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1

Study of fatigue damage in wind turbine blades  

Microsoft Academic Search

The inspection of damages detected in some blades of 300kW wind turbines revealed that the nature of these damages was probably due to a fatigue mechanism. The causes that had originated the failure (superficial cracks, geometric concentrator, abrupt change of thickness) have been studied, verifying, by means of the simplified evaluation procedure of fatigue life of the “Germanischer Lloyd” (GL)

J. C. Marín; A. Barroso; F. París; J. Cañas

2009-01-01

2

Effect of Load Phase Angle on Wind Turbine Blade Fatigue Damage: Preprint  

Microsoft Academic Search

This paper examines the importance of phase angle variations with respect to fatigue damage. The operating loads on a generic conventional three-bladed upwind 1.5-MW wind turbine blade were analyzed over a range of operating conditions, and an aggregate probability distribution for the actual phase angles between the in-plane (lead-lag) and out-of-plane (flap) loads was determined. Using a finite element model

D. L. White; W. D. Musial

2003-01-01

3

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

4

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

5

A simulation model for wind turbine blade fatigue loads  

Microsoft Academic Search

The paper describes a horizontal axis wind turbine time domain simulation and fatigue estimation program written using the DelphiTM language. The program models the flapwise motion of a single rotor blade to determine the blade-root fatigue damage of a medium size wind turbine. The effects of turbulence intensity, mean wind speed, wind shear, vertical wind component, dynamic stall, stall hysteresis,

M. Noda; R. G. J. Flay

1999-01-01

6

Determining equivalent damage loading for full-scale wind turbine blade fatigue tests  

Microsoft Academic Search

This paper describes a simplified method for converting wind turbine rotor design loads into equivalent-damage, constant-amplitude loads and load ratios for both flap and lead-lag directions. It is an iterative method that was developed at the National Renewable Energy Laboratory (NREL) using Palmgren-Miner's linear damage principles. The general method is unique because it does not presume that any information about

G. Freebury; W. Musial

2000-01-01

7

Fatigue life estimation procedure for a turbine blade under transient loads  

Microsoft Academic Search

A technique for fatigue damage assessment during variable speed operations is presented. Transient resonant stresses for a blade with nonlinear damping have been determined using a numerical procedure. A fatigue damage assessment procedure is described. The fatigue failure surface is generated on the S-N-mean stress axes, and Miner's rule is employed to estimate the cumulation of fatigue.

N. S. Vyas; J. S. Rao

1992-01-01

8

Fatigue life estimation procedure for a turbine blade under transient loads  

Microsoft Academic Search

Fatigue analysis and consequent life prediction of turbomachine blading requires the stress load history of the blade. A blade designed for safe operation at particular constant rotor speeds may, however, incur damaging stresses during start-up and shut-down operations. During such operations the blade experiences momentary resonant stresses while passing through the criticals, which may lie in the speed range through

N. S. Vyas; J. S. Rao

1994-01-01

9

Fatigue of fiberglass wind turbine blade materials  

Microsoft Academic Search

Fatigue behavior for a variety of generic materials used in wind turbine blades was explored. Coupon testing was carried out under constant amplitude tensile fatigue loading to beyond 10(exp 7) cycles for most materials. Unidirectional materials performed close to expectations despite fiber misalignment. Materials with triaxial (0\\/plus or minus 45) reinforcement showed greater fatigue sensitivity than expected, but lifetime trends

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

1992-01-01

10

Turbine blade thermal fatigue testing Pratt and Whitney aircraft hollow core blades  

NASA Technical Reports Server (NTRS)

The results of low cycle fatigue testing on turbine blades for use in hydrogen/oxygen rocket engines is presented. Cored blade and cored blades with circulation were tested in the MSFC thermal fatigue tester. Both blade configurations showed significant low cycle fatigue life improvements when compared to baseline solid blades.

Ingram, J.; Gross, L.

1985-01-01

11

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

12

Subrupture tendon fatigue damage.  

PubMed

The mechanical and microstructural bases of tendon fatigue, by which damage accumulates and contributes to degradation, are poorly understood. To investigate the tendon fatigue process, rat flexor digitorum longus tendons were cyclically loaded (1-16 N) until reaching one of three levels of fatigue damage, defined as peak clamp-to-clamp strain magnitudes representing key intervals in the fatigue life: i) Low (6.0%-7.0%); ii) Moderate (8.5%-9.5%); and iii) High (11.0%-12.0%). Stiffness, hysteresis, and clamp-to-clamp strain were assessed diagnostically (by cyclic loading at 1-8 N) before and after fatigue loading and following an unloaded recovery period to identify mechanical parameters as measures of damage. Results showed that tendon clamp-to-clamp strain increased from pre- to post-fatigue loading significantly and progressively with the fatigue damage level (p fatigue level (p fatigue was characterized by isolated, transverse patterns of kinked fiber deformations. At higher fatigue levels, tendons exhibited fiber dissociation and localized ruptures of the fibers. Histomorphometric analysis showed that damage area fraction increased significantly with fatigue level (p fatigue process and indicate that tendon deformation can be used to accurately assess the progression of damage accumulation in tendons. PMID:18683881

Fung, David T; Wang, Vincent M; Laudier, Damien M; Shine, Jean H; Basta-Pljakic, Jelena; Jepsen, Karl J; Schaffler, Mitchell B; Flatow, Evan L

2009-02-01

13

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

Microsoft Academic Search

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 that may be obtained as part of a routine site characterization study. By using the model to simulate

J. C. Barnard; L. L. Wendell

1997-01-01

14

General method for fatigue analysis of vertical-axis wind-turbine blades  

Microsoft Academic Search

The fatigue life of wind-turbine blades, which are exposed to the random loading environment of atmospheric winds, is described with random data analysis procedures. The incident windspeed and the stresses caused by these winds are expressed in terms of probability density functions while the fatigue life vs. stress level relationship is treated deterministically. This approach allows the fatigue damage to

Paul S. Veers

1983-01-01

15

Computation Method on Fatigue Life of a Full Composite Wind Turbine Blade  

Microsoft Academic Search

The generation of load spectrum for epoxy resin blade of large-scale wind turbine is researched in this paper, so are an engineering estimating method of the fatigue failure and accumulated fatigue damage. Meanwhile, Load cases are considered, calculated and evaluated. First, a 3 dimensional finite element modal for calculation of fatigue failure is proposed based on the composite laminated technology

Jing Wang; Zhihua Huang; Yinghui Li

2010-01-01

16

Fatigue of fiberglass wind turbine blade materials  

NASA Astrophysics Data System (ADS)

Fatigue behavior for a variety of generic materials used in wind turbine blades was explored. Coupon testing was carried out under constant amplitude tensile fatigue loading to beyond 10(exp 7) cycles for most materials. Unidirectional materials performed close to expectations despite fiber misalignment. Materials with triaxial (0/plus or minus 45) reinforcement showed greater fatigue sensitivity than expected, but lifetime trends flattened at high cycles. The uniaxial and triaxial materials could be normalized to a single S-N lifetime trend for each case. Results include the effects of differing matrix materials, manufacturing methods, reinforcement structure, and ply terminations.

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

1992-08-01

17

Simulation of fatigue failure in a full composite wind turbine blade  

Microsoft Academic Search

Lifetime prediction of a horizontal axis wind turbine composite blade is considered. Load cases are identified, calculated and evaluated. Static analysis is performed with a full 3-D finite element method and the critical zone where fatigue failure begins is extracted. Accumulated fatigue damage modeling is employed as a damage estimation rule based on generalized material property degradation. Since wind flow

Mahmood M. Shokrieh; Roham Rafiee

2006-01-01

18

Annotated Bibliography on Cumulative Fatigue Damage and Structural Reliability Models.  

National Technical Information Service (NTIS)

The authors selected almost one hundred publications in the area of modeling cumulative fatigue damage of airframe and helicopter rotor blade structures bringing to light the salient contributions as well as the limitations and assumptions in each of thes...

G. B. Swartz V. K. Murthy

1972-01-01

19

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

20

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

Microsoft Academic Search

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

J. C. Barnard; L. L. Wendell

1995-01-01

21

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

22

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

23

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

24

Effect of Mean Stress on the Damage of Wind Turbine Blades  

Microsoft Academic Search

In many analyses of composite wind turbine blades, the effects of mean stress on the determination of damage are either ignored completely or they are characterized inadequately. An updated Goodman diagram for the fiberglass materials that are typically used in wind turbine blades has been released recently. This diagram, which is based on the MSU\\/DOE Fatigue Database, contains detailed information

Herbert J. Sutherland; John F. Mandell

2004-01-01

25

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

NASA Astrophysics Data System (ADS)

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

26

Thermographic measurement of fatigue damage  

NASA Technical Reports Server (NTRS)

The paper presents a thermographic technique developed to measure the extent of fatigue damage in composite materials during fatigue loading. It is noted that heat generated by cyclic loading of fatigue damaged material raises the surface temperature. These temperatures were measured with an infrared camera and were used as boundary conditions in a finite element heat transfer program, which has been developed especially to calculate the extent of the heat generation zone, and thereby to define the fatigue damage zone. It is reported that the finite element program was verified by comparing calculated heat generation with the actual heat generation for a simple heat transfer problem that had a closed form solution. Damage zones are calculated for several boron/epoxy fatigue specimens from thermograms of specimens. The calculated damage zones were compared with damage detected by C-scan, X-ray, and scanning electron microscope (SEM) examinations. It is concluded that the analysis was effective in locating the boundaries of the fatigue damage zones.

Whitcomb, J. D.

1979-01-01

27

COMPOSITE MATERIALS FATIGUE ISSUES IN WIND TURBINE BLADE CONSTRUCTION  

Microsoft Academic Search

This paper provides an overview of the results of recent studies of composite laminates of interest for wind turbine blade construction. In addition to the primary requirements of stiffness, strength, and ease of processing, wind blade materials must withstand severe fatigue loading under service environments. The large material volumes and cost constraints also lead to unusually thick plies and fabrics,

John F. Mandell; Daniel D. Samborsky

28

Reliability-based fatigue design of wind-turbine rotor blades  

Microsoft Academic Search

A probabilistic model for analysis of the safety of a wind-turbine rotor blade against fatigue failure in flapwise bending is presented. The model is based on a Miner's rule approach to cumulative damage and capitalizes on a conventional S–N curve formulation for fatigue resistance in conjunction with a new `distorted Weibull' distribution for representation of wind-induced bending moment ranges. The

Knut O. Ronold; Jakob Wedel-Heinen; Carl J. Christensen

1999-01-01

29

Fatigue Evaluation of WTS-3 Glassfibre Blade Material.  

National Technical Information Service (NTIS)

A first step in assessing the fatigue properties of the WTS-3 wind turbine blade material has been undertaken. Hereby flat test specimens of filament-wound material have been used for the fatigue tests. Woehler-diagrams (SN-curves) have been produced both...

A. F. Blom

1982-01-01

30

Fatigue Evaluation of Wts-3 Glass Fiber Blade Material.  

National Technical Information Service (NTIS)

The fatigue properties of the WTS-3 wind turbine blade material were assessed. Flat test specimens of filament wound material were used for the fatigue tests. Wohler diagrams (SN curves) were produced both at purely tensile loading R = delta min/max = 0 a...

A. F. Blom

1982-01-01

31

Assessment of fatigue life for small composite wind turbine blades  

Microsoft Academic Search

The present design and assessment of fatigue life for the small composite wind turbine blades (SCWTBs) can be certified by IEC 61400-2 “Wind Turbines - Part2: Design requirements of small wind turbines”. The paper will establish an analytical method on the fatigue life analysis of SCWTBs. Using the Microsoft Office EXCEL to calculate the maximum stress, minimum stress and stress

Jia-Hroung Wu

2010-01-01

32

PZT Active Frequency Based Wind Blade Fatigue to Failure Testing Results for Various Blade Designs.  

National Technical Information Service (NTIS)

This paper summarizes NASA PZT Health Monitoring System results previously reported for 9 meter blade Fatigue loading to failure conducted at The National Renewable Energy Lab Wind blade testing facility results using the on the CX-100, TX-100 and BSDS de...

R. J. Werlink

2011-01-01

33

Erosion-fatigue of steam turbine blades  

Microsoft Academic Search

The premature failure of steam turbine rotor blades, manufactured in forged 12% Cr–NiMoV martensitic stainless steel, was investigated using visual inspection, non-destructive testing, macro and microfractography, microstructural characterization, EDS microanalysis, chemical analysis, micro hardness and tensile testing. The blades belonged to the last stage of a thermoelectric plant steam turbine generator (140MVA). The results indicated that the failure of the

C. R. F. Azevedo; A. Sinátora

2009-01-01

34

Microstructural evaluation of cumulative fatigue damage below the fatigue limit  

Microsoft Academic Search

The objective of this work is to evaluate the microstructural changes induced near and below the fatigue limit in a pressure vessel steel plate, SA508. Dislocation cell to cell misorientation differences, θ, which increase with fatigue damage accumulation, are measured by the Selected Area Diffraction (SAD) method. The misorientation difference, θ, of the sample failed just above the fatigue limit

C. Fukuoka; Y. G. Nakagawa

1996-01-01

35

Microstructural evaluation of cumulative fatigue damage below the fatigue limit  

SciTech Connect

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

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

1996-05-01

36

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

Microsoft Academic Search

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

Nobuhiro Isobe; Shuhei Nogami

2009-01-01

37

The nature of fatigue damage in bone  

Microsoft Academic Search

Bone is unusual among structural materials as it is alive and capable of self-repair. Fatigue-induced microdamage is repaired by bone remodelling, but if damage accumulates too quickly, or remodelling is deficient, fatigue failure may result. Fatigue is thought to contribute to both stress and fragility fractures which are of major clinical importance. Despite this, we do not fully understand the

T. Clive Lee; Fergal J. O'Brien; David Taylor

2000-01-01

38

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

39

APPLICATION OF LOW PLASTICITY BURNISHING TO IMPROVE DAMAGE TOLERANCE OF A Ti6Al4V FIRST STAGE FAN BLADE  

Microsoft Academic Search

This paper describes the application of Low Plasticity Burnishing (LPB) to increase the damage tolerance and fatigue strength of a Ti-6Al-4V fan blade that is fatigue life limited by the occurrence of leading edge foreign object damage (FOD) as small as 0.1mm (0.005 in.). The size and location distributions of service generated FOD were documented; no FOD exceeded a depth

Ravi Ravindranath

40

How surface damage removal affects fatigue life  

NASA Technical Reports Server (NTRS)

The effect of the removal of work hardened surface layers from specimens of 2024-T4 aluminum alloy and AISI-4130 steel on their fatigue lives has been investigated. Specimens were fatigued at selected stress levels for a given number of cycles, and the surface layer was removed followed by subsequent fatigue cycling. Results confirm that when a material is subjected to fatigue loading, damage accumulates in the surface layers in the form of work hardening. Removal of the surface layer brings the specimen back to its pre-fatigued condition.

Jeelani, S.; Scott, M. A.

1988-01-01

41

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

42

Probabilistic Evaluation of Blade Impact Damage.  

National Technical Information Service (NTIS)

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 (geome...

C. C. Chamis G. H. Abumeri

2003-01-01

43

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

Microsoft Academic Search

This paper presents experimental results of several structural health monitoring (SHM) methods applied to a 9-meter CX-100 wind turbine blade that underwent fatigue loading. The blade was instrumented with piezoelectric transducers, accelerometers, acoustic emission sensors, and foil strain gauges. It underwent harmonic excitation at its first natural frequency using a hydraulically actuated resonant excitation system. The blade was initially excited

Stuart G. Taylor; Kevin M. Farinholt; Hyomi Jeong; JaeKyung Jang; Gyu Hae Park; Michael D. Todd; Charles R. Farrar; Curtt N. Ammerman

2012-01-01

44

A Cumulative Damage Theory of Fatigue Failure.  

National Technical Information Service (NTIS)

A rational phenomenological theory of fatigue lifetime prediction under arbitrary variation of cycle amplitude is presented. The theory is based on the concept of damage curve families and on an equivalent loading postulate which defines specimens that ha...

Z. Hashin A. Rotom

1977-01-01

45

A new method for dual-axis fatigue testing of large wind turbine blades using resonance excitation and spectral loading  

NASA Astrophysics Data System (ADS)

The demand for cost effective renewable energy sources has resulted in the continual refinement of modern wind turbine designs. These refinements generally result in larger wind turbines and wind turbine blades. In order to reduce maintenance expenses, and improve quality and reliability, each new blade design must be subjected to a high cycle fatigue test. With blades expected to soon reach 70 meters in length, traditional fatigue test systems and methods are becoming less practical. Additionally, the relationship between the flap and lead-lag bending moments has not been well understood. This work explores the accuracy of current test methods compared to service loads, presents a new method for fatigue testing larger blades and experimentally validates the analysis. A dynamic model of a generic wind turbine blade and test system has been developed to evaluate the strain profiles during testing, evaluate control strategies and optimize the test accuracy. The relationship between the flap and lead-lag strains resulting from service bending moments has been analyzed. A load spectrum based on the relationship between the flap and lead-lag loads has been developed and compared to traditional test conditions. The effect of using the load spectrum on the test system stability has been analyzed and a new state-space controller has been designed. A 3-D finite element model of a generic wind turbine blade has been used to evaluate the damage accumulation for current test load conditions and the proposed load spectrum. A nonlinear damage accumulation model has been derived to evaluate the effects of load sequencing. Additionally, a new method for applying the fatigue loads to the blades has been developed and implemented. A system that applies a harmonic force at the resonance frequency of the blade in the flap direction has been designed. The new system will reduce the costs and time associated with performing a fatigue test on wind turbine blades. The new system is also capable of matching a greater range of service load distribution than the current test system. An optimization routine has been used to make the test load distribution match the target: load distribution.

White, Darris L.

46

METHOD TO PREDICT FATIGUE LIFETIMES OF GRP WIND TURBINE BLADES AND COMPARISON WITH EXPERIMENTS  

Microsoft Academic Search

This paper describes a method to predict fatigue lifetimes of fiber reinforced plastics in wind turbine blades. It is based on extensive testing within the EU-Joule program. The method takes the measured fatigue properties of a material into account so that credit can be given to materials with improved fatigue properties. The large number of test results should also give

A. T. Echtermeyer; C. Kensche; P. Bach; M. Poppen; H. Lllholt; S. I. Andersen; P. Brøndsted

1996-01-01

47

Fatigue Damage Mechanics of Composite Laminates,  

National Technical Information Service (NTIS)

The mechanics of fatigue damage in composite laminates is developed. Damage which results from such mechanisms as delamination and matrix cracking results in a loss of stiffness of the material. A change in stiffness is modelled in terms of the dominant m...

P. W. R. Beaumont

1987-01-01

48

Fatigue damage interaction behavior of PWA 1480  

NASA Technical Reports Server (NTRS)

The fatigue damage interaction behavior of PWA 1480 single crystal alloy has been experimentally established for the two-level loading case in which a block of low-cycle fatigue loading is followed by high-cycle fatigue loading to failure. A relative life ratio N1/N2 (where N1 and N2 are the low- and high-cycle fatigue baseline lives, respectively) of approximately 0.002 was explored to assess the interaction behavior. The experimental results thus far show evidence of a loading order interaction effect to a similar degree of detriment as has been observed in polycrystalline materials. Current generation single crystal alloys in general, and PWA 1480 in particular, contain pores; indeed, it was observed in all cases that specimen failure initiated from pores connected with or immediately below the surface. Detailed fractographic and metallographic studies are currently being made to assess the nature of the porosity in terms of its effect on fatigue life.

Mcgaw, Michael A.

1987-01-01

49

Bayesian Network Combined Fuzzy C-means Methodology for Turbine Blades Fatigue Performance Evaluation  

Microsoft Academic Search

In this paper, a fatigue performance evaluation model for steam turbine blades based on Bayesian network combined fuzzy c-means algorithm was proposed. Bayesian network was viewed as a classification technique to evaluate fatigue performance. Fuzzy c-means algorithm was applied to perform cluster analysis of fatigue performance values and made them discrete. Low-cycle fatigue tests on certain kind of steam turbine

Jihong Yan; Xingman Xiong; Shifeng Zhu

2010-01-01

50

Fatigue damage accumulation in carbon\\/epoxy laminated composites  

Microsoft Academic Search

The precise prediction of fatigue damage progress and fatigue life in laminated composites has been always a concern to designers. The present work is focused on the fatigue damage mechanisms and damage accumulation rate in laminated composites. Results showed that the dominant damage mechanism depends on the applied stress and total delamination only observed under the cyclic stress of less

J. Aghazadeh Mohandesi; B. Majidi

2009-01-01

51

Basic mechanisms of tendon fatigue damage  

PubMed Central

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

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

2012-01-01

52

Piezoelectric active sensing techniques for damage detection on wind turbine blades  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

53

High-Cycle Fatigue Testing of Turbine Blades Under Multiaxial Loading.  

National Technical Information Service (NTIS)

Gas turbine engine blades are subjected to a centrifugal force in the radial direction and high frequency transverse excitation under operating conditions. A multiaxial loading machine was proposed in the present SBIR program to perform high-cycle fatigue...

M. Balan B. Bornhorst S. R. Soni M. Xie

2001-01-01

54

Full-Scale Fatigue Test of 9-m CX-100 Wind Turbine Blades.  

National Technical Information Service (NTIS)

This paper presents the SHM result of a 9m CX-100 wind turbine blade under full-scale fatigue loads. The test was performed at the National Renewable Energy Laboratory. The 9-meter blade was instrumented with piezoelectric transducers, accelerometers, aco...

C. R. Farrar G. Park K. M. Farinholt S. G. Taylor

2011-01-01

55

The development of a fatigue loading spectrum for small wind turbine blades  

Microsoft Academic Search

This paper details a formulation to create a fatigue loading procedure for the blade of a small wind turbine using a combination of detailed short-term aeroelastic and wind measurements and averaged long-term wind data from the Australian Bureau of Meteorology. Detailed aeroelastic measurements from the blade of an operating small wind turbine were acquired simultaneously with wind speed measurements and

Jayantha A. Epaarachchi; Philip D. Clausen

2006-01-01

56

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

Microsoft Academic Search

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

A. G. Beattie

1997-01-01

57

Fatigue Testing of 9 m Carbon Fiber Wind Turbine Research Blades  

Microsoft Academic Search

Fatigue testing was conducted on Carbon Experimental and Twist-Bend Experimental (CX-100 and TX-100) 9-m wind turbine research blades. The CX-100 blade was designed to investigate the use of a carbon spar cap to reduce weight and increase stiffness while being incorporated using conventional manufacturing techniques. The TX-100 blade used carbon in the outboard portion of the skin to produce twist-bend

J. Paquette; J. van Dam; S. Hughes; J. Johnson

2008-01-01

58

Fatigue damage accumulation: Aspects of environmental interaction  

Microsoft Academic Search

The corrosion fatigue lifetime of materials can be predicted by simulating the multi-stage damage process with regard for\\u000a the action of both corrosion and mechanical factors. This action can be represented in the form of damage accumulation maps,\\u000a where the processes of pitting, pit-crack transition, and cracking are identified. For the construction of the models, we\\u000a develop localized electrochemical methods

R. Akid; I. M. Dmytrakh; J. Gonzalez-Sanchez

2006-01-01

59

Double Linear Damage Rule for Fatigue Analysis  

NASA Technical Reports Server (NTRS)

Double Linear Damage Rule (DLDR) method for use by structural designers to determine fatigue-crack-initiation life when structure subjected to unsteady, variable-amplitude cyclic loadings. Method calculates in advance of service how many loading cycles imposed on structural component before macroscopic crack initiates. Approach eventually used in design of high performance systems and incorporated into design handbooks and codes.

Halford, G.; Manson, S.

1985-01-01

60

Frequency domain analysis of the fatigue loads on typical wind turbine blades  

Microsoft Academic Search

The fatigue analysis of a wind turbine blade typically depends on converting time-series data to a series of load cycles using one of several cyclic counting algorithms. However, many structural analysis techniques yield frequency-domain stress spectra, and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the fatigue analysis of this class of

Herbert J. Sutherland

1996-01-01

61

New Method for Dual-Axis Fatigue Testing of Large Wind Turbine Blades Using Resonance Excitation and Spectral Loading  

SciTech Connect

The blades of a wind turbine are generally considered to be the most critical component of the wind turbine system. The fundamental purpose of performing fatigue tests on wind turbine blades is to demonstrate that a blade, when manufactured to a certain set of specifications, has the prescribed reliability and service life. The purpose of the research conducted for this project is the advancement of knowledge and capabilities in the area of wind turbine blade fatigue testing.

White, D.

2004-04-01

62

Fatigue life prediction and strength degradation of wind turbine rotor blade composites  

Microsoft Academic Search

Wind turbine rotor blades are subjected to a large number of highly variable loads, but life predictions are typically based on constant amplitude fatigue behaviour. Therefore, it is important to determine how service life under variable amplitude fatigue can be estimated from constant amplitude fatigue behaviour.\\u000a\\u000aA life prediction contains different, partly independent, elements:\\u000a·\\u0009the counting method, used for

R. P. L. Nijssen

2006-01-01

63

Cumulative Fatigue Damage Behavior of MAR M-247.  

National Technical Information Service (NTIS)

The objective was to examine the room temperature fatigue and nonlinear cumulative fatigue damage behavior of the cast nickel-based superalloy, MAR M-247. The fatigue test matrix consisted of single-level, fully reversed fatigue experiments. Two series of...

M. A. Mcgaw G. R. Halford S. Kalluri

1991-01-01

64

A continuum Damage Approach of Asphalt Concrete Fatigue Tests  

Microsoft Academic Search

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

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

65

Fatigue crack growth simulation in a generator fan blade  

Microsoft Academic Search

The blades of Iran Montazer-Ghaem-Unit4 power plant failed just 10h after resuming operation following the last overhaul. The initial investigation showed that the design shortcoming was the main cause of the failure. A series of analytical, finite element and experimental analysis were utilized to determine the steady-state stresses and dynamic characteristic of the blade. It is concluded that the blade

E. Poursaeidi; M. Salavatian

2009-01-01

66

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

Microsoft Academic Search

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

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

1997-01-01

67

Effect of Impact Damage on the Fatigue Response of TiAl Alloy-ABB-2  

NASA Technical Reports Server (NTRS)

The ability of gamma-TiAl to withstand potential foreign or domestic object damage is a technical risk to the implementation of gamma-TiAl in low pressure turbine (LPT) blade applications. In the present study, the impact resistance of TiAl alloy ABB-2 was determined and compared to the impact resistance of Ti(48)Al(2)Nb(2)Cr. Specimens were impacted with four different impact conditions with impact energies ranging from 0.22 to 6.09 J. After impacting, the impact damage was characterized by crack lengths on both the front and backside of the impact. Due to the flat nature of gamma-TiAl's S-N (stress vs. cycles to failure) curve, step fatigue tests were used to determine the fatigue strength after impacting. Impact damage increased with increasing impact energy and led to a reduction in the fatigue strength of the alloy. For similar crack lengths, the fatigue strength of impacted ABB-2 was similar to the fatigue strength of impacted Ti(48)Al(2)Nb(2)Cr, even though the tensile properties of the two alloys are significantly different. Similar to Ti(48)Al(2)Nb(2)Cr, ABB-2 showed a classical mean stress dependence on fatigue strength. The fatigue strength of impacted ABB-2 could be accurately predicted using a threshold analysis.

Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Nazmy, M. Y.; Staubli, M.; Clemens, D. R.

2001-01-01

68

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

Microsoft Academic Search

This paper demonstrates a methodology for predicting the service lifetime of wind turbine blades using the high-cycle fatigue data base for typical U.S. blade materials developed by Mandell, et al. (1995). The first step in the analysis is to normalize the data base (composed primarily of data obtained from specialized, relatively small coupons) with fatigue data from typical industrial laminates

Herbert J. Sutherland; John F. Mandell

1995-01-01

69

Cumulative fatigue damage behavior of MAR M-247  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

70

Cumulative fatigue damage behavior of MAR M-247  

NASA Astrophysics Data System (ADS)

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

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

1991-05-01

71

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

72

New Method for Dual-Axis Fatigue Testing of Large Wind Turbine Blades Using Resonance Exicitation and Spectral Loading.  

National Technical Information Service (NTIS)

The blades of a wind turbine are generally considered to be the most critical component of the wind turbine system. The fundamental purpose of performing fatigue tests on wind turbine blades is to demonstrate that a blade, when manufactured to a certain s...

D. White

2004-01-01

73

A new method for dual-axis fatigue testing of large wind turbine blades using resonance excitation and spectral loading  

Microsoft Academic Search

The demand for cost effective renewable energy sources has resulted in the continual refinement of modern wind turbine designs. These refinements generally result in larger wind turbines and wind turbine blades. In order to reduce maintenance expenses, and improve quality and reliability, each new blade design must be subjected to a high cycle fatigue test. With blades expected to soon

Darris L. White

2003-01-01

74

New Method for Dual-Axis Fatigue Testing of Large Wind Turbine Blades Using Resonance Excitation and Spectral Loading  

Microsoft Academic Search

The blades of a wind turbine are generally considered to be the most critical component of the wind turbine system. The fundamental purpose of performing fatigue tests on wind turbine blades is to demonstrate that a blade, when manufactured to a certain set of specifications, has the prescribed reliability and service life. The purpose of the research conducted for this

2004-01-01

75

Accelerated Full Scale Fatigue Testing Of A Small Composite Wind Turbine Blade Using A Mechanically Operated Test Rig  

Microsoft Academic Search

A 2.5m long glass fibre reinforced plastic composite wind turbine blade was fatigue tested by means of a mechanically operated test rig. The rig uses a crank eccentric mechanism to flex the blade by a constant displacement in the flapwise direction for each load cycle. A yearly fatigue-loading spectrum for the blades has been developed from using short-term detailed aeroelastic

Jayantha A. Epaarachchi; Philip D. Clausen

2004-01-01

76

A fatigue damage accumulation model based on continuum damage mechanics and ductility exhaustion  

Microsoft Academic Search

Using continuum damage mechanics, a fatigue damage accumulation model related to ductility exhaustion has been developed. This model was applied to study fatigue damage evolution in a pressure vessel steel and two-level cyclic tests have been carried out to verify the damage accumulation model. The experimental results showed that a damage variable, D, based on ductility exhaustion can be used

Guangxu Cheng; Alan Plumtree

1998-01-01

77

Investigation of fatigue life for a medium scale composite wind turbine blade  

Microsoft Academic Search

In order to satisfy fatigue requirements in designing a cost effective wind turbine, the wind turbine blade, which is an expensive key component of the wind turbine system, must achieve very long operating life of 20–30 years. In this study, the fatigue life of a medium scale (750kW) horizontal axis wind turbine system (HAWIS), which has been developed by the

Changduk Kong; Taekhyun Kim; Dongju Han; Yoshihiko Sugiyama

2006-01-01

78

Very-High-Cycle-Fatigue of in-service air-engine blades, compressor and turbine  

NASA Astrophysics Data System (ADS)

In-service Very-High-Cycle-Fatigue (VHCF) regime of compressor vane and turbine rotor blades of the Al-based alloy VD-17 and superalloy GS6K, respectively, was considered. Surface crack origination occurred at the lifetime more than 1500 hours for vanes and after 550 hours for turbine blades. Performed fractographic investigations have shown that subsurface crack origination in vanes took place inspite of corrosion pittings on the blade surface. This material behavior reflected lifetime limit that was reached by the criterion VHCF. In superalloy GS6K subsurface fatigue cracking took place with the appearance of flat facet. This phenomenon was discussed and compared with specimens cracking of the same superalloy but prepared by the powder technology. In turbine blades VHCF regime appeared because of resonance of blades under the influenced gas stream. Both cases of compressor-vanes and turbine blades in-service cracking were discussed with crack growth period and stress equivalent estimations. Recommendations to continue aircrafts airworthiness were made for in-service blades.

Shanyavskiy, A. A.

2014-01-01

79

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

80

Novelty detection applied to vibration data from a CX100 wind turbine blade under fatigue loading  

Microsoft Academic Search

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

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

2012-01-01

81

Early stages of fatigue damage in aluminium and aluminium alloys  

Microsoft Academic Search

In this paper fatigue damage initiation is considered as both microcrack nucleation from microheterogeneities within fatigued material and microcrack growth over distances corresponding to the size of the microstructure. A brief review of the literature shows that, depending on fatigue conditions and microstructure three different types of nucleation sites exist in aluminium and aluminium alloys : slip bands, grain boundaries

R. FOUGERES

1993-01-01

82

Fatigue testing of low-cost fiberglass composite wind turbine blade materials  

NASA Technical Reports Server (NTRS)

The static and fatigue behavior of transverse filament tape (TFT) fiberglass/epoxy and TFT/polyester composites was established by the testing of specimens cut from panels fabricated by a filament winding process used for the construction of large experimental wind turbine blades.

Hofer, K. E.; Bennett, L. C.

1981-01-01

83

Fatigue testing of low-cost fiberglass composite wind turbine blade materials  

Microsoft Academic Search

The static and fatigue behavior of transverse filament tape (TFT) fiberglass\\/epoxy and TFT\\/polyester composites was established by the testing of specimens cut from panels fabricated by a filament winding process used for the construction of large experimental wind turbine blades.

K. E. Hofer; L. C. Bennett

1981-01-01

84

Fatigue testing of low-cost fiberglass composite wind turbine blade materials  

NASA Astrophysics Data System (ADS)

The static and fatigue behavior of transverse filament tape (TFT) fiberglass/epoxy and TFT/polyester composites was established by the testing of specimens cut from panels fabricated by a filament winding process used for the construction of large experimental wind turbine blades.

Hofer, K. E.; Bennett, L. C.

1981-11-01

85

WISPER and WISPERX: Final definition of two standardised fatigue loading sequences for wind turbine blades  

Microsoft Academic Search

Relevant information used to develop WISPER (Wind turbine reference Spectrum) and WISPERX, standardized variable amplitude test loading histories for use in the fatigue design of horizontal axis wind turbine blades, is presented. WISPER and WISPERX are based on flap load service measurements on nine different horizontal axis wind turbines, covering a wide range of materials, rotor diameters and geographical locations.

A. A. Tenhave

1992-01-01

86

A study of cumulative fatigue damage in AISI 4130 steel  

NASA Technical Reports Server (NTRS)

Experimental data were obtained using AISI 4130 steel under stress ratios of -1 and 0. A study of cumulative fatigue damage using Miner's and Kramer's equations for stress ratios of -1 and 0 for low-high, low-high-mixed, high-low, and high-low-mixed stress sequences has revealed that there is a 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 the popularly used Miner's rule does.

Jeelani, S.; Musial, M.

1986-01-01

87

Fatigue damage accumulation and residual strength assessment of CFRP laminates  

Microsoft Academic Search

The method of progressive damage modelling has been used to assess fatigue damage accumulation and residual strength of carbon-fibre reinforced plastic (CFRP) laminates under fully reversed cyclic loading (R=?min\\/?max=?1). The accumulation of different damage modes has been assessed, as a function of number of cycles, using a three-dimensional fatigue progressive damage model (FPDM). The residual strength of the CFRP laminates

K. I Tserpes; P Papanikos; G Labeas; Sp Pantelakis

2004-01-01

88

Conditioning monitoring by microstructural evaluation of cumulative fatigue damage  

NASA Astrophysics Data System (ADS)

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

Fukuoka, C.; Nakagawa, Y. G.; Lance, J. J.; Pangborn, R. N.

1996-12-01

89

Conditioning monitoring by microstructural evaluation of cumulative fatigue damage  

SciTech Connect

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

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

1996-12-01

90

Conditioning monitoring by microstructural evaluation of cumulative fatigue damage  

Microsoft Academic Search

The objective of this work is to evaluate the damage induced below and above the fatigue limit (??\\u000a \\u000a t\\u000a =360 MPa) in pressure vessel steels, such as SA508. Fatigue damage was induced in samples taken from an SA508 steel plate\\u000a by various loading histories in order to examine the influence of prior cyclic loading below the fatigue limit. Cell-to-cell\\u000a misorientation

C. Fukuoka; Y. G. Nakagawa; J. J. Lance; R. N. Pangborn

1996-01-01

91

Conditioning monitoring by microstructural evaluation of cumulative fatigue damage  

Microsoft Academic Search

The objective of this work is to evaluate the damage induced below and above the fatigue limit (Delta sigma t =360 MPa) in pressure vessel steels, such as SA508. Fatigue damage was induced in samples taken from an SA508 steel plate by various loading histories in order to examine the influence of prior cyclic loading below the fatigue limit. Cell-to-cell

C. Fukuoka; Y. G. Nakagawa; J. J. Lance; R. N. Pangborn

1996-01-01

92

Exoelectron emission from torsional fatigue damage in hardened steels  

Microsoft Academic Search

Exoelectron emission associated with surface fatigue damage in two types of steel was measured by means of an ultraviolet laser scanning system. The localized emission from damage areas in quenched and tempered 1541 steel increased systematically with continued fatigue cycling. Plots of emission vs cycles were in good agreement with earlier results for 1018 steel. Much of this emission resulted

William J. Baxter

1977-01-01

93

Fatigue damage analysis on body shell of a passenger vehicle  

Microsoft Academic Search

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

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

2002-01-01

94

Causes of damages to fan blades of the generator of a steam turbine  

Microsoft Academic Search

It is shown that the fracture of blades of the fan of a TGV-200 generator is induced by corrosion fatigue intensified by residual\\u000a hydrogen accumulated in steel in the process of electroplating of a cadmium coating on the surface of blades.

H. M. Krutsan; V. H. Zdanovs'kyi; L. M. Karvats'kyi; M. S. Khoma

1997-01-01

95

An experiemental and computational study of the aerodynamics of turbine blades with damage  

Microsoft Academic Search

Investigations have been made of the aerodynamic effects of in-service damage on the performance of axial turbine blades. Two aspects of blade damage were considered: surface roughening and trailing edge damage. The work is related to gas turbine engine health monitoring. Correlations for the effects of surface roughness were developed based on a database obtained from Kind et al. (1998).

Alamgir M. T. Islam

1999-01-01

96

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

97

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

National Technical Information Service (NTIS)

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 load...

S. D. Hughes W. D. Musial T. Stensland

1999-01-01

98

Blade fatigue life assessment with application to VAWTs  

Microsoft Academic Search

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

P. S. Veers

1982-01-01

99

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

100

Evaluation of the New B-REX Fatigue Testing System for Multi-Megawatt Wind Turbine Blades. Preprint. Conference Paper.  

National Technical Information Service (NTIS)

The National Renewable Energy Laboratory (NREL) recently developed a new hybrid fatigue testing system called the Blade Resonance Excitation (B-REX) test system. The new system uses 65% less energy to test large wind turbine blades in half the time of NRE...

D. White W. Musial S. Engberg

2004-01-01

101

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

102

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

103

Cumulative fatigue damage analysis under conditions of competing mechanisms  

NASA Astrophysics Data System (ADS)

Two special cumulative damage problems in which two competing mechanisms operate have been examined. One of the mechanisms, active in both problems and detrimental to fatigue life, is the nonlinear damage interaction between the different levels of the applied loading. The second mechanism, which is beneficial to fatigue life, arises due to the nature of the applied loading and material behavior. The first problem is encountered when dealing with an irreversibly hardening material. In such a material, initial cycles applied at high strainranges can alter the material such that subsequently applied cycles are essentially on a new material with improved fatigue properties. In this case, life relations determined from conventional constant amplitude fatigue data are inadequate for treatment of cumulative fatigue damage. A procedure, which uses two-level step test data in conjunction with a nonlinear cumulative damage model, is proposed for establishing effective life relations which can be used successfully under any loading history. Tests conducted at room temperature on 304 stainless steel, a material which irreversibly hardens, indicate that cumulative fatigue damage behavior can be accurately predicted using the proposed procedure. The second problem is found in applications involving creep-fatigue loading. Compressive and tensile creep strains imposed at different times during the life of a material can interact to produce a "healing" effect. Under variable amplitude loading, this benign interaction can compete with the unfavorable interactions occurring between the different loading levels. Life prediction analyses were carried out for two loading histories and three types of materials classified according to their creep-fatigue life relations. The results suggest that the beneficial effects of the creep strain interactions on creep-fatigue life are very substantial, and that the detrimental load interaction effects are usually insignificant. Experimental results obtained from creep-fatigue tests conducted on MAR-M-247, a nickel-base superalloy, at 1600sp°F showed good agreement with analytically determined creep-fatigue life behavior.

Hailu, Sissay

104

Comparison of Tensile Fatigue Resistance and Constant Life Diagrams for Several Potential Wind Turbine Blade Laminates  

Microsoft Academic Search

New fatigue test results are presented for four multidirectional laminates of current and potential interest for wind turbine blades, representing three types of fibers: E-glass, WindStrandTM glass, and carbon, all with epoxy resins. A broad range of loading conditions are included for two of the laminates, with the results represented as mean and 95\\/95 confidence level constant life diagrams. The

Daniel D. Samborsky; Timothy J. Wilson; John F. Mandell

2009-01-01

105

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

Microsoft Academic Search

This paper presents a quantitative analysis of the fatigue loads in a down wind, yaw-controlled, fixed pitch, two-bladed teetered-rotor wind turbine using proportional-integral, full-state optimal, and fuzzy logic controllers. Time-domain simulation data is generated using the EASY5x\\/WT software developed at the University of Texas at El Paso. The simulation data reveal that the choice of controller type, or the controller

K. C. Wu; R. De La Guardia

1996-01-01

106

Prevention of fatigue failures in elastic coupling discs and in fan blades  

Microsoft Academic Search

It is proven by fatigue tests that the generalized SN curve is an invariant in relation to a load cycle asymmetry. It is shown by tests on a large batch of coupling elastic discs and fan blades that the SN curve, represented in relative stresses (relative to the endurance limit Sar), i.e. S\\/Sar-N, can be effectively applied to studies of

L. A. Pereyaslavets

1996-01-01

107

71 FR 19928 - Aging Aircraft Program: Widespread Fatigue Damage  

Federal Register 2010, 2011, 2012, 2013

...rules regarding aviation safety is found...Subtitle VII, Aviation Programs, describes...civil aircraft in air commerce by prescribing...Title: Widespread Fatigue Damage. Summary...holders and foreign air carriers and foreign...Aircraft Values = Aviation Specialists Group...performed additional fatigue tests,...

2006-04-18

108

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

Microsoft Academic Search

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

Thomas N Claytor; Curtt N Ammerman; Gyu Hae Park; Kevin M Farinholt; Charles R Farrar; Marie K Atterbury

2010-01-01

109

Mechanisms of fatigue damage in boron/aluminum composites  

NASA Technical Reports Server (NTRS)

Tensile fatigue tests were conducted on several laminates of boron/aluminum (6061-0). In laminates with 0 deg fibers on the outside, an analysis that identifies "shakedown" conditions predicted the stress amplitude below which no fatigue damage accumulated. A fatigue damage accumulation model which relates matrix fatigue cracking and the overall laminate properties is described. A model for the saturation damage stage development is presented, that identical laminates, tested in directions 90 deg apart (such that one layup has 90 deg outer plies and the other 0 deg), have different fatigue behaviors due to the stacking sequence. The 90 deg plies on the surface develop cracks earlier than predicted by shakedown. An attempt was made to explain this stacking sequence effect. Variable load history effects on the fatigue damage response were investigated. Tests reveal that for a given stress ratio the specimen seeks the saturation damage state for the largest stress range to which it is subjected. It was also found that little damage is generated by shifting a given stress range down, whereas significant damage may be created by shifting it upward. The laminate stresses were always tensile.

Johnson, W. S.

1980-01-01

110

Ultrasonic and Acoustic Emission Detection of Fatigue Damage.  

National Technical Information Service (NTIS)

The purpose of the present research is to optimize existing ultrasonic and acoustic emission techniques and to investigate new ones for early detection of fatigue damage in aluminum alloys used in aircraft construction. Ultrasonic attenuation measurements...

R. E. Green R. B. Pond

1978-01-01

111

Estimation of Peak Probability Functions and Structural Fatigue Damage.  

National Technical Information Service (NTIS)

This report develops theoretical and statistical formulas for estimating peak probability functions and structural fatigue damage. Narrowband Gaussian processes, wideband Gaussian processes, and non-Gaussian processes are considered. Results cover both si...

J. S. Bendat R. E. Beckwith S. C. Choi

1967-01-01

112

Mean stress and the exhaustion of fatigue-damage resistance  

NASA Technical Reports Server (NTRS)

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

Berkovits, Avraham

1989-01-01

113

Exoelectron emission from torsional fatigue damage in hardened steels  

Microsoft Academic Search

Exoelectron emission associated with surface fatigue damage in two types of steel was measured by means of an ultraviolet\\u000a laser scanning system. The localized emission from damage areas in quenched and tempered 1541 steel increased systematically\\u000a with continued fatigue cycling. Plots of emissionvs cycles were in good agreement with earlier results for 1018 steel. Much of this emission resulted from

William J. Baxter

1977-01-01

114

Fatigue damage analysis on body shell of a passenger vehicle  

Microsoft Academic Search

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

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

2002-01-01

115

An experiemental and computational study of the aerodynamics of turbine blades with damage  

NASA Astrophysics Data System (ADS)

Investigations have been made of the aerodynamic effects of in-service damage on the performance of axial turbine blades. Two aspects of blade damage were considered: surface roughening and trailing edge damage. The work is related to gas turbine engine health monitoring. Correlations for the effects of surface roughness were developed based on a database obtained from Kind et al. (1998). The correlations account for the effects of the roughness height as well as the location and extent of the roughness patch on the blade surface. The effect of trailing edge damage at transonic flow conditions was investigated both experimentally and computationally. Computational investigation was conducted for only trailing-edge damage using a three- dimensional Navier-Stokes solver developed by Dawes (1988). The computations with trailing edge damage represent a novel application of the code and the wind tunnel measurements were therefore used to validate the computations. Results showed that surface roughening and trailing edge damage produced significantly different aerodynamic behavior of the flow. Surface roughening largely influences the profile losses and trailing edge damage has a considerable effect on the flow deviation. The effect of trailing edge damage on the loss characteristics of the blades was found to be fairly small over the full range of flow conditions. In fact, the overall measured profile losses were actually lower for 20% damage than for the undamaged blade. The measured flow deviation increased with the increase in damage size as well as cascade exit Mach number. Computational investigations were made to identify the parameters that influence flow deviation in turbines with both undamaged and damaged blades so that correlations could be developed. It was found that the deviation is primarily determined by the blade loading towards the trailing edge. The blade row parameters which influence this pressure difference were identified. The deviation correlation for undamaged blades is applicable for subsonic flow cases and that for damaged blades is applicable for the full range of Mach numbers studied. The new subsonic deviation correlation for undamaged blades appears to be significantly more successful than existing correlations. The three dimensional Navier-Stokes solver of Dawes predicted many of the measured results for damaged blades. Particularly, predictions of deviation for different undamaged and damaged blade geometries were found to be quite satisfactory and the code was extensively used to generate deviation data to supplement experimental measurements. (Abstract shortened by UMI.)

Islam, Alamgir M. T.

1999-10-01

116

Detect, troubleshoot gas-turbine blade failures  

Microsoft Academic Search

Approximately 40% of all gas-turbine failures stem from blading problems. This article describes state-of-the-art condition monitoring technologies that can help avoid or minimize the damage, and troubleshoot failures when they occur. In today`s gas-turbine (GT) fleet, predominant blade-failure mechanism and commonly affected components include: low-cycle fatigue--compressor and turbine disks; high-cycle fatigue--compressor and turbine blades and disks, compressor stator vanes; thermal

Meher-Homji

1995-01-01

117

A probabilistic fatigue analysis of multiple site damage  

NASA Astrophysics Data System (ADS)

The variability in initial crack size and fatigue crack growth is incorporated in a probabilistic model that is used to predict the fatigue lives for unstiffened aluminum alloy panels containing multiple site damage (MSD). The uncertainty of the damage in the MSD panel is represented by a distribution of fatigue crack lengths that are analytically derived from equivalent initial flaw sizes. The variability in fatigue crack growth rate is characterized by stochastic descriptions of crack growth parameters for a modified Paris crack growth law. A Monte-Carlo simulation explicitly describes the MSD panel by randomly selecting values from the stochastic variables and then grows the MSD cracks with a deterministic fatigue model until the panel fails. Different simulations investigate the influences of the fatigue variability on the distributions of remaining fatigue lives. Six cases that consider fixed and variable conditions of initial crack size and fatigue crack growth rate are examined. The crack size distribution exhibited a dominant effect on the remaining fatigue life distribution, and the variable crack growth rate exhibited a lesser effect on the distribution. In addition, the probabilistic model predicted that only a small percentage of the life remains after a lead crack develops in the MSD panel.

Rohrbaugh, S. M.; Ruff, D.; Hillberry, B. M.; McCabe, G.; Grandt, A. F., Jr.

1994-09-01

118

Role of foreign-object damage on thresholds for high-cycle fatigue in Ti6Al4V  

Microsoft Academic Search

The increasing incidence of military aircraft engine failures that can be traced to high-cycle fatigue (HCF) has prompted\\u000a a reassessment of the design methodologies for HCF-critical components, such as turbine blades and disks. Because of the high-frequency\\u000a vibratory loading involved, damagetolerant design methodologies based on a threshold for no crack growth offer a preferred\\u000a approach. As impact damage from ingested

J. O. Peters; B. L. Boyce; A. W. Thompson; R. O. Ritchie; O. Roder

2000-01-01

119

High Cycle Fatigue Crack Initiation Study of Case Blade Alloy Rene 125  

NASA Technical Reports Server (NTRS)

This study was conducted in order to investigate and document the high cycle fatigue crack initiation characteristics of blade alloy Rene 125 as cast by three commercially available processes. This alloy is typically used in turbine blade applications. It is currently being considered as a candidate alloy for high T3 compressor airfoil applications. This effort is part of NASA's Advanced Subsonic Technology (AST) program which aims to develop improved capabilities for the next generation subsonic gas turbine engine for commercial carriers. Wrought alloys, which are customarily used for airfoils in the compressor, cannot meet the property goals at the higher compressor exit temperatures that would be required for advanced ultra-high bypass engines. As a result cast alloys are currently being considered for such applications. Traditional blade materials such as Rene 125 have the high temperature capabilities required for such applications. However, the implementation of cast alloys in compressor airfoil applications where airfoils are typically much thinner does raise some issues of concern such as thin wall castability, casting cleaningness, and susceptibility to high-cycle fatigue (HCF) loading.

Kantzos, P.; Gayda, J.; Miner, R. V.; Telesman, J.; Dickerson, P.

2000-01-01

120

Influence of foreign-object damage on crack initiation and early crack growth during high-cycle fatigue of Ti–6Al–4V  

Microsoft Academic Search

The objective of this work is to provide a rationale approach to define the limiting conditions for high-cycle fatigue (HCF) in the presence of foreign-object damage (FOD). This study focused on the role of simulated FOD in affecting the initiation and early growth of small surface fatigue cracks in a Ti–6Al–4V alloy, processed for typical turbine blade applications. Using high-velocity

J. O. Peters; R. O. Ritchie

2000-01-01

121

Investigation on fatigue-creep interaction damage model for solder  

Microsoft Academic Search

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

Na Liu; Xiaoyan Li; Yongchang Yan

2008-01-01

122

Damage Tolerance Improvement of Ti6-4 Fan Blades with Low Plasticity Burnishing  

Microsoft Academic Search

Low plasticity burnishing (LPB) has been demonstrated to increase the damage tolerance of Ti- 6Al-4V fan blades by an order of magnitude. First stage Ti-6Al-4V fan blades were LPB processed using a conventional 4-axis CNC machine tool. LPB dramatically improved surface finish with negligible blade distortion and produced compressive residual stresses of -690 MPa (-100 ksi) through the entire thickness

P. S. Prevéy; D. J. Hornbach; J. T. Cammett; R. Ravindranath

123

Damage Mechanisms in High Cycle Fatigue.  

National Technical Information Service (NTIS)

This program was designed to allow interaction between MURI investigators and Southwest Research Institute and to allow SwRI to perform independent research on high cycle fatigue mechanisms. The program goals were met. Two students performed experiments w...

D. L. Davidson

1999-01-01

124

Multiaxial Fatigue Damage in Metals. Final Report.  

National Technical Information Service (NTIS)

This review summarizes empirical trends and discusses available life prediction approaches. An evaluation of three of the more promising approaches for predicting multiaxial fatigue life is then presented. Evaluation of the approaches is based on the lite...

A. Rostami D. Nelson

1985-01-01

125

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

126

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

127

Fatigue Strength and Evaluation of Creep Damage During Fatigue Cycling of Inconel Alloy 625.  

National Technical Information Service (NTIS)

Evaluation of high strain rate and corresponding low strain rate tests indicate no creep-fatigue interaction. For T greater than or equal to 900 exp 0 C, creep damage predominates during the cyclic straining. For tests in which creep damage is largely sup...

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

1983-01-01

128

WISPER and WISPERX: Final definition of two standardised fatigue loading sequences for wind turbine blades  

NASA Astrophysics Data System (ADS)

Relevant information used to develop WISPER (Wind turbine reference Spectrum) and WISPERX, standardized variable amplitude test loading histories for use in the fatigue design of horizontal axis wind turbine blades, is presented. WISPER and WISPERX are based on flap load service measurements on nine different horizontal axis wind turbines, covering a wide range of materials, rotor diameters and geographical locations. Their backgrounds are reported, basic data and associated data handling procedures are described, and quantitative data analysis results and statistical information on both standards are presented. The information given will enable fatigue specialists to judge whether the standard will suit their test objectives and to check for correct application of the load sequences on their test equipment.

Tenhave, A. A.

1992-09-01

129

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

NASA Astrophysics Data System (ADS)

The load spectrum unposed upon a horizontal-axis wind turbine blade is typically decomposed into two primary bending moments; flap and edgewise bending. The critical fatigue loads (stress cycles) imposed on the blade may not be on one of these axes, especially if die two bending loads are in-phase with one another. To quantify the correlation of these two bending moments and determine the impact of this correlation on off-axis fatigue loads, an extensive data set for a typical wind turbine blade is examined. The results are compared using their respective cycle count matrices. These results illustrate that the harmonic components of die principal bending stresses are correlated, and that the random components are not. The analysis techniques described in the paper provide the turbine designer with a spectral technique for combining primary bending spectra into off-axis fatigue loads.

Sutherland, H. J.

130

Developing impact and fatigue damage prognosis solutions for composites  

NASA Astrophysics Data System (ADS)

An approach to developing a damage prognosis solution that integrates advanced sensing technology, data interrogation procedures for damage detection, novel model validation and uncertainty quantification techniques, and reliability-based decision-making algorithms is summarized in this article. In parallel, experimental efforts are underway to deliver a proof-of-principle technology demonstration by assessing impact damage and predicting the subsequent fatigue damage accumulation in a composite plate. This article provides an overview of the various technologies that are being integrated to address this damage prognosis problem.

Farrar, Charles; Hemez, Francois; Park, Gyuhae; Sohn, Hoon; Robertson, Amy; Williams, Todd

2004-03-01

131

Effect of Helicopter Main Rotor Blade Damage on the Rotor Disk (Whole Rotor) Motion.  

National Technical Information Service (NTIS)

When a helicopter main rotor blade is ballistically damaged, an imbalance is created in the rotor, causing the rotor disk to execute unwanted motions, which are detrimental to performance. The normally smooth-flying helicopter develops new vibrations that...

J. Fries

2000-01-01

132

Evaluation of the New B-REX Fatigue Testing System for Multi-Megawatt Wind Turbine Blades: Preprint  

Microsoft Academic Search

The National Renewable Energy Laboratory (NREL) recently developed a new hybrid fatigue testing system called the Blade Resonance Excitation (B-REX) test system. The new system uses 65% less energy to test large wind turbine blades in half the time of NREL's dual-axis forced-displacement test method with lower equipment and operating costs. The B-REX is a dual-axis test system that combines

D. White; W. Musial; S. Engberg

2004-01-01

133

FATIGUE DAMAGE ACCUMULATION MECHANISMS IN STRUCTURAL FILMS  

Microsoft Academic Search

The maturation of thin film processing technologies has made it possible to manufacture micron-scale structures such as microelectromechanical systems (MEMS) from a variety of ductile and brittle materials. In contrast to conventional applications, these micron-scale structures and components are almost immediately employed in safety critical applications with little regard for crack initiation and growth phenomena such as fatigue. Furthermore, these

C. L. Muhlstein

134

Linear and nonlinear acoustic control of accumulated fatigue damage in steel  

Microsoft Academic Search

We present results of linear and nonlinear acoustic testing of steel samples with different levels of fatigue damage. The steel specimens were tested under programed cyclic loading on a fatigue testing machine and accumulated different levels of fatigue damage. No visible surface-crack formations during fatigue cycling were observed. In other words, the emphasis was placed on the characterization of continued

Alexander Sutin; Yulian Kin; Paul Johnson

2001-01-01

135

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

136

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

SciTech Connect

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

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

1999-03-04

137

Long-term fatigue life loss of turbine blades owing to noncharacteristic harmonic currents in asynchronous HVDC links  

Microsoft Academic Search

The long-term effect of noncharacteristic harmonic currents in asynchronous HVDC links on fatigue life expenditure in turbine–generator blades is studied in this paper. Because the frequencies of the two main harmonic current terms are subsynchronous and offer a probability distribution due to the asynchronous operation in a HVDC link, a systematic fatigue estimation approach was devised to investigate the long-term

Jong-Ian Tsai; Chi-Hshiung Lin; Ta-Peng Tsao

2003-01-01

138

Damage detection of engine bladed-disks using multivariate statistical analysis  

NASA Astrophysics Data System (ADS)

The timely detection of damage in aero-engine bladed-disks is an extremely important and challenging research topic. Bladed-disks have high modal density and, particularly, their vibration responses are subject to significant uncertainties due to manufacturing tolerance (blade-to-blade difference or mistuning), operating condition change and sensor noise. In this study, we present a new methodology for the on-line damage detection of engine bladed-disks using their vibratory responses during spin-up or spin-down operations which can be measured by blade-tip-timing sensing technique. We apply a principle component analysis (PCA)-based approach for data compression, feature extraction, and denoising. The non-model based damage detection is achieved by analyzing the change between response features of the healthy structure and of the damaged one. We facilitate such comparison by incorporating the Hotelling's statistic T2 analysis, which yields damage declaration with a given confidence level. The effectiveness of the method is demonstrated by case studies.

Fang, X.; Tang, J.

2006-04-01

139

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

Microsoft Academic Search

Ligaments can be subjected to creep and fatigue damage when loaded to higher than normal stresses due to injury of a complementary joint restraint. Continuum damage mechanics (CDM) assumes that diffuse damage accumulates in a material, thereby reducing the effective cross-sectional area and leading to eventual rupture. The objective of this study was to apply CDM modelling to ligament creep

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

2007-01-01

140

Fatigue damage analysis under variable amplitude cycling  

NASA Technical Reports Server (NTRS)

This paper explores the suitability of a recently proposed mean stress parameter and introduces a nonlinear damage accumulation procedure. Data covering a range of positive and negative stress ratios from +0.6 to -2.66, for several aluminum alloys and steels, are assembled and shown to be well correlated by a simple damage parameter. A nonlinear damage accumulation postulate is advanced to replace the usual linear procedure. Results of critical experiments performed to assess the suitability of the postulate are introduced and shown to support a non-linear criterion. The implications of this work related to variable amplitude life prediction are discussed.

Leis, B. N.; Forte, T. P.

1983-01-01

141

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

142

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

Microsoft Academic Search

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

S. D. Hughes; W. D. Musial; T. Stensland

1999-01-01

143

Sliding contact fatigue damage in layered ceramic structures.  

PubMed

Porcelain-veneered restorations often chip and fracture from repeated occlusal loading, making fatigue studies relevant. Most fatigue studies are limited to uni-axial loading without sliding motion. We hypothesized that bi-axial loading (contact-load-slide-liftoff, simulating a masticatory cycle), as compared with uni-axial loading, accelerates the fatigue of layered ceramics. Monolithic glass plates were epoxy-joined to polycarbonate substrates as a transparent model for an all-ceramic crown on dentin. Uni-and bi-axial cyclic contact was applied through a hard sphere in water, by means of a mouth-motion simulator apparatus. The uni-axial (contact-load-hold-liftoff) and traditional R-ratio fatigue (indenter never leaves the specimen surface) produced similar lifespans, while bi-axial fatigue was more severe. The accelerated crack growth rate in bi-axial fatigue is attributed to enhanced tensile stresses at the trailing edges of a moving indenter. Fracture mechanics descriptions for damage evolution in brittle materials loaded repeatedly with a sliding sphere are provided. Clinical relevance is addressed. PMID:17959894

Kim, J-W; Kim, J-H; Thompson, V P; Zhang, Y

2007-11-01

144

Damage estimates for European and US sites using the US high-cycle fatigue data base.  

National Technical Information Service (NTIS)

This paper uses two high-cycle fatigue data bases, US blade materials and one for European materials the service lifetime of a wind turbine blade sit WISPER load spectrum for northern European sit 19921 and the WISPER protocol load spectrum farm sites. Th...

H. J. Sutherland

1996-01-01

145

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

146

Fatigue damage development of various CFRP-laminates  

NASA Technical Reports Server (NTRS)

The chronic strength and fatigue behavior of a woven carbon-fiber reinforced laminate in a balanced eight-shaft satin weave style was compared to nonwoven laminates with an equivalent cross-ply layup. Half the fibers were arranged in the direction of the load and the other half perpendicular to it. Two types of nonwoven laminates consisting of continuous fibers and aligned discontinuous fibers, both produced from carbon fiber prepregs, were studied. The cross-ply laminate with continuous fiber showed the best characteristics with regard to both static strength and fatigue. The similarities and differences in damage mechanisms in the laminates are described.

Schulte, K.; Baron, CH.

1988-01-01

147

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

148

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

149

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

150

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

151

Thermal fatigue damage of Cu-Cr-Zr alloys  

NASA Astrophysics Data System (ADS)

The primary aim of this investigation is to examine thermal fatigue damage (TFD) in Cu-Cr-Zr alloys used in High Heat Flux components of Tokamak and its subsystems. Thermal fatigue experiments have been carried out between 290 °C and 30 °C, which is analogous to the condition of service application on two Cu-Cr-Zr alloys having different aging treatments. The extents of TFD have been examined by standard measurements of electrical conductivity, lattice strain, residual stress and dynamic elastic modulus, supplemented by characterizations of microstructure and determination of hardness and tensile properties. The results lead to infer that the relative amounts of damage are different in the two alloys which are further dependent on their aging conditions; the reasons for the observed difference have been explained. The operative mechanisms of TFD are revealed to be as formation and subsequent coalescence of microvoids, and/or initiation and growth of microcracks.

Chatterjee, Arya; Mitra, R.; Chakraborty, A. K.; Rotti, C.; Ray, K. K.

2013-11-01

152

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

153

Fatigue Crack Growth Database for Damage Tolerance Analysis  

NASA Technical Reports Server (NTRS)

The objective of this project was to begin the process of developing a fatigue crack growth database (FCGD) of metallic materials for use in damage tolerance analysis of aircraft structure. For this initial effort, crack growth rate data in the NASGRO (Registered trademark) database, the United States Air Force Damage Tolerant Design Handbook, and other publicly available sources were examined and used to develop a database that characterizes crack growth behavior for specific applications (materials). The focus of this effort was on materials for general commercial aircraft applications, including large transport airplanes, small transport commuter airplanes, general aviation airplanes, and rotorcraft. The end products of this project are the FCGD software and this report. The specific goal of this effort was to present fatigue crack growth data in three usable formats: (1) NASGRO equation parameters, (2) Walker equation parameters, and (3) tabular data points. The development of this FCGD will begin the process of developing a consistent set of standard fatigue crack growth material properties. It is envisioned that the end product of the process will be a general repository for credible and well-documented fracture properties that may be used as a default standard in damage tolerance analyses.

Forman, R. G.; Shivakumar, V.; Cardinal, J. W.; Williams, L. C.; McKeighan, P. C.

2005-01-01

154

Crack initiation under thermal fatigue: An overview of CEA experience. Part I: Thermal fatigue appears to be more damaging than uniaxial isothermal fatigue  

Microsoft Academic Search

For nuclear reactor components, uniaxial isothermal fatigue curves are used to estimate the crack initiation under thermal fatigue. However, such approach would be not sufficient in some cases where cracking was observed. To investigate differences between uniaxial and thermal fatigue damage, tests have been carried out using the thermal fatigue devices SPLASH and FAT3D: a bi-dimensional (2D) loading condition is

A. Fissolo; S. Amiable; O. Ancelet; F. Mermaz; J. M. Stelmaszyk; A. Constantinescu; C. Robertson; L. Vincent; V. Maillot; F. Bouchet

2009-01-01

155

Prediction of sand particle trajectories and sand erosion damage on helicopter rotor blades  

NASA Astrophysics Data System (ADS)

Therefore, in this dissertation, accurate and time-efficient methodologies were developed for performing sand particle tracking and predicting sand erosion damage on actual helicopter rotor blades under realistic hover and vertical lift conditions. In this dissertation, first, injection (release) conditions of solid particles with new injection parameter, sand particle mass flow rate (SPmFR), were specified to deal with the effect of non-uniform and unsteady flow conditions surrounding at each injection point from which solid particles are released. The SPmFR defines the number of solid particles released from the same injection position per unit time. Secondly, a general definition of erosion rate, "mass or volume loss from the metal surface due to the impact of a unit "mass" of solid particles" was also modified by multiplying with SPmFR in order to solve the limitation for predicting erosion damage on actual helicopter rotor blade. Next, a suitable empirical particle rebound model and an erosion damage model for spherical sand particles with diameters ranging from 10 microm to 500 microm impacting on the material Ti-6A1-4V, the material of helicopter rotor blade, were developed. Finally, C++ language based codes in the form of User Defined Functions (UDFs) were developed and implemented into the commercially available multi-dimensional viscous flow solver ANSYS-FLUENT in order to develop and integrate with the general purpose flow solver, ANSYS-FLUENT, for a specific Lagrangian particle trajectory computing algorithm and rebound and erosion quantification purposes. In the erosion simulation, a reasonably accurate fluid flow solution is necessary. In order to validate the numerical results obtained in this dissertation, computations for flow-only around 2D RAE2822 airfoil and 3D rotating rotor blade (NACA0012) without any sand particle were performed. In the comparison of these results with experimental results, it is found that the flow solutions are in good agreement with the experimental data. Next, second computational validation for flow around the SC1095 airfoil for various turbulence models were performed in order to select a suitable turbulence model. These results concluded that numerical results with k -- o SST model have a reasonably best accuracy. Relative inflow conditions to the blade section of helicopter rotor blades are highly dependent upon rotor blade geometric conditions and helicopter rotor operational conditions. Therefore, in this dissertation, 3D erosion simulations for four different rotating blades with uniform airfoil profile (SC1095) were performed in order to understand the details of erosion mechanism. These results indicate that erosion patterns including maximum erosion rate position and the extent of erosion damaged area on the blade section were highly dependent upon a spanwise twist distribution. It is found that the magnitude of erosion damage on the blade section is affected by not a spanwise twist but a swept tip. Next, in this dissertation, UH-60A helicopter rotor blades rotating in the computational domain for various collective pitch angles and climb velocities were simulated. These results indicate that overall erosion characteristics for helicopter rotor blades can be considered to be not dependent upon these operational parameters though there is a little difference in the magnitude of erosion damage and the maximum erosion rate position. These results concluded that a hover condition can be chosen as a reference operational condition for predicting erosion characteristics or for investigating erosion reduction methods. The final phase of this research is a generalization for particle trajectories and erosion characteristics on 3D helicopter rotor blades in order to reduce very expensive erosion computational cost. The generalized results show that aerodynamic and erosion characteristics for a 3D rotor blade can be predicted by using the 2D airfoil results for corresponding relative inflow angle of attack with coefficient for inflow velocity magnitude and

Shin, Bong Gun

156

The effect of combined cycle fatigue upon the fatigue performance of TI–6AL–4V fan blade material  

Microsoft Academic Search

Samples of Ti–6Al–4V (wt.%) were tested to failure under low cycle fatigue (LCF), high cycle fatigue (HCF), and combined cycle fatigue (CCF), respectively, in order to ascertain the effects of the combined cycle situation upon the total fatigue life. The results indicate that the effect of the combined loading is variable and dependent upon the conditions during testing. It has

C. Dungey; P. Bowen

2004-01-01

157

Estimation of fatigue damage parameters using guided wave technique  

NASA Astrophysics Data System (ADS)

In the present work we have considered the problem of monitoring a fatigue crack growth in a thin plate specimen. The problem is first solved analytically by modeling the structure with a cyclic plastic zone around the crack. The damaged region is modeled as a visco-elastic zone and other regions are modeled as elastic zones. Using the one-dimensional guided wave model, the reflected and transmitted energies of the guided waves from the fatigue crack and plastic zone are studied. Experimental study of the reflected and transmitted energies is done using guided waves generated and received by piezoelectric wafers. The reflected and transmitted energies are derived at various cycles of fatigue loading till the failure of the structure. Validation of the results from the analytical model is done by comparing the results obtained from the experiments. The reflected and transmitted energy is related to the size of crack size or the magnitude of loading. Using crack size and the nature of loading, a method is proposed to estimate the fatigue life using fracture mechanics approach.

Rathod, V. T.; Roy Mahapatra, D.

2014-03-01

158

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

159

Determination of Turbine Blade Life from Engine Field Data  

NASA Technical Reports Server (NTRS)

It is probable that no two engine companies determine the life of their engines or their components in the same way or apply the same experience and safety factors to their designs. Knowing the failure mode that is most likely to occur minimizes the amount of uncertainty and simplifies failure and life analysis. Available data regarding failure mode for aircraft engine blades, while favoring low-cycle, thermal mechanical fatigue as the controlling mode of failure, are not definitive. Sixteen high-pressure turbine (HPT) T-1 blade sets were removed from commercial aircraft engines that had been commercially flown by a single airline and inspected for damage. Each set contained 82 blades. The damage was cataloged into three categories related to their mode of failure: (1) Thermal-mechanical fatigue, (2) Oxidation/Erosion, and (3) "Other." From these field data, the turbine blade life was determined as well as the lives related to individual blade failure modes using Johnson-Weibull analysis. A simplified formula for calculating turbine blade life and reliability was formulated. The L(sub 10) blade life was calculated to be 2427 cycles (11 077 hr). The resulting blade life attributed to oxidation/erosion equaled that attributed to thermal-mechanical fatigue. The category that contributed most to blade failure was Other. If there were there no blade failures attributed to oxidation/erosion and thermal-mechanical fatigue, the overall blade L(sub 10) life would increase approximately 11 to 17 percent.

Zaretsky, Erwin V.; Litt, Jonathan S.; Hendricks, Robert C.; Soditus, Sherry M.

2012-01-01

160

Increasing the FOD tolerance of composites. [gas turbine engine blade foreign object damage  

NASA Technical Reports Server (NTRS)

An experimental program was conducted for the purpose of increasing the foreign object damage tolerance of resin matrix composites in gas turbine engine fan blade applications. The superhybrid concept consisting of a resin matrix composite core surrounded by a sheath of boron/aluminum and titanium was found to be the most promising approach.

Novak, R. C.

1978-01-01

161

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

Microsoft Academic Search

One of the most sensitive problems regarding the application of SHM (Structural Health Monitoring) is found in the aeronautical segment. This field presents the necessity of monitoring small structural changes representing damage, due both to economic aspects and safety. In this contribution two helicopter blade structures (pertaining to a civil and a military helicopter) are studied. In both cases, two

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

2008-01-01

162

Accuracy enhancement of fatigue damage counting using design sensitivity analysis  

NASA Astrophysics Data System (ADS)

Recent studies have suggested fatigue damage counting of a linear elastic system using only the output data; design sensitivity analysis based on the transmissibility function was studied in order to identify the most sensitive response location under intact conditions. The design sensitivity index was derived to be proportional to the response energy at the measured point through reformulation of the previous equation for the sensitivity index. The accuracy of the damage counting method can be enhanced with design sensitivity analysis by selecting the location with the maximum response energy; the method is optimally robust against unexpected noise in the output data. Simulation and testing of a notched simple specimen under uniaxial excitation were used to verify that sensitivity analysis enhances the accuracy of the predicted damage counting.

Kim, Chan-Jung; Lee, Bong-Hyun; Kang, Yeon June; Ahn, Hyeong-Joon

2014-06-01

163

Assessment of material fatigue damage using nonlinear vibro-modulation technique  

Microsoft Academic Search

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

Andrei Zagrai; Dimitri Donskoy; Alexander Chudnovsky; Hudson Wu

2001-01-01

164

Fatigue damage model for injection-molded short glass fibre reinforced thermoplastics  

Microsoft Academic Search

The present paper is a contribution to the phenomenological modelling of fatigue non-linear cumulative diffuse damage in short glass fibre reinforced thermoplastic matrix composites. In such materials, fatigue damage kinetic exhibits three stages, namely: (i) material softening and damage initiation, (ii) coalescence and propagation of micro-cracks and (iii) macroscopic cracks propagation and material failure. The proposed model is built in

H. Nouri; F. Meraghni; P. Lory

2009-01-01

165

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

166

Damage assessment of small-scale wind turbine blade using piezoelectric sensors  

NASA Astrophysics Data System (ADS)

Real-time structural health monitoring (SHM) systems are applied many fields. Recently, the interest about wind energy was increased by the demand of clean energy in the world and many researches were actively performed for applying SHM technology to wind turbine systems. Piezoelectric sensor is one kind of sensor which is widely used for SHM system to assess damage creation. In this paper, the small scale wind turbine blade was fabricated and health monitoring of the blade was performed using the piezoelectric sensor. The quasi-static bending test of the blade was carried out and the PVDF (Polyvinylidene fluoride) sensors, which are polymer type piezoelectric materials, were used for health monitoring. Two-cycle test was performed; the load was applied during 350 sec and removed at the first cycle, and load was applied again until the blade was broken completely at the second cycle. The voltage of PVDF sensors were measured during the quasi-static bending test in order to find out the moment when the damage occurrence started. The voltage of the sensor critically changed at the moment of damage occurred.

Rim, Mi-Sun; Kim, Sang-Woo; Kim, Eun-Ho; Lee, In

2012-03-01

167

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

168

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

PubMed

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

Leinenbach, C; Eifler, D

2009-09-01

169

Multiple damage identification on a wind turbine blade using a structural neural system  

NASA Astrophysics Data System (ADS)

A large number of sensors are required to perform real-time structural health monitoring (SHM) to detect acoustic emissions (AE) produced by damage growth on large complicated structures. This requires a large number of high sampling rate data acquisition channels to analyze high frequency signals. To overcome the cost and complexity of having such a large data acquisition system, a structural neural system (SNS) was developed. The SNS reduces the required number of data acquisition channels and predicts the location of damage within a sensor grid. The sensor grid uses interconnected sensor nodes to form continuous sensors. The combination of continuous sensors and the biomimetic parallel processing of the SNS tremendously reduce the complexity of SHM. A wave simulation algorithm (WSA) was developed to understand the flexural wave propagation in composite structures and to utilize the code for developing the SNS. Simulation of AE responses in a plate and comparison with experimental results are shown in the paper. The SNS was recently tested by a team of researchers from University of Cincinnati and North Carolina A&T State University during a quasi-static proof test of a 9 meter long wind turbine blade at the National Renewable Energy Laboratory (NREL) test facility in Golden, Colorado. Twelve piezoelectric sensor nodes were used to form four continuous sensors to monitor the condition of the blade during the test. The four continuous sensors are used as inputs to the SNS. There are only two analog output channels of the SNS, and these signals are digitized and analyzed in a computer to detect damage. In the test of the wind turbine blade, multiple damages were identified and later verified by sectioning of the blade. The results of damage identification using the SNS during this proof test will be shown in this paper. Overall, the SNS is very sensitive and can detect damage on complex structures with ribs, joints, and different materials, and the system relatively inexpensive and simple to implement on large structures.

Kirikera, Goutham R.; Schulz, Mark J.; Sundaresan, Mannur J.

2007-03-01

170

75 FR 793 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures  

Federal Register 2010, 2011, 2012, 2013

...to the Office of Management and Budget (OMB...Damage Tolerance and Fatigue Evaluation of Composite...considered in the fatigue evaluation; (3...procedures to minimize the risk of catastrophic failure...considered in the fatigue evaluation; (3...procedures to minimize the risk of catastrophic...

2010-01-06

171

Fatigue crack initiation and damage evolution of unnotched titanium matrix composites  

Microsoft Academic Search

Fatigue crack initiation, multiplication, matrix crack density evolution, and stiffness reduction of several unnotched SCS-6 silicon carbide fiber-reinforced titanium and titanium aluminide matrix composites have been investigated experimentally and analytically. The effects of the thickness of the interfacial reaction layer and fiber coating on fatigue crack initiation life, crack growth rate, and fatigue damage evolution of the composites were examined.

Yung-Chiun Her

1998-01-01

172

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

Microsoft Academic Search

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

Veers

1981-01-01

173

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

174

Study of crack initiation or damage in very high cycle fatigue using ultrasonic fatigue test and microstructure analysis.  

PubMed

Fatigue damage behaviors of four metal materials in the very high cycle fatigue (VHCF) regime have been studied using ultrasonic fatigue test and microstructure analysis. The results show that the fatigue crack initiation in VHCF regime could occur at subsurface non-defect fatigue crack origin (SNDFCO), where the accumulated cyclic strains or damage in the specimens were highly localized, especially in the materials with some softer phase, where the local maximum strain can be eight times higher than the average strain value in the specimen. This high strain localization can cause a local plasticity exhaustion that leads to a stress concentration and consequently fatigue crack initiation, and finally the formation of SNDFCO. For pure single phase austenitic material, strain localization can also occur due to dislocation accumulation at or near grain boundaries, which can become fatigue crack initiation origin in the VHCF regime. The results in this study show that fatigue damage and crack initiation mechanisms in the VHCF regime can be different in different metals due to the mechanisms for local plasticity exhaustion. PMID:23850182

Chai, Guocai; Zhou, Nian

2013-12-01

175

Effects of foreign object damage from small hard particles on the high-cycle fatigue life of titanium-(6)aluminum-(4)vanadium  

NASA Astrophysics Data System (ADS)

Thin rectangular samples of Ti-6Al-4V were damaged by four methods to represent foreign object damage found in turbine engine blades: (1) impact with 2 mm. and 5 mm diameter glass spheres at 305 m/s, (2) impact with 2 mm and 4 mm diameter steel spheres at 305 m/s, (3) quasi-static displacement controlled indentation using steel chisels with 1 mm, 2 nun and 5 mm diameter tips and (4) shearing notches with a 2 mm. diameter chisel point under a quasi-static loading condition. Finite element analysis was used to study the relationship between the stress state created by the plastic damage and the fatigue strength. A new method of quantifying the amount of plastic damage from multiple methods was developed. The fatigue strength required for crack initiation at 10E7 cycles was found to be a function of the total depth from the edge of the undeformed specimen up to the end of the plastically deformed zone. For damage depths less than 1750 mum, the reduction in fatigue strength is proportional to the depth of total damage. For depths > 1750 mum, there appears to be a threshold value of fatigue strength.

Hamrick, Joseph L., II

176

Effects of fatigue induced damage on the longitudinal fracture resistance of cortical bone.  

PubMed

As a composite material, cortical bone accumulates fatigue microdamage through the repetitive loading of everyday activity (e.g. walking). The accumulation of fatigue microdamage is thought to contribute to the occurrence of fragility fractures in older people. Therefore it is beneficial to understand the relationship between microcrack accumulation and the fracture resistance of cortical bone. Twenty longitudinally orientated compact tension fracture specimens were machined from a single bovine femur, ten specimens were assigned to both the control and fatigue damaged groups. The damaged group underwent a fatigue loading protocol to induce microdamage which was assessed via fluorescent microscopy. Following fatigue loading, non-linear fracture resistance tests were undertaken on both the control and damaged groups using the J-integral method. The interaction of the crack path with the fatigue induced damage and inherent toughening mechanisms were then observed using fluorescent microscopy. The results of this study show that fatigue induced damage reduces the initiation toughness of cortical bone and the growth toughness within the damage zone by three distinct mechanisms of fatigue-fracture interaction. Further analysis of the J-integral fracture resistance showed both the elastic and plastic component were reduced in the damaged group. For the elastic component this was attributed to a decreased number of ligament bridges in the crack wake while for the plastic component this was attributed to the presence of pre-existing fatigue microcracks preventing energy absorption by the formation of new microcracks. PMID:24715332

Fletcher, Lloyd; Codrington, John; Parkinson, Ian

2014-07-01

177

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

Microsoft Academic Search

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

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

178

ACOUSTIC EMISSION MONITORING DURING CERTIFICATION TESTING OF WIND TURBINE BLADES  

Microsoft Academic Search

Wind turbine blade certification tests, comprising a static test, a fatigue test, and finally a residual strength test, often involve sudden audible cracking sounds from somewhere within the blade, without the operators being able to locate the noise source, or to determine whether damage (minor or major) has occurred. A current EC-funded research project is looking at the possibility of

A G Dutton; M J Blanch; P Vionis; D Lekou; D R V van Delft; P A Joosse; A Anastassopoulos; D Kouroussis; T Kossivas; T. P. Philippidis; Y. G. Kolaxis; G Fernando; A Proust

179

Acoustic Emission Monitoring of Small Wind Turbine Blades  

Microsoft Academic Search

Wind turbine blade certification tests, comprising a static test, a fatigue test, and finally a residual strength test, often involve sudden audible cracking sounds from somewhere within the blade, without the operators being able to locate the noise source, or to determine whether damage (minor or major) has occurred. A current EC-funded research project is looking at the possibility of

P. A. Joosse; A. G. Dutton; D. A. Kouroussis; T. P. Philippidis; P. S. Vionis

2002-01-01

180

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

181

Damage in adhesively bonded CFRP joints: Sinusoidal and impact-fatigue  

Microsoft Academic Search

The main aim of this paper is to investigate the behaviour of adhesively bonded CFRP joints subjected to cyclic low-velocity impacts and to compare this with fracture in specimens tested in standard fatigue (i.e. non-impacting, constant amplitude, sinusoidal fatigue). It is seen that the accumulated energy associated with damage in impact-fatigue is significantly lower than that associated with similar damage

J. P. Casas-Rodriguez; I. A. Ashcroft; V. V. Silberschmidt

2008-01-01

182

Knee joint neuromuscular activation performance during muscle damage and superimposed fatigue  

Microsoft Academic Search

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

Claire Minshull; Roger Eston; David Rees; Nigel Gleeson

2012-01-01

183

Thermal fatigue tests on disruption-damaged first-wall components  

Microsoft Academic Search

The possible synergistic effects between the thermal damage of a plasma disruption and the thermal fatigue lifetime of a bare first wall are investigated. The heat flux of a typical plasma disruption was applied on three stainless steel first-wall mock-ups by means of an electron beam gun. Then these damaged components were subjected to a thermal fatigue test to study

M. Merola; R. Matera; F. Sevini; G. Vieider

1997-01-01

184

Statistical pattern analysis of ultrasonic signals for fatigue damage detection in mechanical structures  

Microsoft Academic Search

This paper addresses online monitoring of fatigue damage in polycrystalline alloy structures based on statistical pattern analysis of ultrasonic sensor signals. The real-time data-driven method for fatigue damage monitoring is based on the concepts derived from statistical mechanics, symbolic dynamics and statistical pattern identification. The underlying concept is detection and identification of small changes in statistical patterns of ultrasonic data

Shalabh Gupta; Dheeraj S. Singh; Asok Ray

2008-01-01

185

High Cycle Fatigue Damage Model for Delamination Crack Growth in CF\\/Epoxy Composite Laminates  

Microsoft Academic Search

This article presents the development of a fatigue damage model which helps to carry out simulation of the evolution of delamination in the laminated composite structures under cyclic loadings. A classical interface damage evolution law, which is commonly used to predict the static debonding process, is modified further to incorporate fatigue delamination effects due to high cycle loadings. An improved

Laurent Gornet; Hassan Ijaz

2011-01-01

186

A Numerical Fatigue Damage Model for Life Scatter of MEMS Devices  

Microsoft Academic Search

This paper presents a fatigue damage model to estimate fatigue lives of microelectromechanical systems (MEMS) devices and account for the effects of topological randomness of material microstructure. For this purpose, the damage mechanics modeling approach is incorporated into a new Voronoi finite-element model (VFEM). The VFEM developed for this investigation is able to consider both intergranular crack initiation (debonding) and

Behrooz Jalalahmadi; Farshid Sadeghi; Dimitrios Peroulis

2009-01-01

187

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

188

14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.  

Code of Federal Regulations, 2010 CFR

...structural failure, or partial failure, the effect on damage tolerance...or (2) Catastrophic failure caused by sonic cracks is...critical; (2) Uncontained fan blade impact; (3) Uncontained engine failure; or (4)...

2009-01-01

189

Impact behavior of filament-wound graphite/epoxy fan blades. [foreign object damage to turbofan engines  

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 m/sec retained their structural integrity. Two blades were each impacted with a 454-g slice of a 908-g simulated bird at a tip speed of 263 deg and impact angles of 22 deg 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. The results of a failure mode analysis are also discussed.

Bowles, K. J.

1978-01-01

190

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

191

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

192

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

193

Thermomechanical fatigue life assessment of aluminium components using the damage rate model of Sehitoglu  

Microsoft Academic Search

Different lifetime approaches were tested to fulfil the requirements for the fatigue analysis of engine components made of aluminium. Besides damage parameters and energy criteria, the complex damage rate model of Neu\\/Sehitoglu was evaluated. Approximately 20 parameters have to be determined to take into account damage due to mechanical fatigue, oxidation and creep.Many LCF- and TMF-tests, including experiments in argon

Robert Minichmayr; Martin Riedler; Gerhard Winter; Heinz Leitner; Wilfried Eichlseder

2008-01-01

194

Damage Assessment of CFRP [90/±45/0] Composite Laminates over Fatigue Cycles  

NASA Astrophysics Data System (ADS)

The present paper develops a stiffness-based model to characterize the progressive fatigue damage in quasi-isotropic carbon fiber reinforced polymer (CFRP) [90/±45/0] composite laminates with various stacking sequences. The damage model is 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 plies of 90°, 0° and angle-ply laminates of ±45° as the number of cycles progresses. The proposed model accumulates damages of constituent plies constructing [90/±45/0] laminates by means of weighting factor ? 90, ? 0 and ? 45. These weighting factors were defined based on the damage progress over fatigue cycles within the plies 90°, 0° and ±45° of the composite laminates. Damage model has been verified using CFRP [90/±45/0] laminates samples made of graphite/epoxy 3501-6/AS4. Experimental fatigue damage data of [90/±45/0] composite laminates have fell between the predicted damage curves of 0°, 90° plies and ±45°, 0/±45° laminates over life cycles at various stress levels. Predicted damage results for CFRP [90/±45/0] laminates showed good agreement with experimental data. Effect of stacking sequence on the model of stiffness reduction has been assessed and it showed that proposed fatigue damage model successfully recognizes the changes in mechanism of fatigue damage development in quasi-isotropic composite laminates.

Ahmadzadeh, G. R.; Shirazi, A.; Varvani-Farahani, A.

2011-12-01

195

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

196

Finite Element Analysis on the Impact-Induced Damage of Composite Fan Blades Subjected to a Bird Strike  

NASA Astrophysics Data System (ADS)

Carbon fiber-reinforced composites have been recently applied for engine fan blades, because of their high specific strength. In the design of the fan blade, the bird-strike impact is one of the greatest concerns, since impact-induced damage can lead to the engine stall. This study presented a numerical method to analyze the bird-strike impact as a soft-body impact on cantilevered composite panel. Especially, we coupled a stabilized dynamic contact analysis, which enables predicting impact force on the panel appropriately, with laminate damage analysis to predict the impact-induced progressive damage in the composite. This method was verified through the comparison with the experimental results. With the numerical method, we investigated the effect of impact condition, blade thickness and shape on the impact-induced damage in composite fan blade subjected to a bird strike. An intermediate blade thickness and a large blade curvature help improving the bird-striking impact resistance of the composite.

Nishikawa, Masaaki; Hemmi, Kei; Park, Sangchul; Nadabe, Takeaki; Takeda, Nobuo

197

Fatigue and damage tolerance behaviour of corroded 2024 T351 aircraft aluminum alloy  

Microsoft Academic Search

The fatigue and damage tolerance behaviour of pre-corroded 2024 T351 aluminum alloy specimens has been investigated and compared to the behaviour of the uncorroded material. The experimental investigation was performed on specimens pre-corroded in exfoliation corrosion environment and included the derivation of S–N and fatigue crack growth curves as well as measurements of fracture toughness. The fatigue crack growth tests

Al. Th. Kermanidis; P. V. Petroyiannis; Sp. G. Pantelakis

2005-01-01

198

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

Microsoft Academic Search

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

Manjoine

1994-01-01

199

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

200

Fatigue Damage in CFRP Woven Fabric Composites through Dynamic Modulus Measurements  

SciTech Connect

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

Chiaki Miyasaka; K. L. Telschow

2004-07-01

201

Fatigue and Residual Strength Characteristics of Fiber Metal Laminates Subjected to Incidental Damage.  

National Technical Information Service (NTIS)

The fatigue and residual strength characteristics of the fiber metal laminates GLARE and ARALL, following damage typically encountered in the service environment, were investigated. Comparative impact tests showed a gereral trend of increasing impact resi...

R. Fredell, A. Vlot, M. Verbruggen

1992-01-01

202

Development of Methods to Observe Material's Fatigue and Corrosion Damage through Surface Characteristics Monitoring.  

National Technical Information Service (NTIS)

White Light Interferometry was used for surface characterization accompanied by other methods to observe materials damage caused by corrosion and fatigue. White Light Interferometry has a spatial resolution of 0.2 micrometer and depth resolution of 3 nm. ...

L. B. Simon J. L. Schroeder

2000-01-01

203

Fatigue damage monitoring for basalt fiber reinforced polymer composites using acoustic emission technique  

NASA Astrophysics Data System (ADS)

Basalt fiber reinforced polymer (BFRP) is a structural material with superior mechanical properties. In this study, unidirectional BFRP laminates with 14 layers are made with the hand lay-up method. Then, the acoustic emission technique (AE) combined with the scanning electronic microscope (SEM) technique is employed to monitor the fatigue damage evolution of the BFRP plates in the fatigue loading tests. Time-frequency analysis using the wavelet transform technique is proposed to analyze the received AE signal instead of the peak frequency method. A comparison between AE signals and SEM images indicates that the multi-frequency peaks picked from the time-frequency curves of AE signals reflect the accumulated fatigue damage evolution and fatigue damage patterns. Furthermore, seven damage patterns, that is, matrix cracking, delamination, fiber fracture and their combinations, are identified from the time-frequency curves of the AE signals.

Wang, Wentao; Li, Hui; Qu, Zhi

2012-03-01

204

Fatigue testing and damage development in continuous fiber reinforced metal matrix composites  

NASA Technical Reports Server (NTRS)

A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

Johnson, W. S.

1988-01-01

205

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

206

In-situ ultrasonic surface wave assessment of mechanical fatigue damage accumulation in metal matrix composites  

Microsoft Academic Search

This study demonstrates that an in-situ nondestructive, ultrasonic surface wave technique can successfully detect the onset and extent of matrix cracking fatigue damage in a titanium metal matrix composite (MMC). A quasi-isotropic [0\\/±45\\/90]sSCS-6\\/Timetal® 21S MMC material was used for room temperature fatigue tests and the resultant matrix cracking damage was ultrasonically monitored in situ as a function of cycle count.

Patrick T. MacLellan; David A. Stubbs; Prasanna Karpur

1995-01-01

207

Sliding Contact Fatigue Damage in Layered Ceramic Structures  

Microsoft Academic Search

Porcelain-veneered restorations often chip and fracture from repeated occlusal loading, making fatigue studies relevant. Most fatigue studies are limited to uni-axial loading without sliding motion. We hypothesized that bi-axial loading (contact-load-slide-liftoff, simulating a masticatory cycle), as compared with uni-axial loading, accelerates the fatigue of layered ceramics. Monolithic glass plates were epoxy-joined to polycarbonate substrates as a transparent model for an

J.-W. Kim; J.-H. Kim; V. P. Thompson; Y. Zhang

2007-01-01

208

Fatigue-Induced Micro-damage Characterization of Austenitic Stainless Steel 316 Using Innovative Nonlinear Acoustics  

NASA Astrophysics Data System (ADS)

We present innovative nonlinear acoustics for characterizing fatigue-induced micro-damage of austenitic stainless steel 316 subjected to high-cycle fatigue. Various fatigue-driven deformations are accumulated at several positions near the middle of hourglass-shaped specimens. A bell-shaped curve of acoustic nonlinearity as a function of position is observed, and the variation in acoustic nonlinearity is attributed to the evolution of a lattice defect (dislocation) and stress-induced martensite based on transmission electron microscopy (TEM) observations. An oblique incidence technique using a longitudinal waveform is a potentially viable method for characterizing the high-cycle fatigue deformation of austenitic stainless steel 316 alloys.

Chung-Seok, Kim; Kyung-Young, Jhang

2012-06-01

209

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

210

Aeroelastic simulation of wind turbine blades  

Microsoft Academic Search

\\u000a The aim of this chapter is to compute dynamic stresses acting on wind turbine blades. These stresses are essential in predicting\\u000a fatigue of the rotor.\\u000a \\u000a \\u000a The turbine rotor is exposed to wind loading of a cyclic nature, making it vulnerable to cumulative fatigue damage.\\u000a \\u000a \\u000a The approach used in this chapter is based on the analysis of the blade movement, by

Z. L. Mahri; M. S. Rouabah; Z. Said

211

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

212

A low-order model for analysing effects of blade fatigue load control  

NASA Astrophysics Data System (ADS)

A new low-order mathematical model is introduced to analyse blade dynamics and blade load-reducing control strategies for wind turbines. The model consists of a typical wing section model combined with a rotor speed model, leading to four structural degrees of freedom (flapwise, edgewise and torsional blade oscillations and rotor speed). The aerodynamics is described by an unsteady aerodynamic model. The equations of motion are derived in non-linear and linear form. The linear equations of motion are used for stability analysis and control design. The non-linear equations of motion are used for time simulations to evaluate control performance. The stability analysis shows that the model is capable of predicting classical flutter and stall-induced vibrations. The results from the stability analysis are compared with known results, showing good agreement. The model is used to compare the performance of one proportional-integral-derivative controller and two full-state feedback controllers. Copyright

Kallesøe, B. S.

2006-09-01

213

Fatigue life variability and reliability analysis of a wind turbine blade.  

National Technical Information Service (NTIS)

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 variab...

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

1991-01-01

214

Fatigue damage mechanisms in (0, 90) s composite laminate  

Microsoft Academic Search

The high strength to weight ratio of CFRP composite materials is certainly an attractive structural characteristic. However, in many circumstances consideration must also be given to the fatigue properties. It is well established by now that the failure of multidirectional composite laminates during either monotonic load or fatigue initiates in the plies that are most desoriented with respect to the

E. Petitpas; M. Renault; D. Valentin

1989-01-01

215

Modelling fatigue damage accumulation in two-dimensional Voronoi honeycombs  

Microsoft Academic Search

Trabecular bone, a porous, cellular type of bone found at the ends of the long bones and within the vertebrae, is subject to cyclic compressive loading resulting from the activities of daily living. Such fatigue loading can result in fracture, especially in vertebrae of patients with osteoporosis. As an initial step in understanding compressive fatigue of trabecular bone we previously

Grant Schaffner; Xiang-Dong E Guo; Matthew J Silva; Lorna J Gibson

2000-01-01

216

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

217

Fatigue behavior of line pipes subjected to severe mechanical damage  

SciTech Connect

Fatigue behavior of electrically resistance welded (ERW) line pipes with a gouge in a dent was experimentally investigated. After denting and machining a gouge, fluctuating internal pressure was applied to line pipes. The fatigue behavior differed above and below the threshold Q(Q{sub th}), as a function of defect size and fracture toughness. When Q {lt} Q{sub th}, ductile crack growth was observed with a consequent decrease in fatigue life. On the contrary, fatigue crack growth was observed when Q {ge} Q{sub th}. Fatigue life was predictable with an experimentally based power law equation incorporating dent depth, gouge depth, and hoop stress amplitude when Q {ge} Q{sub th}.

Hagiwara, N.; Oguchi, N.

1999-11-01

218

Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads  

NASA Astrophysics Data System (ADS)

This paper studies and compares the effects of pull–pull and 3-point bending cyclic loadings on the mechanical fatigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respectively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.

Ren, Huai-Hui; Wang, Xi-Shu

2014-04-01

219

Corrosion and fatigue failure analysis of a forced draft fan blade  

Microsoft Academic Search

The present work was carried out to investigate the failure mechanism of a power plant forced draft fan (FDF) blade made of 2014-T6 Al alloy, using visual examination, microstructural characterizations, study of the fracture surface and hardness testing. Based on the obtained results, surface defects including corrosion pits due to the existence of Cl ion and also erosion pits due

H. Kazempour-Liacy; M. Mehdizadeh; M. Akbari-Garakani; S. Abouali

2011-01-01

220

Improved drive-train and blade fatigue mitigation in flexible wind turbines using disturbance utilization control  

Microsoft Academic Search

Modern wind turbines are experiencing rapid growth in both physical size and rated capacity. As wind turbines grow larger with necessarily lighter construction materials, dampening flexible modes with active control becomes more critical. In this paper we apply the theory of ldquodisturbance utilization controlrdquo (DUC) to a 600 kW upwind machine to dampen drive-train torsion and blade flap while regulating

Glenn A. Parker; C. D. Johnson

2009-01-01

221

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

222

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

223

APPLICATION OF POSITRON ANNIHILATION TO FATIGUE AND PLASTIC DAMAGE DETECTION IN SA508 AND TYPE 304 STEELS  

Microsoft Academic Search

The positron annihilation(PA) lineshape analysis method was applied to evaluate the fatigue damage in SA508 Ierritic steel and type 304 stainless steel, and the damage distribution in a type 304 sample plastically deformed by 3-point bending. The PA was found to be effective to detect early stages of the fatigue damage (less than 25% of the cycles to failure) in

M. UCHIDA; K. YOSHIDA; Y. G. NAKAGAWA; A. J. ALLEN; A. D. WHAPHAM

1992-01-01

224

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

PubMed Central

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

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

2011-01-01

225

Computational fluid dynamics analysis of blade tip clearances on hemodynamic performance and blood damage in a centrifugal ventricular assist device.  

PubMed

An important challenge facing the design of turbodynamic ventricular assist devices (VADs) intended for long-term support is the optimization of the flow path geometry to maximize hydraulic performance while minimizing shear-stress-induced hemolysis and thrombosis. For unshrouded centrifugal, mixed-flow and axial-flow blood pumps, the complex flow patterns within the blade tip clearance between the lengthwise upper surface of the rotating impeller blades and the stationary pump housing have a dramatic effect on both the hydrodynamic performance and the blood damage production. Detailed computational fluid dynamics (CFD) analyses were performed in this study to investigate such flow behavior in blade tip clearance region for a centrifugal blood pump representing a scaled-up version of a prototype pediatric VAD. Nominal flow conditions were analyzed at a flow rate of 2.5 L/min and rotor speed of 3000 rpm with three blade tip clearances of 50, 100, and 200 microm. CFD simulations predicted a decrease in the averaged tip leakage flow rate and an increase in pump head and axial thrust with decreasing blade tip clearances from 200 to 50 microm. The predicted hemolysis, however, exhibited a unimodal relationship, having a minimum at 100 microm compared to 50 microm and 200 microm. Experimental data corroborate these predictions. Detailed flow patterns observed in this study revealed interesting fluid dynamic features associated with the blade tip clearances, such as the generation and dissipation of tip leakage vortex and its interaction with the primary flow in the blade-blade passages. Quantitative calculations suggested the existence of an optimal blade tip clearance by which hydraulic efficiency can be maximized and hemolysis minimized. PMID:19832736

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

2010-05-01

226

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

227

A LIFETIME PREDICTION MODEL FOR SINGLE CRYSTAL SUPERALLOYS SUBJECTED TO THERMOMECHANICAL CREEP-FATIGUE-OXIDATION DAMAGE  

Microsoft Academic Search

This paper contains a brief description of a lifetime prediction model for Single Crystal Superalloys operated at high temperatures and subjected to creep, fatigue and oxidation damage mechanisms. The model aims at predicting engineering life to crack initiation and describing dominatin g damage mechanisms and their non-linear interaction in such materials. Microcracks propagation from initial casting pores is considered as

A. M. ALAM; L. REMY

228

Classical fatigue analysis and load cycle mix-event damage accumulation in fibre reinforced laminates  

Microsoft Academic Search

A survey of Classical Fatigue Analysis predictions has been carried out for fibre reinforced composite laminate specimens subjected to spectrum loading. Results illustrate acceptable predictions for matrix dominated composites but unreliable and generally un-conservative predictions for fibre dominated composites. A need for cyclic damage event definition relating to composite behaviour has been identified. Load-cycle “Mix” damage events have been proposed

P. A. Filis; I. R. Farrow; I. P. Bond

2004-01-01

229

The relationship between cement fatigue damage and implant surface finish in proximal femoral prostheses  

Microsoft Academic Search

The majority of cemented femoral hip replacements fail as a consequence of loosening. One design feature that may affect loosening rates is implant surface finish. To determine whether or not surface finish effects fatigue damage accumulation in a bone cement mantle, we developed an experimental model of the implanted proximal femur that allows visualisation of damage growth in the cement

A. B. Lennon; B. A. O. McCormack; P. J. Prendergast

2003-01-01

230

Fatigue and residual strength characteristics of fiber metal laminates subjected to incidental damage  

NASA Astrophysics Data System (ADS)

The fatigue and residual strength characteristics of the fiber metal laminates GLARE and ARALL, following damage typically encountered in the service environment, were investigated. Comparative impact tests showed a gereral trend of increasing impact resistance from carbon thermoplastic composites (poorest) to ARALL, monolithic aluminum 2024-T3, and GLARE 3 (best). Fatigue and residual strength tests carried out on impact and scratch damaged fiber metal laminates demonstrated the excellent tolerance of laminates to in-service damage. The extremely slow crack growth characteristics of laminates were not deteriorated by scratches. Impacts which caused perforations in GLARE and ARALL continued to exhibit the extremely slow fatigue crack growth for which the laminates are known. Repair criteria based on the blunt notch strength of the laminates have been proposed for in-service damage to riveted fiber metal laminate structures. Techniques used for the repair of aluminium structures can apply to laminates.

Fredell, Robert; Vlot, Ad; Verbruggen, Marc

1992-12-01

231

Evaluation of micro-damage accumulation in holed plain-woven CFRP composite under fatigue loading  

NASA Astrophysics Data System (ADS)

Fluorescence method was used to detect the micro-damage caused by fatigue in a plain-woven carbon fiber reinforced polymer (CFRP). Fluorescence measurement is a method which estimates micro-damage by measuring fluorescent intensity change inside materials. The principle is, larger micro-damage means larger plastic strain, thus more space in that damaged spot which allows more fluorescent dyes coming in the material. By detecting fluorescent intensity in CFRP layer by layer using confocal laser microscopy, micro-damage can be estimated. Results show that there's a good relationship between micro-damage and fluorescent intensity gradient.

Ying, Jia; Nishikawa, Masaaki; Hojo, Masaki

2014-03-01

232

Structural investigation of composite wind turbine blade considering various load cases and fatigue life  

Microsoft Academic Search

This study proposes a structural design for developing a medium scale composite wind turbine blade made of E-glass\\/epoxy for a 750kW class horizontal axis wind turbine system. The design loads were determined from various load cases specified at the IEC61400-1 international specification and GL regulations for the wind energy conversion system. A specific composite structure configuration, which can effectively endure

C. Kong; J. Bang; Y. Sugiyama

2005-01-01

233

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

NASA Technical Reports Server (NTRS)

NASA has conducted an Airframe Structural Integrity Program to develop the methodology to predict the onset of widespread fatigue damage to 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-splice-joint 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).

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

1998-01-01

234

Simplification of Fatigue Test Requirements for Damage Tolerance of Composite Interstage Launch Vehicle Hardware  

NASA Technical Reports Server (NTRS)

The issue of fatigue loading of structures composed of composite materials is considered in a requirements document that is currently in place for manned launch vehicles. By taking into account the short life of these parts, coupled with design considerations, it is demonstrated that the necessary coupon level fatigue data collapse to a static case. Data from a literature review of past studies that examined compressive fatigue loading after impact and data generated from this experimental study are presented to support this finding. Damage growth, in the form of infrared thermography, was difficult to detect due to rapid degradation of compressive properties once damage growth initiated. Unrealistically high fatigue amplitudes were needed to fail 5 of 15 specimens before 10,000 cycles were reached. Since a typical vehicle structure, such as the Ares I interstage, only experiences a few cycles near limit load, it is concluded that static compression after impact (CAI) strength data will suffice for most launch vehicle structures.

Nettles, A. T.; Hodge, A. J.; Jackson, J. R.

2010-01-01

235

A physical-base model for life prediction of single crystal turbine blades under creep-fatigue loading and thermal transient conditions  

Microsoft Academic Search

The damage estimation model developed herein can be used to predict service life under creep-fatigue loading in both isothermal (LCF) and variable temperature (TMF) conditions. This model is based upon a careful identification of basic physical mechanisms taking part in the damage process of a unit microstructural element. The damage is, in fact, considered to be the growth of micro

A. Koster; A. M. Alam; L. Rémy

2002-01-01

236

Creep-fatigue damage and life prediction in P92 alloy by focused ultrasound measurements  

Microsoft Academic Search

In the present study, the characteristics of creep damage in P92 alloy were investigated via nondestructive evaluation. Generally,\\u000a as the hold time of a static load increases, the degradation of the material becomes more severe along with a reduction of\\u000a service life. Therefore, in power plants, the reduction of creep-fatigue strength and the creep-fatigue life of high pressure\\u000a vessels at

Bum-joon Kim; Hak-joon Kim; Byeong-soo Lim

2008-01-01

237

Application of positron annihilation line-shape analysis to fatigue damage for nuclear plant materials  

Microsoft Academic Search

Positron annihilation line-shape analysis is sufficiently sensitive to detect microstructural defects such as vacancies and dislocations. We are developing a portable positron annihilation system and applying this technique to fatigue damage in type 316 stainless steel and SA508 low alloy steel. The positron annihilation technique was found to be sensitive in the early fatigue life, i.e. up to 10% of

Noriyoshi Maeda; Noriko Nakamura; Misako Uchida; Yoshio Ohta; Kazuo Yoshida

1996-01-01

238

An Intelligent Sensor System for Monitoring Fatigue Damage in Welded Steel Components  

SciTech Connect

A system for monitoring fatigue damage in steel components is described. The sensor, a thin steel sheet with a pre-crack in it, is attached to the component. Its crack length increases by fatigue in service and is recorded using a microcontroller. Measurement is accomplished using conductive tracks in a circuit whose output voltage changes when the crack propagates past a track. Data stored in memory can be remotely downloaded using Bluetooth{sup TM} technology to a PC.

Fernandes, B.; Gaydecki, P. [Department of Instrumentation and Analytical Science, UMIST, PO Box 88, Manchester M60 1QD (United Kingdom); Burdekin, F. Michael [Fatigue Monitoring Bureau, Macclesfield, Sk10 5LX (United Kingdom)

2005-04-09

239

An Intelligent Sensor System for Monitoring Fatigue Damage in Welded Steel Components  

NASA Astrophysics Data System (ADS)

A system for monitoring fatigue damage in steel components is described. The sensor, a thin steel sheet with a pre-crack in it, is attached to the component. Its crack length increases by fatigue in service and is recorded using a microcontroller. Measurement is accomplished using conductive tracks in a circuit whose output voltage changes when the crack propagates past a track. Data stored in memory can be remotely downloaded using Bluetooth™ technology to a PC.

Fernandes, B.; Gaydecki, P.; Burdekin, F. Michael

2005-04-01

240

Analysis of Hysteresis Damage Accumulation and the Effect on Fatigue Life  

Microsoft Academic Search

\\u000a In order to validate an existing energy-based fatigue life prediction understanding, the strain energy accumulation for interrupted\\u000a loading cycles was analyzed. The life prediction method being validated was developed based on the understanding that strain\\u000a energy density accumulated during monotonic fracture is a physical damage quantity that is equal to total cumulative hysteresis\\u000a strain energies in a fatigue process. If

Onome Scott-Emuakpor; Tommy George; Charles Cross; M.-H. Herman Shen

241

Fatigue damage of notched boron/epoxy laminates under constant amplitude loading  

NASA Technical Reports Server (NTRS)

Fatigue damage in (0, + or - 45) and (0, + or - 45,90) boron/epoxy laminates was studied with X-ray radiography and scanning electron microscopy. In addition, limited tests for residual strength and stiffness were performed. The results of this study suggest that in boron/epoxy laminates the 45-degree plies play a key role in the fatigue process of boron/epoxy laminates that contain them. The fatigue process in the + or - 45-degree plies starts as intralaminar matrix cracks.

Roderick, G. L.; Whitcomb, J. D.

1976-01-01

242

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

NASA Astrophysics Data System (ADS)

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

2014-05-01

243

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

244

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) will be discussed. Results from titanium matrix/silicon-carbide fiber composites will be the primary topic of discussion. Results have been obtained from both notched and unnotched specimens at room and elevated temperatures. The stress in the 0 deg fibers has been indentified as the controlling factor in fatigue life. Fatigue of the notched specimens indicated that cracks can grow many fiber spacings in the matrix materials without breaking fibers.

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

1990-01-01

245

Evaluation of fatigue damage in steel structural components by magnetoelastic Barkhausen signal analysis  

SciTech Connect

This paper is concerned with using a magnetic technique for the evaluation of fatigue damage in steel structural components. It is shown that Barkhausen effect measurements can be used to indicate impending failure due to fatigue under certain conditions. The Barkhausen signal amplitude is known to be highly sensitive to changes in density and distribution of dislocations in materials. The sensitivity of Barkhausen signal amplitude to fatigue damage has been studied in the low-cycle fatigue regime using smooth tensile specimens of a medium strength steel. The Barkhausen measurements were taken at depths of penetration of 0.02, 0.07, and 0.2 mm. It was found that changes in magnetic properties are sensitive to microstructural changes taking place at the surface of the material throughout the fatigue life. The changes in the Barkhausen signals have been attributed to distribution of dislocations in stage I and stage II of fatigue life and the formation of a macrocrack in the final stage of fatigue.

Govindaraju, M.R.; Strom, A.; Jiles, D.C.; Biner, S.B.; Chen, Z. (Ames Laboratory and Center for NDE, Iowa State University, Ames, Iowa 50011 (United States))

1993-05-15

246

On the Micromechanism of Fatigue Damage in an Interstitial-Free Steel Sheet  

NASA Astrophysics Data System (ADS)

The micromechanism of fatigue damage in an interstitial-free (IF) steel sheet has been studied using fully reversed stress amplitudes (? ?/2). The stress-life (S-N) curve of the steel sheet has been generated, together with a series of interrupted fatigue tests at each of the chosen ? ?/2, to study the progress of fatigue damage in terms of the initiation, growth, and coalescence of the fatigue cracks on the surfaces of the sheet specimens using scanning electron microscopy. The steel sheet possesses a higher endurance limit (0.98 times its yield strength (YS)), as compared to conventional low-carbon steel sheets. This is attributed to (1) the occurrence of nonpropagating microcracks initiating primarily at the inclusions below the endurance limit and (2) a significant delay in the spread of plastic deformation, until ? ?/2 is close to YS. Above the endurance limit, widespread plastic deformation through slip bands promotes the formation of fatigue cracks at the ferrite grain boundaries and occasionally within a ferrite grain body, as well as at inclusions. Fatigue failure is preceded by the significant growth of grain-boundary cracks over and above those at inclusions and the ferrite grain body. A series of grain-boundary cracks link up to form mesocracks, one of which grows to cause the final failure. The predominance of grain-boundary cracks in the process of fatigue failure is attributed to the lesser cohesive strength of the grain boundaries caused by the depletion of interstitials.

Majumdar, Shrabani; Bhattacharjee, D.; Ray, K. K.

2008-07-01

247

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

248

Improving Fatigue Damage Resistance of Alumina through Surface Grading  

PubMed Central

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

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

2011-01-01

249

Fatigue load spectra for upwind and downwind rotors  

NASA Technical Reports Server (NTRS)

Effect of both alternating and mean load on the fatigue life of an upwind and downwind MOD-2 wind turbine system is presented. It was shown that the fatigue damage varies as the product of the stress range cubed and the maximum stress. Hence, the alternating flapwise load caused by tower shadow and wind gradient is an important factor in determining rotor blade life.

Andrews, J. S.

1978-01-01

250

Thermo-elastic nondestructive evaluation of fatigue damage in PMR-15 resin  

NASA Astrophysics Data System (ADS)

Thermoset polyimide resins are used as the polymer matrix in high temperature composites for aerospace applications such as engine shrouds. At these locations the components have to withstand high temperatures and significant vibration. A number of studies have investigated the effects of thermal exposure on mechanical properties of polyimide resins, and the effects of fatigue on thermoplastics have been discussed at length. However, the effects of fatigue on thermosets, in particular polyimides, have largely been overlooked. In this paper we present studies of nondestructive evaluation of fatigue damage in a thermoset polyimide resin, PMR-15, performed by measuring the changes in the evolution of heat in the samples during cyclic loading. The temperature changes are measured using a high sensitivity IR camera as a function of number of fatigue cycles. Interrupted fatigue tests were performed on four samples. The temperature rise during an increment of fatigue cycling shows two linear regions each with a different slope (region 1 and region 2). Region 1 remains constant for every increment of fatigue, while region 2 increases. The onset of region 2 occurs at the same increase in temperature due to hysteretic heating for all samples. Experimental observations are explained using a phenomenological two phase model based on crosslinking density variations in observed in other thermoset resins at microscopic scales. The results of these experiments are discussed in reference to utilizing this technique for detection and evaluation of fatigue in PMR-15 resin and composites.

Welter, J. T.; Sathish, S.; Tandon, G. P.; Schehl, N.; Cherry, M.; Nalladega, V.; Lindgren, E. A.; Hall, R.

2012-05-01

251

Nonlinear Resonant Ultrasound Spectroscopy (NRUS) applied to fatigue damage evaluation in a pure copper  

NASA Astrophysics Data System (ADS)

We studied a monitoring technique of fatigue damage in 3N polycrystalline copper under a cyclic zero-to-tension loading by the nonlinear resonant ultrasound spectroscopy (NRUS). In NRUS, the resonant frequency of an object is studied as a function of the excitation level. As the excitation level increases, the elastic nonlinearity is manifest by a shift in the resonance frequency. We used an electromagnetic acoustic transducer (EMAT) to monitor NRUS of bulk-shear-wave propagating in the thickness direction of the plate sample. NRUS exhibits much larger sensitivity to the damage accumulation than the velocity. It rapidly increases from 70% of fatigue life to the fracture. The attenuation shows the peak at 80% of the life. This NRUS novel phenomenon is interpreted in terms of dislocation mobility. This technique has potential to assess the damage advance and to predict the fatigue life of metals.

Ohtani, Toshihiro; Ishii, Yutaka

2012-09-01

252

Use of atomic force microscopy for characterizing damage evolution during fatigue  

NASA Astrophysics Data System (ADS)

A study of the development of surface fatigue damage in PH 13-8 Mo stainless steel and copper by atomic force microscopy (AFM) was performed. AFM observations allow highly automated, quantitative characterization of surface deformation with a resolution of 5 nm or better, which is ideal for understanding fatigue damage evolution. A secondary objective was to establish a correlation between fatigue life exhausted and impedance spectroscopy. Strain controlled fatigue tests were conducted both in high and low cycle fatigue regimes, and interruptions of the fatigue tests allowed characterizing the evolution of the surface upset at various life-fractions. In the low strain amplitude tests on stainless steel (Deltaepsilonpl/2 = 0.0026%), surface damage occurred in the shape of narrow streaks at the interface between martensite laths where reverted austenite was present. The streaks eventually coalesced to form crack nuclei. In high strain amplitude tests (Deltaepsilon pl/2 = 0.049%), fatigue surface damage was essentially dominated by the formation of extrusions. In copper, both low (Deltaepsilonpl/2 = 0.061%) and high (Deltaepsilonpl/2 = 0.134%) strain amplitude tests showed the formation of slip bands (mainly extrusions) across entire grains. Protrusions were present only in copper specimens tested at the high strain amplitude. Crack nucleation in the low strain amplitude tests occurred in both materials at the interface between a region that sustained a high level of deformation and one with little evidence of surface upset. This commonality between these two materials that are otherwise very dissimilar in nature suggests a universal scheme for location of fatigue crack nucleation sites during HCF. A procedure was developed in this study to quantitatively characterize the amount of irreversible surface strain. The proposed formalism is applicable to any material, independently of the type of surface damage, and leads to a criterion for crack nucleation based on physical evidence of surface damage. A correlation between fatigue damage and impedance spectroscopy measurements was shown in copper, in particular during the primary cyclic hardening stage. The measurements were however less sensitive to the development of surface upset that occurred beyond that stage.

Cretegny, Laurent

2000-10-01

253

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

254

Determination of Turbine Blade Life from Engine Field Data  

NASA Technical Reports Server (NTRS)

It is probable that no two engine companies determine the life of their engines or their components in the same way or apply the same experience and safety factors to their designs. Knowing the failure mode that is most likely to occur minimizes the amount of uncertainty and simplifies failure and life analysis. Available data regarding failure mode for aircraft engine blades, while favoring low-cycle, thermal-mechanical fatigue (TMF) as the controlling mode of failure, are not definitive. Sixteen high-pressure turbine (HPT) T-1 blade sets were removed from commercial aircraft engines that had been commercially flown by a single airline and inspected for damage. Each set contained 82 blades. The damage was cataloged into three categories related to their mode of failure: (1) TMF, (2) Oxidation/erosion (O/E), and (3) Other. From these field data, the turbine blade life was determined as well as the lives related to individual blade failure modes using Johnson-Weibull analysis. A simplified formula for calculating turbine blade life and reliability was formulated. The L10 blade life was calculated to be 2427 cycles (11 077 hr). The resulting blade life attributed to O/E equaled that attributed to TMF. The category that contributed most to blade failure was Other. If there were no blade failures attributed to O/E and TMF, the overall blade L(sub 10) life would increase approximately 11 to 17 percent.

Zaretsky, Erwin V.; Litt, Jonathan S.; Hendricks, Robert C.; Soditus, Sherry M.

2013-01-01

255

Fatigue damage analysis of aluminized glass fiber composites  

Microsoft Academic Search

Aluminized glass fiber composite with epoxy and polyester matrix were used in this work in order to study fatigue properties and its comparison to conventional glass fiber composites. Until now aluminized glass fiber materials have been only used as decoy flares in military applications. The innovative advantages of these composites, using modified fibers, are potentially the improvement of thermal and

J. M. Ferreira; J. T. B. Pires; J. D. Costa; Z. Y. Zhang; O. A. Errajhi; M. Richardson

2005-01-01

256

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.

257

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

Microsoft Academic Search

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

D. T. Rusk; W. Hoppe

2009-01-01

258

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

259

Evaluation of plane bending fatigue damage in metallic plates using the thin-film flux-gate magnetic sensor  

Microsoft Academic Search

To estimate the amount of fatigue damage in metallic plates such as steel and stainless steel, we have investigated the relationship between the amount of plane bending fatigue damage and residual magnetization. The magnetic flux density in the Z component (Bz) at 1 mm above a specimen caused by residual magnetization is measured by using a thin-film flux-gate magnetic sensor.

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

2002-01-01

260

Infrared thermographic techniques for non-destructive damage characterization of carbon fibre reinforced polymers during tensile fatigue testing  

Microsoft Academic Search

A non-destructive fatigue damage characterization technique is needed in the scope of the development of new processing techniques for carbon fibre reinforced polymer (CFRP) composites. This study investigates two thermographic testing techniques with the aim of providing an in situ characterization technique of damage during fatigue testing of the mentioned CFRP specimens. A passive thermographic approach is used by measuring

R. Steinberger; T. I. Valadas Leitão; E. Ladstätter; G. Pinter; W. Billinger; R. W. Lang

2006-01-01

261

Three technical issues in fatigue damage assessment of nuclear power plant components  

SciTech Connect

This paper addresses three technical issues that affect the fatigue damage assessment of nuclear power plant components: the effect of the environment on the fatigue life, the importance of the loading sequence in calculating the fatigue crack-initiation damage, and the adequacy of current inservice inspection requirements and methods to characterize fatigue cracks. The environmental parameters that affect the fatigue life of carbon and low alloy steel components are the sulphur content in the steel, the temperature, the amount of dissolved oxygen in the coolant, and the presence of oxidizing agents such as copper oxide. The occurrence of large-amplitude stress cycles early in a component's life followed by low-amplitude stress cycles may cause crack initiation at a cumulative usage factor less than 1.0. The current inservice inspection requirements include volumetric inspections of welds but not of some susceptible sites in the base metal. In addition, the conventional ultrasonic testing techniques need to be improved for reliable detection and accurate sizing of fatigue cracks. 28 refs., 4 figs., 1 tab.

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

1991-01-01

262

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

263

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

264

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

265

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

266

Fatigue damage in centrally notched GR/EP laminates  

SciTech Connect

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

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

1990-12-01

267

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

268

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

SciTech Connect

Self-organized substructural arrangements of dislocations formed during cyclic stress-induced fatigue of metals produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter {beta} extracted from acoustic harmonic generation measurements. The contributions to {beta} from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell model [Proc. R. Soc. London, Ser. A 460, 757 (2004)] 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 fatigue damage included in the total volume of material swept out by an interrogating acoustic wave. For cyclic stress-controlled loading at 551 MPa and f{sub WI}=0.013 the model predicts a monotonic increase in {beta} from dislocation substructures of almost 100% from the virgin state to roughly 95% full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, during the last 5% of fatigue life the model predicts a rapid monotonic increase of {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. [NASA Langley Research Center, Mail Stop 231, Hampton, Virginia 23681 (United States)

2006-09-15

269

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

270

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

271

Under-filled BGA solder joint vibration fatigue damage  

Microsoft Academic Search

The paper (1) experimentally determines the survivability\\/durability of the solder joints of ball grid array (BGA) with\\/without under-filled materials when subjected to military vibration environment and (2) develops a vibration fatigue life prediction model, which is qualitatively calibrated by test. A test vehicle (TV), on which various sizes of BGA daisy-chained packages with\\/without under-filled materials, e.g., Hysol (non-reworkable) and Hacthane

T. E. Wong; F. W. Palmieri; H. S. Fenger

2002-01-01

272

Cumulative damage fatigue tests on nuclear reactor Zircaloy-2 fuel tubes at room temperature and 300°C  

NASA Astrophysics Data System (ADS)

Cumulative damage fatigue tests were conducted on the Zircaloy-2 fuel tubes at room temperature and 300°C on the modified Moore type, four-point-loaded, deflection-controlled, rotating bending fatigue testing machine. The cumulative cycle ratio at fracture for the Zircaloy-2 fuel tubes was found to depend on the sequence of loading, stress history, number of cycles of application of the pre-stress and the test temperature. A Hi-Lo type fatigue loading was found to be very much damaging at room temperature and this feature was not observed in the tests at 300°C. Results indicate significant differences in damage interaction and damage propagation under cumulative damage tests at room temperature and at 300°C. Block-loading fatigue tests are suggested as the best method to determine the life-time of Zircaloy-2 fuel tubes under random fatigue loading during their service in the reactor.

Pandarinathan, P. R.; Vasudevan, P.

1980-06-01

273

Thermography inspection for early detection of composite damage in structures during fatigue loading  

NASA Astrophysics Data System (ADS)

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, Jeff P.; Wright, Christopher W.; Bly, James B.

2012-05-01

274

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

275

Fatigue damage rule of LY12CZ aluminium alloy under sequential biaxial loading  

NASA Astrophysics Data System (ADS)

A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ aluminium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-phase are utilized. The fatigue damage cumulative rules under two-level step loading of three loading paths are analyzed. By introducing a parameter ? which is a function of the phase lag angle between the axial and the torsional loading, a new multiaxial nonlinear fatigue damage cumulative model is proposed. The proposed model is evaluated by the experimental data for two-level loading, multi-level loading of LY12CZ aluminium alloy, and multi-level loading of 45 steel. Fatigue lives predicted are within a factor of 2 scatter band.

Wang, YingYu; Zhang, DaChuan; Yao, WeiXing

2014-01-01

276

Modeling of fatigue damage evolution on the basis of the kinetic concept of strength  

Microsoft Academic Search

On the basis of the kinetic theory of strength, a new approach to the modeling of material degradation in cyclic loading has\\u000a been suggested. Assuming that not stress changes, but acting stresses cause the damage growth in materials under fatigue conditions,\\u000a we applied the kinetic theory of strength to model the material degradation. The damage growth per cycle, the effect

Leon Mishnaevsky Jr; Povl Brøndsted

2007-01-01

277

A micro-damage healing model that improves prediction of fatigue life in asphalt mixes  

Microsoft Academic Search

The focus of the current paper is on the development and validation of a micro-damage healing model that improves the ability of an integrated nonlinear viscoelastic, viscoplastic, and viscodamage constitutive model based on continuum damage mechanics for predicting the fatigue life of asphalt paving mixtures. The model parameters of the continuum-based healing model are related to fundamental material properties. Recursive–iterative

Rashid K. Abu Al-Rub; Masoud K. Darabi; Dallas N. Little; Eyad A. Masad

2010-01-01

278

Nondestructive determination of fatigue crack damage in composites using vibration tests.  

NASA Technical Reports Server (NTRS)

The vibration response of glass reinforced epoxy and polyester laminates was investigated. The complex modulus and the damping capacity were measured as fatigue crack damage accumulated. Changes in the Young's modulus as well as the damping capacity correlated with the amount of crack damage. The damping was especially sensitive to debonding of the reinforcement from the resin matrix. Measurement of these vibration response changes shows promise as a means to nondestructively test the structural integrity of filament-reinforced composite structural members.

Dibenedetto, A. T.; Gauchel, J. V.; Thomas, R. L.; Barlow, J. W.

1972-01-01

279

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

280

ORIENTATION EFFECT ON FATIGUE LIFE OF CORROSION DAMAGED AA2024-T3 SPECIMEN  

Microsoft Academic Search

The goal of this study is to correlate fatigue life with corrosion damage in AA2024-T3 with special emphasis on specimen orientation. Corrosion pits ranging from 100 to 400 microns in depth were electrochemically created on the surface of dogbone specimens aligned in five different orientations. A detailed topography of the corrosion pit surface was conducted using white light interference microscopy

Mohammad Khobaib; Chris Kacmar

281

A generalized frequency modified damage function model for high temperature low cycle fatigue life prediction  

Microsoft Academic Search

The models for predicting high temperature low cycle fatigue (HTLCF) life are significant in the design of engineering components and structures working under high temperature and cyclic loading. In this paper, a review of the earlier models is given first, and then a new model for the HTLCF life prediction, a generalized frequency modified damage function (GFMDF) model, is set

Wang Yonglian

1997-01-01

282

Progression of fretting fatigue damage in Ti–6Al–4V  

Microsoft Academic Search

An investigation was conducted to explore the nature of fretting fatigue damage in the stages prior to crack formation. In the unique experimental apparatus employed in this study, where total slip never occurs, several locations on each test specimen exist where cracks can develop due to local contact conditions. Under the test conditions used, not all of the sites had

Alisha Hutson; Shamachary Sathish; Ted Nicholas

2006-01-01

283

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.

Huang, Hong-Zhong; Yuan, Rong

2014-01-01

284

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

Microsoft Academic Search

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

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

1995-01-01

285

The interactions between fatigue, creep and environmental damage in Ti 6246 and Udimet 720Li  

Microsoft Academic Search

The paper reports the results of a comprehensive research programme on two different compressor disc alloys: titanium alloy Ti 6246 and the nickel based superalloy Udimet 720Li. Both alloys are used for disc applications in gas turbine engines under conditions where the rims are exposed to fatigue, creep and environmental damage. The titanium alloy was investigated at temperatures of 80,

W. J. Evans; J. P. Jones; S. Williams

2005-01-01

286

A fatigue damage estimator using RBF, backpropagation, and CID4 neural algorithms  

NASA Technical Reports Server (NTRS)

Fatigue damage estimation using neural networks is described in the paper. Attention is focused on the method of data generation for both the training and test data used by radial basis function (RBF), backpropagation, and CID4 algorithms used in this study. The performance results of the three neural algorithms are analyzed in terms of their strengths and weaknesses in training.

Cios, Krzysztof J.; Tjia, Robert E.; Liu, Ning

1992-01-01

287

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

288

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

289

Dependence of the Perpendicular Residual Leakage Magnetic Flux Density on Fatigue Damage in an Austenitic Stainless Steel  

NASA Astrophysics Data System (ADS)

In order to estimate the amount of plane bending fatigue damage in an austenitic stainless steel (SUS304), we were investigating the relationship between plane bending fatigue damage and the perpendicular residual leakage magnetic flux density caused by martensitic structure induced by plane bending fatigue. A specimen such as SUS304 had been excited in a constant external magnetic field perpendicularly to measure dependence of the perpendicular residual leakage magnetic flux density on plane bending fatigue damage accurately. The Z component of the magnetic flux density at 1 mm above a specimen is measured by using a thin-film flux-gate (FG) magnetic sensor. Residual magnetization is caused by partial martensitic structure in an austenitic stainless steel induced by cyclic bending stress. From our experiments, we can evaluate dependence of the perpendicular residual leakage magnetic flux density on plane bending fatigue damage and know the relationship between growth of a crack and the perpendicular residual leakage magnetic flux density.

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

2003-03-01

290

Fatigue Damage Mechanisms in Advanced Hybrid Titanium Composite Laminates.  

National Technical Information Service (NTIS)

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 previou...

W. S. Johnson D. W. Rhymer

2000-01-01

291

Piezoelectric active sensing techniques for damage detection on wind turbine blades  

Microsoft Academic Search

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

Kevin M. Farinholt; Stuart G. Taylor; Charles R. Farrar

2011-01-01

292

Post-Impact Fatigue Damage Monitoring Using Fiber Bragg Grating Sensors  

PubMed Central

It has been shown that impact damage to composite materials can be revealed by embedded Fiber Bragg Gratings (FBG) as a broadening and splitting of the latter's characteristic narrow peak reflected spectrum. The current work further subjected the impact damaged composite to cyclic loading and found that the FBG spectrum gradually submerged into a rise of background intensity as internal damages progressed. By skipping the impact, directing the impact to positions away from the FBG and examining the extracted fibers, we concluded that the above change is not a result of deterioration/damage of the sensor. It is caused solely by the damages initiated in the composite by the impact and aggravated by fatigue loading. Evolution of the grating spectrum may therefore be used to monitor qualitatively the development of the incurred damages.

Shin, Chow-Shing; Liaw, Shien-Kuei; Yang, Shi-Wei

2014-01-01

293

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

294

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

295

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

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. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:1097-1103, 2014. PMID:24838769

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

2014-09-01

296

Structural-Response Analysis, Fatigue-Life Prediction, and Material Selection for 1 MW Horizontal-Axis Wind-Turbine Blades  

NASA Astrophysics Data System (ADS)

The problem of mechanical design, performance prediction (e.g., flap-wise/ edge-wise bending stiffness, fatigue-controlled life, the extent of bending-to-torsion coupling), and material selection for a prototypical 1 MW horizontal-axis wind turbine (HAWT) blade is investigated using various computer-aided engineering tools. For example, a computer program was developed which can automatically generate both a geometrical model and a full finite-element input deck for a given single HAWT-blade with a given airfoil shape, size, and the type and position of the interior load-bearing longitudinal beam/shear-webs. In addition, composite-material laminate lay-up can be specified and varied in order to obtain a best combination of the blade aerodynamic efficiency and longevity. A simple procedure for HAWT-blade material selection is also developed which attempts to identify the optimal material candidates for a given set of functional requirements, longevity and low weight.

Grujicic, M.; Arakere, G.; Subramanian, E.; Sellappan, V.; Vallejo, A.; Ozen, M.

2010-08-01

297

FATIGUE DAMAGE ACCUMULATION AND MITIGATION IN SILICON STRUCTURAL FILMS  

Microsoft Academic Search

Although a wide variety of structural films have been developed over the past decade, silicon continues to maintain its position as the dominant material in microelectromechanical systems (MEMS). However, the limited damage tolerance of silicon leaves it particularly vulnerable to failure due to crack initiation and subcritical crack growth. Although it is well established that silicon thin films are susceptible

C. L. Muhlstein

298

Active sensing of fatigue damage using embedded ultrasonics  

Microsoft Academic Search

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

Andrei Zagrai; Walter A. Kruse; Vlasi Gigineishvili

2009-01-01

299

Fatigue damage mechanisms in advanced hybrid titanium composite laminates  

Microsoft Academic Search

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

D. W. Rhymer; W. S. Johnson

2002-01-01

300

Matrix Fatigue Damage Evolution in a Longitudinal CFRP Composite  

Microsoft Academic Search

Three point bend tests were conducted on 45o off-axis 60% volume carbon fibre reinforced polymer composites under stress control (stress ratio, R=1) and frequency of 4Hz. This allowed a fundamental study to be carried out on the continuous damage accumulation in the matrix without the influence of delamination. Permanent bending was observed at all stress levels and found to be

A. Plumtree; M. Ostgathe

301

Structural-Response Analysis, Fatigue-Life Prediction, and Material Selection for 1 MW Horizontal-Axis Wind-Turbine Blades  

Microsoft Academic Search

The problem of mechanical design, performance prediction (e.g., flap-wise\\/edge-wise bending stiffness, fatigue-controlled life, the extent of bending-to-torsion coupling), and material selection for a prototypical\\u000a 1 MW horizontal-axis wind turbine (HAWT) blade is investigated using various computer-aided engineering tools. For example,\\u000a a computer program was developed which can automatically generate both a geometrical model and a full finite-element input\\u000a deck for a

M. Grujicic; G. Arakere; E. Subramanian; V. Sellappan; A. Vallejo; M. Ozen

2010-01-01

302

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

NASA Astrophysics Data System (ADS)

Tensile fatigue tests were carried out at 77 K for YBCO-coated conductors fabricated by metal-organic chemical vapor deposition (MOCVD). The S-N relationship, variation of critical current (Ic) during cyclic loading and microscopic fatigue damage were investigated. Fatigue strength at 106 cycles was evaluated to be ?max = 1300 MPa and 890 MPa under the stress ratios of 0.5 and 0.1. Two different mechanisms of fatigue damage, depending on the number of stress cycles to failure, were observed. In one of the fracture mechanisms, fatigue behavior is characterized by overall fracture which occurs at 104-105 cycles. For these specimens, Ic after unloading does not degrade before overall fracture. Although only shallow slip bands were found at the Ag surface, fatigue cracks were found on the Hastelloy C-276 surface of the fractured specimen. These results suggest that overall fracture due to cyclic stress was caused by fatigue of the Hastelloy substrate. In the other fracture mechanism, even though overall fracture did not occur at 106 cycles, a slight decrease of Ic was detected after 105 cycles. No fatigue crack was found on the Hastelloy surface, while deep slip bands corresponding to the initial stage of fatigue crack were observed on the Ag surface. From these results, we concluded that Ic degradation at a high cycle number is attributed to the fatigue of the Ag stabilizing layer.

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

2008-05-01

303

A strain energy density method for the prediction of creep–fatigue damage in high temperature components  

Microsoft Academic Search

The accumulation of creep–fatigue damage over time is the principal damage mechanism which will eventually lead to crack initiation in critical high temperature equipment. A model has been developed that assumes on a macroscopic level that the energy dissipated in the material may be taken as a measure of the creep damage induced in the material and hence the creep

Warwick M. Payten; David W. Dean; Ken U. Snowden

2010-01-01

304

On the feasibility of detecting pre-cracking fatigue damage in metal-matrix composites by ultrasonic techniques  

Microsoft Academic Search

The feasibility of using ultrasonic techniques to detect fatigue damage in metal-matrix composites at an early stage has been investigated theoretically. The lack of direct independent experimental evidence for such damage required damage mechanisms and levels to be postulated in a somewhat arbitrary fashion. Estimates have been made of the effect of matrix porosity, microcrack formation, particle debonding and dislocation

L. W. Anson; R. C. Chivers; K. E. Puttick

1995-01-01

305

Evaluation of plane bending fatigue damage in metallic plates using the thin-film flux-gate magnetic sensor  

NASA Astrophysics Data System (ADS)

To estimate the amount of fatigue damage in metallic plates such as steel and stainless steel, we have investigated the relationship between the amount of plane bending fatigue damage and residual magnetization. The magnetic flux density in the Z component (Bz) at 1 mm above a specimen caused by residual magnetization is measured by using a thin-film flux-gate magnetic sensor. From the results of our experiment, the magnetic flux density has clear dependence on the increase of bending stress and the number of stress cycles in austenitic stainless steel. The distribution of Bz on steel plates is changed by the amount of plane bending fatigue damage. But, the relationship between the change of Bz and the number of stress cycles is not clear in the case of steel plates. In this paper, the relationship between the amount of plane bending fatigue damage and residual magnetization in metallic plates is discussed. .

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

2002-05-01

306

Detection Method of Fatigue Damage in Carbon Steel Using Laser Ultrasonics  

Microsoft Academic Search

Ultrasonic attenuation was measured by the laser ultrasonic technique among the carbon steel specimens which were subjected to five stages of fatigue damage by constant cyclic tensile stress amplitude. Irradiation of a Q-switched laser was used for ultrasonic generation, and a laser interferometer which consists of a frequency-doubled continuous wave laser and a Fabry-Perot etalon was used for detection of

Takao TANAKA; Yasukazu IZAWA

2002-01-01

307

An efficient explicit algorithm for damage-coupled viscoplastic fatigue model  

Microsoft Academic Search

This paper describes the development of an efficient and a robust numerical algorithm for a damage-coupled viscoplastic-fatigue material model. The material chosen for the investigation is eutectic material, Sn–Pb solder, exhibiting strain-softening behavior. The numerical algorithm employs a modified explicit method with adaptive sub-stepping based on the local error control for which the stress (constitutive) Jacobian explicit solution is derived.

A. H. Zhao; C. L. Chow

2007-01-01

308

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

309

The effects of hail damage on the fatigue strength of a graphite\\/epoxy composite laminate  

Microsoft Academic Search

An investigation was undertaken to determine the effects of hail damage on the fatigue strength of a graphite\\/epoxy composite laminate. Skteen-ply coupons were subjected to simulated hail impact by iceballs of 25.4 or 38.1 mm in diameter. Upon impact, the 25.4 mm diameter iceball possessed 7.1 J of kinetic energy, while the 38.1 mm diameter iceball possessed a kinetic energy

Mohammad Mahinfalah; Richard A. Skordahl

1998-01-01

310

TEM observations of fatigue damage accumulation at the surface of the near-? titanium alloy IMI 834  

Microsoft Academic Search

A high performance near-? 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) characterisation of the damage accumulation was performed as a function of depth below the surface on samples from

G. J. Baxter; W. M. Rainforth; L. Grabowski

1996-01-01

311

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

Microsoft Academic Search

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

Takenobu Sakai; Keita Yasui; Shuichi Wakayama

312

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

Microsoft Academic Search

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

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

2008-01-01

313

Fatigue damage of medium carbon steel under sequential application of axial and torsional loading  

Microsoft Academic Search

Fatigue tests were conducted on S45C steel under fully reversed strain control conditions with axial\\/torsional (at) and torsional\\/axial (ta) loading sequences. The linear damage value (n1\\/N 1 + n2\\/N 2) was found to depend on the sequence of loading mode (at or ta), sequence of strain amplitude (low\\/high or high\\/low) and life fraction spent in the first loading. In general,

X. C HEN; D. J IN; K. S. KIM

314

Repeated Plastic Deformation as a Cause of Mechanical Surface Damage in Fatigue, Wear, Fretting-Fatigue, and Rolling Fatigue: A Review.  

National Technical Information Service (NTIS)

Statements bringing together essential features of the fatigue behavior of metal structures in service are reviewed. It is shown that the elementary phenomena of plastic deformation and fatigue crack propagation, which explain the fatigue behaviour of not...

W. Barrois

1979-01-01

315

Parameters identification of fatigue damage model for short glass fiber reinforced polyamide (PA6GF30) using digital image correlation  

Microsoft Academic Search

The work deals with the parameters identification and the experimental validation of a phenomenological model for fatigue anisotropic damage in short glass fiber reinforced polyamide (PA6-GF30). The damage fatigue model has been formulated in terms of strain energy and was implemented into the finite element code ABAQUS\\/Standard through a user defined material subroutine UMAT. The present paper focuses mainly on

F. Meraghni; H. Nouri; N. Bourgeois; C. Czarnota; P. Lory

2011-01-01

316

Thermal fatigue damage in monofilament reinforced copper for heat sink applications in divertor elements  

NASA Astrophysics Data System (ADS)

In fusion reactor systems extreme conditions require materials with high temperature and radiation resistance. The divertor component consists of a plasma facing W plate attached to a Cu heat sink to extract the heat from the nuclear reaction chamber coolant. The Coefficient of Thermal Expansion (CTE) mismatch between the W plate and the Cu heat sink causes interface delamination reducing the long term stability of the divertor. To avert this problem, composites are developed as interlayer materials with a high thermal conducting Cu matrix reinforced with up to 50 vol.% SiC or W monofilaments to increase the mechanical strength and to reduce the CTE mismatch. Thermal stresses are transferred from the macroscopic interface between the components into the bulk of the composite. Oscillating micro stresses may lead to fiber delamination and matrix damage during thermal cycling. Different matrix alloys, fiber materials and interface designs are investigated. In situ neutron diffraction performed during thermal cycling show the effect of bonding strength on the stress amplitudes expected under service conditions. The long term stability is tested by measurements after further ex situ cycling. Thermal fatigue damage and its propagation are visualized by in situ as well as ex situ high resolution synchrotron tomography. The combination of both methods helps to understand the strain induced damage mechanisms. Weak bonding leads to delamination of the fiber-matrix interfaces. Strong bonding causes severe matrix deformation and damage. Fiber cracks originating from sample production cause accumulating thermal fatigue damage during thermal cycling.

Schöbel, M.; Jonke, J.; Degischer, H. P.; Paffenholz, V.; Brendel, A.; Wimpory, R. C.; Di Michiel, M.

2011-02-01

317

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

Microsoft Academic Search

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

P. Lukáš; L. Kunz; M. Svoboda

2005-01-01

318

Applications of a new magnetic monitoring technique to in situ evaluation of fatigue damage in ferrous components  

SciTech Connect

This project consisted of research into the use of magnetic inspection methods for the estimation of fatigue life of nuclear pressure vessel steel. Estimating the mechanical and magnetic properties of ferromagnetic materials are closely interrelated, therefore, measurements of magnetic properties could be used to monitor the evolution of fatigue damage in specimens subjected to cyclic loading. Results have shown that is possible to monitor the fatigue damage nondestructively by magnetic techniques. For example, in load-controlled high-cycle fatigue tests, it has been found that the plastic strain and coercivity accumulate logarithmically during the fatigue process. Thus a quantitative relationship between coercivity and the number of fatigue cycles could be established based on two empirical coefficients, which can be determined from the test conditions and material properties. Also it was found that prediction of the onset of fatigue failure in steels was possible under certain conditions. In strain-controlled low cycle fatigue, critical changes in Barkhausen emissions, coercivity and hysteresis loss occurred in the last ten to twenty percent of fatigue life.

Jiles, D.C.; Biner, S.B.; Govindaraju, M.R.; Chen, Z.J. [Iowa State Univ. of Science and Technology, Ames, IA (United States). Center for Nondestructive Evaluation

1994-06-01

319

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

SciTech Connect

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

Tsai, G.C.

1984-01-01

320

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

2014-05-01

321

Modeling of long-term fatigue damage of soft tissue with stress softening and permanent set effects.  

PubMed

One of the major failure modes of bioprosthetic heart valves is non-calcific structural deterioration due to fatigue of the tissue leaflets. Experimental methods to characterize tissue fatigue properties are complex and time-consuming. A constitutive fatigue model that could be calibrated by isolated material tests would be ideal for investigating the effects of more complex loading conditions. However, there is a lack of tissue fatigue damage models in the literature. To address these limitations, in this study, a phenomenological constitutive model was developed to describe the stress softening and permanent set effects of tissue subjected to long-term cyclic loading. The model was used to capture characteristic uniaxial fatigue data for glutaraldehyde-treated bovine pericardium and was then implemented into finite element software. The simulated fatigue response agreed well with the experimental data and thus demonstrates feasibility of this approach. PMID:22945802

Martin, Caitlin; Sun, Wei

2013-08-01

322

Three-dimensional constitutive model considering transformation-induced damage and resulting fatigue failure in shape memory alloys  

NASA Astrophysics Data System (ADS)

In this work, a constitutive model is developed that describe the behavior of shape memory alloys undergoing a large number of cycles, developing internal damage, and eventually failing. Physical mechanisms associated with martensitic phase transformation occurring during cyclic loadings such as transformation strain generation and recovery, transformation-induced plasticity, and fatigue damage are all taken into account within a thermo-dynamically consistent framework. Fatigue damage is described utilizing a continuum theory of damage. The damage growth rate has been formulated as a function of both the stress state and also the magnitude of the transformation strain, while the complete or partial nature of the transformation cycles is also considered as per experimental observations. Simulation results from the model developed are compared to uniaxial actuation fatigue tests at different stress levels. It is shown that both lifetime and the evolution irrecoverable strain can be accurately simulated.

Hartl, Darren J.; Chemisky, Yves; Meraghni, Fodil

2014-03-01

323

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

324

Probabilistic Fatigue Damage Localization at Unknown Temperatures Using Guided Wave Methods  

NASA Astrophysics Data System (ADS)

This research examines the current challenges of using Lamb wave interrogation methods to localize fatigue crack damage in a complex metallic structural component subjected to unknown temperatures. The goal of this work is to improve damage localization results for a structural component interrogated at an unknown temperature, by developing a probabilistic and reference-free framework for estimating Lamb wave velocities and the damage location. The methodology for damage localization at unknown temperatures includes the following key elements: i) a model that can describe the change in Lamb wave velocities with temperature; ii) the extension of an advanced time-frequency based signal processing technique for enhanced time-of-flight feature extraction from a dispersive signal; iii) the development of a Bayesian damage localization framework incorporating data association and sensor fusion. The technique requires no additional transducers to be installed on a structure, and allows for the estimation of both the temperature and the wave velocity in the component. Additionally, the framework of the algorithm allows it to function completely in an unsupervised manner by probabilistically accounting for all measurement origin uncertainty. The novel algorithm was experimentally validated using an aluminum lug joint with a growing fatigue crack. The lug joint was interrogated using piezoelectric transducers at multiple fatigue crack lengths, and at temperatures between 20°C and 80°C. The results showed that the algorithm could accurately predict the temperature and wave speed of the lug joint. The localization results for the fatigue damage were found to correlate well with the true locations at long crack lengths, but loss of accuracy was observed in localizing small cracks due to time-of-flight measurement errors. To validate the algorithm across a wider range of temperatures the electromechanically coupled LISA/SIM model was used to simulate the effects of temperatures. The numerical results showed that this approach would be capable of experimentally estimating the temperature and velocity in the lug joint for temperatures from -60°C to 150°C. The velocity estimation algorithm was found to significantly increase the accuracy of localization at temperatures above 120°C when error due to incorrect velocity selection begins to outweigh the error due to time-of-flight measurements.

Hensberry, Kevin

325

Panel resonant behavior of wind turbine blades  

Microsoft Academic Search

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

Joshua A. Paquette; Daniel Todd Griffith

2010-01-01

326

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

327

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

328

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

329

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.

330

Damage assessment of alumina fibre-reinforced mullite ceramic matrix composites subjected to cyclic fatigue at ambient and elevated temperatures  

Microsoft Academic Search

The damage evaluation behaviour of alumina fibre-reinforced mullite ceramic matrix composites subjected to cyclic fatigue was investigated by means of acoustic emission (AE) monitoring and forced resonance techniques. AE technique provided sufficient information about the damage initiation and progression in real time whilst the forced resonance (FR) technique allowed the detection of changes in elastic modulus (E) and internal friction

C Kaya; F Kaya; H Mori

2002-01-01

331

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

332

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

333

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

334

Fatigue  

MedlinePLUS

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

335

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

336

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

NASA Astrophysics Data System (ADS)

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

Montesano, John

337

Smoother Turbine Blades Resist Thermal Shock Better  

NASA Technical Reports Server (NTRS)

Surface treatment increases resistance of turbine blades to low-cycle fatigue. Smoothing removes small flaws where cracks start. Intended for blades in turbines subject to thermal shock of rapid starting. No recrystallization occurs at rocket-turbine operating temperatures.

Czerniak, Paul; Longenecker, Kent; Paulus, Don; Ullman, Zane

1991-01-01

338

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

339

Assessment of causes of fracture in 14Kh17N2 steel blades of GTK-25I gas-pumping unit axial-flow compressors  

Microsoft Academic Search

Causes of fracture of the martensitic-ferritic steel blades of the variable inlet guide vane for an axial-flow compressor\\u000a of the gas pumping unit GTK-25I have been studied. There are several stages of blade fracture: corrosion, fatigue, and fracture.\\u000a At the initial state, corrosion damage occurs at the martensite-ferrite interface, which is followed by intragranular corrosion\\u000a damage along martensite needles and

K. A. Yushchenko; V. S. Savchenko; L. V. Chervyakova; V. I. Izbash; G. Solyanik

2008-01-01

340

Fatigue and damage tolerance of Y-TZP ceramics in layered biomechanical systems.  

PubMed

The fatigue properties of fine-grain Y-TZP in cyclic flexural testing are studied. Comparative tests on a coarser-grain alumina provide a baseline control. A bilayer configuration with ceramic plates bonded to a compliant polymeric substrate and loaded with concentrated forces at the top surfaces, simulating basic layer structures in dental crowns and hip replacement prostheses, is used as a basic test specimen. Critical times to initiate radial crack failure at the ceramic undersurfaces at prescribed maximum surface loads are measured for Y-TZP with as-polished surfaces, mechanically predamaged undersurfaces, and after a thermal aging treatment. No differences in critical failure conditions are observed between monotonic and cyclic loading on as-polished surfaces, or between as-polished and mechanically damaged surfaces in monotonic loading, consistent with fatigue controlled by slow crack growth. However, the data for mechanically damaged and aged specimens show substantial declines in sustainable stresses and times to failure in cyclic loading, indicating an augmenting role of mechanical and thermal processes in certain instances. In all cases, however, the sustainable stresses in the Y-TZP remain higher than that of the alumina, suggesting that with proper measures to avoid inherent structural instabilities, Y-TZP could provide superior performance in biomechanical applications. PMID:15368241

Zhang, Yu; Pajares, Antonia; Lawn, Brian R

2004-10-15

341

An advanced test technique to quantify thermomechanical fatigue damage accumulation in composite materials  

NASA Technical Reports Server (NTRS)

A mechanical test technique was developed to assist in quantifying the accumulation of damage in composite materials during thermomechanical fatigue (TMF) cycling. This was accomplished by incorporating definitive elastic mechanical property measurements into an ongoing load-controlled TMF test without disturbing the test specimen or significantly altering the test conditions. The technique allows two fundamental composite properties consisting of the isothermal elastic static moduli and the macroscopic coefficient of thermal expansion (CTE) to be measured and collected as functions of the TMF cycles. The specific implementation was incorporated into the commonly employed idealized in-phase and out-of-phase TMF cycles. However, the techniques discussed could be easily implemented into any form of load-controlled TMF mission cycle. By quantifying the degradations of these properties, tremendous insights are gained concerning the progression of macroscopic composite damage and often times the progression of damage within a given constituent. This information should also be useful for the characterization and essential for the verification of analytical damage modeling methodologies. Several examples utilizing this test technique are given for three different fiber lay-ups of titanium metal matrix composites.

Castelli, Michael G.

1993-01-01

342

Structural health monitoring of composite wind blades by fiber bragg grating  

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

343

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

NASA Technical Reports Server (NTRS)

The durability and damage tolerance of laminated composites are critical design considerations for airframe composite structures. Therefore, the ability to model damage initiation and growth and predict the life of laminated composites is necessary to achieve structurally efficient and economical designs. The purpose of this research is to experimentally verify the application of a continuum damage model to predict progressive damage development in a toughened material system. Damage due to monotonic and tension-tension fatigue was documented for IM7/5260 graphite/bismaleimide laminates. Crack density and delamination surface area were used to calculate matrix cracking and delamination internal state variables to predict stiffness loss in unnotched laminates. A damage dependent finite element code predicted the stiffness loss for notched laminates with good agreement to experimental data. It was concluded that the continuum damage model can adequately predict matrix damage progression in notched and unnotched laminates as a function of loading history and laminate stacking sequence.

Coats, Timothy W.; Harris, Charles E.

1995-01-01

344

Dynamic stress analysis and a fracture mechanics approach to life prediction of turbine blades  

Microsoft Academic Search

Emerging blade technologies are finding it increasingly essential to correlate blade vibrations to blade fatigue in order to assess the residual life of existing blading and for development of newer designs. In this paper an analytical code for dynamic stress analysis and fatigue life prediction of blades is presented. The life prediction algorithm is based on a combination method, which

J. S. Rao

1997-01-01

345

Fatigue life assessment of cardiovascular balloon-expandable stents: a two-scale plasticity-damage model approach.  

PubMed

Cardiovascular disease has become a major global health care problem in the present decade. 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, as a result of the high number of cyclic loads these devices are subjected to in vivo, numerical approaches for fatigue life assessment of stents has gained special interest in the engineering community. Numerical fatigue predictions can be used to modify the design and prevent failure, without making and testing numerous physical devices, thus preventing from undesired fatigue failures. This work presents a fatigue life numerical method for the analysis of cardiovascular balloon-expandable stainless steel stents. The method is based on a two-scale continuum damage mechanics model in which both plasticity and damage mechanisms are assumed to take place at a scale smaller than the scale of the representative volume element. The fatigue failure criterion is based on the Soderberg relation. The method is applied to the fatigue life assessment of both PalmazShatz and Cypher stent designs. Validation of the method is performed through comparison of the obtained numerical results with some experimental results available for the PalmazShatz stent design. The present study gives also possible directions for future research developments in the framework of the numerical fatigue life assessment of real balloon-expandable stents. PMID:23032428

Argente dos Santos, H A F; Auricchio, F; Conti, M

2012-11-01

346

An anisotropic damage mechanics model for concrete with applications for fatigue loading and freeze-thaw effects  

NASA Astrophysics Data System (ADS)

It is well known that the formation and propagation of microcracks within concrete is anisotropic in nature, and has a degrading effect on its mechanical performance. In this thesis an anisotropic damage mechanics model is formulated for concrete which can predict the behavior of the material subjected to monotonic loading, fatigue loading, and freeze-thaw cycles. The constitutive model is formulated using the general framework of the internal variable theory of thermodynamics. Kinetic relations are used to describe the directionality of damage accumulation and the associated softening of mechanical properties. The rate independent model is then extended to cover fatigue loading cycles and freeze-thaw cycles. Two simple softening functions are used to predict the mechanical properties of concrete as the number of cyclic loads as well as freeze-thaw cycles increases. The model is compared with experimental data for fatigue and freeze-thaw performance of plain concrete.

Reberg, Andrew Steven

347

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

348

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

349

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

Microsoft Academic Search

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

Marko Nagode; Frank Längler; Michael Hack

2011-01-01

350

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

Microsoft Academic Search

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.''

Williford

1989-01-01

351

Effects of multiaxial stress state and saltwater on fatigue damage and failure of glass/epoxy composite  

NASA Astrophysics Data System (ADS)

Fiber composites used in advanced mechanical systems are generally subjected to cyclic loading with multiaxial stress state. Thus multiaxial fatigue is a subject of major importance in design and evaluation of long-term performance of composite structures and components. Theoretical work was initially performed to address the fundamental issues of damage evolution and material degradation in glass/epoxy composites subject to multiaxial cyclic stresses. A continuum damage mechanics formulation based on irreversible thermodynamics was used to construct multiaxial cyclic constitutive equations of the composite. With coupling of damage anisotropy and multiaxial stress state and using Gibb's free energy function, damage driving force was determined. Based on the second principle of thermodynamics, evolution equations were also obtained to describe the change of the damage state in the composite under multiaxial fatigue loading. A newly introduced failure-life theory was employed for the fiber composite, based on anisotropic nature of composite strength property and distinct mechanisms of microcrack formation and growth under different multiaxial cyclic stresses. A driving force for fatigue failure was formulated with a governing function, involving combined cyclic shear and transverse tensile stresses along the weakest principal material plane of the composite. Multiaxial fatigue life of the composite was related to the forcing function using a power-law. A formulation of thermomechanical response of a fiber composite based on the general thermodynamics theory was proposed to establish a model that can couple water sorption, applied stress and damage in the composite. Starting from general Gibbs free energy, constitutive equations, which describe the relationships between state variables and corresponding driving forces, were derived. The evolution laws that describe relationships of damage driving force-damage evolution and chemical potential gradient-water flux were also given. Critical multiaxial fatigue experiments were conducted on filament-wound glass/epoxy composite tubular specimens to characterize the damage initiation and evolution. At the same time, experiment data were also been used to determine the material and multiaxial stress parameters of the fatigue-life laws for the composite and to demonstrate the validity of the theory.

Wang, Feng

352

Simulation of long-term fatigue damage in bioprosthetic heart valves: effects of leaflet and stent elastic properties.  

PubMed

One of the major failure modes of bioprosthetic heart valves (BHVs) is noncalcific structural deterioration due to fatigue of the tissue leaflets; yet, the mechanisms of fatigue are not well understood. BHV durability is primarily assessed based on visual inspection of the leaflets following accelerated wear testing. In this study, we developed a computational framework to simulate BHV leaflet fatigue, which is both efficient and quantitative, making it an attractive alternative to traditional accelerated wear testing. We utilize a phenomenological soft tissue fatigue damage model developed previously to describe the stress softening and permanent set of the glutaraldehyde-treated bovine pericardium leaflets in BHVs subjected to cyclic loading. A parametric study was conducted to determine the effects of altered leaflet and stent elastic properties on the fatigue of the leaflets. The simulation results show that heterogeneity of the leaflet elastic properties, poor leaflet coaptation, and little stent-tip deflection may accelerate leaflet fatigue, which agrees with clinical findings. Therefore, the developed framework may be an invaluable tool for evaluating leaflet durability in new tissue valve designs, including traditional BHVs as well as new transcatheter valves. PMID:24092257

Martin, Caitlin; Sun, Wei

2014-08-01

353

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

354

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

Code of Federal Regulations, 2011 CFR

...Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures. ...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures. ...applicant must evaluate the composite rotorcraft...

2014-01-01

355

14 CFR 29.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.  

Code of Federal Regulations, 2012 CFR

...Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures. ...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures. ...applicant must evaluate the composite rotorcraft...

2014-01-01

356

Fatigue damage behaviors of carbon fiber-reinforced epoxy composites containing nanoclay  

Microsoft Academic Search

The effects of nanoclay inclusion on cyclic fatigue behavior and residual properties of carbon fiber-reinforced composites (CFRPs) after fatigue have been studied. The tension–tension cyclic fatigue tests are conducted at various load levels to establish the S-N curve. The residual strength and modulus are measured at different stages of fatigue cycles. The scanning electron microscopy (SEM) and scanning acoustic microscopy

Shafi Ullah Khan; Arshad Munir; Rizwan Hussain; Jang-Kyo Kim

2010-01-01

357

The DF4 fuel damage experiment in ACRR (Annual Core Research Reactor) with a BWR (Boiling Water Reactor) control blade and channel box  

Microsoft Academic Search

The DF-4 test was an experimental investigation into the melt progression behavior of boiling water reactor (BWR) core components under high temperature severe core damage conditions. In this study 14 zircaloy clad UOâ fuel rods, and representations of the zircaloy fuel canister and stainless steel\\/BâC control blade were assembled into a 0.5 m long test bundle. The test bundle was

R. O. Gauntt; R. D. Gasser; L. J. Ott

1989-01-01

358

76 FR 74655 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures  

Federal Register 2010, 2011, 2012, 2013

...to qualify for a fatigue evaluation. Finally...procedures to minimize the risk of catastrophic failure...considered in the fatigue evaluation; (3...procedures to minimize the risk of catastrophic failure...considered in the fatigue evaluation; (3...procedures to minimize the risk of catastrophic...

2011-12-01

359

Thermal-Transient Testing Of Turbine Blades  

NASA Technical Reports Server (NTRS)

Testing apparatus applies pulses of heat to turbine blade to determine resistance to thermal fatigue. Uses nonintrusive inductive heating and records distribution of temperature on blade with infrared video camera. Allows precise control of heating and cooling. Designed for testing blades used in advanced high-pressure, high-temperature turbines.

Wagner, William R.; Pidcoke, Louis H.

1990-01-01

360

Modeling of Damage Interaction in Fatigue Relaxation for Long-Term Life Prediction. Case of Alloy 800 Grade 2 Study at 550°C  

Microsoft Academic Search

Prediction of fatigue life in creep-fatigue at a temperature of 550°C has been made for an Inconel alloy with the help of 3 models of damage evolution: the Chaboche model, the Levaillant model, and a new model of creep-fatigue relaxation. The main advantages of the new model are that it requires only a few constants and provides high accuracy of

A. El Gharad; G. Pluvinage; Z. Azari; A. Elamraoui; A. Kifani

2002-01-01

361

Modelling of pavement materials on steel decks using the five-point bending test: Thermo mechanical evolution and fatigue damage  

NASA Astrophysics Data System (ADS)

This paper deals with the modelling of wearing courses on steel orthotropic decks such as the Millau viaduct in France. This is of great importance when dealing with durability: due to the softness of such a support, the pavement is subjected to considerable strains that may generate top-down cracks in the layer at right angles of the orthotropic plate stiffeners and shear cracks at the interface between pavement and steel. Therefore, a five-point bending fatigue test was developed and improved since 2003 at the ENTPE laboratory, to test different asphalt concrete mixes. This study aims at modelling the mechanical behavior of the wearing course throughout the fatigue test by a finite element method (Comsol Multiphysics software). Each material - steel, sealing sheet, asphalt concrete layer - is considered and modelled. The modelling of asphalt concrete is complex since it is a heterogeneous material, a viscoelastic medium and it thermosensitive. The actual characteristics of the asphalt concrete (thermo physical parameter and viscoelastic complex modulus) are determined experimentally on cylindrical cores. Moreover, a damage law based on Miner's damage is included in the model. The modelling of the fatigue test leads to encouraging results. Finally, results from the model are compared to the experimental data obtained from the five-point bending fatigue test device. The experimental data are very consistent with the numerical simulation.

Arnaud, L.; Houel, A.

2010-06-01

362

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

363

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

364

The effect of composite damage on fatigue life of the high pressure vessel for natural gas vehicles  

Microsoft Academic Search

In order to examine how the damages such as scratches, cuts and gouges on the composite materials have effects on the fatigue life of NGV vessels, several experiments on real vessels were conducted and finite element analyses were applied. The flaw depths of COPV used in the experiments were 1.5mm, 2.0mm, 3.0mm, and 4.0mm, while the flaw lengths were 50mm,

Young-Seob Kim; Lae-Hyun Kim; Ji-Sang Park

365

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

Microsoft Academic Search

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

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

2007-01-01

366

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

Microsoft Academic Search

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

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

2002-01-01

367

Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage  

Microsoft Academic Search

Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da\\/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the

Robert S. Piascik; Richard P. Gangloff

1992-01-01

368

ThermoMechanical Fatigue Lifetime Assessment with Damage-Parameters, Energy-Criterions and Cyclic-J-Integral Concepts  

Microsoft Academic Search

The simulation of the thermo-mechanical fatigue (TMF) behaviour of cylinder heads is an important design step in the automotive\\u000a industry. The steady rise of engine power and the demand of lightweight construction with a concurrent enhanced reliability\\u000a require an optimised dimensioning process. The goal of this paper is to apply classical damage parameters, plastic and total\\u000a energy criterions and cyclic

M. Riedler; R. Minichmayr; G. Winter; W. Eichlseder

369

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

Microsoft Academic Search

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

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

2001-01-01

370

Fatigue crack growth from foreign object damage under combined low and high cycle loading. Part I: Experimental studies  

Microsoft Academic Search

The study aims to understand small crack growth behaviour in Ti–6Al–4V plate specimens after foreign object damage (FOD), under combined low and high cycle fatigue (LCF\\/HCF) loading conditions. The loading block studied represents one of the simplest loading sequences experienced by aero-engines and each block includes a single LCF cycle at a load ratio (R) of 0.01 with 1000 HCF

J. Ding; R. F. Hall; J. Byrne; J. Tong

2007-01-01

371

Load Mitigation with Bending/Twist-coupled Blades on Rotors using Modern Control Strategies  

NASA Astrophysics Data System (ADS)

The prospect of installing blades that twist as they bend and/or extend on horizontal axis wind turbines provides opportunities for enhanced energy capture and/or load mitigation. Although this coupling could be achieved in either an active or a passive manner, the passive approach is much more attractive owing to its simplicity and economy. As an example, a blade design might employ coupling between bending and twisting, so that as the blade bends owing to the action of the aerodynamic loads, it also twists, modifying the aerodynamic performance in some way. For reducing loads the blades are designed to twist towards feather as they bend. For variable-speed pitch-controlled rotors, dynamic computer simulations with turbulent inflow show that twist coupling substantially decreases fatigue damage over all wind speeds, without reducing average power. Maximum loads also decrease modestly. For constant-speed stall-controlled and variable-speed stall-controlled rotors, significant decreases in fatigue damage are observed at the lower wind speeds and smaller decreases at the higher wind speeds. Maximum loads also decrease slightly. As a general observation, whenever a rotor is operating in the linear aerodynamic range (lower wind speeds for stall control and all wind speeds for pitch control), substantial reductions in fatigue damage are realized.

Lobitz, Don W.; Veers, Paul S.

2003-04-01

372

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

373

Fatigue failure of a centrifugal compressor  

Microsoft Academic Search

A single stage centrifugal type compressor failed during operation and a blade detached. Failure analysis was carried out to delineate the cause of the failure.Investigation shows that multiple fatigue cracks were generated during service from forging defects in the root area of the blade. When they grew to a critical size under (high cycle fatigue) HCF, the blade detached from

N. Ejaz; I. Salam; A. Tauqir

2007-01-01

374

Fatigue damage and environment interaction of polyester aluminized glass fiber composites  

Microsoft Academic Search

Aluminized glass fiber composites in a polyester matrix were used in this work in an attempt to study their fatigue resistance under both dry and water saturated ambient conditions (compared to conventional glass fiber composites). These composites, containing specially modified fibers, exhibit increased thermal and electrical conduction properties whilst still being potentially adequate for many structural applications. The fatigue tests

J. M. Ferreira; J. T. B. Pires; J. D. Costa; O. A. Errajhi; M. Richardson

2007-01-01

375

OVERVIEW OF LOW PLASTICITY BURNISHING FOR MITIGATION OF FATIGUE DAMAGE MECHANISMS  

Microsoft Academic Search

Surface enhancement technologies such as shot peening (SP), laser shock peening (LSP), and low plasticity burnishing (LPB) can provide substantial fatigue life improvement. However, to be effective, the compressive residual stresses that increase fatigue strength must be retained in service. LPB provides thermally stable compression and can be performed in conventional machine shop environments on CNC machine tools. LPB enables

Paul S. Prevéy; N. Jayaraman; John Cammett

2005-01-01

376

Review of the fatigue damage tolerance of high-speed railway axles in Japan  

Microsoft Academic Search

Railway axles are one of the most important components in railway systems since a fail-safe design is not available. In the present paper, the fatigue tolerance of the high-speed railway axle in Japan is reviewed. To maintain the safety, the fatigue strength of the axle has been extensively studied. Theses case histories and consequent improvements in manufacturing process are presented.

Taizo Makino; Takanori Kato; Kenji Hirakawa

2011-01-01

377

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.

378

Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage  

NASA Astrophysics Data System (ADS)

Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode.

Piascik, Robert S.; Gangloff, Richard P.

1992-05-01

379

Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage  

NASA Technical Reports Server (NTRS)

Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode.

Piascik, Robert S.; Gangloff, Richard P.

1992-01-01

380

On the Fatigue Analysis of Wind Turbines  

Microsoft Academic Search

Modern wind turbines are fatigue critical machines that are typically used to produce electricalpower from the wind. Operational experiences with these large rotating machines indicated thattheir components (primarily blades and blade joints) were failing at unexpectedly high rates, whichled the wind turbine community to develop fatigue analysis capabilities for wind turbines. Ourability to analyze the fatigue behavior of wind turbine

Herbert J. Sutherland

1999-01-01

381

Investigation of waviness in wind turbine blades: Structural health monitoring  

NASA Astrophysics Data System (ADS)

Waviness in composite wind turbine blades was detected and characterized with the help of air coupled ultrasonics. Based on the aspect ratio, the detected marcels are either accepted or rejected. A passive structural health monitoring approach has been presented here to monitor the accepted marcels above a threshold. The fatigue life of specimen is most affected in the presence of a marcel. Hence this study focused on the damage evaluation after fatigue testing. Wavy laminate was subjected to fatigue load to investigate the fracture mechanisms near the marcel. Different types of defects were identified from this study and were used to develop appropriate instrumentation for health monitoring of a wavy laminate using PVDF patches.

Chakrapani, Sunil Kishore; Dayal, Vinay; Barnard, Daniel J.

2013-01-01

382

Non-contact acousto-thermal signatures in as received and fatigue damaged Ti-6Al-4V  

NASA Astrophysics Data System (ADS)

Interaction of high amplitude acoustic waves with materials produces a small increase in the temperature that can be detected and measured using an IR camera. The changes in temperature as a function of time, due to interaction of high amplitude 20 kHz acoustics, with as received and fatigue damaged polycrystalline Ti-6Al-4V samples are compared. The maximum temperature reached by the sample has been found to increase with increasing fatigue cycles. The role of multiple physical mechanisms, responsible for conversion acoustic energy to heat, like the sample geometry (finite dimension), the microstructure (grain size), and dislocation density are examined. The theoretically evaluated temperature changes are observed to be in reasonable agreement with experimental measurements. The significance of the details of microstructure and dislocation properties needed in theoretical evaluation of temperature changes are used to explain the observed differences between experimental measurements and theoretical calculations.

Sathish, Shamachary; Welter, John T.; Schehl, Norm; Jata, Kumar V.

2014-02-01

383

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

384

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

385

Evaluation of fatigue damage at welded tube joint under cyclic pressure using surface hardness measurement  

Microsoft Academic Search

In this paper, fatigue tests were conducted on 1Cr18Ni9Ti stainless steel and its welded joints were subjected to cyclic inner pressure. During the fatigue tests, the HL hardness of base metal (BM), weld metal (WM) and heat affected zone (HAZ) were measured. The results showed that 1Cr18Ni9Ti was a cyclic hardening material and the WM was a cyclic softening material.

Xu Chen; Shuang-Mei Zhao

2005-01-01

386

Positron Annihilation Studies of Cyclic Fatigue Damage in Metals and Aging in Polymers  

Microsoft Academic Search

Positron lifetime measurements have been performed on fatigued nickel samples. Both ex-situ type of source (^{22}Na source deposited on a nickel foil in a sandwich geometry) and in-situ source (^{58}Co) (produced by proton irradiation of the nickel sample through the reaction ^{61}Ni(p,alpha )^{58}Co) were used. Specimens were both flexurally and axially fatigued. Spectra were analyzed by resolving into three and

Nokuleswar Panigrahi

1987-01-01

387

Cumulative Damage of Fiber-Reinforced Elastomer Composites under Fatigue Loading  

Microsoft Academic Search

Fracture mechanisms under fatigue loading were assessed in the case of nylon fiber-reinforced elastomer matrix composite which represents the actual carcass of bias aircraft tires. Under uniaxial tension, the angle-plied carcass composite specimens were subjected to a considerably large interply shear strain before failure. The composite specimens exhibited semi-infinite fatigue life when stress amplitude was below a threshold level, i.e.,

B. L. Lee; D. S. Liu

1994-01-01

388

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

Microsoft Academic Search

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

John H. Cantrell; John H

2006-01-01

389

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

Microsoft Academic Search

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

John H. Cantrell

2006-01-01

390

Blade fragment energy analysis  

NASA Technical Reports Server (NTRS)

Two classes of fan blade fragments were considered in an analysis of blade fragment energy. The first, of relatively small size (.15 pound) and energy, tends to rebound from the fan and case when liberated in an FOD encounter. These small fragments have relatively low secondary damage potential and are less demanding in terms of protection. The larger fan blade fragments are ejected in a more direct release trajectory with higher energy and hence can represent a higher potential hazard. Simplified analytical methods were used to describe blade fragment energy transfer kinematics, establish fragment energy levels, evaluate damage potential and configure protection. The approach, methodology, and application are discussed as a possible building block for other applications. Development of effective local protection using Kevlar is also discussed. Analysis methods developed and applied to the rebound fragment problem and to the large direct release fragment problem are described.

Oconnor, M. A., Jr.

1977-01-01

391

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

392

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

393

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

394

Laws of the accumulation of fatigue damage in steels St. 45 and 1Kh13 under the influence of programmed variable loads  

Microsoft Academic Search

1.The fatigue strength characteristics of steels St. 45 and 1Kh13 and the kinetics of the variation in cyclic inelastic strains of these materials were investigated; it was shown that the stabilized value of the inelastic strain per cycle is a measure of the intensity of the accumulation of fatigue damage under constant loading conditions.2.A method based on taking into account

V. T. Troshchenko

1973-01-01

395

Fatigue damage assessment by the continuous examination of the magnetomechanical and mechanical behavior  

NASA Astrophysics Data System (ADS)

To evaluate the material degradation of ferritic steels caused by low cycle stress-induced fatigue, the continuous examination of changes in the magnetomechanical behavior during the cyclic mechanical loading is proposed, and this is validated by comparing with the continuous examination of changes in the mechanical stress-strain behavior. In this context two magnetomechanical examination methods are investigated, differing only in the magnetic field that is continuously applied to the sample during the stress-controlled cyclic mechanical loading, i.e., a constant magnetic field (method Hstat) or a time-varying magnetic field (method Hdyn), with the magnetic frequency significantly larger than the mechanical frequency. In both methods the magnetization variation M(?,H) during each stress cycle due to the magnetomechanical effect and the strain ?(?) are continuously measured throughout the complete cyclic mechanical loading test. When analyzing the fatigue-induced changes in the magnetization trajectory M(?,H) determined by both methods (Hstat and Hdyn), several stages in the fatigue lifetime can be distinguished (i.e., a steady state and a final stage for as-received samples and an initial stage, a steady state and a final stage for annealed samples), which fully mimic the corresponding stages in the inelastic strain-stress behavior. All investigated magnetomechanical and mechanical parameters change significantly during the final fatigue stage (i.e., the last 2%-5% of the fatigue lifetime). This information can be used to estimate the remaining life of steel components.

Vandenbossche, Lode; Dupré, Luc

2009-04-01

396

Positron-annihilation studies of cyclic fatigue damage in metals and aging in polymers  

SciTech Connect

Positron-lifetime measurements were performed on fatigued nickel samples. Both ex-situ type of source (/sup 22/Na source deposited on a nickel foil in a sandwich geometry) and in-situ source (/sup 58/Co) (produced by proton irradiation of the nickel sample through the reaction /sup 61/Ni(p,..cap alpha..)/sup 58/Co) were used. Specimens were both flexurally and axially fatigued. Spectra were analyzed by resolving into three and four exponentials. In contrast to other studies, positrons are found to be sensitive to defects formed during the cyclic fatiguing. These data were analyzed in terms of various trapping models. The results could be explained by assuming the detrapping of positrons from defect sites. In both types of fatigued specimens the lifetimes of the defect clusters decreased with increasing intensities, showing either the proliferation of smaller clusters or the formation of the new relaxed microstructures. Advantage of using in-situ source for the study of fatigue cycling is stressed. Quenching experiments were performed on polystyrene and polyvinyl acetate samples. In the former the long lifetime (tau/sub 3/) increased with aging, while the intensity decreased. These indicate that the cavities in the polymers getting bigger while becoming fewer in number.

Panigrahi, N.

1987-01-01

397

Characterisation of foreign object damage (FOD) and early fatigue crack growth in laser shock peened Ti–6Al–4V aerofoil specimens  

Microsoft Academic Search

Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage.In this study, a generic aerofoil specimen of Ti–6Al–4V alloy was used. The specimens were treated by laser shock peening (LSP) to generate compressive residual stresses in the leading edge

S. Spanrad; J. Tong

2011-01-01

398

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

399

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

400

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

401

Positron Annihilation Studies of Cyclic Fatigue Damage in Metals and Aging in Polymers.  

NASA Astrophysics Data System (ADS)

Positron lifetime measurements have been performed on fatigued nickel samples. Both ex-situ type of source (^{22}Na source deposited on a nickel foil in a sandwich geometry) and in-situ source (^{58}Co) (produced by proton irradiation of the nickel sample through the reaction ^{61}Ni(p,alpha )^{58}Co) were used. Specimens were both flexurally and axially fatigued. Spectra were analyzed by resolving into three and four exponentials. In contradistinction to other studies, positrons are found to be sensitive to defects formed during the cyclic fatiguing. These data were analyzed in terms of various trapping models. The results could be explained by assuming the detrapping of positrons from defect sites. In both types of fatigued specimens the lifetimes of the defect clusters decreased with increasing intensities, showing either the proliferation of smaller clusters or the formation of the new "relaxed" microstructures. Advantage of using in-situ source for the study of fatigue cycling is stressed. Also in the analysis of the results in the third set of the flexurally fatigued samples, rich details of data could be obtained which occurred beyond the saturation of the average lifetime. Quenching experiments were performed on polystyrene and polyvinyl acetate samples. In the former the long lifetime (tau_3) increased with aging, while the intensity decreased. These indicate that the cavities in the polymers getting bigger while becoming fewer in number. In the preliminary results of the PVAC, the tau_3 showed oscillations with aging. A 2-Dimensional angular correlation system was set up. A 2D spectrum could have been taken, but for the lack of a 2D-ADC, an 1D spectrum for nickel was acquired. A model calculation showing the relative merits of the 1D -angular correlation, Doppler Broadening and 2D-angular correlation is presented. Suggestions for improvement are made.

Panigrahi, Nokuleswar

1987-09-01

402

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

403

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

404

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

NASA Astrophysics Data System (ADS)

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

2006-03-01

405

Damage accumulation during isothermal fatigue of Ti-SiC laminates  

Microsoft Academic Search

Titanium-based composites have been under investigation for the last three decades because titanium alloys have the highest strength-to-weight ratio of all common structural metals. The high strength at low to intermediate temperatures (up to 550 C), coupled with a high impact fracture energy, makes these materials candidates for applications such as gas turbine fan blades. Perhaps more important for this

P. Lipetzky; G. J. Dvorak; N. S. Stoloff

1996-01-01

406

Current Developments in Aircraft Fatigue Evaluation Procedures.  

National Technical Information Service (NTIS)

Current developments in the field of aircraft fatigue evaluation are reviewed including the description of loads for fatigue evaluation, the damage tolerance concept, concepts for the prediction of fatigue life, fatigue life improvement during production,...

O. Buxaum D. Schutz

1979-01-01

407

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

Microsoft Academic Search

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

A. E. Antoniou; T. P. Philippidis

408

Post-impact fatigue damage growth in fiber–metal laminates  

Microsoft Academic Search

Fiber–metal laminates (FMLs) are a family of hybrid materials currently being considered for use in airframe structural applications. Post-impact fatigue strength tests were carried out on several varieties of GLAss REinforced (GLARE) aluminum laminates. The panels were impacted in a drop weight impact tower located at the Institute for Aerospace Research of the National Research Council of Canada. Observations made

J. F Laliberté; C Poon; P. V Straznicky; A Fahr

2002-01-01

409

Monitoring and modeling stress corrosion and corrosion fatigue damage in nuclear reactors  

Microsoft Academic Search

Stress corrosion and corrosion fatigue are significant problems in many industries, causing economic penalties from decreased plant availability and component repair or replacement. In nuclear power reactors, environmental cracking occurs in a wide variety of components, including reactor piping and steam generator tubing, bolting materials and pressure vessels. Life assessment for these components is complicated by the belief that cracking

P. L. Andresen; F. P. Ford; H. D. Solomon; D. F. Taylor

1990-01-01

410

Damaging by Fatigue and Creep of PWR Fuel Cans. Programme and Work in Progress.  

National Technical Information Service (NTIS)

The experimental programme consists in the study of rods, tubes and irradiated cans of zircaloy 4. Up to now only rods have been examined. Tensile properties, creep, low cycle fatigue and microstructure of industrial zircaloy 4 are determined at 20 exp 0 ...

G. Brun

1983-01-01

411

Quantitative assessment of fatigue damage accumulation in wavy slip metals from acoustic harmonic generation  

Microsoft Academic Search

A comprehensive, analytical treatment is presented of the microelastic–plastic nonlinearities resulting from the interaction of a stress perturbation with dislocation substructures and cracks that evolve during cyclic fatigue of wavy slip metals. The interaction is quantified by a material nonlinearity parameter ? extracted from acoustic harmonic generation measurements. The contribution to ? from the substructures is obtained from the Cantrell

J. H. Cantrell

2006-01-01

412

Quantitative assessment of fatigue damage accumulation in wavy slip metals from acoustic harmonic generation  

Microsoft Academic Search

A comprehensive, analytical treatment is presented of the microelastic-plastic nonlinearities resulting from the interaction of a stress perturbation with dislocation substructures and cracks that evolve during cyclic fatigue of wavy slip metals. The interaction is quantified by a material nonlinearity parameter ß extracted from acoustic harmonic generation measurements. The contribution to ß from the substructures is obtained from the Cantrell

J. H. Cantrell

2006-01-01

413

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

Microsoft Academic Search

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

Matthew D. Landrigan; Ryan K. Roeder

2009-01-01

414

Windmill blade  

SciTech Connect

A windmill rotor of the vertical axis type is described, comprising: a rotatably mounted, upstanding shaft member; elongate upstanding blade members of airfoil design arranged in a helical configuration in surrounding relation to the shaft member; blade members being three in number and being spaced one hundred twenty degrees from one another and each blade member extending about twenty degrees of arc about an imaginary circle that is swept when the blade members rotate about the shaft member; horizontally disposed, radially extending upper strut members, each upper strut member connecting its associated blade member to the shaft member near the upper end of the shaft member, there being as many upper strut members as there are blade members; horizontally disposed, radially extending lower strut members; constant speed means for maintaining constant speed rotation of the blade members during conjoint rotation of the blade members, their associated strut members, and the shaft member.

Clancy, B.D.

1988-01-12

415

Time-incremental creep–fatigue damage rule for single crystal Ni-base superalloys  

Microsoft Academic Search

In the present paper a damage model for single crystal Ni-base superalloys is proposed that integrates time-dependent and cyclic damage into a generally applicable time-incremental damage rule. A criterion based on the Orowan stress is introduced to detect slip reversal on the microscopic level and the cyclic damage accumulation is quantified using the dislocation loop immobilization mechanism. Further, the interaction

T. Tinga; W. A. M. Brekelmans; M. G. D. Geers

2009-01-01

416

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

Microsoft Academic Search

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

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

1988-01-01

417

Failure analysis of generator rotor fan blades  

Microsoft Academic Search

The failure analysis of a generator rotor fan blade was investigated by mechanical analysis and metallurgical examination of fracture surface. Fracture took place at the airfoil root, surface examination showed that the blade had cracked by a high cycle fatigue mechanism. However, there was no evidence of material defect. A series of analytical, finite element and experimental analysis was utilized

E. Poursaeidi; M. Salavatian

2007-01-01

418

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

419

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

420

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

SciTech Connect

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

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

1984-06-18

421

Dynamic analysis tool development for advanced geometry wind turbine blades  

Microsoft Academic Search

This dissertation describes work to develop a dynamic analysis code for swept wind turbine blades. Because of their aeroelastic behavior, swept blades offer the potential to increase energy capture and lower fatigue loads. This work was an outgrowth of United States Department of Energy contract on swept blades, where the author used the Adams(TM)dynamic software. The author based the new

Scott Michael Larwood

2009-01-01

422

Prediction of Delamination in Wind Turbine Blade Structural Details  

Microsoft Academic Search

Delamination between plies is the root cause of many failures of composite materials structures such as wind turbine blades. Design methodologies to prevent such failures have not been widely available for the materials and processes used in blades. This paper presents simplified methodologies for the prediction of delamination under both static and fatigue loading at typical structural details in blades.

John F. Mandell; Douglas S. Cairns; Daniel D. Samborsky; Robert B. Morehead; Darrin J. Haugen

2003-01-01

423

Fatigue and damage tolerance of Y-TZP ceramics in layered biomechanical systems  

Microsoft Academic Search

The fatigue properties of fine-grain Y-TZP in cyclic flexural testing are studied. Comparative tests on a coarser-grain alumina provide a baseline control. A bilayer configu- ration with ceramic plates bonded to a compliant polymeric substrate and loaded with concentrated forces at the top surfaces, simulating basic layer structures in dental crowns and hip replacement prostheses, is used as a basic

Yu Zhang; Antonia Pajares; Brian R. Lawn

2004-01-01

424

Characterization and prediction of post-impact fatigue damage in stitched composites. Ph.D. Thesis  

Microsoft Academic Search

The post-impact fatigue response of stitched carbon\\/epoxy composite materials was characterized and modeled in this investigation. The five material configurations evaluated were composed of uni-woven AS4 graphite lamina arranged in a (45\\/0\\/ - 45\\/90)(sub 6s) preform. Four preforms were reinforced by a modified lock stitch process, and each material was fabricated with a specific stitch row spacing of either 1\\/4,

Moon

1993-01-01

425

Fatigue damage accumulation in nickel modified by ion beam surface microalloying  

Microsoft Academic Search

The formation, distribution, and surface morphology of persistent slip band (PSB) structures have been studied in polycrystalline\\u000a nickel with ion beam microalloyed Ni-Al surface layers. Both supersaturated solid solutions of Al in Ni and?-?? dual-phase structures were formed on surfaces of low cycle fatigue specimens by ion beam mixing vapor-deposited Ni and Al\\u000a layers, using 1 ? 1016 ions\\/cm2 of

D. S. Grummon; J. W. Jones

1988-01-01

426

Fatigue damage accumulation in nickel modified by ion beam surface microalloying  

Microsoft Academic Search

The formation, distribution, and surface morphology of persistent slip band (PSB) structures have been studied in polycrystalline nickel with ion beam microalloyed Ni-Al surface layers. Both supersaturated solid solutions of Al in Ni and gamma-gamma' dual-phase structures were formed on surfaces of low cycle fatigue specimens by ion beam mixing vapor-deposited Ni and Al layers, using 1 × 1016 ions\\/cm2

D. S. Grummon; J. W. Jones

1988-01-01

427

Fatigue damage in aluminum single crystals—I. On the surface containing the slip burgers vector  

Microsoft Academic Search

An aluminum single crystal with the axial direction of [211?0 was fatigued in push-pull at the constant resolved shear stress amplitude 4 MPa, frequency 20 Hz room temperature. Microcracks, microvoids, macrobands, extrusions and intrusions were observed on the side-surface containing the Burgers vector b. Most microcracks were opened, and were within, but approximately perpendicular to, PSBs. Slip steps were found

T. Zhai; J. W. Martin; G. A. D. Briggs

1995-01-01

428

Fiber composite fan blade impact improvement program  

NASA Technical Reports Server (NTRS)

The results of a 20-month program, designed to investigate parameters which effect the foreign object damage resulting from ingestion of birds into fan blades are described. Work performed on this program included the design, fabrication, and impact testing of QCSEE fan blades to demonstrate improvement in resistance relative to existing blades and also the design and demonstration of a pin root attachment concept.

Oller, T. L.

1976-01-01

429

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

Microsoft Academic Search

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

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

1984-01-01

430

High cycle fatigue limit stresses for airfoils subjected to foreign object damage  

Microsoft Academic Search

The foreign object damage (FOD) on leading edge geometries from particles ingested into gas turbine engines found to be comprised of geometric discontinuities like a notch, the residual stresses in regions adjacent to the notch, and material degradation in the form of micro-cracks, plastic deformation, voids, etc. The extent of the damage is related to the geometry and characteristics of

John Ruschau; Steven R Thompson; Ted Nicholas

2003-01-01

431

Damage accumulation during isothermal fatigue of Ti-SiC laminates  

SciTech Connect

Titanium-based composites have been under investigation for the last three decades because titanium alloys have the highest strength-to-weight ratio of all common structural metals. The high strength at low to intermediate temperatures (up to 550 C), coupled with a high impact fracture energy, makes these materials candidates for applications such as gas turbine fan blades. Perhaps more important for this application is the fact that Ti composites can have high stiffness, which raises the critical vibration frequencies and lowers the necessary blade thickness and mass. Efforts to reinforce these alloys began with the inclusion of boron filaments. However, complications arose due to reactivity between Ti and the fibers. Since that time compatibility problems have been overcome by either altering the matrix composition or coating the fibers. Subsequently, interest has turned to continuous SiC reinforcements with a variety of fiber diameters, volume fractions and coatings. A full description of the experimental test methods as well as the sample manufacturing procedure was given previously. Therefore, only a brief summary is given here. Fiber volume fraction for all lay-ups was approximately 30%. Prismatic coupons were subjected to a cyclic tensile load history (load ratio = 0.1) with frequencies of 0.001 Hz and 0.1 Hz. Temperature in the entire gauge section was held constant at 650 C. Strain was measured directly from the sample using a high-temperature extensometer. Following failure, portions of the gauge section were mounted in epoxy and polished by hand on conventional diamond wheels for metallographic analysis. Because the composite section was inclined at a small angle relative to the grinding surface, a wedge of material was removed during grinding so that features from a range of depths could be viewed simultaneously.

Lipetzky, P.; Dvorak, G.J.; Stoloff, N.S. [Rensselaer Polytechnic Inst., Troy, NY (United States)] [Rensselaer Polytechnic Inst., Troy, NY (United States)

1996-11-01

432

Special features in the effect of sulfur compounds in a gaseous flow of combustion products containing seawater salts on the thermal fatigue fracture of operating turbine blades  

Microsoft Academic Search

Since the actual operating conditions of ship gas turbines are characterized bythe presence of seawater salts entering the engine from the atmosphere, as well as an increased content of sulfur compounds in the gas flow, in the present investigation we have studied the combined action of these corrosive components on the thermal cycling endurance of turbine blades. The concentrations of

G. N. Tret'yachenko; É. P. Kosygin

1979-01-01

433

Equivalent Damage and Fatigue Testing of the HB 2060 Pads, Project Summary.  

National Technical Information Service (NTIS)

Accelerated Pavement Testing (APT) technology has the potential to provide valuable information that, in a relatively short time, could demonstrate the damage caused by heavily loaded trucks to the load-zoned road network. Accelerated Pavement Testing of ...

J. A. Prozzi K. Kapoor V. Gossain

2006-01-01

434

Structural Damage Identification in Stiffened Plate Fatigue Specimens Using Piezoelectric Active Sensing.  

National Technical Information Service (NTIS)

This paper presents a guided wave structural health monitoring (SHM) technique, based on the use of piezoelectric active-sensors, used to determine the structural integrity of stiffened aluminum plates. For damage detection, the transmitted power between ...

B. L. Grisso C. R. Farrar G. Park L. W. Salvino

2011-01-01

435

Repair of Damage to Marine Sandwich Structures: Part II - Fatigue Testing.  

National Technical Information Service (NTIS)

Sandwich construction panels, comprising glass reinforced polymer (GRP) composite skins and PVC foam core, are in use in the current generation of naval vessels of the mine hunting class. Such structures will inevitably be subjected to damage and any repa...

M. Z. Shah Khan I. Grabovac

2000-01-01

436

Effect of cyclic fatigue damage accumulation on the elastic-plastic properties of SAC305 solders  

Microsoft Academic Search

This study examines the effect of cyclic damage on the constitutive response of Sn3.0Ag0.5Cu (SAC305) solder material. Cyclic damage is induced through isothermal, mechanical cycling tests at high strain rate and room temperature, using a modified lap-shear microscale specimen (180 mum wide solder joint). The elastic, plastic, and yield response of the cycled solder joints are measured as a function

Gayatri Cuddalorepatta; Abhijit Dasgupta

2009-01-01

437

Fatigue damage accumulation modelling in the range of complex low-cycle loadings – The strain approach and its experimental verification on the basis of EN AW2007 aluminum alloy  

Microsoft Academic Search

The paper presents the fatigue damage accumulation model created to analyse fatigue life of structure elements operating in conditions of multiaxial, non-proportional low-cycle loadings. The authors used the approach connected with the critical plane in the presented model. In the discussed approach the damage variable depends on the stress damage accumulation function and the increments of plastic non-dilatational strain. The

J. Szusta; A. Seweryn

2011-01-01

438

Tubomachinery blade vibration amplitude measurement through tip timing with capacitance tip clearance probes  

Microsoft Academic Search

Turbomachinery blade vibrations can cause high cycle fatigue (HCF), which reduces blade life. In order to observe this vibration a non-intrusive monitoring system is sought. The vibration can be detected by measuring blade tip timing since in the presence of vibration the blade timing will differ slightly from the passing time calculated from rotor speed. Much research and development has

Craig P. Lawson; Paul C. Ivey

2005-01-01

439

A review and design study of blade testing systems for utility-scale wind turbines  

Microsoft Academic Search

Since the blades are one of the most critical components of a wind turbine, representative samples must be experimentally tested in order to ensure that the actual performance of the blades is consistent with their specifications. In particular, it must be demonstrated that the blade can withstand both the ultimate loads and the fatigue loads to which the blade is

P. Malhotra; R. W. Hyers; J. F. Manwell; J. G. McGowan

440

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

441

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.

Li, Xiang; Yang, Zhibo; Chen, Xuefeng

2014-01-01

442

Compressor Blade Manufacture by Electrochemical Machining. Advanced Turbine Engine Gas Generator.  

National Technical Information Service (NTIS)

Compressor blades for the ATEGG GE14 engine manufactured using electrochemical machining to form the airfoils. Elaborate dimensional inspections were performed on the as-machined surfaces. The blades were tested for frequency, nodal patterns, and fatigue ...

W. I. Westphal A. Lingen

1977-01-01

443

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

PubMed

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

Taylor; Zhai; Wilkinson; Martin

1999-09-01

444

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

SciTech Connect

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

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

1989-11-01

445

Fatigue damage caused to the material by inelastic loading with periods of load holding  

Microsoft Academic Search

Conclusions 1.New parameters of state obtained in analyzing the structural model and describing the strain properties of structural materials in a cyclically stable condition during repeated-variable loading with periods of holding the load are proposed here for use in the model of damage accumulation. These parameters, regardless of the fact that they can be macroscopically determined, characterize integrally the effects

K. M. Kononov; V. B. Poroshin; O. S. Sadakov

1982-01-01

446

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

Microsoft Academic Search

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

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

1997-01-01

447

Fatigue properties and design of wing blades for wind turbines. Final report for the period April 1, 1990 to March 31, 1993.  

National Technical Information Service (NTIS)

This project is a continuation of the work on fatigue properties of materials for wingblades, which was carried out in the subproject under the general activity on 'Design-basis for wind turbines' (EC-project No. EN3W.0024). The present project has three ...

S. I. Andersen H. Lilholt A. Lystrup

1994-01-01

448

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

449

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

450

Effect of interstitial content on high- temperature fatigue crack propagation and low- cycle fatigue of alloy 720  

NASA Astrophysics Data System (ADS)

Alloy 720 is a high-strength cast and wrought turbine disc alloy currently in use for temperatures up to about 650 °C in Allison’s T800, T406, GMA 2100, and GMA 3007 engines. In the original composition in-tended for use as turbine blades, large carbide and boride stringers formed and acted as preferred crack initiators. Stringering was attributed to relatively higher boron and carbon levels. These interstitials are known to affect creep and ductility of superalloys, but the effects on low-cycle fatigue and fatigue crack propagation have not been studied. Recent emphasis on the total life approach in the design of turbine discs necessitates better understanding of the interactive fatigue crack propagation and low-cycle fatigue behavior at high temperatures. The objective of this study was to improve the damage tolerance of Alloy 720 by systematically modifying boron and carbon levels in the master melt, without altering the low-cy-cle fatigue and strength characteristics of the original composition. Improvement in strain-controlled low-cycle fatigue life was achieved by fragmenting the continuous stringers via composition modifica-tion. The fatigue crack propagation rate was reduced by a concurrent reduction of both carbon and bo-ron levels to optimally low levels at which the frequency of brittle second phases was minimal. The changes in composition have been incorporated for production disc forgings.

Bashir, S.; Thomas, M. C.

1993-08-01

451

Fatigue Life and Short Crack Behavior in Ti-6Al-4V Alloy; Interactions of Foreign Object Damage, Stress, and Temperature  

NASA Astrophysics Data System (ADS)

High-cycle fatigue (HCF) failures associated with foreign object damage (FOD) in turbine engines of military aircrafts have been of major concern for the aeronautic industry in recent years. The present work is focused on characterizing the effects of FOD on crack initiation and small crack growth of a Ti-6Al-4V alloy at ambient and also elevated temperatures. Results show that the preferred crack initiation site depends on applied stress and temperature as maximum fractions of cracks emanating from the simulated damage site, and naturally initiated cracks are observed at 25 °C under the maximum stress of 700 MPa and at 300 °C under the maximum stress of 300 MPa. The fatigue crack growth rate is influenced by increasing temperature, and the FCG rate at 300 °C is higher than that at room temperature under the same ? K, whereas this effect for FOD-site initiated cracks is not so remarkable. This observation seems to be due to the effect of stress relaxation at 300 °C. Results also indicate that fatigue crack initiation life ( N i ) and fatigue life ( N f ) are expressed by three-parameter Weibull distribution function.

Majidi, Behzad

2008-04-01

452

Effect of thermal fatigue on mechanical characteristics and contact damage of zirconia-based thermal barrier coatings with HVOF-sprayed bond coat  

Microsoft Academic Search

Mechanical characteristics, such as hardness, elastic modulus and indentation stress–strain curves, and contact damage of a thermal barrier coating (TBC) system with a top coat prepared using an air-plasma spraying (APS) process and a bond coat using a high-velocity oxygen flow (HVOF) process have been investigated using the nanoindentation and Hertzian indentation tests, as a function of the thermal fatigue

Jae-Young Kwon; Jae-Hyun Lee; Hyeon-Cheol Kim; Yeon-Gil Jung; Ungyu Paik; Kee-Sung Lee

2006-01-01

453

Health risk assessment and prognosis of gas turbine blades by simulation and statistical methods  

Microsoft Academic Search

Algorithmic approaches for failure risk assessment, anomaly detection and life prognosis of gas turbine blade are discussed. Modeling of blade tip clearance and Monte Carlo simulation considering creep, vibration and other damaging effects lead to two probabilistic distributions with blade tip clearance data. Failure risk can be determined during blade life usage based on blade tip tolerance limits. Statistical treatments

N. Goel; A. Kumar; V. Narasimhan; A. Nayak; A. Srivastava

2008-01-01

454

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

Microsoft Academic Search

The objective of this research is to understand the frequency effect on the fatigue behavior of graphite\\/epoxy and glass\\/epoxy composite materials. Fatigue tests were conducted on (+\\/-45)\\/sub (2s)\\/ layups using 0.05, 0.5, and 5 Hz frequencies. Basically, the fatigue life increased as the loading frequency increased. Experimental results showed that the initial dynamic modulus of the composites is larger for

Tsai

1984-01-01

455

THE EFFECT OF TENSION-TENSION FATIGUE AND LAY-UP CONFIGURATION ON DAMAGE ACCUMULATION IN CARBON\\/EPOXY COMPOSITES  

Microsoft Academic Search

The effect of tension-tension fatigue (T-T) on carbon\\/epoxy composites (CFC) has been investigated in this paper. Load controlled fatigue tests were conducted in the tension-tension (T-T) cyclic mode with the R-ratio values of 0.1 and 0.3 and subsequently the specimens with the fatigue life over 106 cycles have been studied by means of tensile testing, ultrasonic inspection and quantitative data

M. Henzel; M. Scheerer; A. Pönninger; E. Ladstaetter

456

Mechanical characterization of composite repairs for fiberglass wind turbine blades  

NASA Astrophysics Data System (ADS)

While in service, wind turbine blades experience various modes of loading. An example is impact loading in the form of hail or bird strikes, which might lead to localized damage or formation of cracks a few plies deep on the blade surface. One of the methods to conduct repairs on wind turbine blades that are damaged while in service is hand lay-up of the repair part after grinding out the damaged portion and some of its surrounding area. The resin used for such repairs usually differs from the parent plate resin in composition and properties such as gel time, viscosity, etc. As a result the properties of the repaired parts are not the same as that of the undamaged blades. Subsequent repetitive loading can be detrimental to weak repairs to such an extent so as to cause delamination at the parent-repair bondline causing the repairs to eventually fall off the blade. Thus the strength and toughness of the repair are of critical importance. Initial part of this work consists of an effort to increase repair strength by identifying an optimum hand layup repair resin for fiberglass wind turbine blades currently being manufactured by a global company. As delamination of the repair from the parent blade is a major concern and unidirectional glass fibers along with a polymer resin are used to manufacture blades under consideration, testing method detailed in ASTM D 5528 (Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites) was followed to determine propagation fracture toughness values of the prospective vinyl ester repair resin candidates. These values were compared to those for a base polyester repair resin used by the company. Experimental procedure and results obtained from the above mentioned testing using double cantilever beam (DCB) specimens are detailed. Three new repair resins were shortlisted through mode I testing. It was also found that variation in the depth of the ground top ply of the parent part affects the propagation fracture toughness values of the repair. Repairs conducted on surfaces with partially ground top plies possess higher fracture toughness values than those conducted on surfaces with complete top plies ground off. The three top repair resin candidates were then evaluated against the base repair resin under fatigue loading. The specimen configuration and testing method were chosen so as to be able to test hand layup repairs under tension -- tension cyclic loading. It was observed that all three new repair resins perform better than the base repair resin. The selection of the optimum repair resin was based on results from mode I and fatigue testing. Global manufacturing regulations and standards were also of prime concern. The final new repair resin is being used by the company in all of its plants over the globe. The balance of this work involves study of the effect of mixed mode I -- mode II loading on the strength of repairs conducted on fiber reinforced composite parts using hand lay-up technique. The specimens for this part were similar to those manufactured for mode I testing but with different dimensions and layup. They were made and tested in accordance with ASTM D 6671 (Standard Test Method for Mixed Mode I -- Mode II Interlaminar Fracture Toughness of Unidirectional Fiber Reinforced Polymer Matrix Composites). Comparison was made between the fracture toughness of the above chosen optimum repair resin and the base repair resin. At least two levels of mode mixture GII/G (Mode II fracture toughness / Mode I and II fracture toughness) were examined. Also, two levels of grinding were considered (complete ply vs. partial ply ground off) in order to establish the influence of varying top-ply grinding depths on the strength of hand layup repairs conducted on fiberglass composite structures. The results of this work have the potential to improve the repair process for current fiberglass wind turbine blades.

Chawla, Tanveer Singh

457

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

PubMed

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

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

2009-06-01

458

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