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1

Fatigue life evaluation in composite rotor blade of multipurpose helicopter  

Microsoft Academic Search

The prediction of fatigue life and strength of the composite rotor blade for multipurpose helicopter was studied using a residual strength degradation concept. A flight-by-flight load spectrum was introduced on the basis of FELIX standard data. The composite structure analysis was performed to obtain the local stress near blade root in laminate skin and glass roving spar where fatigue damage

Jung-Ho Kwon; Kyung-Jung Hwang; Seok-Soo Kim; Pan-Jo Kim; Choon-Sam Kim

2002-01-01

2

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

3

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

Microsoft Academic Search

A novel fracture mechanics approach has been used to predict crack propagation lives in gas turbine engine blades subjected to vibratory high cycle fatigue (HCF). The vibratory loading included both a resonant mode and a nonresonant mode, with one blade subjected to only the nonresonant mode and another blade to both modes. A life prediction algorithm was utilized to predict

D. P. Walls; R. E. deLaneuville; S. E. Cunningham

1997-01-01

4

Fatigue life variability and reliability analysis of a wind turbine blade  

NASA Astrophysics Data System (ADS)

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

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

5

Astudy on life prediction of low cycle fatigue in superalloy for gas turbine blades  

Microsoft Academic Search

A more accurate life prediction for gas turbine blade takes into account the material behaviour under the Low Cycle Fatigue cycles normally encountered in turbine operation. In this study, low cycle fatigue tests are performed as the variables of total strain range and temperatures. The relations between plastic and total strain energy densities and number of cycles to failure are

Jae-Hoon Kim; Ho-Young Yang; Keun-Bong Yoo

2011-01-01

6

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

7

Blade fatigue life assessment with application to VAWTs  

NASA Astrophysics Data System (ADS)

The possibility of satisfactory modeling of the vibratory stress level history of a vertical axis wind turbine (VAWT) is considered. Fatigue life prediction is expressed as a function of the vibratory stress level, the wind speed, and the wind speed distribution on-site. A statistical distribution of stress levels is asserted to more accurately simulate the stress level than determination of the stress levels at each wind speed. Miner's cumulative damage rule is examined as a tool to generate a vibratory stress level distribution in terms of peak vibrations in a narrow-band Gaussian process. Examples are given for 30-40 sec intervals on the 17 m VAWT at Sandia Laboratories. A threshold was set beneath which no vibrations were recorded, yielding a Rayleigh distribution at the 0.5 significance level. It is concluded that a Rayleigh distribution from test data produces a cycle to failure versus wind speed curve which is superior to constant amplitude fatigue life data such as appropriate to Miner's Rule.

Veers, P. S.

1982-05-01

8

Fatigue life estimation procedure for a turbine blade under transient loads  

SciTech Connect

A technique for fatigue damage assessment during variable speed operations is presented. Transient resonant stresses for a blade with nonlinear damping have been determined using a numerical procedure. A fatigue damage assessment procedure is described. The fatigue failure surface is generated on the S-N-mean stress axes, and Miner's rule is employed to estimate the cumulation of fatigue. 16 refs.

Vyas, N.S.; Rao, J.S. (Indian Inst. of Technology, Kanpur (India) Indian Inst. of Technology, New Delhi (India))

1992-01-01

9

Probabilistic prediction of the fatigue life of gas-turbine engine compressor blades under two-level programmed loading  

Microsoft Academic Search

The authors devise and substantiate a combined theoretical and experimental method of probalistic evaluation of the fatigue life of the compressor blades of gas turbine engines in programmed loading based on the Monte Carlo method. The possible variants of the result of events of fatigue crack propagation in a material in programmed two-level completely reversed loading are examined. It was

M. V. Baumshtein; V. N. Fzhov; A. V. Prokopenko

1986-01-01

10

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

11

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

NASA Technical Reports Server (NTRS)

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

Ingram, J.; Gross, L.

1985-01-01

12

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

SciTech Connect

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

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

1997-01-01

13

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

14

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

Microsoft Academic Search

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

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

2011-01-01

15

Fatigue Failure of Space Shuttle Main Engine Turbine Blades  

NASA Technical Reports Server (NTRS)

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

Swanson, Gregrory R.; Arakere, Nagaraj K.

2000-01-01

16

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

17

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

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

18

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

19

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

20

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

21

Fatigue Analysis of the Compressor Blades with V- Notches  

Microsoft Academic Search

\\u000a This paper presents results of experimental and numerical fatigue analysis of damaged compressor blades, subjected to vibration.\\u000a The blades used in experimental investigations were preliminary defected to simulate the foreign object damage. The crack\\u000a propagation process was conducted in resonance condition. During the fatigue investigations, the crack length and amplitude\\u000a of the blade tip displacement were monitored. The main result

Lucjan Witek

22

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 Materials · Recent Findings, Resin and Fabric Structure Interactions for InfusedStructure Interactions and potential fibers, fabrics, resins, fiber sizings, processes, processing aids, laminate lay-ups, fiber

23

Fatigue Testing of 9 m Carbon Fiber Wind Turbine Research Blades  

SciTech Connect

Fatigue testing was conducted on Carbon Experimental and Twist-Bend Experimental (CX-100 and TX-100) 9-m wind turbine research blades. The CX-100 blade was designed to investigate the use of a carbon spar cap to reduce weight and increase stiffness while being incorporated using conventional manufacturing techniques. The TX-100 blade used carbon in the outboard portion of the skin to produce twist-bend coupling to passively alleviate aerodynamic loads. In the fatigue tests, the CX-100 blade was loaded by a single hydraulic cylinder while the TX-100 blade was loaded via a hydraulically-actuated resonant loading system called the Universal Resonant Exciter. The blades were outfitted with approximately 30 strain gages as well as displacement and load sensors. Both blades survived to cycle counts sufficient to demonstrate a 20-year operational life. The CX-100 blade failed at approximately 1.6 million cycles because of a buckle and crack that formed and grew just outboard of max-chord. The TX-100 blade failed because of a crack that grew from the termination point of the spar cap at the midspan of the blade. This paper covers the results of the fatigue tests.

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

2008-01-01

24

Fretting Fatigue of Single Crystal/Polycrystalline Nickel Subjected to Blade/Disk Contact Loading  

NASA Astrophysics Data System (ADS)

Fretting fatigue describes the formation and growth of cracks at the edge-of-contact of nominally clamped components subjected to cyclic loading. Components that are known to be subject to fretting fatigue include riveted lap joints and blade/disk contacts in launch vehicle turbomachinery. Recent efforts have shown that conventional mechanics tools, both fatigue and fracture based, can be used to model fretting fatigue experiments leading to successful life predictions. In particular, experiments involving contact load configurations similar to those that occur in the blade/disk connection of gas turbine engines have been performed extensively. Predictions of fretting fatigue life have been compared favorably to experimental observations [1]. Recent efforts are aimed at performing experiments at higher temperatures as shown in the photograph below along with a sample fracture surface. The talk will describe the status of these experiments as will as model developments relevant to the single crystal material properties.

Matlik, J. F.; Murthy, H.; Farris, T. N.

2002-01-01

25

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

26

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.

1981-01-01

27

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

NASA Technical Reports Server (NTRS)

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

Arakere, Nagaraj K.; Swanson, Gregory R.

2000-01-01

28

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

29

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

SciTech Connect

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

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

2014-09-01

30

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

31

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

Microsoft Academic Search

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

Paul S. Prevéy; N. Jayaraman; Ravi Ravindranath

32

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

33

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

34

Procedure for estimating the fatigue strength of gas turbine blades by method of acoustic emission  

Microsoft Academic Search

For the purpose of estimating the fatigue characteristics of blades of gas turbine engines in industrial laboratories, one subjects a control lot of such blades to fatigue tests until the first symptoms of fracture appear. As such a symptom one usually regards a decrease of the natural frequency of the blade fin by a certain amount. Experience in such testing

M. D. Banov; E. A. Konyaev; D. A. Troenkin

1983-01-01

35

Crack propagation analysis of mechanically damaged compressor blades subjected to high cycle fatigue  

Microsoft Academic Search

This paper presents results of experimental crack propagation analysis of damaged compressor blades of the helicopter engine, subjected to high cycle fatigue. The blades used in investigations were preliminary defected to simulate the foreign object damage. The blades during experiment were entered into transverse vibration. The crack propagation process was conducted in resonance condition. During fatigue investigations the crack length

Lucjan Witek

2011-01-01

36

The static and fatigue computation of the propeller blades retention system  

NASA Astrophysics Data System (ADS)

The static and the fatigue computation of the propeller blades retention system to the monobloc hub with four blades is considered. The retention system contains a three-row ball bearing. The steel balls in parallel circumferential rows are placed around the blade root and are working along raceways of the blade retaining socket and those of the barrel.

Martin, Olga

1992-02-01

37

Isothermal Fatigue Life Prediction Techniques  

NASA Astrophysics Data System (ADS)

Substantial progress has been made in advancing a pre-existing energy-based fatigue life prediction method into a powerful tool for real-world application through three distinct analyses, resulting in considerable improvements to the fidelity and capability of the existing model. First, a torsional fatigue life prediction method with consideration for the identification and incorporation of loading multiaxiality was developed and validated against experimental results from testing of Aluminum 6061-T6 specimens at room temperature. Second, a unique isothermal-mechanical fatigue life testing capability was constructed and utilized in the development of an isothermal-mechanical fatigue life prediction method. This method was validated against experimental data generated from testing of Aluminum 6061-T6 specimens at multiple operating temperatures. Third, alternative quasi-static and dynamic constitutive relationships were applied to the isothermal-mechanical fatigue life prediction method. The accuracy of each new relationship was verified against experimental data generated from testing of two material systems with dissimilar properties: Aluminum 6061-T6 at multiple operating temperatures and Titanium 6Al-4V at room temperature. Each investigation builds upon a previously-developed energy-based life prediction capability, which states: the total strain energy dissipated during both a quasi-static process and a dynamic process are equivalent and a fundamental property of the material. Through these three analyses, the energy-based life prediction framework has acquired the capability of assessing the fatigue life of structures subjected to unplanned multiaxial loading and elevated isothermal operating temperatures; furthermore, alternative constitutive relationships have been successfully employed in improving the fidelity of the life prediction models. This work represents considerable advancements of the energy-based method, and provides a firm foundation for the growth of the energy-based life prediction framework into the thermo-mechanical fatigue regime. This future work will utilize many of the models developed for isothermal-mechanical fatigue; additionally, the isothermal-mechanical testing capability will be readily modified to perform thermo-mechanical fatigue.

Wertz, John Nicholas

38

Integrated approach for stress based lifing of aero gas turbine blades  

NASA Astrophysics Data System (ADS)

In order to analyse the turbine blade life, the damage due to the combined thermal and mechanical loads should be adequately accounted for. This is more challenging when detailed component geometry is limited. Therefore, a compromise between the level of geometric detail and the complexity of the lifing method to be implemented would be necessary. This research focuses on how the life assessment of aero engine turbine blades can be done, considering the balance between available design inputs and adequate level of fidelity. Accordingly, the thesis contributes to developing a generic turbine blade lifing method that is based on the engine thermodynamic cycle; as well as integrating critical design/technological factors and operational parameters that influence the aero engine blade life. To this end, thermo-mechanical fatigue was identified as the critical damage phenomenon driving the life of the turbine blade.. The developed approach integrates software tools and numerical models created using the minimum design information typically available at the early design stages. Using finite element analysis of an idealised blade geometry, the approach captures relevant impacts of thermal gradients and thermal stresses that contribute to the thermo-mechanical fatigue damage on the gas turbine blade. The blade life is evaluated using the Neu/Sehitoglu thermo-mechanical fatigue model that considers damage accumulation due to fatigue, oxidation, and creep. The leading edge is examined as a critical part of the blade to estimate the damage severity for different design factors and operational parameters. The outputs of the research can be used to better understand how the environment and the operating conditions of the aircraft affect the blade life consumption and therefore what is the impact on the maintenance cost and the availability of the propulsion system. This research also finds that the environmental (oxidation) effect drives the blade life and the blade coolant side was the critical location. Furthermore, a parametric and sensitivity study of the Neu/Sehitoglu model parameters suggests that in addition to four previously reported parameters, the sensitivity of the phasing to oxidation damage would be critical to overall blade life..

Abu, Abdullahi Obonyegba

39

Fatigue strength of model active gas turbine blades subjected to programmed temperature changes close to operating temperatures  

Microsoft Academic Search

Conclusions 1.The static tensile load leads to a sharp reduction of the amplitudes of the failure stress for the ZhS6K alloy at higher temperatures.2.Under steady temperature conditions and sign-constant tensile cyclic loading the difference in fatigue strength and life between testpieces and model blades is insignificant.3.With programmed temperature changes similar to those in operating gas turbine engines the fatigue strength

B. N. Sinaiskii

1971-01-01

40

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

NASA Astrophysics Data System (ADS)

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

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

41

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

NASA Astrophysics Data System (ADS)

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

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

1987-08-01

42

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

43

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

44

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

Microsoft Academic Search

This paper presents a technique of estimating blade fatigue damage at potential wind turbine sites. The cornerstone of this technique is a simple model for the blade`s root flap bending moment. The model requires as input a simple set of wind measurements that may be obtained as part of a routine site characterization study. By using the model to simulate

J. C. Barnard; L. L. Wendell

1997-01-01

45

Fatigue life of laser cut metals  

NASA Technical Reports Server (NTRS)

Fatigue tests were conducted to determine the actual reduction in fatigue life due to weight removal for balancing by: hand grinding, low power (20 watt) Nd:glass laser, and high power (400 watt) Nd:YAG laser.

Martin, M. R.

1986-01-01

46

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

E-print Network

1 AIAA-2003-0692 NEW FATIGUE DATA FOR W IND TURBINE BLADE M ATERIALS John F. Mandell, Daniel D of the University of Montana Butte, Montana 59701 ABSTRACT This paper reports on recent fatigue data of interest) effects of fiber waviness; and (d) large tow carbon fibers. Tensile fatigue results from a specialized

47

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

48

Procedure for estimating the fatigue strength of gas turbine blades by method of acoustic emission  

SciTech Connect

For the purpose of estimating the fatigue characteristics of blades of gas turbine engines in industrial laboratories, one subjects a control lot of such blades to fatigue tests until the first symptoms of fracture appear. As such a symptom one usually regards a decrease of the natural frequency of the blade fin by a certain amount. Experience in such testing indicates that this criterion is applicable only when a fatigue crack has become sufficiently long. In many cases the natural frequency has been found to change nonmonotonically, moreover, owing to defectiveness buildup and changes in the forces constraining the test object in the course of testing. These circumstances call for new methods of objective determination of the fatigue strength when active blades of gas turbine engines are under test. In this study the method of acoustic emission is considered from such a standpoint.

Banov, M.D.; Konyaev, E.A.; Troenkin, D.A.

1983-04-01

49

Nitinol Fatigue Life for Variable Strain Amplitude Fatigue  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

50

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

51

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

52

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

E-print Network

Effects of Glass Fabric and Laminate Construction on the Fatigue of Resin Infused Blade Materials fabrics with epoxy resins over a range of fiber contents. Significant improvements in tensile fatigue on fabric architecture and stitching details. All stitched fabric laminates show a transition to lower

53

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

E-print Network

, then adhesively bonded together. The large size coupled with cost constraints result in bond lines at least1 Mixed Mode Static and Fatigue Crack Growth in Wind Blade Paste Adhesives Daniel D. Samborsky and fatigue crack growth in thick adhesive joints with fiberglass laminate adherends, for three adhesive

54

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

NASA Technical Reports Server (NTRS)

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

Janetzke, D. C.

1983-01-01

55

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

56

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

Wito?, Miros?aw

2013-01-01

57

High sensitive methods for health monitoring of compressor blades and fatigue detection.  

PubMed

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

Wito?, Miros?aw

2013-01-01

58

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

59

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

SciTech Connect

This paper presents a technique of estimating blade fatigue damage at potential wind turbine sites. The cornerstone of this technique is a simple model for the blade`s root flap bending moment. The model requires as input a simple set of wind measurements which may be obtained as part of a routine site characterization study. By using the model to simulate a time series of the root flap bending moment, fatigue damage rates may be estimated. The technique is evaluated by comparing these estimates with damage estimates derived from actual bending moment data; the agreement between the two is quite good. The simple connection between wind measurements and fatigue provided by the model now allows one to readily discriminate between damaging and more benign wind environments.

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

1995-06-01

60

Fatigue Life Characteristics of Waterworks Pipe Welds  

NASA Astrophysics Data System (ADS)

The fatigue characteristic of a material or a structure is derived from fatigue tests of standard specimens. However, many test results of standard specimens are very different from those of real structures or components because of geometrical effect, surface condition and so on. In this study, fatigue tests with specimens and pipes were carried out to evaluate the fatigue characteristic of a real waterworks pipe. Standard fatigue specimens and non-standard specimens were extracted from a steel pipe used in waterworks system. Also, fatigue tests of real pipes used in water service were carried out. This result was compared with that of standard specimens and non-standard specimens. To evaluate pipe's fatigue characteristics based on life distribution, the statistical analysis method was introduced. Probability density functions of the specimen based on the normal distribution function were obtained from fatigue tests at particular stress levels. These functions were then transformed to probability density functions based on a specific number of cycles to failure. This procedure was also adapted to the pipe's test results. From these results, the fatigue characteristic of waterworks pipe was evaluated.

Park, Jae Sil; Seok, Chang-Sung; Choi, Jung Hun

61

Fatigue strength of working blades of turbines and compressors repaired by welding  

SciTech Connect

A method of determining the welding repair zones of working blades of gas turbine engines is proposed based on the principle of equal strength of the component using the fatigue strength criteria. The method takes into account the difference of the mechanical properties of the deposit and the parent metal. Investigations were carried out on new and repaired working blades of turbines and compressors of different gas-pumping systems. The experimental results are used to prepare recommendations for repairing the working blades subjected to pilot-plant service conditions.

Gryaznov, B.A.; Gorodetskii, S.S.; Nalimov, Y.S. [Institute of Problems of Strength, Kiev (Ukraine)] [and others

1995-07-01

62

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

63

Multiaxial fatigue models for short glass fiber reinforced polyamide. Part II: Fatigue life estimation.  

E-print Network

Multiaxial fatigue models for short glass fiber reinforced polyamide. Part II: Fatigue life in the automotive industry, and more and more frequently subjected to fatigue loadings during their service life. The determination of a predictive fatigue criterion is therefore a serious issue for the designers, and requires

Paris-Sud XI, Université de

64

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

SciTech Connect

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

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

2012-06-28

65

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

66

Considerations concerning fatigue life of metal matrix composites  

NASA Technical Reports Server (NTRS)

Since metal matrix composites (MMC) are composed from two very distinct materials each having their own physical and mechanical properties, it is feasible that the fatigue resistance depends on the strength of the weaker constituent. Based on this assumption, isothermal fatigue lives of several MMC's were analyzed utilizing a fatigue life diagram approach. For each MMC, the fatigue life diagram was quantified using the mechanical properties of its constituents. The fatigue life regions controlled by fiber fracture and matrix were also quantitatively defined.

Radhakrishnan, V. M.; Bartolotta, Paul A.

1993-01-01

67

On the impact of variability and assembly on turbine blade cooling flow and oxidation life  

E-print Network

The life of a turbine blade is dependent on the quantity and temperature of the cooling flow sup- plied to the blade. The focus of this thesis is the impact of variability on blade cooling flow and, subsequently, its impact ...

Sidwell, Carroll Vincent, 1972-

2004-01-01

68

Scale levels for fatigue fracture mechanisms of in-service crack growth in longerons of helicopter rotor blades  

Microsoft Academic Search

Cases of in-service fatigue crack growth in aluminium longerons of helicopter Mi-8 rotor blades were reviewed. Fatigue fracture\\u000a surface patterns for micro- and meso-scale levels of crack growth mechanisms for in-service fatigued longerons are discussed.\\u000a Meso-beach-marks were used to estimate the fatigue crack growth period in one of the damaged longerons with the least crack\\u000a size. Results of these estimations

A. A. Shaniavski

2004-01-01

69

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

SciTech Connect

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

Beattie, A.G.

1997-01-01

70

Predicting fatigue life of metal bellows  

NASA Technical Reports Server (NTRS)

Classical method of presenting fatigue data in plots of alternating stress vs number of deflection cycles is applied to bellows formed of various metals, including corrosion-resistant steel, nickel alloys, and aluminum alloys. The expected life of a new bellows design can then be determined before fabrication and testing.

Daniels, C. M.

1968-01-01

71

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

SciTech Connect

This paper examines the importance of phase angle variations with respect to fatigue damage. The operating loads on a generic conventional three-bladed upwind 1.5-MW wind turbine blade were analyzed over a range of operating conditions, and an aggregate probability distribution for the actual phase angles between the in-plane (lead-lag) and out-of-plane (flap) loads was determined. Using a finite element model of a generic blade and Miner's Rule, the accumulated theoretical damage (based on axial strains) resulting from a fatigue test with variable phase angles was compared to the damage resulting from a fatigue test with a constant phase angle. The nodal damage distribution at specific blade cross-sections are compared for the constant and variable phase angle cases. The sequence effects of various phase angle progressions were also considered. For this analysis, the finite element results were processed using the nonlinear Marco-Starkey damage accumulation model. Each phase angle sequence was constrained to have the same overall phase angle distribution and the same total number of cycles but the order in which the phase angles were applied was varied.

White, D. L.; Musial, W. D.

2003-11-01

72

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

NASA Astrophysics Data System (ADS)

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

Reiso, M.; Muskulus, M.

2014-12-01

73

["Fatigue of life" aging. Balneology cures].  

PubMed

The process of getting old involves involution and is influenced by the personal circumstances which affected the person's life. Biological studies have established the "hope of life" in 120 years, even if that age is hard to reach for people who lead an ordinate life. To grow old does not mean being ill though it carries frequently "pluripathology", certain functional troubles such as the psychical and sensorial ones. The "fatigue of life" has special importance as it can get to be incapacitant. Balneotherapic cures can be very beneficial. The Crenotherapy and the climatological influence and the sociotherapy under the control of the Doctor, can be very favorable. PMID:14619547

Armijo Valenzuela, Manuel

2003-01-01

74

The—S\\/N—Fatigue-life gage: A direct means of measuring cumulative fatigue damage  

Microsoft Academic Search

This paper describes the present state of development of a new type of sensor, a fatigue-life gage which generates an irreversible resistance change that is a continuous function of the fatigue experience of the structure to which it is attached. The gage accumulates fatigue-damage information whether or not it is connected to excitation or readout devices. Measurements of cumulative fatigue

Darrell R. Harting

1966-01-01

75

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

76

Fatigue life and backface strain predictions in adhesively bonded joints  

Microsoft Academic Search

Fatigue is a very important factor in any adhesively bonded structure subject to service loads. Prediction of fatigue life using finite element analysis (FEA) techniques is very complicated due to the complex nature of fatigue damage. This paper presents experimental data obtained by testing single lap joints (SLJs) in constant amplitude fatigue at a range of load levels and associated

A. Graner Solana; A. D. Crocombe; I. A. Ashcroft

2010-01-01

77

Fatigue of Composite Materials and Substructures for Wind Turbine Blades  

SciTech Connect

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

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

2002-03-01

78

Fatigue, Creep-Fatigue, and Thermomechanical Fatigue Life Testing of Alloys  

NASA Technical Reports Server (NTRS)

The fatigue crack initiation resistance of an alloy is determined by conducting a series of tests over a range of values of stress amplitude or strain range. The observed number of cycles to failure is plotted against the stress amplitude or strain range to obtain a fatigue curve. The fatigue properties quoted for an alloy are typically the constants used in the equation(s) that describe the fatigue curve. Fatigue lives of interest may be as low as 10(exp 2) or higher than 10(exp 9) cycles. Because of the enormous scatter associated with fatigue, dozens of tests may be needed to confidently establish a fatigue curve, and the cost may run into several thousands of dollars. To further establish the effects on fatigue life of the test temperature, environment, alloy condition, mean stress effects, creep-fatigue effects, thermomechanical cycling, etc. requires an extraordinarily large and usually very costly test matrix. The total effort required to establish the fatigue resistance of an alloy should not be taken lightly. Fatigue crack initiation tests are conducted on relatively small and presumed to be initially crack-free, samples of an alloy that are intended to be representative of the alloy's metallurgical and physical condition. Generally, samples are smooth and have uniformly polished surfaces within the test section. Some may have intentionally machined notches of well-controlled geometry, but the surface at the root of the notch is usually not polished. The purpose of polishing is to attain a reproducible surface finish. This is to eliminate surface finish as an uncontrolled variable. Representative test specimen geometries will be discussed later. Test specimens are cyclically loaded until macroscopically observable cracks initiate and eventually grow to failure. Normally, the fatigue failure life of a specimen is defined as the number of cycles to separation of the specimen into two pieces. Alternative definitions are becoming more common, particularly for low-cycle fatigue testing, wherein some prescribed indication of impending failure due to cracking is adopted. Specific criteria will be described later. As a rule, cracks that develop during testing are not measured nor are the test parameters intentionally altered owing to the presence of cracking.

Halford, Gary R.; Lerch, Bradley A.; McGaw, Michael A.

2000-01-01

79

Fatigue life prediction of bonded primary joints  

NASA Technical Reports Server (NTRS)

The validation of a proposed fatigue life prediction methodology was sought through the use of aluminum butt and scarf joint and graphite/epoxy butt joint specimens in a constant amplitude fatigue environment. The structural properties of the HYSOL 9313 adhesive system were obtained by mechanical test of molded heat adhesive specimens. Aluminum contoured double cantilever beam specimens were used to generate crack velocity versus stress intensity factor data. The specific objectives were: (1) to ascertain the feasibility of predicting fatigue failure of an adhesive in a primary bonded composite structure by incorporating linear elastic crack growth behavior; and (2) to ascertain if acoustic emission and/or compliance measurement techniques can be used to detect flaws.

Knauss, J. F.

1979-01-01

80

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

Microsoft Academic Search

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

Stephan Issler; Eberhard Roos

2003-01-01

81

Study of the effect of technical factors on the fatigue limit of the working blades of gas turbine motors  

Microsoft Academic Search

Conclusions 1.The examined deviations in the production technology for working blades in a turbine of one of the gas turbine motors (patterns, burn-ons, additional glossing operation) do not have any essential effect on the magnitude of the maximum fatigue limit of the blade on the basis of 108 cycles at temperatures of 20 and 570°. The range of changes in

V. T. Troshchenko; B. A. Gryaznov; S. S. Gorodetskii; A. B. Roitman; Yu. S. Nalimov

1972-01-01

82

Fatigue of Composite Materials: Damage Mechanisms and Fatigue-Life Diagrams  

Microsoft Academic Search

The basic fatigue damage mechanisms in composite laminates are reviewed. Based on these mechanisms a pattern in the fatigue-life diagrams is proposed. Several experimental data are shown to agree with this basic pattern. Fatigue ratio is defined in terms of strains, and fatigue limit is shown to exist for unidirectional, cross-plied and angle-plied laminates. The limitations to the fatigue performance

R. Talreja

1981-01-01

83

Common bearing material has highest fatigue life at moderate temperature  

NASA Technical Reports Server (NTRS)

AISI 52100, a high carbon chromium steel, has the longest fatigue life of eight bearing materials tested. Fatigue lives of the other materials ranged from 7 to 78 percent of the fatigue life of AISI 52100 at a temperature of 340 K (150 F).

Parker, R. J.; Zaretsky, E. V.; Dietrich, M. W.

1972-01-01

84

Fatigue Life of Superalloy Haynes 188 in Hydrogen  

NASA Astrophysics Data System (ADS)

The effects of hydrogen and surface finish on the mean low cycle fatigue life of Haynes 188 were studied. Specimens were prepared and fatigue tested with gage sections having low stress ground (LSG) and electro-discharge machined (EDM) surfaces. Fatigue tests were performed at temperatures of 25 to 650 °C with varied strain conditions, in hydrogen and helium environments. Fatigue life decreased with increasing strain range, strain ratio, temperature, and with hydrogen atmosphere. A Smith-Watson-Topper stress parameter could be used to account for variations in strain range and strain ratio, and most strongly influenced life. Hydrogen reduced fatigue life by about 5× (80%) at 25 °C, but was much less harmful at 650 °C. Standard EDM finish did not consistently reduce mean fatigue life from that of LSG finish specimens. Additional tests indicated fatigue life in hydrogen was maintained for varied EDM conditions, provided specimen roughness and maximum recast layer thickness were not excessive.

Gabb, T. P.; Webster, H.; Ribeiro, G.; Gorman, T.; Gayda, J.

2012-08-01

85

Fatigue life and fatigue crack propagation behavior of JLF-1 steel  

Microsoft Academic Search

The objective of this study is to investigate fatigue life and fatigue crack propagation behavior in the reduced activation ferritic steel JLF-1. The experiment of fatigue life for JLF-1 steel have been carried out for the stress ratio R=0 at room temperature and 400°C. The fatigue crack propagation behavior of the JLF-1 steel was investigated by the constant amplitude loading

H. K Yoon; S. P Lee; B. H Min; S. W Kim; Y Katoh; A Kohyama

2002-01-01

86

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

87

Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations  

NASA Technical Reports Server (NTRS)

A methodology is presented for determining the fatigue life of composite structures based on fatigue characterization data and geometric nonlinear finite element (FE) analyses. To demonstrate the approach, predicted results were compared to fatigue tests performed on specimens which represented a tapered composite flange bonded onto a composite skin. In a first step, tension tests were performed to evaluate the debonding mechanisms between the flange and the skin. In a second step, a 2D FE model was developed to analyze the tests. To predict matrix cracking onset, the relationship between the tension load and the maximum principal stresses transverse to the fiber direction was determined through FE analysis. Transverse tension fatigue life data were used to -enerate an onset fatigue life P-N curve for matrix cracking. The resulting prediction was in good agreement with data from the fatigue tests. In a third step, a fracture mechanics approach based on FE analysis was used to determine the relationship between the tension load and the critical energy release rate. Mixed mode energy release rate fatigue life data were used to create a fatigue life onset G-N curve for delamination. The resulting prediction was in good agreement with data from the fatigue tests. Further, the prediction curve for cumulative life to failure was generated from the previous onset fatigue life curves. The results showed that the methodology offers a significant potential to Predict cumulative fatigue life of composite structures.

Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin; Minguet, Pierre J.

2001-01-01

88

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

89

Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations  

NASA Technical Reports Server (NTRS)

A methodology is presented for determining the fatigue life of bonded composite skin/stringer structures based on delamination fatigue characterization data and geometric nonlinear finite element analyses. Results were compared to fatigue tests on stringer flange/skin specimens to verify the approach.

Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin

2000-01-01

90

Effects of cavitation on high-cycle fatigue life  

SciTech Connect

Cavitation was measured in 304 stainless steel after creep tests. Results show that cavitation is highly inhomogeneous. This has a significant effect on the interaction between small amounts of creep damage and high-cycle fatigue life. The low-cycle creep-fatigue and the high-cycle fatigue are not independent and may have large interactive effects. (DLC)

Majumdar, S.

1985-09-01

91

Fatigue life prediction of vulcanized natural rubber subjected to heat-aging  

Microsoft Academic Search

Fatigue life prediction and evaluation are the key technologies to assure the safety and reliability of automotive rubber components. In this paper, fatigue life prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Heat-aging effects on the fatigue life prediction of natural rubber were experimentally investigated. Fatigue

Chang-Su Woo; Wan-Doo Kim; Seong-Hoon Lee; Byung-Ik Choi; Hyun-Sung Park

2009-01-01

92

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

93

High-Strength Bolt Corrosion Fatigue Life Model and Application  

PubMed Central

The corrosion fatigue performance of high-strength bolt was studied. Based on the fracture mechanics theory and the Gerberich-Chen formula, the high-strength bolt corrosion fracture crack model and the fatigue life model were established. The high-strength bolt crack depth and the fatigue life under corrosion environment were quantitatively analyzed. The factors affecting high-strength bolt corrosion fatigue life were discussed. The result showed that the high-strength bolt corrosion fracture biggest crack depth reduces along with the material yield strength and the applied stress increases. The material yield strength was the major factor. And the high-strength bolt corrosion fatigue life reduced along with the increase of material strength, the applied stress or stress amplitude. The stress amplitude influenced the most, and the material yield strength influenced the least. Low bolt strength and a low stress amplitude level could extend high-strength bolt corrosion fatigue life. PMID:25152916

Hui-li, Wang; Si-feng, Qin

2014-01-01

94

High-strength bolt corrosion fatigue life model and application.  

PubMed

The corrosion fatigue performance of high-strength bolt was studied. Based on the fracture mechanics theory and the Gerberich-Chen formula, the high-strength bolt corrosion fracture crack model and the fatigue life model were established. The high-strength bolt crack depth and the fatigue life under corrosion environment were quantitatively analyzed. The factors affecting high-strength bolt corrosion fatigue life were discussed. The result showed that the high-strength bolt corrosion fracture biggest crack depth reduces along with the material yield strength and the applied stress increases. The material yield strength was the major factor. And the high-strength bolt corrosion fatigue life reduced along with the increase of material strength, the applied stress or stress amplitude. The stress amplitude influenced the most, and the material yield strength influenced the least. Low bolt strength and a low stress amplitude level could extend high-strength bolt corrosion fatigue life. PMID:25152916

Hui-li, Wang; Si-feng, Qin

2014-01-01

95

Fatigue life of automotive rubber jounce bumper  

NASA Astrophysics Data System (ADS)

It is evident that most rubber components in the automotive industry are subjected to repetitive loading. Vigorous research is needed towards improving the safety and reliability of the components. The study was done on an automotive rubber jounce bumper with a rubber hardness of 60 IRHD. The test was conducted in displacement-controlled environment under compressive load. The existing models by Kim, Harbour, Woo and Li were adopted to predict the fatigue life. The experimental results show strong similarities with the predicted models.

Sidhu, R. S.; Ali, Aidy

2010-05-01

96

Impact of aerothermal modeling on the estimation of turbine blade life  

E-print Network

The impact of aerothermal modeling on estimates of turbine blade heat transfer and life was assessed for three high pressure turbine blades. The work was conducted as part of a project aimed at the evaluation of the effect ...

Collin, Jean E., 1978-

2004-01-01

97

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

98

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

NASA Astrophysics Data System (ADS)

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

Xu, Jinlong; Dong, Yongkang; Li, Hui

2014-03-01

99

Rolling-element fatigue life of AMS 5900 balls  

NASA Technical Reports Server (NTRS)

The rolling-element fatigue life of AMS 5900 12.7-mm (1/2-in.) dia was determined in five-ball fatigue testers. The 10% life with the warm headed AMS 5900 balls was equivalent to that of AMS 5749 and over eight times that of AISI M-50. The AMS balls fabricated by cold heading had small surface cracks which initiated fatigue spalls where these cracks were crossed by running tracks. The cold-headed AMS 5900 balls had a 10% fatigue life an order of magnitude less than that of the warm headed balls even when failures on the cold headed balls at visible surface cracks were omitted.

Parker, R. J.

1983-01-01

100

Airframe structural optimization for maximum fatigue life  

NASA Technical Reports Server (NTRS)

A methodology is outlined for optimization of airframe structures under dynamic constraints to maximize service life of specified fatigue-critical components. For practical airframe structures, this methodology describes the development of sensitivity analysis and computational procedures for constraints on the steady-state dynamic response displacements and stresses. Strain energy consideration is used for selection of structural members for modification. Development of a design model and its relation to an analysis model, as well as ways to reduce the dimensionality of the problem via approximation concepts, are described. This methodology is demonstrated using an elastic stick model for the MH-53J helicopter to show service life improvements of the hinge fold region.

Schrage, D. P.; Sareen, A. K.

1990-01-01

101

Effect of surface irregularities on bellows fatigue life  

NASA Technical Reports Server (NTRS)

Report presents test data on the bending fatigue life of notched sheet specimens. The influence of a surface irregularity on the fatigue life of a metal bellows is evaluated, with emphasis on accidental defects in ducting bellows which are impossible to avoid short of completely eliminating human contact.

Schmidt, E. H.; Sheaffer, E. F.; Turner, J. D.; Zeimer, R. L.

1968-01-01

102

A sensitivity analysis on component reliability from fatigue life computations  

Microsoft Academic Search

Some uncertainties in determining high component reliability at a specified lifetime from a case study involving the fatigue life of a helicopter component are identified. Reliabilities are computed from results of a simulation process involving an assumed variability (standard deviation) of the load and strength in determining fatigue life. The uncertainties in the high reliability computation are then examined by

Donald M. Neal; William T. Matthews; Mark G. Vangel; Trevor Rudalevige

1992-01-01

103

2004-01-0628 Fatigue Life Comparisons of Competing Manufacturing  

E-print Network

), and the acceptance criteria were no crack initiation and no permanent deformation until 2x105 cycles. Among five1 2004-01-0628 Fatigue Life Comparisons of Competing Manufacturing Processes: A Study of Steering ABSTRACT A vehicle steering knuckle undergoes time-varying loadings during its service life. Fatigue

Fatemi, Ali

104

Effect of spectral shape on acoustic fatigue life estimates  

NASA Technical Reports Server (NTRS)

Methods for estimating fatigue life due to random loading are briefly reviewed. These methods include a probabilistic approach in which the expected value of the rate of damage accumulation is computed by integrating over the probability density of damaging events and a method which consists of analyzing the response time history to count damaging events. It is noted that it is necessary to employ a time domain approach to perform Rainflow counting, while simple peak counting may be accomplished using the probabilistic method. Data obtained indicate that Rainflow counting produces significantly different fatigue life predictions than other methods that are commonly used in acoustic fatigue predictions. When low-frequency oscillations are present in a signal along with high-frequency components, peak counting will produce substantially shorter fatigue lives than Rainflow counting. It is concluded that Rainflow counting is capable of providing reliable fatigue life predictions for acoustic fatigue studies.

Miles, R. N.

1992-01-01

105

Creep-fatigue life prediction of in situ composite solders  

SciTech Connect

Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. Intermetallic reinforcements of Ni{sub 3}Sn{sub 4} and Cu{sub 6}Sn{sub 5} are incorporated into eutectic tin-lead alloy by rapid solidification processes to form in situ composite solders. In this study, the in situ composite solders were subjected to combined creep and fatigue deformation at room temperature. Under cyclic deformation, the dominant damage mechanism of in situ composite solders is proposed to be growth of cavities. A constrained cavity growth model is applied to predict creep-fatigue life by taking into account the tensile loading component as well as the compressive loading component when reversed processes can occur. An algorithm to calculate cavity growth in each fatigue cycle is used to predict the number of fatigue cycles to failure, based on a critical cavity size of failure. Calculated lives are compared to experimental data under several fatigue histories, which include fully reversed stress-controlled fatigue, zero-tension stress-controlled fatigue, stress-controlled fatigue with tension hold time, fully reversed strain-controlled fatigue, and zero-tension strain-controlled fatigue. The model predicts the creep-fatigue lives within a factor of 2 with the incorporation of an appropriate compressive healing factor in most cases. Discrepancy between calculated lives and experimental results is discussed.

Kuo, C.G.; Sastry, S.M.L.; Jerina, K.L. [Washington Univ., St. Louis, MO (United States)

1995-12-01

106

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

107

Reinforced wind turbine blades--an environmental life cycle evaluation.  

PubMed

A fiberglass composite reinforced with carbon nanofibers (CNF) at the resin-fiber interface is being developed for potential use in wind turbine blades. An energy and midpoint impact assessment was performed to gauge impacts of scaling production to blades 40 m and longer. Higher loadings force trade-offs in energy return on investment and midpoint impacts relative to the base case while remaining superior to thermoelectric power generation in these indicators. Energy-intensive production of CNFs forces impacts disproportionate to mass contribution. The polymer nanocomposite increases a 2 MW plant's global warming potential nearly 100% per kWh electricity generated with 5% CNF by mass in the blades if no increase in electrical output is realized. The relative scale of impact must be compensated by systematic improvements whether by deployment in higher potential zones or by increased life span; the trade-offs are expected to be significantly lessened with CNF manufacturing maturity. Significant challenges are faced in evaluating emerging technologies including uncertainty in future scenarios and process scaling. Inventories available for raw materials and monte carlos analysis have been used to gain insight to impacts of this development. PMID:22857256

Merugula, Laura; Khanna, Vikas; Bakshi, Bhavik R

2012-09-01

108

Prediction of residual fatigue life using nonlinear ultrasound  

NASA Astrophysics Data System (ADS)

Prediction of fatigue life of components during service is an on-going and unsolved challenge for the NDT and structural health monitoring community. It has been demonstrated by a number of researchers that nonlinear guided waves or the acoustic nonlinear signature of fatigued cracked material provides clear signs of the progressive fatigue damage in the material, unlike linear guided waves. However, even with nonlinear acoustic-ultrasound methods there is a necessity to compare the current nonlinear feature to a previously measured cracked material state to assess the absolute residual fatigue life. In this paper, a new procedure based on the measurement of the second-order acoustic nonlinearity is presented which is able to assess the fatigue life of a metallic component without the need of a baseline. The Nazarov-Sutin crack nonlinearity equation and the Paris law are combined in order to obtain an analytical solution able to evaluate the theoretical second-order quadratic nonlinear parameters as a function of the crack growth and fatigue life that evolve during cyclic loading in metals. The model makes the assumption that the crack surface topology has variable geometrical parameters. The method was tested on aluminum alloy specimens AA2024-T351, containing fatigue fracture of different sizes, and excellent correlation was obtained between the theoretical and measured second-order nonlinear parameter. Then, it was demonstrated clearly that by measuring the nonlinear parameters it is possible to estimate crack size and fatigue life. Finally, advantages and limitations of the procedure are discussed.

Amura, Mikael; Meo, Michele

2012-04-01

109

Fatigue properties of jointed wood composites Part I Statistical analysis, fatigue master curves and constant life diagrams  

Microsoft Academic Search

The primary aim of this work was to assess the fatigue performance of scarf-jointed laminated wood composites used to manufacture wind turbine blades and establish simple fatigue design procedures. Laminates made from poplar (Populus canadensis\\/serotina), Khaya (Khaya ivorensis) and beech (Fagus sylvatica), incorporating typical scarf joints, were assessed under reversed loading (R =-1). Scarf joints were found to be great

I. P. Bond; M. P. Ansell

1998-01-01

110

Fatigue life estimation of an engine rubber mount  

Microsoft Academic Search

Fatigue life of an engine mount made of natural rubber was estimated, considering the effects of mean load. In order to develop an appropriate fatigue damage parameter of the rubber material, load-controlled fatigue tests were conducted using three-dimensional dumbbell specimens at different levels of mean load. It was shown that the maximum Green–Lagrange strain and the maximum strain energy density

W. D. Kim; H. J. Lee; J. Y. Kim; S.-K. Koh

2004-01-01

111

Development of an improved method of consolidating fatigue life data  

NASA Technical Reports Server (NTRS)

A fatigue data consolidation model that incorporates recent advances in life prediction methodology was developed. A combined analytic and experimental study of fatigue of notched 2024-T3 aluminum alloy under constant amplitude loading was carried out. Because few systematic and complete data sets for 2024-T3 were available in the program generated data for fatigue crack initiation and separation failure for both zero and nonzero mean stresses. Consolidations of these data are presented.

Leis, B. N.; Sampath, S. G.

1978-01-01

112

Fatigue Life Estimation under Cumulative Cyclic Loading Conditions  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

113

Extremely low cycle fatigue life prediction based on a new cumulative fatigue damage model  

Microsoft Academic Search

In order to predict an extremely low cycle fatigue (ELCF) life for annealed low carbon steel of S20C, a new cumulative fatigue damage model has been proposed. The model was based on the concept that the damage due to ductility exhaustion should be considered besides the damage generated by crack propagation in the ELCF regime where excessive strain was applied.

Masatoshi Kuroda

2002-01-01

114

Residual fatigue life estimation using a nonlinear ultrasound modulation method  

NASA Astrophysics Data System (ADS)

Predicting the residual fatigue life of a material is not a simple task and requires the development and association of many variables that as standalone tasks can be difficult to determine. This work develops a modulated nonlinear elastic wave spectroscopy method for the evaluation of a metallic components residual fatigue life. An aluminium specimen (AA6082-T6) was tested at predetermined fatigue stages throughout its fatigue life using a dual-frequency ultrasound method. A modulated nonlinear parameter was derived, which described the relationship between the generation of modulated (sideband) responses of a dual frequency signal and the linear response. The sideband generation from the dual frequency (two signal output system) was shown to increase as the residual fatigue life decreased, and as a standalone measurement method it can be used to show an increase in a materials damage. A baseline-free method was developed by linking a theoretical model, obtained by combining the Paris law and the Nazarov–Sutin crack equation, to experimental nonlinear modulation measurements. The results showed good correlation between the derived theoretical model and the modulated nonlinear parameter, allowing for baseline-free material residual fatigue life estimation. Advantages and disadvantages of these methods are discussed, as well as presenting further methods that would lead to increased accuracy of residual fatigue life detection.

Piero Malfense Fierro, Gian; Meo, Michele

2015-02-01

115

Development of generic creep–fatigue life prediction models  

Microsoft Academic Search

This paper presents a data bank that was compiled from published and unpublished sources. Using these data, low cycle fatigue curves were generated under a range of test conditions showing the effect of test parameters on the Coffin–Manson behavior of steel alloys. Phenomenological methods of creep–fatigue life prediction are summarized in a table showing number of material parameters required by

Tarun Goswami

2004-01-01

116

Cyclic calculations and life estimation in thermomechanical fatigue  

E-print Network

Cyclic calculations and life estimation in thermomechanical fatigue F. Azzouz1, G. Cailletaud1, J thermomechanical loading, (2) in a short review of an advanced fatigue model which can reproduce the Woehler curve, associated with high mean stresses. One of the difficulties of the inelastic analysis of the component

Paris-Sud XI, Université de

117

Flexural fatigue life prediction of closed hat-section using materially nonlinear axial fatigue characteristics  

NASA Technical Reports Server (NTRS)

Straight or curved hat-section members are often used as structural stiffeners in aircraft. For instance, they are employed as stiffeners for the dorsal skin as well as in the aerial refueling adjacent area structure in F-106 aircraft. The flanges of the hat-section are connected to the aircraft skin. Thus, the portion of the skin closing the hat-section interacts with the section itself when resisting the stresses due to service loads. The flexural fatigue life of such a closed section is estimated using materially nonlinear axial fatigue characteristics. It should be recognized that when a structural shape is subjected to bending, the fatigue life at the neutral axis is infinity since the normal stresses are zero at that location. Conversely, the fatigue life at the extreme fibers where the normal bending stresses are maximum can be expected to be finite. Thus, different fatigue life estimates can be visualized at various distances from the neural axis. The problem becomes compounded further when significant portions away from the neutral axis are stressed into plastic range. A theoretical analysis of the closed hat-section subjected to flexural cyclic loading is first conducted. The axial fatigue characteristics together with the related axial fatigue life formula and its inverted form given by Manson and Muralidharan are adopted for an aluminum alloy used in aircraft construction. A closed-form expression for predicting the flexural fatigue life is then derived for the closed hat-section including materially nonlinear action. A computer program is written to conduct a study of the variables such as the thicknesses of the hat-section and the skin, and the type of alloy used. The study has provided a fundamental understanding of the flexural fatigue life characteristics of a practical structural component used in aircraft when materially nonlinear action is present.

Razzaq, Zia

1989-01-01

118

Fatigue life prediction under service load considering strengthening effect of loads below fatigue limit  

NASA Astrophysics Data System (ADS)

Lightweight design requires an accurate life prediction for structures and components under service loading histories. However, predicted life with the existing methods seems too conservative in some cases, leading to a heavy structure. Because these methods are established on the basis that load cycles would only cause fatigue damage, ignore the strengthening effect of loads. Based on Palmgren-Miner Rule (PMR), this paper introduces a new method for fatigue life prediction under service loadings by taking into account the strengthening effect of loads below the fatigue limit. In this method, the service loadings are classified into three categories: damaging load, strengthening load and none-effect load, and the process for fatigue life prediction is divided into two stages: stage I and stage II, according to the best strengthening number of cycles. During stage I, fatigue damage is calculated considering both the strengthening and damaging effect of load cycles. While during stage II, only the damaging effect is considered. To validate this method, fatigue lives of automobile half shaft and torsion beam rear axle are calculated based on the new method and traditional methods, such as PMR and Modified Miner Rule (MMR), and fatigue tests of the two components are conducted under service loading histories. The tests results show that the percentage errors of the predicted life with the new method to mean life of tests for the two components are -3.78% and -1.76% separately, much lesser than that with PMR and MMR. By considering the strengthening effect of loads below the fatigue limit, the new method can significantly improve the accuracy for fatigue life prediction. Thus lightweight design can be fully realized in the design stage.

Zhao, Lihui; Zheng, Songlin; Feng, Jinzhi

2014-11-01

119

Fatigue life prediction under service load considering strengthening effect of loads below fatigue limit  

NASA Astrophysics Data System (ADS)

Lightweight design requires an accurate life prediction for structures and components under service loading histories. However, predicted life with the existing methods seems too conservative in some cases, leading to a heavy structure. Because these methods are established on the basis that load cycles would only cause fatigue damage, ignore the strengthening effect of loads. Based on Palmgren-Miner Rule (PMR), this paper introduces a new method for fatigue life prediction under service loadings by taking into account the strengthening effect of loads below the fatigue limit. In this method, the service loadings are classified into three categories: damaging load, strengthening load and none-effect load, and the process for fatigue life prediction is divided into two stages: stage I and stage II, according to the best strengthening number of cycles. During stage I, fatigue damage is calculated considering both the strengthening and damaging effect of load cycles. While during stage II, only the damaging effect is considered. To validate this method, fatigue lives of automobile half shaft and torsion beam rear axle are calculated based on the new method and traditional methods, such as PMR and Modified Miner Rule (MMR), and fatigue tests of the two components are conducted under service loading histories. The tests results show that the percentage errors of the predicted life with the new method to mean life of tests for the two components are -3.78% and -1.76% separately, much lesser than that with PMR and MMR. By considering the strengthening effect of loads below the fatigue limit, the new method can significantly improve the accuracy for fatigue life prediction. Thus lightweight design can be fully realized in the design stage.

Zhao, Lihui; Zheng, Songlin; Feng, Jinzhi

2014-09-01

120

A parametric physics based creep life prediction approach to gas turbine blade conceptual design  

NASA Astrophysics Data System (ADS)

The required useful service lives of gas turbine components and parts are naturally one of the major design constraints limiting the gas turbine design space. For example, the required service life of a turbine blade limits the firing temperature in the combustor, which in turn limits the performance of the gas turbine. For a cooled turbine blade, it also determines the necessary cooling flow, which has a strong impact on the turbine efficiency. In most gas turbine design practices, the life prediction is only emphasized during or after the detailed design has been completed. Limited life prediction efforts have been made in the early design stages, but these efforts capture only a few of the necessary key factors, such as centrifugal stress. Furthermore, the early stage prediction methods are usually hard coded in the gas turbine system design tools and hidden from the system designer's view. The common failure mechanisms affecting the service life, such as creep, fatigue and oxidation, are highly sensitive to the material temperatures and/or stresses. Calculation of these temperatures and stresses requires that the geometry, material properties, and operating conditions be known; information not typically available in early stages of design. Even without awareness of the errors, the resulting inaccuracy in the life prediction may mislead the system designers when examining a design space which is bounded indirectly by the inaccurate required life constraints. Furthermore, because intensive creep lifing analysis is possible only towards the end of the design process, any errors or changes will cost the engine manufacturer significant money; money that could be saved if more comprehensive creep lifing predictions were possible in the early stages of design. A rapid, physics-based life prediction method could address this problem by enabling the system designer to investigate the design space more thoroughly and accurately. Although not meant as a final decision method, the realistic trends will help to reduce risk, by providing greater insight into the bounded space at an earlier stage of the design. The method proposed by this thesis was developed by first identifying the missing pieces in the system conceptual design tools. Then, by bringing some key features from later stages of design and analysis forward through 0/1/2Ds dimensional modeling and simulation, the method allows estimation of the geometry, material selection, and the loading stemming from the operating conditions. Finally, after integration with a system design platform, the method provides a rapid and more complete way to allow system designers to better investigate the required life constraints. It also extracts the creep life as a system level metric to allow the designers to see the impact of their design decisions on life. The method was first applied to a cooled gas turbine blade and could be further developed for other critical parts. These new developments are integrated to allow the system designers to better capture the blade creep life as well as its impact on the overall design.

Smith, Marcus Edward Brockbank

121

Rotorcraft fatigue life-prediction: Past, present, and future  

NASA Astrophysics Data System (ADS)

In this paper the methods used for calculating the fatigue life of metallic dynamic components in rotorcraft is reviewed. In the past, rotorcraft fatigue design has combined constant amplitude tests of full-scale parts with flight loads and usage data in a conservative manner to provide 'safe life' component replacement times. This is in contrast to other industries, such as the automobile industry, where spectrum loading in fatigue testing is a part of the design procedure. Traditionally, the linear cumulative damage rule has been used in a deterministic manner using a conservative value for fatigue strength based on a one in a thousand probability of failure. Conservatism on load and usage are also often employed. This procedure will be discussed along with the current U.S. Army fatigue life specification for new rotorcraft which is the so-called 'six nines' reliability requirement. In order to achieve the six nines reliability requirement the exploration and adoption of new approaches in design and fleet management may also be necessary if this requirement is to be met with a minimum impact on structural weight. To this end a fracture mechanics approach to fatigue life design may be required in order to provide a more accurate estimate of damage progression. Also reviewed in this paper is a fracture mechanics approach for calculating total fatigue life which is based on a crack-closure small crack considerations.

Everett, Richard A., Jr.; Elber, W.

1994-03-01

122

Rotorcraft fatigue life-prediction: Past, present, and future  

NASA Technical Reports Server (NTRS)

In this paper the methods used for calculating the fatigue life of metallic dynamic components in rotorcraft is reviewed. In the past, rotorcraft fatigue design has combined constant amplitude tests of full-scale parts with flight loads and usage data in a conservative manner to provide 'safe life' component replacement times. This is in contrast to other industries, such as the automobile industry, where spectrum loading in fatigue testing is a part of the design procedure. Traditionally, the linear cumulative damage rule has been used in a deterministic manner using a conservative value for fatigue strength based on a one in a thousand probability of failure. Conservatism on load and usage are also often employed. This procedure will be discussed along with the current U.S. Army fatigue life specification for new rotorcraft which is the so-called 'six nines' reliability requirement. In order to achieve the six nines reliability requirement the exploration and adoption of new approaches in design and fleet management may also be necessary if this requirement is to be met with a minimum impact on structural weight. To this end a fracture mechanics approach to fatigue life design may be required in order to provide a more accurate estimate of damage progression. Also reviewed in this paper is a fracture mechanics approach for calculating total fatigue life which is based on a crack-closure small crack considerations.

Everett, Richard A., Jr.; Elber, W.

1994-01-01

123

A sensitivity analysis on component reliability from fatigue life computations  

NASA Astrophysics Data System (ADS)

Some uncertainties in determining high component reliability at a specified lifetime from a case study involving the fatigue life of a helicopter component are identified. Reliabilities are computed from results of a simulation process involving an assumed variability (standard deviation) of the load and strength in determining fatigue life. The uncertainties in the high reliability computation are then examined by introducing small changes in the variability for the given load and strength values in the study. Results showed that for a given component lifetime, a small increase in variability of load or strength produced large differences in the component reliability estimates. Among the factors involved in computing fatigue lifetimes, the component reliability estimates were found to be most sensitive to variability in loading. Component fatigue life probability density functions were obtained from the simulation process for various levels of variability. The range of life estimates were very large for relatively small variability in load and strength.

Neal, Donald M.; Matthews, William T.; Vangel, Mark G.; Rudalevige, Trevor

1992-02-01

124

A method for multiaxial fatigue life prediction using energy approaches  

SciTech Connect

Fatigue criteria based on the concept of damage energy have been proposed and evaluated with experimental fatigue data generated under uniaxial as well as biaxial loading conditions. Most of the energy-based methods utilize plastic energy of stress-strain hysteresis loops as a correlating parameter. Limited success has been made in predicting fatigue life in the low-cycle fatigue range where the plastic energy of the hysteresis loops is well defined. However, is is difficult to estimate the plastic hysteresis energy in the high-cycle range where the stress-strain behavior is virtually elastic. Failure to adequately predict high-cycle fatigue life is an obvious shortcoming of the plastic energy-based method. A new method is proposed for multiaxial fatigue life prediction using strain energy as a correlating parameter which is physically associated with modes of fatigue fracture on a critical plane of the material that may be sensitive to either axial stress or shear at a given temperature. Biaxial fatigue data were analyzed for type 304 stainless steel and SAE 1045 steel subjected to in-phase and 90{degrees} out-of-phase tension/torsion loading at room and elevated temperatures. Comparisons were made between the experimental data and theoretical predictions to show the effectiveness to the new energy-based approach.

Liu, K.C.

1991-01-01

125

Bending fatigue life properties of MCrAlY alloy coating systems: Study of life properties of high-temperature corrosion-resistant coating systems (4th report)  

Microsoft Academic Search

The low-pressure plasma spray coating process is established in gas turbine production for application to components (turbine blades, duct segments, etc) exposed to corrosive gases at high temperatures. Overlay coatings based on the MCrAlY alloy system (where M is Ni, Co, or Fe) are commonly used as oxidation- and corrosion- resistant coatings. The mechanical properties, such as the fatigue life,

Y. Ito; M. Saito; Y. Ishiwata

1999-01-01

126

Predicting the fatigue life of asphalt concrete overlay systems  

E-print Network

Photograph of Ultrasonic Transducers Taken Apart. 14 Ultrasonic Transducers Epoxied to Overlay Sample. 15 Ultrasonic Calibration Curve - Normalized Voltage Versus Crack Height . 16 Schematic of Duomorhp Apparatus . 17 Duomorph Output as Viewed... to predict fatigue life and to explain crack growth, a mechanistic model was developed at Ohio State University ( 15, 17, 18). From fracture mechanics, fatigue life can be described by the process of crack initiation, crack growth, and ultimate fracture...

Germann, Frederick P

1979-01-01

127

Numerical life prediction of mechanical fatigue for hot forging tools  

Microsoft Academic Search

In the forging industry, tools represent an important part in term of production and costs. Enhancing their life cycle is\\u000a then a challenging issue. Several mechanical and thermal mechanisms are responsible for hot forging tools damage such as wear,\\u000a thermal and mechanical fatigue. This work will be focused only on the mechanical fatigue life prediction for hot forging tools.\\u000a Both

Katia Mocellin; Matthieu Ferraro; Vincent Velay; Roland Logé; Farhad Rézaï-Aria

2009-01-01

128

Development of fatigue life evaluation method using small specimen  

NASA Astrophysics Data System (ADS)

For developing the fatigue life evaluation method using small specimen, the effect of specimen size and shape on the fatigue life of the reduced activation ferritic/martensitic steels (F82H-IEA, F82H-BA07 and JLF-1) was investigated by the fatigue test at room temperature in air using round-bar and hourglass specimens with various specimen sizes (test section diameter: 0.85-10 mm). The round-bar specimen showed no specimen size and no specimen shape effects on the fatigue life, whereas the hourglass specimen showed no specimen size effect and obvious specimen shape effect on it. The shorter fatigue life of the hourglass specimen observed under low strain ranges could be attributed to the shorter micro-crack initiation life induced by the stress concentration dependent on the specimen shape. On the basis of this study, the small round-bar specimen was an acceptable candidate for evaluating the fatigue life using small specimen.

Nogami, Shuhei; Nishimura, Arata; Wakai, Eichi; Tanigawa, Hiroyasu; Itoh, Takamoto; Hasegawa, Akira

2013-10-01

129

Prestraining and Its Influence on Subsequent Fatigue Life  

NASA Technical Reports Server (NTRS)

An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid uniform gage section were fatigued to failure under fully-reversed strain-control. Additional specimens were prestrained to 2 percent, 5 percent, and 10 percent (engineering strains) in the tensile direction and to 2 percent (engineering strain) in the compressive direction under stroke-control, and were subsequently fatigued to failure under fully-reversed strain-control. Experimental results are compared with estimates of remaining fatigue lives (after prestraining) using three life prediction approaches: (1) the Linear Damage Rule; (2) the Linear Strain and Life Fraction Rule; and (3) the nonlinear Damage Curve Approach. The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, best remaining fatigue life predictions were obtained with the nonlinear Damage Curve Approach.

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

1995-01-01

130

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

NASA Astrophysics Data System (ADS)

Wind turbines are fatigue-critical machines used to produce electrical energy from the wind. These rotating machines are subjected to environmental loadings that are highly irregular in nature. Historical examples of fatigue problems in both research and commercial wind turbine development are presented. Some example data on wind turbine environments, loadings and material properties are also shown. Before a description of how the authors have chosen to attack the cumulative damage assessment, questions are presented for the reader's reflection. The solution technique used by the authors is then presented, followed by a case study applying the procedures to an actual wind turbine blade joint. The wind turbine is the 34-meter diameter vertical axis wind turbine (VAWT) erected by Sandia National Laboratories near Bushland, Texas. The case study examines parameter sensitivities for realistic uncertainties in inputs defining the turbine environment, stress response and material properties. The fatigue lifetimes are calculated using a fatigue analysis program, called LIFE2, which was developed at Sandia. The LIFE2 code, described in some detail in an appendix, is a PC-based, menu-driven package that leads the user through the steps required to characterize the loading and material properties, then uses Miner's rule or a linear crack propagation rule to numerically calculate the time to failure. Only S-n based cumulative damage applications are illustrated here. The LIFE2 code is available to educational institutions for use as a case study in describing complicated loading histories and for use by students in examining, hands on, parameter sensitivity of fatigue life analysis.

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

131

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

SciTech Connect

Wind turbines are fatigue-critical machines used to produce electrical energy from the wind. These rotating machines are subjected to environmental loadings that are highly irregular in nature. Historical examples of fatigue problems in both research and commercial wind turbine development are presented. Some example data on wind turbine environments, loadings and material properties are also shown. Before a description of how the authors have chosen to attack the cumulative damage assessment, questions are presented for the reader's reflection. The solution technique used by the authors is then presented, followed by a case study applying the procedures to an actual wind turbine blade joint. The wind turbine is the 34-meter diameter vertical axis wind turbine (VAWT) erected by Sandia National Laboratories near Bushland, Texas. The case study examines parameter sensitivities for realistic uncertainties in inputs defining the turbine environment, stress response and material properties. The fatigue lifetimes are calculated using a fatigue analysis program, called LIFE2, which was developed at Sandia. The LIFE2 code, described in some detail in an appendix, is a PC-based, menu-driven package that leads the user through the steps required to characterize the loading and material properties, then uses Miner's rule or a linear crack propagation rule to numerically calculate the time to failure. Only S-n based cumulative damage applications are illustrated here. The LIFE2 code is available to educational institutions for use as a case study in describing complicated loading histories and for use by students in examining, hands on, parameter sensitivity of fatigue life analysis.

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

1992-01-01

132

Heat aging effects on the material property and the fatigue life of vulcanized natural rubber, and fatigue life prediction equations  

Microsoft Academic Search

When natural rubber is used for a long period of time, it becomes aged; it usually becomes hardened and loses its damping\\u000a capability. This aging process affects not only the material property but also the (fatigue) life of natural rubber. In this\\u000a paper the aging effects on the material property and the fatigue life were experimentally investigated. In addition, several

Jae-Hyeok Choi; Hee-Jin Kang; Hyun-Yong Jeong; Tae-Soo Lee; Sung-Jin Yoon

2005-01-01

133

Probabilistic mesomechanics for high cycle fatigue life prediction  

SciTech Connect

This paper presents an analytical modeling approach to characterize and understand high cycle fatigue life in gas turbine alloys. It is recognized that the design of structures subjected to fatigue cannot be based on average material behavior but that designs must consider {minus}3{sigma} or some other appropriate extreme value (tail of the distribution) loading and/or material properties. Thus, a life prediction capability useful in a design application must address the scatter inherent in material response to fatigue loading. Further, the life prediction capability should identify the key micromechanical variables that are critical in the tail of the materials durability distribution. The proposed method addresses the scatter in fatigue by investigating the microstructural variables responsible for the scatter and developing analytical and semi-analytical models to quantitatively relate the variables to the response. The model is general and considers the entire range of damage accumulation sequences; from crack nucleation of the initially unflawed structure to final fast fracture.

Tryon, R.G.; Cruse, T.A.

2000-04-01

134

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

135

A comparison of fatigue life prediction methodologies for rotorcraft  

NASA Technical Reports Server (NTRS)

Because of the current U.S. Army requirement that all new rotorcraft be designed to a 'six nines' reliability on fatigue life, this study was undertaken to assess the accuracy of the current safe life philosophy using the nominal stress Palmgrem-Miner linear cumulative damage rule to predict the fatigue life of rotorcraft dynamic components. It has been shown that this methodology can predict fatigue lives that differ from test lives by more than two orders of magnitude. A further objective of this work was to compare the accuracy of this methodology to another safe life method called the local strain approach as well as to a method which predicts fatigue life based solely on crack growth data. Spectrum fatigue tests were run on notched (k(sub t) = 3.2) specimens made of 4340 steel using the Felix/28 tests fairly well, being slightly on the unconservative side of the test data. The crack growth method, which is based on 'small crack' crack growth data and a crack-closure model, also predicted the fatigue lives very well with the predicted lives being slightly longer that the mean test lives but within the experimental scatter band. The crack growth model was also able to predict the change in test lives produced by the rainflow reconstructed spectra.

Everett, R. A., Jr.

1990-01-01

136

Dramatic increase in fatigue life in hierarchical graphene composites.  

PubMed

We report the synthesis and fatigue characterization of fiberglass/epoxy composites with various weight fractions of graphene platelets infiltrated into the epoxy resin as well as directly spray-coated on to the glass microfibers. Remarkably only ?0.2% (with respect to the epoxy resin weight and ?0.02% with respect to the entire laminate weight) of graphene additives enhanced the fatigue life of the composite in the flexural bending mode by up to 1200-fold. By contrast, under uniaxial tensile fatigue conditions, the graphene fillers resulted in ?3-5-fold increase in fatigue life. The fatigue life increase (in the flexural bending mode) with graphene additives was ?1-2 orders of magnitude superior to those obtained using carbon nanotubes. In situ ultrasound analysis of the nanocomposite during the cyclic fatigue test suggests that the graphene network toughens the fiberglass/epoxy-matrix interface and prevents the delamination/buckling of the glass microfibers under compressive stress. Such fatigue-resistant hierarchical materials show potential to improve the safety, reliability, and cost effectiveness of fiber-reinforced composites that are increasingly the material of choice in the aerospace, automotive, marine, sports, biomedical, and wind energy industries. PMID:20863061

Yavari, F; Rafiee, M A; Rafiee, J; Yu, Z-Z; Koratkar, N

2010-10-01

137

Fatigue properties of single lap joints using rubber toughened epoxy adhesive - Effect of adhesive thickness on fatigue life  

Microsoft Academic Search

This paper presents the fatigue properties of single lap bonded joints under cyclic tension shear loading. A newly developed rubber toughened epoxy adhesive was used. The effect of adhesive thickness on the fatigue life of the joint was investigated.

K. Miyazaki; T. Fujii; S. Amijima; Y. Okubo; K. Nejigaki

1992-01-01

138

Contact fatigue : life prediction and palliatives  

E-print Network

Fretting fatigue is defined as damage resulting from small magnitude (0.5-50 microns) displacement between contacting bodies where at least one of the bodies has an applied bulk stress. The applicability and limits of a ...

Conner, Brett P. (Brett Page), 1975-

2002-01-01

139

Non-destructive measurement and role of surface residual stress monitoring in residual life assessment of a steam turbine blading material  

NASA Astrophysics Data System (ADS)

Steam turbine blades in power generation equipment are made from martensitic stainless steels having high strength, good toughness and corrosion resistance. However, these steels are susceptible to pitting which can promote early failures of blades in the turbines, particularly in the low pressure dry/wet areas by stress corrosion and corrosion fatigue. Presence of tensile residual stresses is known to accelerate failures whereas compressive stresses can help in delaying failures. Shot peening has been employed as an effective tool to induce compressive residual stresses which offset a part of local surface tensile stresses in the surface layers of components. Maintaining local stresses at stress raisers, such as pits formed during service, below a threshold level can help in preventing the initiation microcracks and failures. The thickness of the layer in compression will, however, depend of the shot peening parameters and should extend below the bottom of corrosion pits. The magnitude of surface compressive drops progressively during service exposure and over time the effectiveness of shot peening is lost making the material susceptible to micro-crack initiation once again. Measurement and monitoring of surface residual stress therefore becomes important for assessing residual life of components in service. This paper shows the applicability of surface stress monitoring to life assessment of steam turbine blade material based on data generated in laboratory on residual surface stress measurements in relation to fatigue exposure. An empirical model is proposed to calculate the remaining life of shot peened steam turbine blades in service.

Prabhu-Gaunkar, Gajanana; Rawat, M. S.; Prasad, C. R.

2014-02-01

140

Surface Fatigue Life of High Temperature Gear Materials  

NASA Technical Reports Server (NTRS)

Three high temperature gear materials were evaluated using spur gear surface fatigue tests. These materials were, VASCO max 350, VASCO matrix 2, and nitralloy N and were evaluated for possible use in high temperature gear applications. The fatigue life of the three high temperature gear materials were compared with the life of the standard AISI 9310 aircraft gear material. Surface fatigue tests were conducted at a lubricant inlet temperature of 321 K (120 F), a lubricant outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), a speed of 10,000 rpm, and with a synthetic paraffinic lubricant. The life of the nitralloy N was approximately the same as the AISI 9310, the life of the VASCO max 350 was much less than the AISI 9310 while the life of the VASCO matrix 2 was several times the life of the AISI 9310. The VASCO max 350 also showed very low fracture toughness with approximately half of the gears failed by tooth fracture through the fatigue spall. The VASCO matrix 2 had approximately 10-percent fracture failure through the fatigue spalls indicating moderate to good fracture toughness.

Townsend, Dennis P.

1994-01-01

141

Corrosion fatigue behavior of coated 4340 steel for blade retention bolts of the AH1G helicopter. Final report  

Microsoft Academic Search

The main rotor blade bolt for the 540 helicopter rotor system of the AH-1G, UH-1C, and UH-1M helicopters is proposed to be improved by substituting plasma-sprayed tungsten carbide coating on the outer shank of the 4340 steel bolt for the present cadmium or chromium plate. This study was undertaken to determine the effects of these coating systems on the fatigue

M. Levy; J. L. Morrossi

1976-01-01

142

Thermomechanical fatigue, oxidation, and Creep: Part II. Life prediction  

NASA Astrophysics Data System (ADS)

A life prediction model is developed for crack nucleation and early crack growth based on fatigue, environment (oxidation), and creep damage. The model handles different strain-temperature phasings (i.e., in-phase and out-of-phase thermomechanical fatigue, isothermal fatigue, and others, including nonproportional phasings). Fatigue life predictions compare favorably with experiments in 1070 steel for a wide range of test conditions and strain-temperature phasings. An oxide growth (oxide damage) model is based on the repeated microrupture process of oxide observed from microscopic measurements. A creep damage expression, which is stress-based, is coupled with a unified constitutive equation. A set of interrupted tests was performed to provide valuable damage progression information. Tests were performed in air and in helium atmospheres to isolate creep damage from oxidation damage.

Neu, R. W.; Sehitoglu, Huseyin

1989-09-01

143

Development of Fatigue Life Monitoring of Rmaf Fighter Airplanes  

Microsoft Academic Search

The Royal Malaysian Airforce (RMAF) operates fighter squadrons of F\\/A-18D, MiG-29, and Sukhoi-30 which were designed on Safe\\u000a Life principle. RMAF has been conducting an intensive fatigue life monitoring program to the RMAF F\\/A-18D and is developing\\u000a fatigue life monitoring (FLM) program to other fighters in its inventory. For this purpose, RMAF MiG-29 became the focus of\\u000a the development and

Wahyu Kuntjoro; M Suhaimi Ashari; M Yazid Ahmad; Assanah M. Mydin

144

Flight-by-flight fatigue crack growth life assessment  

Microsoft Academic Search

Conventionally, fatigue crack growth in aircraft structures under flight spectrum loading is often analysed and predicted based on crack growth rates obtained from constant-amplitude crack growth testing with cycle-by-cycle life prediction methods or models. Because the mechanism of fatigue crack growth under spectrum loading is yet to be fully understood, no matter how closely the models are able to account

W. Zhuang; S. Barter; L. Molent

2007-01-01

145

Fatigue life prediction modeling for turbine hot section materials  

NASA Technical Reports Server (NTRS)

A major objective of the fatigue and fracture efforts under the Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.

1988-01-01

146

Fatigue life prediction modeling for turbine hot section materials  

NASA Technical Reports Server (NTRS)

A major objective of the fatigue and fracture efforts under the NASA Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.

1989-01-01

147

NASA GRC Fatigue Crack Initiation Life Prediction Models  

NASA Technical Reports Server (NTRS)

Metal fatigue has plagued structural components for centuries, and it remains a critical durability issue in today's aerospace hardware. This is true despite vastly improved and advanced materials, increased mechanistic understanding, and development of accurate structural analysis and advanced fatigue life prediction tools. Each advance is quickly taken advantage of to produce safer, more reliable, more cost effective, and better performing products. In other words, as the envelope is expanded, components are then designed to operate just as close to the newly expanded envelope as they were to the initial one. The problem is perennial. The economic importance of addressing structural durability issues early in the design process is emphasized. Tradeoffs with performance, cost, and legislated restrictions are pointed out. Several aspects of structural durability of advanced systems, advanced materials and advanced fatigue life prediction methods are presented. Specific items include the basic elements of durability analysis, conventional designs, barriers to be overcome for advanced systems, high-temperature life prediction for both creep-fatigue and thermomechanical fatigue, mean stress effects, multiaxial stress-strain states, and cumulative fatigue damage accumulation assessment.

Arya, Vinod K.; Halford, Gary R.

2002-01-01

148

A parametric physics based creep life prediction approach to gas turbine blade conceptual design  

Microsoft Academic Search

The required useful service lives of gas turbine components and parts are naturally one of the major design constraints limiting the gas turbine design space. For example, the required service life of a turbine blade limits the firing temperature in the combustor, which in turn limits the performance of the gas turbine. For a cooled turbine blade, it also determines

Marcus Edward Brockbank Smith

2008-01-01

149

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

150

Fatigue life analysis of a cannon barrel  

Microsoft Academic Search

A steel cannon barrel was tested and analyzed in order to predict its lifetime. Mechanical properties, fracture toughness and fatigue behavior were determined experimentally. The cannon barrel was assumed to have a smooth inner surface. On that basis, finite element analyses were carried out in order to determine the stress intensity factor as a function of crack length for the

Leslie Banks-Sills; R. Eliasi

1999-01-01

151

Fatigue life estimates for helicopter loading spectra  

NASA Technical Reports Server (NTRS)

Helicopter loading histories applied to notch metal samples are used as examples, and their fatigue lives are calculated by using a simplified version of the local strain approach. This simplified method has the advantage that it requires knowing the loading history in only the reduced form of ranges and means and number of cycles from the rain-flow cycle counting method. The calculated lives compare favorably with test data.

Khosrovaneh, A. K.; Dowling, N. E.; Berens, A. P.; Gallagher, J. P.

1989-01-01

152

Fatigue life estimates for helicopter loading spectra  

NASA Technical Reports Server (NTRS)

Helicopter loading histories applied to notch metal samples are used as examples, and their fatigue lives are calculated by using a simplified version of the local strain approach. This simplified method has the advantage that it requires knowing the loading history in only the reduced form of ranges and means and number of cycles from the rain-flow cycle counting method. The calculated lives compare favorably with test data.

Khosrovaneh, A. K.; Dowling, N. E.; Berens, A. P.; Gallagher, J. P.

1990-01-01

153

Optimization method of multi-body structure based on the fatigue life  

NASA Astrophysics Data System (ADS)

A new optimization method based on the fatigue life of multi-body structure is proposed in this paper with the computeraided engineering software. Taking the nose landing gear of some aero transports as an example, the loading history of the nose landing gear is firstly gained by the multi-body dynamics simulation, and then the fatigue life is predicted through the finite element method and fatigue analysis. In accordance with the forecasting results, the weakest parts of the components are identified, and then they are optimized based on the fatigue life to lengthen the fatigue life of structural weaknesses thus to the fatigue lives of the whole structures.

Ma, Jian; Xue, Caijun; Deng, Yaquan; Wang, Hong

2008-11-01

154

The effect of warm water surface treatments on the fatigue life in shear of aluminum joints  

Microsoft Academic Search

The effect of warm water treatment on the fatigue life of 2024 T3 aluminum alloy adhesively bonded with FM73 epoxy adhesive was investigated. As expected, the fatigue life was shown to depend on the surface preparation of the bonds. Fatiguing the specimens in wet conditions led to a slightly shorter life than under dry conditions. There was a correlation between

P. R. Underhill; A. N. Rider; D. L. DuQuesnay

2006-01-01

155

High-Cycle Constant Amplitude Fatigue Life Variability of Welded Round HSS Y-Joints  

E-print Network

High-Cycle Constant Amplitude Fatigue Life Variability of Welded Round HSS Y-Joints By John L for generating accurate fatigue life predictions for these structures. Cracking found in existing sign support 2003 #12;i Preface The variability in fatigue life estimates for welded pipe joints commonly found

Foley, Christopher M.

156

Enhancement of flip-chip fatigue life by encapsulation  

Microsoft Academic Search

Encapsulation of controlled collapse chip connection (C4) joints, using a filled epoxy resin with a matched coefficient of thermal expansion (CTE), has provided a substantial increase in the life of C4 joints in accelerated thermal cycle (ATC) fatigue testing on both low CTE organic and ceramic chip carriers. The C4 joints are encapsulated by dispensing a bead of the resin

Darbha Suryanarayana; Richard Hsiao; Thomas P. Gall; Jack M. McCreary

1991-01-01

157

Effect of spectral shape on acoustic fatigue life estimates  

Microsoft Academic Search

Methods for estimating fatigue life due to random loading are briefly reviewed. These methods include a probabilistic approach in which the expected value of the rate of damage accumulation is computed by integrating over the probability density of damaging events and a method which consists of analyzing the response time history to count damaging events. It is noted that it

R. N. Miles

1992-01-01

158

Rainflow counting algorithm for the LIFE2 fatigue analysis code  

Microsoft Academic Search

The LIFE2 computer code is a fatigue\\/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. In this formulation, each stress cycle is counted or binsed according to the magnitude of its mean stress

L. L. Schluter; H. J. Sutherland

1989-01-01

159

Paper No. 9 ANALYSIS OF FATIGUE LIFE UNDER COMPLEX LOADING  

E-print Network

Paper No. 9 ANALYSIS OF FATIGUE LIFE UNDER COMPLEX LOADING: REVISITING CADWELL, MERILL, SLOMAN, AND YOST W. V. MARS* COOPER TIRE & RUBBER COMPANY FINDLAY, OHIO A. FATEMI UNIVERSITY OF TOLEDO TOLEDO, OHIO Presented at a meeting of the Rubber Division, American Chemical Society Grand Rapids, Michigan May 17

Fatemi, Ali

160

Simulation work of fatigue life prediction of rubber automotive components  

Microsoft Academic Search

The usage of rubbers has always been so important, especially in automotive industries. Rubbers have a hyper elastic behaviour which is the ability to withstand very large strain without failure. The normal applications for rubbers are used for shock absorption, sound isolation and mounting. In this study, the predictions of fatigue life of an engine mount of rubber automotive components

M. S. A. Samad; Aidy Ali

2010-01-01

161

Developments in blade shape design for a Darrieus vertical axis wind turbine  

NASA Astrophysics Data System (ADS)

A new computer program package has been developed that determines the troposkein shape for a Darrieus Vertical Axis Wind Turbine Blade with any geometrical configuration or rotation rate. This package allows users to interact and develop a buildable blade whose shape closely approximates the troposkein. Use of this package can significantly reduce flatwise mean bending stresses in the blade and increase fatigue life.

Ashwill, T. D.; Leonard, T. M.

1986-09-01

162

Evolution of creep-fatigue life prediction models  

NASA Technical Reports Server (NTRS)

The evolution of high-temperature, creep-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940s. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches have been identified as being combinations of fourteen different classifications. This review is intended to aid both developers and users of high-temperature fatigue life prediction methods by providing a background from which choices can be made.

Halford, Gary R.

1991-01-01

163

Fatigue life analysis of a turboprop reduction gearbox  

NASA Technical Reports Server (NTRS)

A fatigue life analysis of the Allison T56/501 turboprop reduction gearbox was developed. The life and reliability of the gearbox was based on the lives and reliabilities of the main power train bearings and gears. The bearing and gear lives were determined using the Lundberg-Palmgren theory and a mission profile. The five planet bearing set had the shortest calculated life among the various gearbox components, which agreed with field experience where the planet bearing had the greatest incidences of failure. The analytical predictions of relative lives among the various bearings were in reasonable agreement with field experience. The predicted gearbox life was in excellent agreement with field data when the material life adjustment factors alone were used. The gearbox had a lower predicted life in comparison with field data when no life adjustment factors were used or when lubrication life adjustment factors were used either alone or in combination with the material factors.

Lewicki, D. G.; Black, J. D.; Savage, M.; Coy, J. J.

1985-01-01

164

Relationship between fatigue life in the creep-fatigue region and stress-strain response  

NASA Technical Reports Server (NTRS)

On the basis of mechanical tests and metallographic studies, strainrange partitioned lives were predicted by introducing stress-strain materials parameters into the Universal Slopes Equation. This was the result of correlating fatigue damage mechanisms and deformation mechanisms operating at elevated temperatures on the basis of observed mechanical and microstructural behavior. Correlation between high temperature fatigue and stress strain properties for nickel base superalloys and stainless steel substantiated the method. Parameters which must be evaluated for PP- and CC- life are the maximum stress achievable under entirely plastic and creep conditions respectively and corresponding inelastic strains, and the two more pairs of stress strain parameters must be ascertained.

Berkovits, A.; Nadiv, S.

1988-01-01

165

Ductility normalized-strain-range partitioning life relations for creep-fatigue life predictions  

NASA Technical Reports Server (NTRS)

Techniques utilizing strainrange partitioning may be used to estimate the effects of the environment on the high-temperature, low-cycle, creep-fatigue resistance of alloys. Three levels of ductility-normalized strainrange-partitioning life relations are discussed: (1) strainrange partitioning relations from ductility data, (2) strainrange partitioning relations scaled by ductility ratios, and (3) strainrange partitioning life relations with measured PP lines. The procedures have demonstrated good agreement with available creep-fatigue data.

Halford, G. R.; Saltsman, J. F.; Hirschberg, M. H.

1978-01-01

166

Simulation work of fatigue life prediction of rubber automotive components  

NASA Astrophysics Data System (ADS)

The usage of rubbers has always been so important, especially in automotive industries. Rubbers have a hyper elastic behaviour which is the ability to withstand very large strain without failure. The normal applications for rubbers are used for shock absorption, sound isolation and mounting. In this study, the predictions of fatigue life of an engine mount of rubber automotive components were presented. The finite element analysis was performed to predict the critical part and the strain output were incorporated into fatigue model for prediction. The predicted result shows agreement in term of failure location of rubber mount.

Samad, M. S. A.; Ali, Aidy

2010-05-01

167

A study on the material properties and fatigue life prediction of natural rubber component  

Microsoft Academic Search

Fatigue life prediction and evaluation are very important in design procedure to assure the safety and reliability of the rubber components. Fatigue lifetime prediction methodology of the rubber component was proposed by incorporating the finite element analysis and fatigue damage parameter from fatigue test. Finite element analysis of rubber component was performed based on a hyper-elastic material model determined from

Chang-Su Woo; Wan-Doo Kim; Jae-Do Kwon

2008-01-01

168

Life prediction for bridged fatigue cracks  

SciTech Connect

One of the more promising classes of composites touted for high temperature applications, and certainly the most available, is that of relatively brittle matrices, either ceramic or intermetallic, reinforced by strong, aligned, continuous fibers. Under cyclic loading in the fiber direction, these materials develop matrix cracks that often run perpendicular to the fibers, while the fibers remain intact in the crack wake, supplying bridging tractions across the fracture surfaces. The bridging tractions shield the crack tip from the applied load, dramatically reducing the crack velocity from that expected in an unreinforced material subjected to the same value, {Delta}K{sub a}, of the cyclic applied stress intensity factor. An important issue in reliability is the prediction of the growth rates of the bridged cracks. The growth rates of matrix fatigue cracks bridged by sliding fibers are now commonly predicted by models based on the micromechanics of frictional interfaces. However, there exist many reasons, both theoretical and experimental, for suspecting that the most popular micromechanical models are probably wrong in detail in the context of fatigue cracks. Furthermore, a review of crack growth data reveals that the validity of the micromechanics-based predictive model has never been tested and may never be tested. In this paper, two alternative approaches are suggested to the engineering problem of predicting the growth rates of bridged cracks without explicit recourse to micromechanics. Instead, it is shown that the material properties required to analyze bridging effects can be deduced directly from crack growth data. Some experiments are proposed to test the validity of the proposals.

Cox, B.N.

1994-08-01

169

Sickle blade life-history and the transition to agriculture: an early Neolithic case study from Southwest Asia  

E-print Network

Sickle blade life-history and the transition to agriculture: an early Neolithic case study from Use-wear Curation Sickle blades Scanning electron microscope analysis Southwest Asia a b s t r a c t In Southwest Asia, sickle blades first appear early in the sequence of the transition to agriculture

Kohler, Tim A.

170

Multiaxial plasticity and fatigue life prediction in coiled tubing  

SciTech Connect

Coiled tubing is being used increasingly in the oil well drilling and servicing industry. Continuous steel tubing of structural dimensions (up to 89 mm or 3.5 in. in diameter) is wound onto a large-diameter reel for repeated deployment into and out of a well bore. The bending strain range associated with each wrap-unwrap cycle can exceed 3% with lives well below 100 cycles. During constant internal pressure fatigue testing, tubing has been observed to grow in diameter by as much as 30%. This paper describes an analytical model to predict the fatigue behavior of coiled tubing subjected to variable pressure service conditions. The approach utilizes standard low-cycle fatigue data but requires additional experimental results from constant pressure fatigue testing. The algorithm is based on estimates of biaxial ratcheting from an incremental plasticity model using a hybrid associated flow rule, a modified kinematic hardening rule with multiple von Mises yield surfaces, and a specialized limit surface concept. An empirical damage parameter was formulated based on constant pressure fatigue data using mean and fluctuating von Mises equivalent strain components occurring throughout the life of a section of tubing. This parameters is used with the Palmgren-Miner definition of cumulative damage to track damage that is accumulating nonlinearly under constant or variable pressure histories. Modifications to standard incremental plasticity components and implementation assumptions used to apply the model are presented and discussed. The predictive capability of the model is demonstrated relative to data generated under constant and variable pressure histories.

Tipton, S.M. [Univ. of Tulsa, OK (United States). Mechanical Engineering Dept.

1996-12-31

171

Simplified fatigue life analysis for traction drive contacts  

NASA Technical Reports Server (NTRS)

A simplified fatigue life analysis for traction drive contacts of arbitrary geometry is presented. The analysis is based on the Lundberg-Palmgren theory used for rolling-element bearings. The effects of torque, element size, speed, contact ellipse ratio, and the influence of traction coefficient are shown. The analysis shows that within the limits of the available traction coefficient, traction contacts exhibit longest life at high speeds. Multiple, load-sharing roller arrangements have an advantageous effect on system life, torque capacity, power-to-weight ratio and size.

Rohn, D. A.; Loewenthal, S. H.; Coy, J. J.

1980-01-01

172

Fatigue life prediction of a rubber mount based on test of material properties and finite element analysis  

Microsoft Academic Search

Failure analysis and fatigue life prediction are very important in the design procedure to assure the safety and reliability of rubber components. The fatigue life of a rubber mount was predicted by combining test of material properties and finite element analysis (FEA). The natural rubber material material’s fatigue life equation was acquired based on uniaxial tensile test and fatigue life

Qian Li; Jian-cai Zhao; Bo Zhao

2009-01-01

173

FACTORS THAT AFFECT THE FATIGUE LIFE OF RUBBER: A LITERATURE SURVEY  

E-print Network

FACTORS THAT AFFECT THE FATIGUE LIFE OF RUBBER: A LITERATURE SURVEY W. V. MARS* ADVANCED RESEARCH, TOLEDO, OHIO, 43606 ABSTRACT Many factors are known to influence the mechanical fatigue life of rubber and reviewed. Rubber's fatigue behavior is extremely sensitive to both the maximum and minimum cyclic load

Fatemi, Ali

174

Heat-Aging Effects on the Material Properties and Fatigue Life Prediction of Vulcanized Natural Rubber  

Microsoft Academic Search

The fatigue analysis and lifetime evaluation are very important in design procedure to assure the safety and reliability of the rubber components. Heat-aging process affects not only the material properties but also the fatigue life of vulcanized natural rubber. In this paper, the heat-aging effects on the material properties and fatigue life prediction of natural rubber were experimentally investigated. The

Chang Su Woo; Wan Doo Kim

2006-01-01

175

Statistical fatigue properties in the large strain region of a stainless steel sheet for use as an abrasion strip on helicopter rotor blades  

Microsoft Academic Search

The objective of this study was to evaluate the statistical fatigue properties of a thin sheet of a stainless steel for use as an abrasion strip on helicopter rotor blades made of glass fiber\\/epoxy composite materials. The sheet was an AISI 301 1\\/4-hard stainless steel. Tensile fatigue tests were conducted up to 107 cycles on unnotched specimens under constant amplitude

Toshiyuki Shimokawa; Yasumasa Hamaguchi; Shigeru Machida; Takeshi Ogawa; Hiroaki Itabe

2005-01-01

176

Equivalent linearization for fatigue life estimates of a nonlinear structure  

NASA Technical Reports Server (NTRS)

An analysis is presented of the suitability of the method of equivalent linearization for estimating the fatigue life of a nonlinear structure. Comparisons are made of the fatigue life of a nonlinear plate as predicted using conventional equivalent linearization and three other more accurate methods. The excitation of the plate is assumed to be Gaussian white noise and the plate response is modeled using a single resonant mode. The methods used for comparison consist of numerical simulation, a probabalistic formulation, and a modification of equivalent linearization which avoids the usual assumption that the response process is Gaussian. Remarkably close agreement is obtained between all four methods, even for cases where the response is significantly linear.

Miles, R. N.

1989-01-01

177

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

178

Investigating the Effects of Corrosion on the Fatigue Life of Welded Steel Attachments  

E-print Network

and determine whether this relationship is beneficial, neutral, or detrimental to the fatigue behavior of welded attachments. In order to investigate the effects of corrosion on the fatigue life of welded steel attachments, a testing methodology simulating...

Soape, Jack

2012-07-16

179

Thermal plastic strain fatigue life of the roll  

NASA Astrophysics Data System (ADS)

Fracture mechanics are applied to the roll, a crucial part of a mill, in order to solve engineering problems. The calculations of the thermal stress fields and temperature field are outlined. The estimation of the thermal plastic strain fatigue life of the roll, using Neuber's plastic stress-strain concentration theory, a path independent J integral defined by Rice, and cyclic strain growth rates, is shown.

Li, Zhenzi; Huang, Xiangan; Liao, Fuchang

1992-07-01

180

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

NASA Technical Reports Server (NTRS)

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

Moreno, V.

1983-01-01

181

Determination of engineering strain distribution in a rotor blade with fibre Bragg grating array and a rotary optic coupler  

Microsoft Academic Search

Structural damage occurs in materials subjected to repeated or fluctuating stresses that must be minimized by design to increase fatigue life, and strains distributed in a blade need to be experimentally determined for evaluating stress levels. In order to measure local strains in a rotating blade, efficient signal transmission between a sensor installed on a blade and a stationary interrogator

Kyungmok Kim; Jong Min Lee; Yoha Hwang

2008-01-01

182

A comparison of two total fatigue life prediction methods  

SciTech Connect

A 2-D analytical model which is termed the PICC-RICC model combines the effects of plasticity-induced crack closure (PICC) and roughness-induced crack closure (RICC). The PICC-RICC model handles naturally the gradual transition from RICC to PICC dominated crack growth. In this study, the PICC-RICC model is combined with a crack nucleation model to predict the total fatigue life of a notched component. This modified PICC-RICC model will be used to examine several controversial aspects of an earlier, computationally simpler total-life model known as the IP model.

Chen, N.; Lawrence, F.V.

1999-07-01

183

Development, reliability evaluation and service experiences of gas turbine blade life regeneration technology  

Microsoft Academic Search

To reduce the maintenance cost by extending the replacement life of gas turbine hot parts, various methods are being developed\\u000a and practically used. The life-regeneration process using hot iso-static pressing (HIP), BLE (Blade Life Extension) process\\u000a ™, for the 1100°C-class gas turbine buckets is one of our accomplishments and is applied for more than 16 sets since 1999.\\u000a Based on

Yomei Yoshioka; Daizo Saito; Reki Takaku; Shoko Itou; Iwataro Sato; Kazutoshi Ishibashi; Yoshiaki Sakai

2010-01-01

184

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

185

Cumulative life stress in chronic fatigue syndrome.  

PubMed

We studied the impact of cumulative life stress on CFS in a population-based study. We found that exposure to stressors was significantly more common in persons with CFS compared to NF controls; those with CFS reported experiencing significantly higher levels of psychological distress. Also, post-traumatic stress disorder was significantly more common in people with CFS. These results not only corroborate findings from other studies but, importantly, extend those by: a) measuring a comprehensive spectrum of stress variables, b) for the first time presenting data on stress in a population-based study, thus minimizing the effects of recruitment bias, and c) diagnosing CFS by means of standardized, validated scales, thus allowing replication and extension of our findings. Stress may be an important factor in the pathophysiology of CFS. Consequently, future studies should provide a more detailed understanding of the processes that lead from stress to CFS using longitudinal designs. PMID:21840607

Nater, Urs M; Maloney, Elizabeth; Heim, Christine; Reeves, William C

2011-09-30

186

A review of the effects of coolant environments on the fatigue life of LWR structural materials.  

SciTech Connect

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code specifies design curves for the fatigue life of structural materials in nuclear power plants. However, the effects of light water reactor (LWR) coolant environments were not explicitly considered in the development of the design curves. The existing fatigue-strain-versus-life ({var_epsilon}-N) data indicate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. Under certain environmental and loading conditions, fatigue lives in water relative to those in air can be a factor of 15 lower for austenitic stainless steels and a factor of {approx}30 lower for carbon and low-alloy steels. This paper reviews the current technical basis for the understanding of the fatigue of piping and pressure vessel steels in LWR environments. The existing fatigue {var_epsilon}-N data have been evaluated to identify the various material, environmental, and loading parameters that influence fatigue crack initiation and to establish the effects of key parameters on the fatigue life of these steels. Statistical models are presented for estimating fatigue life as a function of material, loading, and environmental conditions. An environmental fatigue correction factor for incorporating the effects of LWR environments into ASME Code fatigue evaluations is described. This paper also presents a critical review of the ASME Code fatigue design margins of 2 on stress (or strain) and 20 on life and assesses the possible conservatism in the current choice of design margins.

Chopra, O. K.; Shack, W. J.

2009-04-01

187

Effects of cyclic stress distribution models on fatigue life predictions  

NASA Astrophysics Data System (ADS)

The fatigue analysis of a wind turbine component typically uses representative samples of cyclic loads to determine lifetime loads. In this paper, several techniques currently in use are compared to one another based on fatigue life analyses. The generalized Weibull fitting technique is used to remove the artificial truncation of large-amplitude cycles that is inherent in relatively short data sets. Using data from the Sandia/DOE 34-m Test Bed, the generalized Weibull file technique is shown to be excellent for matching the body of the distribution of cyclic loads and for extrapolating the tail of the distribution. However, the data also illustrate that the fitting technique is not a substitute for an adequate data base.

Sutherland, H. J.; Veers, P. S.

1994-10-01

188

The Effect of Geometry on Fatigue Life for Bellows  

NASA Astrophysics Data System (ADS)

A bellows is a component installed in the automobile exhaust system to reduce or prevent the impact from engine. Generally, the specifications on the bellows are determined in the system design process of exhaust system and the component design is carried out to meet the specifications such as stiffness. Consideration of fatigue is generally an important aspect of design on metallic bellows expansion joints. These components are subject to displacement loading which frequently results in cyclic strains. This study has been investigated to analyze the effect of geometry on fatigue life for automotive bellows. 8 node shell element and non-linear method is employed for the analysis. The optimized shapes of the bellows are expected to give good guidelines to the practical designs.

Kim, Jinbong

189

Fatigue  

MedlinePLUS

... 21, 2014 Select a Language: Fact Sheet 551 Fatigue WHAT IS FATIGUE? IS FATIGUE IMPORTANT? HOW DO ... It can be physical or psychological. With physical fatigue , your muscles cannot do things as easily as ...

190

Fatigue-life behavior and matrix fatigue crack spacing in unnotched SCS-6/Timetal 21S metal matrix composites  

NASA Technical Reports Server (NTRS)

Fatigue tests of the SCS-6/Timetal 21S composite system were performed to characterize the fatigue behavior for unnotched conditions. The stress-life behavior of the unnotched (9/90)2s laminates was investigated for stress ratios of R = 0.1 and R = 0.3. The occurrence of matrix cracking was also examined in these specimens. This revealed multiple matrix crack initiation sites throughout the composite, as well as evenly spaced surface cracks along the length of the specimens. No difference in fatigue lives were observed for stress ratios of R = 0.1 and R = 0.3 when compared on a stress range basis. The unnotched SCS-6/Timetal 21S composites had shorter fatigue lives than the SCS-6/Ti-15-3 composites, however the neat Timetal 21S matrix material had a longer fatigue life than the neat Ti-15-3.

Ward, G. T.; Herrmann, D. J.; Hillberry, B. M.

1993-01-01

191

Fatigue analysis and life prediction of bridges with structural health monitoring data — Part II: application  

Microsoft Academic Search

This paper is a continuation of the paper titled “FATIGUE ANALYSIS AND LIFE PREDICTION OF BRIDGES WITH STRUCTURAL HEALTH MONITORING DATA — PART I: METHODOLOGY AND STRATEGY” with the emphasis on application of the developed method to the fatigue damage assessment of the Tsing Ma Bridge. Based on the methodology and strategy of the fatigue analysis presented in Part I,

T. H. T. Chan; Z. X. Li; J. M. Ko

2001-01-01

192

Effects of temperature change on fatigue life of carbon steel in high temperature water  

SciTech Connect

Strain controlled fatigue tests of a carbon steel in oxygenated high temperature water were carried out under the condition of combined and synchronized mechanical and thermal strain cycling. The effects of temperature change on environmental fatigue life were investigated, showing basic conceptual data to evaluate the fatigue damage under the condition of transient temperature change of actual plant components.

Kanasaki, Hiroshi [Mitsubishi Heavy Industries, Ltd., Takasago, Hyogo (Japan). Takasago Research and Development Center; Hayashi, Makoto [Hitachi Ltd., Ibaraki (Japan). Mechanical Engineering Research Lab.; Iida, Kunihiro [Shibaura Inst. of Technology, Tokyo (Japan). Dept. of Mechanical Engineering; Asada, Yasuhide [Univ. of Tokyo (Japan). Dept. of Mechanical Engineering

1995-12-31

193

Fatigue life analysis and predictions for NR and SBR under variable amplitude and multiaxial loading conditions  

E-print Network

on the fatigue lives of multiaxial rubber specimens. Two filled rubber materials were used and compared of rubber; Variable amplitude loading; Fatigue life prediction; Equivalence parameters 1. Introduction- lytical methods used for predicting fatigue lives of rubber components, a better understanding

Fatemi, Ali

194

Modeling cyclic ratcheting based fatigue life of HSLA steels using crystal plasticity FEM simulations and experiments  

E-print Network

into the faster crack propagation regime. The phenomena of high-cycle and low-cycle fatigue have been; Cyclic ratcheting; Nucleation cycles; Total fatigue life 1. Introduction High strength low alloy (HSLA a fatigue crack and propa- gate it to failure has been the prime objective of these mod- els. In the stress

Ghosh, Somnath

195

Life extension of components with high cumulative fatigue usage  

SciTech Connect

The current ASME Boiler and Pressure Vessel Code fatigue design approach has significant margins of safety as evidenced by fatigue data on full-scale vessels. In order to extend qualification (life) of components which have reached the Code design usage limit of unity, improved criteria are needed which address crack initiation and propagation separately such that safe operation of these components is ensured. The fatigue initiation phase is composed of two processes: initial microcracking of internal particles or accumulation of local strain (cyclic slip) creating discontinuities which form microcracks, and the growth of the microcracks in a noncontinuum manner. The microcracks which initiate will eventually grow to a size in which continuum mechanics apply, and fracture mechanics concepts have been employed. The later propagation to failure of a component is also composed of two parts, continuum crack growth in a stable manner and eventual unstable fracture of the remaining ligament of material. This paper reviews the current status of technology in assessing initiation and propagation relative to the current design Code and suggests areas of improvement to cover extended life of high usage factor components. To illustrate some of these considerations, a case study for a small manufacturing defect was reviewed. A realistic component was analyzed to investigate the interrelationship between the ASME Code Section III design life and crack propagation behavior of a small manufacturing defect. A pressurized water reactor (PWR) primary coolant system was used in the analysis, and the terminal end of the hot-leg pipe at the safe end weld was selected since usage factors as high as 0.95 had been reported. The particular plant chosen was Zion-1 because the necessary information on loading, including thermal transients, was available in the open literature. 11 refs., 1 fig., 1 tab.

Server, W.L.

1985-01-01

196

Development of a Generic Creep-Fatigue Life Prediction Model  

NASA Technical Reports Server (NTRS)

The objective of this research proposal is to further compile creep-fatigue data of steel alloys and superalloys used in military aircraft engines and/or rocket engines and to develop a statistical multivariate equation. The newly derived model will be a probabilistic fit to all the data compiled from various sources. Attempts will be made to procure the creep-fatigue data from NASA Glenn Research Center and other sources to further develop life prediction models for specific alloy groups. In a previous effort [1-3], a bank of creep-fatigue data has been compiled and tabulated under a range of known test parameters. These test parameters are called independent variables, namely; total strain range, strain rate, hold time, and temperature. The present research attempts to use these variables to develop a multivariate equation, which will be a probabilistic equation fitting a large database. The data predicted by the new model will be analyzed using the normal distribution fits, the closer the predicted lives are with the experimental lives (normal line 1 to 1 fit) the better the prediction. This will be evaluated in terms of a coefficient of correlation, R 2 as well. A multivariate equation developed earlier [3] has the following form, where S, R, T, and H have specific meaning discussed later.

Goswami, Tarun

2002-01-01

197

On the fatigue failure and life prediction for notched specimens  

Microsoft Academic Search

We present a brief description of some typical macromechanical models for fatigue-life prediction. According to their theoretical\\u000a bases, they can be classified as hot-spot, average-stress, stress-field-intensity, and volumetric approaches. We propose a\\u000a new model largely based on the stress-field-intensity and volumetric approaches, capable of giving better description of the\\u000a role of the most important factors acting in the process of

G. Qylafku; Z. Azari; M. Gjonaj; G. Pluvinage

1998-01-01

198

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

199

Modeling fatigue crack growth for life-extending control  

NASA Astrophysics Data System (ADS)

This dissertation presents a nonlinear dynamic model of fatigue crack growth in the state-space setting under variable amplitude cyclic load. The model is especially suited to the needs of real-time decision-making for life-extending control. The state variables are crack length and crack opening stress. The model is capable of capturing the effects of a single-cycle overload, block loads, random loads, and irregular sequences through a fading memory algorithm. Model predictions are in good agreement with experimental data on 7075-T6 and 2024-T3 aluminum alloys. Compiled results also demonstrate that the proposed model compares well with one of the most comprehensive models, FASTRAN-II that is used by the aircraft industry. Specifically, the state-space model recursively computes the crack opening stress via a simple functional relationship based on the principle of fading memory and does not require the storage of the stress history for its execution. Therefore, savings in both computation time and memory requirements are significant. The need for a reliable damage model for life-extending control is addressed with reference to the colossal inaccuracies that could occur in controller synthesis for a reusable rocket engine if a simplistic damage model is used under variable-amplitude load conditions. The seemingly counter-intuitive notion of overload injection could be gainfully utilized for life-extending optimization. The proof of this concept is demonstrated on a laboratory test apparatus by life-extension of test specimens with intentionally injected overload pulses at specific intervals. A stochastic model of fatigue crack growth under variable-amplitude load is proposed using the framework of the state-space model. The stochastic model is validated with four sets of constant-amplitude load test data and a set under variable-amplitude load test. The crack growth process is observed to be nearly deterministic for a cyclic load applied to a given specimen, provided that its microstructure does not undergo any major change. Therefore, a reliable deterministic model is a prerequisite for a stochastic model of fatigue crack growth. The stochastic model of fatigue crack growth does not require expensive computations to obtain a solution to the stochastic difference equations.

Patankar, Ravindra Prakash

1999-12-01

200

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

201

Low Cycle Fatigue Behavior and Life Prediction of a Cast Cobalt-Based Superalloy  

NASA Astrophysics Data System (ADS)

Co-base superalloys have been applied in the stationary components of gas turbine owing to their excellent high temperature properties. Low cycle fatigue data on ECY-768 reported in a companion paper were used to evaluate fatigue life prediction models. In this study, low cycle fatigue tests are performed as the variables of total strain range and temperatures. The relations between plastic and total strain energy densities and number of cycles to failure are examined in order to predict the low cycle fatigue life of Cobalt-based super alloy at different temperatures. The fatigue lives is evaluated using predicted by Coffin-Manson method and strain energy methods is compared with the measured fatigue lives at different temperatures. The microstructure observing was performed for how affect able to low-cycle fatigue life by increasing the temperature.

Yang, Ho-Young; Kim, Jae-Hoon; Yoo, Keun-Bong

202

Fatigue Life Methodology for Tapered Composite Flexbeam Laminates  

NASA Technical Reports Server (NTRS)

The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delamination fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to nonlinear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axial-tension and transverse cyclic bending loads. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen. Continued cycling resulted in multiple delaminations. A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed. The global responses of the model and test specimens agreed very well in terms of the transverse flexbeam tip-displacement and flapping angle. The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode 2, whereas delamination growth toward the thin region was almost completely mode 1. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.

Murri, Gretchen B.; O''Brien, T. Kevin; Rousseau, Carl Q.

1997-01-01

203

Fatigue Life Methodology for Tapered Composite Flexbeam Laminates  

NASA Technical Reports Server (NTRS)

The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delamination fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to non-linear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axial-tension and transverse cyclic bending. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen. Continued cycling resulted in multiple delaminations. A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed. The global responses of the model and test specimens agreed very well in terms of the transverse displacement. The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode 2, whereas delamination growth toward the thin region was almost completely mode 1. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.

Murri, Gretchen B.; OBrien, T. Kevin; Rousseau, Carl Q.

1997-01-01

204

An Energy Based Fatigue Life Prediction Framework for In-Service Structural Components  

SciTech Connect

An energy based fatigue life prediction framework has been developed for calculation of remaining fatigue life of in service gas turbine materials. The purpose of the life prediction framework is to account aging effect caused by cyclic loadings on fatigue strength of gas turbine engines structural components which are usually designed for very long life. Previous studies indicate the total strain energy dissipated during a monotonic fracture process and a cyclic process is a material property that can be determined by measuring the area underneath the monotonic true stress-strain curve and the sum of the area within each hysteresis loop in the cyclic process, respectively. The energy-based fatigue life prediction framework consists of the following entities: (1) development of a testing procedure to achieve plastic energy dissipation per life cycle and (2) incorporation of an energy-based fatigue life calculation scheme to determine the remaining fatigue life of in-service gas turbine materials. The accuracy of the remaining fatigue life prediction method was verified by comparison between model approximation and experimental results of Aluminum 6061-T6. The comparison shows promising agreement, thus validating the capability of the framework to produce accurate fatigue life prediction.

H. Ozaltun; M. H.H. Shen; T. George; C. Cross

2011-06-01

205

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

206

Determination of Turboprop Reduction Gearbox System Fatigue Life and Reliability  

NASA Technical Reports Server (NTRS)

Two computational models to determine the fatigue life and reliability of a commercial turboprop gearbox are compared with each other and with field data. These models are (1) Monte Carlo simulation of randomly selected lives of individual bearings and gears comprising the system and (2) two-parameter Weibull distribution function for bearings and gears comprising the system using strict-series system reliability to combine the calculated individual component lives in the gearbox. The Monte Carlo simulation included the virtual testing of 744,450 gearboxes. Two sets of field data were obtained from 64 gearboxes that were first-run to removal for cause, were refurbished and placed back in service, and then were second-run until removal for cause. A series of equations were empirically developed from the Monte Carlo simulation to determine the statistical variation in predicted life and Weibull slope as a function of the number of gearboxes failed. The resultant L(sub 10) life from the field data was 5,627 hr. From strict-series system reliability, the predicted L(sub 10) life was 774 hr. From the Monte Carlo simulation, the median value for the L(sub 10) gearbox lives equaled 757 hr. Half of the gearbox L(sub 10) lives will be less than this value and the other half more. The resultant L(sub 10) life of the second-run (refurbished) gearboxes was 1,334 hr. The apparent load-life exponent p for the roller bearings is 5.2. Were the bearing lives to be recalculated with a load-life exponent p equal to 5.2, the predicted L(sub 10) life of the gearbox would be equal to the actual life obtained in the field. The component failure distribution of the gearbox from the Monte Carlo simulation was nearly identical to that using the strict-series system reliability analysis, proving the compatibility of these methods.

Zaretsky, Erwin V.; Lewicki, David G.; Savage, Michael; Vlcek, Brian L.

2007-01-01

207

Structural health monitoring of wind towers: residual fatigue life estimation  

NASA Astrophysics Data System (ADS)

In a recent paper (Benedetti et al 2011 Smart Mater. Struct. 20 055009), the authors investigated the possibility of detecting cracks in critical sites of onshore wind towers using a radial arrangement of strain sensors around the tower periphery in the vicinity of the base welded joint. Specifically, the strain difference between adjacent strain sensors is used as a damage indicator. The number of sensors to be installed is determined by the minimum crack size to be detected, which in turn depends on the expected extreme wind conditions and programmed inspection/repair schedule. In this companion paper, we address these issues by investigating possible strategies for residual fatigue life assessment and management of onshore wind towers once the crack has been detected. For this purpose, fracture mechanics tests are carried out using welded samples to quantify the resistance to fatigue crack growth as well as the elastic-plastic fracture toughness of the welded joint at the tower base. These material strength characteristics are used to estimate (i) the critical crack size for structural integrity on the basis of fracture toughness tests, elastoplastic finite element analyses and loading spectra under extreme wind conditions, (ii) the residual life before structural collapse, applying a frequency-domain method to typical in-service wind actions and wind directionality.

Benedetti, M.; Fontanari, V.; Battisti, L.

2013-04-01

208

Rainflow counting algorithm for the LIFE2 fatigue analysis code  

SciTech Connect

The LIFE2 computer code is a fatigue/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. In this formulation, each stress cycle is counted or binsed'' according to the magnitude of its mean stress and alternating stress components and by the operating condition of the turbine. This paper describes a set of numerical algorithms that have been incorporated into the LIFE2 code. These algorithms determine the cycle count matrices for a turbine component using stress-time histories of the imposed stress states. Example problems are used to illustrate the use of these algorithms. 4 refs., 4 figs.

Schluter, L.L.; Sutherland, H.J. (Sandia National Labs., Albuquerque, NM (USA))

1989-01-01

209

A study on the material properties and fatigue life of natural rubber with different carbon blacks  

Microsoft Academic Search

Natural rubber compounds filled with N330, N650 or N990 were experimentally investigated in order to examine the effects of carbon black on the fatigue life, the hysteresis, the fracture surface morphology and the critical J-value. The fatigue life was obtained by conducting a displacement-controlled fatigue test on an hourglass-shaped specimen, and the hysteresis was calculated from the loading and unloading

J.-H. Kim; H.-Y. Jeong

2005-01-01

210

Relations between sleep, fatigue and health-related quality of life in individuals with insomnia  

PubMed Central

Objective This study explored the relations between sleep, fatigue and health-related quality of life in a sample of individuals with chronic insomnia. Methods A total of 160 adults meeting diagnostic criteria for chronic insomnia underwent three nights of polysomnography (PSG) and completed sleep diaries and questionnaires assessing daytime functioning including fatigue and health-related quality of life. Results A cluster analysis was conducted based on PSG-defined sleep disturbances and fatigue severity. A four-cluster solution (R2 = 0.68) was found, classifying individuals as having either (a) both severe sleep disturbance and severe fatigue (n = 15); (b) severe sleep disturbance but milder fatigue (n = 15); (c) milder sleep disturbance but severe fatigue (n = 68) or (d) both milder sleep disturbance and milder fatigue (n = 61). Health-related quality of life was lower in both clusters with severe fatigue compared to those with milder fatigue, and was further decreased when severe sleep disturbances were present. Relations between several indicators of fatigue and health-related quality of life were then examined using factor analysis in order to identify different domains of impairment. A three-factor structure was selected, suggesting that daytime symptoms can be classified as relating to fatigue, physical health, or mental health. These different subtypes of daytime impairment were predicted by distinct sets of variables. Conclusion More severe fatigue is not necessarily related to poorer PSG-defined sleep but appears associated with greater impairment in health-related quality of life. Fatigue and health-related quality of life appear to be distinct but interrelated constructs. PMID:20955867

Fortier-Brochu, Émilie; Beaulieu-Bonneau, Simon; Ivers, Hans; Morin, Charles M.

2010-01-01

211

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, ...

212

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 ...

213

Estimation of fatigue strain-life curves for austenitic stainless steels in light water reactor environments.  

SciTech Connect

The ASME Boiler and Pressure Vessel Code design fatigue curves for structural materials do not explicitly address the effects of reactor coolant environments on fatigue life. Recent test data indicate a significant decrease in fatigue lives of austenitic stainless steels (SSs) in light water reactor (LWR) environments. Unlike those of carbon and low-alloy steels, environmental effects on fatigue lives of SSs are more pronounced in low-dissolved-oxygen (low-DO) water than in high-DO water, This paper summarizes available fatigue strain vs. life data on the effects of various material and loading variables such as steel type, DO level, strain range, and strain rate on the fatigue lives of wrought and cast austenitic SSs. Statistical models for estimating the fatigue lives of these steels in LWR environments have been updated with a larger data base. The significance of the effect of environment on the current Code design curve has been evaluated.

Chopra, O. K.; Smith, J. L.

1998-02-12

214

Probabilistic fatigue life prediction model for alloys with defects: applied to A206  

SciTech Connect

Presented here is a model for the prediction of fatigue life based on the statistical distribution of pores, intermetallic particles and grains. This has been applied to a cast Al alloy A206, before and after friction stir processing (FSP). The model computes the probability to initiate a small crack based on the probability of finding combinations of defects and grains on the surface. The crack initiation and propagation life of small cracks due to these defect and grain combinations are computed and summed to obtain the total fatigue life. The defect and grain combinations are ranked according to total fatigue life and the failure probability computed. Bending fatigue experiments were carried out on A206 before and after FSP. FSP eliminated the porosity, broke down the particles and refined the microstructure. The model predicted the fatigue life of A206 before and after FSP well. The cumulative probability distribution vs. fatigue life was fitted to a three parameter Weibull distribution function. The scatter reduced after FSP and the threshold of fatigue life increased. The potential improvement in the fatigue life of A206 for a microstructure consisting of a finer distribution of particle sizes after FSP was predicted using the model.

Kapoor, Rajeev; Sree Hari Rao, V.; Mishra, Rajiv S.; Baumann, John A.; Grant, Glenn J.

2011-05-31

215

Notch sensitivity of fatigue life in a Sylramic TM composite at elevated temperature  

E-print Network

in advanced gas turbine engines. The motivation for this activity is the desire to increase operatingNotch sensitivity of fatigue life in a Sylramic TM /SiC composite at elevated temperature J.C. Mc The effects of holes and notches on the fatigue life of an advanced SylramicTM /SiC composite at 815 C have

Zok, Frank

216

The Effect of Aircraft Gas Turbine Oils on Roller Bearing Fatigue Life  

Microsoft Academic Search

A series of fatigue life tests on aircraft gear box size (45 mm bore) roller bearings were conducted with various aircraft gas turbine lubricants and with specific reference to Mil-L-7808 and variations thereof. It is shown that the 7808 lubricants generally cause a marked reduction in fatigue life as compared to that obtained with a medium viscosity mineral oil. It

Mark E. Otterbein

1958-01-01

217

Calculation of thermomechanical fatigue life based on isothermal behavior  

NASA Technical Reports Server (NTRS)

The isothermal and thermomechanical fatigue (TMF) crack initiation response of a hypothetical material was analyzed. Expected thermomechanical behavior was evaluated numerically based on simple, isothermal, cyclic stress-strain - time characteristics and on strainrange versus cyclic life relations that have been assigned to the material. The attempt was made to establish basic minimum requirements for the development of a physically accurate TMF life-prediction model. A worthy method must be able to deal with the simplest of conditions: that is, those for which thermal cycling, per se, introduces no damage mechanisms other than those found in isothermal behavior. Under these assumed conditions, the TMF life should be obtained uniquely from known isothermal behavior. The ramifications of making more complex assumptions will be dealt with in future studies. Although analyses are only in their early stages, considerable insight has been gained in understanding the characteristics of several existing high-temperature life-prediction methods. The present work indicates that the most viable damage parameter is based on the inelastic strainrange.

Halford, Gary R.; Saltsman, James F.

1987-01-01

218

Calculation of thermomechanical fatigue life based on isothermal behavior  

NASA Technical Reports Server (NTRS)

The isothermal and thermomechanical fatigue (TMF) crack initiation response of a hypothetical material was analyzed. Expected thermomechanical behavior was evaluated numerically based on simple, isothermal, cyclic stress-strain-time characteristics and on strainrange versus cyclic life relations that have been assigned to the material. The attempt was made to establish basic minimum requirements for the development of a physically accurate TMF life-prediction model. A worthy method must be able to deal with the simplest of conditions: that is, those for which thermal cycling, per se, introduces no damage mechanisms other than those found in isothermal behavior. Under these assumed conditions, the TMF life should be obtained uniquely from known isothermal behavior. The ramifications of making more complex assumptions will be dealt with in future studies. Although analyses are only in their early stages, considerable insight has been gained in understanding the characteristics of several existing high-temperature life-prediction methods. The present work indicates that the most viable damage parameter is based on the inelastic strainrange.

Halford, G. R.; Saltsman, J. F.

1987-01-01

219

The fatigue life prediction of aluminium alloy using genetic algorithm and neural network  

NASA Astrophysics Data System (ADS)

The behavior of the fatigue life of the industrial materials is very important. In many cases, the material with experiencing fatigue life cannot be avoided, however, there are many ways to control their behavior. Many investigations of the fatigue life phenomena of alloys have been done, but it is high cost and times consuming computation. This paper report the modeling and simulation approaches to predict the fatigue life behavior of Aluminum Alloys and resolves some problems of computation. First, the simulation using genetic algorithm was utilized to optimize the load to obtain the stress values. These results can be used to provide N-cycle fatigue life of the material. Furthermore, the experimental data was applied as input data in the neural network learning, while the samples data were applied for testing of the training data. Finally, the multilayer perceptron algorithm is applied to predict whether the given data sets in accordance with the fatigue life of the alloy. To achieve rapid convergence, the Levenberg-Marquardt algorithm was also employed. The simulations results shows that the fatigue behaviors of aluminum under pressure can be predicted. In addition, implementation of neural networks successfully identified a model for material fatigue life.

Susmikanti, Mike

2013-09-01

220

Heat-Aging Effects on the Material Properties and Fatigue Life Prediction of Vulcanized Natural Rubber  

NASA Astrophysics Data System (ADS)

The fatigue analysis and lifetime evaluation are very important in design procedure to assure the safety and reliability of the rubber components. Heat-aging process affects not only the material properties but also the fatigue life of vulcanized natural rubber. In this paper, the heat-aging effects on the material properties and fatigue life prediction of natural rubber were experimentally investigated. The stress-strain curves were obtained from the results of tensile test. The rubber specimens were heat-aged in an oven at the temperature ranging from 50°C to 100°C for a period ranging from 1 day to 90 days. Fatigue life prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Fatigue life tests were performed using the 3-dimensional dumbbell specimen, which were aged in different amounts. The Green-Lagrange strain at the critical location determined from the finite element method used for evaluating the fatigue damage parameter. Fatigue life prediction equation effectively represented by a single function using the Green-Lagrange strain.

Woo, Chang Su; Kim, Wan Doo

221

Finite Element Based Fatigue Life Prediction of a New Free Piston Engine Mounting  

NASA Astrophysics Data System (ADS)

This study presents the finite element based fatigue life prediction of a new free piston linear generator engine mounting. The objective of this research is to assess the critical fatigue locations on the component due to loading conditions. The effects of mean stress and probabilistic nature on the fatigue life are also investigated. Materials SAE 1045-450-QT and SAE 1045-595-QT are considered in this study. The finite element modeling and analysis was performed using computer-aided design and finite element analysis codes. In addition, the fatigue life prediction was carried out utilizing the finite element based fatigue code. Total-life approach and crack initiation approach were applied to predict the fatigue life of the free piston linear engine mounting. The results show the contour plots of fatigue life and damage histogram at the most damaging case. The comparison between the total-life approach and crack initiation approach were investigated. From the results, it can be concluded that Morrow mean stress correction method gives the most conservative (less life) results for crack initiation method. It can be seen that SAE 1045-595-QT material gives consistently higher life than SAE 1045-450-QT material for all loading conditions for both methods.

Rahman, M. M.; Ariffin, A. K.; Jamaludin, N.; Abdullah, S.; Noor, M. M.

222

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

223

Tensile and bending thermo-mechanical fatigue testing on cylindrical and flat specimens of CMSX-4 for design of turbine blades  

Microsoft Academic Search

This paper briefly describes thermo-mechanical fatigue tests performed on cylindrical and flat specimens of the single crystal material CMSX-4 in ?001?, ?011? and ?111?-orientation. The test matrix was defined based on the thermo-mechanical loading identified at different positions of actual turbine rotor blades. It included tensile strain-controlled TMF-test conditions on the cylindrical plain specimens and tensile load-controlled TMF-test conditions on

J. Xu; S. Reuter; W. Rothkegel

2008-01-01

224

Procedure and results of the investigation of full-scale lock joints of blades of compressors of gas-turbine engines for fretting fatigue  

Microsoft Academic Search

We analyze the experimental procedures aimed at testing specimens which simulate contact pairs and full-scale lock joints\\u000a of blades of compressors of gas-turbine engines with grooved disks for fretting fatigue. The experimental results corroborate\\u000a the efficiency of these procedures and enable one to choose coatings and procedures of treatment of contacting surfaces which\\u000a guarantee the attainment of higher values of

G. V. Tsybanev; Yu. S. Nalimov; O. N. Gerasimchuk

1997-01-01

225

Development of a Composite Delamination Fatigue Life Prediction Methodology  

NASA Technical Reports Server (NTRS)

Delamination is one of the most significant and unique failure modes in composite structures. Because of a lack of understanding of the consequences of delamination and the inability to predict delamination onset and growth, many composite parts are unnecessarily rejected upon inspection, both immediately after manufacture and while in service. NASA Langley is leading the efforts in the U.S. to develop a fatigue life prediction methodology for composite delamination using fracture mechanics. Research being performed to this end will be reviewed. Emphasis will be placed on the development of test standards for delamination characterization, incorporation of approaches for modeling delamination in commercial finite element codes, and efforts to mature the technology for use in design handbooks and certification documents.

OBrien, Thomas K.

2009-01-01

226

Effect of lubricant extreme pressure additives on rolling element fatigue life  

NASA Technical Reports Server (NTRS)

The effects of surface active additives on rolling-element fatigue life were investigated with the five-ball fatigue tester at conditions where classical subsurface initiated rolling-element fatigue is the sole mode of failure. Test balls of AISI 52100, AISI M-50, and AISI 1018 were run with an acid-treated white oil containing either 2.5 percent sulfurized terpene, 1 percent didodecyl phosphite, or 5 percent chlorinated wax. In general, it was found that the influence of surface active additives was detrimental to rolling-element fatigue life. The chlorinated-wax additive significantly reduced fatigue life by a factor of 7. The base oil with the 2.5 percent sulfurized-terpene additive can reduce fatigue life by as much as 50 percent. No statistical change in fatigue life occurred with the base oil having the 1 percent didodecyl-phosphite additive. The additives used with the base oil did not change the ranking of the bearing steels where rolling-element fatigue life was of subsurface origin.

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

1973-01-01

227

Evaluation of Creep-Fatigue Life by Fraction of Cavity Area  

NASA Astrophysics Data System (ADS)

The components of power plant such as main steam pipe and gas turbines are operated under static and cyclic load conditions. As the period of static load increases, the service life of these components decreases. Generally, the increase of cyclic load results in fatigue damage and the increase of static load period results in the metallurgical degradation by the effect of creep. Under the creep-fatigue interaction, cavities cause rapid degradation of material and decreases the creep-fatigue life of high temperature components. In this paper, creep-fatigue tests were performed to investigate the relationship between the cavity and creep-fatigue life under various tensile hold times. Test materials were HAZ and base metal of P122 (12Cr-2W) alloy weldment. The effect of hold times on the cavity damage was examined and the fraction of cavity area was analyzed. From the linear relationship of Fca (fraction of cavity area) and experimental life, a new parameter for life evaluation, Fca, was introduced and the creep-fatigue life was predicted by Fca. Good agreement was found between experimental and predicted life. Under the same hold time condition, the Fca of HAZ was greater than that of base metal while the creep-fatigue life of HAZ was shorter than that of base metal.

Kim, Bumjoon; Lim, Byeongsoo

228

High cycle fatigue life of 70 series engine cast aluminum rotor housing. Final report on task 2. 1. 6 extended life studies  

Microsoft Academic Search

Fatigue studies conducted to project the expected life and safety factors of the rotor housing of cast aluminum 2013R natural gas fueled rotary engines (NGREs) are documented. The rotor housing was selected because previous studies showed this major engine component to be the critical item in determining fatigue life. The report describes the sequential steps required for fatigue life calculations,

Bazaz

1988-01-01

229

Multiaxial fatigue life prediction for a natural rubber  

Microsoft Academic Search

This study deals with the fatigue crack initiation under multiaxial non-proportional loadings in a natural rubber. Push–pull, torsion and tension-compression with a superimposed static torsion fatigue test results are presented. A short presentation of some important features concerning short fatigue crack growth is given. Two fatigue crack criteria are proposed, the first one based on the first and second invariant

N. Saintier; G. Cailletaud; R. Piques

2006-01-01

230

Evaluation of Pressurization Fatigue Life of 1441 Al-li Fuselage Panel  

NASA Technical Reports Server (NTRS)

A study was conducted to evaluate the pressurization fatigue life of fuselage panels with skins fabricated from 1441 Al-Li, an attractive new Russian alloy. The study indicated that 1441 Al-Li has several advantages over conventional aluminum fuselage skin alloy with respect to fatigue behavior. Smooth 1441 Al-Li sheet specimens exhibited a fatigue endurance limit similar to that for 1163 Al (Russian version of 2024 Al) sheet. Notched 1441 Al-Li sheet specimens exhibited greater fatigue strength and longer fatigue life than 1163 Al. In addition, Tu-204 fuselage panels fabricated by Tupolev Design Bureau using Al-Li skin and ring frames with riveted 7000-series aluminum stiffeners had longer pressurization fatigue lives than did panels constructed from conventional aluminum alloys. Taking into account the lower density of this alloy, the results suggest that 1441 Al-Li has the potential to improve fuselage performance while decreasing structural weight.

Bird, R. Keith; Dicus, Dennis I.; Fridlyander, Joseph; Davydov, Valentin

1999-01-01

231

Probabilistic fatigue life prediction using ultrasonic inspection data considering equivalent initial flaw size uncertainty  

NASA Astrophysics Data System (ADS)

This study presents a systematical method for probabilistic fatigue life prediction using ultrasonic inspection data. A probabilistic model to correlate the ultrasonic inspection reported size and the actual size is proposed based on historical data of rotor flaw sizing. Both of the reported size and the actual size are quantified in terms of the equivalent reflector diameter. The equivalent initial flaw size (EIFS) is then calculated based on the actual size for fatigue propagation analysis. All major uncertainties, such as EIFS uncertainty, fatigue crack growth model parameter uncertainty, and experimental data measurement uncertainty are explicitly included in the fatigue life prediction. Bayesian parameter estimation is used to estimate fatigue crack growth model parameters and measurement uncertainties using a limited number of fatigue testing data points. The overall procedure is demonstrated using a Cr-Mo-V rotor segment with ultrasonic inspection data. Interpretations of the probabilistic prediction results are given.

Guan, X.; Zhang, J.; Kadau, K.; Zhou, S. K.

2013-01-01

232

Cumulative Damage Models and Multi-Stress Fatigue Life Prediction  

Microsoft Academic Search

Cumulative damage during fatigue is studied analytically. Extensive reviews are per formed on the published damage models. Three different cumulative damage models are defined using several physical variables such as fatigue modulus and resultant strain. Proposed model I is defined using fatigue modulus, while models II and III are defined using resultant strains. Proposed models are derived as functions of

W. Hwang; K. S. Han

1986-01-01

233

Effects of strain rate change on fatigue life of carbon steel in high temperature water  

SciTech Connect

Strain controlled fatigue tests of carbon steels in oxygenated high temperature water were carried out with various wave shapes of strain, e.g. triangle, slow/fast saw tooth, fast/slow saw tooth, stepwise changed and continuously changed sine waves. The effects of strain rate change on environmental fatigue life were investigated, showing basic conceptual data to evaluate the fatigue damage under the condition of transient strain change of actual plant components.

Higuchi, Makoto [Ishikawajima-Harima Heavy Industries, Yokohama (Japan); Iida, Kunihiro [Shibaura Inst. of Technology, Tokyo (Japan). Dept. of Mechanical Engineering; Asada, Yasuhide [Univ. of Tokyo (Japan). Dept. of Mechanical Engineering

1995-12-31

234

Effect of carbide distribution on rolling-element fatigue life of AMS 5749  

NASA Technical Reports Server (NTRS)

Endurance tests with ball bearings made of corrosion resistant bearing steel which resulted in fatigue lives much lower than were predicted are discussed. Metallurgical analysis revealed an undesirable carbide distribution in the races. It was shown in accelerated fatigue tests in the RC rig that large, banded carbides can reduce rolling element fatigue life by a factor of approximately four. The early spalling failures on the bearing raceways are attributed to the large carbide size and banded distribution.

Parker, R. J.; Bamberger, E. N.

1983-01-01

235

Fatigue Life of Titanium Alloys Fabricated by Additive Layer Manufacturing Techniques for Dental Implants  

NASA Astrophysics Data System (ADS)

Additive layer deposition techniques such as electron beam melting (EBM) and laser beam melting (LBM) have been utilized to fabricate rectangular plates of Ti-6Al-4V with extra low interstitial (ELI) contents. The layer-by-layer deposition techniques resulted in plates that have different surface finishes which can impact significantly on the fatigue life by providing potential sites for fatigue cracks to initiate. The fatigue life of Ti-6Al-4V ELI alloys fabricated by EBM and LBM deposition techniques was investigated by three-point testing of rectangular beams of as-fabricated and electro-discharge machined surfaces under stress-controlled conditions at 10 Hz until complete fracture. Fatigue life tests were also performed on rolled plates of Ti-6Al-4V ELI, regular Ti-6Al-4V, and CP Ti as controls. Fatigue surfaces were characterized by scanning electron microscopy to identify the crack initiation site in the various types of specimen surfaces. The fatigue life data were analyzed statistically using both analysis of variance techniques and the Kaplan-Meier survival analysis method with the Gehan-Breslow test. The results indicate that the LBM Ti-6Al-4V ELI material exhibits a longer fatigue life than the EBM counterpart and CP Ti, but a shorter fatigue life compared to rolled Ti-6Al-4V ELI. The difference in the fatigue life behavior may be largely attributed to the presence of rough surface features that act as fatigue crack initiation sites in the EBM material.

Chan, Kwai S.; Koike, Marie; Mason, Robert L.; Okabe, Toru

2013-02-01

236

Subjective quality of life in patients with chronic fatigue syndrome.  

PubMed

The aim of this study was to (1) assess Subjective Quality of Life (SQOL) of patients with Chronic Fatigue Syndrome (CFS) using a generic concept and to compare the findings with those in groups with mental disorders and healthy subjects, and (2) investigate whether and, if so, to what extent socio-demographic and clinical variables predict SQOL in CFS patients. Seventy-three patients diagnosed with CFS were randomly selected and interviewed from two specialised clinics. CFS was diagnosed using the Oxford Criteria. SQOL was assessed on the Manchester Short Assessment of Quality of Life (MANSA) and Health-Related Quality of Life (HRQOL) on the Medical Outcome Study Short-Form 36 (MOS) SF-36. A battery of mood and symptom questionnaires, including the Symptom Checklist Questionnaire (SCL-90-R), was administered to assess various aspects of symptomatology as potential predictor variables. Multiple regression analyses were conducted to identify predictors of SQOL. Overall, SQOL was low in CFS patients and less favourable than in groups with mental disorders and healthy subjects. Satisfaction was particularly low with life as a whole, leisure activities and financial situation. Whilst SQOL was only moderately correlated with HRQOL, the SCL-90-R score, especially SCL-90-R Depression scale score, was the best predictor of SQOL explaining 35% of the variance. HRQOL and generic SQOL appear distinct despite some overlap. The findings underline that SQOL is significantly disrupted in CFS patients. Depressive symptoms are statistically the strongest 'predictor' of SQOL, although the direction of the relationship is not established. These data suggest that treatment of depression associated with CFS, regardless of causation, could help to improve SQOL in CFS patients. PMID:15789937

Rakib, A; White, P D; Pinching, A J; Hedge, B; Newbery, N; Fakhoury, W K; Priebe, S

2005-02-01

237

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

PubMed

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

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

2014-01-01

238

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

PubMed Central

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

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

2014-01-01

239

Fatigue life of dovetail joints - Verification of a simple biaxial model  

SciTech Connect

A biaxial fatigue specimen, designed to model the state of stress of the blade to disk joint in a typical gas turbine, has been analyzed and tested. The method of analysis was shown to predict the location of the worst damage and of crack initiation. This paper describes the analysis and testing of a simplified model that may be used in preference to the previous one. 5 refs.

He, M.J.; Ruiz, C. (Nanjing Aeronautical Institute (People's Republic of China); Oxford Univ. (England))

1989-06-01

240

Effects of blade bending on aerodynamic control of fluctuating loads on teetered HAWT rotors  

Microsoft Academic Search

Active aerodynamic control, in the form of closed-loop actuation of blade-tip ailerons or all-movable blades, is investigated as a means of increasing the structural fatigue life of HAWT rotors. The rotor considered is upwind and teetered, with two blades of diameter 29.2 m., fiberglass construction and other properties representative of modern light-weight construction. The paper begins with a review of

A. J. Jr. Eggers; H. Ashley; S. M. Rock; K. Chaney; R. Digumarthi

1996-01-01

241

Application of a new model proposal for fatigue life prediction on notches and key-seats  

Microsoft Academic Search

The aim of this paper is to introduce a new macro-mechanical model for fatigue life prediction, taking into consideration an elastic–plastic stress distribution and the stress gradient evolution. Mainly based on the stress field intensity approach, this new model tries to better take into account the role of the most important factors influencing the fatigue failure process. A very brief

G. Qylafku; Z. Azari; N. Kadi; M. Gjonaj; G. Pluvinage

1999-01-01

242

FATIGUE PERFORMANCE COMPARISON AND LIFE PREDICTION OF FORGED STEEL AND DUCTILE CAST IRON CRANKSHAFTS  

E-print Network

1 FATIGUE PERFORMANCE COMPARISON AND LIFE PREDICTION OF FORGED STEEL AND DUCTILE CAST IRON. The crankshafts used in the study were forged steel and ductile cast iron from a one-cylinder gasoline engine fatigue strength than the ductile cast iron, while component tests showed that the forged steel crankshaft

Fatemi, Ali

243

Prediction of the Fatigue Life of Cast Steel Containing Shrinkage Porosity  

E-print Network

(FEA) software to determine the complex stress field resulting from the porosity. In the stress model is developed to reduce the dependence of the fatigue life predictions on the numerical mesh chosen the fatigue lives of the specimens vary by more than four orders of magnitude for the same nominal stress

Beckermann, Christoph

244

Fatigue life retro estimation of wing structure under different load spectra  

Microsoft Academic Search

The macro and micro fatigue cracking characteristics of actual wing structures under two load spectra were observed. It was found that the macro and micro fracture characteristics of the failed structures were the reflection of stress changes in load spectrum and that the fatigue life of the structures could be retro estimated by fractography. The crack propagation lives for several

Weifang Zhang; Yunju Li; Gaoyuan Liu; Aiguo Zhao; Chunhu Tao

2004-01-01

245

ElastoPlastic Fatigue Life Improvement of Bolted Joints and Introducing FBI Method  

Microsoft Academic Search

The failures of bolted joints, which are the basic and popular fasteners in industry, are mostly due to fatigue. This paper presents an effective method to improve the elasto-plastic fatigue life of a bolt. A complete bolted joint is considered and modeled with the finite element approach to calculate stress and strain. The code based on crack initiation theory is

Peyman Honarmandi; Jean W. Zu; Kamran Behdinan

2005-01-01

246

Life extension of self-healing polymers with rapidly growing fatigue cracks  

E-print Network

periods, effectively training the self-healing polymeric material to achieve higher endurance limits. Keywords: autonomic materials; self-healing polymers; fatigue 1. INTRODUCTION Fatigue and the associated complete arrest of crack growth (infinite life). The materials system consists of a self-healing polymer

Sottos, Nancy R.

247

Acoustic fatigue life prediction for nonlinear structures with multiple resonant modes  

NASA Technical Reports Server (NTRS)

This report documents an effort to develop practical and accurate methods for estimating the fatigue lives of complex aerospace structures subjected to intense random excitations. The emphasis of the current program is to construct analytical schemes for performing fatigue life estimates for structures that exhibit nonlinear vibration behavior and that have numerous resonant modes contributing to the response.

Miles, R. N.

1992-01-01

248

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

Microsoft Academic Search

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

Paul S. Prevéy; Ravi A. Ravindranath; Michael Shepard; Timothy Gabb

2006-01-01

249

Analysis of the fatigue life of riveted sheet metal helicopter airframe joints  

Microsoft Academic Search

This paper provides a brief review of a literature search on fatigue life of riveted airframe sheet metal joints and then a description of a test and analysis program conducted for common riveted joints used in rotorcraft airframe structures. Many papers dealing with fatigue test and analysis of fastened sheet metal have been published. These papers reveal a wide range

M. R Urban

2003-01-01

250

A micro-mechanically based continuum damage model for fatigue life prediction of filled rubbers  

E-print Network

during high cycle fatigue test is a very hard task because multi-physics and multi-scale effectsA micro-mechanically based continuum damage model for fatigue life prediction of filled rubbers J: decohesion between fillers and matrix at a micro-scale followed by a crack nucleation at a macro

Paris-Sud XI, Université de

251

Accumulative fatigue life expenditure of turbine/generator shafts following worst-case system disturbances  

SciTech Connect

The paper reviews phenomena which influence accumulative fatigue life expenditure of turbine/generator exciter shafts following severe disturbances on the electrical supply. Fatigue models for estimating cumulative fatigue of Machine shafts are discussed. The importance of allowing for mean stress and of simulating steam and electrical damping is examined for both worst-case 3-phase fault clearance and bad synchronising. The effect of auto-reclosure on fatigue life expenditure of shafts is also considered. The effect of variation of stress concentration factor (or shaft diameter) on cumulative fatigue is illustrated as is the effectiveness of torque limiting shearing couplings in protecting shaft systems from damage following a severe switching event. The effect of machine disconnection following a severe electrical disturbance is examined. Shaft torsional monitors for estimating fatigue life expenditure of shafts are also discussed. It is concluded that fatigue life expenditure at shaft couplings following worst-case 3-phase fault clearance may be up to double that corresponding to worst-case synchronising although peak shaft torques are only marginally higher. Cumulative fatigue will quite often be higher at couplings along the shaft than at the turbine/generator coupling on account of electrical damping although peak torque is generally highest at the turbine/generator coupling and reduces progressively along the turbine shaft.

Hammons, T.J.

1982-07-01

252

A numerical method for predicting the bending fatigue life of NiTi and stainless steel root canal  

E-print Network

A numerical method for predicting the bending fatigue life of NiTi and stainless steel root canal. A numerical method for predicting the bending fatigue life of NiTi and stainless steel root canal instruments of endodontic files. Keywords: bending fatigue, finite element analysis, nickel­titanium, root canal instruments

Zheng, Yufeng

253

Predictive analysis of metal fatigue in the high cyclic life range  

NASA Technical Reports Server (NTRS)

This report summarizes various aspects of predictive approaches in high cycle fatigue, hcf. The distinction between hcf and low cycle fatigue, lcf, is discussed in relation to the transition life and strainrange, and curves are presented to establish regions wherein each range predominates depending on the properties of any material of interest. The role of loading order on hcf in cumulative damage analysis is also discussed, together with mean stress effects and their relaxation. Also briefly discussed are high temperature fatigue and ultra-high cycle fatigue.

Manson, S. S.

1979-01-01

254

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

255

Study of the Fatigue Life of Steel Catenary Risers in Interaction with the Seabed  

E-print Network

1.2.2. Limit States .......................................................................................... 4 1.3.?Fatigue Life of SCR ...................................................................................... 4 1.4.?Riser... .................................................................................................. 11 2.2. Equation of Motion ...................................................................................... 11 2.3. Numerical Implementation .......................................................................... 17 2...

Nakhaee, Ali

2011-02-22

256

Childhood Adversity and Cumulative Life Stress: Risk Factors for Cancer-Related Fatigue  

PubMed Central

Fatigue is a common symptom in healthy and clinical populations, including cancer survivors. However, risk factors for cancer-related fatigue have not been identified. On the basis of research linking stress with other fatigue-related disorders, we tested the hypothesis that stress exposure during childhood and throughout the life span would be associated with fatigue in breast cancer survivors. Stress exposure was assessed using the Stress and Adversity Inventory, a novel computer-based instrument that assesses for 96 types of acute and chronic stressors that may affect health. Results showed that breast cancer survivors with persistent fatigue reported significantly higher levels of cumulative lifetime stress exposure, including more stressful experiences in childhood and in adulthood, compared to a control group of nonfatigued survivors. These findings identify a novel risk factor for fatigue in the growing population of cancer survivors and suggest targets for treatment. PMID:24377083

Bower, Julienne E.; Crosswell, Alexandra D.; Slavich, George M.

2013-01-01

257

Childhood Adversity and Cumulative Life Stress: Risk Factors for Cancer-Related Fatigue.  

PubMed

Fatigue is a common symptom in healthy and clinical populations, including cancer survivors. However, risk factors for cancer-related fatigue have not been identified. On the basis of research linking stress with other fatigue-related disorders, we tested the hypothesis that stress exposure during childhood and throughout the life span would be associated with fatigue in breast cancer survivors. Stress exposure was assessed using the Stress and Adversity Inventory, a novel computer-based instrument that assesses for 96 types of acute and chronic stressors that may affect health. Results showed that breast cancer survivors with persistent fatigue reported significantly higher levels of cumulative lifetime stress exposure, including more stressful experiences in childhood and in adulthood, compared to a control group of nonfatigued survivors. These findings identify a novel risk factor for fatigue in the growing population of cancer survivors and suggest targets for treatment. PMID:24377083

Bower, Julienne E; Crosswell, Alexandra D; Slavich, George M

2014-01-01

258

Residual stress evaluation and fatigue life prediction in the welded joint by x-ray diffraction  

NASA Astrophysics Data System (ADS)

In the fossil power plant, the reliability of the components which consist of the many welded parts depends on the quality of welding. The residual stress is occurred by the heat flux of high temperature during weld process. This decreases the mechanical properties as the strength of fatigue and fracture. The residual stress of the welded part in the recently constructed power plants has been the cause of a variety of accidents. The objective of this study is measurement of the residual stress and the full width at half maximum intensity (FWHM) by X-ray diffraction method and to estimate the feasibility of this application for fatigue life assessment of the high-temperature pipeline. The materials used for the study is P92 steel for the use of high temperature pipe on super critical condition. The test results were analyzed by the distributed characteristics of residual stresses and FWHM in x-ray diffraction intensity curve. Also, X-ray diffraction tests using specimens simulated low cycle fatigue damage were performed in order to analyze fatigue properties when fatigue damage conditions become various stages. As a result of X-ray diffraction tests for specimens simulated fatigue damages, we conformed that the ratio of the FWHM due to fatigue damage has linear relationship with fatigue life ratio algebraically. From this relationship, it was suggested that direct expectation of the life consumption rate was feasible.

Yoo, Keun Bong; Hwang, Kwon Tae; Chang, Jung Chel; Kim, Jae Hoon

2009-07-01

259

Joint design for improved fatigue life of diffusion-bonded box-stiffened panels  

NASA Technical Reports Server (NTRS)

Simple photoelastic models were used to identify a cross-section geometry that would eliminate the severe stress concentrations at the bond line between box stiffeners diffusion bonded to a panel skin. Experimental fatigue-test data from titanium test specimens quantified the allowable stress in terms of cycle life for various joint geometries. It is shown that the effect of stress concentration is reduced and an acceptable fatigue life is achieved.

Davis, R. C.; Moses, P. L.; Kanenko, R. S.

1985-01-01

260

Fatigue Life Analysis of Tapered Hybrid Composite Flexbeams  

NASA Technical Reports Server (NTRS)

Nonlinear-tapered flexbeam laminates from a full-size composite helicopter rotor hub flexbeam were tested under combined constant axial tension and cyclic bending loads. The two different graphite/glass hybrid configurations tested under cyclic loading failed by delamination in the tapered region. A 2-D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. The analysis results from two geometrically nonlinear finite element codes, ANSYS and ABAQUS, are presented and compared. Strain energy release rates (G) obtained from the above codes using the virtual crack closure technique (VCCT) at a resin crack location in the flexbeams are presented for both hybrid material types. These results compare well with each other and suggest that the initial delamination growth from the resin crack toward the thick region of the flexbeam is strongly mode II. The peak calculated G values were used with material characterization data to calculate fatigue life curves and compared with test data. A curve relating maximum surface strain to number of loading cycles at delamination onset compared reasonably well with the test results.

Murri, Gretchen B.; Schaff, Jeffery R.; Dobyns, Alan L.

2002-01-01

261

Fatigue Life Methodology for Tapered Hybrid Composite Flexbeams  

NASA Technical Reports Server (NTRS)

Nonlinear-tapered flexbeam specimens from a full-size composite helicopter rotor hub flexbeam were tested under combined constant axial tension and cyclic bending loads. Two different graphite/glass hybrid configurations tested under cyclic loading failed by delamination in the tapered region. A 2-D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. The analysis results from two geometrically nonlinear finite element codes, ANSYS and ABAQUS, are presented and compared. Strain energy release rates (G) associated with simulated delamination growth in the flexbeams are presented from both codes. These results compare well with each other and suggest that the initial delamination growth from the tip of the ply-drop toward the thick region of the flexbeam is strongly mode II. The peak calculated G values were used with material characterization data to calculate fatigue life curves for comparison with test data. A curve relating maximum surface strain to number of loading cycles at delamination onset compared well with the test results.

urri, Gretchen B.; Schaff, Jeffery R.

2006-01-01

262

Probability approach for prediction of corrosion and corrosion fatigue life  

SciTech Connect

A probability approach for life prediction is developed and illustrated through a simplified model for the pitting corrosion and corrosion fatigue crack growth in aluminum alloys in aqueous environments. A method for estimation of the cumulative distribution function (CDF) for the lifetime is demonstrated by using an assumed CDF for each key random variable (RV). The basic aim of this approach is to make predictions for the lifetime, reliability, and durability beyond the range of typical data by integrating the CDFs of the individual RVs into a mechanistically based model. The contribution of each key RV is considered, and its significance is assessed. Thus, the usefulness of probability-based modeling is demonstrated. It is noted that physically realistic parameters were assumed for the illustrations. As such, the results from analysis of the model qualitatively agree quite well with experimental observations. However, these results should not be construed to represent behavior in actual systems. Because of these assumptions, confidence levels for the predictions are not addressed. 9 refs.

Harlow, D.G.; Wei, R.P. [Lehigh Univ., Bethlehem, PA (United States)

1994-10-01

263

Fatigue in children with juvenile idiopathic arthritis: reliability of the "Pediatric Quality of Life Inventory-Multidimensional Fatigue Scale".  

PubMed

The aim of the study was (1) to translate the "Pediatric Quality of Life Inventory-Multidimensional Fatigue Scale" (PedsQL-Fatigue) into Brazilian Portuguese language and culture and evaluate its reliability and (2) to measure fatigue among patients with juvenile idiopathic arthritis (JIA): (1) Translation of the PedsQL-Fatigue by two bilingual researchers; (2) Backtranslation into English assessed by the authors of the original version; (3) Pilot study with five patients followed in the Pediatric Rheumatology Outpatient Clinic and their parents; and (4) Field study and assessment of measurement properties (internal consistency, reproducibility, and construct validity). In this stage, the scale was administered to 67 patients with JIA and 63 healthy individuals, aged from 2 to 18 years old, matched by age (from 2 to 4, 5 to 7, 8 to 12, and from 13 to 18 years old). Cronbach's alpha coefficient ranged from 0.6 to 0.8 for children and parents, indicating the instrument's good internal consistency. The scale's construct validity was confirmed by a satisfactory Spearman's coefficient between the PedsQL-Fatigue and the generic PedsQL 4.0 (0.840 for the children and 0.742 for the parents). Reproducibility was also adequate (0.764 for the children and 0.938 for the parents). No differences were found between the scores obtained by the JIA group and control group, though lower scores were observed among patients with clinically active JIA when compared to those without clinical activity. The PedsQL-Fatigue is a valid and reliable tool, and that can be used to measure fatigue among patients with JIA. PMID:24941921

Paulo, Luciana Tudech S P; Len, Claudio A; Hilario, Maria Odete E; Pedroso, Soraya A; Vitalle, Maria Sylvia S; Terreri, Maria Teresa

2015-01-01

264

Continuum damage mechanics modeling for fatigue life of elastomeric materials  

Microsoft Academic Search

Purpose – The purpose of this paper is to investigate the fatigue behavior of rubber using dumb-bell test specimens under uniaxial loading. Design\\/methodology\\/approach – The material used is a vulcanized natural rubber with a formulation typical for engine mounts and an international rubber hardness degree of 60. Fatigue tests are conducted under the displacement controlled condition with a sine waveform

Aidy Ali; Maryam Hosseini; Barkawi Sahari

2010-01-01

265

Ductility normalized-strainrange partitioning life relations for creep-fatigue life predictions  

NASA Technical Reports Server (NTRS)

Procedures based on Strainrange Partitioning (SRP) are presented for estimating the effects of environment and other influences on the high temperature, low cycle, creep fatigue resistance of alloys. It is proposed that the plastic and creep, ductilities determined from conventional tensile and creep rupture tests conducted in the environment of interest be used in a set of ductility normalized equations for making a first order approximation of the four SRP inelastic strainrange life relations. Different levels of sophistication in the application of the procedures are presented by means of illustrative examples with several high temperature alloys. Predictions of cyclic lives generally agree with observed lives within factors of three.

Halford, G. R.; Saltsman, J. F.; Hirschberg, M. H.

1977-01-01

266

Thermal-barrier-coated turbine blade study  

NASA Technical Reports Server (NTRS)

The effects of coating TBC on a CF6-50 stage 2 high-pressure turbine blade were analyzed with respect to changes in the mean bulk temperature, cooling air requirements, and high-cycle fatigue. Localized spallation was found to have a possible deleterious effect on low-cycle fatigue life. New blade design concepts were developed to take optimum advantage of TBCs. Process and material development work and rig evaluations were undertaken which identified the most promising combination as ZrO2 containing 8 w/o Y2O3 applied by air plasma spray onto a Ni22Cr-10Al-1Y bond layer. The bond layer was applied by a low-pressure, high-velocity plasma spray process onto the base alloy. During the initial startup cycles the blades experienced localized leading edge spallation caused by foreign objects.

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

1981-01-01

267

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

NASA Technical Reports Server (NTRS)

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

Everett, Richard A., Jr.

2004-01-01

268

Multiaxial Fatigue Life Prediction for Steels Based on Some Simple Approximations  

NASA Astrophysics Data System (ADS)

The Roessle-Fatemi's hardness method (HM) and Muralidharan-Manson's modified universal slopes method (MUSM) were employed to determine the uniaxial fatigue properties of steels from easily obtained tensile properties. Both methods give good life predictions, while the Roessle-Fatemi's HM is somewhat better. Furthermore, for predicting multiaxial fatigue lives of steels in the absence of any fatigue data, the Li's modified Wang-Brown model (MWB) was used in combination with the HM method (MWB-HM) as well as the MUSM method (MWB-MUSM), respectively. Correlation between the yield strength and the Brinell hardness was also developed to estimate the multiaxial fatigue lives of steels based only on hardness and elasticity modulus. It is shown that multiaxial fatigue lives were predicted fairly well by all the methods, and the MWB-MUSM method is slightly more accurate. In addition, a computer-based procedure for multiaxial fatigue life assessment incorporating MWB-MUSM approach was proposed and implemented to predict the fatigue life of an intermediate compressor casing. The predicted results are promising.

Li, Jing; Yao, Zhi-feng; Zhang, Zhong-ping

2015-01-01

269

Empirical modeling of environment-enhanced fatigue crack propagation in structural alloys for component life prediction  

NASA Technical Reports Server (NTRS)

This research aims to develop the methods and understanding needed to incorporate time and loading variable dependent environmental effects on fatigue crack propagation (FCP) into computerized fatigue life prediction codes such as NASA FLAGRO (NASGRO). In particular, the effect of loading frequency on FCP rates in alpha + beta titanium alloys exposed to an aqueous chloride solution is investigated. The approach couples empirical modeling of environmental FCP with corrosion fatigue experiments. Three different computer models have been developed and incorporated in the DOS executable program. UVAFAS. A multiple power law model is available, and can fit a set of fatigue data to a multiple power law equation. A model has also been developed which implements the Wei and Landes linear superposition model, as well as an interpolative model which can be utilized to interpolate trends in fatigue behavior based on changes in loading characteristics (stress ratio, frequency, and hold times).

Richey, Edward, III

1995-01-01

270

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

PubMed

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

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

2011-07-01

271

Application of an Energy-Based Life Prediction Model to Bithermal and Thermomechanical Fatigue  

NASA Technical Reports Server (NTRS)

The inelastic hysteresis energy applied to the material in a cycle is used as the basis for predicting nonisothermal fatigue life of a wrought cobalt-base superalloy, Haynes 188, from isothermal fatigue data. Damage functions that account for hold-time effects and time-dependent environmental phenomena such as oxidation and hot corrosion are proposed in terms of the inelastic hysteresis energy per cycle. The proposed damage functions are used to predict the bithermal and thermomechanical fatigue lives of Haynes 188 between 316 and 760 C from isothermal fatigue data. Predicted fatigue lives of all but two of the nonisothermal tests are within a factor of 1.5 of the experimentally observed lives.

Radhakrishnan, V. M.; Kalluri, Sreeramesh; Halford, Gary R.

1994-01-01

272

Fatigue life scatter of aluminium alloy helicopter lugs  

Microsoft Academic Search

Fatigue tests were performed on lugs in five cases with stress ratio R=0.1 and maximum load Fmax=44 kN. However, it was found that there was a remarkable scatter of fatigue lives even in identical tests. Fractography of the fractured lugs has shown that each crack initiated at one origin, which was on the hole surface and near one side of

N. S Xi; M. L Xie; Z. L Zhang; C. H Tao

2000-01-01

273

Baseline-free estimation of residual fatigue life using a third order acoustic nonlinear parameter.  

PubMed

Prediction of crack growth and fatigue life estimation of metals using linear/nonlinear acousto-ultrasound methods is an ongoing issue. It is known that by measuring nonlinear parameters, the relative accumulated fatigue damage can be evaluated. However, there is still a need to measure two crack propagation states to assess the absolute residual fatigue life. A procedure based on the measurement of a third-order acoustic nonlinear parameter is presented to assess the residual fatigue life of a metallic component without the need of a baseline. The analytical evaluation of how the cubic nonlinear-parameter evolves during crack propagation is presented by combining the Paris law to the Nazarov-Sutin crack equation. Unlike other developed models, the proposed model assumes a crack surface topology with variable geometrical parameters. Measurements of the cubic nonlinearity parameter on AA2024-T351 specimens demonstrated high sensitivity to crack propagation and excellent agreement with the predicted theoretical behavior. The advantages of using the cubic nonlinearity parameter for fatigue cracks on metals are discussed by comparing the relevant results of a quadratic nonlinear parameter. Then the methodology to estimate crack size and residual fatigue life without the need of a baseline is presented, and advantages and limitations are discussed. PMID:21973336

Amura, Mikael; Meo, Michele; Amerini, F

2011-10-01

274

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

275

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

276

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

277

Fatigue life prediction of an intermetallic matrix composite at elevated temperatures  

NASA Technical Reports Server (NTRS)

A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the Universal Slopes method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio, number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.

Bartolotta, Paul A.

1991-01-01

278

Fatigue life prediction of an intermetallic matrix composite at elevated temperatures  

NASA Technical Reports Server (NTRS)

A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the 'Universal Slopes' method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio (Vf), number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.

Bartolotta, P. A.

1991-01-01

279

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

E-print Network

Element Analysis by Patricio Andres Lillo Gallardo B.Sc., Catholic University of Chile, 1999 M Turbine Blades Subject to Cold Weather Conditions Using Finite Element Analysis by Patricio Andres Lillo using finite element models of the blade. The work opens with a quantification of the extremes of cold

Victoria, University of

280

Fatigue life prediction of circumferentially notched component based on elastic-plastic fracture mechanics  

Microsoft Academic Search

The elastic-plastic fracture mechanics parameters for the 3D surface and circumferential cracks generated in the circumferentially grooved cylinder component were analyzed from the viewpoint of engineering. Then, fatigue life spent during crack growth was estimated for the bluntly and acutely notched cylindrical components. Consequently, it was found that the crack propagation life of the notched cylinder component was successfully predicted

K. Hatanaka; T. Fujimitsu; J. Omori

1992-01-01

281

Evaluation of the EHL Film Thickness and Extreme Pressure Additives on Gear Surface Fatigue Life  

NASA Technical Reports Server (NTRS)

Surface pitting fatigue life tests were conducted with seven lubricants, using AISI 9310 spur gears. The test lubricants can be classified as synthetic polyol-esters with various viscosities and additive packages. The lubricant with a viscosity that provided a specific film thickness greater than one and with an additive package produced gear surface fatigue lives that were 8.6 times that for lubricants with a viscosity that provided specific film thickness less than one. Lubricants with the same viscosity and similar additive packages gave equivalent gear surface fatigue lives.

Townsend, Dennis P.; Shimski, John

1994-01-01

282

Effect of viscosity on rolling-element fatigue life at cryogenic temperature with fluorinated ether lubricants  

NASA Technical Reports Server (NTRS)

Rolling-element fatigue tests were conducted with 12.7-mm-(1/2-in.-) diameter AISI 52100 steel balls in the NASA five-ball fatigue tester, with a maximum hertz stress of 5500 mN/m2 (800 000 psi), a shaft speed of 4750 rpm, lubricant temperature of 200 K (360 R), a contact angle of 20 deg, using four fluorinated ether lubricants of varying viscosities. No statistically significant differences in rolling-element fatigue life occurred using the four viscosity levels. Elastohydrodynamic calculations indicate that values of the lubricant film parameter were approximately 2 or greater.

Dietrich, M. W.; Zaretsky, E. V.

1975-01-01

283

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

NASA Technical Reports Server (NTRS)

Evaluation of hot-pressed silicon nitride as a rolling-element bearing material. Two grades of hot-pressed silicon nitride balls were tested under rolling contact conditions in a five-ball fatigue tester. A digital computer program was used to predict the dynamic performance characteristics and fatigue life of high-speed ball bearings with silicon nitride balls relative to that with bearings containing steel balls. The results obtained include the finding that fatigue spalls on silicon nitride balls are similar in appearance to those obtained with typical bearing steels.

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

1974-01-01

284

Pressure vessel fracture, fatigue, and life management: PVP-Volume 233  

SciTech Connect

This volume contains papers relating to the structural integrity assessment of pressure vessels and piping, with special emphasis on the effects of aging. The papers are organized in the following five areas: (1) pressure vessel life management; (2) fracture characterization using local and dual-parameter approaches; (3) stratification and thermal fatigue; (4) creep, fatigue, and fracture; and (5) integrated approach to integrity assessment of pressure components. Separate abstracts were prepared for 39 papers in this conference.

Bhandari, S.; Milella, P.P.; Pennell, W.E. (eds.)

1992-01-01

285

Fatigue life estimation of steel girder of Yangpu cable-stayed Bridge due to buffeting  

Microsoft Academic Search

As the main span of modern cable-stayed bridges becomes longer and longer, the buffeting-induced fatigue damage problem of steel girders located in strong wind regions may have to be taken into consideration in the design of the bridge. This paper presents a method in the mixed frequency–time domain for estimating the fatigue life of steel girders of the Yangpu cable-stayed

M. Gu; Y. L. Xu; L. Z. Chen; H. F. Xiang

1999-01-01

286

Thermomechanical fatigue behaviour and life assessment of hot work tool steels  

Microsoft Academic Search

The surface of the hot work tools is damaged under coupled non-isothermal fatigue, wear or erosion and reactive environment (oxidation or corrosion). A thermomechanical fatigue (TMF) experiment using tubular specimens is developed. Tests are carried out under out-of-phase TMF cycle with strain ratio R = -?. The behaviour, the damage and life of two tempered martensitic steels X38CrMoV5 and 55NiCrMoV7

A. Oudin; P. Lamesle; L. Penazzi; S. Le Roux; F. Rézaï-Aria

2002-01-01

287

Effect of grinding conditions on the fatigue life of titanium 5Al-2.5Sn alloy  

NASA Technical Reports Server (NTRS)

An investigation into the effect of grinding conditions on the fatigue life of titanium 5Al-2.5Sn is presented. Damage to surface integrity and changes in the residual stresses distribution are studied to assess changes in fatigue life. A surface grinding machine, operating at speeds ranging from 2000 to 6000 fpm and using SiC wheels of grit sizes 60 and 120, was used to grind flat subsize specimens of 0.1-in. thickness. After grinding, the specimens were fatigued at a chosen stress and compared with the unadulterated material. A standard profilometer, a microhardness tester, and a scanning electron microscope were utilized to examine surface characteristics and measure roughness and hardness. Increased grinding speed in both wet and dry applications tended to decrease the fatigue life of the specimens. Fatigue life increased markedly at 2000 fpm under wet conditions, but then decreased at higher speeds. Grit size had no effect on the fatigue life.

Rangaswamy, P.; Terutung, H.; Jeelani, S.

1991-01-01

288

Low cycle notched fatigue behavior and life predictions of A723 high strength steels  

SciTech Connect

Two types of ASTM A723 steels have been investigated for their low cycle fatigue behavior. Specimens were tested in four-point bending, both with and without notches, and the measured fatigue lives were compared with those predicted by Neubers notch analysis, and standard fracture mechanics life prediction techniques. Comparison of measured and predicted lives indicate that the elastic/plastic Neuber analysis under predicts the measured fatigue life by as much as 67% at large strains, and becomes a better predictor of life as the applied strains decrease. The elastic Neubers analysis also under predicts the measured fatigue lives by 45% at large applied strains, but seems to accurately predict lives at reversals to failure greater than 100. The fracture mechanics approach assumes elastic stresses at the crack tip, and predicts lives within 30% over the full range of strains investigated. The results show that the Neuber notch analysis is not as good an indicator of the low cycle fatigue behavior of A723 steels as is the fracture mechanics life prediction techniques. As the life cycles to failure decreases, the Neubers analysis predicts lives that are two to three times more conservative than those experimentally measured.

Troiano, E.; Underwood, J.H.; Crayon, D. [Army Armament Research, Development and Engineering Center, Watervliet, NY (United States). Benet Labs.

1995-12-31

289

Fatigue life estimation for different notched specimens based on the volumetric approach  

NASA Astrophysics Data System (ADS)

In this paper, the effects of notch radius for different notched specimens has been studied on the values of stress concentration factor, notch strength reduction factor, and fatigue life duration of the specimens. The material which has been selected for this investigation is Al 2024T3 . Volumetric approach has been applied to obtain the values of notch strength reduction factor and results have been compared with those obtained from the Neuber and Peterson methods. Load controlled fatigue tests of mentioned specimens have been conducted on the 250kN servo-hydraulic Zwick/Amsler fatigue testing machine with the frequency of 10Hz. The fatigue lives of the specimens have also been predicted based on the available smooth S-N curve of Al2024-T3 and also the amounts of notch strength reduction factor which have been obtained from volumetric, Neuber and Peterson methods. The values of stress and strain around the notch roots are required to predict the fatigue life of notched specimens, so Ansys finite element code has been used and non-linear analyses have been performed to obtain the stress and strain distributions around the notches. The plastic deformations of the material have been simulated using multi-linear kinematic hardening and cyclic stress-strain relation. The work here shows that the volumetric approach does a very good job for predicting the fatigue life of the notched specimens.

Zehsaz, M.; Hassanifard, S.; Esmaeili, F.

2010-06-01

290

Effect of helium on fatigue crack growth and life of reduced activation ferritic/martensitic steel  

NASA Astrophysics Data System (ADS)

The effects of helium on the fatigue life, micro-crack growth behavior up to final fatigue failure, and fracture mode under fatigue in the reduced activation ferritic/martensitic steel, F82H IEA-heat, were investigated by low cycle fatigue tests at room temperature in air at a total strain range of 0.6-1.5%. Significant reduction of the fatigue life due to helium implantation was observed for a total strain range of 1.0-1.5%, which might be attributable to an increase in the micro-crack propagation rate. However, the reduction of fatigue life due to helium implantation was not significant for a total strain range of 0.6-0.8%. A brittle fracture surface (an original point of micro-crack initiation) and a cleavage fracture surface were observed in the helium-implanted region of fracture surface. A striation pattern was observed in the non-implanted region. These fracture modes of the helium-implanted specimen were independent of the strain range.

Nogami, Shuhei; Takahashi, Manabu; Hasegawa, Akira; Yamazaki, Masanori

2013-11-01

291

Fatigue life of fine-grain Al–Mg–Sc alloys produced by equal-channel angular pressing  

Microsoft Academic Search

The effect of severe plastic deformation through equal-channel angular pressing (ECAP) on the fatigue life of Al–Mg–Sc alloys with different concentration of magnesium is discussed. Both high-cyclic and low-cyclic fatigue properties have been assessed in terms of the fatigue strength, fatigue ductility, cyclic stress–strain curves, etc. It is shown that the addition of Sc significantly increases the thermal stability of

A Vinogradov; A Washikita; K Kitagawa; V. I Kopylov

2003-01-01

292

Major Effects of Nonmetallic Inclusions on the Fatigue Life of Disk Superalloy Demonstrated  

NASA Technical Reports Server (NTRS)

The fatigue properties of modern powder metallurgy disk alloys can vary because of the different steps of materials and component processing and machining. Among these variables, the effects of nonmetallic inclusions introduced during the powder atomization and handling processes have been shown to significantly degrade low-cycle fatigue life. The levels of inclusion contamination have, therefore, been reduced to less than 1 part per million in state-of-the-art nickel disk powder-processing facilities. Yet the large quantities of compressor and turbine disks weighing from 100 to over 1000 lb have enough total volume and surface area for these rare inclusions to still be present and limit fatigue life. The objective of this study was to investigate the effects on fatigue life of these inclusions, as part of the Crack Resistant Disk Materials task within the Ultra Safe Propulsion Project. Inclusions were carefully introduced at elevated levels in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were then performed on extracted test specimens at 650 C. Analyses were performed to compare the low-cycle fatigue lives and failure initiation sites as functions of inclusion content and fatigue conditions. Powder of the nickel-base superalloy U720 was atomized in argon at Special Metals Corporation, Inc., using production-scale high-cleanliness powder-processing facilities and handling practices. The powder was then passed through a 270-mesh screen. One portion of this powder was set aside for subsequent consolidation without introduced inclusions. Two other portions of this powder were seeded with alumina inclusions. Small, polycrystalline soft (Type 2) inclusions of about 50 mm diameter were carefully prepared and blended into one powder lot, and larger hard (Type 1) inclusions of about 150 mm mean diameter were introduced into the other seeded portion of powder. All three portions of powder were then sealed in separate containers, hot isostatically pressurized, extruded, forged into subscale disks, and heat treated. Low-cycle-fatigue specimens were then extracted, machined, and tested. Fatigue tests were performed at 650 C in closed-loop servohydraulic testing machines using induction heating and axial extensometers. All tests were continued to failure, and fractographic evaluations were performed on all specimens to determine the crack initiation sites. A large majority of the failures in specimens with introduced inclusions occurred at cracks initiating from inclusions at the specimen surface, as shown for each type of inclusion in the following bar chart. The inclusions significantly reduced fatigue life from unseeded material levels, as shown in the bar chart. These effects were found to depend on the strain range, strain ratio, and inclusion size. Tests at lower strain ranges and higher strain ratios resulted in larger effects of inclusions on life. Inclusion effects on life were thereby maximized in tests at the lowest strain range of 0.6 percent and the most positive strain ratio of 0.5. Under these conditions, small Type 2 inclusions reduced life substantially-- about 20 times, whereas large Type 1 inclusions dramatically reduced life 100 times. These results clearly demonstrate that it is essential to include the effects of inclusions for realistic predictions of disk fatigue life. Important issues, including temperature dependence, crack initiation versus propagation, surface treatments, realistic disk features and machining, and realistic disk spin testing will be addressed to accurately model inclusion effects on disk fatigue life. Fatigue life varied from well over 105 cycles for no inclusions to a little over 103 cycles for 100-micrometer inclusions. A single crack initiating at a surface-connected seeded inclusion caused failure in each case.

Gabb, Timothy P.; Telesman, Jack; Kantzos, Peter T.; Bonacuse, Peter J.; Barrie, Robert L.

2002-01-01

293

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

294

An Experimental Investigation of the Effects of Vacuum Environment on the Fatigue Life, Fatigue-Crack-Growth Behavior, and Fracture Toughness of 7075-T6 Aluminum Alloy. Ph.D. Thesis - North Carolina State Univ.  

NASA Technical Reports Server (NTRS)

Axial load fatigue life, fatigue-crack propagation, and fracture toughness tests were conducted on 0.090-inch thick specimens made of 7075-T6 aluminum alloy. The fatigue life and fatigue-crack propagation experiments were conducted at a stress ratio of 0.02. Maximum stresses ranged from 33 to 60 ksi in the fatigue life experiments, and from 10 to 40 ksi in the fatigue-crack propagation experiments, and fatigue life experiments were conducted at gas pressures of 760, 0.5, 0.05, and 0.00000005 torr. Fatigue-crack-growth and fracture toughness experiments were conducted at gas pressures of 760 and 5 x 10 to the minus 8th power torr. Residual stress measurements were made on selected fatigue life specimens to determine the effect of such stresses on fatigue life. Analysis of the results from the fatigue life experiments indicated that fatigue life progressively increased as the gas pressure decreased. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue crack growth rates were approximately twice as high in air as in vacuum. Fracture toughness data showed there was essentially no difference in the fracture toughness of 7075-T6 in vacuum and in air.

Hudson, C. M.

1972-01-01

295

Dynamic loads in Francis runners and their impact on fatigue life  

NASA Astrophysics Data System (ADS)

Reliable fatigue life assessment of Francis runners combines two parts: At first, the load universe describing how the plant will be operated. And secondly, for all essential operating conditions, component stresses due to static and dynamic loading have to be predicted and considered in the design process by the manufacturer. Therefore, dynamic loading conditions and the resulting impact on the fatigue life of hydroelectric components are an integral part of research activities. Especially off-design conditions and transient operations have been addressed in the last years. Based on strain gauge measurements in prototype runners, model test experiences, and advanced numerical simulations, the understanding of dynamic loads has been highly improved. From correlations of measurement and simulation, standard procedures have been developed to enhance the fatigue life. The present paper summarizes findings of recent investigations enabling Francis runners which combine high efficiency and a robust mechanical design.

Seidel, U.; Mende, C.; Hübner, B.; Weber, W.; Otto, A.

2014-12-01

296

A study of stiffness, residual strength and fatigue life relationships for composite laminates  

NASA Technical Reports Server (NTRS)

Qualitative and quantitative exploration of the relationship between stiffness, strength, fatigue life, residual strength, and damage of unnotched, graphite/epoxy laminates subjected to tension loading. Clarification of the mechanics of the tension loading is intended to explain previous contradictory observations and hypotheses; to develop a simple procedure to anticipate strength, fatigue life, and stiffness changes; and to provide reasons for the study of more complex cases of compression, notches, and spectrum fatigue loading. Mathematical models are developed based upon analysis of the damage states. Mathematical models were based on laminate analysis, free body type modeling or a strain energy release rate. Enough understanding of the tension loaded case is developed to allow development of a proposed, simple procedure for calculating strain to failure, stiffness, strength, data scatter, and shape of the stress-life curve for unnotched laminates subjected to tension load.

Ryder, J. T.; Crossman, F. W.

1983-01-01

297

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

SciTech Connect

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

Moreno, V.; Nissley, D.; Lin, L.J.

1985-03-01

298

Effects of High Temperature Exposures on Fatigue Life of Disk Superalloys  

NASA Technical Reports Server (NTRS)

The effects on fatigue life of high temperature exposures simulating service conditions were considered for two disk superalloys. Powder metallurgy processed, supersolvus heat treated Udimet (trademark) 720 and ME3 fatigue specimens were exposed in air at temperatures of 650 to 704 C, for times of 100 h to over 1000 h. They were then tested using conventional fatigue tests at 650 and 704 C, to determine the effects of exposure on fatigue resistance. Cyclic dwell verification tests were also performed to contrast the effects of intermixed exposures and fatigue cycles. The prior exposures reduced life by up to 70% and increased the scatter in life, compared to unexposed levels. Cyclic dwell tests reduced lives even more. Fractographic evaluations indicated the failure mode was shifted by the exposures and cyclic dwells from predominantly internal to often surface crack initiations. The increased scatter in life was related to the competition between internal crack initiations at inclusions or large grains producing longer lives, and surface crack initiations at an environmentally affected surface layer producing shorter lives.

Gabb, Tim P.; Telesman, Jack; Kantzos, Pete T.; Smith, James W.; Browning, Paul F.

2004-01-01

299

Acoustic fatigue life prediction for non-linear structures  

NASA Technical Reports Server (NTRS)

Using an approach based on a time domain analysis, a method of equivalent linearization is applied for an estimation of the strain response of complex nonlinear structures having nearly arbitrary complexity. Fatigue lives estimated for a nonlinear beam with random excitation using the approximate method were compared with results obtained using a conventional numerical simulation, yielding nearly identical results.

Sun, J. Q.; Miles, R. N.

1991-01-01

300

Fatigue life prediction for GRP subjected to variable amplitude loading  

Microsoft Academic Search

A method of predicting lifetime to failure for any glass fibre reinforced composite system subjected to a complex load–time history has been developed. The prediction first requires the generation of a model to characterize the general fatigue response of the particular composite system. Once the models are derived they can be used to predict lifetimes to failure for any load–time

I. P. Bond

1999-01-01

301

Rubber fatigue life under multiaxial loading: Numerical and experimental investigations  

Microsoft Academic Search

Numerical and experimental aspects of rubber fatigue crack initiation are investigated in this study. A parameter based on the strain energy density (SED) and predicting the onset of primary crack and its probable orientation was identified for such materials according to the investigations of Mars and Fatemi [1]. In a last work, we have analytically developed this criterion for simple

A. Zine; N. Benseddiq; M. Naït Abdelaziz

2011-01-01

302

Thermomechanical fatigue life prediction in gas turbine superalloys: A fracture mechanics approach  

SciTech Connect

A model is presented that was developed to predict thermomechanical fatigue crack initiation and estimate mode I crack growth of gas turbine hot section gas path superalloys. The model is based on a strain energy density fracture mechanics approach modified to account for thermal exposure and single crystal anisotropy. Thermomechanical fatigue crack initiation and small crack growth is modeled by employing an initial material defect size. Model capability was quantified by applying the model to two hot section gas path superalloys: uncoated MAR-M509 and MCrAlY overlay coated PWA 1480. Thermomechanical fatigue model stresses were obtained from nonlinear finite element analysis of thermomechanical fatigue specimen strain-temperature history. Nonlinear stress-strain behavior was predicted using unified viscoplastic constitutive models. Model thermomechanical fatigue life predictions were in good agreement with observed uniaxial thermomechanical fatigue specimen lives. Thermomechanical fatigue cracking effects captured by the model included coating thickness, single crystal anisotropy, cycle waveshape, dwell, and thermal exposure. 45 refs.

Nissley, D.M. [United Technologies Corp., East Hartford, CT (United States)

1995-06-01

303

Effect of electric discharge machining on the fatigue life of Inconel 718  

NASA Technical Reports Server (NTRS)

The effect of electric discharge machining on the fatigue life of Inconel 718 alloy at room temperature was investigated. Data were generated in the uniaxial tension fatigue mode at ambient temperature using flat 3.175 mm thick specimens. The specimens were machined on a wire-cut electric discharge machine at cutting speeds ranging from 0.5 to 2 mm per minute. The specimens were fatigued at a selected stress, and the resulting fatigue lives compared with that of the virgin material. The surfaces of the fatigued specimens were examined under optical and scanning electron microscopes, and the roughness of the surfaces was measured using a standard profilometer. From the results of the investigation, it was concluded that the fatigue life of the specimens machined using EDM decreased slightly as compared with that of the virgin material, but remained unchanged as the cutting speed was changed. The results are explained using data produced employing microhardness measurements, profilometry, and optical and scanning microscopy.

Jeelani, S.; Collins, M. R.

1988-01-01

304

Shape optimization of a pressure vessel under plastic flow, plastic instability, weight and fatigue life criteria  

NASA Astrophysics Data System (ADS)

The structural shape optimization of a complex shell under complex criteria is presented. The shell is one of various cases of a turboshaft, and optimization criteria are associated with the cost, the technology, and above all the working conditions for the turboshaft. Optimization criteria involved are of course the weight of the structure, but also the plastic flow, plastic instability and fatigue life. The fatigue life criterion is an extension to the three-dimensional state of the one-dimensional Lemaitre-Chaboche rule, taking into account the elasto-plastic Neuber correction. All computations have been made with the ANSYS finite element program in which an optimization module exists.

El Abdi, R.; Touratier, M.; Convert, P.; Lalanne, B.

1994-06-01

305

Shape optimization of a pressure vessel under plastic flow, plastic instability, weight and fatigue life criteria  

SciTech Connect

The structural shape optimization of a complex shell under complex criteria is presented. The shell is one of various cases of a turboshaft, and optimization criteria are associated with the cost, the technology, and above all the working conditions for the turboshaft. Optimization criteria involved are of course the weight of the structure, but also the plastic flow, plastic instability and fatigue life. The fatigue life criterion is an extension to the three-dimensional state of the one-dimensional Lemaitre-Chaboche rule, taking into account the elasto-plastic Neuber correction. All computations have been made with the ANSYS finite element program in which an optimization module exists. 20 refs.

El Abdi, R.; Touratier, M.; Convert, P.; Lalanne, B. [Lab Genie de Production, Tarbes (France)] [Lab Genie de Production, Tarbes (France)

1994-06-01

306

Fatigue Life Prediction of Ductile Iron Based on DE-SVM Algorithm  

NASA Astrophysics Data System (ADS)

the model, predicting fatigue life of ductile iron, based on SVM (Support Vector Machine, SVM) has been established. For it is easy to fall into local optimum during parameter optimization of SVM, DE (Differential Evolution algorithm, DE) algorithm was adopted to optimize to improve prediction precision. Fatigue life of ductile iron is predicted combining with concrete examples, and simulation experiment to optimize SVM is conducted adopting GA (Genetic Algorithm), ACO (Ant Colony Optimization) and POS (Partial Swarm Optimization). Results reveal that DE-SVM algorithm is of a better prediction performance.

Yiqun, Ma; Xiaoping, Wang; lun, An

307

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

308

Corrosion fatigue of high strength fastener materials in seawater  

NASA Astrophysics Data System (ADS)

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.

1983-12-01

309

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

SciTech Connect

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

Chen, Xiang [ORNL] [ORNL; Sokolov, Mikhail A [ORNL] [ORNL; Sham, Sam [ORNL] [ORNL; ERDMAN III, DONALD L [ORNL] [ORNL; Busby, Jeremy T [ORNL] [ORNL; Mo, Kun [ORNL] [ORNL; Stubbins, James [ORNL] [ORNL

2013-01-01

310

Quasi-static strength and fatigue life of hybrid (bonded\\/bolted) composite single-lap joints  

Microsoft Academic Search

The strength and fatigue life of hybrid (bonded\\/bolted) joints with carbon-fibre reinforced plastic adherends have been investigated. The effect of adhesive material properties and laminate stacking sequence on the joint structural behaviour and failure modes were determined experimentally. Hybrid joints were shown to have greater strength, stiffness and fatigue life in comparison to adhesive bonded joints. However, the benefits were

Gordon Kelly

2006-01-01

311

Enhancing fatigue life of cylinder-crown integrated structure by optimizing dimension  

NASA Astrophysics Data System (ADS)

Cylinder-crown integrated hydraulic press (CCIHP) is a new press structure. The hemispherical hydraulic cylinder also functions as a main portion of crown, which has lower weight and higher section modulus compared with the conventional hydraulic cylinder and press crown. As a result, the material strength capacity is better utilized. During the engineering design of cylinder-crown integrated structure, in order to increase the fatigue life, structural optimization on the basis of the adaptive macro genetic algorithms (AMGA) is first conducted to both reduce weight and decrease peak stress. It is shown that the magnitude of the maximum principal stress is decreased by 28.6%, and simultaneously the total weight is reduced by 4.4%. Subsequently, strain-controlled fatigue test is carried out, and the stress-strain hysteresis loops and cyclic hardening curve are obtained. Based on linear fit, the fatigue properties are calculated and used for the fatigue life prediction. It is shown that the predicted fatigue life is significantly increased from 157000 to 1070000 cycles after structural optimization. Finally, according to the optimization design, a 6300 kN CCIHP has been manufactured, and priority application has been also suggested.

Zhang, Weiwei; Wang, Xiaosong; Wang, Zhongren; Yuan, Shijian

2015-02-01

312

Fatigue life improvement of an autofrettage thick-walled pressure vessel with an external groove  

NASA Astrophysics Data System (ADS)

This report presents an investigation into a fatigue life improvement of an autofrettaged thick-walled pressure vessel with an external groove subjected to pulsating internal pressure, along with mean strain and mean stress effects on strain-controlled low cycle fatigue behavior. Linear elastic stress analysis of an autofrettaged thick-walled pressure vessel with an external groove is done using a finite element method. Autofrettage loading is performed using a thermal loading analogy. Change of external groove geometry is made using a quasi-optimization technique and finite element method to achieve longer fatigue life by relieving the stress concentration at the groove root. Surface treatment using shot peening is employed to produce compressive residual stresses at the vulnerable surface of the groove root to counteract the high tensile stresses. An evaluation of the fatigue life of an autofrettaged thick-walled pressure vessel with an external groove is done through a series of simulation fatigue tests using C-shaped specimens taken from the thick-walled pressure vessel.

Koh, Seung K.; Stephens, Ralph I.

1992-01-01

313

Damage rate is a predictor of fatigue life and creep strain rate in tensile fatigue of human cortical bone samples.  

PubMed

We present results on the growth of damage in 29 fatigue tests of human femoral cortical bone from four individuals, aged 53-79. In these tests we examine the interdependency of stress, cycles to failure, rate of creep strain, and rate of modulus loss. The behavior of creep rates has been reported recently for the same donors as an effect of stress and cycles. In the present paper we first examine how the evolution of damage (drop in modulus per cycle) is associated with the stress level or the "normalized stress" level (stress divided by specimen modulus), and results show the rate of modulus loss fits better as a function of normalized stress. However, we find here that even better correlations can be established between either the cycles to failure or creep rates versus rates of damage than any of these three measures versus normalized stress. The data indicate that damage rates can be excellent predictors of fatigue life and creep strain rates in tensile fatigue of human cortical bone for use in practical problems and computer simulations. PMID:15971698

Cotton, John R; Winwood, Keith; Zioupos, Peter; Taylor, Mark

2005-04-01

314

Improved High-Cycle Fatigue (HCF) Life Prediction  

NASA Astrophysics Data System (ADS)

An overall building block approach facilitated the development and adaptation of models for immediate application to each of the three in-service generated damage states (the foreign object damage (FOD) and fretting damage models are dependent on the low cycle fatigue / high cycle fatigue (LCF/HCF) and base-line models). The program demonstrated the overall approach for developing methods that can be adapted and integrated into engine company design practices. Approaches and models were developed to set go, no-go limits for predicting the onset of HCF- induced failures; these can be adapted and incorporated into engine company design systems and address: threshold crack nucleation and propagation behaviors, mean stresses, multiaxial stress states, load interaction (LCF/HCF) loadings, notch shapes, FOD, and contact conditions and fretting. In addition to these overall accomplishments, a great number of individual accomplishments in the baseline and LCF/HCF areas provided synergism for generating accomplishments in the FOD and fretting damage areas.

Gallagher, J. P.; van Stone, R. H.; deLaneuville, R. E.; Gravett, P.; Bellows, R. S.

2001-01-01

315

Fatigue Life of Cast Titanium Alloys Under Simulated Denture Framework Displacements  

NASA Astrophysics Data System (ADS)

The objective of the study was to evaluate the hypothesis that the mechanical properties and fatigue behavior of removable partial dentures (RPD) made from cast titanium alloys can be improved by alloying with low-cost, low-melting elements such as Cu, Al, and Fe using commercially pure Ti (CP-Ti) and Ti-6Al-4V as controls. RPD specimens in the form of rest-shaped, clasp, rectangular-shaped specimens and round-bar tensile specimens were cast using an experimental Ti-5Al-5Cu alloy, Ti-5Al-1Fe, and Ti-1Fe in an Al2O3-based investment with a centrifugal-casting machine. The mechanical properties of the alloys were determined by performing tensile tests under a controlled displacement rate. The fatigue life of the RPD specimens was tested by the three-point bending in an MTS testing machine under a cyclic displacement of 0.5 mm. Fatigue tests were performed at 10 Hz at ambient temperature until the specimens failed into two pieces. The tensile data were statistically analyzed using one-way ANOVA (? = 0.05) and the fatigue life data were analyzed using the Kaplan-Meier survival analysis (? = 0.05). The experimental Ti-5Al-5Cu alloy showed a significantly higher average fatigue life than that of either CP-Ti or Ti-5Al-1Fe alloy ( p < 0.05). SEM fractography showed that the fatigue cracks initiated from surface grains, surface pores, or hard particles in surface grains instead of the internal casting pores. Among the alloys tested, the Ti-5Al-5Cu alloy exhibited favorable results in fabricating dental appliances with an excellent fatigue behavior compared with other commercial alloys.

Koike, Mari; Chan, Kwai S.; Hummel, Susan K.; Mason, Robert L.; Okabe, Toru

2013-02-01

316

Prediction of Rubber Fatigue Life under Multiaxial Loading  

Microsoft Academic Search

The process of fatigue failure of rubbers is generally described by two phases: crack initiation and crack propagation. This\\u000a study concerns the crack initiation in such materials submitted to a cyclical loading. Concerning this aspect, either criteria\\u000a based upon maximum stretch or strain energy density have been developed in the literature [1, 2, 3]. More recently, a parameter predicting the

A. Zine; N. Benseddiq; M. Nait-Abdelaziz; N. Ait Hocine

317

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

NASA Technical Reports Server (NTRS)

A series of high temperature strain controlled fatigue tests have been completed to study the effects of thermomechanical fatigue, multiaxial loading, reactive environments, and imposed mean stresses. The baseline alloy used in these tests was cast B1900+Hf (with and without coatings); a small number of tests of wrought INCO 718 are also included. A strong path dependence was demonstrated during the thermomechanical fatigue testing, using in-phase, out-phase, and non-proportional (elliptical and 'dogleg') strain-temperature cycles. The multiaxial tests also demonstrated cycle path to be a significant variable, using both proportional and non-proportional tension-torsion loading. Environmental screening tests were conducted in moderate pressure oxygen and purified argon; the oxygen reduced the specimen lives by two, while the argon testing produced ambiguous data. Both NiCoCrAlY overlay and diffusion aluminide coatings were evaluated under isothermal and TMF conditions; in general, the lives of the coated specimens were higher that those of uncoated specimens. Controlled mean stress TMF tests showed that small mean stress changes could change initiation lives by orders of magnitude; these results are not conservatively predicted using traditional linear damage summation rules. Microstructures were evaluated using optical, SEM and TEM methods.

Nelson, R. S.; Levan, G. W.; Schoendorf, J. F.

1992-01-01

318

Extending the fatigue life of aircraft engine components by hole cold expansion technology  

SciTech Connect

The split-sleeve cold expansion process has been used successfully for over 20 years to extend the fatigue life of holes in aircraft structures. Cold expansion technology can also be applied to enhance engine low-cycle fatigue (LCF) performance in both production and repair applications. Specific test data are presented showing that fatigue life extension can be attained by cold expansion of holes in a wide range of situations (including nonround hole geometries and low edge margins), and in components subjected to high operating temperatures. A cold expanded bushing system is compared to standard shrink-fit bushing installations. Finally, two case studies are used to illustrate the application of cold expansion of full-scale engine components.

Rufin, A.C. (Fatigue Technology Inc., Seattle, WA (United States))

1993-01-01

319

The fatigue life of a cobalt-chromium alloy after laser welding.  

PubMed

The aim of this study was to investigate the fatigue life of laser welded joints in a commercially available cast cobalt-chromium alloy. Twenty rod shaped specimens (40 mm x 1.5 mm) were cast and sand blasted. Ten specimens were used as controls and the remaining ten were sectioned and repaired using a pulsed Nd: YAG laser welder. All specimens were subjected to fatigue testing (30N - 2Hz) in a controlled environment. A statistically significant difference in median fatigue life was found between as-cast and laser welded specimens (p < 0.001). Consequently, the technique may not be appropriate for repairing cobalt chromium clasps on removable partial dentures. Scanning electron microscopy indicated the presence of cracks, pores and constriction of the outer surface in the welded specimens despite 70% penetration of the weld. PMID:21528682

Al-Bayaa, Nabil Jalal Ahmad; Clark, Robert K F; Juszczyk, Andrzej S; Radford, David R

2011-03-01

320

A Study on the Effects of Ball Defects on the Fatigue Life in Hybrid Bearings  

NASA Technical Reports Server (NTRS)

Hybrid ball bearings using silicon nitride ceramic balls with steel rings are increasingly being used in space mechanism applications due to their high wear resistance and long rolling contact fatigue life. However, qualitative and quantitative reports of the effects of ball defects that cause early fatigue failure are rare. We report on our approach to study these effects. Our strategy includes characterization of defects encountered in use, generation of similar defects in a laboratory setting, execution of full-scale bearing tests to obtain lifetimes, post-test characterization, and related finite-element modeling to understand the stress concentration of these defects. We have confirmed that at least one type of defect of appropriate size can significantly reduce fatigue life. Our method can be used to evaluate other defects as they occur or are encountered.

Tang, Ching-Yao; Foerster, Chad E.; O'Brien, Michael J.; Hardy, Brian S.; Goyal, Vinay K.; Nelson, Benjamin A.; Robinson, Ernest Y.; Ward, Peter C.; Hilton, Michael R.

2014-01-01

321

Effect of creep and oxidation on reduced fatigue life of Ni-based alloy 617 at 850 °C  

NASA Astrophysics Data System (ADS)

Low cycle fatigue (LCF) and creep-fatigue testing of Ni-based alloy 617 was carried out at 850 °C. Compared with its LCF life, the material's creep-fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep-fatigue tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material's fatigue life.

Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A.; Erdman, Donald L.; Mo, Kun; Stubbins, James F.

2014-01-01

322

Effect of Creep and Oxidation on Reduced Creep-Fatigue life of Ni-based Alloy 617 at 850 C  

SciTech Connect

Low cycle fatigue (LCF) and creep fatigue testing of Ni-based alloy 617 was carried out at 850 C. Compared with its LCF life, the material s creep fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep fatigue tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material s fatigue life.

Chen, Xiang [ORNL] [ORNL; Yang, Zhiqing [ORNL] [ORNL; Sokolov, Mikhail A [ORNL] [ORNL; ERDMAN III, DONALD L [ORNL] [ORNL; Mo, Kun [ORNL] [ORNL; Stubbins, James [ORNL] [ORNL

2014-01-01

323

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

324

A Statistical Simulation Approach to Safe Life Fatigue Analysis of Redundant Metallic Components  

NASA Technical Reports Server (NTRS)

This paper introduces a dual active load path fail-safe fatigue design concept analyzed by Monte Carlo simulation. The concept utilizes the inherent fatigue life differences between selected pairs of components for an active dual path system, enhanced by a stress level bias in one component. The design is applied to a baseline design; a safe life fatigue problem studied in an American Helicopter Society (AHS) round robin. The dual active path design is compared with a two-element standby fail-safe system and the baseline design for life at specified reliability levels and weight. The sensitivity of life estimates for both the baseline and fail-safe designs was examined by considering normal and Weibull distribution laws and coefficient of variation levels. Results showed that the biased dual path system lifetimes, for both the first element failure and residual life, were much greater than for standby systems. The sensitivity of the residual life-weight relationship was not excessive at reliability levels up to R = 0.9999 and the weight penalty was small. The sensitivity of life estimates increases dramatically at higher reliability levels.

Matthews, William T.; Neal, Donald M.

1997-01-01

325

Effect of Crystal Orientation on Analysis of Single-Crystal, Nickel-Based Turbine Blade Superalloys  

NASA Technical Reports Server (NTRS)

High-cycle fatigue-induced failures in turbine and turbopump blades is a pervasive problem. Single-crystal nickel turbine blades are used because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities. Single-crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant and complicating factor. A fatigue failure criterion based on the maximum shear stress amplitude on the 24 octahedral and 6 cube slip systems is presented for single-crystal nickel superalloys (FCC crystal). This criterion greatly reduces the scatter in uniaxial fatigue data for PWA 1493 at 1,200 F in air. Additionally, single-crystal turbine blades used in the Space Shuttle main engine high pressure fuel turbopump/alternate turbopump are modeled using a three-dimensional finite element (FE) model. This model accounts for material orthotrophy and crystal orientation. Fatigue life of the blade tip is computed using FE stress results and the failure criterion that was developed. Stress analysis results in the blade attachment region are also presented. Results demonstrate that control of crystallographic orientation has the potential to significantly increase a component's resistance to fatigue crack growth without adding additional weight or cost.

Swanson, G. R.; Arakere, N. K.

2000-01-01

326

A method of calculating the safe fatigue life of compact, highly-stressed components  

NASA Technical Reports Server (NTRS)

This paper describes a method which has been developed for estimating the safe fatigue life of compact, highly-stressed and inaccessible components for aeroplanes and helicopters of the Royal Air Force. It is explained why the Design Requirements for British Military Aircraft do not favor the use of a damage-tolerance approach in these circumstances.

Cardick, Arthur W.; Pike, Vera J.

1994-01-01

327

Fatigue life prediction of complex 2D components under mixed-mode variable amplitude loading  

Microsoft Academic Search

Accurate residual fatigue life predictions under variable amplitude (VA) loading are essential to maximize the time between the required inspections in defect-tolerant structures. However, this is not a trivial task for real structural components, in which cracks may change direction as they grow due to mixed-mode loading. Such curved crack paths can be predicted using finite element (FE) techniques, but

Oliveira Miranda; Marco Antonio Meggiolaro; Jaime TupiassuPinho de Castro; Luiz Fernando Martha

2003-01-01

328

Biomaterials 27 (2006) 19882000 Fatigue and life prediction for cobalt-chromium stents  

E-print Network

Biomaterials 27 (2006) 1988­2000 Fatigue and life prediction for cobalt-chromium stents: A fracture of testing to failure. This is typically achieved using one of two ARTICLE IN PRESS www.elsevier.com/locate/biomaterials 0142-9612/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials

Ritchie, Robert

329

Surface pitting fatigue life of noninvolute, low-contact-ratio gears  

NASA Technical Reports Server (NTRS)

Spur gear endurance tests were conducted to investigate the surface pitting fatigue life of noninvolute gears with low numbers of teeth and low contact ratios for use in advanced applications. The results were compared with those for a standard involute design with a low number of teeth. The gear pitch diameter was 8.89 cm (3.50 in.) with 12 teeth on both gear designs. Test conditions were an oil inlet temperature of 320 K (116 F), an oil outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.49 GPa (216 ksi), and a speed of 10 000 rpm. The following results were obtained: the noninvolute gear had a surface pitting fatigue life approximately 1.6 times that of the standard involute gear of a similar design; and the surface pitting fatigue life of the 3.43-pitch AISI 8620 noninvolute gear was approximately equal to the surface pitting fatigue life of an 8-pitch, 28-tooth AISI 9310 gear at the same load but at a considerably higher maximum Hertz stress.

Townsend, Dennis P.

1990-01-01

330

Quality of Life in Patients with Multiple Sclerosis: The Impact of Depression, Fatigue, and Disability  

ERIC Educational Resources Information Center

Aim: The aim of this study was to assess the quality of life (QoL) in patients with multiple sclerosis (MS), and to evaluate its association with disability and psychosocial factors especially depression and fatigue. Methods: Demographic characteristics, education level, disease severity, and disease duration were documented for each patient. QoL,…

Goksel Karatepe, Altlnay; Kaya, Taciser; Gunaydn, Rezzan; Demirhan, Aylin; Ce, Plnar; Gedizlioglu, Muhtesem

2011-01-01

331

Structural integrity and fatigue crack propagation life assessment of welded and weld-repaired structures  

Microsoft Academic Search

Structural integrity is the science and technology of the margin between safety and disaster. Proper evaluation of the structural integrity and fatigue life of any structure (aircraft, ship, railways, bridges, gas and oil transmission pipelines, etc.) is important to ensure the public safety, environmental protection, and economical consideration. Catastrophic failure of any structure can be avoided if structural integrity is

Mohammad Shah Alam

2005-01-01

332

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

Microsoft Academic Search

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

Hong Tang

2008-01-01

333

Isothermal and thermo-mechanical fatigue life modelling of components and structures at elevated temperature  

Microsoft Academic Search

Elevated temperature fatigue-life projects, funded by leading automotive manufacturers and component suppliers, are being carried out at nCode International Limited. These projects aim to develop an integrated durability solution for engineering components at elevated temperature, and involve material characterisation, software development of numerical damage models, software validation and verification. It is expected that the procedure developed can eventually allow industry

X. B. Lin; P. R. G. Anderson; V. Ogarevic; M. Bennebach

2002-01-01

334

Influence of correlations between stresses on calculated fatigue life of machine elements  

Microsoft Academic Search

The correlation between components of the random stress tensor and its influence on the calculated fatigue life of machine elements were analysed. Three covariance matrices of components of biaxial stress state were considered. They were determined from measurements of strains in an element of a vibrating screen for aggregate, in the back wall of a bus, and in a welded

T. ?agoda; E. Macha; A. Dragon; J. Petit

1996-01-01

335

Finite element based fatigue life prediction for electronic components under random vibration loading  

Microsoft Academic Search

This work develops an assessment methodology based on experiments and finite element analysis (FEA) to determine the solder joint fatigue life of electronic components under random vibration loading. Specially designed PCB with Ball Grid Array (BGA) packages attached was mounted to the Electro dynamic shaker and was applied to different random vibration excitations at the supports. Meanwhile, an event detector

Da Yu; Abdullah Al-Yafawi; Soonwan Chung

2010-01-01

336

High-cycle fatigue life prediction for Pb-free BGA under random vibration loading  

Microsoft Academic Search

This paper develops an assessment methodology based on vibration tests and finite element analysis (FEA) to predict the fatigue life of electronic components under random vibration loading. A specially designed PCB with ball grid array (BGA) packages attached was mounted to the electro-dynamic shaker and was subjected to different vibration excitations at the supports. An event detector monitored the resistance

Da Yu; Abdullah Al-Yafawi; Tung T. Nguyen; Soonwan Chung

2011-01-01

337

Prediction of fatigue life improvement in natural rubber using configurational stress  

Microsoft Academic Search

To some extent, continua can no longer be considered as free of defects. Experimental observations on natural rubber revealed the existence of distributed microscopic defects which grow upon cyclic loading. However, these observations are not incorporated in the classical fatigue life predictors for rubber, i.e. the maximum principal stretch, the maximum principal stress and the strain energy. Recently, Verron et

A. Andriyana; E. Verron

2007-01-01

338

Effect of lubricant extreme-pressure additives on surface fatigue life of AISI 9310 spur gears  

NASA Technical Reports Server (NTRS)

Surface fatigue tests were conducted with AISI 9310 spur gears using a formulated synthetic tetraester oil (conforming to MIL-L-23699 specifications) as the lubricant containing either sulfur or phosphorus as the EP additive. Four groups of gears were tested. One group of gears tested without an additive in the lubricant acted as the reference oil. In the other three groups either a 0.1 wt % sulfur or phosphorus additive was added to the tetraester oil to enhance gear surface fatigue life. Test conditions included a gear temperature of 334 K (160 F), a maximum Hertz stress of 1.71 GPa (248 000 psi), and a speed of 10,000 rpm. The gears tested with a 0.1 wt % phosphorus additive showed pitting fatigue life 2.6 times the life of gears tested with the reference tetraester based oil. Although fatigue lives of two groups of gears tested with the sulfur additive in the oil showed improvement over the control group gear life, the results, unlike those obtained with the phosphorus oil, were not considered to be statistically significant.

Scibbe, H. W.; Townsend, D. P.; Aron, P. R.

1984-01-01

339

A method of calculating the safe fatigue life of compact, highly-stressed components  

NASA Astrophysics Data System (ADS)

This paper describes a method which has been developed for estimating the safe fatigue life of compact, highly-stressed and inaccessible components for aeroplanes and helicopters of the Royal Air Force. It is explained why the Design Requirements for British Military Aircraft do not favor the use of a damage-tolerance approach in these circumstances.

Cardick, Arthur W.; Pike, Vera J.

1994-09-01

340

Compassion Fatigue, Compassion Satisfaction, and Burnout: Factors Impacting a Professional's Quality of Life  

ERIC Educational Resources Information Center

This study examined the relationship between three variables, compassion fatigue (CF), compassion satisfaction (CS), and burnout, and provider and setting characteristics in a sample of 1,121 mental health providers in a rural southern state. Respondents completed the Professional Quality of Life Scale as part of a larger survey of provider…

Sprang, Ginny; Whitt-Woosley, Adrienne; Clark, James J.

2007-01-01

341

Fatigue Life of Haynes 188 Superalloy in Direct Connect Combustor Durability Rig  

NASA Technical Reports Server (NTRS)

The Direct Connect Combustor Durability Rig (DCR) will provide NASA a flexible and efficient test bed to demonstrate the durability of actively cooled scramjet engine structure, static and dynamic sealing technologies, and thermal management techniques. The DCR shall be hydrogen fueled and cooled, and test hydrogen coolded structural panels at Mach 5 and 7. Actively cooled Haynes 188 superalloy DCR structural panels exposed to the combustion environment shall have electrodischarge machined (EDM) internal cooling holes with flowing liquid hydrogen. Hydrogen combustion could therefore produce severe thermal conditions that could challenge low cycle fatigue durability of this material. The objective of this study was to assess low cycle fatigue capability of Haynes 188 for DCR application. Tests were performed at 25 and 650 C, in hydrogen and helium environments, using specimens with low stress ground (LSG) and electro-discharge machined (EDM) surface finish. Initial fatigue tests in helium and hydrogen indicate the low cycle fatigue life capability of Haynes 188 in hydrogen appears quite satisfactory for the DCR application. Fatigue capability did not decrease with increasing test temperature. Fatigue capability also did not decrease with EDM surface finish. Failure evaluations indicate retention of ductility in all conditions. Additional tests are planned to reconfirm these positive trends.

Gabb, TIm; Gayda, John; Webster, Henry; Ribeiro, Greg

2007-01-01

342

Effects of High-Temperature Exposures on the Fatigue Life of Disk Superalloys Examined  

NASA Technical Reports Server (NTRS)

Tests used to characterize the low-cycle-fatigue resistance of disk superalloys are usually performed at cyclic frequencies of 0.33 Hz or faster. However, service conditions for disks in some aerospace and land-based gas turbine engines can produce major cycle periods extending from minutes to hours and days. Over a service life, this can produce total service times near the maximum temperature that exceed 100 hr for aerospace applications and 100,000 hr for land-based applications. Such time-dependent effects of realistic mission cycles on fatigue resistance can be significant in superalloy disks, and need to be considered for accurate disk life prediction. The purpose of this study at the NASA Glenn Research Center was to examine the effects of extended exposures and extended cycle periods on the fatigue resistance of two disk superalloys. Current alloy Udimet 720 (Special Metals Corporation, Huntington, WV) disk material was provided by Solar Turbines/Caterpillar Co., and advanced alloy ME3 was provided by the NASA Ultra-Efficient Engine Technologies (UEET) Project, in powder-metallurgy-processed, supersolvus heat-treated form. Fatigue specimens were fully machined and exposed in air at temperatures of 650 to 704 C for extended times. Then, they were tested using conventional fatigue tests with a total strain range of 0.70 percent and a minimum-to-maximum strain ratio of zero to determine the effects of prior exposure on fatigue resistance. Subsequent tests with extended dwells at minimum strain in each fatigue cycle were performed to determine cyclic exposure effects.

Gabb, Timothy P.; Telesman, Jack; Kantzos, Pete T.; Smith, James W.

2005-01-01

343

Stress-life relation of the rolling-contact fatigue spin rig  

NASA Technical Reports Server (NTRS)

The rolling-contact fatigue spin rig was used to test groups of SAE 52100 9.16-inch-diameter balls lubricated with a mineral oil at 600,000-, 675,000-, and 750,000-psi maximum Hertz stress. Cylinders of AISI M-1 vacuum and commercial melts and MV-1 (AISI M-50) were used as race specimens. Stress-life exponents produced agree closely with values accepted in industry. The type of failure obtained in the spin rig was similar to the subsurface fatigue spells found in bearings.

Butler, Robert H; Carter, Thomas L

1957-01-01

344

Substrate creep on the fatigue life of a model dental multilayer structure.  

PubMed

In this article, we investigated the effects of substrate creep on the fatigue life of a model dental multilayer structure, in which a top glass layer was bonded to a polycarbonate substrate through a dental adhesive. The top glass layers were ground using 120 or 600 grit sand papers before bonding to create different subsurface crack sizes and morphologies. The multilayer structures were tested under cyclic Hertzian contact loading to study crack growth and obtain fatigue life curves. The experiment results showed that the fatigue lives of the multilayer structures were impaired by increasing crack sizes in the subsurfaces. They were also significantly reduced by the substrate creep when tested at relatively low load levels, i.e. P(m) < 60 N (P(m) is the maximum magnitude of cyclic load). But at relatively high load levels, i.e. P(m) > 65 N, slow crack growth was the major failure mechanism. A modeling study was then carried out to explore the possible failure mechanisms over a range of load levels. It is found that fatigue life at relatively low load levels can be better estimated by considering the substrate creep effect. PMID:17245742

Zhou, J; Huang, M; Niu, X; Soboyejo, W O

2007-08-01

345

Grain boundary oxidation and an analysis of the effects of oxidation on fatigue crack nucleation life  

NASA Technical Reports Server (NTRS)

The effects of preoxidation on subsequent fatigue life were studied. Surface oxidation and grain boundary oxidation of a nickel-base superalloy (TAZ-8A) were studied at 600 to 1000 C for 10 to 1000 hours in air. Surface oxides were identified and the kinetics of surface oxidation was discussed. Grain boundary oxide penetration and morphology were studied. Pancake type grain boundary oxide penetrates deeper and its size is larger, therefore, it is more detrimental to fatigue life than cone-type grain boundary oxide. Oxide penetration depth, a (sub m), is related to oxidation temperature, T, and exposure time, t, by an empirical relation of the Arrhenius type. Effects of T and t on statistical variation of a (sub m) were analyzed according to the Weibull distribution function. Once the oxide is cracked, it serves as a fatigue crack nucleus. Statistical variation of the remaining fatigue life, after the formation of an oxide crack of a critical length, is related directly to the statistical variation of grain boundary oxide penetration depth.

Oshida, Y.; Liu, H. W.

1988-01-01

346

Fretting Stresses in Single Crystal Superalloy Turbine Blade Attachments  

NASA Technical Reports Server (NTRS)

Single crystal nickel base superalloy turbine blades are being utilized in rocket engine turbopumps and turbine engines because of their superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal nickel base turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. High Cycle Fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Blade attachment regions are prone to fretting fatigue failures. Single crystal nickel base superalloy turbine blades are especially prone to fretting damage because the subsurface shear stresses induced by fretting action at the attachment regions can result in crystallographic initiation and crack growth along octahedral planes. Furthermore, crystallographic crack growth on octahedral planes under fretting induced mixed mode loading can be an order of magnitude faster than under pure mode I loading. This paper presents contact stress evaluation in the attachment region for single crystal turbine blades used in the NASA alternate Advanced High Pressure Fuel Turbo Pump (HPFTP/AT) for the Space Shuttle Main Engine (SSME). 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. Blades and the attachment region are modeled using a large-scale 3D finite element (FE) model capable of accounting for contact friction, material orthotrophy, and variation in primary and secondary crystal orientation. Contact stress analysis in the blade attachment regions is presented as a function of coefficient of friction and primary and secondary crystal orientation, Stress results are used to discuss fretting fatigue failure analysis of SSME blades. Attachment stresses are seen to reach peak values at locations where fretting cracks have been observed. Fretting stresses at the attachment region are seen to vary significantly as a function of crystal orientation. Attempts to adapt techniques used for estimating fatigue life in the airfoil region, for life calculations in the attachment region, are presented. An effective model for predicting crystallographic crack initiation under mixed mode loading is required for life prediction under fretting action.

Arakere, Nagaraj K.; Swanson, Gregory

2000-01-01

347

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

NASA Technical Reports Server (NTRS)

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

Gyekenyesi, Andrew L.

1998-01-01

348

A reliability assessment method in strain-based fatigue life analysis  

SciTech Connect

For the purpose of fatigue reliability assessment based on strain-life analysis, a family of reliability defined {var_epsilon}-N{sub f} curves, called R-{var_epsilon}-N{sub f} curves, is constructed by considering the interference model of fatigue strain capacity and applied strain history. The main effort of this work is to define reliability factors which are used to modify the conventional {var_epsilon}-N{sub f} curve into a family of R-{var_epsilon}-N{sub f} curves. A major contribution of this paper is to define two unique reliability factors, one for elastic-strain-life relation and the other for plastic-strain-life relation, for a certain reliability by using an empirical {var_epsilon}-N{sub f} curve. A numerical example is presented to demonstrate the method.

Zhao, J.; Tang, J.; Wu, H.C. [Univ. of Iowa, Iowa City, IA (United States). Coll. of Engineering

1996-12-01

349

A probabilistic method for the fatigue life assessment of powder metallurgy parts of aircraft engines  

SciTech Connect

This paper will present a probabilistic approach developed in order to assess the fatigue life of aircraft engine parts (turbine disks) obtained by powder metallurgy technique. First of all, the main issues will be pointed out and the theoretical principles of the method will be described. Then the design implications and the experimental correlation will be emphasized. The scale effect is a major concern for the fatigue life assessment of a powder metallurgy part. It no longer allows the designer to evaluate the life of a massive part directly from experimental results based on small specimen fatigue tests as is done in the classical methodology. In order to describe this scale effect correctly, incubation sites (inhomogeneities like ceramic inclusions) must be characterized. The size of these inhomogeneities and their positions in the part appeared to be the most relevant parameters. Hence the methodology developed at SNECMA integrates the scale effect scatter through a binomial probability distribution as well as a temperature and stress-dependent life evaluation for each inhomogeneity size and position. The life calculation of a part implies an analysis of its whole volume and surface. An iterative process determines the number of cycles corresponding to a global reliability level requirement for the part. The complete methodology is then validated by comparing the calculated initiation distribution with experimental results on small specimens and test disks.

Krafft, R.; Mosset, S. [SNECMA, Moissy-Cramayel (France)

1996-04-01

350

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

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

351

Rolling-element fatigue life of silicon nitride balls: Preliminary test results  

NASA Technical Reports Server (NTRS)

Hot pressed silicon nitride was evaluated as a rolling element bearing material. The five-ball fatigue tester was used to test 12.7 mm (0.500 in.) diameter balls at a maximum Hertz stress of 800,000 psi at a race temperature of 130 F. The fatigue spalls in the silicon nitride resembled those in typical bearing steels. The ten-percent fatigue life of the silicon nitride balls was approximately one-eighth to one-fifth that of typical bearing steels (52100 and M-50). The load capacity of the silicon nitride was approximately one-third that of typical bearing steels. The load capacity of the silicon nitride was significantly higher than previously tested ceramic materials for rolling element bearings.

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

1972-01-01

352

Rolling-element fatigue life of AISI M-50 and 18-4-1 balls  

NASA Technical Reports Server (NTRS)

Rolling element fatigue studies were conducted with AISI M-50, EFR 18-4-1, and VAR 18-4-1. Groups of 12.7 mm (1/2-in) diameter balls of each material were tested in the five ball fatigue tester. Test conditions included a load of 1540 N (347 lbf) giving a maximum Hertz stress of 5520 MPa (800 000 psi), a shaft speed of 10,700 rpm, and a contact angle of 30 deg. Tests were run at a race temperature of 339 K (150 F) with a type 2 ester lubricant. The rolling element fatigue life of AISI M-50 was not significantly different from that of EFR 18-4-1 or VAR 18-4-1 based on a statistical comparison of the test results.

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

1978-01-01

353

Fatigue life prediction for high-heat-load components made of GlidCop by elastic-plastic analysis.  

PubMed

A procedure to predict the fatigue fracture life of high-heat-load components made of GlidCop has been successfully established. This method is based upon the Manson-Coffin equation with a cumulative linear damage law. This prediction was achieved by consolidating the results of experiments and analyses, and considered the effects of environment and creep. A low-cycle-fatigue test for GlidCop was conducted so that environment-dependent Delta(t)-N(f) diagrams for any temperature could be prepared. A special test piece was designed to concentrate the strain in a central area locally, resulting in the low-cycle-fatigue fracture. The experiments were carried out by repeatedly irradiating a test piece with an electron beam. The results of the experiment confirmed that the observed fatigue life was within a factor of two when compared with the predicted fatigue life, yet located on the safer side. PMID:18296780

Takahashi, Sunao; Sano, Mutsumi; Mochizuki, Tetsuro; Watanabe, Atsuo; Kitamura, Hideo

2008-03-01

354

Corrosion-fatigue life of commercially pure titanium and Ti6Al4V alloys in different storage environments  

Microsoft Academic Search

Statement of Problem. Removable partial dentures are affected by fatigue because of the cyclic mechanism of the masticatory system and frequent insertion and removal. Titanium and its alloys have been used in the manufacture of denture frameworks; however, preventive agents with fluorides are thought to attack titanium alloy surfaces. Purpose. This study evaluated, compared, and analyzed the corrosion-fatigue life of

Ricardo A. Zavanelli; Guilherme E. Pessanha Henriques; Itamar Ferreira; João M. D. de Almeida Rollo

2000-01-01

355

Predictions for fatigue crack growth life of cracked pipes and pipe welds using RMS SIF approach and experimental validation  

Microsoft Academic Search

The objective of the present study is to understand the fatigue crack growth behavior in austenitic stainless steel pipes and pipe welds by carrying out analysis\\/predictions and experiments. The Paris law has been used for the prediction of fatigue crack growth life. To carry out the analysis, Paris constants have been determined for pipe (base) and pipe weld materials by

Punit Arora; P. K. Singh; Vivek Bhasin; K. K. Vaze; A. K. Ghosh; D. M. Pukazhendhi; P. Gandhi; G. Raghava

2011-01-01

356

Fatigue and quality of life in women treated for various types of gynaecological cancers: a cross-sectional study  

PubMed Central

Aims and objectives To examine the prevalence of cancer-related fatigue in women treated for various types of gynaecological cancers and, for these cancers, to assess fatigue in relation to distress, health-related quality of life, demography and treatment characteristics. Background Advances in treatment of cancer have improved the likelihood of survival. Consequently, there are a growing number of patients who become survivors after cancer and who face side effects even years after treatment. One of the most frequently reported side effects across all types and stages of the disease is cancer-related fatigue. Design A descriptive cross-sectional study. Methods One hundred and twenty women treated for gynaecological cancers who were participants in an intervention study were included. Fatigue, psychological distress, health-related QoL and demographics were assessed by questionnaires. Disease and treatment characteristics were extracted from medical records. Results Cancer-related fatigue was reported in 53% of the women treated for gynaecological cancers, with a higher proportion in the group of cervical cancer, followed by ovarian cancer. Younger participants reported fatigue more frequently than older participants. When adjusting for age, the type of cancer a woman experiences was shown to have little impact on her risk of experiencing fatigue. The participants with fatigue reported higher levels of anxiety and depression than participants without fatigue. There was a relationship between fatigue and quality of life as measured by SF-36 domains. Conclusion The findings underscore the importance of screening for fatigue, patient education and symptom management. This should be included in a standard procedure during treatment and follow-up. Both somatic and psychological aspects of fatigue should be emphasised. Relevance to clinical practice The findings imply the need for health personnel to have focus on fatigue during the entire cancer trajectory of women after gynaecological cancers, as well as the need for screening, information, guidance and symptom management. PMID:25040957

Sekse, Ragnhild Johanne Tveit; Hufthammer, Karl Ove; Vika, Margrethe Elin

2015-01-01

357

A crystal plasticity based methodology for modeling fatigue crack initiation and estimating material coefficients to predict fatigue crack initiation life at micro, nano and macro scales  

NASA Astrophysics Data System (ADS)

Fatigue failure is a dominant mechanism that governs the failure of components and structures in many engineering applications. In conventional engineering applications due to the design specifications, a significant proportion of the fatigue life is spent in the crack initiation phase. In spite of the large number of works addressing fatigue life modeling, the problem of modeling crack initiation life still remains a major challenge. In this work, a novel computational methodology based upon crystal plasticity formulations has been developed to predict crack initiation life at macro, micro and nano length scales. The crystal plasticity based constitutive model has been employed to model the micromechanical deformation and damage accumulation under cyclic loading in polycrystalline metals. This work provides a first of its kind, fundamental basis for employing crystal plasticity formulations for evaluating a quantifiable estimate of fatigue crack initiation life. A semi-empirical energy based fatigue crack initiation criterion s employed to allow for accurate modeling of the underlying microstructural phenomenon leading to the initiation of cracks at different material length scales. The results of the fatigue crack initiation life prediction in case of polycrystalline metals such as Copper and Nickel demonstrated that the crack initiation life prediction using the proposed methodology yielded an improvement of more than 30% in comparison to the existing continuum methodologies for fatigue crack initiation prediction and more than 80% improvement compared to the existing analytical models. The computational methodology developed in this work also provides a first of its kind technique to evaluate the fatigue crack initiation coefficient in the form of energy dissipation coefficient that can be used at varying length scales. The methodology and the computational framework proposed in this work, are developed such that experimental inputs are used to improve computational model performance and the closed loop feedback system enables the modeling of micro, macro and nano scale mechanisms very well. The computational models for the representative material microstructures were built by creating randomized Voronoi tessellations of the representative region that allows for reducing the need for extensive testing which is the major challenge in crack initiation predictions in engineering structures. In order to facilitate the use of the model for engineering applications, an analytical expression for fatigue crack initiation prediction using macro-scale loading conditions has been developed. The analytical model developed for fatigue crack initiation using macro-scale conditions has been validated using benchmark data in the literature to allow for the identification of the material co-efficients necessary to predict the fatigue crack initiation life while considering surface finish, grain size and crack size. The computational modeling and prediction of fatigue crack initiation life in nanostructured graphene reinforced materials is also studied by creating an effective interface method based computational model. The results of the model prediction showed good agreement with the trend of fatigue crack initiation life compared with the experimental results. This work lays the foundation for linking micromechanical plastic deformation to the nano-scale phenomenon while simultaneously providing a tool for engineers predicting crack initiation in macro-scale applications.

Voothaluru, Rohit

358

Substrate Creep on The Fatigue Life of A Model Dental Multilayer Structure  

SciTech Connect

In this paper, we investigated the effects of substrate creep on the fatigue behavior of a model dental multilayer structure, in which a top glass layer was bonded to a polycarbonate substrate through a dental adhesive. The top glass layers were ground using 120 grit or 600 grit sand papers before bonding to create different sub-surface crack sizes and morphologies. The multilayer structures were tested under cyclic Hertzian contact loading to study crack growth and obtain fatigue life curves. The experiment results showed that the fatigue lives of the multilayer structures were impaired by increasing crack sizes in the sub-surfaces. They were also significantly reduced by the substrate creep when tested at relatively low load levels i.e. P{sub m} < 60 N (Pm is the maximum magnitude of cyclic load). But at relatively high load levels i.e. P{sub m} > 65 N, slow crack growth (SCG) was the major failure mechanisms. A modeling study was then carried out to explore the possible failure mechanisms over a range of load levels. It is found that fatigue life at relatively low load levels can be better estimated by considering the substrate creep effect (SCE).

Zhou, J; Huang, M; Niu, X; soboyejo, W

2006-10-09

359

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

360

Life extending control of gas turbine engines for aircraft propulsion  

Microsoft Academic Search

This paper examines the incorporation of a damage prediction model into the control systems synthesis of an aircraft gas turbine engine, with the objective of extending the life of critical engine components while maintaining the required level of system performance. Turbine blades are used as an example, with the primary modes of damage being high-cycle fatigue and low-cycle thermomechanical fatigue

Jeffrey Caplin; Asok Ray

1997-01-01

361

Compressive fatigue life of subchondral bone of the metacarpal condyle in thoroughbred racehorses.  

PubMed

In racehorses, fatigue related subchondral bone injury leads to overt fracture or articular surface collapse and subsequent articular cartilage degeneration. We hypothesised that the fatigue behaviour of equine subchondral bone in compression follows a power law function similar to that observed in cortical and trabecular bone. We determined the fatigue life of equine metacarpal subchondral bone in-vitro and investigated the factors influencing initial bone stiffness. Subchondral bone specimens were loaded cyclically in compression [54MPa (n=6), 66MPa (n=6), 78MPa (n=5), and 90MPa (n=6)] until failure. The fatigue life curve was determined by linear regression from log transformed number of cycles to failure and load. A general linear model was used to investigate the influence of the following variables on initial Young's Modulus: age (4-8years), specimen storage time (31-864days), time in training since most recent rest period (6-32weeks), limb, actual density (1.6873-1.8684g/cm(3)), subchondral bone injury grade (0-3), and cause of death (fatigue injury vs. other). Number of cycles to failure was (median, range) 223,603, 78,316-806,792 at 54MPa; 69,908, 146-149,855 at 66MPa; 13204, 614-16,425 at 78MPa (n=3); and 4001, 152-11,568 at 90MPa. The fatigue life curve was ?=112.2-9.6 log10Nf, (R(2)=0.52, P<0.001), where Nf is number of cycles to failure and ? is load. Removal of the three horses with the highest SCBI grade resulted in: ?=134.2-14.1 log10Nf, (R(2)=0.72, P<0.001). Initial Young's Modulus (mean±SD) was 2500±494MPa (n=22). Actual density (?) was the only variable retained in the model to describe initial Young's Modulus (E): E=-8196.7+5880.6?, (R(2)=0.34, P=0.0044). The fatigue behaviour of equine subchondral bone in compression is similar to that of cortical and trabecular bone. These data can be used to model the development of SCBI to optimize training regimes. PMID:24063945

Martig, Sandra; Lee, Peter V S; Anderson, Garry A; Whitton, R Chris

2013-12-01

362

Improvement of rolling contact fatigue life of ion implanted M50 steel  

NASA Astrophysics Data System (ADS)

With the overall objective to improve the service life and reliability of gas turbine engine bearings by increasing their corrosion resistance and rolling contact fatigue life a collaborative project under the EEC BRITE/EURAM program has been initiated and is now in its third year. The aim of the project is to develop an ion implantation technique to implant bearing components with metallic species and to optimise the process, particularly for applications where salt water contamination of the lubricant may occur. As part of the programme leading up to implantation of bearing components, test specimens of M50 bearing steel implanted with Cr + and Ta + at several doses have been characterised by various techniques. This article reports on the implantation work and the rolling contact fatigue measurements which have been performed in order to determine the optimum treatment.

Torp, B.; Nielsen, B. R.; Dodd, A.; Kinder, J.; Rangel, C. M.; DaSilva, M. F.; Courage, B.

1993-06-01

363

Comparison of Fatigue Life Estimation Using Equivalent Linearization and Time Domain Simulation Methods  

NASA Technical Reports Server (NTRS)

The Monte Carlo simulation method in conjunction with the finite element large deflection modal formulation are used to estimate fatigue life of aircraft panels subjected to stationary Gaussian band-limited white-noise excitations. Ten loading cases varying from 106 dB to 160 dB OASPL with bandwidth 1024 Hz are considered. For each load case, response statistics are obtained from an ensemble of 10 response time histories. The finite element nonlinear modal procedure yields time histories, probability density functions (PDF), power spectral densities and higher statistical moments of the maximum deflection and stress/strain. The method of moments of PSD with Dirlik's approach is employed to estimate the panel fatigue life.

Mei, Chuh; Dhainaut, Jean-Michel

2000-01-01

364

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

NASA Technical Reports Server (NTRS)

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

Carek, Gerald A.

1987-01-01

365

Strainrange partitioning life predictions of the long time Metal Properties Council creep-fatigue tests  

NASA Technical Reports Server (NTRS)

The method of Strainrange Partitioning is used to predict the cyclic lives of the Metal Properties Council's long time creep-fatigue interspersion tests of several steel alloys. Comparisons are made with predictions based upon the Time- and Cycle-Fraction approach. The method of Strainrange Partitioning is shown to give consistently more accurate predictions of cyclic life than is given by the Time- and Cycle-Fraction approach.

Saltsman, J. F.; Halford, G. R.

1979-01-01

366

A neural network approach to elevated temperature creep–fatigue life prediction  

Microsoft Academic Search

A new approach using a back-propagation neural network for life prediction was developed and demonstrated for predicting the elevated temperature (0.7–0.8Tm) creep–fatigue behavior of Ni-base alloy INCONEL 690. The neural network was trained with five extrinsic parameters, characterized via a 25–1 fractional factorial design methodology, and an intrinsic parameter (final grain size). The back-propagation network training error, prediction error and

Vasisht Venkatesh; H. J Rack

1999-01-01

367

Fatigue life under non-Gaussian random loading from various models  

Microsoft Academic Search

Fatigue test results on the 10HNAP steel under constant amplitude and random loading with non-Gaussian probability distribution function, zero mean value and wide-band frequency spectrum have been used to compare the life time estimation of the models proposed by Bannantine, Fatemi–Socie, Socie, Wang–Brown, Morel and ?agoda–Macha. Except the Morel proposal which accumulates damage step by step with a proper methodology,

A. Banvillet; T. ?agoda; E. Macha; A. Nies?ony; T. Palin-Luc; J.-F. Vittori

2004-01-01

368

Strainrange partitioning life predictions of the long time metal properties council creep-fatigue tests  

NASA Technical Reports Server (NTRS)

The method of strainrange partitioning is used to predict the cyclic lives of the Metal Properties Council's long time creep-fatigue interspersion tests of several steel alloys. Comparisons are made with predictions based upon the time- and cycle-fraction approach. The method of strainrange partitioning is shown to give consistently more accurate predictions of cyclic life than is given by the time- and cycle-fraction approach.

Saltsman, J. F.; Halford, G. R.

1979-01-01

369

Numerical life prediction method for fatigue failure of rubber-like material under repeated loading condition  

Microsoft Academic Search

Predicting fatigue life by numerical methods was almost impossible in the field of rubber materials. One of the reasons is\\u000a that there is not obvious fracture criteria caused by non-standardization of material and excessively various way of mixing\\u000a process. But, tearing energy as fracture factor can be applied to a rubber-like material regardless of different types of\\u000a fillers, relative to

Ho Kim; Heon-Young Kim

2006-01-01

370

Low-cycle fatigue life assessment for gas turbine engine disks under flight cycle conditions  

Microsoft Academic Search

We address the effects of the actual flight cycle on durability of gas turbine engine disks under low-cycle fatigue. An approach\\u000a is proposed which improves reliability of life cycle prediction owing to schematization of flight cycle with a criterion for\\u000a reaching the maximum intensity of total strain range. Contribution of subcycles to the cumulative damage is demonstrated.

K. D. Karimbaev; A. N. Servetnik

2009-01-01

371

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

372

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

PubMed

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

Silva, Matthew J; Touhey, Daniel C

2007-02-01

373

Condition monitoring techniques for composite wind turbine blades  

NASA Astrophysics Data System (ADS)

The range of possible NDT techniques that might be applied to wind turbine blades is reviewed. Thermal techniques are selected and implemented in various active and passive modes. Theoretical modeling of 3D thermal interactions is performed using a finite difference model. Several thermal condition monitoring methods are evaluated experimentally on both composites and composite wood blades. The relative detectability of various effects using the active heating approach is shown. Internal generation of heat was detected during a full-size wood laminate blade fatigue test. Temperature differences of over 1 C were measured at the surface above the underlying butt joint some 12 hr before failure occurred at the point. The hot spot was identified as early as at two-thirds of the final blade life.

Bond, Leonard J.; Aftab, Nadeem; Clayton, Brian R.; Dutton, A. G.; Irving, Andrew D.; Lipman, Norman H.

374

Helicopter rotor blade design for minimum vibration  

NASA Technical Reports Server (NTRS)

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

Taylor, R. B.

1984-01-01

375

Prediction of Contact Fatigue Life of Alloy Cast Steel Rolls Using Back-Propagation Neural Network  

NASA Astrophysics Data System (ADS)

In this study, an artificial neural network (ANN) was employed to predict the contact fatigue life of alloy cast steel rolls (ACSRs) as a function of alloy composition, heat treatment parameters, and contact stress by utilizing the back-propagation algorithm. The ANN was trained and tested using experimental data and a very good performance of the neural network was achieved. The well-trained neural network was then adopted to predict the contact fatigue life of chromium alloyed cast steel rolls with different alloy compositions and heat treatment processes. The prediction results showed that the maximum value of contact fatigue life was obtained with quenching at 960 °C, tempering at 520 °C, and under the contact stress of 2355 MPa. The optimal alloy composition was C-0.54, Si-0.66, Mn-0.67, Cr-4.74, Mo-0.46, V-0.13, Ni-0.34, and Fe-balance (wt.%). Some explanations of the predicted results from the metallurgical viewpoints are given. A convenient and powerful method of optimizing alloy composition and heat treatment parameters of ACSRs has been developed.

Jin, Huijin; Wu, Sujun; Peng, Yuncheng

2013-12-01

376

Fatigue life analysis for traction drives with application to a toroidal type geometry  

NASA Technical Reports Server (NTRS)

A contact fatigue life analysis for traction drives was developed which was based on a modified Lundberg-Palmgren theory. The analysis was used to predict life for a cone-roller toroidal traction drive. A 90-percent probability of survival was assumed for the calculated life. Parametric results were presented for life and Hertz contact stress as a function of load, drive ratio, and size. A design study was also performed. The results were compared to previously published work for the dual cavity toroidal drive as applied to a typical compact passenger vehicle drive train. For a representative duty cycle condition wherein the engine delivers 29 horsepower at 2000 rpm with the vehicle moving at 48.3 km/hr (30 mph) the drive life was calculated to be 19,200 km (11 900 miles).

Coy, J. J.; Loewenthal, S. H.; Zaretsky, E. V.

1976-01-01

377

On the relationship between statistical distributions of defect size and fatigue life in 7050-T7451 thick plate and A356-T6 castings  

Microsoft Academic Search

The relationship between the distributions for the size of fatigue-initiating defects and fatigue life of 7050-T7451 thick plate and A356-T6 alloy castings reported previously in the literature were analyzed. Results showed that (i) the size of fatigue-initiating defects in all four datasets follow the Gumbel distribution, (ii) the fatigue life model based on the Paris-Erdo?an law for crack propagation provides

Murat Tiryakio?lu

2009-01-01

378

Laser Peening and Shot Peening Effects on Fatigue Life and Surface Roughness of Friction Stir Welded 7075-T7351 Aluminum  

NASA Technical Reports Server (NTRS)

The effects of laser peening, shot peening, and a combination of both on the fatigue life of Friction Stir Welds (FSW) was investigated. The fatigue samples consisted of dog bone specimens and the loading was applied in a direction perpendicular to the weld direction. Several laser peening conditions with different intensities, durations, and peening order were tested to obtain the optimum peening parameters. The surface roughness resulting from various peening techniques was assessed and characterized. The results indicate a significant increase in fatigue life using laser peening compared to shot peened versus their native welded specimens.

Hatamleh, Omar; Lyons, Jed; Forman, Royce

2006-01-01

379

Life Time Estimation under Probabilistic Fatigue of Cracked Plates for Multiple Limits States  

NASA Astrophysics Data System (ADS)

The fatigue failure is most critical factor in lifetime estimation of industrial elements. The failure of a device in fatigue is due to a crack growth becoming instable and leading to strength decreasing. Based on Paris equation and S-N curves of WhÖler, the probabilistic fatigue crack growth is studied where each parameter can be considered as random variable. A reliability analysis was developed here for plates under fatigue crack; the failure event taken can be expressed by many performance functions called limits states depending on possible failure modes. We study 3 limit states, the first is the reaching of a critical value of crack width acr, the second is the reaching of the capacity value of tenacity of materials KIC, the third is the reaching of a critical number of cycles of applied stresses Ncr. Between theses 3 modes, we choose the most critical one toward the reliability value. A model of crack growth with respect to time is chosen to evaluate the time-reliability variation and hence to estimate the life time corresponding to a desired level of reliability.

EL-Tawil, Khaled; Kadry, Seifedine; AbouJaoude, Abdo

2009-09-01

380

Integrated actuation system for individual control of helicopter rotor blades  

NASA Astrophysics Data System (ADS)

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

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

1996-05-01

381

Effects of High-Temperature Exposures on the Fatigue Life of Superalloy Udimet(Registered Trademark) 720  

NASA Technical Reports Server (NTRS)

The purpose of this study was to examine the effects of extended exposures on the near-surface fatigue resistance of a disk superalloy. Powder metallurgy processed, supersolvus heat-treated Udimet 720 (U720) fatigue specimens were exposed in air at temperatures from 650 to 705 C for 100 hr to over 1000 hr. They were then tested using conventional fatigue tests at 650 C to determine the effects of exposure on fatigue resistance. The exposures reduced life by up to 70% and increased the scatter in life, compared to unexposed levels. Fractographic evaluations indicated the failure mode was shifted by the exposures from internal to surface crack initiations. The increased scatter in life was related to the competition between internal crack initiations at inclusions or large grains producing longer lives, and surface crack initiations at an environmentally affected surface layer producing shorter lives.

Gabb, Timothy P.; Telesman, Jack; Kantzos, Peter T.; Sweeney, Joseph W.; Browning, Paul F.

2002-01-01

382

Effect of double vacuum melting and retained austenite on rolling-element fatigue life of AMS 5749 bearing steel  

NASA Technical Reports Server (NTRS)

AMS 5749 steel combines the tempering, hot hardness, and hardness retention characteristics of AISI M-50 steel with the corrosion and oxidation resistance of AISI 440C stainless steel. The five-ball fatigue tester was used to evaluate the rolling-element fatigue life of AMS 5749. Double vacuum melting (vacuum induction melting plus vacuum arc remelting, VIM-VAR) produced AMS 5749 material with a rolling-element fatigue life at least 14 times that of vacuum induction melting alone. The VIM-VAR AMS 5749 steel balls gave lives from 6 to 12 times greater than VIM-VAR AISI M-50 steel balls. The highest level of retained austenite, 14.6 percent, was significantly detrimental to rolling-element fatigue life relative to the intermediate level of 11.1 percent.

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

1977-01-01

383

One-Year Longitudinal Study of Fatigue, Cognitive Functions, and Quality of Life After Adjuvant Radiotherapy for Breast Cancer  

SciTech Connect

Purpose: Most patients with localized breast cancer (LBC) who take adjuvant chemotherapy (CT) complain of fatigue and a decrease in quality of life during or after radiotherapy (RT). The aim of this longitudinal study was to compare the impact of RT alone with that occurring after previous CT on quality of life. Methods and Materials: Fatigue (the main endpoint) and cognitive impairment were assessed in 161 CT-RT and 141 RT patients during RT and 1 year later. Fatigue was assessed with Functional Assessment of Cancer Therapy-General questionnaires, including breast and fatigue modules. Results: At baseline, 60% of the CT-RT patients expressed fatigue vs. 33% of the RT patients (p <0.001). Corresponding values at the end of RT were statistically similar (61% and 53%), and fatigue was still reported at 1 year by more than 40% of patients in both groups. Risk factors for long-term fatigue included depression (odds ratio [OR] = 6), which was less frequent in the RT group at baseline (16% vs. 28 %, respectively, p = 0.01) but reached a similar value at the end of RT (25% in both groups). Initial mild cognitive impairments were reported by RT (34 %) patients and CT-RT (24 %) patients and were persistent at 1 year for half of them. No biological disorders were associated with fatigue or cognitive impairment. Conclusions: Fatigue was the main symptom in LBC patients treated with RT, whether they received CT previously or not. The correlation of persistent fatigue with initial depressive status favors administering medical and psychological programs for LBC patients treated with CT and/or RT, to identify and manage this main quality-of-life-related symptom.

Noal, Sabine [Medical Oncology Department, Centre Francois Baclesse, Caen (France); Clinical Research Department, Centre Francois Baclesse, Caen (France); Levy, Christelle [Medical Oncology Department, Centre Francois Baclesse, Caen (France); Hardouin, Agnes [Department of Medical Biology, Centre Francois Baclesse, Caen (France); Rieux, Chantal [Clinical Research Department, Centre Francois Baclesse, Caen (France); Heutte, Natacha [Universite de Caen Basse Normandie GRECAN, Caen (France); Segura, Carine [Medical Oncology Department, Centre Francois Baclesse, Caen (France); Collet, Fabienne [Clinical Research Department, Centre Francois Baclesse, Caen (France); Allouache, Djelila; Switsers, Odile; Delcambre, Corinne; Delozier, Thierry [Medical Oncology Department, Centre Francois Baclesse, Caen (France); Henry-Amar, Michel [Clinical Research Department, Centre Francois Baclesse, Caen (France); Joly, Florence, E-mail: f.joly@baclesse.fr [Medical Oncology Department, Centre Francois Baclesse, Caen (France); Clinical Research Department, Centre Francois Baclesse, Caen (France); CHU, Cote de Nacre, Caen (France)

2011-11-01

384

Influence of fatigue, depression, and demographic, socioeconomic, and clinical variables on quality of life of patients with epilepsy.  

PubMed

The purpose of this study was to define the influence of fatigue, depression, and clinical, demographic, and socioeconomic factors on the quality of life of patients with epilepsy. The study was performed on 103 adult patients who visited Erciyes University Epilepsy Outpatient Clinic between 2004 and 2005. Patients were evaluated with the Form of Negotiation, Quality of Life in Epilepsy Inventory (QOLIE-89), Beck Depression Inventory, and Fatigue Severity Scale. Mean age of the patients was 34.3+/-12.6, and mean duration of disease was 12.6+/-9.3 years. Among these patients, 52.4% were men, 49.5% were married, 15.5% had a university education, 53.4% had low incomes, 45.6% had generalized seizures, and 35.0% had experienced one or more seizures per month during the preceding year. The most significant variables in the domain of Overall quality of life were seizure frequency (P<0.001), depression (P<0.001), and fatigue (P<0.001); the variables in the domain of Mental Health were seizure frequency (P<0.001) and fatigue (P<0.001); the variable in the Cognitive domain was fatigue (P<0.001); the variables in the domain of Physical Health were social insurance coverage (P<0.01), fatigue (P<0.01), and age (P<0.01); the variables in the Epilepsy Targeted domain were depression (P<0.001), seizure frequency (P<0.001), and fatigue (P<0.01). Although quality of life has multiple determinants, seizure frequency, fatigue, and depression are the most important factors affecting quality of life in patients with epilepsy. One or more seizures per month, severe fatigue, and depression are associated with lower quality of life in some but not all domains. Partial correlations demonstrated that fatigue was a significant independent predictor of quality of life. The present study confirms that fatigue can be a powerful predictor of quality of life. PMID:17097354

Senol, Vesile; Soyuer, Ferhan; Arman, Fehim; Oztürk, Ahmet

2007-02-01

385

The effect of surface modification on fretting fatigue in Ti Alloy turbine components  

NASA Astrophysics Data System (ADS)

Severe fretting damage has been observed on the pressure surfaces of fan and compressor blade dovetails/disks in an aerospace gas turbine engine. A study has been carried out to evaluate the effect of an ion implantation technique in combination with the presently used surface treatments, such as shot peening and coating, on the fretting fatigue life of titanium alloy gas turbine engine components. The results from fretting fatigue tests, residual stress measurements, and nanoindentation tests were used to quantitatively evaluate the effect of various surface treatments on the fretting fatigue life of the fan blade and disk materials. Results from microstructural characterization and analyses of elemental and phase distributions within the implanted region are used to understand the effect of ion implantation on the surface properties of the alloys. Finally, an attempt has been made to evaluate the potential for improving the fretting fatigue life of the engine components using various surface modification techniques.

Chakravarty, S.; Andrews, R. G.; Painaik, P. C.; Koul, A. K.

1995-04-01

386

The Surface Fatigue Life of Contour Induction Hardened AISI 1552 Gears  

NASA Technical Reports Server (NTRS)

Two groups of spur gears manufactured from two different materials and heat treatments were endurance tested for surface fatigue life. One group was manufactured from AISI 1552 and was finished ground to a 0.4 micron (16 micro-in.) rms surface finish and then dual frequency contour induction hardened. The second group was manufactured from CEVM AISI 9310 and was carburized, hardened, and ground to a 0.4 micron (16 micro-in.) rms surface finish. The gear pitch diameter was 8.89 cm (3.5 in.). Test conditions were a maximum Hertz stress of 1.71 GPa (248 ksi), a bulk gear temperature of approximately 350 K (170 F) and a speed of 10,000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The test results showed that the 10 percent surface fatigue (pitting) life of the contour hardened AISI 1552 test gears was 1.7 times that of the carburized and hardened AISI 9310 test gears. Also there were two early failures of the AISI 1552 gears by bending fatigue.

Townsend, Dennis P.; Turza, Alan; Chaplin, Mike

1995-01-01

387

A generalized fitting technique for the LIFE2 fatigue analysis code  

SciTech Connect

The analysis of component fatigue lifetime for a wind energy conversion system (WECS) requires that the component load spectrum be formulated in terms of stress cycles. Typically, these stress cycles are obtained from time series data using a cycle identification scheme. As discussed by many authors, the matrix or matrices of cycle counts that describe the stresses on a turbine are constructed from relatively short, representative samples of time series data. The ability to correctly represent the long-term behavior of the distribution of stress cycles from these representative samples is critical to the analysis of service lifetimes. Several techniques are currently used to convert representative samples to the lifetime cyclic loads on the turbine. There has been recently developed a set of fitting algorithms that is particularly useful for matching the body of the distribution of fatigue stress cycles on a turbine component. Fitting techniques are now incorporated into the LIFE2 fatigue/fracture analysis code for wind turbines. In this paper, the authors provide an overview of the fitting algorithms and describe the pre- and post-count algorithms developed to permit their use in the LIFE2 code. Typical case studies are used to illustrate the use of the technique.

Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States). Wind Energy Research Dept.; Wilson, T. [Univ. of New Mexico, Albuquerque, NM (United States). New Mexico Engineering Research Inst.

1996-08-01

388

Fatigue-Life Computational Analysis for the Self-Expanding Endovascular Nitinol Stents  

NASA Astrophysics Data System (ADS)

Self-expanding endovascular stents made of Nitinol (a Ni-Ti intermetallic compound possessing superelastic and shape-memory properties) are being widely used to treat a common circulatory problem in which narrowed arteries, primarily due to fatty deposits, hamper blood flow to the extremities (the problem commonly referred to as "peripheral artery disease"). The stents of this type unfortunately occasionally fail structurally (and, in turn, functionally) rendering the stenting procedure ineffective. The failure is most often attributed to the fatigue-induced damage since over its expected ten-year life span, the stent will normally experience 370-400 million pulsating-blood flow-induced loading cycles. Redesign/redevelopment of the stents using the conventional make-and-test approaches is quite expensive and time consuming and therefore is being increasingly complemented by computational engineering methods and tools. In the present study, advanced structural and fluid-structure interaction finite element computational methods are combined with the advanced fatigue-based durability analysis techniques to further enhance the use of the computational engineering analysis tools in the development of vascular stents with improved high-cycle fatigue life.

Grujicic, M.; Pandurangan, B.; Arakere, A.; Snipes, J. S.

2012-11-01

389

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

390

A fracture mechanics based model for cumulative damage assessment as part of fatigue life prediction  

NASA Astrophysics Data System (ADS)

Cumulative damage related phenomena are considered, and a model for fatigue life prediction in the crack initiation stage is presented. The model interprets damage accumulation as a process of crack growth and takes into account load sequence dependent crack opening and closing levels which are controlled by the elastoplastic strain history and damage sum dependent decrease of the fatigue limit. A crack-driving parameter based on elastoplastic fracture mechanics is derived. Experiments based on two steels, an aluminum alloy, and several types of loading spectra revealed the improved accuracy of the model in comparison with previous approaches. It is concluded that the model can successfully predict load interaction effects which control the effective material straining and the phenomenon of a transient endurance limit for variable amplitude loading sequences.

Vormwald, M.; Heuler, P.; Seeger, T.

391

Slow Crack Growth and Fatigue Life Prediction of Ceramic Components Subjected to Variable Load History  

NASA Technical Reports Server (NTRS)

Present capabilities of the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code include probabilistic life prediction of ceramic components subjected to fast fracture, slow crack growth (stress corrosion), and cyclic fatigue failure modes. Currently, this code has the capability to compute the time-dependent reliability of ceramic structures subjected to simple time-dependent loading. For example, in slow crack growth (SCG) type failure conditions CARES/Life can handle the cases of sustained and linearly increasing time-dependent loads, while for cyclic fatigue applications various types of repetitive constant amplitude loads can be accounted for. In real applications applied loads are rarely that simple, but rather vary with time in more complex ways such as, for example, engine start up, shut down, and dynamic and vibrational loads. In addition, when a given component is subjected to transient environmental and or thermal conditions, the material properties also vary with time. The objective of this paper is to demonstrate a methodology capable of predicting the time-dependent reliability of components subjected to transient thermomechanical loads that takes into account the change in material response with time. In this paper, the dominant delayed failure mechanism is assumed to be SCG. This capability has been added to the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code, which has also been modified to have the ability of interfacing with commercially available FEA codes executed for transient load histories. An example involving a ceramic exhaust valve subjected to combustion cycle loads is presented to demonstrate the viability of this methodology and the CARES/Life program.

Jadaan, Osama

2001-01-01

392

Detect, troubleshoot gas-turbine blade failures  

Microsoft Academic Search

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

Meher-Homji

1995-01-01

393

Effect of speed and press fit on fatigue life of roller-bearing inner-race contact  

NASA Technical Reports Server (NTRS)

An analysis was performed to determine the effects of inner ring speed and press fit on the rolling element fatigue life of a roller bearing inner race contact. The effects of the resultant hoop and radial stresses on the principal stresses were considered. The maximum shear stresses below the Hertzian contact were determined for different conditions of inner ring speed, load, and geometry and were applied to a conventional ring life analysis. The race contact fatigue life was reduced by more than 90 percent for some conditions when speed and press fit were considered. The depth of the maximum shear stress remained virtually unchanged.

Coe, H. H.; Zaretsky, E. V.

1985-01-01

394

Dynamic Capacity and Surface Fatigue Life for Spur and Helical Gears  

NASA Technical Reports Server (NTRS)

A mathematical model for surface fatigue life of gear, pinion, or entire meshing gear train is given. The theory is based on a previous statistical approach for rolling-element bearings. Equations are presented which give the dynamic capacity of the gear set. The dynamic capacity is the transmitted tangential load which gives a 90 percent probability of survival of the gear set for one million pinion revolutions. The analytical results are compared with test data for a set of AISI 9310 spur gears operating at a maximum Hertz stress of 1.71 billion N/sq m and 10,000 rpm. The theoretical life predictions are shown to be good when material constants obtained from rolling-element bearing tests were used in the gear life model.

Coy, J. J.; Townsend, D. P.; Zaretsky, E. V.

1975-01-01

395

Dynamic capacity and surface fatigue life for spur and helical gears  

NASA Technical Reports Server (NTRS)

A mathematical model for surface fatigue life of gear, pinion, or entire meshing gear train is given. The theory is based on the statistical approach used by Lundberg and Palmgren for rolling-element bearings. Also equations are presented which give the dynamic capacity of the gear set. The dynamic capacity is the transmitted tangential load which gives a 90 percent probability of survival of the gear set for one million pinion revolutions. The analytical results were compared with test data for a set of AISI 9310 spur gears operating at a maximum Hertz stress of 1.71 billion N per sq m (248,000 psi) and 10,000 rpm. The theoretical life predictions were very good when material constants obtained from rolling-element bearing tests were used in the gear life model.

Coy, J. J.; Townsend, D. P.; Zaretsky, E. V.

1975-01-01

396

The application of probabilistic design theory to high temperature low cycle fatigue  

NASA Technical Reports Server (NTRS)

Metal fatigue under stress and thermal cycling is a principal mode of failure in gas turbine engine hot section components such as turbine blades and disks and combustor liners. Designing for fatigue is subject to considerable uncertainty, e.g., scatter in cycles to failure, available fatigue test data and operating environment data, uncertainties in the models used to predict stresses, etc. Methods of analyzing fatigue test data for probabilistic design purposes are summarized. The general strain life as well as homo- and hetero-scedastic models are considered. Modern probabilistic design theory is reviewed and examples are presented which illustrate application to reliability analysis of gas turbine engine components.

Wirsching, P. H.

1981-01-01

397

Deterioration of rolling contact fatigue life of pearlitic rail steel due to dry-wet rolling-sliding line contact  

Microsoft Academic Search

This study is aimed at the deterioration of rolling contact fatigue (RCF) life of pearlitic rail steel, under rolling-sliding conditions, where the wet phase of the test is preceded by different numbers of dry cycles. It is shown that initial dry cycles above a critical number causes sudden and significant deterioration in RCF life. This effect has been explained using

W. R. Tyfour; J. H. Beynon; A. Kapoor

1996-01-01

398

Multifrequency Eddy Current Inspection of Corrosion in Clad Aluminum Riveted Lap Joints and Its Effect on Fatigue Life  

SciTech Connect

Aging aircraft are prone to corrosion damage and fatigue cracks in riveted lap joints of fuselage skin panels. This can cause catastrophic failure if not detected and repaired. Hence detection of corrosion damage and monitoring its effect on structural integrity are essential. This paper presents multifrequency eddy current (EC) inspection of corrosion damage and machined material loss defect in clad A1 2024-T3 riveted lap joints and its effect on fatigue life. Results of eddy current inspection, corrosion product removal and fatigue testing are presented.

Okafor, A. C.; Natarajan, S. [Nondestructive Evaluation and Structural Health Monitoring Laboratory, Department of Mechanical and Aerospace Engineering, University of Missouri - Rolla, 1870 Miner Circle, Rolla, MO 65409-0050 (United States)

2007-03-21

399

The impact of regular physical activity on fatigue, depression and quality of life in persons with multiple sclerosis  

Microsoft Academic Search

BACKGROUND: The purpose of this study was to compare fatigue, depression and quality of life scores in persons with multiple sclerosis who do (Exercisers) and do not (Non-exercisers) regularly participate in physical activity. METHODS: A cross-sectional questionnaire study of 121 patients with MS (age 25–65 yr) living in Queensland, Australia was conducted. Physical activity level, depression, fatigue and quality of

Nicole M Stroud; Clare L Minahan

2009-01-01

400

CARES/Life Ceramics Durability Evaluation Software Enhanced for Cyclic Fatigue  

NASA Technical Reports Server (NTRS)

The CARES/Life computer program predicts the probability of a monolithic ceramic component's failure as a function of time in service. The program has many features and options for materials evaluation and component design. It couples commercial finite element programs--which resolve a component's temperature and stress distribution--to reliability evaluation and fracture mechanics routines for modeling strength-limiting defects. The capability, flexibility, and uniqueness of CARES/Life have attracted many users representing a broad range of interests and has resulted in numerous awards for technological achievements and technology transfer. Recent work with CARES/Life was directed at enhancing the program s capabilities with regards to cyclic fatigue. Only in the last few years have ceramics been recognized to be susceptible to enhanced degradation from cyclic loading. To account for cyclic loads, researchers at the NASA Lewis Research Center developed a crack growth model that combines the Power Law (time-dependent) and the Walker Law (cycle-dependent) crack growth models. This combined model has the characteristics of Power Law behavior (decreased damage) at high R ratios (minimum load/maximum load) and of Walker law behavior (increased damage) at low R ratios. In addition, a parameter estimation methodology for constant-amplitude, steady-state cyclic fatigue experiments was developed using nonlinear least squares and a modified Levenberg-Marquardt algorithm. This methodology is used to give best estimates of parameter values from cyclic fatigue specimen rupture data (usually tensile or flexure bar specimens) for a relatively small number of specimens. Methodology to account for runout data (unfailed specimens over the duration of the experiment) was also included.

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

1999-01-01

401

Strength and fatigue life evaluation of composite laminate with embedded sensors  

NASA Astrophysics Data System (ADS)

Prognosis regarding durability of composite structures using various Structural Health Monitoring (SHM) techniques is an important and challenging topic of research. Ultrasonic SHM systems with embedded transducers have potential application here due to their instant monitoring capability, compact packaging potential toward unobtrusiveness and noninvasiveness as compared to non-contact ultrasonic and eddy current techniques which require disassembly of the structure. However, embedded sensors pose a risk to the structure by acting as a flaw thereby reducing life. The present paper focuses on the determination of strength and fatigue life of the composite laminate with embedded film sensors like CNT nanocomposite, PVDF thin films and piezoceramic films. First, the techniques of embedding these sensors in composite laminates is described followed by the determination of static strength and fatigue life at coupon level testing in Universal Testing Machine (UTM). Failure mechanisms of the composite laminate with embedded sensors are studied for static and dynamic loading cases. The coupons are monitored for loading and failure using the embedded sensors. A comparison of the performance of these three types of embedded sensors is made to study their suitability in various applications. These three types of embedded sensors cover a wide variety of applications, and prove to be viable in embedded sensor based SHM of composite structures.

Rathod, Vivek T.; Hiremath, S. R.; Roy Mahapatra, D.

2014-04-01

402

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

NASA Astrophysics Data System (ADS)

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

Sung, In-Kyung

403

Cable connected active tuned mass dampers for control of in-plane vibrations of wind turbine blades  

NASA Astrophysics Data System (ADS)

In-plane vibrations of wind turbine blades are of concern in modern multi-megawatt wind turbines. Today's turbines with capacities of up to 7.5 MW have very large, flexible blades. As blades have grown longer the increasing flexibility has led to vibration problems. Vibration of blades can reduce the power produced by the turbine and decrease the fatigue life of the turbine. In this paper a new active control strategy is designed and implemented to control the in-plane vibration of large wind turbine blades which in general is not aerodynamically damped. A cable connected active tuned mass damper (CCATMD) system is proposed for the mitigation of in-plane blade vibration. An Euler-Lagrangian wind turbine model based on energy formulation has been developed for this purpose which considers the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations and also the interaction between the blades and the tower including the CCATMDs. The CCATMDs are located inside the blades and are controlled by an LQR controller. The turbine is subject to turbulent aerodynamic loading simulated using a modification to the classic Blade Element Momentum (BEM) theory with turbulence generated from rotationally sampled spectra. The turbine is also subject to gravity loading. The effect of centrifugal stiffening of the rotating blades has also been considered. Results show that the use of the proposed new active control scheme significantly reduces the in-plane vibration of large, flexible wind turbine blades.

Fitzgerald, B.; Basu, B.

2014-11-01

404

Notch fatigue crack initiation in high temperature water environments: Experiments and life prediction  

SciTech Connect

Test results, experimental techniques and analytical interpretations are reported from notched compact type (CT) tests of SA 333 Gr. 6 carbon steel to determine quantitatively fatigue initiation lives in high temperature oxygenated water. Parameters explored include environments of air, 0.2 ppm O/sub 2/ and 8 ppm O/sub 2/-water at 10.3 MPa (1500 psi), temperatures of 149, 232 and 288/sup 0/C, frequencies of 0.00021, 0.0021 and 0.21 Hz, notch radii of 0.051 and 0.51 mm and R-values of 0.2, 0.5 and 0.8. Pseudostress amplitudes were calculated elastically and by Neuber notch analysis procedures using a worst case notch concept. Results were compared to ASME Section III fatigue data curves. Test results showed that the fatigue initiation life of carbon steel is substantially lowered as oxygen level is raised, as frequency is lowered or as temperature is raised.

Prater, T.A.; Coffin, L.F.

1987-02-01

405

Effect of Environmental Exposures on Fatigue Life of P/M Disk Superalloys  

NASA Technical Reports Server (NTRS)

As the temperature capability of Ni-base superalloy powder metallurgy disks is steadily increased, environmental resistance and protection of advanced nickel-based turbine disk components are becoming increasingly important. Localized surface hot corrosion attack and damage from oxidation have been shown to impair disk fatigue life and may eventually limit disk operating temperatures. NASA Research Announcement (NRA) contracts have been awarded to GE Aviation and Honeywell Aerospace to separately develop fatigue resistant metallic and ceramic coatings for corrosion resistance and the corrosion/fatigue results of selected coatings will be presented. The microstructural response of a bare ME3 disk superalloy has been evaluated for moderate (704 C) and aggressive (760-816 C) oxidizing exposures up to 2,020 hours. Cross section analysis reveals sub-surface damage (significant for aggressive exposures) that consists of Al2O3 "fingers", interfacial voids, a recrystallized precipitate-free layer and GB carbide dissolution. The effects of a Nichrome corrosion coating on this microstructural response will also be presented.

Draper, Susan

2011-01-01

406

The Prediction of Fatigue Life for Arbitrary Geometries From the Statistical Analysis of Plain Specimen Data  

NASA Astrophysics Data System (ADS)

Engine manufacturers are under constant commercial pressure to produce engines with improved performance, with increased reliability and at lower cost. As a result, the materials from which fracture critical components are made are increasingly being pushed to the limit of their capability. To ensure that uncontained failures of these components are reduced below current levels, it is critically important to understand the behaviour of these materials under the extremes of stress and temperature they are now expected to endure in service. However, since practical understanding of materials derives largely from laboratory specimen studies, it is necessary to know how the observed properties are reflected in full scale components. The current paper introduces a statistical model for the size effect in fatigue, which, when combined with fully non-linear stress analysis, advanced materials models and fracture mechanics calculations, provides a means of predicting fatigue life distributions for arbitrary geometries and loadings. The model is applied to an extensive fatigue database for a modern engine alloy, which contains both notched specimen and full scale component results. It is demonstrated that the model can predict both types of results accurately, which is important because they represent the relative extremes in terms of both stress and volume.

Shepherd, Duncan P.

2002-10-01

407

A review of the Workshop on Fatigue Life Methodologies for Wind Turbines  

NASA Astrophysics Data System (ADS)

From March 31 - April 1, 1993, Sandia National Laboratories (SNL) and the National Renewable Energy Laboratory (NREL) hosted a workshop entitled 'Fatigue Life Methodologies.' The purpose of this workshop was to bring together a representative panel of experts to discuss the prediction and measurement of infrequent events that contribute significantly to the damage of wind turbine components. The diverse backgrounds of the participants yielded discussions that covered a wide range of research and design activities from many varying viewpoints. Consensus was not reached on most of the questions raised at the workshop; however, the workshop laid the foundation for a program that now knows what questions must be answered.

Sutherland, H. J.; Butterfield, C. P.

408

Advanced Failure Determination Measurement Techniques Used in Thermal Fatigue Life Testing of Electronic Packaging  

NASA Technical Reports Server (NTRS)

Thermal fatigue life testing of various electronic packaging technologies is being performed by the Reliability Technology Group at the Jet Propulsion Laboratory. These testing efforts are in progress to improve uderstanding of the reliability issues associated with low volume packaging technologies for space applications and to develop qualification and acceptance approaches for these technologies. The work described here outlines the electrical failure detection techniques used during testing by documenting the circuits and components used to make these measurements, the sensitivity of the measurements, and the applicability of each specific measurement.

Wallace, A. P.; Cornford, S. L.; Gross, M. A.

1996-01-01

409

Interference fits and stress-corrosion failure. [aircraft parts fatigue life analysis  

NASA Technical Reports Server (NTRS)

It is pointed out that any proper design of interference fit fastener, interference fit bushings, or stress coining processes should consider both the stress-corrosion susceptibility and fatigue-life improvement together. Investigations leading to such a methodology are discussed. A service failure analysis of actual aircraft parts is considered along with the stress-corrosion susceptibility of cold-working interference fit bushings. The optimum design of the amount of interference is considered, giving attention to stress formulas and aspects of design methodology.

Hanagud, S.; Carter, A. E.

1976-01-01

410

Creep fatigue life prediction for engine hot section materials (isotropic): Fourth year progress review  

NASA Technical Reports Server (NTRS)

As gas turbine technology continues to advance, the need for advanced life prediction methods for hot section components is becoming more and more evident. The complex local strain and temperature histories at critical locations must be accurately interpreted to account for the effects of various damage mechanisms (such as fatigue, creep, and oxidation) and their possible interactions. As part of the overall NASA HOST effort, this program is designed to investigate these fundamental damage processes, identify modeling strategies, and develop practical models which can be used to guide the early design and development of new engines and to increase the durability of existing engines.

Nelson, Richard S.; Schoendorf, John F.

1986-01-01

411

Surface fatigue life and failure characteristics of EX-53, CBS 1000M, and AISI 9310 gear materials  

NASA Technical Reports Server (NTRS)

Spur gear endurance tests and rolling-element surface fatigue tests are conducted to investigate EX-53 and CBS 1000M steels for use as advanced application gear materials, to determine their endurance characteristics, and to compare the results with the standard AISI 9310 gear material. The gear pitch diameter is 8.89 cm (3.50 in). Gear test conditions are an oil inlet temperature of 320 K (116 F), an oil outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. Bench-type rolling-element fatigue tests are conducted at ambient temperature with a bar specimen speed of 12,500 rpm and a maximum Hertz stress of 4.83 GPa (700 ksi). The EX-53 test gears have a surface fatigue life of twice that of the AISI 9310 spur gears. The CBS 1000M test gears have a surface fatigue life of more than twice that of the AISI 9310 spur gears. However, the CBS 1000M gears experience a 30-percent tooth fracture failure which limits its use as a gear material. The rolling-contact fatigue lines of RC bar specimens of EX-53 and ASISI 9310 are approximately equal. However, the CBS 1000M RC specimens have a surface fatigue life of about 50 percent that of the AISI 9310.

Townsend, D. P.

1985-01-01

412

Prediction of fatigue life of high-heat-load components made of oxygen-free copper by comparing with Glidcop.  

PubMed

Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep-fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep-fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment. PMID:23254657

Takahashi, Sunao; Sano, Mutsumi; Watanabe, Atsuo; Kitamura, Hideo

2013-01-01

413

Prediction of fatigue life of high-heat-load components made of oxygen-free copper by comparing with Glidcop  

PubMed Central

Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep–fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep–fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment. PMID:23254657

Takahashi, Sunao; Sano, Mutsumi; Watanabe, Atsuo; Kitamura, Hideo

2013-01-01

414

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

415

Oxidation and the Effects of High Temperature Exposures on Notched Fatigue Life of an Advanced Powder Metallurgy Disk Superalloy  

NASA Technical Reports Server (NTRS)

Oxidation and the effects of high temperature exposures on notched fatigue life were considered for a powder metallurgy processed supersolvus heat-treated ME3 disk superalloy. The isothermal static oxidation response at 704 C, 760 C, and 815 C was consistent with other chromia forming nickel-based superalloys: a TiO2-Cr2O3 external oxide formed with a branched Al2O3 internal subscale that extended into a recrystallized - dissolution layer. These surface changes can potentially impact disk durability, making layer growth rates important. Growth of the external scales and dissolution layers followed a cubic rate law, while Al2O3 subscales followed a parabolic rate law. Cr- rich M23C6 carbides at the grain boundaries dissolved to help sustain Cr2O3 growth to depths about 12 times thicker than the scale. The effect of prior exposures was examined through notched low cycle fatigue tests performed to failure in air at 704 C. Prior exposures led to pronounced debits of up to 99 % in fatigue life, where fatigue life decreased inversely with exposure time. Exposures that produced roughly equivalent 1 m thick external scales at the various isotherms showed statistically equivalent fatigue lives, establishing that surface damage drives fatigue debit, not exposure temperature. Fractographic evaluation indicated the failure mode for the pre-exposed specimens involved surface crack initiations that shifted with exposure from predominately single intergranular initiations with transgranular propagation to multi-initiations from the cracked external oxide with intergranular propagation. Weakened grain boundaries at the surface resulting from the M23C6 carbide dissolution are partially responsible for the intergranular cracking. Removing the scale and subscale while leaving a layer where M23C6 carbides were dissolved did not lead to a significant fatigue life improvement, however, also removing the M23C6 carbide dissolution layer led to nearly full recovery of life, with a transgranular initiation typical to that observed in unexposed specimens.

Sudbrack, Chantal K.; Draper, Susan L.; Gorman, Timothy T.; Telesman, Jack; Gab, Timothy P.; Hull, David R.

2012-01-01

416

Overview of the fatigue/fracture/life working group program at the Lewis Research Center  

NASA Technical Reports Server (NTRS)

Constitutive and life prediction models are developed and verified for materials typically used in hot gas path components of reusable space propulsion systems over the range of relevant operating environments. The efforts were centered on the development of crack initiation life prediction methods, while the efforts of a counterpart group were centered on the development of cyclic crack propagation life prediction methods. The complexion of the active tasks are presented. A significant new task started this year will incorporate the various material constitutive and life prediction models developed in this program into a comprehensive creep-fatigue damage analysis and life assessment computer code. The program will function as a postprocessor to general structural analysis programs (such as finite element or boundary element codes) using the output of such analyses (stress, strain, and temperature fields as functions of time) as the input to the damage analysis and life assessment code. The code will be designed to execute on engineering/scientific workstations and will feature a windowing, mouse-driven user interface. Current plans call for the code to be finished and made available for use in mid 1991.

Mcgaw, Michael A.

1989-01-01

417

Application of fracture mechanics and half-cycle method to the prediction of fatigue life of B-52 aircraft pylon components  

NASA Technical Reports Server (NTRS)

Stress intensity levels at various parts of the NASA B-52 carrier aircraft pylon were examined for the case when the pylon store was the space shuttle solid rocket booster drop test vehicle. Eight critical stress points were selected for the pylon fatigue analysis. Using fracture mechanics and the half-cycle theory (directly or indirectly) for the calculations of fatigue-crack growth ,the remaining fatigue life (number of flights left) was estimated for each critical part. It was found that the two rear hooks had relatively short fatigue life and that the front hook had the shortest fatigue life of all the parts analyzed. The rest of the pylon parts were found to be noncritical because of their extremely long fatigue life associated with the low operational stress levels.

Ko, W. L.; Carter, A. L.; Totton, W. W.; Ficke, J. M.

1989-01-01

418

Fatigue oxidation interaction in a superalloy—application to life prediction in high temperature low cycle fatigue  

Microsoft Academic Search

A study of the interaction between fatigue and oxidation has been carried out in the case of a cast cobalt base superalloy\\u000a MARM 509 tested in laboratory air at 900 C. The influence of fatigue cycling on oxidation of this alloy has been studied\\u000a by quantitative metallography on polished specimens exposed to air in a furnace and on strain-cycled low-cycle

J. Reuchet; L. Remy

1983-01-01

419

Fatigue oxidation interaction in a superalloy—application to life prediction in high temperature low cycle fatigue  

NASA Astrophysics Data System (ADS)

A study of the interaction between fatigue and oxidation has been carried out in the case of a cast cobalt base superalloy MARM 509 tested in laboratory air at 900 °C. The influence of fatigue cycling on oxidation of this alloy has been studied by quantitative metallography on polished specimens exposed to air in a furnace and on strain-cycled low-cycle fatigue specimens. The oxidation kinetics were determined by thickness measurements for matrix oxidation and by oxidized depth measurements for the preferential oxidation of MC carbides. In both cases the oxidation kinetics were found to be dramatically enhanced by cycling for the matrix oxidation according to a linear relationship with plastic strain amplitude and less dramatically for carbides according to an exponential relationship with the maximum cyclic stress. From these observations a damage equation which describes fatigue damage as a crack growth process has been proposed: the elementary crack advance is a summation of a mechanical contribution due to the fatigue process itself which is described by Tomkins’ equation and of an oxidation contribution which has been evaluated from metallographic measurements. Integration of this crack growth equation gives predicted fatigue lives which are in good agreement with experimental results within a factor of two.

Reuchet, J.; Remy, L.

1983-01-01

420

Investigation of Bearing Fatigue Damage Life Prediction Using Oil Debris Monitoring  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

421

Investigation of the fatigue behaviour of butt-welded joints treated by ultrasonic peening process and compared with fatigue life assessment standards  

Microsoft Academic Search

Ultrasonic peening is a technique to be used for improving the fatigue life of welded structures. The technique makes use\\u000a of an ultrasonically vibrated pin which is pressed against the toe regions of the weld. The beneficial effect is mainly due\\u000a to the introduction of favourable compressive stresses on weld toe regions, causing local plastic deformation and reducing\\u000a stress concentration

G. R. Jinu; P. Sathiya; G. Ravichandran; A. Rathinam

2009-01-01

422

Damage evolution during thermo-mechanical fatigue of a coated monocrystalline nickel-base superalloy  

Microsoft Academic Search

To prevent hot gas corrosion nickel-base turbine blades used in today’s jet engines, they are protected with so called Pt-modified ?-NiAl coatings which are also subjected to thermo-mechanical loading during service. The effects of thermo-mechanical fatigue (TMF) loading on the coating as well as TMF life are the subjects of this paper. Microstructural investigations before, during and after thermo-mechanical fatigue

R. Nützel; E. Affeldt; M. Göken

2008-01-01

423

Analysis of aeroelastic loads and their contributions to fatigue damage  

NASA Astrophysics Data System (ADS)

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

Bergami, L.; Gaunaa, M.

2014-12-01

424

Pre-crack fatigue life assessment of relevant aircraft materials using fractal analysis of eddy current test data  

NASA Astrophysics Data System (ADS)

Successful determination of residual fatigue life requires a comprehensive understanding of the fatigue related material deformation mechanism. Neither macroscopic continuum mechanics nor micromechanic observations provide sufficient data to explain subsequent deformation structures occurring during the fatigue life of a metallic structure. Instead mesomechanic deformation on different scaling levels can be studied by applying fractal analysis of various means of nondestructive inspection measurements. The resulting fractal dimension data can be correlated to the actual material damage states, providing an estimation of the remaining residual fatigue life before macroscopic fracture develops. Recent efforts were aimed to apply the fractal concept to aerospace relevant materials AA7075-T6 and Ti-6Al-4V. Proven and newly developed fractal analysis methods were applied to eddy current (EC) measurements of fatigued specimens, with the potential to transition this approach to an aircraft for an in-situ nondestructive inspection. The occurrence of mesomechanic deformation at the material surface of both AA7075-T6 and Ti-6Al-4V specimens could be established via topography images using confocal microscopy (CM). Furthermore, a pulsed eddy current (PEC) approach was developed, combined with a sophisticated new fractal analysis algorithm based on short pulse excitation and evaluation of EC relaxation behavior. This paper presents concept, experimental realization, fractal analysis procedures, and results of this effort.

Schreiber, Jürgen; Cikalova, Ulana; Hillmann, Susanne; Meyendorf, Norbert; Hoffmann, Jochen

2013-01-01

425

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

426

Creep-Fatigue Life Prediction and Reliability Analysis of P91 Steel Based on Applied Mechanical Work Density  

NASA Astrophysics Data System (ADS)

A creep-fatigue (CF) life prediction model and its simplified expression were developed based on the applied mechanical work density (AMWD). The foundation of this model was an integration of N- S curve. Comparisons of the model predicted fatigue lifetimes with the experimental data of load-controlled CF tests on P91 base metal and welded metal at 848 K from the reference were made and apparently illustrated that the model predictions were in a good agreement with the experimental fatigue lifetimes. In addition, the curve of the numbers of cycles to failure versus AMWD at the associated probability was deduced. A reliability model was constructed by combining the curve and the simplified life prediction model.

Ji, D. M.; Shen, M.-H. H.; Wang, D. X.; Ren, J. X.

2015-01-01

427

Initial Assessment of the Effects of Nonmetallic Inclusions on Fatigue Life of Powder-Metallurgy-Processed Udimet(TM) 720  

NASA Technical Reports Server (NTRS)

The fatigue lives of modern powder metallurgy (PM) disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary due to the different steps of materials/component processing and machining. One of these variables, the presence of nonmetallic inclusions, has been shown to significantly degrade low-cycle fatigue (LCF) life. Nonmetallic inclusions are inherent defects in powder alloys that are a by-product of powder-processing techniques. Contamination of the powder can occur in the melt, during powder atomization, or during any of the various handling processes through consolidation. In modern nickel disk powder processing facilities, the levels of inclusion contamination have been reduced to less than 1 part per million by weight. Despite the efforts of manufacturers to ensure the cleanliness of their powder production processes, the presence of inclusions remains a source of great concern for the designer. the objective of this study was to investigate the effects on fatigue life of these inclusions. Since natural inclusions occur so infrequently, elevated levels of inclusions were carefully introduced in a nickel-based disk superalloy, Udimet 720 (registered trademark of Special Metals Corporation), produced using PM processing. Multiple strain-controlled fatigue tests were then performed on this material at 650 C. Analyses were performed to compare the LCF lives and failure initiation sites as functions of inclusion content and fatigue conditions. A large majority of the failures in specimens with introduced inclusions occurred at cracks initiating from inclusions at the specimen surface. The inclusions could reduce fatigue life by up to 100 times. These effects were found to be dependent on strain range and strain ratio. Tests at lower strain ranges and higher strain ratios produced larger effects of inclusions on life.

Gabb, T. P.; Telesman, J.; Kantzos, P. T.; Bonacuse, P. J.; Barrie, R. L.

2002-01-01

428

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

429

Fatigue life prediction for finite ratchetting of bellows at cryogenic temperatures  

SciTech Connect

The expansion bellows, used in the magnet interconnections of the Large Hadron Collider (LHC), are designed for severe service conditions (cryogenic temperatures, high internal pressure, large cyclic deflections). According to the results of the material research, a stainless steel of grade AISI 316 exhibits a high ductility at cryogenic temperatures. This results in the development of the plastic strain fields in the bellows wall, subjected to cyclic loadings, and to failure after a comparatively low number of cycles. In the present work the progressive deformation (ratchetting) of bellows subjected to a sustained load (internal pressure) and to a superimposed cyclic deflection programme at cryogenic temperatures is examined. In order to estimate the number of cycles to failure a generalized Manson-Coffin equation was developed. The model is based on two parameters: the ratchetting induced mean plastic strain and the plastic strain amplitude. The material model is based on the bilinear elastic-plastic response with kinematic hardening. The cyclic hardening and the evolution of the material model parameters (yield strength and hardening modulus) are accounted for. The finite element simulation of the initial 20 cycles leads to an estimation of the accumulated plastic strains and enables the calculation of the fatigue life of the bellows. An experimental stand for cryogenic fatigue tests is also presented and the first verification tests are reported.

Skoczen, B.; Kurtyka, T.; Brunet, J.C.; Poncet, A. [CERN, Geneve (Switzerland)

1997-06-01

430

Fatigue life calculation of desuperheater for solving pipe cracking issue using finite element method (FEM) software  

NASA Astrophysics Data System (ADS)

Desuperheater assembly experiences thermal cycling in operation by design. During power plant's start up, load change and shut down, thermal gradient is highest. Desuperheater should be able to handle rapid ramp up or ramp down of temperature in these operations. With "hump style" two nozzle desuperheater, cracks were appearing in the pipe after only few cycles of operation. From the field data, it was clear that desuperheater is not able to handle disproportionate thermal expansion happening in the assembly during temperature ramp up and ramp down in operation and leading to cracks appearing in the piping. Growth of thermal fatigue crack is influenced by several factors including geometry, severity of thermal stress and applied mechanical load. This paper seeks to determine cause of failure of two nozzle "hump style" desuperheater using Finite Element Method (FEM) simulation technique. Thermal stress simulation and fatigue life calculation were performed using commercial FEA software "ANSYS" [from Ansys Inc, USA]. Simulation result showed that very high thermal stress is developing in the region where cracks are seen in the field. From simulation results, it is also clear that variable thermal expansion of two nozzle studs is creating high stress at the water manifold junction. A simple and viable solution is suggested by increasing the length of the manifold which solved the cracking issues in the pipe.

Kumar, Aravinda; Singh, Jeetendra Kumar; Mohan, K.

2012-06-01

431

Simulated Bladed MMC Disk LCF Validation  

NASA Technical Reports Server (NTRS)

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

Merrick, H. F.; Costen, M.

1998-01-01

432

STRESS ANALYSIS OF HEAVY DUTY TRUCK CHASSIS AS A PRELIMINARY DATA FOR ITS FATIGUE LIFE PREDICTION USING FEM  

Microsoft Academic Search

This paper presents the stress analysis of heavy duty truck chassis. The stress analysis is important in fatigue study and life prediction of components to determine the critical point which has the highest stress. The analysis was done for a truck model by utilizing a commercial finite element packaged ABAQUS. The model has a length of 12.35 m and width

Roslan Abd Rahman; Mohd Nasir Tamin; Ojo Kurdi

2008-01-01

433

Sensitivity study on material properties for the fatigue life prediction of solder joints under cyclic thermal loading  

Microsoft Academic Search

A computational study is presented in this paper to investigate the effect of variation in material properties on the fatigue life prediction of solder joints subjected to cyclic thermal loading. The package under investigation was a plastic quad flat pack (PQFP) with gull-wing leads. A commercial finite element code, ABAQUS, was employed to perform a two-dimensional plane stress analysis. While

Shi-Wei Ricky Lee; Xiaowu Zhang

1998-01-01

434

A creep cavity growth model for creep-fatigue life prediction of a unidirectional W/Cu composite  

NASA Technical Reports Server (NTRS)

A microstructural model was developed to predict creep-fatigue life in a (0)(sub 4), 9 volume percent tungsten fiber-reinforced copper matrix composite at the temperature of 833 K. The mechanism of failure of the composite is assumed to be governed by the growth of quasi-equilibrium cavities in the copper matrix of the composite, based on the microscopically observed failure mechanisms. The methodology uses a cavity growth model developed for prediction of creep fracture. Instantaneous values of strain rate and stress in the copper matrix during fatigue cycles were calculated and incorporated in the model to predict cyclic life. The stress in the copper matrix was determined by use of a simple two-bar model for the fiber and matrix during cyclic loading. The model successfully predicted the composite creep-fatigue life under tension-tension cyclic loading through the use of this instantaneous matrix stress level. Inclusion of additional mechanisms such as cavity nucleation, grain boundary sliding, and the effect of fibers on matrix-stress level would result in more generalized predictions of creep-fatigue life.

Kim, Young-Suk; Verrilli, Michael J.; Halford, Gary R.

1992-01-01

435

Fatigue life prediction of regulating valves on the intermediate-pressure section of a 400 MW steam turbine  

Microsoft Academic Search

Fatigue life prediction of regulating valves on the intermediate-pressure (IP) section of steam turbine is presented in this paper. The transient temperature fields and stress fields of the valve body are calculated using finite element method, and the operating records of a 400MW steam turbine located in Hubei Province of China, is used as input, and all practical operating processes

Zhongbing Chen; Guoqing Li; Hui Zhang; Chuanyao Chen

2009-01-01

436

Stress and fatigue in sound engineers: the effect of broadcasting in a life show and shift work.  

PubMed

The aim was to study the time-of-day variations of cortisol, fatigue and sleep disturbances in sound engineers in relation to job task and shift work. The concentration of saliva cortisol and feeling of stress, sleepiness and fatigue were followed at three hour intervals in 21 sound engineers: 13 sound engineers, aged 45.1 +/- 7.3 years, broadcasting in a life show during fast forward rotating shifts and 8 sound engineers, aged 47.1 +/- 9.8 years, making records in a studio during fast rotating day shifts. Cortisol concentration was assessed in saliva with radioimmunological kits. The participants reported for stress symptoms during the shifts and filled sleep diary. The data were analyzed by tests of between-subjects effects (SPSS). A trend for higher cortisol was found with the group broadcasting in a life show. The sound engineers broadcasting in a life show reported higher scores of stress, sleepiness and fatigue, but no significant differences concerning the sleep disturbances between the groups were found. In conclusion our data show moderate level of stress and fatigue with the studied sound engineers, higher with the subjects broadcasting in a life show. The quality of sleep showed no significant differences between the studied groups, an indication that the sound engineers were able to tolerate the fast forward rotating shifts. PMID:18661812

Vangelova, Katia K

2008-06-01

437

Successful Solutions to SSME/AT Development Turbine Blade Distress  

NASA Technical Reports Server (NTRS)

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

Montgomery, Stuart K.

1999-01-01

438

Failure of a low pressure turbine rotor blade of an aeroengine  

Microsoft Academic Search

During a test run of an aeroengine, a low-pressure turbine rotor blade had failed. The turbine blades were made of Ni-base superalloy of CM 247 LC grade and fabricated by DS investment casting. The blades were coated with platinum aluminide. Investigation revealed that the blade had failed by fatigue. It was concluded that the coating on the blade had developed

S. K. Bhaumik; M. Sujata; M. A. Venkataswamy; M. A. Parameswara

2006-01-01

439

User`s guide for the frequency domain algorithms in the LIFE2 fatigue analysis code  

SciTech Connect

The LIFE2 computer code is a fatigue/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. However, many structural analysis techniques yield frequency-domain stress spectra and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the analysis of this class of data, a Fourier analysis is used to transform a frequency-domain spectrum to an equivalent time series suitable for rainflow counting by other modules in the code. This paper describes the algorithms incorporated into the code and their numerical implementation. Example problems are used to illustrate typical inputs and outputs.

Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States); Linker, R.L. [New Mexico Engineering Research Inst., Albuquerque, NM (United States)

1993-10-01

440