reducing the blade bending stresses. The program demonstrated the ability of the blades to sustain impacts with up to 681 g slices of birds at 0.38 rad with little damage (only 1.4 percent max weight loss) and 788 g slices of birds at 0.56 rad with only 3.2 percent max weight loss. Unbonding did not exceed 1.1 percent of the post-test blade area during any of the tests. All blades in the post-test condition were judged capable of operation in accordance with the FAA guidelines for medium and large bird impacts.

Graff, J.; Stoltze, L.; Varholak, E. M.

1976-01-01

345

Case Studies of Fatigue Life Improvement Using Low Plasticity Burnishing in Gas Turbine Engine Applications  

NASA Technical Reports Server (NTRS)

Surface enhancement technologies such as shot peening, 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 strength must be retained in service. For successful integration into turbine design, the process must be affordable and compatible with the manufacturing environment. LPB provides thermally stable compression of comparable magnitude and even greater depth than other methods, and can be performed in conventional machine shop environments on CNC machine tools. LPB provides a means to extend the fatigue lives of both new and legacy aircraft engines and ground-based turbines. Improving fatigue performance by introducing deep stable layers of compressive residual stress avoids the generally cost prohibitive alternative of modifying either material or design. The X-ray diffraction based background studies of thermal and mechanical stability of surface enhancement techniques are briefly reviewed, demonstrating the importance of minimizing cold work. The LPB process, tooling, and control systems are described. An overview of current research programs conducted for engine OEMs and the military to apply LPB to a variety of engine and aging aircraft components are presented. Fatigue performance and residual stress data developed to date for several case studies are presented including: * The effect of LPB on the fatigue performance of the nickel based super alloy IN718, showing fatigue benefit of thermal stability at engine temperatures. * An order of magnitude improvement in damage tolerance of LPB processed Ti-6-4 fan blade leading edges. * Elimination of the fretting fatigue debit for Ti-6-4 with prior LPB. * Corrosion fatigue mitigation with LPB in Carpenter 450 steel. *Damage tolerance improvement in 17-4PH steel. Where appropriate, the performance of LPB is compared to conventional shot peening after exposure to engine operating temperatures.

Prevey, Paul S.; Shepard, Michael; Ravindranath, Ravi A.; Gabb, Timothy

2003-01-01

346

A real time neural net estimator of fatigue life  

NASA Technical Reports Server (NTRS)

A neural network architecture is proposed to estimate, in real-time, the fatigue life of mechanical components, as part of the intelligent Control System for Reusable Rocket Engines. Arbitrary component loading values were used as input to train a two hidden-layer feedforward neural net to estimate component fatigue damage. The ability of the net to learn, based on a local strain approach, the mapping between load sequence and fatigue damage has been demonstrated for a uniaxial specimen. Because of its demonstrated performance, the neural computation may be extended to complex cases where the loads are biaxial or triaxial, and the geometry of the component is complex (e.g., turbopumps blades). The generality of the approach is such that load/damage mappings can be directly extracted from experimental data without requiring any knowledge of the stress/strain profile of the component. In addition, the parallel network architecture allows real-time life calculations even for high-frequency vibrations. Owing to its distributed nature, the neural implementation will be robust and reliable, enabling its use in hostile environments such as rocket engines.

Troudet, T.; Merrill, W.

1990-01-01

347

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

348

High temperature low cycle fatigue  

Microsoft Academic Search

Fatigue at high temperature is a complex phenomenon as it is influenced by a number of time-dependent processes which become\\u000a important at elevated temperatures. These processes include creep, oxidation, phase instabilities and dynamic strain ageing\\u000a (DSA), acting either independently or synergistically influence fatigue behaviour, often lowering the fatigue life. Current\\u000a design approaches employ linear summation of fatigue and creep damage

P Rodriguez; S L Mannan

1995-01-01

349

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

350

Design, fabrication, and test of a steel spar wind turbine blade  

NASA Technical Reports Server (NTRS)

The design and fabrication of wind turbine blades based on 60 foot steel spars are discussed. Performance and blade load information is given and compared to analytical prediction. In addition, performance is compared to that of the original MOD-O aluminum blades. Costs for building the two blades are given, and a projection is made for the cost in mass production. Design improvements to reduce weight and improve fatigue life are suggested.

Sullivan, T. L.; Sirocky, P. J., Jr.; Viterna, L. A.

1979-01-01

351

An investigation of fatigue and fretting in a dovetail joint  

Microsoft Academic Search

Specimens designed to reproduce the state of stress of the dovetail joint between blade and disk in a typical gas-turbine configuration have been tested in a 250-kN capacity biaxial fatigue machine. The materials tested were Ti-IMI 829 (disk and blade), Inco 901 and steel FV535 (blades only). The investigation highlights the importance of fretting at the disk\\/blade interface. A design

C. Ruiz; P. H. B. Boddington; K. C. Chen

1984-01-01

352

Growian rotor blades: Production development, construction and test  

NASA Technical Reports Server (NTRS)

Development and construction of three 50 m rotor blades for a 3 MW wind turbine are described. A hybrid concept was chosen, i.e., a load carrying inflexible steel spar and a glass fiber reinforced plastic skin. A test blade was constructed and static loading tests, dynamic vibration tests and fatigue tests on critical welds as well as at the connection between spar and blade skin were performed. All test results show good accordance with calculated values, and were taken into consideration during the construction of two rotor blades.

Thiele, H. M.

1984-01-01

353

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

354

Fatigue life prediction under variable loading based on a new non-linear continuum damage mechanics model  

Microsoft Academic Search

This work presents a non-linear continuum damage mechanics model based on general thermodynamic framework developed by Lemaitre and Chaboche. The proposed model has been formulated to take into account the material damage evolution at different load levels and it allows the effect of the loading sequence to be included; by means of a recurrence formula derived for multilevel loading, complex

V. Dattoma; S. Giancane; R. Nobile; F. W. Panella

2006-01-01

355

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

356

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

357

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

358

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

2013-02-28

359

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

360

Impact resistance of current design composite fan blades tested under short-haul operating conditions  

NASA Technical Reports Server (NTRS)

Boron/epoxy and graphite/epoxy composite blades were impacted in a rotating whirligig facility with conditions closely simulating those which might be experienced by a STOL engine impacted with various foreign objects. The tip speed of the rotating blades was 800 feet per second. The blades were impacted with simulated birds, real birds, ice balls, and gravel. The results of composite blade impact tests were compared with a titanium blade tested under similar conditions. Neither composite material indicated a clear superiority over the other. Blades made from both composite materials showed more damage than the titanium blades.

Steinhagen, C. A.; Salemme, C. T.

1973-01-01

361

Damage Resistance of Titanium Aluminide Evaluated  

NASA Technical Reports Server (NTRS)

As part of the aviation safety goal to reduce the aircraft accident rate, NASA has undertaken studies to develop durable engine component materials. One of these materials, g-TiAl, has superior high-temperature material properties. Its low density provides improved specific strength and creep resistance in comparison to currently used titanium alloys. However, this intermetallic is inherently brittle, and long life durability is a potential problem. Of particular concern is the material s sensitivity to defects, which may form during the manufacturing process or in service. To determine the sensitivity of TiAl to defects, a team consisting of GE Aircraft Engines, Precision Cast Parts, and NASA was formed. The work at the NASA Glenn Research Center at Lewis Field has concentrated on the fatigue response to specimens containing defects. The overall objective of this work is to determine the influence of defects on the high cycle fatigue life of TiAl-simulated low-pressure turbine blades. Two types of defects have been introduced into the specimens: cracking from impact damage and casting porosity. For both types of defects, the cast-to-size fatigue specimens were fatigue tested at 650 C and 100 Hz until failure.

Lerch, Bradley A.; Draper, Susan L.; Baaklini, George Y.; Pereira, J. Michael; Austin, Curt

2000-01-01

362

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

363

Forced Response Analysis of Integrally Bladed Disks with Friction Ring Dampers  

E-print Network

either made as single components or assembled by welding blades on the disk. There are many advantages vibration levels and resonances leading to High Cycle Fatigue phenomena and in worst cases to failure. This

Boyer, Edmond

364

Fretting Fatigue of Gamma TiAl Studied  

NASA Technical Reports Server (NTRS)

Gamma titanium-aluminum alloy (g-TiAl) is an attractive new material for aerospace applications because of its low density and high specific strength in comparison to currently used titanium and nickel-base alloys. Potential applications for this material are compressor and low-pressure turbine blades. These blades are fitted into either the compressor or turbine disks via a dovetail connection. The dovetail region experiences a complex stress state due to the alternating centrifugal force and the natural high-frequency vibration of the blade. Because of the dovetail configuration and the complex stress state, fretting is often a problem in this area. Furthermore, the local stress state becomes more complex when the influence of the metal-metal contact and the edge of the contact is evaluated. Titanium and titanium-based alloys in the clean state exhibit strong adhesive bonds when in contact with themselves and other materials (refs. 1 and 2). This adhesion causes heavy surface damage and high friction in practical cases. Although the wear produced by fretting may be mild, the reduction in fatigue life can be substantial. Thus, there is the potential for fretting problems with these TiAl applications. Since TiAl is an emerging material, there has been limited information about its fretting behavior.

Miyoshi, Kazuhisa; Lerch, Bradley A.; Draper, Susan L.

2003-01-01

365

SSME HPFTP/AT Turbine Blade Platform Featherseal Damper Design  

NASA Technical Reports Server (NTRS)

During the Space Shuttle Main Engines (SSM) HPFtP/AT development program, engine hot fire testing resulted in turbine blade fatigue cracks. The cracks were noted after only a few tests and a several hundred seconds versus the design goal of 60 tests and >30,000 seconds. Subsequent investigation attributed the distress to excessive steady and dynamic loads. To address these excessive turbine blade loads, Pratt & Whitney Liquid Space Propulsion engineers designed and developed retrofitable turbine blade to blade platform featherseal dampers. Since incorporation of these dampers, along with other turbine blade system improvements, there has been no observed SSME HPFTP/AT turbine blade fatigue cracking. The high time HPFTP/AT blade now has accumulated 32 starts and 19,200 seconds hot fire test time. Figure #1 illustrates the HPFTP/AT turbine blade platform featherseal dampers. The approached selected was to improve the turbine blade structural capability while simultaneously reducing loads. To achieve this goal, the featherseal dampers were designed to seal the blade to blade platform gap and damp the dynamic motions. Sealing improves the steady stress margins by increasing turbine efficiency and improving turbine blade attachment thermal conditioning. Load reduction was achieved through damping. Thin Haynes 188 sheet metal was selected based on its material properties (hydrogen resistance, elongation, tensile strengths, etc.). The 36,000 rpm wheel speed of the rotor result in a normal load of 120#/blade. The featherseals then act as micro-slip dampers during actual SSME operation. After initial design and analysis (prior to full engine testing), the featherseal dampers were tested in P&W's spin rig facility in West Palm Beach, Florida. Both dynamic strain gages and turbine blade tip displacement measurements were utilized to quantify the featherseal damper effectiveness. Full speed (36,000 rpm), room temperature rig testing verified the elimination of fundamental mode (i.e, modes 1 & 2) resonant response. The reduction in turbine blade dynamic response is shown for a typical turbine blade. This paper discusses the design and verification of these dampers. The numerous benefits associated with this design concept warrants consideration in existing and future turbomachinery applications.

Montgomery, S. K.

1999-01-01

366

Turbine blade structural dynamic analysis. [for space shuttle main engine  

NASA Technical Reports Server (NTRS)

The paper presents structural dynamic analysis and test results for the Space Shuttle Main Engine turbine blades. Athough these blades are designed to avoid coincidence of natural frequencies with harmonic excitation forces, the complexity of the turbine hardware, its nonlinearities and lack of information regarding the forcing function have led to fatigue failures. A comparison of single-blade analysis and test modal frequencies, shapes, and stresses is given; analysis techniques to describe the forcing function, compute dynamic responses, and incorporate the nonlinearities of Coulomb-friction dampers are presented. Recommendations are made for new research to improve forcing function computations and structural damping estimates used in the analysis.

Dickerson, E. O.

1980-01-01

367

Wind Turbine Blade Design  

NSDL National Science Digital Library

Students go through the design process and the scientific method to test the effect of blade design on power output. There is an optional extension to use the data to create an optimal set of wind turbine blades.

Project, Kidwind

368

Wind turbine blade testing system using base excitation  

DOEpatents

An apparatus (500) for fatigue testing elongate test articles (404) including wind turbine blades through forced or resonant excitation of the base (406) of the test articles (404). The apparatus (500) includes a testing platform or foundation (402). A blade support (410) is provided for retaining or supporting a base (406) of an elongate test article (404), and the blade support (410) is pivotally mounted on the testing platform (402) with at least two degrees of freedom of motion relative to the testing platform (402). An excitation input assembly (540) is interconnected with the blade support (410) and includes first and second actuators (444, 446, 541) that act to concurrently apply forces or loads to the blade support (410). The actuator forces are cyclically applied in first and second transverse directions. The test article (404) responds to shaking of its base (406) by oscillating in two, transverse directions (505, 507).

Cotrell, Jason; Thresher, Robert; Lambert, Scott; Hughes, Scott; Johnson, Jay

2014-03-25

369

Investigation of Solder Fatigue Acceleration Factors  

Microsoft Academic Search

Solder fatigue was investigated experimentally for effects of the strain loading waveform in isothermal mechanical fatigue, and frequency and strain range in true thermal cycling. Rapid strain loading followed by a long hold period at constant strain was found to be very damaging compared to constant rate cycling at the same peak amplitude and period. Thermal cycle fatigue data showed

L. R. FOX; J. W. SOFIA; M. C. SHINE

1985-01-01

370

Vibration reliability analysis of turbine blade based on ANN and Monte Carlo simulation  

Microsoft Academic Search

Dynamic stress of turbine blade has great influence on its reliability and fatigue life. In order to decrease the magnitude of dynamic stress, frequency modulation method is often used to avoid resonance, which implies the frequency of active force must be kept away from the inherent vibration frequency of blade. At present, many models of calculating inherent vibration frequency of

Wei Duan; Zhangqi Wang

2010-01-01

371

Composite Fan Blade Design for Advanced Engine Concepts  

NASA Technical Reports Server (NTRS)

The aerodynamic and structural viability of composite fan blades of the revolutionary Exo-Skeletal engine are assessed for an advanced subsonic mission using the NASA EST/BEST computational simulation system. The Exo-Skeletal Engine (ESE) calls for the elimination of the shafts and disks completely from the engine center and the attachment of the rotor blades in spanwise compression to a rotating casing. The fan rotor overall adiabatic efficiency obtained from aerodynamic analysis is estimated at 91.6 percent. The flow is supersonic near the blade leading edge but quickly transitions into a subsonic flow without any turbulent boundary layer separation on the blade. The structural evaluation of the composite fan blade indicates that the blade would buckle at a rotor speed that is 3.5 times the design speed of 2000 rpm. The progressive damage analysis of the composite fan blade shows that ply damage is initiated at a speed of 4870 rpm while blade fracture takes place at 7640 rpm. This paper describes and discusses the results for the composite blade that are obtained from aerodynamic, displacement, stress, buckling, modal, and progressive damage analyses. It will be demonstrated that a computational simulation capability is readily available to evaluate new and revolutionary technology such as the ESE.

Abumeri, Galib H.; Kuguoglu, Latife H.; Chamis, Christos C.

2004-01-01

372

Hydrodynamic blade guide  

SciTech Connect

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, K.L.; Davis, P.J.; Landram, C.S.

2000-07-04

373

Turbine blade damping study  

NASA Technical Reports Server (NTRS)

Research results and progress on the performance of bladed systems is reported the different topics discussed include: the study of turbine blade damping; forced vibrations of friction damped beam moistures in two dimensions; and a users manual for a computer program for dynamic analysis of bladed systems.

Dominic, R. J.

1984-01-01

374

Multiscale/Multifunctional Probabilistic Composite Fatigue  

NASA Technical Reports Server (NTRS)

A multilevel (multiscale/multifunctional) evaluation is demonstrated by applying it to three different sample problems. These problems include the probabilistic evaluation of a space shuttle main engine blade, an engine rotor and an aircraft wing. The results demonstrate that the blade will fail at the highest probability path, the engine two-stage rotor will fail by fracture at the rim and the aircraft wing will fail at 109 fatigue cycles with a probability of 0.9967.

Chamis, Christos C.

2010-01-01

375

Development of heat-treatment process for a P\\/M superalloy for turbine blades  

Microsoft Academic Search

Powder metallurgy (P\\/M) superalloy turbine blades are increasingly being used in jet-aircraft engines. A notable advancement in the manufacture of P\\/M turbine blades is the development of a powder forge IN-792 nickel-based superalloy: APK-6. Although fatigue strength of the P\\/M material is 212 times superior as compared to cast blades, its creep strength is poor. The improvement in creep strength

Zainul Huda

2007-01-01

376

Experimental study on creep-fatigue loading history effect  

SciTech Connect

In order to extend the applicability of a creep-fatigue life prediction method based on the overstress to a loading history effect, a series of creep-fatigue tests has been conducted with 316FR stainless steel at 923K in a high vacuum environment. The creep-fatigue test program includes changes of strain wave form: changed from creep-fatigue type to fatigue type and that from fatigue type to creep-fatigue type. Additional tests have been conducted to simulate an effect of a safe shutdown earthquake (SSE) on a creep-fatigue. A fatigue type strain cycling with a large strain range from 50 to 120 cycles is introduced into the creep-fatigue cycling. It was experimentally investigated how the fatigue loading with a larger strain range affects the total creep-fatigue life. In these tests the conventional linear cumulative damage rule is used in evaluating the creep-fatigue life under the complex loading history.

Nakai, Tatsuro; Ishikawa, Akiyoshi; Asada, Yasuhide [Univ. of Tokyo (Japan). Dept. of Mechanical Engineering

1995-12-31

377

Structural qualification testing and operational loading on a fiberglass rotor blade for the Mod-OA wind turbine  

NASA Technical Reports Server (NTRS)

Fatigue tests were performed on full- and half-scale root end sections, first to qualify the root retention design, and second to induce failure. Test methodology and results are presented. Two operational blades were proof tested to design limit load to ascertain buckling resistance. Measurements of natural frequency, damping ratio, and deflection under load made on the operational blades are documented. The tests showed that all structural design requirements were met or exceeded. Blade loads measured during 3000 hr of field operation were close to those expected. The measured loads validated the loads used in the fatigue tests and gave high confidence in the ability of the blades to achieve design life.

Sullivan, T. L.

1983-01-01

378

Blades and Towers Modal Analysis Code (BModes): Verification of Blade Modal Analysis Capability  

SciTech Connect

BModes is a finite-element code we developed to provide coupled modes for flexible blades, rotating or non-rotating, and for towers, onshore or offshore (supported either on floating platforms or on monopile foundations). Both the blade and the tower allow a tip attachment, which is modeled as a rigid body with mass, six moments of inertia, and a mass centroid that may be offset from the blade or tower axis. Examples of tip attachments are aerodynamic brakes for blades and nacelle-rotor subassemblies for towers. Allowable supports for the tower include tension wires, floating platforms, and shallow-water monopiles with elastic foundation. Coupled modes (implying coupling of flap, lag, axial, and torsion motions) have several applications. Examples are: modeling of major flexible components for modal-based aeroelastic codes such as FAST, validation of turbine models using experimental data, modal-based fatigue analysis, and understanding of aeroelastic-stability behavior of turbines. This paper presents verification of the blade modal analysis capability of BModes. Verification begins with simple uniform beams, rotating and non-rotating, and progresses to realistic blades. BModes-computed modes for all models are compared with analytical modes, if possible to obtain, and with modes generated by RCAS. All results, presented in terms of frequencies and mode shapes, show excellent agreement.

Bir, G.

2009-01-01

379

Aspects of high-cycle fatigue performance in a Ti-6Al-4V alloy  

SciTech Connect

Determination of critical levels of microstructural damage that can lead to fatigue crack propagation under high-cycle fatigue loading conditions is a major concern for the aircraft industry regarding structural integrity of turbine engine components. The cyclic frequencies characteristic of service loading spectra are extremely high and appear to require a damage-tolerant design approach. One idea for such an approach is to attempt to define a practical, appropriate crack-propagation threshold, {Delta}K{sub TH}. The present study identifies a practical lower-bound large-crack threshold under high-cycle fatigue conditions in a Ti-6 Al-4V blade alloy (with {approximately}60% primary {alpha} in a matrix of lamellar {alpha}+{beta}). The authors suggest that lower-bound thresholds can be determined by modifying standard large-crack propagation tests to simulate small-crack behavior. Modification techniques include high load-ratio testing under both constant-R and constant-K{sub max} conditions, performed at cyclic loading frequencies up to 1 kHz and R ratios up to 0.95. The results of these tests are compared to the near-threshold behavior of naturally-initiated small cracks, and to the crack initiation and early growth behavior of small cracks emanating from sites of simulated foreign object damage.

Boyce, B.L.; Campbell, J.P.; Roder, O.; Thompson, A.W.; Ritchie, R.O.

1999-07-01

380

Nitinol Fatigue Life for Variable Strain Amplitude Fatigue  

NASA Astrophysics Data System (ADS)

Nitinol fatigue testing results are presented for variable strain amplitude cycling. The results indicate that cycles smaller than the constant amplitude fatigue limit may contribute to significant fatigue damage when they occur in a repeating sequence of large and small amplitude cycles. The testing utilized two specimen types: stent-like diamond specimens and Z-shaped wire specimens. The diamond specimens were made from nitinol tubing with stent-like manufacturing processes and the Z-shaped wire specimens were made from heat set nitinol wire. The study explored the hypothesis that duty cycling can have an effect on nitinol fatigue life. Stent-like structures were subjected to different in vivo loadings in order to create more complex strain amplitudes. The main focus in this study was to determine whether a combination of small and large amplitudes causes additional damage that alters the fatigue life of a component.

Lin, Z.; Pike, K.; Schlun, M.; Zipse, A.; Draper, J.

2012-12-01

381

Reliability assessments of vibration-induced tube fatigue failure  

Microsoft Academic Search

This paper devotes to the fatigue damage analysis of a solenoid tube under vibration-induced fatigue stresses and is concerned with the estimation of tube reliability from variable amplitude stress histories in the time domain. The complete procedure of reliability assessments for the tube fatigue failure has been presented in this paper. The fatigue strength of the tube material was represented

Jianxiong Chen; Wenzhen Yan

2008-01-01

382

Wireless Inductive Power Device Suppresses Blade Vibrations  

NASA Technical Reports Server (NTRS)

Vibration in turbomachinery can cause blade failures and leads to the use of heavier, thicker blades that result in lower aerodynamic efficiency and increased noise. Metal and/or composite fatigue in the blades of jet engines has resulted in blade destruction and loss of lives. Techniques for suppressing low-frequency blade vibration, such as gtuned circuit resistive dissipation of vibratory energy, h or simply "passive damping," can require electronics incorporating coils of unwieldy dimensions and adding unwanted weight to the rotor. Other approaches, using vibration-dampening devices or damping material, could add undesirable weight to the blades or hub, making them less efficient. A wireless inductive power device (WIPD) was designed, fabricated, and developed for use in the NASA Glenn's "Dynamic Spin Rig" (DSR) facility. The DSR is used to simulate the functionality of turbomachinery. The relatively small and lightweight device [10 lb (approx.=4.5 kg)] replaces the existing venerable and bulky slip-ring. The goal is the eventual integration of this technology into actual turbomachinery such as jet engines or electric power generators, wherein the device will facilitate the suppression of potentially destructive vibrations in fan blades. This technology obviates slip rings, which require cooling and can prove unreliable or be problematic over time. The WIPD consists of two parts: a remote element, which is positioned on the rotor and provides up to 100 W of electrical power to thin, lightweight piezoelectric patches strategically placed on/in fan blades; and a stationary base unit that wirelessly communicates with the remote unit. The base unit supplies inductive power, and also acts as an input and output corridor for wireless measurement, and active control command to the remote unit. Efficient engine operation necessitates minimal disturbance to the gas flow across the turbine blades in any effort to moderate blade vibration. This innovation makes it possible to moderate vibration on or in turbomachinery blades by providing 100 W of wireless electrical power and actuation control to thin, lightweight vibration-suppressing piezoelectric patches (eight actuation and eight sensor patches in this prototype, for a total of 16 channels) positioned strategically on the surface of, or within, titanium fan blades, or embedded in composite fan blades. This approach moves significantly closer to the ultimate integration of "active" vibration suppression technology into jet engines and other turbomachinery devices such as turbine electrical generators used in the power industry. The novel feature of this device is in its utilization of wireless technology to simultaneously sense and actively control vibration in rotating or stationary turbomachinery blades using piezoelectric patches. In the past, wireless technology was used solely for sensing and diagnostics. This technology, however, will accomplish much more, in terms of simultaneously sensing, suppressing blade vibration, and making it possible for detailed study of vibration impact in turbomachinery blades.

Morrison, Carlos R.; Provenza, Andrew J.; Choi, Benjamin B.; Bakhle, Milind A.; Min, James B.; Stefko, George L.; Duffy, Kirsten P.; Fougers, Alan J.

2011-01-01

383

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

384

Dynamic alongwind fatigue of slender vertical structures  

Microsoft Academic Search

The wind-excited vibrations of structures induce fluctuating stresses around mean deformation states that lead to fatigue damage accumulation and can determine structural failure without exceeding design wind actions. This paper proposes a mathematical model aimed at deriving a histogram of the stress cycles, the accumulated damage and the fatigue life of slender vertical structures (e.g. towers, chimneys, poles and masts)

Maria Pia Repetto; Giovanni Solari

2001-01-01

385

Mechanics of fretting fatigue crack formation  

Microsoft Academic Search

Fretting is a contact damage process arising from surface microslip associated with small-scale oscillatory motion of clamped structural members. The fretting damage process is a synergistic competition among wear, corrosive and fatigue phenomena driven by both the microslip at the contact surface and cyclic fretting contact stresses. Fretting fatigue is one mechanism of the formation of cracks in many common

Matthew P. Szolwinski; Thomas N. Farris

1996-01-01

386

Environmental Cracking— Corrosion Fatigue  

Microsoft Academic Search

1 CORROSION FATIGUE (CF) is an important but complex mode of failure for high-performance structural metals operating in deleterious environments. This view is based on the like- lihood of cyclically varying loads and chemical environ- ments in service, the need for predictable long-life component performance and life extension, the universal susceptibility of pure metals and alloys to CF damage, and

Richard P. Gangloff

387

Cyclic mechanical property degradation during fatigue loading of cortical bone  

Microsoft Academic Search

Fatigue damage accumulation has been demonstrated in living bone and postulated as a stimulus to the bone modeling and remodeling response. Mechanical property degradation is one manifestation of fatigue damage accumulation. This study examines changes in secant modulus and cyclic energy dissipation behavior during axial load-controlled fatigue loading of cortical bone specimens. The findings suggest that secant modulus degradation and

C. A. Pattin; W. E. Caler; D. R. Carter

1996-01-01

388

Dual-axis resonance testing of wind turbine blades  

DOEpatents

An apparatus (100) for fatigue testing test articles (104) including wind turbine blades. The apparatus (100) includes a test stand (110) that rigidly supports an end (106) of the test article (104). An actuator assembly (120) is attached to the test article (104) and is adapted for substantially concurrently imparting first and second forcing functions in first and second directions on the test article (104), with the first and second directions being perpendicular to a longitudinal axis. A controller (130) transmits first and second sets of displacement signals (160, 164) to the actuator assembly (120) at two resonant frequencies of the test system (104). The displacement signals (160, 164) initiate the actuator assembly (120) to impart the forcing loads to concurrently oscillate the test article (104) in the first and second directions. With turbine blades, the blades (104) are resonant tested concurrently for fatigue in the flapwise and edgewise directions.

Hughes, Scott; Musial, Walter; White, Darris

2014-01-07

389

Impact behavior of filament wound graphite/epoxy fan blades  

NASA Technical Reports Server (NTRS)

The fabrication and impact tests of graphite/epoxy filament wound fan blades are discussed. Blades which were spin tested at tip speeds up to 305 meters per second retained their structural integrity. Two blades were each impacted with a 454 gram slice of a 908 gram simulated bird at a tip speed of 263 meters per second and impact angles of 22 and 32 deg. The impact tests were recorded with high-speed movie film. The blade which was impacted at 22 deg sustained some root delamination but remained intact. The 32 deg impact separated the blade from the root. No local damage other than leading edge debonding was observed for either blade. Results of a failure mode analysis are also discussed.

Bowles, K. J.

1978-01-01

390

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

391

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

392

Impact resistance of composite fan blades. [fiber reinforced graphite and boron epoxy blades for STOL operating conditions  

NASA Technical Reports Server (NTRS)

The resistance of current-design Pratt and Whitney Aircraft low aspect ratio advanced fiber reinforced epoxy matrix composite fan blades to foreign object damage (FOD) at STOL operating conditions was investigated. Five graphite/epoxy and five boron/epoxy wide chord fan blades with nickel plated stainless steel leading edge sheath protection were fabricated and impact tested. The fan blades were individually tested in a vacuum whirlpit under FOD environments. The FOD environments were typical of those encountered in service operations. The impact objects were ice balls, gravel, stralings and gelatin simulated birds. Results of the damage sustained from each FOD impact are presented for both the graphite boron reinforced blades. Tests showed that the present design composite fan blades, with wrap around leading edge protection have inadequate FOD impact resistance at 244 m/sec (800 ft/sec) tip speed, a possible STOL operating condition.

Premont, E. J.; Stubenrauch, K. R.

1973-01-01

393

Fatigue analyses of the prototype Francis runners based on site measurements and simulations  

NASA Astrophysics Data System (ADS)

With the increasing development of solar power and wind power which give an unstable output to the electrical grid, hydropower is required to give a rapid and flexible compensation, and the hydraulic turbines have to operate at off-design conditions frequently. Prototype Francis runners suffer from strong vibrations induced by high pressure pulsations at part load, low part load, speed-no-load and during start-stops and load rejections. Fatigue and damage may be caused by the alternating stress on the runner blades. Therefore, it becomes increasingly important to carry out fatigue analysis and life time assessment of the prototype Francis runners, especially at off-design conditions. This paper presents the fatigue analyses of the prototype Francis runners based on the strain gauge site measurements and numerical simulations. In the case of low part load, speed-no-load and transient events, since the Francis runners are subjected to complex hydraulic loading, which shows a stochastic characteristic, the rainflow counting method is used to obtain the number of cycles for various dynamic amplitude ranges. From middle load to full load, pressure pulsations caused by Rotor-stator- Interaction become the dominant hydraulic excitation of the runners. Forced response analysis is performed to calculate the maximum dynamic stress. The agreement between numerical and experimental stresses is evaluated using linear regression method. Taking into account the effect of the static stress on the S-N curve, the Miner's rule, a linear cumulative fatigue damage theory, is employed to calculate the damage factors of the prototype Francis runners at various operating conditions. The relative damage factors of the runners at different operating points are compared and discussed in detail.

Huang, X.; Chamberland-Lauzon, J.; Oram, C.; Klopfer, A.; Ruchonnet, N.

2014-12-01

394

Propeller blade retention system  

NASA Technical Reports Server (NTRS)

The invention concerns the mounting of propeller blades to a ring-shaped rotor. The blades are of the variable pitch type, and the shank of each blade extends through a respective hole in the rotor. Each hole contains an annular shelf which is fastened to the wall of the hole and surrounds each shank. Each shank bears a pair of bearing races which sandwich the annular shelf in order to connect the blade to the rotor. Bearing rollers are positioned between the annular shelf and the bearing races.

Elston, III, Sidney B. (Inventor); Simon, III, Victor H. (Inventor); Tseng, Wu-Yang (Inventor); Butler, Lawrence (Inventor)

1993-01-01

395

Compassion Fatigue  

Microsoft Academic Search

Compassion fatigue is characterized by physical and psychological exhaustion resulting from excessive professional demands that drain available personal resources. While all helping professionals are vulnerable to compassion fatigue, the authors believe that social workers working with the elderly have unique stresses that make them a high-risk group for compassion fatigue. Increased frustration over limited financial, social and medical services for

Ana M. Leon; Judith A. S. Altholz; Sophia F. Dziegielewski

1999-01-01

396

The SNL100-03 Blade: Design Studies with Flatback Airfoils for the Sandia 100-meter Blade.  

SciTech Connect

A series of design studies were performed to inv estigate the effects of flatback airfoils on blade performance and weight for large blades using the Sandi a 100-meter blade designs as a starting point. As part of the study, the effects of varying the blade slenderness on blade structural performance was investigated. The advantages and disadvantages of blad e slenderness with respect to tip deflection, flap- wise & edge-wise fatigue resistance, panel buckling capacity, flutter speed, manufacturing labor content, blade total weight, and aerodynamic design load magn itude are quantified. Following these design studies, a final blade design (SNL100-03) was prod uced, which was based on a highly slender design using flatback airfoils. The SNL100-03 design with flatback airfoils has weight of 49 tons, which is about 16% decrease from its SNL100-02 predecessor that used conventional sharp trailing edge airfoils. Although not systematically optimized, the SNL100 -03 design study provides an assessment of and insight into the benefits of flatback airfoils for la rge blades as well as insights into the limits or negative consequences of high blade slenderness resulting from a highly slender SNL100-03 planform as was chosen in the final design definition. This docum ent also provides a description of the final SNL100-03 design definition and is intended to be a companion document to the distribution of the NuMAD blade model files for SNL100-03, which are made publicly available. A summary of the major findings of the Sandia 100-meter blade development program, from the initial SNL100-00 baseline blade through the fourth SNL100-03 blade study, is provided. This summary includes the major findings and outcomes of blade d esign studies, pathways to mitigate the identified large blade design drivers, and tool development that were produced over the course of this five-year research program. A summary of large blade tec hnology needs and research opportunities is also presented.

Griffith, Daniel; Richards, Phillip William

2014-09-01

397

Fatigue reliability of wind turbine components  

NASA Astrophysics Data System (ADS)

Fatigue life estimates for wind turbine components can be extremely variable due to both inherently random and uncertain parameters. A structural reliability analysis is used to qualify the probability that the fatigue life will fall short of a selected target. Reliability analysis also produces measures of the relative importance of the various sources of uncertainty and the sensitivity of the reliability to each input parameter. The process of obtaining reliability estimates is briefly outlined. An example fatigue reliability calculation for a blade joint is formulated; reliability estimates, importance factors, and sensitivities are produced. Guidance in selecting distribution functions for the random variables used to model the random and uncertain parameters is also provided.

Veers, P. S.

398

Characterization of Fatigue Cracking and Healing of Asphalt Mixtures  

E-print Network

Fatigue cracking is one of the most common distresses of asphalt pavements, whereas healing is a counter process to cracking which alleviates cracking damage and extends fatigue life of asphalt pavements. Most of existing methods to characterize...

Luo, Xue

2012-07-16

399

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.

2012-04-01

400

Thermo-acoustic fatigue characterization.  

PubMed

The nondestructive detection of early fatigue damage states is of high importance for safety in aircraft, automobiles, railways, nuclear energy industries and chemical industries. Titanium alloys commonly used in aerospace for structures and engine components are subject to fatigue damage during service. In the current study fatigue damage progression in a titanium alloy (Ti-6Al-4V) was investigated using thermographic detection of the heat dissipated during short-term mechanical loading. The initial rate of temperature increase induced by the short-term mechanical loading was used to indicate the current microstructural state and presence of prior fatigue damage. Two methods for thermal excitation were investigated (a) high amplitude mechanical loading and (b) small amplitude ultrasonic loading. A formula that describes the temperature enhancement due to heat generation during one loading cycle is derived from high amplitude loading data. A correlation between the temperature increase during short-term ultrasonic loading and accumulated fatigue cycles is used to suggest a methodology for in-field assessment of fatigue condition. PMID:12159978

Meyendorf, Norbert G H; Rösner, Henrik; Kramb, Victoria; Sathish, Shamachary

2002-05-01

401

Composite fan blade  

Microsoft Academic Search

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

Farr

1993-01-01

402

Titanium steam turbine blading  

SciTech Connect

After a long research and development period, beginning with the commercial availability of titanium in early 1950's, the steam turbine manufacturers and users have been developing titanium alloy blading for the long last row and steam transition row applications. Commercial introduction of titanium blading into low pressure steam turbines is just beginning in many countries over the world. A workshop was organized by the Electric Power Research institute and held in Palo Alto, California on November 9 and 10, 1988, to provide a record of the status of the development and to facilitate and accelerate the introduction of the titanium blading into commercial use. After an introductory paper that provided a historical background on the titanium blade application in low pressure steam turbine, the workshop was organized into the following sessions: A, Design and Application of Titanium Blades; B. Manufacture of Titanium Blades; C. Properties and Characteristics of Titanium Blades; D. Discussion of Workshop Issues and Conclusions. In total, there were 23 papers presented, including the final discussion. These are presented, with records of discussions after each paper, in the present volume. Attendance at the workshop was limited to 40 participants, session chairmen, and utility users. The attendance included representatives from eastern and western Europe, Japan, and the United States. As such, it is a complete statement of the science, technology, and application of titanium steam turbine blading worldwide.

Jaffee, R.I. (Electric Power Research Inst. (US))

1990-01-01

403

Fluid blade disablement tool  

Microsoft Academic Search

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,

Juan-Carlos Jakaboski; Chance G. Hughs; Steven N. Todd

2012-01-01

404

Turbine blade platform seal  

DOEpatents

A rotating blade group 90 for a turbo-machine having an improved device for sealing the gap 110 between the edges 112,114 of adjacent blade platforms 96,104. The gap 110 between adjacent blades 92,100 is sealed by a seal pin 20 its central portion 110 and by a seal plate 58,60 at each of the front 54 and rear 56 portions. The seal plates 58,60 are inserted into corresponding grooves 62,64 formed in the adjacent edges 112,114 of adjoining blades 92,100 and held in place by end plates 40,42. The end of the seal plates 58,60 may be chamfered 78,80 to improve the seal against the end plate 40,42. The seal pin 20 provides the required damping between the blades 92,100 and the seal plates 58,60 provide improved sealing effectiveness.

Zagar, Thomas W. (Winter Springs, FL); Schiavo, Anthony L. (Oviedo, FL)

2001-01-01

405

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

406

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

407

Simulated Bladed MMC Disk LCF Validation  

NASA Technical Reports Server (NTRS)

The goal of this program was to evaluate the low cycle fatigue behavior of an SCS-6/Ti-6Al-4V sub-component under bi-axial loading conditions at 316 C(600 F). A simulated bladed TMC disk was designed having thirty four blades representing the number that would be used in Allied Signal's JTAGG II impeller. The outer diameter of the bladed ring was 254 mm (10.0 inch) and the inner diameter 114.3 mm (4.50 inch). The outer and inner diameter of the composite zone was 177.8 mm (7.00 inch) and 127.O mm(5.00 inch) respectively. Stress analysis showed that the fatigue life of the bladed composite ring would be about 12000 cycles for the test conditions applied. A modal analysis was conducted which showed that the blades would have sufficient life margin from dynamic excitation. The arbor design was the same as that employed in the spin-to burst test of NAS3-27027. A systematic stress analysis of each part making up the arbor was undertaken to assure the design would meet the low cycle fatigue requirements of the program. The Textron Systems grooved foil-fiber process was chosen to make the SCS-6/Ti-6Al-4V core ring based on the success they had in contract NAS3-27027. Fiber buckling, however, was observed at several locations in the first ring made which rendered it unsuitable for spin testing. The fiber buckling was attributed to cracking of the graphite tooling during the consolidation process. On this basis a second ring was made but it too contained fiber buckling defects. Analysis by Textron indicated that the fiber buckling was most likely due to poor placement of the SCS-6 fiber in the etched grooves of the Ti-6Al-4V foil. This was also a contributor to the defects in the first ring. Since there was little indication of control in the process to manufacture a quality ring a third attempt at making a ring was not undertaken.

Merrick, H. F.; Costen, M.

1998-01-01

408

Fatigue life prediction for wind turbines: A case study on loading spectra and parameter sensitivity  

NASA Astrophysics Data System (ADS)

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.

409

Relevance of aerodynamic modelling for load reduction control strategies of two-bladed wind turbines  

NASA Astrophysics Data System (ADS)

A new load reduction concept is being developed for the two-bladed prototype of the Skywind 3.5MW wind turbine. Due to transport and installation advantages both offshore and in complex terrain two-bladed turbine designs are potentially more cost-effective than comparable three-bladed configurations. A disadvantage of two-bladed wind turbines is the increased fatigue loading, which is a result of asymmetrically distributed rotor forces. The innovative load reduction concept of the Skywind prototype consists of a combination of cyclic pitch control and tumbling rotor kinematics to mitigate periodic structural loading. Aerodynamic design tools must be able to model correctly the advanced dynamics of the rotor. In this paper the impact of the aerodynamic modelling approach is investigated for critical operational modes of a two-bladed wind turbine. Using a lifting line free wake vortex code (FVM) the physical limitations of the classical blade element momentum theory (BEM) can be evaluated. During regular operation vertical shear and yawed inflow are the main contributors to periodic blade load asymmetry. It is shown that the near wake interaction of the blades under such conditions is not fully captured by the correction models of BEM approach. The differing prediction of local induction causes a high fatigue load uncertainty especially for two-bladed turbines. The implementation of both cyclic pitch control and a tumbling rotor can mitigate the fatigue loading by increasing the aerodynamic and structural damping. The influence of the time and space variant vorticity distribution in the near wake is evaluated in detail for different cyclic pitch control functions and tumble dynamics respectively. It is demonstrated that dynamic inflow as well as wake blade interaction have a significant impact on the calculated blade forces and need to be accounted for by the aerodynamic modelling approach. Aeroelastic simulations are carried out using the high fidelity multi body simulation software SIMPACK. The aerodynamic loads are calculated using ECN's AeroModule and NREL's BEM code Aerodynl3.

Luhmann, B.; Cheng, P. W.

2014-06-01

410

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)] [National Renewable Energy Lab., Golden, CO (United States); Hansen, A.C. [Utah Univ., Salt Lake City, UT (United States)] [Utah Univ., Salt Lake City, UT (United States)

1991-12-01

411

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...

412

Fatigue and fracture overview  

NASA Technical Reports Server (NTRS)

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

Halford, Gary R.

1986-01-01

413

fatigue analysis under variable amplitude loading using an energy parameter  

Microsoft Academic Search

An energy parameter accounting for normal and shear deformation is used to predict fatigue lives under variable amplitude multiaxial loading. Fatigue damage is computed as a function of orientation of the plane, and the maximum damage plane is considered as the critical plane. The linear damage rule is employed with rainflow cycle counting either on the shear or on the

B. L Lee; K. S Kim; K. M Nam

2003-01-01

414

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

415

Sparkr Blade Test Centre Static tests of wind turbine blades  

E-print Network

gauges in a number up to 160 are applied to the blade skin and internal blade structure the test are the strain values measured on the blade surface. Non-linearity of the graphs often indicates that structural buckling in the blade skin is building up, although difficult to spot at an early stage. The slope

416

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

417

Self-Tuning Impact Dampers Designed for Turbomachinery Blade Vibration Suppression  

NASA Technical Reports Server (NTRS)

Turbomachinery blades are subject to aerodynamic forces that can lead to high-cycle-fatigue (HCF) failures. These failures will only increase as engineers begin to design blades without shrouds or as integrally bladed disks (blisks). These new designs will decrease blade damping significantly because the mechanical damping from shroud and blade joints will be eliminated. Also, it is difficult to design dampers for the engine environment with its extremely high centrifugal loads and high temperatures. The self-tuning impact damper has been designed to provide the additional damping required to avoid HCF while withstanding the harsh engine environment. In addition, the damper is placed within the engine blade itself rather than external to it.

Duffy, Kirsten P.; Mehmed, Oral

2002-01-01

418

Probabilistic Fatigue: Computational Simulation  

NASA Technical Reports Server (NTRS)

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

Chamis, Christos C.

2002-01-01

419

Integrated actuation system for individual control of helicopter rotor blades  

NASA Astrophysics Data System (ADS)

The unique configuration of the rotorcraft generates problems unknown to fixed wing aircraft. These problems include high vibration and noise levels. This paper presents the development and test results of a Terfenol-D based actuator designed to operate in an individual blade control system in order to reduce vibration and noise and increase performance on Army UH- 60A helicopter. The full-scale, magnetostrictive, Terfenol-D based actuator was tested on a specially designed testbed that simulated operational conditions of a helicopter blade in the laboratory. Tests of actuator performance (strike, force moment, bandwidth, fatigue life under operational loading) were performed.

Bushko, Dariusz A.; Fenn, Ralph C.; Gerver, Michael J.; Berry, John R.; Phillips, Frank; Merkley, Donald J.

1996-05-01

420

Shielding turbine blades from cvitation: Experiments with polymer overlays  

Microsoft Academic Search

Cavitation damage to hydroelectric machinery produces one of the most prevalent maintenance problems at any hydro plant. Damage to the turbine runner blades, draft tube liner and discharge ring, and sometimes even the runner hub can require extensive welding repair. Typically, each unit develops its own cavitation characteristics that continue throughout the life of the machine. The traditional cavitation repair

Armentrout

1993-01-01

421

Resistance of Titanium Aluminide to Domestic Object Damage Assessed  

NASA Technical Reports Server (NTRS)

A team consisting of GE Aircraft Engines, Precision Cast Parts, Oremet, and Chromalloy were awarded a NASA-sponsored Aerospace Industry Technology Program (AITP) to develop a design and manufacturing capability that will lead to the engine test demonstration and eventual implementation of a ?-Ti-47Al-2Nb-2Cr (at. %) titanium aluminide (TiAl) low-pressure turbine blade into commercial service. One of the main technical risks of implementing TiAl low-pressure turbine blades is the poor impact resistance of TiAl in comparison to the currently used nickel-based superalloy. The impact resistance of TiAl is being investigated at the NASA Lewis Research Center as part of the Aerospace Industry Technology Program and the Advanced High Temperature Engine Materials Program (HITEMP). The overall objective of this work is to determine the influence of impact damage on the high cycle fatigue life of TiAl-simulated low-pressure turbine blades. To this end, impact specimens were cast to size in a dog-bone configuration and given a typical processing sequence followed by an exposure to 650 degrees Celsius for 20 hours to simulate embrittlement at service conditions. Then, the specimens were impacted at 260 degrees Celsius under a 69-MPa load. Steel projectiles with diameters 1.6 and 3.2 mm were used to impact the specimens at 90 degrees Celsius to the leading edge. Two different impact energies (0.74 and 1.5 joules) were used to simulate fairly severe domestic object damage on a low-pressure turbine blade.

Lerch, Bradley A.; Draper, Susan L.; Pereira, J. Michael; Nathal, Michael V.; Austin, Curt

1999-01-01

422

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

423

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

424

Fatigue life estimation under complex loading  

NASA Astrophysics Data System (ADS)

The cyclic property of aluminum alloy sheet LY12-CZ is quantitatively reported using accumulated plastic hysteresis energy under cyclic loading as the damage criterion. Nonlinearity of damage accumulation with cycle number under cyclic loading is demonstrated. The formula used to calculate instantaneous plastic strain energy is derived. The total dissipated plastic strain energy for the whole life period is calculated and its variation with stress range is shown. Fatigue damage is separated into static tension damage and cyclic damage. The above analysis is used to develop a fatigue life estimation model. Comparisons of the model predictions and corresponding experimental data show satisfactory agreement.

Tian, Dingshuan; Wu, Fumin

1991-02-01

425

Fatigue of Small-Scale Metal Materials: From Micro to Nano-Scale  

Microsoft Academic Search

This work considers currently-developed fatigue testing techniques and evaluation methods for the small-scale metal materials.\\u000a Then, a number of studies on fatigue damage behavior and fatigue properties are presented and highlighted as a function of\\u000a the length scales. The relationship between length-scale-dependent microstructure evolution and fatigue behavior is addressed\\u000a to understand fatigue damage mechanisms at small scales. Finally, the perspectives

G. P. Zhang; Z. G. Wang

426

Blade Testing Trends (Presentation)  

SciTech Connect

As an invited guest speaker, Michael Desmond presented on NREL's NWTC structural testing methods and capabilities at the 2014 Sandia Blade Workshop held on August 26-28, 2014 in Albuquerque, NM. Although dynamometer and field testing capabilities were mentioned, the presentation focused primarily on wind turbine blade testing, including descriptions and capabilities for accredited certification testing, historical methodology and technology deployment, and current research and development activities.

Desmond, M.

2014-08-01

427

Wind Turbine Blade Design  

NSDL National Science Digital Library

In this activity, learners design, build and test wind turbines. Learners go through the design process and use the scientific method to test important blade variables. Learners then use this data to create an optimal set of wind turbine blades. Educators can do the basic lesson in 3-4 class periods (about 3-4 hours) or extend the activity with a larger challenge that takes 5-7 class periods in total (about 5-7 hours).

Project, Kidwind

2006-01-01

428

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

NASA Astrophysics Data System (ADS)

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

Ranjan, Srikant

2005-11-01

429

Impact resistance of hybrid composite fan blade materials  

NASA Technical Reports Server (NTRS)

Improved resistance to foreign object damage was demonstrated for hybrid composite simulated blade specimens. Transply metallic reinforcement offered additional improvement in resistance to gelatin projectile impacts. Metallic leading edge protection permitted equivalent-to-titanium performance of the hybrid composite simulated blade specimen for impacts with 1.27 cm and 2.54 cm (0.50 and 1.00 inch) diameter gelatin spheres.

Friedrich, L. A.

1974-01-01

430

Low-cost directionally-solidified turbine blades, volume 2. [TFE731-3 turbofan engine  

NASA Technical Reports Server (NTRS)

An endothermically heated technology was used to manufacture low cost, directionally solidified, uncooled nickel-alloy blades for the TFE731-3 turbofan engine. The MAR-M 247 and MER-M 100+Hf blades were finish processed through heat treatment, machining, and coating operations prior to 150 hour engine tests consisting of the following sequences: (1) 50 hours of simulated cruise cycling (high fatigue evaluation); (2) 50 hours at the maximum continuous power rating (stress rupture endurance (low cycle fatigue). None of the blades visually showed any detrimental effects from the test. This was verified by post test metallurgical evaluation. The specific fuel consumption was reduced by 2.4% with the uncooled blades.

Dennis, R. E.; Hoppin, G. S., III; Hurst, L. G.

1979-01-01

431

A model to study the reduction of turbine blade vibration using the snubbing mechanism  

NASA Astrophysics Data System (ADS)

Blade vibration reduction is an important task in high performance turbo machinery for power generation, in order to avoid the risk of blade failure due to the overcoming of fatigue limit. A possible way to obtain this result is a contact related phenomenon, i.e. by physically limiting the vibration amplitude on the blade tip leaving a small gap between the shrouds of adjacent blades. When the relative displacement between adjacent blades exceeds the gap, in a certain vibration mode of the blade row, a contact occurs between the shrouds, the relative motion is restricted and energy is dissipated by friction and impact during the contact. This is called the snubbing mechanism. In this paper, an original simplified model of bladed disks, in which the snubbing mechanism can occur, is presented and numerical integration in time domain furnishes the time histories of the vibrations of the blades. The level of vibration reduction is then evaluated in some different modes that could be excited for instance by the fluid flow. It is also shown that unlucky combinations of system and excitation parameters can effect also a certain magnification instead of a reduction of the vibration amplitudes. Experimental results on single blade and blade groups of a steam turbine are used to tune the parameters of the system.

Pennacchi, Paolo; Chatterton, Steven; Bachschmid, Nicolò; Pesatori, Emanuel; Turozzi, Giorgio

2011-05-01

432

Dynamic response characteristics of dual flow-path integrally bladed rotors  

NASA Astrophysics Data System (ADS)

New turbine engine designs requiring secondary flow compression often look to dual flow-path integrally bladed rotors (DFIBRs) since these stages have the ability to perform work on the secondary, or bypassed, flow-field. While analogous to traditional integrally bladed rotor stages, DFIBR designs have many differences that result in unique dynamic response characteristics that must be understood to avoid fatigue. This work investigates these characteristics using reduced-order models (ROMs) that incorporate mistuning through perturbations to blade frequencies. This work provides an alternative to computationally intensive geometric-mistuning approaches for DFIBRs by utilizing tuned blade mode reductions and substructure coupling in cyclic coordinates. Free and forced response results are compared to full finite element model (FEM) solutions to determine if any errors are related to the reduced-order model formulation reduction methods. It is shown that DFIBRs have many more frequency veering regions than their single flow-path integrally blade rotor (IBR) counterparts. Modal families are shown to transition between system, inner-blade, and outer-blade motion. Furthermore, findings illustrate that while mode localization of traditional IBRs is limited to a single or small subset of blades, DFIBRs can have modal energy localized to either an inner- or outer-blade set resulting in many blades responding above tuned levels. Lastly, ROM forced response predictions compare well to full FEM predictions for the two test cases shown.

Beck, Joseph A.; Brown, Jeffrey M.; Scott-Emuakpor, Onome E.; Cross, Charles J.; Slater, Joseph C.

2015-02-01

433

Probabilistic fatigue methodology for six nines reliability  

NASA Technical Reports Server (NTRS)

Fleet readiness and flight safety strongly depend on the degree of reliability that can be designed into rotorcraft flight critical components. The current U.S. Army fatigue life specification for new rotorcraft is the so-called six nines reliability, or a probability of failure of one in a million. The progress of a round robin which was established by the American Helicopter Society (AHS) Subcommittee for Fatigue and Damage Tolerance is reviewed to investigate reliability-based fatigue methodology. The participants in this cooperative effort are in the U.S. Army Aviation Systems Command (AVSCOM) and the rotorcraft industry. One phase of the joint activity examined fatigue reliability under uniquely defined conditions for which only one answer was correct. The other phases were set up to learn how the different industry methods in defining fatigue strength affected the mean fatigue life and reliability calculations. Hence, constant amplitude and spectrum fatigue test data were provided so that each participant could perform their standard fatigue life analysis. As a result of this round robin, the probabilistic logic which includes both fatigue strength and spectrum loading variability in developing a consistant reliability analysis was established. In this first study, the reliability analysis was limited to the linear cumulative damage approach. However, it is expected that superior fatigue life prediction methods will ultimately be developed through this open AHS forum. To that end, these preliminary results were useful in identifying some topics for additional study.

Everett, R. A., Jr.; Bartlett, F. D., Jr.; Elber, Wolf

1990-01-01

434