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1

Prediction of fatigue performance in gas turbine blades after foreign object damage  

Microsoft Academic Search

Foreign object damage is a significant cause of failure in gas turbine engines. This paper describes a series of experiments conducted on ‘blade-like’ fatigue specimens. The specimens were impacted with a cubical projectile at 250 m\\/s using a gas gun. They were subsequently fatigue loaded using the step method of testing to establish the fatigue strength in the damaged state.

D. Nowell; P. Duó; I. F. Stewart

2003-01-01

2

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

Microsoft Academic Search

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

Paul S. Prevéy; N. Jayaraman; Michael Shepard

2007-01-01

3

An analysis of fatigue damage inflicted to the blades of gas turbine units during their long-term operation on gas mains  

NASA Astrophysics Data System (ADS)

Results from studies of factors due to which fatigue damage is inflicted to the turbine and compressor blades of stationary gas turbine units operating at the compressor stations installed on gas mains of Russia are considered.

Dashunin, N. V.; Laskin, A. S.; Getsov, L. B.; Rybnikov, A. I.; Mozhaiskaya, N. V.

2012-09-01

4

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

E-print Network

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

5

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

6

Fatigue life estimation procedure for a turbine blade under transient loads  

SciTech Connect

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 which the rotor is accelerated. Fatigue due to these transient influences may accumulate to lead to failure. In this paper 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 accumulation of fatigue.

Vyas, N.S. (Indian Inst. of Tech., Kanpur (India). Dept. of Mechanical Engineering); Rao, J.S. (Indian Inst. of Tech., New Delhi (India). Dept. of Mechanical Engineering)

1994-01-01

7

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

8

Composite blade damaging under impact  

NASA Astrophysics Data System (ADS)

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

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

2006-08-01

9

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

10

Jumplike fatigue crack growth in compressor blades  

NASA Astrophysics Data System (ADS)

It is shown that power relations between the two main fractographic characteristics of fracture surfaces forming during jumplike fatigue crack growth, namely, the crack depth and the corresponding crack front length, can be used to estimate the fracture stress during vibration tests of the compressor blades of an aviation gas turbine engine, which are made of VT3-1 titanium alloy.

Limar', L. V.; Demina, Yu. A.; Botvina, L. R.

2014-04-01

11

Application of the US high cycle fatigue data base to wind turbine blade lifetime predictions  

SciTech Connect

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

Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States). Wind Energy Technology; Mandell, J.F. [Montana State Univ., Bozeman, MT (United States). Dept. of Chemical Engineering

1996-10-01

12

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

SciTech Connect

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

Veers, P.S.

1981-09-01

13

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

14

Structural fatigue test results for large wind turbine blade sections  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

15

High Sensitive Methods for Health Monitoring of Compressor Blades and Fatigue Detection  

PubMed Central

The diagnostic and research aspects of compressor blade fatigue detection have been elaborated in the paper. The real maintenance and overhaul problems and characteristic of different modes of metal blade fatigue (LCF, HCF, and VHCF) have been presented. The polycrystalline defects and impurities influencing the fatigue, along with their related surface finish techniques, are taken into account. The three experimental methods of structural health assessment are considered. The metal magnetic memory (MMM), experimental modal analysis (EMA) and tip timing (TTM) methods provide information on the damage of diagnosed objects, for example, compressor blades. Early damage symptoms, that is, magnetic and modal properties of material strengthening and weakening phases (change of local dislocation density and grain diameter, increase of structural and magnetic anisotropy), have been described. It has been proven that the shape of resonance characteristic gives abilities to determine if fatigue or a blade crack is concerned. The capabilities of the methods for steel and titanium alloy blades have been illustrated in examples from active and passive experiments. In the conclusion, the MMM, EMA, and TTM have been verified, and the potential for reliable diagnosis of the compressor blades using this method has been confirmed. PMID:24191135

Witos, Miroslaw

2013-01-01

16

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

17

Composite blade damaging under impact  

Microsoft Academic Search

Composites materials are now being used in primary aircraft structures, and other domains because of numerous advantages. A part of a continuous in-flight operating costs, gas turbine engine manufacturers are always looking for ways to decrease engine weight. This is the case of compressor blades which have to satisfy, for example, the standard bird strike or debris in order to

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

2006-01-01

18

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

SciTech Connect

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

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

1995-12-01

19

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

20

Selection of Wind Turbine Blade Materials for Fatigue Resistance  

E-print Network

Selection of Wind Turbine Blade Materials for Fatigue Resistance John Mandell Montana StateE glass and similar compositions · High Performance Glass (WindStrand) C b· Carbon #12;Tensile Fatigue E Gl (2 f b i )E-Glass (2 fabrics), WindStrand, Carbon ; Epoxy Resins; Stress Based (top) and Stress

21

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

22

Fatigue Failure Analysis of Small Wooden Wind Turbine Blade  

E-print Network

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

Maldhure S. S; Dr. Kharde Y. R

23

Widespread Fatigue Damage Assessment Approach  

Microsoft Academic Search

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

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

24

Fatigue Life Analysis of Small Composite Sandwich Wind Tuebine Blades  

Microsoft Academic Search

The present fatigue life analysis of the small composite sandwich wind turbine blades (SCSWTBs) can be certified by IEC 61400-2:Wind Turbines - Part2: Design requirements of small wind turbines (IEC 61400-2 2006). The paper will establish an analytical method for the fatigue life analysis of SCSWTBs. Microsoft Office EXCEL is used to calculate the maximum stress, minimum stress, and stress

J. H. Wu; F. M. Lai

2011-01-01

25

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

NASA Astrophysics Data System (ADS)

Canada has aggressive targets for introducing wind energy across the country, but also faces challenges in achieving these goals due to the harsh Canadian climate. One issue which has received little attention in other countries not experiencing these extremes is the behaviour of composite blades in winter conditions. The scope of the work presented is to analyze the static stresses and fatigue response in cold climates using finite element models of the blade. The work opens with a quantification of the extremes of cold experienced in candidate Canadian wind turbine deployment locations. The thesis then narrows its focus to a consideration of the stresses in the root of the composite blades, specifically two common blade-hub connection methods: embedded root carrots and T-bolts. Finite element models of the root are proposed to properly simulate boundary conditions, applied loading and thermal stresses for a 1.5 MW wind turbine. It is shown that the blade root is strongly affected by the thermal stresses caused by the mismatch and orthotrophy of the coefficients of thermal expansion of the blade root constituents. Fatigue analysis of a blade is then presented using temperature dependent material properties including estimated fatigue coefficients.It was found that the natural frequencies of a 1.5 MW wind turbine blade are not significantly altered at cold temperatures. Additionally, cold temperatures slightly increase stresses in the composite blade skin when the blade is loaded, due to an increase in stiffness. Cold temperatures also lead to higher cyclic flapwise bending moments acting on the blade. However, this increase was found not to affect the lifetime fatigue damage. Finally, it was found that the cold climate as seen in Canada improves the fatigue strength of the saturated composite materials used in the blade. The predicted fatigue damage of the triaxial fabric and the spar cap layers in cold climates was therefore predicted to be half that of the fatigue damage at room temperature. This is caused solely by the temperature dependence of the fatigue coefficient b which requires further experimental verification to validate the numerical results of the current study.

Lillo Gallardo, Patricio Andres

26

Power-exponent function model for low-cycle fatigue life prediction and its applications – Part II: Life prediction of turbine blades under creep–fatigue interaction  

Microsoft Academic Search

This paper is concerned with the applications of the proposed models, namely the modified linear damage summation (MLDS) method and the modified strain range partitioning (MSRP) method described in Part I of the series papers, to life prediction of turbine blades under creep–fatigue interaction. To begin with, a detailed FEM analysis is conducted considering peak loading of thermal load, centrifugal

Lijie Chen; Yinghua Liu; Liyang Xie

2007-01-01

27

A fatigue damage model of composite materials  

Microsoft Academic Search

The mechanical properties of composite materials degrade progressively with the increasing of the number of cyclic loadings. Based on the stiffness degradation rule of composites, a phenomenological fatigue damage model is presented in this paper, which contains two material parameters. They are proportional to the fatigue life of materials and inversely proportional to the fatigue loading level. Thirteen sets of

Fuqiang Wu; WeiXing Yao

2010-01-01

28

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

29

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

E-print Network

DAMAGE DETECTION METHODS ON WIND TURBINE BLADE TESTING WITH WIRED AND WIRELESS ACCELEROMETER for nonstationary blade excitations. KEYWORDS : Structural Health Monitoring, Damage Detection, Wind Turbine, Wireless sensing, Wavelets. INTRODUCTION Detecting damage in wind turbine blades is a very

Paris-Sud XI, Université de

30

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

SciTech Connect

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

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

2013-04-01

31

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

32

Fatigue and damage tolerance scatter models  

NASA Technical Reports Server (NTRS)

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

Raikher, Veniamin L.

1994-01-01

33

Identification of Foreign Objects Damaging Compressor Blades in Turbojet Engines  

NASA Technical Reports Server (NTRS)

Damage to the compressor blades of turbojet engines due to ingestion of foreign objects is a growing problem, the solution of which has been made more difficult by the large percentage of damaging materials that have remained unknown. A rapid emission spectroscopic method was devised to identify the chemical composition of these foreign objects. Results on laboratory-prepared specimens and blades from damaged engines show that the method can be utilized to determine the nature of the ingested foreign objects.

Spakowski, A E; Graab, J

1957-01-01

34

Structural Damage and Chemical Contaminants on Reprocessed Arthroscopic Shaver Blades  

Microsoft Academic Search

Background: In response to socioeconomic pressure to cut budgets in medicine, single-use surgical instruments are often reprocessed despite potential biological hazard.Purpose: To evaluate the quality and contaminants of reprocessed shaver blades.Hypothesis: Reprocessed shaver blades have mechanical damage and chemical contamination.Study Design: Controlled laboratory study.Methods: Seven blades and 3 abraders were reprocessed 1 time or 3 times and then were assessed.

Masahiko Kobayashi; Yasuaki Nakagawa; Yukihiro Okamoto; Shinichiro Nakamura; Takashi Nakamura

2009-01-01

35

Vortex-induced vibration effect on fatigue life estimate of turbine blades  

Microsoft Academic Search

An analysis of a turbine blade fatigue life that includes the physics of fluid–structure interaction on the high cycle fatigue (HCF) life estimate of turbine blades is carried out. The rotor wake excitation is modeled by rows of Karman vortices superimposed on an inviscid uniform flow. The vortex-induced vibration problem is modeled by a linear cascade composed of five turbine

Y. L. Lau; R. C. K. Leung; R. M. C. So

2007-01-01

36

Reliability assessment of high cycle fatigue design of gas turbine blades using the probabilistic Goodman Diagram  

Microsoft Academic Search

A probability-based procedure has been developed to predict the reliability of gas turbine engine blades subjected to high cycle fatigue. The procedure provides a systemic approach for predicting and designing turbomachinery blading reliability against various potential high cycle fatigue problems for all relevant vibratory modes, and taking into account variability in geometry (e.g. dimensional variation, surface smoothness, etc.). The variability

M.-H. Herman Shen

1999-01-01

37

An investigation of fatigue failures of turbine blades in a gas turbine engine by mechanical analysis  

Microsoft Academic Search

Blade failures in gas turbine engines often lead to loss of all downstream stages and can have a dramatic effect on the availability of the turbine engines. Thorough failure investigation is essential for the effective management of engine airworthiness. In this paper blade fatigue failures are investigated by mechanical analyses and by examination of failed blades. A series of mechanical

Jianfu Hou; Bryon J Wicks; Ross A Antoniou

2002-01-01

38

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

SciTech Connect

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

Galib Abumeri; Frank Abdi (PhD)

2012-02-16

39

The relationship between observed fatigue damage and life estimation models  

NASA Technical Reports Server (NTRS)

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

Kurath, Peter; Socie, Darrell F.

1988-01-01

40

AIAA-2003-0692 NEW FATIGUE DATA FOR W IND TURBINE BLADE M ATERIALS  

E-print Network

were obtained for tensile fatigue with low cyclic amplitudes, close to R=1.0, to clarify the shape: (a) very high cyclic tension fatigue; (b) refinements to the Goodman Diagram in the low amplitude1 AIAA-2003-0692 NEW FATIGUE DATA FOR W IND TURBINE BLADE M ATERIALS John F. Mandell, Daniel D

41

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

NASA Astrophysics Data System (ADS)

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

Han, Y.; Leithead, W. E.

2014-06-01

42

Damage accumulation model for low cycle fatigue  

Microsoft Academic Search

This paper presents the description of damage accumulation for analysis of fatigue life of structural elements under non-proportional loading states. Damage accumulation rule has been formulated incrementally and connected with a monotonic work-hardening curve. The numerical algorithm is decomposed into two calculation blocks. The first presents method for calculation components of stress and strain tensors using a multisurface hardening rule

A. Seweryn; A. Buczy?ski; J. Szusta

2008-01-01

43

Thermal fatigue and oxidation data for directionally solidified MAR-M 246 turbine blades  

NASA Technical Reports Server (NTRS)

Thermal fatigue and oxidation data were obtained for 11 plasma spray coated and 13 uncoated directionally solidified and single crystal MAR-M 246 blades. Blade coatings on the airfoil included several metal-oxide thermal barrier layers based on Al2O3, Cr2O3, or ZrO2. The 24 turbine blades were tested simultaneously for 3000 cycles in fluidized beds maintained at 950 and 25 C using a symmetrical 360 set thermal cycle. In 3000 cycles, only uncoated turbine blades exhibited cracking on the trailing edge near the platform; 3 of the 13 uncoated blades did not crack. Cracking occurred over the range 400 to 2750 cycles, with single crystal blades indicating the poorest thermal fatigue resistance. Oxidation of the uncoated blades was limited in 3000 cycles. All coatings indicated microscopically visible spalling at the trailing edge radius after 3000 cycles. Severe general spalling on the airfoil was observed for two multilayered coatings.

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

1980-01-01

44

Piezoelectric active sensing techniques for damage detection on wind turbine blades  

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

45

Thermal activation of fatigue damage  

SciTech Connect

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

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

2000-01-01

46

Material testing for fatigue design of heavy-duty gas turbine blading with film cooling  

Microsoft Academic Search

Heavy-duty gas turbine blades, which contain film cooling holes, are subjected to a complicated dynamic mechanical loading. Special material tests have been developed to ensure the long-term operational reliability of the blading. This paper presents results of the testing and appropriate finite element (FE-) calculations, showing that a reliable fatigue life assessment can be achieved with the local approach concept.

Ying Pan; Burkhard Bischoff-Beiermann; Thomas Schulenberg

1999-01-01

47

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

48

Service load fatigue damage — a historical perspective  

Microsoft Academic Search

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

Paul C Paris; Hiroshi Tada; J. Keith Donald

1999-01-01

49

Operational Damage Detection of Turbine Rotors using Integrated Blade Sensors  

Microsoft Academic Search

\\u000a Predictive maintenance of wind turbines could provide an estimated 81% reduction in cost when compared to reactive maintenance,\\u000a the current industry standard. The ability to identify damage using wind turbine operating data is necessary for a predictive\\u000a maintenance approach. To identify such damage, strain measurements were performed on a Whisper 100 blade using a Trilion DIC\\u000a System with flap-wise applied

S. R. Dana; D. E. Adams

50

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

SciTech Connect

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

Donohoo, P.E.; Cotrell, J.

2008-01-01

51

Brittleness Effect on Rock Fatigue Damage Evolution  

NASA Astrophysics Data System (ADS)

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

Nejati, Hamid Reza; Ghazvinian, Abdolhadi

2014-09-01

52

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

53

DETECTION OF IMPULSE-LIKE AIRBORNE SOUND FOR DAMAGE IDENTIFICATION IN ROTOR BLADES OF WIND TURBINES  

E-print Network

DETECTION OF IMPULSE-LIKE AIRBORNE SOUND FOR DAMAGE IDENTIFICATION IN ROTOR BLADES OF WIND TURBINES burdens of wind turbines. To detect damage of rotor blades, several research projects focus on an acoustic, rotor blade, wind turbine INTRODUCTION There are several publications of non destructive damage

Boyer, Edmond

54

Analysis of fatigue damage in composite laminates  

NASA Technical Reports Server (NTRS)

An attempt is made to give a comprehensive characterization of processes of degradation in type 1 and 2 laminated composites under cyclic (fatigue) loading; based on the discovery of a 'characteristic damage state' that forms independently of load history and is determined by laminae properties, orientation and stacking sequence alone. The detailed nature of this state, its formation and its influence on strength, life and stiffness, is discussed.

Reifsnider, K. L.; Talug, A.

1980-01-01

55

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

NASA Astrophysics Data System (ADS)

Nicks and dents caused by foreign object damage (FOD) in leading edges of turbine engine blades often provide crack initiation sites that may grow under high cycle fatigue (HCF) conditions and lead to reduced life. Leading edge specimens simulating the geometry of these engine blades were fabricated from STOA Ti-6Al-4V. The leading edges were then ballistically impacted with small steel spheres and the subsequent damage was characterized with SEM according to the crater dimensions (depth and length), material lost, cracks and extrusions. A few specimens were sectioned after impact and SEM of the area beneath the impacts revealed adiabatic shear bands as well as a surface impact transformation layer with a fine transformed microstructure. These shear bands contained micro-cracks, tears and some shrinkage porosity, which indicated the magnitude of the localized high temperatures achieved during the impact. The remaining specimens were subjected to tension-tension axial HCF testing using a step loading fatigue procedure. Fatigue fracture initiation always occurred at the exit side of the impact crater and at the crater center. Extrusions, loss of material and cracks caused by the impact did not correlate well with the normalized fatigue strength. However, SEM of the fractured surfaces beneath the impacts revealed adiabatic shear band traces as well as a surface impact transformation layer exhibiting a fine texture at the fracture initiation sites. Only a moderate correlation existed between the depth of the impact crater and the normalized fatigue stress. No correlation existed between the crater length and the normalized fatigue strength. The failure of several craters with the smaller crater depth strongly suggested that factors not related to the crater geometry were involved. The fatigue limit stress model was able to predict the fatigue limit for craters less than 0.4 mm deep. However, this model underestimated the fatigue strength loss for deeper craters, indicating that another mechanism, such as microstructural damage played an important role. Considering the presence of the transformed microstructure and adiabatic shear bands, the use of slower strain rate methods for producing FOD on the leading edge of a test specimen may need to be re-evaluated.

Birkbeck, Janine C.

56

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

E-print Network

-cycle fatigue (HCF)- related titanium alloy fan and compressor blade failures in military gas-turbine engines failures of gas-turbine jet engines have prompted a re-examination of the design methodologies for HCF-critical components, such as titanium alloy turbine blades. As foreign-object damage (FOD) from ingested debris

Ritchie, Robert

57

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

NASA Technical Reports Server (NTRS)

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

Arakere, N. K.; Swanson, G.

2002-01-01

58

Modeling Fatigue Damage in Long-Fiber Thermoplastics  

Microsoft Academic Search

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

Ba Nghiep Nguyen; Vlastimil Kunc; Satish K. Bapanapalli

2009-01-01

59

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

60

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

SciTech Connect

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

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

2010-12-01

61

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

62

Cumulative creep fatigue damage in 316 stainless steel  

NASA Technical Reports Server (NTRS)

The cumulative creep-fatigue damage behavior of 316 stainless steel at 1500 F was experimentally established for the two-level loading cases of fatigue followed by fatigue, creep fatigue followed by fatigue, and fatigue followed by creep fatigue. The two-level loadings were conducted such that the lower life (high strain) cycling was applied first for a controlled number of cycles and the higher life (low strain) cycling was conducted as the second level to failure. The target life levels in this study were 100 cycles to failure for both the fatigue and creep-fatigue lowlife loading, 5000 cycles to failure for the higher life fatigue loading and 10,000 cycles to failure for the higher life creep-fatigue loading. The failed specimens are being examined both fractographically and metallographically to ascertain the nature of the damaging mechanisms that produced failure. Models of creep-fatigue damage accumulation are being evaluated and knowledge of the various damaging mechanisms is necessary to ensure that predictive capability is instilled in the final failure model.

Mcgaw, Michael A.

1989-01-01

63

Fatigue Damage Evolution in Silicon Films for Micromechanical Applications  

E-print Network

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

Suo, Zhigang

64

Detection of blade damage and ice accretion for health monitoring of wind turbines using integrated blade sensors  

Microsoft Academic Search

Predictive maintenance of wind turbines could provide an estimated 50% reduction in cost when compared to reactive maintenance, which is the current industry approach. The ability to identify damage using wind turbine operating data is necessary for implementing a predictive maintenance approach. Wind turbine blade damage is the most costly type of damage to repair and requires significant down time.

Scott Robert Dana

2011-01-01

65

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

66

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

E-print Network

FATIGUE RESISTANT FIBERGLASS LAMINATES FOR WIND TURBINE BLADES (published for Wind Energy 1996 fatigue resistance depending on the overall fiber content and the relative amounts of reinforcement in each direction. S-N fatigue data are presented for a range of laminates under both tensile

67

Surface Texture of Fretting Fatigue Damaged Shot Peened Titanium  

SciTech Connect

Fretting fatigue damage occurs at the contact between two surfaces, when a static load perpendicular to the interface and a cyclic load parallel to the surfaces are present. The fretting fatigue damage occurring on the surface is known to be responsible for initiation of surface breaking cracks and dramatic reduction of fatigue life of the materials and components. Many premature failures of the engine components of advanced fighter aircrafts have been attributed to the fretting fatigue damage. Though fretting fatigue damage occurs at the surface, NDE techniques have limited success in detecting early stages of damage. This paper presents a methodology based on optical profiling of the surface to evaluate the progression of damage in fretting fatigue damaged specimens of shot peened Ti-6Al-4V. Surface topography measurements performed using a white light interference microscope were analyzed to identify the surface texture parameters sensitive to progressive damage. Results of the relation between the number of fretting fatigue cycles, surface texture parameters, residual stress and the changing microstructure are presented. Potential of the optical surface profiling as a nondestructive evaluation tool for characterization of the fretting fatigue damage is discussed.

Martinez, S. A.; Blodgett, M. P. [Air Force Research Laboratory, Wright Patterson Air Force Base, OH 45433 (United States); Sathish, S. [University of Dayton Research Institute, 300 College Park, Dayton, OH 45467-0127 (United States); Mall, S. [Air Force Institute of Technology, Wright Patterson Air Force Base, OH 45433 (United States)

2006-03-06

68

Aspect of cumulative fatigue damage under multiaxial strain cycling.  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

69

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

70

Detection of localized fatigue damage in steel by thermography  

Microsoft Academic Search

Fatigue damage of unalloyed steels in the high cycle regime is governed by localized cyclic plastic deformations and subsequent crack initiation. The extent of early microplastic deformations depends on the applied stress level, stress concentration at macroscopic notches, surface treatment, residual stresses etc. The onset of a nonlinear material response can be regarded as an early indicator of fatigue damage.

Justus Medgenberg; Thomas Ummenhofer

2007-01-01

71

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

Federal Register 2010, 2011, 2012, 2013

...RIN 2120-AJ52 Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures...final rule, ``Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures...final rule, ``Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft...

2012-08-22

72

Damage detection of cracked thick rotating blades by a spatial wavelet based approach  

Microsoft Academic Search

This paper presents a technique for blade damage detection based on spatial wavelet analysis. The wavelet transform is used to analyze spatially distributed signals (e.g. mode shape) of cracked thick rotating blades. First, a finite element model is applied to the vibration of a thick rotating blade with a single edge crack. The effects of transverse shear deformation and rotatory

Chih-Chieh Chang; Lien-Wen Chen

2004-01-01

73

Helicopter rotor blade frequency evolution with damage growth and signal processing  

NASA Astrophysics Data System (ADS)

Structural damage in materials evolves over time due to growth of fatigue cracks in homogenous materials and a complicated process of matrix cracking, delamination, fiber breakage and fiber matrix debonding in composite materials. In this study, a finite element model of the helicopter rotor blade is used to analyze the effect of damage growth on the modal frequencies in a qualitative manner. Phenomenological models of material degradation for homogenous and composite materials are used. Results show that damage can be detected by monitoring changes in lower as well as higher mode flap (out-of-plane bending), lag (in-plane bending) and torsion rotating frequencies, especially for composite materials where the onset of the last stage of damage of fiber breakage is most critical. Curve fits are also proposed for mathematical modeling of the relationship between rotating frequencies and cycles. Finally, since operational data are noisy and also contaminated with outliers, denoising algorithms based on recursive median filters and radial basis function neural networks and wavelets are studied and compared with a moving average filter using simulated data for improved health-monitoring application. A novel recursive median filter is designed using integer programming through genetic algorithm and is found to have comparable performance to neural networks with much less complexity and is better than wavelet denoising for outlier removal. This filter is proposed as a tool for denoising time series of damage indicators.

Roy, Niranjan; Ganguli, Ranjan

2005-05-01

74

Wind turbine blade damage detection using an active sensing approach  

NASA Astrophysics Data System (ADS)

The wind energy sector is one of the fastest growing parts of the clean energy industry. As the wind energy sector grows, so does an increasing concern for the damage detection of wind turbine blades. This paper proposes an active sensing approach by utilizing piezoceramic transducers as actuators and sensors. The influence of the crack quantity, location, length and depth on the wave propagation was experimentally studied. Sweep sine signals ranging from 1 khz to 50 khz were used as input signals for active sensing. The change in the energy that propagated through the cracks was verified as feasible in detecting crack-related damage. An innovative polar plot analysis method based on Fast Fourier transform was developed to compare the minuscule difference between the damage signals and the baseline signal. The polar plot was able to make apparent differences in both the magnitude and the phase of the signals, which could be correlated to crack depth and plane geometry, respectively, based on the observation of the damage.

Ruan, Jiabiao; Ho, Siu Chun Michael; Patil, Devendra; Li, Mo; Song, Gangbing

2014-10-01

75

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

76

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

SciTech Connect

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

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

1999-12-31

77

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

78

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

79

Fatigue Damage Assessment for Drillship Structure based on Stochastic Method  

Microsoft Academic Search

TOI drillship, first drillship of DSME, was designed to have more than 25 years' fatigue life against given environmental conditions. Fatigue damage in hull and hull-topside interface structures was assessed based on stochastic method. D-SAFS, developed by DSME, generates stress RAO based on 'Component Based Method'. Structural analyses were carried out for each load component. Resultant stress was combined with

Sung-Gun Park; Chang-Hwan Jang; Jae-Hyung Park; Joo-Ho Heo

80

Dynamics and Fatigue Damage of Wind Turbine Rotors  

E-print Network

6 3 RiS0-Rr512 Dynamics and Fatigue Damage of Wind Turbine Rotors during Steady Operation Peter OF WIND TURBINE ROTORS DURING STEADY OPERATION Peter Hauge Madsen, Sten Frandsen, William E. Holley-carrying capacity of a wind turbine rotor with respect to short-term strength and material fatigue are presented

81

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

82

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

Microsoft Academic Search

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

S. S. Manson; G. R. Halford

1981-01-01

83

Drag amplification and fatigue damage in vortex-induced vibrations  

E-print Network

Fatigue damage and drag force amplification due to Vortex-Induced-Vibrations (VIV) continue to cause significant problems in the design of structures which operate in ocean current environments. These problems are magnified ...

Jhingran, Vikas Gopal

2008-01-01

84

A probabilistic fatigue analysis of multiple site damage  

NASA Technical Reports Server (NTRS)

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.

1994-01-01

85

Fatigue damage mechanisms in boron-aluminium composite laminates  

NASA Technical Reports Server (NTRS)

The relationship between fatigue and shakedown in metal matrix composites is investigated theoretically and experimentally for unidirectional and laminated 6061 Al-B materials. It is shown that no fatigue damage takes place if the applied stress range is such that the material remains elastic, or shakes down, i.e., resumes elastic cyclic straining after a small number of plastic strain cycles. Fatigue damage occurs only in specimens subjected to stress ranges which cause sustained cyclic plastic straining in the aluminum matrix. If the applied stress range is smaller than that required for fatigue failure, after about 10 to the 6th cycles a saturation damage state is reached which remains essentially unchanged with increasing number of cycles.

Dvorak, G. J.; Johnson, W. S.

1980-01-01

86

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

87

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

88

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

Microsoft Academic Search

The paper* on implementation of the double linear damage rule for cumulative fatigue damage included Appendices for treatment of two major factors that enter into the analysis - inversion of the fatigue life relationship so that life fractions can more easily be calculated, and treatment of mean stress effects. The discussion of these two subjects represented the state of development

S. S. Manson; G. R. Halford

1981-01-01

89

An empirical modified fatigue damage model for impacted GFRP laminates  

NASA Astrophysics Data System (ADS)

The aim of the present paper is to evaluate the residual strength of GFRP laminates following a low-velocity impact event under cyclic loading. The residual strength is calculated using a linear fatigue damage model. According to an investigation into the effect of low-velocity impact on the fatigue behavior of laminates, it seems laminate fatigue life decreases after impact. By normalizing the fatigue stress against undamaged static strength, the Fatigue Damage parameter “FD” is presented with a linear relationship as its slope which is a linear function of the initial impact energy; meanwhile, the constants were attained from experimental data. FD is implemented into a plane-stress continuum damage mechanics based model for GFRP composite laminates, in order to predict damage threshold in composite structures. An S-N curve is implemented to indicate the fatigue behavior for 2 mm thickness encompassing both undamaged and impacted samples. A decline in lifespan is evident when the impact energy level increases. Finally, the FD is intended to capture the unique GFRP composite characteristics.

Naderi, S.; Hassan, M. A.; Bushroa, A. R.

2014-10-01

90

Laser scanning technique for fatigue damage evolution detection  

NASA Astrophysics Data System (ADS)

Metal components subjected to cyclic stress develop surface-evident defects (microcracks, slip bands, etc). Monitoring the formation and evolution of these fatigue damage precursors (FDPs) with increasing numbers of cycles can be an effective tool for determining the fatigue state of the component, which can be used in remaining fatigue life prognostics. In this paper a laser scanning technique (LST) for FDP detection is described and experimental results from examination of specimens made of nickel-based superalloy and aluminum are presented. The proposed detection technique is based on scanning a focused laser beam over the specimen surface and detecting variations in spatial characteristics of the scattered light signal. These variations indicate the presence of surface abnormalities and therefore can be associated with incremental fatigue damage formation. The studies performed show that the proposed LST can serve as a basis for design of a portable non-contact instrument for in situ structural health monitoring.

Markov, Vladimir B.; Buckner, Benjamin D.; Earthman, J. C.

2005-02-01

91

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

Microsoft Academic Search

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

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

2009-01-01

92

Mechanisms of fatigue damage and crack growth in advanced materials  

NASA Astrophysics Data System (ADS)

In terms of in-service failures, cyclic fatigue is the most prevalent form of fracture. Despite the wealth of information on fatigue failures in traditional structural materials such as (ductile) metals and alloys, far less is understood about the susceptibility of the newer advanced materials, such as (brittle) intermetallics, ceramics and their composites. In this presentation, the mechanics and mechanisms of fatigue damage and crack propagation are examined with particular emphasis on the similarities and differences between cyclic crack growth in ductile metallic materials, and corresponding behavior in the more brittle advanced materials. This is achieved by considering the process of subcritical crack growth as a mutual competition between intrinsic mechanisms of microstructural damage ahead of the crack tip, which promote crack growth, and extrinsic mechanisms of crack-tip shielding behind the tip, which impede it. This approach is shown to be important for the understanding of the structural fatigue properties of advanced materials, such as monolithic and composite ceramics, and a range of intermetallics (e.g., TiAl, MoSi2, Nb3Al), as the mechanisms of fatigue in these brittle materials are conceptually distinct from that associated with the well known metal fatigue. Examples of the application and life-prediction methodologies for such materials in fatigue-critical situations will be given from the aerospace and bioengineering industries.

Ritchie, Robert O.

2001-03-01

93

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

94

Reduction in fiber damage thresholds due to static fatigue  

SciTech Connect

Damage mechanisms may occur during the transmission of Q-switched, Nd/YAG laser pulses through fused silica fibers. Fiber end-face characteristics, laser characteristics, and aspects of the laser-to-fiber injection typically determine dominant damage mechanisms. However, an additional damage process has been observed at internal sites where fibers were experiencing significant local stresses due to fixturing or bends in the fiber path. A transmission reduction prior to damage was typically not measurable at these sites. Damage would not always occur during initial testing, but sometimes occurred later in time at laser levels that previously had been transmitted without damage. In these cases the time at stress appeared to be more important than the number of transmitted shots prior to damage. A possible relation between internal damage thresholds at stressed sites and the total time under stress is suggested by the fact that silica fibers experience static fatigue processes. These processes involve the slow growth of local defects under tensile stress at rates that depend upon environmental conditions. Defects reaching sufficient size and having appropriate location could be sites for reduced laser-induced damage thresholds. The present work looks into the possibility that static fatigue processes can affect damage thresholds. The experiments used a laser injection and fiber routing configuration that produced significantly elevated fluences within fiber core regions under tensile stress. In order to establish initial strength and fatigue properties for these fibers, a number of samples were used to generate time-to-failure data at various stress levels. Other fiber samples were subjected to conditions that greatly accelerated fatigue processes. Internal damage thresholds were then measured in these fibers and compared to thresholds measured in fresh fibers. Conclusive comparisons were frustrated by sample-to-sample and lot-to-lot variations in fiber defects.

Setchell, R.E.

1995-01-01

95

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

Code of Federal Regulations, 2012 CFR

...damage tolerance and fatigue evaluation of commuter...catastrophic failure due to fatigue, corrosion, defects...catastrophic failure. (b) Fatigue (safe-life) evaluation. ...structure must be shown, by analysis supported by test...

2012-01-01

96

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

Code of Federal Regulations, 2011 CFR

...damage tolerance and fatigue evaluation of commuter...catastrophic failure due to fatigue, corrosion, defects...catastrophic failure. (b) Fatigue (safe-life) evaluation. ...structure must be shown, by analysis supported by test...

2011-01-01

97

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

...damage tolerance and fatigue evaluation of commuter...catastrophic failure due to fatigue, corrosion, defects...catastrophic failure. (b) Fatigue (safe-life) evaluation. ...structure must be shown, by analysis supported by test...

2014-01-01

98

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

Code of Federal Regulations, 2010 CFR

...damage tolerance and fatigue evaluation of commuter...catastrophic failure due to fatigue, corrosion, defects...catastrophic failure. (b) Fatigue (safe-life) evaluation. ...structure must be shown, by analysis supported by test...

2010-01-01

99

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

Code of Federal Regulations, 2013 CFR

...damage tolerance and fatigue evaluation of commuter...catastrophic failure due to fatigue, corrosion, defects...catastrophic failure. (b) Fatigue (safe-life) evaluation. ...structure must be shown, by analysis supported by test...

2013-01-01

100

FULL-SCALE BLADE TESTING ENHANCED BY ACOUSTIC EMISSION MONITORING  

Microsoft Academic Search

SUMMARY To ensure that the static and fatigue design loads are sustained, current wind turbine blade certification procedures require full-scale tests on the prototype blade. During these tests sudden audible cracking sounds from within the blade are often generated, without the operators being able to locate the noise source or to evaluate the existence or extent of any damage. As

D. J. Lekou; P. Vionis; P. A. Joosse; D. R. V. van Delft; D. Kouroussis; A. Anastasopoulos; M. J. Blanch

101

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

102

Active sensing of fatigue damage using embedded ultrasonics  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

103

75 FR 24502 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures; Reopening of Comment...  

Federal Register 2010, 2011, 2012, 2013

...Notice No. 10-09] RIN 2120-AJ52 Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures; Reopening of...793) Notice No. 09-12, entitled ``Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures'' that...

2010-05-05

104

Author's personal copy Statistical pattern analysis of ultrasonic signals for fatigue damage detection  

E-print Network

Author's personal copy Statistical pattern analysis of ultrasonic signals for fatigue damage online 6 June 2008 Keywords: Fatigue damage monitoring Ultrasonic sensing nethodology Pattern structures based on statistical pattern analysis of ultrasonic sensor signals. The real-time data

Ray, Asok

105

Early detection of fatigue damage in composite materials  

NASA Technical Reports Server (NTRS)

Early detection of fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for glass/epoxy, graphite/glass/epoxy, and graphite/epoxy composites. Modulus and temperature were monitored and a correlation between them observed. Axial modulus and torsional modulus changes were a function of the laminate orientation. Torsional modulus measurements and coin tap tests were performed at 0, 1 million, 5 million, and 10 million cycles, on axial fatigue specimens. Three distinct regions were noted. In the primary region a small but rapid change in stiffness was noted in the first few thousand cycles. This was followed by a secondary region of little or no stiffness change. The tertiary region was characterized by an increasing rate of stiffness change leading to fracture. NDI procedures including holographic interferometry, ultrasonics, penetrant, and X-ray radiography were evaluated for fatigue damage detection.

Salkind, M. J.

1975-01-01

106

Stochastic Fatigue Damage Accumulation Due to Nonlinear Ship Loads  

Microsoft Academic Search

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

Alok K. Jha; Steven R. Winterstein

2000-01-01

107

Onboard monitoring of fatigue damage rates in the hull girder  

Microsoft Academic Search

Most new advanced ships have extensive data collection systems to be used for continuous monitoring of engine and hull performance, for voyage performance evaluation etc. Such systems could be expanded to include also procedures for stress monitoring and for decision support, where the most critical wave-induced ship extreme responses and fatigue damage accumulation can be estimated for hypothetical changes in

Ulrik Dam Nielsen; Jørgen Juncher Jensen; Preben Terndrup Pedersen; Yuichi Ito

2011-01-01

108

FATIGUE BEHAVIOR OF IMPACT DAMAGED PRESTRESSED CONCRETE BRIDGE GIRDER REPAIRED  

E-print Network

FATIGUE BEHAVIOR OF IMPACT DAMAGED PRESTRESSED CONCRETE BRIDGE GIRDER REPAIRED WITH CFRP SHEETS (CFRP) materials for repair has an excellent potential to provide a fast and efficient technique AASHTO Type II prestressed girder extracted from a bridge and repaired by CFRP material. The impact

109

EXPERIMENTAL INVESTIGATION OF FATIGUE DAMAGE IN COMPOSITE STRUCTURES CONSIDERING SECOND HARMONIC LAMB WAVES  

E-print Network

EXPERIMENTAL INVESTIGATION OF FATIGUE DAMAGE IN COMPOSITE STRUCTURES CONSIDERING SECOND HARMONIC parameter is an appropriate tool to detect micro-structural damages like plasticity and fatigue in metal as well as thermal fatigue and impact damages in composites. In this work the second harmonic generation

Paris-Sud XI, Université de

110

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

E-print Network

Online fatigue damage monitoring by ultrasonic measurements: A symbolic dynamics approach q Shalabh presents an analytical tool for early detection and online monitoring of fatigue damage in polycrystalline-time fatigue damage monitoring algorithms rely on time series analysis of ultrasonic signals that are sensitive

Ray, Asok

111

Early fatigue damage in carbon-fibre composites observed by electrical resistance measurement  

Microsoft Academic Search

Early fatigue damage during the first tenth (or less) of the fatigue life was observed in carbon fibre composites by d.c. electrical resistance measurement. The damage was most severe in the first loading cycle and the incremental damage in each subsequent cycle diminished cycle by cycle. For the continuous carbon fibre carbon-matrix composite, the resistance increased irreversibly during early fatigue

S. Wang; X. Shui; X. Fu; D. D. L. Chung

1998-01-01

112

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

E-print Network

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

Victoria, University of

113

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

114

Composite Wind Turbine Blade Effects of Defects: Part B--Progressive Damage Modeling of Fiberglass/Epoxy  

E-print Network

Composite Wind Turbine Blade Effects of Defects: Part B-- Progressive Damage Modeling of Fiberglass for the reliability of modern composite wind turbine blades. The DOE has sponsored a comprehensive study to a wind turbine blade reliability infrastructure. To support this development of a reliability

115

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

SciTech Connect

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 resonance excitation with forced hydraulic loading to reduce the total test time required while representing the operating strains on the critical inboard blade stations more accurately than a single-axis test system. The analysis and testing required to fully implement the B-REX was significant. To control unanticipated blade motion and vibrations caused by dynamic coupling between the flap, lead-lag, and torsional directions, we needed to incorporate additional test hardware and control software. We evaluated the B-REX test system under stable operating conditions using a combination of various sensors. We then compared our results with results from the same blade, tested previously using NREL's dual-axis forced-displacement test method. Experimental results indicate that strain levels produced by the B-REX system accurately replicated the forced-displacement method. This paper describes the challenges we encountered while developing the new blade fatigue test system and the experimental results that validate its accuracy.

White, D.; Musial, W.; Engberg, S.

2004-12-01

116

Battle damage repair of a helicopter composite main rotor blade  

Microsoft Academic Search

The ability to repair battle damage is an important capability for helicopter structures, as they are vulnerable to ballistic impact damage from small arms fire and therefore more likely than fixed wing aircraft to suffer damage in a combat environment. This paper outlines computational investigations to aid the development of a battle damage repair capability for a helicopter composite main

W. K. Chiu; Z. Zhou; J. Wang; A. Baker

117

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

Microsoft Academic Search

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. The US data base, developed by Mandell, et al. (1995), contains over 2200 data points that were obtained using

Herbert J. Sutherland

1996-01-01

118

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

119

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

120

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

NASA Technical Reports Server (NTRS)

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

Brewer, John

1994-01-01

121

Single-crystal indicators of fatigue and plastic deformation damage  

NASA Astrophysics Data System (ADS)

Specially prepared thin single-crystal plates rigidly fastened to the sample surface area are shown to be effective as sensor elements (indicators and detectors) of the deformation damage of multi-phase commercial alloys under fatigue and static loading. It is proposed to estimate the lifetime and the strain of basic material by monitoring the geometric characteristics of band patterns on the detector surface. It is shown that density, direction of deformation bands and fractal dimension of band patterns on surfaces of indicators correlate with the number of cycles, maximum applied stress (fatigue loading) and plastic strain, temperature (static loading).

Gordienko, Y. G.; Zasimchuk, E. E.

1994-09-01

122

Damage detection method for wind turbine blades based on dynamics analysis and mode shape difference curvature information  

NASA Astrophysics Data System (ADS)

Blades are among the key components of wind turbines. Blade damage is one of the most common types of structural defects and can cause catastrophic structural failure. Therefore, it is highly desirable to detect and diagnose blade damage as early as possible. In this paper, we propose a method for blade damage detection and diagnosis. This method incorporates finite element method (FEM) for dynamics analysis (modal analysis and response analysis) and the mode shape difference curvature (MSDC) information for damage detection/diagnosis. Finite element models of wind turbine blades have been built and modified via frequency comparison with experimental data and the formula for the model updating technique. Our numerical simulation results have demonstrated that the proposed technique can detect the spatial locations of damages for wind turbine blades. Changes in natural frequencies and modes for smaller size blades with damage are found to occur at lower frequencies and lower modes than in the larger sized blade case. The relationship between modal parameters and damage information (location, size) is very complicated especially for larger size blades. Moreover, structure and dynamic characters for larger size blades are different from those for smaller sized blades. Therefore, dynamic response analysis for a larger sized wind turbine blade with a multi-layer composite material based on aerodynamic loads’ (including lift forces and drag forces) calculation has been carried out and improved the efficiency and precision to damage detection by combining (MSDC) information. This method provides a low cost and efficient non-destructive tool for wind turbine blade condition monitoring.

Wang, Yanfeng; Liang, Ming; Xiang, Jiawei

2014-10-01

123

Widespread fatigue damage monitoring: Issues and concerns  

NASA Technical Reports Server (NTRS)

This paper is intended to illustrate the considerable effect that small in-service undetectable multi-site-damage (MSD) can have on the residual strength capability of aging aircraft structures. In general, very few people in the industry believe that tiny cracks of undetectable size are a problem because they know that many aircraft have been able to survive much larger damage. In fact they have been certified for this large damage capability. However, this is not the issue. The real issue is the effect the tiny cracks, at multiple sites, have on the large damage capability which the industry has become accustomed to expect and which the aircraft have been certified to sustain. The concern is that this message does not appear to be fully understood by many people outside the fracture community. The prime purpose of this paper, therefore, has been to convey this message by describing in simple terms the net section yielding phenomenon in ductile materials which causes loss in lead crack residual strength in the presence of MSD. The explanation continues with a number of examples on complex stiffened structures, using the results of previous finite element analyses, which illustrate that the effect of MSD is extremely sensitive to structural configuration. It is hoped that those members of the aviation community who believe that tiny cracks are not a problem will read this paper very carefully.

Swift, T.

1994-01-01

124

Fatigue damage prognosis using affine arithmetic  

NASA Astrophysics Data System (ADS)

Among the essential steps to be taken in structural health monitoring systems, damage prognosis would be the field that is least investigated due to the complexity of the uncertainties. This paper presents the possibility of using Affine Arithmetic for uncertainty propagation of crack damage in damage prognosis. The structures examined are thin rectangular plates made of titanium alloys with central mode I cracks and a composite plate with an internal delamination caused by mixed mode I and II fracture modes, under a harmonic uniaxial loading condition. The model-based method for crack growth rates are considered using the Paris Erdogan law model for the isotropic plates and the delamination growth law model proposed by Kardomateas for the composite plate. The parameters for both models are randomly taken and their uncertainties are considered as defined by an interval instead of a probability distribution. A Monte Carlo method is also applied to check whether Affine Arithmetic (AA) leads to tight bounds on the lifetime of the structure.

Gbaguidi, Audrey; Kim, Daewon

2014-02-01

125

The treatment of fatigue and damage accumulation in composite design  

NASA Astrophysics Data System (ADS)

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

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

1992-09-01

126

Mechanics and mechanisms of fatigue damage and crack growth in advanced materials  

E-print Network

that they are susceptible to cyclic fatigue failure (e.g., Dauskardt et al., 1987). Ironically, this fatigue susceptibilityMechanics and mechanisms of fatigue damage and crack growth in advanced materials R.O. Ritchie*, C 94720-1760, USA Abstract The mechanisms of fatigue-crack propagation in ceramics and intermetallics

Ritchie, Robert

127

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

128

Fatigue and damage tolerance evaluation of an aircraft spoiler  

NASA Astrophysics Data System (ADS)

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

Hurlebaus, Stefan; Gaul, Lothar

2005-05-01

129

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

E-print Network

A continuum damage modelling of quasi-static fatigue strength of plain concrete S. H. Maia,b , F of concrete. The approach is based on the framework of continuum damage mechanics where the fatigue model fatigue tests have been performed on a concrete the formulation of which is close to the one used

Paris-Sud XI, Université de

130

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

E-print Network

643 In-situ fatigue damage monitoring using symbolic dynamic filtering of ultrasonic signals D a data-driven method of pattern identification for in-situ monitor- ing of fatigue damage of the possible structural degradation under fatigue load. The proposed method is capable of detecting small

Ray, Asok

131

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

132

OPERATIONAL MODAL ANALYSIS AND WAVELET TRANSFORMATION FOR DAMAGE IDENTIFICATION IN WIND TURBINE BLADES  

E-print Network

OPERATIONAL MODAL ANALYSIS AND WAVELET TRANSFORMATION FOR DAMAGE IDENTIFICATION IN WIND TURBINE-frequency modes. KEYWORDS : Wind Turbine Blades, Debonding, Wavelet Transformation, Operational Modal Analysis. INTRODUCTION While failure can happen in any structural component of the wind turbine, one of the most common

Paris-Sud XI, Université de

133

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

E-print Network

experimental results, new suggested method of damage index identification showed very good performance assessment, source location, wind turbine blade, hybrid composites INTRODUCTION Structural health management of technique, that is an in-situ monitoring of integrity of materials or structures, becomes increasingly

Boyer, Edmond

134

REPAIR OF BRIDGE STEEL GIRDERS DAMAGED BY DISTORTION-INDUCED FATIGUE  

E-print Network

This study investigates the repair of steel bridge girders damaged by distortion-induced fatigue. The study is presented in three parts. The first part describes finite element modeling techniques used to evaluate the potential for fatigue cracks...

Alemdar, Fatih

2011-12-31

135

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

136

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

137

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

Microsoft Academic Search

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

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

2008-01-01

138

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

139

The effect of yield strength and ductility to fatigue damage  

NASA Technical Reports Server (NTRS)

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

Yeh, H. Y.

1973-01-01

140

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

Microsoft Academic Search

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

A. Fatemi; L. Yang

1998-01-01

141

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

PubMed Central

Bone damage removal and callus formation in response to fatigue loading are essential to prevent fractures. Periostin (Postn) is a matricellular protein that mediates adaptive response of cortical bone to loading. Whether and how periostin influences damage and the injury response to fatigue remains unknown. We investigated the skeletal response of Postn-/- and Postn+/+ mice after fatigue stimulus by axial compression of their tibia. In Postn+/+ mice, cracks number and surface (CsNb, CsS) increased 1h after fatigue, with a decrease in strength compared to non-fatigued tibia. At 15 days, CsNb had started to decline, while CtTV and CtBV increased in fatigued vs non-fatigued tibia, reflecting a woven bone response that was present in 75% of the fatigued bones. Cortical porosity and remodelling also prominently increased in the fatigued tibia of Postn+/+ mice. At 30 days, paralleling a continuous removal of cortical damage, strength of the fatigued tibia was similar to the non-fatigue tibia. In Postn-/- mice, cracks were detectable even in the absence of fatigue, while the amount of collagen crosslinks and tissue hardness was decreased compared to Postn+/+. Fatigue significantly increased CsNb and CsS in Postn-/-, but was not associated with changes in CtTV and CtBV, as only 16% of the fatigued bones formed some woven bone. Cortical porosity and remodelling did not increase either after fatigue in Postn-/- , and the level of damage remained high even after 30 days. As a result, strength remained compromised in Postn-/- mice. Contrary to Postn+/+ , which osteocytic lacunae showed a change in the degree of anisotropy (DA) after fatigue, Postn-/- showed no DA change. Hence periostin appears to influence bone materials properties, damage accumulation and repair, including local modeling/remodeling processes in response to fatigue. These observations suggest that the level of periostin expression could influence the propensity to fatigue fractures. PMID:24167618

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

2013-01-01

142

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

143

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

144

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

145

REAL-TIME FATIGUE DAMAGE MONITORING VIA IN SITU ULTRASONIC SENSING  

Microsoft Academic Search

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

Shalabh Guptayand; Asok Rayz

146

SUBSPACE-BASED DETECTION OF FATIGUE DAMAGE ON JACKET SUPPORT STRUCTURES OF OFFSHORE WIND TURBINES  

E-print Network

SUBSPACE-BASED DETECTION OF FATIGUE DAMAGE ON JACKET SUPPORT STRUCTURES OF OFFSHORE WIND TURBINES structures of wind energy turbines. Based on results of an experimental fatigue test on a steel frame damage in real size structural components of offshore wind turbines. KEYWORDS : Damage detection

Paris-Sud XI, Université de

147

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

Microsoft Academic Search

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

Shalabh Gupta; Asok Ray; Eric Keller

2007-01-01

148

Integration of structural health monitoring and fatigue damage prognosis  

NASA Astrophysics Data System (ADS)

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

Ling, You; Mahadevan, Sankaran

2012-04-01

149

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

150

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

E-print Network

High cycle fatigue damage mechanisms in cast aluminium subject to complex loads Imade Koutiria to the high cycle fatigue behaviour of cast hypo-eutectic Al­Si alloys. In particular, the AlSi7Cu05Mg03 alloy is investigated. It presents the results of a vast experimental campaign undertaken to investigate the fatigue

Paris-Sud XI, Université de

151

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

E-print Network

Fatigue design 2011 ­ November 23 & 24 ­ Cetim, Senlis - France 1 of 8 MECHANICAL BEHAVIOR of ceramics within the substrate and hence may contribute to the fatigue damage of the circuit lines. Two INTRODUCTION Improving the reliability and the fatigue life of power electronic substrates is a real challenge

152

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

153

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

154

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

155

Modeling of fatigue behavior and damage tolerance/durability in fiber metal laminates  

NASA Astrophysics Data System (ADS)

This dissertation presents the investigation into the fatigue behavior and damage tolerance of fiber metal laminates-S2-glass fiber reinforced aluminum laminates (Glare). Glare laminates exhibit excellent fatigue resistant behavior and damage tolerance based on the experimental work. Methodologies are established to predict the crack initiation life, crack path angle, crack growth rate under constant-amplitude and block-spectrum fatigue loading. The multiple-site-fatigue damage in Glare laminates is investigated as well. Analytical and numerical prediction models are established for fatigue behavior under different cyclic loading cases. In this dissertation, it is intended to research on these areas to have a thorough and complete understanding of Glare laminates in fatigue behavior and ability to damage tolerance and durability.

Chang, Po-Yu

156

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

157

Fatigue damage mechanisms in short fiber reinforced PBT+PET GF30  

Microsoft Academic Search

The fatigue damage of a glass-reinforced PolyButylene Terephthalate and PolyEthylene Terephthalate with the fiber volume fraction of 30% (PBT+PET GF30) is investigated by means of various techniques. Fatigue tests at R=0.1 are carried out on dogbone specimens and tubular specimens with different fiber orientations. The macroscopic evolution of the material behavior is evaluated and fatigue damage mechanisms are observed with

B. Klimkeit; S. Castagnet; Y. Nadot; A. El Habib; G. Benoit; S. Bergamo; C. Dumas; S. Achard

2011-01-01

158

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

159

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

Microsoft Academic Search

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

Thomas Ørts Pedersen

2000-01-01

160

Investigation of Residual Strength and Fatigue Life of Unstiffined Aluminum Panels with Multiple Site Damage.  

National Technical Information Service (NTIS)

Multiple Site Damage (MSD) is the occurrence of small fatigue cracks at several sites within aircraft structures. This is important since it may lower the residual strength and fatigue life of the structure beyond what can be predicted using the damage to...

M. C. Cherry

1995-01-01

161

Failure Mechanisms and Damage Model of Ductile Cast Iron Under Low-Cycle Fatigue Conditions  

NASA Astrophysics Data System (ADS)

Strain-controlled low-cycle fatigue (LCF) tests were conducted on ductile cast iron (DCI) at strain rates of 0.02, 0.002, and 0.0002/s in the temperature range from room temperature to 1073 K (800 °C). A constitutive-damage model was developed within the integrated creep-fatigue theory (ICFT) framework on the premise of strain decomposition into rate-independent plasticity and time-dependent creep. Four major damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement (IE), (iii) creep, and (iv) oxidation were considered in a nonlinear creep-fatigue interaction model which represents the overall damage accumulation process consisting of oxidation-assisted fatigue crack nucleation and propagation in coalescence with internally distributed damage ( e.g., IE and creep), leading to final fracture. The model was found to agree with the experimental observations of the complex DCI-LCF phenomena, for which the linear damage summation rule would fail.

Wu, Xijia; Quan, Guangchun; MacNeil, Ryan; Zhang, Zhong; Sloss, Clayton

2014-10-01

162

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

SciTech Connect

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. The US data base, developed by Mandell, et al. (1995), contains over 2200 data points that were obtained using coupon testing procedures. These data are used to construct a Goodman diagram that is suitable for analyzing wind turbine blades. This result is compared to the Goodman diagram derived from the European fatigue data base FACT. The LIFE2 fatigue analysis code for wind turbines is then used to predict the service lifetime of a turbine blade subjected to the two loading histories. The results of this study indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a US wind farm site; i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a US wind farm site. Further, the analyses demonstrate that the European and the US fatigue material data bases are in general agreement for the prediction of tensile failures. However, for compressive failures, the two data bases are significantly different, with the US data base predicting significantly shorter service lifetimes than the European data base.

Sutherland, H.J.

1996-02-01

163

A SMALL-SCALE DAMAGE APPROACH TO PREDICT FATIGUE CRACK GROWTH IN CERAMIC MATERIALS  

SciTech Connect

This paper proposes a small-scale damage modeling approach to predict fatigue crack growth in ceramic materials. A fatigue damage model is formulated that uses two variables. One variable is the scalar damage variable governing the reduction of stiffness, and the other is the number of cycles. The damage evolution law is obtained based on thermodynamics of continuous media and a damage criterion containing a damage threshold function that depends on the damage variable and the cyclic loading parameters. The model has been implemented into the ABAQUS finite element code via user-subroutines and has been used in a modified boundary layer (MBL) modeling approach to analyze fatigue crack growth in a small fracture process zone situated at an initial crack tip. The model application is illustrated through an analysis of fatigue crack growth in an yttria-stabilized tetragonal zirconia material.

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

2006-05-19

164

Fatigue damage evolution in uni-directional metal matrix composites using a micro-mechanical damage model  

SciTech Connect

In recent years Metal Matrix Composites (MMC) have drawn wide attention as candidate materials for high temperature applications needed in aerospace and aeronautic industries. Especially the Titanium Matrix Composites (TMC) have been favored for such applications mainly due to their high strength to weight ratio and their ability to maintain their structural integrity even at elevated temperatures. Despite the increased use of these TMC`s for the last decade there is still a need for appropriate material models able to simulate the material behavior of such advanced MMC`s under severe loading conditions such as fatigue loading. Modeling fatigue behavior of MMC`s requires the prediction of material degradation during the material lifetime through the concept of damage and damage evolution. A micro-mechanical fatigue damage model is proposed here capable of modeling damage evolution at the constituent level. Damage criteria are defined for each individual constituent and appropriate damage evolution laws are derived. Furthermore damage evolution in the interface region is considered separately. The overall composite damage is obtained through the employment of a homogenization procedure such as the Mori-Tanaka averaging scheme. Numerical results are shown for high cycle fatigue with respect to a variation in various material and damage model parameters. Furthermore the damage evolution in the fiber, the matrix and the overall composite is presented for a complete fatigue simulation.

Echle, R.; Voyiadjis, G.Z. [Louisiana State Univ., Baton Rouge, LA (United States). Dept. of Civil and Environmental Engineering

1997-07-01

165

Early response to tendon fatigue damage accumulation in a novel in vivo model  

PubMed Central

This study describes the development and application of a novel rat patellar tendon model of mechanical fatigue for investigating the early in vivo response to tendon subfailure injury. Patellar tendons of adult female Sprague-Dawley rats were fatigue loaded between 1–35 N using a custom-designed loading apparatus. Patellar tendons were subjected to Low-, Moderate- or High-level fatigue damage, defined by grip-to-grip strain measurement. Molecular response was compared with that of a laceration-repair injury. Histological analyses showed that progression of tendon fatigue involves formation of localized kinked fiber deformations at Low damage, which increased in density with presence of fiber delaminations at Moderate damage, and fiber angulation and discontinuities at High damage levels. RT-PCR analysis performed at 1- and 3-day post-fatigue showed variable changes in type I, III and V collagen mRNA expression at Low and Moderate damage levels, consistent with clinical findings of tendon pathology and were modest compared with those observed at High damage levels, in which expression of all collagens evaluated were increased markedly. In contrast, only type I collagen expression was elevated at the same time points post-laceration. Findings suggest that cumulative fatigue in tendon invokes a different molecular response than laceration. Further, structural repair may not be initiated until reaching end-stage fatigue life, where the repair response may unable to restore the damaged tendon to its pre-fatigue architecture. PMID:19939387

Fung, David T.; Wang, Vincent M.; Andarawis-Puri, Nelly; Basta-Pljakic, Jelena; Li, Yonghui; Laudier, Damien M.; Sun, Hui B.; Jepsen, Karl J.; Schaffler, Mitchell B.; Flatow, Evan L.

2012-01-01

166

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

167

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

168

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

169

Fatigue Damage Identification in Composite Structures Through Ultrasonics and Wavelet Transform Signal Processing  

NASA Astrophysics Data System (ADS)

This is an investigation on the damage behavior of fiberglass/epoxy specimens with embedded piezoelectrics under axial tensile fatigue. The specimen's local and global damage states are complicated by the specimen's own stretching under loading, which varies as a function of damage. A signal processing technique based on wavelet transforms is presented: denoised signals are processed with Gabor wavelet transforms, and the area of one of the contours is tracked throughout the fatigue life.

La Saponara, V.; Lestari, W.; Winkelmann, C.; Arronche, L.; Tang, H.-Y.

2011-06-01

170

Damage-Coupled Constitutive Model for Uniaxial Ratcheting and Fatigue Failure of 304 Stainless Steel  

Microsoft Academic Search

Based on the existed experimental results of 304 stainless steel, the evolution of fatigue damage during the stress-controlled cyclic loading was discussed first. Then, a damage-coupled visco-plastic cyclic constitutive model was proposed in the framework of unified visco-plasticity and continuum damage mechanics to simulate the whole-life ratcheting and predict the fatigue failure life of the material presented during the uniaxial

Guozheng Kang; Jun Ding; Yujie Liu

2008-01-01

171

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

Microsoft Academic Search

The development of fatigue damage in four [0\\/90][sub s] SCS-6\\/Ti-15-3 laminates containing center holes was investigated. A methodology to predict damage initiation based on an effective strain parameter was used to determine the stress levels and the number of cycles required for matrix crack initiation. Damage progression was monitored at various stages of fatigue loading. In general, a saturated state

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

1993-01-01

172

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

173

Sparkr Blade Test Centre Static tests of wind turbine blades  

E-print Network

test, · Edgewise proof test. · Visual inspection of blade After receipt of the blade, a typical blade-wise presentation of the strain distribution can reveal high strain gradients that could reduce the fatigue life

174

Risk assessment of Cumberland unit 2 L-O blades  

SciTech Connect

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

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

1996-12-31

175

Use of Residual Compression in Design to Improve Damage Tolerance in Ti6Al4V Aero Engine Blade Dovetails  

Microsoft Academic Search

The deep stable layer of compressive residual stress produced by low plasticity burnishing (LPB) has been demonstrated to improve the damage tolerance in engine alloys IN718, Ti-6Al-4V, and 17-4PH. This paper describes the application of LPB to the dovetail bedding surface of a Ti-6Al- 4V fan blade to mitigate the adverse effects of fretting-induced microcracks. Blades removed from fielded engines

Paul S. Prevéy; N. Jayaraman; Ravi A. Ravindranath

176

Experimental and analytical study of fatigue damage in notched graphite/epoxy laminates  

NASA Technical Reports Server (NTRS)

Fatigue damage development in notched graphite/epoxy laminates is investigated in both compression and tension, with tested specimens being examined for damage type and location using light microscopy, scanning electron microscopy, ultrasonic C-scans, and X-radiography. Delamination and ply cracking were found to be the dominant types of fatigue damage. Comparison of observed delamination locations with finite element calculations indicates that both interlaminar shear and peel stresses must be considered when predicting delamination. Fatigue loading generally caused only small stiffness losses, and residual strengths were in all cases greater than, or equal to, the virgin strengths.

Whitcomb, J. D.

1981-01-01

177

Acousto-ultrasonics-based fatigue damage characterization: Linear versus nonlinear signal features  

NASA Astrophysics Data System (ADS)

Engineering structures are prone to fatigue damage over service lifespan, entailing early detection and continuous monitoring of the fatigue damage from its initiation through growth. A hybrid approach for characterizing fatigue damage was developed, using two genres of damage indices constructed based on the linear and the nonlinear features of acousto-ultrasonic waves. The feasibility, precision and practicability of using linear and nonlinear signal features, for quantitatively evaluating multiple barely visible fatigue cracks in a metallic structure, was compared. Miniaturized piezoelectric elements were networked to actively generate and acquire acousto-ultrasonic waves. The active sensing, in conjunction with a diagnostic imaging algorithm, enabled quantitative evaluation of fatigue damage and facilitated embeddable health monitoring. Results unveiled that the nonlinear features of acousto-ultrasonic waves outperform their linear counterparts in terms of the detectability. Despite the deficiency in perceiving small-scale damage and the possibility of conveying false alarms, linear features show advantages in noise tolerance and therefore superior practicability. The comparison has consequently motivated an amalgamation of linear and nonlinear features of acousto-ultrasonic waves, targeting the prediction of multi-scale damage ranging from microscopic fatigue cracks to macroscopic gross damage.

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

2014-03-01

178

Cumulative creep-fatigue damage evolution in an austenitic stainless steel  

NASA Technical Reports Server (NTRS)

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

Mcgaw, Michael A.

1992-01-01

179

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

Microsoft Academic Search

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

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

1988-01-01

180

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

181

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

Microsoft Academic Search

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

Bao Rasebolai Mosinyi

2007-01-01

182

Application of nonlinear dynamics to monitoring progressive fatigue damage in human cortical bone  

E-print Network

is manifested by progressive bone density loss, simultaneous with microcracking. It is a serious health issueApplication of nonlinear dynamics to monitoring progressive fatigue damage in human cortical bone T to study progressive material fatigue in human bone are described. Material nonlinear dynamical response

183

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

Microsoft Academic Search

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

Curtis A. Rideout; Scott J. Ritchie

2007-01-01

184

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

E-print Network

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

Sottos, Nancy R.

185

Fatigue properties of MA 6000E, a gamma-prime strengthened ODS alloy. [Oxide Dispersion Strengthened Ni-base alloy for gas turbine blade applications  

NASA Technical Reports Server (NTRS)

MA 6000E is a corrosion resistant, gamma-prime strengthened ODS alloy under development for advanced turbine blade applications. The high temperature, 1093 C, rupture strength is superior to conventional nickel-base alloys. This paper addresses the fatigue behavior of the alloy. Excellent properties are exhibited in low and high cycle fatigue and also thermal fatigue. This is attributed to a unique combination of microstructural features, i.e., a fine distribution of dispersed oxides and other nonmetallics, and the highly elongated grain structure which advantageously modify the deformation characteristics and crack initiation and propagation modes from that characteristic of conventional gamma-prime hardened superalloys.

Kim, Y. G.; Merrick, H. F.

1980-01-01

186

Analysis of fatigue failure of rotor blades of gas turbine engines made of cast nickel-chrome alloys of the ZhS type  

Microsoft Academic Search

Conglusions 1.In the new blades, the fatigue crack initiates and propagates in the stable slip band in the (111) plane (stage I) restricted by one of the largest grains extending to the surface in the zone of the entry or exit edge or on the side of the vane. In subsequent stages, the crack propagates in the plane of action

I. A. Makovetskaya; O. I. Marusii; B. A. Gryaznov; Yu. S. Nalimov

1987-01-01

187

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

2012-04-01

188

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

E-print Network

1 Fatigue Life of Damaged Bridge Deck Panels Strengthened With Carbon Fiber Sheets Hongseob Oh, Jongsung Sim, and Christian Meyer ABSTRACT To simulate fatigue damage to bridge deck slabs, cyclic loading to fatigue loads differed markedly from the results of static tests. Isotropic reinforcement was found

Meyer, Christian

189

Effects Of Single And Three-Pole Switching And High-Speed Reclosing On Turbine-Generator Shafts And Blades  

Microsoft Academic Search

A cause of high cycle fatigue in turbine blades is the resonance of blade vibratory modes with steam excitation. Single-pole switching (SPS) and high-speed reclosing (HSR) can excite 120 Hz torque oscillations that may resonate with the coupled blade-rotor torsional natural frequency and inflict damage on the blades. Using a new advanced continuum model, this paper analyzes the effect of

Avelino Gonzalez; G. C. Kung; C. Raczkowski; C. W. Taylor; D. Thonn

1984-01-01

190

Fatigue damage accumulation and property degradation in flat versus cylindrical specimens  

E-print Network

and property degradation for flat and cylindrical specimens. This study examines the extent that edge effects may influence fatigue damage prior to catastrophic failure. Flat and cylindrical specimens were tested in static tension, static compression, quasi...-static tension, quasi-static compression, and compression- compression fatigue. The information gained from the mechanical tests was used in conjunction with non-destructive evaluation (NDE) techniques to track accumulated damage. The destructive tests...

Andrews, Kristine Bachtel

2012-06-07

191

Numerical Simulation for Predicting Fatigue Damage Progress in Notched CFRP Laminates by Using Cohesive Elements  

NASA Astrophysics Data System (ADS)

This study proposes the cohesive zone model (CZM) for predicting fatigue damage growth in notched carbon-fiber-reinforced composite plastic (CFRP) cross-ply laminates. In this model, damage growth in the fracture process of cohesive elements due to cyclic loading is represented by the conventional damage mechanics model. We preliminarily investigated whether this model can appropriately express fatigue damage growth for a circular crack embedded in isotropic solid material. This investigation demonstrated that this model could reproduce the results with the well-established fracture mechanics model plus the Paris' law by tuning adjustable parameters. We then numerically investigated the damage process in notched CFRP cross-ply laminates under tensile cyclic loading and compared the predicted damage patterns with those in experiments reported by Spearing et al. (Compos. Sci. Technol. 1992). The predicted damage patterns agreed with the experiment results, which exhibited the extension of multiple types of damage (e.g., splits, transverse cracks and delaminations) near the notches.

Okabe, Tomonaga; Yashiro, Shigeki

192

Damage behaviour of composite systems under biaxial fatigue loading  

Microsoft Academic Search

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

Ebrahim Lamkanfi

193

Nondestructive characterization of corrosion damage and fatigue life  

NASA Astrophysics Data System (ADS)

Microradiographic and ultrasonic characterization of fatigue crack emanating from pitting corrosion is discussed. Crack initiation and growth from the artificial pit of different depths in Al-2024-T3 alloy is studied experimentally. The effect of crack closure on the radiographical and ultrasonic detection of fatigue crack is also illustrated. The experimental results were analyzed using fracture mechanics models including those for small cracks. The model shows very good agreement with experiment in describing the initial and growth of a crack emanating from a pit and in predicting the dependence of the reduction of fatigue life on pit size. Using this analysis, a relation between the depth of the corrosion pit and the fatigue life is established, and thus the prediction of fatigue life of the sample with corrosion pit can be predicted based on the radiographic and ultrasonic measurements of pit and crack sizes.

Rokhlin, Stanislov I.; Zoofan, B.; Kim, J.-Y.; Dai, W.

1999-01-01

194

Damage-Coupled Constitutive Model for Uniaxial Ratcheting and Fatigue Failure of 304 Stainless Steel  

NASA Astrophysics Data System (ADS)

Based on the existed experimental results of 304 stainless steel, the evolution of fatigue damage during the stress-controlled cyclic loading was discussed first. Then, a damage-coupled visco-plastic cyclic constitutive model was proposed in the framework of unified visco-plasticity and continuum damage mechanics to simulate the whole-life ratcheting and predict the fatigue failure life of the material presented during the uniaxial stress-controlled cyclic loading with non-zero mean stress. In the proposed model, the whole life ratcheting was described by employing a non-linear kinematic hardening rule, i.e., the Armstrong-Frederick model combined with the Ohno-Wang model I, and considering the effect of fatigue damage. The damage threshold was employed to determine the failure life of the material. The simulated whole-life ratcheting and predicted failure lives are in a fairly good agreement with the experimental ones of 304 stainless steel.

Kang, Guozheng; Ding, Jun; Liu, Yujie

195

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

196

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

197

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

198

Assessment of material fatigue damage using nonlinear vibro-modulation technique  

NASA Astrophysics Data System (ADS)

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

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

2001-05-01

199

Linear and nonlinear acoustic control of accumulated fatigue damage in steel  

NASA Astrophysics Data System (ADS)

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

Sutin, Alexander; Kin, Yulian; Johnson, Paul

2001-05-01

200

Fatigue Analysis of Multiple Site Damage at a Row of Holes in a Wide Panel.  

National Technical Information Service (NTIS)

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 fra...

K. Buhler, A. F. Grandt, E. J. Moukawsher

1994-01-01

201

VOTING NEURAL NETWORK CLASSIFIER FOR DETECTION OF FATIGUE DAMAGE IN AIRCRAFTS  

E-print Network

VOTING NEURAL NETWORK CLASSIFIER FOR DETECTION OF FATIGUE DAMAGE IN AIRCRAFTS Ziemowit Dworakowski1 in aircraft structures is presented in the paper. Damage indices are calculated from Lamb-wave measurements of the structural integrity monitoring of aircraft structures for the operation and main- tenance strategy

Boyer, Edmond

202

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

203

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

204

Effects of pitting damage on fatigue limit and lifetime in mercury target  

NASA Astrophysics Data System (ADS)

High power spallation targets for neutron source are being developed in the world. Mercury target will be installed at the material and life science facility in J-PARC, which will promote innovative science. The moment the proton beams bombard the mercury target, pressure waves will be generated in mercury by thermally shocked heat deposition. Cavitation will be induced through the pressure wave propagation in the mercury and erode the vessel inner surface contacting with mercury, i.e. pitting damage. The eroded vessel wall is damaged by cyclic fatigue because pulsed proton beams strike the target repeatedly. It is, therefore, important to evaluate the fatigue strength of the eroded vessel wall from the viewpoint of target lifetime estimation. In the paper, we describe the effects of pitting damage, cyclic fatigue damage and mercury environment on the lifetime of the mercury target.

Futakawa, M.; Naoe, T.; Kogawa, H.; Teshigawara, M.; Ikeda, Y.

2006-09-01

205

Fatigue  

MedlinePLUS

Home Fact Sheet Categories Internet Bookmarks on AIDS Have Questions? Printing & Downloading ... Sheet 551 Fatigue WHAT IS FATIGUE? IS FATIGUE IMPORTANT? HOW DO I KNOW IF I HAVE FATIGUE? WHAT CAUSES ...

206

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

207

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

208

The fatigue damage behavior of a single crystal superalloy  

NASA Technical Reports Server (NTRS)

The uniaxial fatigue behavior of a single crystal superalloy, PWA 1480, is described. Both monotonic tensile and constant amplitude fatigue tests were conducted at room temperature, in an effort to assess the applicability of polycrystalline-based fatigue life prediction methods to a single crystal superalloy. The observed constant amplitude behavior correlated best using a stress-based life criterion. Nearly all specimens failed at surface or slightly subsurface microporosity; this is thought to be responsible for the unusually large amount of scatter in the test results. An additional term is developed in the stress-life equation for the purpose of accounting for the effect of microporosity on fatigue life. The form chosen is a function of the effective area of the failure-producing microporosity projected on a plane perpendicular to the loading axis, as well as the applied stress. This additional term correlated the data to within factors of two on life. Although speculative, extrapolation of the microporosity relation to zero micropore area indicates that approximately an order of magnitude improvement in fatigue life should result.

Mcgaw, Michael A.

1988-01-01

209

Progressive Fatigue Damage Modeling of Cross-ply Laminates, I: Modeling Strategy  

Microsoft Academic Search

The main goal of this research is the fatigue simulation of cross-ply laminates under cyclic tension—tension loading conditions. For this purpose, a progressive fatigue damage model is developed based on two main assumptions. First, it is assumed that off-axis plies are responsible for stress redistribution into the laminate. Second, on-axis plies are responsible for strength reduction and control failure of

M. M. Shokrieh; F. Taheri-Behrooz

2010-01-01

210

The fatigue behaviour and damage development of 3D woven sandwich composites  

Microsoft Academic Search

In this paper, the bending fatigue behaviour and damage development during fatigue of polyurethane (PUR)-epoxy 3D woven sandwich composites is investigated. 3D sandwich fabrics are produced by a velvet weaving technique. It allows relatively easy production of delamination-resistant sandwich panels, compared to more traditional sandwich structures with honeycomb or foam cores. In this paper, the 3D sandwich fabrics made of

H. Judawisastra; J. Ivens; I. Verpoest

1998-01-01

211

Development of thermal fatigue damage in 1CrMoV rotor steel  

Microsoft Academic Search

Crack initiation endurances have been determined for a 1CrMoV rotor steel in uniaxial service cycle thermo-mechanical fatigue (TMF) tests formulated to simulate a range of steam turbine start cycles with a maximum temperature of 565°C. The experimental details for these TMF tests are described.Post test inspection has been employed to characterise the associated thermal fatigue damage mechanisms for the steel

S. R. Holdsworth; E. Mazza; L. Binda; L. Ripamonti

2007-01-01

212

Repair of Steel Bridge Girders Damaged by Distortion-Induced Fatigue  

E-print Network

Association of State Highway and Transportation Officials BP Back Plate CFRP Carbon Fiber Reinforced Polymer CP Connection Plate DOT Department of Transportation FEA Finite Element Analysis HSS Hot Spot Stress LRFD Load and Resistance Factor Design... to prevent further crack propagation. The second thrust of the study was to investigate the use of composite materials to repair fatigue damage. Assemblies with welded cover plates, a type of connection detail well known for its susceptibility to fatigue...

Nagati, Amr Daniel

2012-08-31

213

Interlaminar Shear Fatigue Damage Evolution of 2-D Carbon-Carbon Composites  

Microsoft Academic Search

Low-cycle and high-cycle bending fatigue experiments were conducted on 2-D woven carbon-carbon composites at room temperature to evaluate the possible evolution of damage within their complex microstructure. Since carbon-carbons are known to be weak in interlaminar shear, a 3-point bending geometry was chosen to produce high interlaminar shear stresses. This paper extends previous work by focusing on interlaminar shear fatigue,

J. C. Williams; S. W. Yurgartis; J. C. Moosbrugger

1996-01-01

214

CREEP-FATIGUE DAMAGE DEVELOPMENT DURING SERVICE-CYCLE THERMOMECHANICAL FATIGUE TESTS OF 1CrMoV ROTOR STEEL  

Microsoft Academic Search

Service-cycle thermo-mechanical fatigue (TMF) tests have been performed on a 1CrMoV steam turbine rotor steel, with unexpected consequences in terms of the observed deformation and damage development characteristics. The tests were conducted on two heats of the rotor steel using service-like cycles without and with hold times at peak temperature. The temperature and mechanical strain control profiles of the cycles

Stuart R Holdsworth; Edoardo Mazza; Arnd Jung

215

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

216

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

217

Analysis and prediction of Multiple-Site Damage (MSD) fatigue crack growth  

NASA Technical Reports Server (NTRS)

A technique was developed to calculate the stress intensity factor for multiple interacting cracks. The analysis was verified through comparison with accepted methods of calculating stress intensity factors. The technique was incorporated into a fatigue crack growth prediction model and used to predict the fatigue crack growth life for multiple-site damage (MSD). The analysis was verified through comparison with experiments conducted on uniaxially loaded flat panels with multiple cracks. Configuration with nearly equal and unequal crack distribution were examined. The fatigue crack growth predictions agreed within 20 percent of the experimental lives for all crack configurations considered.

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

1992-01-01

218

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

219

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

220

Nonlinear ultrasonics for in situ damage detection during high frequency fatigue  

NASA Astrophysics Data System (ADS)

In this paper, we report the use of the feedback signal of an ultrasonic fatigue system to dynamically deduce fatigue damage accumulation via changes in the nonlinear ultrasonic parameter. The applicability of this parameter in comparison to the resonant frequency for assessment of fatigue damage accumulation in a wrought aluminum alloy has been demonstrated, without the need for coupling fluids or independent generation of incident ultrasonic waves. The ultrasonic nonlinearity increased and the resonant frequency of the system decreased with initiation and propagation of the major crack. The nonlinear ultrasonic parameter shows greater sensitivity to damage accumulation than the resonant frequency. The number of cycles for crack propagation, estimated based on the changes in the nonlinear ultrasonic parameter, is in very good agreement with calculated crack growth rates based on the fractography studies.

Kumar, Anish; Torbet, Christopher J.; Jones, J. Wayne; Pollock, Tresa M.

2009-07-01

221

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

222

Second harmonic generation imaging and Fourier transform spectral analysis reveal damage in fatigue-loaded tendons.  

PubMed

Conventional histologic methods provide valuable information regarding the physical nature of damage in fatigue-loaded tendons, limited to thin, two-dimensional sections. We introduce an imaging method that characterizes tendon microstructure three-dimensionally and develop quantitative, spatial measures of damage formation within tendons. Rat patellar tendons were fatigue loaded in vivo to low, moderate, and high damage levels. Tendon microstructure was characterized using multiphoton microscopy by capturing second harmonic generation signals. Image stacks were analyzed using Fourier transform-derived computations to assess frequency-based properties of damage. Results showed 3D microstructure with progressively increased density and variety of damage patterns, characterized by kinked deformations at low, fiber dissociation at moderate, and fiber thinning and out-of-plane discontinuities at high damage levels. Image analysis generated radial distributions of power spectral gradients, establishing a "fingerprint" of tendon damage. Additionally, matrix damage was mapped using local, discretized orientation vectors. The frequency distribution of vector angles, a measure of damage content, differed from one damage level to the next. This study established an objective 3D imaging and analysis method for tendon microstructure, which characterizes directionality and anisotropy of the tendon microstructure and quantitative measures of damage that will advance investigations of the microstructural basis of degradation that precedes overuse injuries. PMID:20232150

Fung, David T; Sereysky, Jedd B; Basta-Pljakic, Jelena; Laudier, Damien M; Huq, Rumana; Jepsen, Karl J; Schaffler, Mitchell B; Flatow, Evan L

2010-05-01

223

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

NASA Astrophysics Data System (ADS)

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

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

1994-09-01

224

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

E-print Network

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

Hutchinson, John W.

225

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

226

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

227

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

228

Assessment of fatigue damage in solid plates through the ultrasonic Lamb wave approach  

NASA Astrophysics Data System (ADS)

Changes (degradations) in the mechanical properties of solid plates induced by cyclic fatigue loading will influence the features of ultrasonic Lamb wave propagation, such as dispersion and attenuation. This paper has qualitatively analyzed the feasibility of using the amplitude-frequency characteristics and the stress wave factors (SWFs) of ultrasonic Lamb wave propagation to assess fatigue damage in solid plates. Liquid wedge transducers located on the surface of solid plates tested are used to generate and detect the Lamb wave signals. Based on the Ritec-SNAP ultrasonic measurement system, the experimental setup for assessing the degree of fatigue damage in solid plates using ultrasonic Lamb wave approach has been established. For several rolled aluminum sheets subjected to tension-tension cyclic loading, the experimental examinations have been performed for the relationships between the amplitude-frequency characteristics of ultrasonic Lamb wave propagation and the numbers of loading cycles (denoted by N), as well as the correlations between the Lamb wave SWFs and N. The experimental results show that the Lamb wave SWFs decrease monotonously and sensitively with the increment of cycles of fatigue loading. Based on the correlations between the Lamb wave SWFs and N, it is further verified that ultrasonic Lamb wave propagation combined with the Lamb wave SWFs can be used to effectively assess early fatigue damage in solid plates.

Deng, Mingxi; Pei, Junfeng

2010-07-01

229

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

230

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

231

Fatigue  

MedlinePLUS

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

232

Fatigue  

MedlinePLUS

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

233

Variations of Fatigue Damage Growth in Cross-Ply and Quasi-Isotropic laminates Under High-Cycle Fatigue Loading  

NASA Astrophysics Data System (ADS)

The behavior of transverse crack growth and delamination growth under high-cycle fatigue loadings was investigated with cross-ply CFRP laminates, [0/902]s and [0/906]s, and quasi-isotropic CFRP laminates, [45/0/-45/90]s. As a result, it was observed that the behavior of damage growth was different depending on the applied stress level. The growth of local or edge delamination was exacerbated under the test conditions of a low applied stress level and high-cycle loadings, because the areas of stress concentration were applied with high-cyclic loadings. On the other hand, when the fatigue tests were conducted under the applied stress level of 40% of the transverse crack initiation, the growth of transverse cracks was hardly observed until 108 cycles with [0/902]s, [0/906]s and [45/0/-45/90]s laminates.

Hosoi, Atsushi; Shi, Jiadi; Sato, Narumichi; Kawada, Hiroyuki

234

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

235

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

236

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

Microsoft Academic Search

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

D S Singh; S Gupta; A Ray

2009-01-01

237

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

238

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

PubMed Central

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

Huang, Hong-Zhong; Yuan, Rong

2014-01-01

239

Ultrasonic Characterization of Fatigue and Impact Damage in Graphite Epoxy Composite Laminates  

Microsoft Academic Search

The objective of this research was to illustrate the potential of quantitative ultrasonic imaging as an approach to materials characterization in inherently inhomogeneous media. Low velocity impact and fatigue damage were investigated alone and in combination in quasi-isotropic graphite epoxy composite laminates. Quantitative images based on the slope of the attenuation coefficient measured as a function of frequency over a

Thomas A. Shoup; J. G. Miller; J. S. Heyman; W. Illg

1982-01-01

240

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

241

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

NASA Astrophysics Data System (ADS)

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

Colin, Julie

242

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

243

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

E-print Network

of small surface fatigue cracks in a Ti±6Al±4V alloy, processed for typical turbine blade applications; Ti±6Al±4V 1. Introduction The high-cycle fatigue (HCF) of aircraft gas-turbine engine components has blades, this approach is currently being re-evaluated [1±3]. Three major concerns have been identi

Ritchie, Robert

244

Influence of interface ply orientation on fatigue damage of adhesively bonded composite joints  

NASA Technical Reports Server (NTRS)

An experimental study of cracked-lap-shear specimens was conducted to determine the influence of adherend stacking sequence on debond initiation and damage growth in a composite-to-composite bonded joint. Specimens consisted of quasi-isotropic graphite/epoxy adherends bonded together with either FM-300 or EC 3445 adhesives. The stacking sequence of the adherends was varied such that 0 deg, 45 deg, or 90 deg plies were present at the adherend-adhesive interfaces. Fatigue damage initiated in the adhesive layer in those specimens with 0 deg nd 45 deg interface plies. Damage initiated in the form of ply cracking in the strap adherend for the specimens with 90 deg interface plies. The fatigue-damage growth was in the form of delamination within the composite adherends for specimens with the 90 deg and 45 deg plies next to the adhesive, while debonding in the adhesive resulted for the specimens with 0 deg plies next to the adhesive. Those joints with the 0 deg and 45 deg plies next to either adhesive has essentially the same fatigue-damage-initiation stress levels. These stress levels were 13 and 71 percent higher, respectively, than those for specimens with 90 deg plies next to the EC 3445 and FM-300 adhesives.

Johnson, W. S.; Mall, S.

1985-01-01

245

The development of fatigue damage around fastener holes in thick graphite/epoxy composite laminates  

NASA Astrophysics Data System (ADS)

Mechanisms involved in the development and growth of damage around countersunk fastener holes in thick mechanically fastened graphite-epoxy composite laminates under fatigue loading conditions are investigated. Results of experiments showed that the erosion of material between ply layers nucleates delaminations which then grow through the laminate under the action of the fatigue loads. The sites for the nucleation of delaminations are produced by the damage at the hole bore. From maps of the morphology of the delaminations and ply cracking, it was found that the volume of material around the fastener hole adapted a characteristic shape; the volume of damaged laminate increased towards the faying surface of the laminate and metal fixture.

Saunders, D. S.; Galea, S. C.; Deirmendjian, G. K.

1993-06-01

246

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

SciTech Connect

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

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

2009-12-15

247

Post-impact fatigue damage monitoring using fiber Bragg grating sensors.  

PubMed

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. PMID:24594609

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

2014-01-01

248

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. PMID:24594609

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

2014-01-01

249

An optimal vibration control logic for minimising fatigue damage in flexible structures  

NASA Astrophysics Data System (ADS)

One of the most common applications of active control on flexible structures is the mitigation of vibrations to reduce stresses and consequently increase lifetime. However, except for a few particular cases, the fatigue phenomenon has never been taken into account in the design of the control algorithm. Moreover, since fatigue is mainly a local effect, in some cases active control could even worsen the structure's integrity (e.g. consider local damage close to the actuators caused by control strategies requiring high control forces). For this reason, control is not able to achieve the best performance in terms of damage reduction and lifetime maximisation. This paper proposes an optimal active control designed to minimise fatigue damage on the structure. A model of the fatigue phenomenon is introduced and included in the definition of the control parameters. The solution is firstly described from a theoretical point of view and then tested both numerically and experimentally, showing a significant improvement over state-of-the-art techniques.

Ambrosio, P.; Cazzulani, G.; Resta, F.; Ripamonti, F.

2014-02-01

250

Low cost corrosion damage mitigation and improved fatigue performance of low plasticity burnished 7075-T6  

NASA Astrophysics Data System (ADS)

Low plasticity burnishing (LPB) has been investigated as a surface enhancement process and corrosion mitigation method for aging aircraft structural applications. Compressive residual stresses reaching the alloy yield strength and extending to a depth of 1.25 mm (0.050 in.) deeper than typical corrosion damage is achievable. Excellent surface finish can be achieved with no detectable metallurgical damage to surface and subsurface material. Salt fog exposures of 100 and 500 h reduced the fatigue strength at 2×106 cycles by 50%. The LPB of the corroded surface, without removal of the corrosion product or pitted material, restored the 2×106 fatigue strength to greater than that of the original machined surface. The fatigue strength of the corroded material in the finite life regime (104 to 106 cycles) after LPB was 140 MPa (20 ksi) higher than the original uncorroded alloy and increased the life by an order of magnitude. Ease of adaptation to computer numerical control (CNC) machine tools allows LPB processing at costs and speeds comparable to machining operations. Low plasticity burnishing offers a promising new technology for mitigation of corrosion damage and improved fatigue life of aircraft structural components with significant cost and time savings over current practices.

Prevéy, Paul S.; Cammett, John

2001-10-01

251

Fatigue damage study in aluminum-2024 T3 alloys  

NASA Technical Reports Server (NTRS)

The grain structure of aluminum 2024, a commonly used commercial alloy is investigated, and these findings are correlated with the fatigue property of the material. Samples of aluminum 2024 were polished and etched in different reagents. Optical micrographs (at 500X) of samples etched in Keller's reagent revealed grain boundaries as well as some particles present in the microstructure. Normal x-ray scans of samples etched for different intervals of time in Keller's reagent indicate no significant variations in diffraction peak positions; however, the width of the rocking curve increased with the time of etching. These results are consistent with the direct dependence of the width of the rocking curve on the range of grain orientation. Etching removes the preferred orientation layer of the sample produced by polishing; thereby, causing the width to increase.

Ferguson, Milton W.

1992-01-01

252

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

253

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

NASA Technical Reports Server (NTRS)

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

Piascik, Robert S.; Willard, Scott A.

1999-01-01

254

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

255

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

PubMed Central

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

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

2014-01-01

256

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. PMID:24838769

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

2014-09-01

257

Influence of interface ply orientation on fatigue damage of adhesively bonded composite joints  

NASA Technical Reports Server (NTRS)

An experimental study of cracked-lap-shear specimens was conducted to determine the influence of adherend stacking sequence on debond initiation and damage growth in a composite-to-composite bonded joint. Specimens consisted of quasi-isotropic graphite/epoxy adherends bonded together with either FM-300 or EC 3445 adhesives. The stacking sequence of the adherends was varied such that 0 deg, 45 deg, or 90 deg plies were present at the adherend-adhesive interfaces. Fatigue damage initiated in the adhesive layer in those specimens with 0 deg and 45 deg interface plies. Damaage initiated in the form of ply cracking in the strap adherend for the specimens with 90 deg interface plies. The fatigue-damage growth was in the form of delamination within the composite adherends for specimens with the 90 deg and 45 deg plies next to the adhesive, while debonding in the adhesive resulted for the specimens with 0 deg plies next to the adhesive. Those joints with the 0 deg and 45 deg plies next to either adhesive has essentially the same fatigue-damage-initiation stress levels. These stress levels were 13 and 71 percent higher, respectively, than those for specimens with 90 deg plies next to the EC 3445 and FM-300 adhesives.

Johnson, W. S.; Mall, S.

1986-01-01

258

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

PubMed

When compact bone is subjected to fatigue loading, it develops matrix microdamage, which reduces the tissue's ability to resist fracture. The relative influence of different strain modes on damage and strength in compact bone has not been characterized, to our knowledge. In this study, the nonuniform strain field produced by four-point bending was used to introduce fatigue damage into tibial bending beam specimens from men 40-49 years old. The specimens were then bulk-stained with basic fuchsin to mark damage surfaces and were examined histologically and with confocal microscopy to describe damage morphologies and position relative to tension and compression-strained regions of the specimen. Histomorphometric methods were used to quantify the amounts of different types of bone microdamage. Three major types were observed. In regions subjected to tensile strains, the bone had focal regions of diffusely increased basic fuchsin staining (i.e., diffuse microdamage). Confocal microscopy of these regions showed them to be composed of extensive networks of fine, ultrastructural-level cracks. In compressive strain regions, the tissue developed linear microcracks in interstitial areas similar to those originally described by Frost. Fine, tearing-type (wispy-appearing) cracks were observed near and in the plane of the neutral axis. The paths of these fine cracks were not influenced by microstructural boundaries. Other minor damage morphologies (sector-stained osteons, delamination of regions of lamellae, and intraosteonal cracking) were observed, but their distribution was unrelated to local strain field. Thus. in fatigue of human compact bone, the principal mechanisms of matrix failure (i.e., linear microcrack, diffuse damage foci, and tearing-type damage) are strongly dependent on local strain type. PMID:9671927

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

1998-05-01

259

Acoustic emission and fatigue damage induced in plasma-sprayed hydroxyapatite coating layers.  

PubMed

In order to improve the adhesive strength of hydroxyapatite (HAp) coatings, grit blasting with Al(2)O(3) powder and then wet blasting with HAp/Ti mixed powders was carried out on a commercially pure Ti (cp-Ti) substrate. Subsequently, an HAp/Ti bond coat layer and HAp top coat layer were deposited by plasma spraying. Fatigue tests of the HAp-coated specimens were carried out under four-point bending. Acoustic emission (AE) signals during the entire fatigue test were monitored to investigate the fatigue cracking behavior of the HAp-coated specimens. The HAp-coated specimens could survive up to 10(7) cycles without spallation of the HAp coating layers at the stress amplitude of 120 MPa. The HAp-coated specimens without HAp/Ti bond coat layer showed shorter fatigue life and easy crack nucleation compared to the HAp-coated specimens with HAp/Ti bond coat layer. The delamination and spallation of the HAp top coat with HAp/Ti bond coat on cp-Ti was not observed until the crack propagated into the cp-Ti during the final fracture stage of the fatigue cycle. Therefore, the HAp/Ti bond coat layer was found to greatly improve the fatigue damage resistance of the HAp coating layer. Three stages of the fatigue failure behavior of the HAp top coat with HAp/Ti bond coat on a cp-Ti substrate can be clearly estimated by the AE monitoring technique. These stages are cracks nucleating and propagating in the coating layer, cracks propagating in the substrate, and cracks propagating unstably to final fracture. PMID:22402159

Laonapakul, Teerawat; Otsuka, Yuichi; Nimkerdphol, Achariya Rakngarm; Mutoh, Yoshiharu

2012-04-01

260

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

261

A continuum damage model of fatigue-induced damage in laminated composites  

NASA Technical Reports Server (NTRS)

A model is presented which predicts the stress-strain behavior of continuous fiber reinforced laminated composites in the presence of microstructural damage. The model is based on the concept of continuum damage mechanics and uses internal state variables to characterize the various damage modes. The associated internal state variable growth laws are mathematical models of the loading history induced development of microstructural damage. The model is demonstrated by using it to predict the response of damaged AS-4/3502 graphite/epoxy laminate panels.

Harris, Charles E.; Allen, David H.

1988-01-01

262

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

263

Genetic fuzzy system for damage detection in beams and helicopter rotor blades  

Microsoft Academic Search

Structural damage detection is an inverse problem of structural engineering having three main parts: finding the existence, location and extent of damage. In this study, a genetic fuzzy system is used to find the location and extent of damage. A finite element model of a cantilever beam is used to calculate the change in beam frequencies because of structural damage.

Prashant M. Pawar; Ranjan Ganguli

2003-01-01

264

Regional but not global brain damage contributes to fatigue in multiple sclerosis.  

PubMed

Purpose To use magnetic resonance (MR) imaging and advanced analysis to assess the role of lesions in normal-appearing white matter ( NAWM normal-appearing white matter ) and gray matter ( GM gray matter ) damage, global versus regional damage, and atrophy versus microstructural abnormalities in the pathogenesis of fatigue in multiple sclerosis ( MS multiple sclerosis ). Materials and Methods Local ethics committee approval and written informed consent were obtained. Dual-echo, double inversion-recovery, high-resolution T1-weighted and diffusion-tensor ( DT diffusion tensor ) MR was performed in 31 fatigued patients, 32 nonfatigued patients, and 35 control subjects. Global and regional atrophy and DT diffusion tensor MR measures of damage to lesions, NAWM normal-appearing white matter , and GM gray matter were compared (analysis of variance). Results Lesional, atrophy, and DT diffusion tensor MR measures of global damage to brain, white matter ( WM white matter ), and GM gray matter did not differ between fatigued and nonfatigued patients. Compared with nonfatigued patients and control subjects, fatigued patients experienced atrophy of the right side of the accumbens (mean volume ± standard deviation, 0.37 mL ± 0.09 in control subjects; 0.39 mL ± 0.1 in nonfatigued patients; and 0.33 mL ± 0.09 in fatigued patients), right inferior temporal gyrus ( ITG inferior temporal gyrus ) (Montreal Neurological Institute [ MNI Montreal Neurological Institute ] coordinates: 51, -51, -11; t value, 4.83), left superior frontal gyrus ( MNI Montreal Neurological Institute coordinates: -10, 49, 24; t value, 3.40), and forceps major ( MNI Montreal Neurological Institute coordinates: 11, -91, 18; t value, 3.37). They also had lower fractional anisotropy ( FA fractional anisotropy ) of forceps major ( MNI Montreal Neurological Institute coordinates: -17, -78, 6), left inferior fronto-occipital fasciculus ( MNI Montreal Neurological Institute coordinates: -25, 2, -11), and right anterior thalamic radiation ( ATR anterior thalamic radiation ) ( MNI Montreal Neurological Institute coordinates: 11, 2, -6) (P < .05, corrected). More lesions were found at T2-weighted imaging in fatigued patients. Multivariable model was used to identify right ITG inferior temporal gyrus atrophy (odds ratio, 0.83; 95% confidence interval [ CI confidence interval ]: 0.82, 0.97; P = .009) and right ATR anterior thalamic radiation FA fractional anisotropy (odds ratio, 0.74; 95% CI confidence interval : 0.61, 0.90; P = .003) as covariates independently associated with fatigue (C statistic, 0.85). Conclusion Damage to strategic brain WM white matter and GM gray matter regions, in terms of microstructural abnormalities and atrophy, contributes to pathogenesis of fatigue in MS multiple sclerosis , whereas global lesional, WM white matter , and GM gray matter damage does not seem to have a role. © RSNA, 2014 Online supplemental material is available for this article. PMID:24927473

Rocca, Maria A; Parisi, Laura; Pagani, Elisabetta; Copetti, Massimiliano; Rodegher, Mariaemma; Colombo, Bruno; Comi, Giancarlo; Falini, Andrea; Filippi, Massimo

2014-11-01

265

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

266

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

NASA Astrophysics Data System (ADS)

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

Trinks, C.; Volkert, C. A.

2013-09-01

267

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

NASA Astrophysics Data System (ADS)

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

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

268

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

269

Wind turbine blade health monitoring using acoustic beamforming techniques.  

PubMed

Wind turbines operate autonomously and can possess reliability issues attributed to manufacturing defects, fatigue failure, or extreme weather events. In particular, wind turbine blades can suffer from leading and trailing edge splits, holes, or cracks that can lead to blade failure and loss of energy revenue generation. In order to help identify damage, several approaches have been used to detect cracks in wind turbine blades; however, most of these methods require transducers to be mounted on the turbine blades, are not effective, or require visual inspection. This paper will propose a new methodology of the wind turbine non-contact health monitoring using the acoustic beamforming techniques. By mounting an audio speaker inside of the wind turbine blade, it may be possible to detect cracks or damage within the structure by observing the sound radiated from the blade. Within this work, a phased array beamforming technique is used to process acoustic data for the purpose of damage detection. Several algorithms are evaluated including the CLEAN-based Subtraction of Point spread function from a Reference (CLSPR) on a composite panel and a section of a wind turbine blade in the laboratory. PMID:25235971

Aizawa, Kai; Niezrecki, Christopher

2014-04-01

270

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

271

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

272

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

PubMed Central

Background To investigate the cause/s of muscle fatigue experienced during a half-iron distance triathlon. Methodology/Principal Findings We recruited 25 trained triathletes (36±7 yr; 75.1±9.8 kg) for the study. Before and just after the race, jump height and leg muscle power output were measured during a countermovement jump on a force platform to determine leg muscle fatigue. Body weight, handgrip maximal force and blood and urine samples were also obtained before and after the race. Blood myoglobin and creatine kinase concentrations were determined as markers of muscle damage. Results Jump height (from 30.3±5.0 to 23.4±6.4 cm; P<0.05) and leg power output (from 25.6±2.9 to 20.7±4.6 W · kg?1; P<0.05) were significantly reduced after the race. However, handgrip maximal force was unaffected by the race (430±59 to 430±62 N). Mean dehydration after the race was 2.3±1.2% with high inter-individual variability in the responses. Blood myoglobin and creatine kinase concentration increased to 516±248 µg · L?1 and 442±204 U · L?1, respectively (P<0.05) after the race. Pre- to post-race jump change did not correlate with dehydration (r?=?0.16; P>0.05) but significantly correlated with myoglobin concentration (r?=?0.65; P<0.001) and creatine kinase concentration (r?=?0.54; P<0.001). Conclusions/significance During a half-iron distance triathlon, the capacity of leg muscles to produce force was notably diminished while arm muscle force output remained unaffected. Leg muscle fatigue was correlated with blood markers of muscle damage suggesting that muscle breakdown is one of the most relevant sources of muscle fatigue during a triathlon. PMID:22900101

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

2012-01-01

273

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

274

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

SciTech Connect

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

Dasgupta, A.

1989-01-01

275

Uniaxial ratcheting and fatigue failure of tempered 42CrMo steel: Damage evolution and damage-coupled visco-plastic constitutive model  

Microsoft Academic Search

Uniaxial ratcheting and fatigue failure of tempered 42CrMo steel were observed by the tests under the uniaxial stress-controlled cyclic loading with non-zero mean stress [G.Z. Kang, Y.J. Liu, Mater. Sci. Eng. A 472 (2008) 258–268]. Based on the obtained experimental results, the evolution features of whole-life ratcheting behavior and low-cycle fatigue (LCF) damage of the material were discussed first. Then,

Guozheng Kang; Yujie Liu; Jun Ding; Qing Gao

2009-01-01

276

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

Microsoft Academic Search

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

Zhiyuan Li; Jonas W. Ringsberg

2012-01-01

277

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

Microsoft Academic Search

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

Zhiyuan Li; Jonas W. Ringsberg

2011-01-01

278

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

279

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

280

DAMAGE DETECTION IN A WIND TURBINE BLADE BASED ON TIME SERIES Simon Hoell, Piotr Omenzetter  

E-print Network

in the past years, thus efficient energy harvesting becomes more important. For the sector of wind energy and are promising for prospective developments of damage detection methods in WTs. KEYWORDS: Damage detection, Wind Efficient wind energy harvesting becomes more important as a consequence of an increasing interest in

Boyer, Edmond

281

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

NASA Technical Reports Server (NTRS)

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

Ferguson, Milton W.

1994-01-01

282

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

Microsoft Academic Search

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

L. Molent; S. Barter; B. Main

2008-01-01

283

A new energy-based fatigue damage parameter in life prediction of high-temperature structural materials  

Microsoft Academic Search

A new life prediction model has been developed with the energy-based fatigue damage parameter of a non-dimensional plastic strain energy density (PSED). Tensile tests and low cycle fatigue tests of 316L austenitic stainless steel and 429EM ferritic stainless steel have been performed at elevated temperature for the prediction. While the cyclic stress response of a material is not stabilized during

Keum-Oh Lee; Seong-Gu Hong; Soon-Bok Lee

2008-01-01

284

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

285

A model for prediction of the damage and effects of explosive projectiles on helicopter composite material rotor blades  

E-print Network

, and changes in blade frequencies and mode shapes . It requires extensive geometric modeling of the blade and engineering manhours to exercise a single shotline case. An IBN 360 computer system or equivalent is required for this model. Like the model of Fitz... with the designer's ability to use a larger amount of structural ms. *erial over an expanded area of distribution, provide a significant survivability advantage to a composite rotor blade over its metal equivalent. The composite main rotor blade selected...

Mikel, Tilden Newton

2012-06-07

286

Micromechanics Fatigue Damage Analysis Modeling for Fabric Reinforced Ceramic Matrix Composites  

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

287

Comparison of strength and load-based methods for testing wind turbine blades  

SciTech Connect

The purpose of this paper is to compare two methods of blade test loading and show how they are applied in an actual blade test. Strength and load-based methods were examined to determine the test load for an Atlantic Orient Corporation (AOC) 15/50 wind turbine blade for fatigue and static testing. Fatigue load-based analysis was performed using measured field test loads extrapolated for extreme rare events and scaled to thirty-year spectra. An accelerated constant amplitude fatigue test that gives equivalent damage at critical locations was developed using Miner`s Rule and the material S-N curves. Test load factors were applied to adjust the test loads for uncertainties, and differences between the test and operating environment. Similar analyses were carried, out for the strength-based fatigue test using the strength of the blade and the material properties to determine the load level and number of constant amplitude cycles to failure. Static tests were also developed using load and strength criteria. The resulting test loads were compared and contrasted. The analysis shows that, for the AOC 15/50 blade, the strength-based test loads are higher than any of the static load-based cases considered but were exceeded in the fatigue analysis for a severe hot/wet environment.

Musial, W.D.; Clark, M.E.; Egging, N. [and others

1996-11-01

288

Characterization of exposure dependent fatigue crack growth kinetics and damage mechanisms for aluminum alloys  

NASA Astrophysics Data System (ADS)

The effect of environmental exposure [given by the ratio of water vapor pressure to the loading frequency (PH2O/f)] on fatigue crack growth rates (FCGR) and damage mechanisms has been investigated for Al-Cu-Li/Mg alloys tested at constant stress intensity range (DeltaK = KMAX - KMIN). Different exposure dependences of the FCGR are explained by H-embrittlement and 3 rate-limiting processes that are similar for each alloy and aging condition. It is shown that the dislocation slip character (heterogeneous planar vs. wavy) controls FCGR at low to moderate exposures, rather than alloy composition and strengthening precipitate reactivity. However, the benefit of planar slip is significantly reduced at higher exposures. An SEM-based electron backscattered diffraction (EBSD)/stereology method was used to successfully quantify changes in fatigue fracture surface crystallography as a function of exposure for a peak aged Al-Cu-Li alloy and an under-aged Al-Cu-Mg alloy. Near-{111} slip band cracking (SBC) observed under high vacuum conditions is gradually replaced by near-{001}/{011} and high index, {hkl}, cracking planes as PH2O/f is increased. The complete absence of near-{111} SBC at higher exposures suggests H enhanced decohesion rather than slip based damage process enhanced by H. This conclusion was substantiated by direct TEM observation. Focused Ion Beam (FIB) milling was used to produce thin foils for TEM, which successfully revealed the underlying dislocation structure at the crack surface and within surrounding materials in under-aged Al-Cu-Mg tested at exposure conditions of ˜10 -8 and 50 Pa·sec. Both conditions exhibit a similar layer of dislocation cells just below the fracture surface which abruptly changes to localized slip bands away from the fracture surface, confirming the presence of a strain gradient at the crack tip. However, the thickness of the substructure layer and slip band width observed at ˜10-8 Pa·sec was larger than those observed at 50 Pa·sec. This infers that less plastic strain accumulation is necessary to produce a fatigue crack extension at high exposures. The dislocation substructure observations also clarify the interpretation of facet crystallography. For instance, the high-index {hkl} crack surface planes produced at higher exposures may be caused by H-enhanced inter/intra-cell structure cracking, based on the observation that the low index crack surface deviates with cell formation just underneath of crack surface. In conclusion, near-{001}/{011) and {hkl} crack surfaces, and lowered plastic strain accumulation in the moist environment imply that fatigue crack growth rates are enhanced by multiple manifestations of H-enhanced decohesion.

Ro, Yunjo

289

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

290

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

SciTech Connect

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

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

1984-09-01

291

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

292

Thermal shock and fatigue resistance evaluation of functionally graded coating for gas turbine blades by laser heating method  

Microsoft Academic Search

This paper presents results of thermal shock and fatigue tests conducted on ZrO2-based thermal barrier coating systems under the temperature environments for advanced gas turbines. A CO2 laser heating method was employed to heat two types of cylindrical specimens with conventional two-layer coating and functionally graded coating. Acoustic emission (AE) signals and temperatures were monitored to detect the fracture process

Masahiro Saito; T HASHIDA; H TAKAHASHI; M SAITO

1995-01-01

293

Space Shuttle main engine powerhead structural modeling, stress and fatigue life analysis. Volume 3: Stress summay of blades and nozzles at FPL and 115 percent RPL loads. SSME HPFTP and HPOTP blades and nozzles  

NASA Technical Reports Server (NTRS)

Gasdynamic environments applied to the turbine blades and nozzles of the HPFTP and HPOTP were analyzed. Centrifugal loads were applied to blades to account for the pump rotation of FPL and 115 percent RPL. The computer models used in the blade analysis with results presented in the form of temperature and stress contour plots are described. Similar information is given for the nozzles.

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

1983-01-01

294

Cross-flow VIV-induced fatigue damage of deepwater steel catenary riser at touch-down point  

NASA Astrophysics Data System (ADS)

A prediction model of the deepwater steel catenary riser VIV is proposed based on the forced oscillation test data, taking into account the riser-seafloor interaction for the cross-flow VIV-induced fatigue damage at touch-down point (TDP). The model will give more reasonable simulation of SCR response near TDP than the previous pinned truncation model. In the present model, the hysteretic riser-soil interaction model is simplified as the linear spring and damper to simulate the seafloor, and the damping is obtained according to the dissipative power during one periodic riser-soil interaction. In order to validate the model, the comparison with the field measurement and the results predicted by Shear 7 program of a full-scale steel catenary riser is carried out. The main induced modes, mode frequencies and response amplitude are in a good agreement. Furthermore, the parametric studies are carried out to broaden the understanding of the fatigue damage sensitivity to the upper end in-plane offset and seabed characteristics. In addition, the fatigue stress comparison at TDP between the truncation riser model and the present full riser model shows that the existence of touch-down zones is very important for the fatigue damage assessment of steel catenary riser at TDP.

Wang, Kun-peng; Tang, Wen-yong; Xue, Hong-xiang

2014-03-01

295

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

E-print Network

tips, or by completely removing a portion of densely cracked web plate material by flame-cutting. In the process of repairing fatigue cracks, stress concentrations result, affecting the fatigue life of the structure. Currently, no standardized criteria...

Wilson, Scott David

2012-06-07

296

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

SciTech Connect

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

Syrett, B.C.; Viswanathan, R.

1982-02-01

297

A probabilistic damage model based on direct 3-D correlation of strain to damage formation following fatigue loading of rat femora.  

PubMed

Microdamage accumulates in bone due to repetitive or excessive mechanical loading, and accumulation of damage can lead to an increase in fracture susceptibility. Understanding the stress or strain criterion for damage formation would allow improved predictive modeling to better assess experimental results or evaluate training regimens. Finite element models coupled with three-dimensional measurements of damage were used to directly correlate damage formation to the local strain state in whole rat femora subjected to three-point bending fatigue. Images of accumulated damage from contrast-enhanced micro-CT were overlaid onto the calculated strain result to determine the strain associated with damage. Most microdamage accumulated in areas where the first principal strain exceeded 0.5%, but damage also occurred at lower strains when applied over sufficiently large volumes. As such, a single threshold strain was not a good predictor of damage. In order to capture the apparently stochastic nature of damage formation, a Weibull statistical model was applied. The model provided a good fit to the data, and a fit based on a subset of the data was able to predict the results in the remaining samples with an RMS error of 17%. These results demonstrate that damage formation is dependent on principal strain, but has a random component that is likely due to the presence of pores or flaws smaller than the resolution of the model that act as stress concentrations in bone. PMID:24333915

Gargac, Joshua A; Turnbull, Travis L; Roeder, Ryan K; Niebur, Glen L

2014-02-01

298

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

299

A COUPLED ELASTOPLASTIC MICROPORE DAMAGE MODEL FOR LOW-CYCLE FATIGUE ANALYSES OF DUCTILE METALS AT FINITE STRAINS  

Microsoft Academic Search

The present paper is concerned with the modeling of low-cycle fatigue of ductile metals at high stress levels. Two models, characterized by a combination of micropore damage models with an elasto-plastic material model incorporating isotropic and kinematic hardening at flnite strains are in- vestigated. Phenomena associated with cyclic plasticity such as the Bauschinger-efiect, ratcheting or mean stress relaxation, cyclic hardening

J.-H. Hommel; O. Kintzel; G. Meschke

300

In vitro simulation of contact fatigue damage found in ultra-high molecular weight polyethylene components of knee prostheses.  

PubMed

An in vitro simulation of fatigue loading of ultra-high molecular weight polyethylene (UHMWPE) knee components was carried out on a knee simulator and on a rolling and sliding wear tester. Tibial components for the knee simulator were gamma-sterilized, implantable components taken from manufacturing inventory. The rolling/sliding UHMWPE discs were machined from bar stock and either gamma sterilized in air and accelerated aged, or left as non-sterilized (controls). Cracking and delamination of samples that had been gamma sterilized in air and aged were observed in both types of tests. Contact fatigue damage was visible in as few as 150,000 cycles using the knee simulator at loads of 122 N (275 1b). The rolling/sliding samples showed signs of damage in as few as 130,000 cycles with an estimated stress of 15 MPa and 25 per cent sliding. However, cracking and delamination were not generated in the never-sterilized or recently sterilized controls. UHMWPE that has been gamma sterilized in air and aged is shown to be susceptible to contact fatigue damage. These results are important to the interpretation of in vitro total knee replacement simulations used to assess the performance of tibial bearings. PMID:9769697

Currier, J H; Duda, J L; Sperling, D K; Collier, J P; Currier, B H; Kennedy, F E

1998-01-01

301

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.

302

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

303

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

304

Probabilistic fatigue methodology and wind turbine reliability  

SciTech Connect

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

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

1996-05-01

305

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

NASA Astrophysics Data System (ADS)

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

Gözcü, M. O.; Kayran, A.

2014-06-01

306

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

307

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

SciTech Connect

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

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

2013-02-01

308

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

Microsoft Academic Search

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

Hiroshi Noguchi; Yun-Hae Kim; Hironobu Nisitani

1995-01-01

309

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

310

Incipient Crack Detection in Composite Wind Turbine Blades  

SciTech Connect

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

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

2012-08-28

311

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

312

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

313

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

314

Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics  

NASA Astrophysics Data System (ADS)

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

Cantrell, John H.

2009-03-01

315

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

316

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

NASA Technical Reports Server (NTRS)

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

Cantrell, John H.

2006-01-01

317

Static and Fatigue Bond Characteristics of Interfaces between CFRP Sheets and Frost Damage Experienced Concrete  

Microsoft Academic Search

Synopsis: Synopsis: Synopsis: Synopsis: Synopsis: Both short and long-term performances of repaired or strengthened concrete structures using external FRP bonding are greatly affected by states of bonding substrates, which are covercrete and may have experienced various damages. One of them is frost damage in cold regions. This paper intends to investigate how the initial frost damages in concrete influence the

Byj. g. Dai; Y. Saito; T. Ueda; Y. Sato

318

Dynamics of cracked rotating blades  

NASA Astrophysics Data System (ADS)

The modeling and formulation of equations of motion for a cracked rotating blade are investigated. A calculation for the connecting spring element simulating the reduced stiffness of the damaged blade area is presented. After generating the governing nonlinear boundary value problem, the simpified relations for the steady state response is described. The equations of motion for superimposed forced vibrations are then derived.

Wauer, Joerg

1991-11-01

319

Numerical Prediction of Fatigue Damage Progress in Holed CFRP Laminates Using Cohesive Elements  

NASA Astrophysics Data System (ADS)

This study presents a numerical simulation to predict damage progress in notched composite laminates under cyclic loading by using a cohesive zone model. A damage-mechanics concept was introduced directly into the fracture process in the cohesive elements in order to express crack growth by cyclic loading. This approach then conformed to the established damage mechanics and facilitated understanding the procedure and reducing computation costs. We numerically investigated the damage progress in holed CFRP cross-ply laminates under tensile cyclic loading and compared the predicted damage patterns with experiment results. The predicted damage patterns agreed with the experiment results that exhibited the extension of multiple types of damage (splits, transverse cracks, and delamination) near the hole. A numerical study indicated that the change in the distribution of in-plane shear stress due to delamination induced the extension of splits and transverse cracks near the hole.

Yashiro, Shigeki; Okabe, Tomonaga

320

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

321

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

E-print Network

&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved by: Chair of Committee, Ramesh Talreja Committee Members, Anastasia Muliana J. N. Reddy Vikram Kinra Head of Department, Dimitris Lagoudas... of China; M.S., Texas A&M University Chair of Advisory Committee: Dr. Ramesh Talreja In this dissertation, experimental investigations and theoretical studies on the stochastic matrix cracking evolution under static and fatigue loading in composite...

Huang, Yongxin

2012-07-16

322

Stress analysis and life prediction of gas turbine blade  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

323

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

NASA Technical Reports Server (NTRS)

The results are given of an investigation to determine the damage states which develop in graphite epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Two quasi-isotropic laminates were selected to give different distributions of interlaminar stresses around the hole. The laminates were tested under cyclic loads (R=0.1, 10 Hz) at maximum stresses ranging between 60 and 95 percent of the notched tensile strength.

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

1985-01-01

324

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

SciTech Connect

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

Stol, K. A.

2003-01-01

325

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

SciTech Connect

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

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

2013-04-01

326

Some observations on cavitation damage under creep and creep-fatigue loading in Type 304 stainless steel  

SciTech Connect

Quantitative data are presented on cavitation damage in type 304 stainless steel caused by creep and creep-fatigue loading. Specimens from tests interrupted at various fractions of their nominal life were fractured intergranularly at cryogenic temperature to reveal cavities on grain boundaries. The results show that creep damage in this material is distributed bimodally. It consists of boundaries that are ''cracked,'' i.e., with area fraction of cavities greater than 20%, and boundaries that are ''cavitated,'' i.e., area fraction of cavities less than 10%. Cracked boundaries appear very early in life (10-20%) and constitute that dominant factor of damage by about 50% of life. Although initially the cavity number density increases with time, the cavity diameter at the peak of the distribution remains relatively constant. The distributions of densely cavitated boundaries with respect to their true and apparent angles with the stress direction were measured in a creep specimen. The results indicate that both normal and shear stresses on the boundary may be important in cavitation.

Majumdar, S.; Don, J.

1986-06-01

327

Mechanisms of microstructural damage during rolling contact fatigue of bearing steels  

E-print Network

.2 Stress state during rolling contacts . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1 Hertzian elastic contact theory . . . . . . . . . . . . . . . . . . . . . 8 2.2.2 Cyclic plasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2... forms of the damage. They are so-called because of their different etching behaviour with respect to the unaffected region. Such damage stems from microstructural changes such as carbide coarsening/dissolution as well as the formation of cellular...

Kang, JeeHyun

2014-04-08

328

Prediction of the Crack Initiation Life of Turbine Blade  

Microsoft Academic Search

High Cycle Fatigue of turbo machinery blades is a significant design problem because one of the turbine stages may operates\\u000a very close to the resonant condition and lead to fatigue failures. In order to assess the crack initiation life of a turbine\\u000a blade, it is essential to correlate vibration to fatigue. Often a crack initiates from the material imperfections under

Sharadchandra D. Jog; Rajeshwar. Baddam

329

Field Measurement of the Acoustic Nonlinearity Parameter in Turbine Blades  

NASA Technical Reports Server (NTRS)

Nonlinear acoustics techniques were used to measure fatigue in turbine blades in a power generation plant. The measurements were made in the field using a reference based measurement technique, and a reference sample previously measured in the laboratory. The acoustic nonlinearity parameter showed significant increase with fatigue in the blades, as indicated by service age and areas of increased stress. The technique shows promise for effectively measuring fatigue in field applications and predicting subsequent failures.

Hinton, Yolanda L.; Na, Jeong K.; Yost, William T.; Kessel, Gregory L.

2000-01-01

330

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

E-print Network

fracture mechanics theory, there are essentially three alternatives to improve fatigue life, if material properties remain the same (Barsom et al. 1999): to reduce the initial flaw size, to reduce the stress range, or to induce a residual stress field....] Elevation View 10 2m m [4 in. ] A-A Section AA 25mm [1in.] 25mm [1in.] a) b) c) Figure 11 : Pull-out test fixture (a,b) pull-out test procedure (c) The pull-out test fixture consisted of a steel plate with dimension of 38 mm x 100 mm x 13 mm (1.5 in. x...

Alemdar, Fatih

2010-01-01

331

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

332

Fatigue Damage Calculated by the Ratio-Method to Materials and Its Machine Part  

Microsoft Academic Search

Several new calculating equations on the damage-evolving rate are suggested for describing the elastic-plastic behavior of some materials under un-symmetric cyclic loading. And the estimating formulas are given of the life relative to varied damage value Doi at each loading history. The method is to adopt the ratio of plastic strain range to elastic strain range as the stress-strain parameter,

Yan-gui YU

2003-01-01

333

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

PubMed Central

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

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

2014-01-01

334

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

NASA Astrophysics Data System (ADS)

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

Magadanz, Christine M.

335

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

NASA Astrophysics Data System (ADS)

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

Gomez, Juan

336

Reducing fatigue damage for ships in transit through structured decision making  

USGS Publications Warehouse

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

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

2014-01-01

337

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

338

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

339

Low-frequency fatigue and neuromuscular performance after exercise-induced damage to elbow flexor muscles.  

PubMed

The purpose of this study was to quantify the association between low-frequency fatigue (LFF) and the increase in EMG and force fluctuations after eccentric exercise of elbow flexor muscles. Ten subjects performed two tasks involving voluntary isometric contractions of elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at five submaximal target forces (5, 10, 20, 40, 60% MVC) while EMG was recorded from biceps and triceps brachii. A third task involved electrical stimulation of biceps brachii at 12 frequencies (1-100 Hz). These tasks were performed before, after, and 2 h and 24 h after concentric or eccentric exercise. MVC force declined after eccentric exercise (34% decline) and remained depressed 24 h later (22% decline), whereas the reduced force following concentric exercise (32%) was recovered 2 h later. Biceps brachii EMG and force fluctuations during the submaximal voluntary contractions increased after eccentric exercise (both approximately 2x greater) with the greatest effect at low forces. LFF was equivalent immediately after both types of exercise (50-60% reduction in 20:100 Hz force) with a slower recovery following eccentric exercise. A significant association was found between the change in LFF and EMG (r(2) values up to 0.52), with the strongest correlations observed at low forces (20% MVC) and at 2 h after exercise. In contrast, there were no significant associations between LFF and force fluctuations during voluntary or electrically evoked contractions, suggesting that other physiological factors located within the muscle are likely to be playing a major role in the impaired motor performance after eccentric exercise. PMID:18687978

Dundon, James M; Cirillo, John; Semmler, John G

2008-10-01

340

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

341

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

342

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

343

Panel resonant behavior of wind turbine blades.  

SciTech Connect

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

Paquette, Joshua A.; Griffith, Daniel Todd

2010-03-01

344

Multiaxial fatigue criteria for AISI 304 and 2-1/4 Cr-1 Mo steel at 538/sup 0/C with applications to strain-range partitioning and linear summation of creep and fatigue damage  

SciTech Connect

An improved multiaxial fatigue failure criterion was developed based on the results of combined axial-torsional strain cycling tests of AISI 304 and 2-1/4 Cr-1 Mo steel conducted at 538/sup 0/C (1000/sup 0/F). The formulation of this criterion involves the shear and normal components of inelastic strain range on the planes of maximum inelastic shear strain range. Optimum values of certain parameters contained in the formulation were obtained for each material by the method of least squares. The ability of this criterion to correlate the test results was compared with that of the usual (Mises) equivalent inelastic strain range criterion. An improved definition of equivalent inelastic strain range resulting from these considerations was used to generalize the theory of Strain Range Partitioning to multiaxial stress-strain conditions and was also applied to the linear summation of creep and fatigue damage.

Blass, J.J.

1982-01-01

345

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

NASA Astrophysics Data System (ADS)

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

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

346

Counterrotating aircraft propulsor blades  

NASA Technical Reports Server (NTRS)

A propulsor blade for an aircraft engine includes an airfoil section formed in the shape of a scimitar. A metallic blade spar is interposed between opposed surfaces of the blade and is bonded to the surfaces to establish structural integrity of the blade. The metallic blade spar includes a root end allowing attachment of the blade to the engine.

Nelson, Joey L. (Inventor); Elston, III, Sidney B. (Inventor); Tseng, Wu-Yang (Inventor); Hemsworth, Martin C. (Inventor)

1993-01-01

347

Test evaluation of a laminated wood wind turbine blade concept  

NASA Technical Reports Server (NTRS)

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

Faddoul, J. R.

1981-01-01

348

A real time neural net estimator of fatigue life  

NASA Technical Reports Server (NTRS)

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

Troudet, T.; Merrill, W.

1990-01-01

349

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

E-print Network

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

350

American Institute of Aeronautics and Astronautics Optical Probe for Monitoring Blade Tip Clearance  

E-print Network

American Institute of Aeronautics and Astronautics 1 Optical Probe for Monitoring Blade Tip system will provide a new tool for engine manufacturers to study and optimize blade tip clearance. The sources of wear mechanisms are rubbing (blade incursion), erosion, and thermal fatigue. In addition, tip

351

Mechanical behavior and fatigue damage of a titanium matrix composite reinforced with continuous SiC fibers  

Microsoft Academic Search

A titanium (Ti-6242) matrix composite reinforced with continuous SiC fibers was studied. The mechanical behavior of the matrix and the composite was characterized by tensile, creep and isothermal fatigue tests at room temperature and up to 550°C. The thermo-mechanical fatigue behavior under in-phase and out-of-phase conditions was investigated for the composite between 100 and 550°C. Fracture surfaces were characterized by

D. Bettge; B. Günther; W. Wedell; P. D. Portella; J. Hemptenmacher; P. W. M. Peters; B. Skrotzki

2007-01-01

352

Turbine blade root design concept promises superior alignment  

NASA Technical Reports Server (NTRS)

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

King, O. D.

1966-01-01

353

Boron/aluminum fan blades for SCAR engines  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

354

Fiber composite fan blade impact improvement  

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

355

Smart structure for small wind turbine blade  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

356

Failure analysis of a third stage gas turbine blade  

Microsoft Academic Search

This paper investigates a third stage turbine blade failure in the 150MW unit of a thermal power plant. This primary event caused extensive damage to the unit, i.e. rupture of all blades present in the third and subsequent stages. The blade is made of nickel-based superalloy, Inconel 738, and the blade failure occurred at approximately 22,400 operating hours (25,600 equivalent

S. Barella; M. Boniardi; S. Cincera; P. Pellin; X. Degive; S. Gijbels

2011-01-01

357

Characterization of fatigue damage in adhesively bonded lap joints through dynamic, full-spectral interrogation of fiber Bragg grating sensors: 1. Experiments  

NASA Astrophysics Data System (ADS)

In this study we measure the in situ response of a fiber Bragg grating (FBG) sensor embedded in the adhesive layer of a single composite lap joint, subjected to harmonic excitation after fatigue loading. After a fully reversed cyclic fatigue loading is applied to the composite lap joint, the full-spectral response of the sensor is interrogated at 100 kHz during two loading conditions: with and without an added harmonic excitation. The full-spectral information avoided dynamic measurement errors often experienced using conventional peak wavelength and edge filtering techniques. The short-time Fourier transform (STFT) is computed for the extracted peak wavelength information to reveal time-dependent frequencies and amplitudes of the dynamic FBG sensor response. The dynamic response of the FBG sensor indicated a transition to strong nonlinear dynamic behavior as fatigue-induced damage progressed. The ability to measure the dynamic response of the lap joint through sensors embedded in the adhesive layer can provide in situ monitoring of the lap joint condition.

Webb, S.; Shin, P.; Peters, K.; Zikry, M. A.; Stan, N.; Chadderdon, S.; Selfridge, R.; Schultz, S.

2014-02-01

358

Design and evaluation of low-cost stainless steel fiberglass foam blades for large wind driven generating systems  

NASA Technical Reports Server (NTRS)

A low cost wind turbine blade based on a stainless steel fiberglass foam Budd blade design concept, was evaluated for its principle characteristics, low cost features, and its advantages and disadvantages. A blade structure was designed and construction methods and materials were selected. A complete blade tooling concepts, various technical and economic analysis, and evaluations of the blade design were performed. A comprehensive fatigue test program is conducted to provide data to verify the design stress allowables.

Eggert, W. S.

1982-01-01

359

FOD Simulation for Ceramic Turbine Blades  

NASA Astrophysics Data System (ADS)

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

Yoshida, Hiro; Li, Yinsheng

360

Feasibility study of pultruded blades for wind turbine rotors  

SciTech Connect

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

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

2000-02-28

361

Ceramic blade attachment system  

DOEpatents

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

Boyd, Gary L. (Alpine, CA)

1995-01-01

362

Acute effects of high-intensity dumbbell exercise after isokinetic eccentric damage: interaction between altered pain perception and fatigue on static and dynamic muscle performance.  

PubMed

This study aimed to determine whether high-intensity dumbbell exercise involving both concentric and eccentric contractions would provide a temporary alleviation of delayed-onset muscle soreness (DOMS). It also examined the effect of alleviated muscle soreness on dynamic muscle performance using a stretch-shortening cycle (SSC; peak angular acceleration and velocity of the elbow during both lowering and concentric phases) to provide indirect evidence that DOMS contributes to the dynamic performance decrement after eccentric injury. Thirteen untrained adults performed 30 maximal isokinetic eccentric contractions of the elbow flexors to induce eccentric damage. Five sets of arm curls using a dumbbell (equivalent to 70% of isometric maximal voluntary contraction) were then performed until failure on days 1, 2, 3, and 5 of recovery. Muscle soreness significantly decreased after each session of dumbbell exercise (p = 0.001). Isometric strength further decreased immediately after dumbbell exercise, indicating muscle fatigue (p < 0.001). Dynamic performance variables were less affected by fatigue, however, with performance being reduced only for peak lowering velocity (p < 0.001). Other measures of dynamic performance were relatively constant after dumbbell exercise, particularly on days 2 and 3 when soreness was greatest. It was concluded that high-intensity concentric/eccentric dumbbell exercise was able to temporarily alleviate DOMS and that this reduction in soreness served to counter the effect of peripheral muscle fatigue during dynamic activities. Practical applications of this study are that after eccentric damage, alleviation of muscle soreness through an optimal warm-up may be helpful to temporarily recover dynamic muscle performance. Free-weight loading is one suggested technique to temporarily manage DOMS. PMID:20634739

Sakamoto, Akihiro; Maruyama, Takeo; Naito, Hisashi; Sinclair, Peter J

2010-08-01

363

Performance of twist-coupled blades on variable speed rotors  

SciTech Connect

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

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

1999-12-07

364

Growian rotor blades: Production development, construction and test  

NASA Technical Reports Server (NTRS)

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

Thiele, H. M.

1984-01-01

365

Viscoelastic Vibration Dampers for Turbomachine Blades  

NASA Technical Reports Server (NTRS)

Simple viscoelastic dampers have been invented for use on the root attachments of turbomachine blades. These dampers suppress bending- and torsion-mode blade vibrations, which are excited by unsteady aerodynamic forces during operation. In suppressing vibrations, these dampers reduce fatigue (thereby prolonging blade lifetimes) while reducing noise. These dampers can be installed in new turbomachines or in previously constructed turbomachines, without need for structural modifications. Moreover, because these dampers are not exposed to flows, they do not affect the aerodynamic performances of turbomachines. Figure 1 depicts a basic turbomachine rotor, which includes multiple blades affixed to a hub by means of dovetail root attachments. Prior to mounting of the blades, thin layers of a viscoelastic material are applied to selected areas of the blade roots. Once the blades have been installed in the hub and the rotor is set into rotation, centrifugal force compresses these layers between the mating load-bearing surfaces of the hub and the blade root. The layers of viscoelastic material provide load paths through which the vibration energy of the blade can be dissipated. The viscoelasticity of the material converts mechanical vibration energy into shear strain energy and then from shear strain energy to heat. Of the viscoelastic materials that have been considered thus far for this application, the one of choice is a commercial polyurethane that is available in tape form, coated on one side with an adhesive that facilitates bonding to blade roots. The thickness of the tape can be chosen to suit the specific application. The typical thickness of 0.012 in. (.0.3 mm) is small enough that the tape can fit in the clearance between the mating blade-root and hub surfaces in a typical turbomachine. In an experiment, a blade was mounted in a test fixture designed to simulate the blade-end conditions that prevail in a turbocompressor. Vibrations were excited in the blade by use of an impact hammer, and damping of the vibrations was measured by use of a dynamic signal analyzer. Tests were performed without and with viscoelastic dampers installed in the dovetail root attachment. The results of the measurements, some of which are presented in Figure 2, show that the viscoelastic dampers greatly increased the rate of damping of vibrations. Accordingly, dynamic stresses on rotor blades were significantly reduced, as shown in Figure 2.

Nguyen, Nhan

2003-01-01

366

SIMULATION OF DELAMINATION UNDER HIGH CYCLE FATIGUE IN COMPOSITE MATERIALS  

Microsoft Academic Search

Mechanical fatigue, especially high-cycle fatigue, is a common cause of failure of aerospace structures. In laminated composite materials, the fatigue process involves several damage mechanisms that result in the degradation of the material. One of the most important fatigue damage mechanisms is interlaminar damage (delamination), especially in the case of laminated structures devoid of reinforcement in the thickness direction. There

Albert Turon; Josep Costa; Pedro P. Camanho; Carlos G. Davila

367

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

Microsoft Academic Search

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

Timothy W. Coats; Charles E. Harris

1995-01-01

368

An investigation of fatigue and fretting in a dovetail joint  

Microsoft Academic Search

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

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

1984-01-01

369

Laser thermal shock and fatigue testing system  

NASA Astrophysics Data System (ADS)

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

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

1997-08-01

370

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

371

A real time neural net estimator of fatigue life  

NASA Technical Reports Server (NTRS)

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

Troudet, T.; Merrill, W.

1990-01-01

372

Modifications on A-F hardening rule to assess ratcheting response of materials and its interaction with fatigue damage under uniaxial stress cycles  

NASA Astrophysics Data System (ADS)

Ratcheting deformation is accumulated progressively over three distinct stages in materials undergoing asymmetrical cyclic stresses. The present thesis evaluates the triphasic ratcheting response of materials from two stand points: (i) Mechanistic approach at which stages of ratcheting progress over stress cycles was related to mechanistic parameters such as stress level, lifespan, mechanical properties and the softening/hardening response of materials. Mechanistic approach formulated in this thesis was employed to assess ratcheting strain over triphasic stages in various steel and copper alloys under uniaxial stress cycles. Good agreements were achieved between the predicted ratcheting strain values based on the proposed formulation and those of experimentally reported. (ii) Kinematic hardening rule approach at which the hardening rule was characterized by the yield surface translation mechanism and the corresponding plastic modulus calculated based on the consistency condition. Various cyclic plasticity models were employed to assess ratcheting response of materials under different loading conditions. The Armstrong-Frederick (A-F) hardening rule was taken as the backbone of ratcheting analysis developed in this thesis mainly due to less complexity and number of coefficients in the hardening rule as compared with other earlier developed hardening rules in the literature. To predict triphasic ratcheting strain over stress cycles, the A-F hardening rule has been further developed by means of new strain rate coefficients gamma 2 and delta. These coefficients improved the hardening rule capability to calibrate and control the rate of ratcheting over its progressive stages. The modified hardening formulation holds the coefficients of the hardening rule to control stress-strain hysteresis loops generated over stress cycles during ratcheting process plus the ratcheting rates over stages I, II, and III. These coefficients were calibrated and defined based on the applied stress levels. The constructed calibration curves were employed to determine strain rate coefficients required to assess ratcheting response of materials under uniaxial loading conditions at various cyclic stress levels. The predicted ratcheting strain values based on the modified hardening rule were found in good agreements with the experimentally obtained ratcheting data over stages I and II under uniaxial loading conditions. The capability of the modified hardening rule to assess ratcheting deformation of materials under multi-step uniaxial loading spectra was also assessed. Subsequent load steps were considerably affected by previous load steps in multi-step loading conditions. Ratcheting strains for low-high stress steps were successfully predicted by the modified hardening rule. High-low loading sequences however resulted in an overestimated reversed ratcheting strain in the later load steps. The modified hardening rule proposed in this thesis was then employed to predict the ratcheting strain and its concurrent interaction with fatigue damage over stress cycles in steel alloys. The interaction of ratcheting and fatigue damage was defined based on mechanistic parameters involving the effects of mean stress, stress amplitude, and cyclic softening/hardening response of materials. The extent of ratcheting effect on the overall damage of steel samples was defined by means of the product of the average ratcheting strain rate over the stress cycles and the applied maximum cyclic stress, while fatigue damage was analysed based on earlier developed energy-based models of Xia-Ellyin and Smith-Watson-Topper. Overall damage induced by both ratcheting and fatigue was calibrated through a weighting factor at various ratios of mean stress/cyclic amplitude stress (sigmam/sigmaa). The estimated lives based on the proposed algorithm at different mean stresses and stress amplitudes showed good agreements as compared with experiments.

Ahmadzadehrishehri, Gholamreza

373

Experiments of Wind Turbine Blades with Rocket Triggered Lightning  

NASA Astrophysics Data System (ADS)

This paper describes the results of the experiments of wind turbine blades with rocket triggered lightning. A number of wind power stations have been projected and planted. Lightning damage to wind turbines has been an increasing problem recently. So development on protection of wind power plants from lightning is necessary to be fully run for the future. In the experiments, the 1.8m long blade was struck by the lightning discharge triggered by rocket. For the blade kept dry inside, the very strong discharge of positive peak current 28kV, total charge 520 Coulombs, was triggered, but the breakdown did not occur through the blade into inside. Another blade polluted by salty wet inside was struck by the lightning discharge of negative peak current of 4kA with 0.5 Coulombs. The lightning was small, nevertheless, the blade was broken at the upper edge and the blade was disconnected by crack. For the protection of blade, the blade surface was covered with stainless steel plate. The blade itself was safe when the big positive lightning discharged, while most part of stainless steel cover was burned out. Supplement breakdown tests of wind turbine blade were carried out with lightning impulse voltage in laboratory. As a result, it became clear that the blade kept dry inside was an effective lightning protection of wind turbine blades.

Minowa, Masayuki; Sumi, Shinichi; Minami, Masayasu; Horii, Kenji

374

Fatigue Test  

MedlinePLUS

... About Your Fatigue 1) During the past two weeks, have you experienced persistent or frequent fatigue? Yes ... fatigue been, on average, during the past two weeks? Not at all 0 Mild fatigue 1 2 ...

375

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

NASA Astrophysics Data System (ADS)

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

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

2008-02-01

376

Program for impact testing of spar-shell fan blades, test report  

NASA Technical Reports Server (NTRS)

Six filament-wound, composite spar-shell fan blades were impact tested in a whirligig relative to foreign object damage resulting from ingestion of birds into the fan blades of a QCSEE-type engine. Four of the blades were tested by injecting a simulated two pound bird into the path of the rotating blade and two were tested by injecting a starling into the path of the blade.

Ravenhall, R.; Salemme, C. T.

1978-01-01

377

Fatigue Considerations for Ocean Towage  

Microsoft Academic Search

Fatigue damage of the structure, sea fastenings, or barge during ocean towage can be a critical consideration in the choice of barge and tugs and of tow route and marine operations. This paper describes the procedures that were followed to assess the risk of fatigue damage and the practical precautions that were taken to control its incidence during the tow

Edmund Hambly; Anthony Edwards; Colin Kohli; Barry Miller

1982-01-01

378

Thermal Imaging of Medical Saw Blades and Guides  

SciTech Connect

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

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

2007-01-01

379

Failure analysis of a large wind tunnel compressor blade  

NASA Technical Reports Server (NTRS)

A failure analysis was performed to establish the cause of a 2014-T6 aluminum compressor rotor blade failure in a large NASA-Ames wind tunnel. Metallurgical failure analysis by light photography, fractographic SEM examinations, and fatigue experiments showed that a 0.13-mm-deep scratch in the shank of the blade had acted as an initiation site for a fatigue crack, which subsequently grew by Stage II fatigue before occurrence of the final fracture by unstable crack growth. Studies of modal deformation plots and blade FEM analysis indicated that Mode-3 was the most likely mode responsible for the resonance condition which produced the vibration loading that effected crack growth. Tunnel measurements data showed that the crack growth was controlled by both the tunnel resonance and the dampening from the crack itself.

Hampton, Roy W.; Nelson, Howard G.

1986-01-01

380

Analysis and Tests of Pultruded Blades for Wind Turbine Rotors  

SciTech Connect

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

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

1999-07-19

381

Fatigue and corrosion in aircraft pressure cabin lap splices  

Microsoft Academic Search

Aircraft structures are susceptible to fatigue and corrosion damage, notably at joints. There may be interactions between fatigue and corrosion, especially as aircraft age. Longitudinal lap splices from several types of transport aircraft pressure cabins were disassembled and investigated for Multiple Site Damage (MSD) fatigue cracking and corrosion. The results are compared with NASA data for a full-scale fatigue test.

R. J. H Wanhill; M. F. J Koolloos

2001-01-01

382

On the inverse power laws for accelerated random fatigue testing  

Microsoft Academic Search

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

G. Allegri; X. Zhang

2008-01-01

383

On the inverse power laws for accelerated random fatigue testing  

Microsoft Academic Search

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

G. Allegri; X. Zhang

2009-01-01

384

Characterization of fatigue damage in adhesively bonded lap joints through dynamic, full-spectral interrogation of fiber Bragg grating sensors: 2. Simulations  

NASA Astrophysics Data System (ADS)

In this paper, we simulate the response of fiber Bragg grating (FBG) sensors embedded in the adhesive layer of a composite lap that is subjected to harmonic excitation. To simulate accumulated fatigue damage at the adhesive layer, two forms of numerical nonlinearities are introduced into the model: (1) progressive plastic deformation of the adhesive and (2) changing the boundary of an interfacial defect at the adhesive layer across the overlap shear area. The simulation results are compared with previous measurements of the dynamic, full-spectral response of such FBG sensors for condition monitoring of the lap joint. Short-time Fourier transforms (STFT) of the locally extracted axial strain time histories reveal a transition to nonlinear behavior of the composite lap joint by means of intermittent frequencies that were observed in the experimental measurements and are not associated with the external excitation. The simulation results verify that the nonlinear changes in measured dynamic FBG responses are due to the progression of damage in the lap joint.

Webb, S.; Shin, P.; Peters, K.; Zikry, M. A.; Stan, N.; Chadderdon, S.; Selfridge, R.; Schultz, S.

2014-02-01

385

Design and evaluation of low cost blades for large wind driven generating systems  

NASA Technical Reports Server (NTRS)

The development and evaluation of a low cost blade concept based on the NASA-Lewis specifications is discussed. A blade structure was designed and construction methods and materials were selected. Complete blade tooling concepts, various technical and economic analysis, and evaluations of the blade design were performed. A comprehensive fatigue test program was conducted to provide data and to verify the design. A test specimen of the spar assembly, including the root end attachment, was fabricated. This is a full-scale specimen of the root end configuration, 20 ft long. A blade design for the Mod '0' system was completed.

Eggert, W. S.

1982-01-01

386

SSME HPFTP/AT Turbine Blade Platform Featherseal Damper Design  

NASA Technical Reports Server (NTRS)

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

Montgomery, S. K.

1999-01-01

387

The analysis of fatigue crack growth mechanism and oxidation and fatigue life at elevated temperatures  

NASA Technical Reports Server (NTRS)

Two quantitative models based on experimentally observed fatigue damage processes have been made: (1) a model of low cycle fatigue life based on fatigue crack growth under general-yielding cyclic loading; and (2) a model of accelerated fatigue crack growth at elevated temperatures based on grain boundary oxidation. These two quantitative models agree very well with the experimental observations.

Liu, H. W.

1988-01-01

388

Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model. Part II: Model development and results  

Microsoft Academic Search

The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. However, there have historically been no analytical methods to quantify the specific fatigue life reduction of individual unfailed corroded components with any reasonable degree of confidence. As part of a NAVAIR high-strength steel corrosion–fatigue assessment program, methods were studied to predict the impact that

D. T. Rusk; W. Hoppe; W. Braisted; N. Powar

2009-01-01

389

Hydrodynamic blade guide  

DOEpatents

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

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

2000-01-01

390

Hydrodynamic blade guide  

SciTech Connect

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

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

2000-07-04

391

Damage Resistance of Titanium Aluminide Evaluated  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

392

2009 ASME WIND ENERGY SYMPOSIUM Static and Fatigue Testing of Thick Adhesive Joints for  

E-print Network

1 2009 ASME WIND ENERGY SYMPOSIUM Static and Fatigue Testing of Thick Adhesive Joints for Wind as wind blade size has increased. Typical blade joints use paste adhesives several millimeters thick aircraft, which are also of relevance to wind blades in many instances. The strengths of lap-shear and many

393

White noise response of turbine blades subjected to heat flux and thermal gradient  

SciTech Connect

Design and production of the complex mechanical structures rarely result in an optimal solution. A typical example for this is a turbine blade design. Fatigue failures of the turbine blades is one of the most vexing problems of turbo-machine manufacturers, ever since the steam turbine became the main stay for power generating equipment and the gas turbines are increasingly used in air transport. Turbine blade failures due to fatigue are predominantly vibration related. The dynamic loads on the blading can arise from many different sources such as the high rotational speed, the high operating temperatures, the asymmetric aerofil tapered form of the turbine blade etc. Therefore, vibratory analysis is one of the most important stage in the designing of the turbine blades. In this study, the random response of the turbine blade to white noise excitation has been consistently calculated, including the internal damping mechanisms of the blade. Beside the damping effects, the rotational speed and the linear thermal gradient along the turbine blade are incorporated into the analysis. Pressure difference between the two surfaces of the turbine blades are modelled as white noise excitation along all over the turbine blade. The system dynamic equation of motion are derived and solved by using the combined Finite Element-Modal Analysis Method.

Karadag, V. [Technical Univ. of Istanbul (Turkey). Dept. of Mechanical Engineering; Aba, E. [Turkish Wagon Industry, Adapazari (Turkey). Dept. of Research and Development; Morguel, O.K. [Sakarya Univ., Adapazari (Turkey). Dept. of Mechanical Engineering

1997-07-01

394

Finite element analysis with an improved failure criterion for composite wind turbine blades  

Microsoft Academic Search

Some interesting studies are made in this paper on the life management of a composite wind turbine\\u000a blade. It presents the details of finite element modeling and validation, blade response under service\\u000a loading conditions, power coefficient evaluation for the optimum design parameters of the blade configuration,\\u000a development of failure envelope and fatigue life estimations. Finite element analysis results are found\\u000a to

J. Selwin Rajadurai; T. Christopher; G. Thanigaiyarasu; B. Nageswara Rao

2008-01-01

395

Fretting Fatigue of Gamma TiAl Studied  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

396

Managing Fatigue  

MedlinePLUS

orig. 08 08, rev. 05 11 PATIENT / FAMILY TEACHING SHEET Managing Fatigue What is fatigue? ? Tiredness, exhaustion, ... stimulate your appetite or relieve fatigue Other HPNA Teaching Sheets on are available at www.HPNA.org. ...

397

Blade design and operating experience on the MOD-OA 200 kW wind turbine at Clayton, New Mexico  

NASA Technical Reports Server (NTRS)

Two 60 foot long aluminum wind turbine blades were operated for over 3000 hours on the MOD-OA wind turbine. The first signs of blade structural damage were observed after 400 hours of operation. Details of the blade design, loads, cost, structural damage, and repair are discussed.

Linscott, B. S.; Shaltens, R. K.

1979-01-01

398

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

NASA Technical Reports Server (NTRS)

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

Sullivan, T. L.

1983-01-01

399

DEVELOPMENT OF AN ULTRASONIC NDT SYSTEM FOR AUTOMATED IN-SITU INSPECTION OF WIND TURBINE BLADES  

E-print Network

DEVELOPMENT OF AN ULTRASONIC NDT SYSTEM FOR AUTOMATED IN- SITU INSPECTION OF WIND TURBINE BLADES Abington, Cambridge, CB21 6AL, UK bic@brunel.ac.uk ABSTRACT It is crucial to maintain wind turbine blades. This work investigates using pulse-echo ultrasound to detect internal damages in wind turbine blades without

Boyer, Edmond

400

Multiscale/Multifunctional Probabilistic Composite Fatigue  

NASA Technical Reports Server (NTRS)

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

Chamis, Christos C.

2010-01-01

401

The effects of fretting on fatigue characteristics of a mechanically fastened aircraft joint  

NASA Astrophysics Data System (ADS)

A research study to investigate the effects of fretting on fatigue characteristics of an aircraft joint was carried out. The selected joint for this study simulates the rotor head of an aircraft capable of taking off vertically. The primary function of this hub-spindle joint is to retain the main rotor blade against the centrifugal forces, both in-plane and out-of-plane bending moments and torsion caused due to the lift, drag and other aerodynamic forces imposed on the rotor blades while the aircraft is in forward flight. The primary objectives of this study were twofold; (a) Verify that the average lives of mechanically fastened joints with combined effects of fretting and fatigue will be lower compared to the average lives due to plain fatigue. (b) Discover whether fretting causes cracks to nucleate and fatigue causes those cracks to propagate. In order to verify the validity of the first hypothesis, seven test joints were tested to failure. Several S/N curves were generated against Mil-Handbook 5H data for comparable plain fatigue response of the same material. Out of the seven specimens that were tested, five were machined from Aluminum 7075-T6, and the other two were machined from Aluminum 7050-T7451. An average fretting fatigue life reduction factor Kff, of 21 was found for all these seven joints. In order to validate the second hypothesis, a detailed investigation under a scanning electron microscope of the fretted/failed surfaces was conducted. Severe fretting damage was observed in all test specimens. It was found that fretting-induced damage provided the crack nucleation sites in all test specimens that failed. These nucleation sites were in the form of fretting scars, pits and gouges providing several regions of stress concentration. Under the influence of high tensile stress fields, these sites allowed several small embryonic cracks to form, coalesce and link up to form primary and multiple cracks, which subsequently propagated under the applied cyclic loads leading to final instability, i.e., fracture. Fretting fatigue should be treated as a major threat against structural integrity of joints. Currently, there are no known analytical models available to design against fretting fatigue. It is therefore recommended that in areas of critical applications full scale tests should be conducted prior to actual use.

Shah, Akbar Hussain

402

Fiber Bragg grating sensors for monitoring of wind turbine blades  

Microsoft Academic Search

Fiber Bragg grating sensor arrays can be used to monitor the mechanical behavior of rotor blades of wind turbines. In order to investigate how stable and reliably work such sensors, different fiber Bragg gratings were embedded into textilereinforced composite. Long-term temperature and tensile (fatigue) tests have been carried out with composite structure specimens. This paper reports on selected results of

K. Krebber; W. Habel; T. Gutmann; C. Schram

2005-01-01

403

Ceramic blade attachment system  

DOEpatents

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

Shaffer, James E. (Maitland, FL)

1995-01-01

404

Ceramic blade attachment system  

DOEpatents

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

Shaffer, J.E.

1995-07-11

405

Application of BSTRAIN software for wind turbine blade testing  

SciTech Connect

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

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

1996-07-01

406

Exploratory Engine Test of Transpiration-cooled Turbine-rotor Blade with Wire-cloth Shell  

NASA Technical Reports Server (NTRS)

Engine tests were made on a transpiration-cooled blade that was fabricated from an internal load-carrying member with an external surface of wire cloth. After operation in the engine, some damage was noted at the tip region of the trailing edge of the blades. On other sections of the blade, the wire cloth did not appear greatly overheated, and it appeared that satisfactory chordwise temperature distribution was provided by orifices in the blade base.

Donoughe, Patrick L; Diaguila, Anthony J

1954-01-01

407

Failure mechanism models for cyclic fatigue  

Microsoft Academic Search

This work illustrates design situations where mechanical fatigue under cyclic loading, of one or more components, can compromise system performance. In this failure mechanism, damage accumulates with each load cycle, thereby causing a physical wearout failure mechanism. Phenomenological continuum length-scale models, based on micromechanical considerations, are presented to predict the onset (or initiation) of fatigue cracking in ductile materials. Fatigue

Abhijit Dasgupta; Reader Aids

1993-01-01

408

Investigation of Solder Fatigue Acceleration Factors  

Microsoft Academic Search

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

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

1985-01-01

409

Fatigue crack propagation in aerospace aluminum alloys  

Microsoft Academic Search

This article reviews fracture mechanics-based, damage tolerant characterizations and predictions of fatigue crack growth in aerospace aluminum alloys. The results of laboratory experimentation and micromechanical modeling are summarized in the areas of 1) the wide range crack growth rate response of conventional aluminum alloys, 2) fatigue crack closure, 3) the fatigue behavior of advanced monolithic aluminum alloys and metal matrix

Richard P. Gangloff; Robert S. Piascik; Dennis L. Dicus; James C. Newman Jr.

1994-01-01

410

Effects of pre-irradiation of low-level laser therapy with different doses and wavelengths in skeletal muscle performance, fatigue, and skeletal muscle damage induced by tetanic contractions in rats.  

PubMed

This study aimed to evaluate the effects of low-level laser therapy (LLLT) immediately before tetanic contractions in skeletal muscle fatigue development and possible tissue damage. Male Wistar rats were divided into two control groups and nine active LLLT groups receiving one of three different laser doses (1, 3, and 10 J) with three different wavelengths (660, 830, and 905 nm) before six tetanic contractions induced by electrical stimulation. Skeletal muscle fatigue development was defined by the percentage (%) of the initial force of each contraction and time until 50 % decay of initial force, while total work was calculated for all six contractions combined. Blood and muscle samples were taken immediately after the sixth contraction. Several LLLT doses showed some positive effects on peak force and time to decay for one or more contractions, but in terms of total work, only 3 J/660 nm and 1 J/905 nm wavelengths prevented significantly (p?fatigue. All doses with wavelengths of 905 nm but only the dose of 1 J with 660 nm wavelength decreased creatine kinase (CK) activity (p?damage in most LLLT-treated groups, with doses of 1-3 J/660 nm and 1, 3, and 10 J/905 nm providing the best results. Optimal doses of LLLT significantly delayed the development skeletal muscle performance and protected skeletal muscle tissue against damage. Our findings also demonstrate that optimal doses are partly wavelength specific and, consequently, must be differentiated to obtain optimal effects on development of skeletal muscle fatigue and tissue preservation. Our findings also lead us to think that the combined use of wavelengths at the same time can represent a therapeutic advantage in clinical settings. PMID:24651950

Santos, Larissa Aline; Marcos, Rodrigo Labat; Tomazoni, Shaiane Silva; Vanin, Adriane Aver; Antonialli, Fernanda Colella; Grandinetti, Vanessa Dos Santos; Albuquerque-Pontes, Gianna Móes; de Paiva, Paulo Roberto Vicente; Lopes-Martins, Rodrigo Alvaro Brandão; de Carvalho, Paulo de Tarso Camillo; Bjordal, Jan Magnus; Leal-Junior, Ernesto Cesar Pinto

2014-09-01

411

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

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

412

American Institute of Aeronautics and Astronautics Comparison of Tensile Fatigue Resistance and Constant  

E-print Network

American Institute of Aeronautics and Astronautics 1 Comparison of Tensile Fatigue Resistance The fatigue of composite laminates appropriate for wind turbine blades has been the topic of research studies in the transverse direction of the laminate are also presented for two of the materials. Constant amplitude fatigue

413

Tungsten fiber reinforced FeCrAlY - A first generation composite turbine blade material  

NASA Technical Reports Server (NTRS)

General and composite turbine blade material requirements are examined to identify a specific tungsten fiber reinforced superalloy (TFRS) having, in addition to strength, the desired combination of other material properties needed in turbine blades. Experimental data indicated that a thoriated tungsten fiber reinforced FeCrAlY matrix composite should have the stress-rupture, creep, tensile, fatigue, and impact strengths required for turbine blades operating from 1250 to 1370 K. Fabrication and design concepts are developed to demonstrate the feasibility of fabricating a hollow TFRS turbine blade at reasonable cost.

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

1979-01-01

414

Turbine blade platform seal  

DOEpatents

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

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

2001-01-01

415

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a first groove and a second groove therein. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings has a first groove and a second groove therein. The space or void formed between the first grooves and the second grooves has a plurality of spherical balls positioned therein. The plurality of spherical balls has a preestablished rate of thermal expansion being equal to the preestablished rate of thermal expansion of the turbine blade.

Shaffer, James E. (Maitland, FL)

1995-01-01

416

Structural health monitoring of wind turbine blade using fiber Bragg grating sensors and fiber optic rotary joint  

NASA Astrophysics Data System (ADS)

Wind energy utilization as a reliable energy source has become a large industry in the last 20 years. Nowadays, wind turbines can generate megawatts of power and have rotor diameters that are on the order of 100 meters in diameter. One of the key components in a wind turbine is the blade which could be damaged by moisture absorption, fatigue, wind gusts or lighting strikes. The wind turbine blades should be routinely monitored to improve safety, minimize downtime, lower the risk of sudden breakdowns and associated huge maintenance and logistics costs, and provide reliable power generation. In this paper, a real-time wind turbine blade monitoring system using fiber Bragg grating (FBG) sensors with the fiber optic rotary joint (FORJ) is proposed, and applied to monitor the structural responses of a 600 W small scale wind turbine. The feasibility and effectiveness of the FORJ is validated by continuously transmitting the optical signals between the FBG interrogator at the stationary side and the FBG sensors on the rotating part. A comparison study between the measured data from the proposed system and those from an IMote2-based wireless strain measurement system is conducted.

Chen, Y.; Ni, Y. Q.; Ye, X. W.; Yang, H. X.; Zhu, S.

2012-04-01

417

Fatigue crack propagation and strain cycling properties  

Microsoft Academic Search

A mechanical model of fatigue crack propagation was studied. It is hypothesized that propagation is caused by cumulative damage due to strain cycling of the material at a crack tip. With Miner's cumulative damage law and Manson and Coffin's strain cycle fatigue: law, crack propagation rate of a material can be calculated. The calculated values are compared with data on

Kenneth R. Lehr; H. W. Liu

1969-01-01

418

Mechanics of fretting fatigue crack formation  

Microsoft Academic Search

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

Matthew P. Szolwinski; Thomas N. Farris

1996-01-01

419

Rotor loading on a three-bladed wind turbine  

NASA Astrophysics Data System (ADS)

For a well designed and adjusted horizontal axis wind turbine, the turbulence in the wind is one of the primary sources of cyclic loading. Wind turbulence not only causes blade loads, but is responsible for the major part of the cyclic rotor loads which are transferred through the rotor shaft. In order to predict the cyclic part of the primary structural rotor loads, the thrust, the yaw and the tilt moment, a model was developed. The model works in the frequency domain and uses the standard engineering representation of turbulence in terms of a coherence function and a power spectrum. The model which accounts for the rotational sampling of the turbulent wind field, shows good agreement with the results of testing programs on wind turbines which are tested at The Test Station for Windmills at Risoe National Laboratory. The comparison is made in terms of both the frequency content of the turbulence induced loads as well as the associated fatigue damage. A parametric study demonstrates the effect of the tower bending and tower torsion flexibility on the magnitude of the cyclic rotor loads.

Madsen, Peter Hauge; Rasmussen, Flemming

420

Cyclic mechanical property degradation during fatigue loading of cortical bone  

Microsoft Academic Search

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

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

1996-01-01

421

Fatigue behavior and damage characteristic of ultra-fine grain low-purity copper processed by equal-channel angular pressing (ECAP)  

Microsoft Academic Search

The S–N and Coffin–Manson plot, cyclic stress–strain response, changes of microstructure, and the surface morphology of ultra-fine grain (UFG) low-purity copper processed by ECAP were tested and observed in present study. And the formation mechanism of shear bands was discussed in detail. The results show that the UFG Cu represents longer lifetime under stress-controlled fatigue, but lower fatigue resistance under

Changzheng Xu; Qingjuan Wang; Maosheng Zheng; Jindou Li; Meiquan Huang; Qingming Jia; Jiewu Zhu; Ludvik Kunz; Michal Buksa

2008-01-01

422

Multiscale Fatigue Life Prediction for Composite Panels  

NASA Technical Reports Server (NTRS)

Fatigue life prediction capabilities have been incorporated into the HyperSizer Composite Analysis and Structural Sizing Software. The fatigue damage model is introduced at the fiber/matrix constituent scale through HyperSizer s coupling with NASA s MAC/GMC micromechanics software. This enables prediction of the micro scale damage progression throughout stiffened and sandwich panels as a function of cycles leading ultimately to simulated panel failure. The fatigue model implementation uses a cycle jumping technique such that, rather than applying a specified number of additional cycles, a specified local damage increment is specified and the number of additional cycles to reach this damage increment is calculated. In this way, the effect of stress redistribution due to damage-induced stiffness change is captured, but the fatigue simulations remain computationally efficient. The model is compared to experimental fatigue life data for two composite facesheet/foam core sandwich panels, demonstrating very good agreement.

Bednarcyk, Brett A.; Yarrington, Phillip W.; Arnold, Steven M.

2012-01-01

423

Corrosion fatigue of high strength fastener materials in seawater  

NASA Technical Reports Server (NTRS)

Environmental effects which significantly reduce the fatigue life of metals are discussed. Corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L4O high strength steel blade to hub attachment bolt at the MOD-OA 200 kW wind turbine generator was investigated. The reduction of fatigue strength of AISI 41L4O in marine environments and to obtain similar corrosion fatigue data for candidate replacement materials was studied. The AISI 4140, PH 13-8Mo stainless steel, alloy 718 and alloy MP-35N were tested in axial fatigue at a frequency of 20 Hz in dry air and natural seawater. The fatigue data are fitted by regression equations to allow determination of fatigue strength for a given number of cycles to failure.

Tipton, D. G.

1983-01-01

424

Postoperative fatigue  

Microsoft Academic Search

Uncomplicated major surgery is followed by a pronounced increased feeling of fatigue extending throughout the first month in about one-third of patients. Postoperative fatigue correlates with the degree of surgical trauma but is not related to duration of general anesthesia and surgery or to preoperative nutritional status, age, or sex. Fatigue also correlates with postoperative deterioration in nutritional parameters and

Tom Christensen; Henrik Kehlet

1993-01-01

425

Mixed-mode, high-cycle fatigue-crack growth thresholds in II. Quantication of crack-tip shielding  

E-print Network

fatigue in the blade dovetail/disk contact section [3]. In the presence of cyclic multiaxial loadingMixed-mode, high-cycle fatigue-crack growth thresholds in Ti±6Al±4V II. Quanti®cation of crack II) fatigue-crack growth thresholds for large, through-thickness cracks in a Ti±6Al±4V turbine blade

Ritchie, Robert

426

Self-Tuning Impact Dampers Designed for Turbomachinery Blade Vibration Suppression  

NASA Technical Reports Server (NTRS)

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

Duffy, Kirsten P.; Mehmed, Oral

2002-01-01

427

Evaluation of flawed composite structural components under static and cyclic loading. [fatigue life of graphite-epoxy composite materials  

NASA Technical Reports Server (NTRS)

The effects of initial defects on the fatigue and fracture response of graphite-epoxy composite laminates are presented. The structural laminates investigated were a typical angle ply laminate, a polar/hoop wound pressure vessel laminate, and a typical engine fan blade laminate. Defects investigated were full and half penetration circular holes, full and half penetration slits, and countersink holes. The effects of the defect size and type on the static fracture strength, fatigue performance, and residual static strength are shown as well as the results of loadings on damage propagation in composite laminates. The data obtained were used to define proof test levels as a qualification procedure in composite structure subjected to cyclic loading.

Porter, T. R.

1979-01-01

428

Ceramic blade attachment system  

DOEpatents

A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a pair of recessed portions thereon. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings have a pair of grooves therein in which are positioned a pair of pins having a generally rectangular cross-section and a reaction surface thereon. A pair of cylindrical rollers interposed respective ones of the pair of reaction surfaces and the pair of recessed portions. The attachment system or turbine assembly provides an economical, reliable and effective attachment of a component having a preestablished rate of thermal expansion to a component having a greater preestablished rate of thermal expansion.

Boyd, Gary L. (Alpine, CA)

1994-01-01

429

Modeling fatigue behavior of electronically conductive adhesive joints under elevated temperature and humidity conditions  

Microsoft Academic Search

This paper describes a novel fatigue- life prediction methodology aimed at providing the design engineer an easy fatigue life predictive tool using experimental data, for both cumulative fatigue damage, as well as constant loading fatigue conditions. This encompasses an integrated approach to joint testing, analysis, and modeling. Utilizing the proposed methodologies, we aim to predict the changes in fatigue life

Rajesh R. Gomatam; Erol Sancaktar

2004-01-01

430

The effect of seismic loading on the fatigue strength of welded joints  

Microsoft Academic Search

Earthquakes sometimes damage steel structures. Structures which are not seriously damaged are still used after earthquakes but their fatigue strength may have been reduced by the large cyclic loadings imposed by the earthquakes. In order to clarify the effect of seismic loading on the fatigue strength of welded joints, high cycle fatigue and variable amplitude fatigue tests after a number

Y. Kondo; K. Okuya

2007-01-01

431

KATP channel deficiency in mouse flexor digitorum brevis causes fibre damage and impairs Ca2+ release and force development during fatigue in vitro  

PubMed Central

Activation of the KATP channels results in faster fatigue rates as the channels depress action potential amplitude, whereas abolishing the channel activity has no effect in whole extensor digitorum longus (EDL) and soleus muscles. In this study, we examined the effects of abolished KATP channel activity during fatigue at 37°C on free intracellular Ca2+() and tetanic force using single muscle fibres and small muscle bundles from the flexor digitorum brevis (FDB). KATP channel deficient muscle fibres were obtained (i) pharmacologically by exposing wild-type fibres to glibenclamide, and (ii) genetically using null mice for the Kir6.2 gene (Kir6.2?/? mice). Fatigue was elicited using 200 ms tetanic contractions every second for 3 min. This study demonstrated for the first time that abolishing KATP channel activity at 37°C resulted in faster fatigue rates, where decreases in peak and tetanic force were faster in KATP channel deficient fibres than in control wild-type fibres. Furthermore, several contractile dysfunctions were also observed in KATP channel deficient muscle fibre. They included partially or completely supercontracted single muscle fibres, greater increases in unstimulated and unstimulated force, and lower force recovery. We propose that the observed faster rate of fatigue in KATP channel deficient fibres is because the decreases in peak and force caused by contractile dysfunctions prevail over the expected slower decreases when the channels do not depress action potential amplitude. PMID:17510189

Cifelli, Carlo; Bourassa, Francois; Gariepy, Louise; Banas, Krystyna; Benkhalti, Maria; Renaud, Jean-Marc

2007-01-01

432

Optimized goodman diagram for the analysis of fiberglass composites used in wind turbine blades.  

SciTech Connect

Mandell, et al have recently presented an updated Goodman diagram for a fiberglass composite that is a typical wind turbine blade material. Their formulation uses the MSU/DOE Fatigue Data Base to develop a Goodman diagram with detailed S-N information at thirteen R-values. This diagram is the most detailed to date, and it includes several loading conditions that have been poorly represented in earlier studies. Sutherland and Mandell have used this formulation to analyze typical loads data from operating wind farms and the failure of coupons subjected to spectral loading. The detailed Goodman diagram used in these analyses requires a significant investment in materials testing that is usually o