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1

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

2

Fatigue Life Analysis of Small Composite Sandwich Wind Tuebine Blades  

Microsoft Academic Search

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

J. H. Wu; F. M. Lai

2011-01-01

3

Fatigue life estimation procedure for a turbine blade under transient loads  

Microsoft Academic Search

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

N. S. Vyas; J. S. Rao

1994-01-01

4

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

Microsoft Academic Search

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

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

2007-01-01

5

Fatigue life estimation procedure for a turbine blade under transient loads  

SciTech Connect

Fatigue analysis and consequent life prediction of turbomachine blading requires the stress load history of the blade. A blade designed for safe operation at particular constant rotor speeds may, however, incur damaging stresses during start-up and shut-down operations. During such operations the blade experiences momentary resonant stresses while passing through the criticals, which may lie in the speed range through which the rotor is accelerated. Fatigue due to these transient influences may accumulate to lead to failure. In this paper a technique for fatigue damage assessment during variable-speed operations is presented. Transient resonant stresses for a blade with nonlinear damping have been determined using a numerical procedure. A fatigue damage assessment procedure is described. The fatigue failure surface is generated on the S-N-mean stress axes and Miner's Rule is employed to estimate the accumulation of fatigue.

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

1994-01-01

6

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

Microsoft Academic Search

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

R. P. L. Nijssen

2006-01-01

7

Blade fatigue life assessment with application to VAWTs  

Microsoft Academic Search

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

P. S. Veers

1982-01-01

8

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

9

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

Microsoft Academic Search

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

Lijie Chen; Yinghua Liu; Liyang Xie

2007-01-01

10

Structural fatigue test results for large wind turbine blade sections  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

11

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

E-print Network

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

12

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

Microsoft Academic Search

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

C. Kong; J. Bang; Y. Sugiyama

2005-01-01

13

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

14

Stress analysis and life prediction of gas turbine blade  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

15

Prediction of the Crack Initiation Life of Turbine Blade  

Microsoft Academic Search

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

Sharadchandra D. Jog; Rajeshwar. Baddam

16

Fatigue of fiberglass wind turbine blade materials  

NASA Astrophysics Data System (ADS)

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

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

1992-08-01

17

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

18

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

19

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

SciTech Connect

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

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

1996-10-01

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

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

Microsoft Academic Search

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

Ying Pan; Burkhard Bischoff-Beiermann; Thomas Schulenberg

1999-01-01

22

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

23

Selection of Wind Turbine Blade Materials for Fatigue Resistance  

E-print Network

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

24

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

25

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

26

Fatigue Failure Analysis of Small Wooden Wind Turbine Blade  

E-print Network

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

Maldhure S. S; Dr. Kharde Y. R

27

Simulation of fatigue failure in composite axial compressor blades  

Microsoft Academic Search

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

Qubo Li; Janusz Piechna; Norbert Müeller

2011-01-01

28

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

29

Sparkr Blade Test Centre Static tests of wind turbine blades  

E-print Network

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

30

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

31

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

32

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

33

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

E-print Network

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

34

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

35

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

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

36

A probabilistic methodology for fatigue life prediction  

Microsoft Academic Search

This paper describes efforts in the probabilistic modelling of fatigue. The methodology proposed deals with crack nucleation from surface defects within a fracture mechanics framework. The methodology provides a quantitative understanding of the effects of bulk defects and their size distribution on the variation of fatigue life. It also considers the contributions of the variations of fatigue crack nucleation life

J. Luo; P. Bowen

2003-01-01

37

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

38

Improved fatigue life for moorings  

NASA Astrophysics Data System (ADS)

Moorings are ubiquitous in man's useful occupation of the ocean. They are used to secure instruments and other unattended apparatus for scientific, civil and military uses and to fix the location for various lengths of time of manned platforms for mineral and hydrocarbon extraction and for marine transportation and ocean construction applications. Subject to wave and current loads, vibration from eddy shedding, and a hostile chemical environment, moorings fatigue and eventually fail if not replaced in time. The research is directed toward significantly improving the reliability and the service life of ocean mooring systems by developing the use of nonconventional materials (particularly advanced composites) and constructions. The work will extend previous and present research by the investigators in highly related areas. Subscale mooring elements (lines, terminations, and flexures) will be tested for fatigue resistance in a seawater environment in the laboratory. The overall project objective is to make substantial improvements in the service life and reliability of ocean moorings by using materials and constructions that are significantly less sensitive to fatigue and stress corrosion than conventional components.

Seymour, R. J.; Massey, S. A.

1992-12-01

39

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

40

The lead crack fatigue lifing framework  

Microsoft Academic Search

A fatigue lifing framework using a lead crack concept has been developed by the DSTO for metallic primary airframe components. The framework is based on years of detailed inspection and analysis of fatigue cracks in many specimens and airframe components, and is an important additional tool for determining aircraft component fatigue lives in the Royal Australian Air Force (RAAF) fleet.

L. Molent; S. A. Barter; R. J. H. Wanhill

2011-01-01

41

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

42

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

43

Fatigue life prediction in bending from axial fatigue information  

NASA Technical Reports Server (NTRS)

Bending fatigue in the low cyclic life range differs from axial fatigue due to the plastic flow which alters the linear stress-strain relation normally used to determine the nominal stresses. An approach is presented to take into account the plastic flow in calculating nominal bending stress (S sub bending) based on true surface stress. These functions are derived in closed form for rectangular and circular cross sections. The nominal bending stress and the axial fatigue stress are plotted as a function of life (N sub S) and these curves are shown for several materials of engineering interest.

Manson, S. S.; Muralidharan, U.

1982-01-01

44

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

PubMed Central

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

Witos, Miroslaw

2013-01-01

45

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

Microsoft Academic Search

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

Darris L. White

2003-01-01

46

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

47

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

48

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

49

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

50

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

Microsoft Academic Search

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

A. A. Tenhave

1992-01-01

51

FATIGUE LIFE OF BOLT SUBJECTED TO FATIGUE LOADING CONDITIONS  

Microsoft Academic Search

With the aim to create awareness amongst designers and to establish database on fatigue life of bolt, this experimental study was conducted. Two sizes of High Strength Friction Grip (HSGF) bolt were chosen and they were subjected to low and high cycle constant amplitude loading condition. Each of them undergone 4 different stress ranges and at 3 means stress level.

K. Din; M. T. H. Ghazali

52

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

E-print Network

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

53

Estimating Fatigue Life of Bridge Components Using Measured Strains  

Microsoft Academic Search

The design fatigue life of a bridge component is based on the stress spectrum the component experiences and the fatigue durability. Changes in traffic patterns, volume, and any degradation of structural components can influence the fatigue life of the bridge. A fatigue life evaluation reflecting the actual conditions has value to bridge owners. Procedures are outlined in the AASHTO Guide

Sreenivas Alampalli

2006-01-01

54

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

NASA Astrophysics Data System (ADS)

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

Birkbeck, Janine C.

55

A real time neural net estimator of fatigue life  

NASA Technical Reports Server (NTRS)

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

Troudet, T.; Merrill, W.

1990-01-01

56

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

57

Considerations concerning fatigue life of metal matrix composites  

Microsoft Academic Search

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

V. M. Radhakrishnan; Paul A. Bartolotta

1993-01-01

58

Deformation and fatigue behavior of SSME turbopump blade materials  

NASA Technical Reports Server (NTRS)

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

Milligan, Walter W.; Antolovich, Stephen D.

1987-01-01

59

Fatigue life evaluation for reactor pressure vessels  

SciTech Connect

In terms of plant safety, the reactor pressure vessel is one of the most critical pressure boundary components in the nuclear power plant. The primary degradation mechanisms for reactor pressure vessels are irradiation embrittlement and thermal fatigue. The effects of irradiation and fatigue damage should then be considered in determining the overall lifetime of the reactor pressure vessel. For the radiation damage, related issues have been studied. For the case of fatigue resulting from the pressure and temperature changes, however, relatively less attention has been paid. The fatigue damage is generally regarded as one of the limiting factors for the safe operation life of the reactor pressure vessel. In this paper, the simplified fatigue damage evaluation procedures are applied to the commercially operating reactor vessel which is currently subjected to plant lifetime management study. Specifically, fatigue lifetime evaluation procedures for RPV inlet/outlet nozzles, shell and studs are therefore investigated based on the design basis approaches and the evaluation results are presented based on the assumed operating transient occurrences.

Roh, H.Y.; Jin, T.E. [Korea Power Engineering Co., Inc., Seoul (Korea, Republic of). Power Engineering Research Inst.; Jeong, I.S.; Hong, S.Y. [Korea Electric Power Research Inst., Daejon (Korea, Republic of). Nuclear Div.

1996-12-31

60

Probability distribution of fatigue life controlled by defects  

Microsoft Academic Search

An equation is derived for determining the cumulative probability distribution of fatigue life controlled by the defects in the material, and a method is proposed to determine the most deleterious to the fatigue life group of defects. The equation avoids some serious drawbacks of the classical approach to determine the fatigue life distribution, which are revealed on the basis of

M. T. Todinov

2001-01-01

61

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

62

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

63

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

NASA Technical Reports Server (NTRS)

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

Liu, H. W.

1988-01-01

64

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

65

Die fatigue life design and assessment via CAE simulation  

Microsoft Academic Search

In die design process, the design and prediction of die fatigue life is a non-trivial issue. Many factors in die life cycle\\u000a from design, fabrication to service all affect die life. The die life in cold forging processes is basically determined by\\u000a die fatigue failure. The design and assessment of die fatigue life needs to consider all the affecting factors

M. W. Fu; M. S. Yong; T. Muramatsu

2008-01-01

66

Fatigue mediates the effects of exercise on quality of life  

Microsoft Academic Search

Purpose: Fatigue is a common side effect of cancer treatment that impacts quality of life. Exercise is one approach suggested to improve fatigue. The purpose of this study was to explore the relationship of exercise to fatigue and quality of life. Methods: Thirty-one subjects with breast cancer were enrolled prior to beginning chemotherapy and 27 completed the study. All baseline

Anna L. Schwartz

1999-01-01

67

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

68

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

69

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

70

Tension fatigue analysis and life prediction for composite laminates  

NASA Technical Reports Server (NTRS)

A methodology is presented for the tension fatigue analysis and life prediction of composite laminates subjected to tension fatigue loading. The methodology incorporates both the generic fracture mechanics characterization of delamination and the assessment of the infuence of damage on laminate fatigue life. Tension fatigue tests were conducted on quasi-isotropic and orthotropic glass epoxy, graphite epoxy, and glass/graphite epoxy hybrid laminates, demonstrating good agreement between measured and predicted lives.

O'Brien, T. K.; Rigamonti, M.; Zanotti, C.

1989-01-01

71

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

72

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

73

Fatigue life of silicon nitride balls  

SciTech Connect

Because its specific weight is 40 percent that of steel, silicon nitride has been considered as a rolling element material in very high speed ball and roller bearings. Furthermore, similar to steel components, hot pressed silicon nitride rolling components, when properly manufactured, have demonstrated the capacity to fail in a non-catastrophic manner, i.e., fatigue of the rolling contact surfaces. In this investigation, hot isostatically-pressed silicon nitride balls were endurance-tested using a NASA 5-ball rig and the results were compared against similarly tested VIMVAR M50 balls. The silicon nitride balls demonstrated fatigue lives many times those obtained for the M50 balls. Therefore it is concluded that silicon nitride can be effectively employed in applications where steel rolling element life has previously proved to be a limiting factor. 12 refs.

Galbato, A.T.; Cundill, R.T.; Harris, T.A. (MRC Bearings, Jamestown, NY (United States) SKF Engineering and Research Center, Nieuwegein (Netherlands) Pennsylvania State Univ., University Park (United States))

1992-11-01

74

Research on compiling fatigue load spectrum of individual aircraft and analysis of fatigue life based on flight data  

Microsoft Academic Search

Compiling fatigue load spectrum is the precondition and basement of fatigue life prediction, simulation experiments and fatigue strength analysis of aircraft. The method of air fleet life is used on management of homotype aircraft life for a long term, that is the process of achievement on safe life index by fatigue experiment of aircraft overall dimension on condition of standard

Yan Li; Zhao Wang; YueLiang Chen; Yong Zhang; WengSheng Sun

2012-01-01

75

Gas turbine blade service life assessment with account of fracture stage  

Microsoft Academic Search

The numerical simulation of creep, continuum fracture zone evolution and crack propagation in a gas turbine blade uner cyclic\\u000a loading conditions have been performed using a semianalytic finite-element method. The blade basic life (before fracture zone\\u000a appearance) and additional resource (concerned with fracture process) of a blade have been determined.

V. A. Bazhenov; A. I. Gulyar; S. O. Piskunov; A. A. Shkryl’

2008-01-01

76

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

77

Fatigue Life Methodology for Bonded Composite Skin\\/Stringer Configurations  

Microsoft Academic Search

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.

Ronald Krueger; Isabelle L. Paris; T. Kevin O'Brien; Pierre J. Minguet

2000-01-01

78

Oxidation and low cycle fatigue life prediction  

NASA Technical Reports Server (NTRS)

When a metallic material is exposed to a high temperature in an ambient atmosphere, oxidation takes place on the metallic surface. The formed oxides (both surface and grain boundary oxides) are mechanically brittle so that if the stress is high enough the oxides will be cracked. The grain boundary oxide formation in TAZ-8A nickel-base superalloy was studied. The effect of oxide crack nucleus on low cycle fatigue life will be analyzed. The TAZ-8A was subjected to high temperature oxidation tests in air under the stress-free condition. The oxidation temperatures were 600, 800, and 1000 C. The oxidation time varies from 10 to 1000 hours.

Oshida, Y.; Liu, H. W.

1984-01-01

79

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

80

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

81

Fatigue criterion to system design, life and reliability  

NASA Technical Reports Server (NTRS)

A generalized methodology to structural life prediction, design, and reliability based upon a fatigue criterion is advanced. The life prediction methodology is based in part on work of Weibull and Lundberg and Palmgren. The approach incorporates the computed life of elemental stress volumes of a complex machine element to predict system life. The results of coupon fatigue testing can be incorporated into the analysis allowing for life prediction and component or structural renewal rates with reasonable statistical certainty.

Zaretsky, E. V.

1985-01-01

82

Fatigue criterion to system design, life and reliability  

NASA Technical Reports Server (NTRS)

A generalized methodology to structural life prediction, design, and reliability based upon a fatigue criterion is advanced. The life prediction methodology is based in part on work of W. Weibull and G. Lundberg and A. Palmgren. The approach incorporates the computed life of elemental stress volumes of a complex machine element to predict system life. The results of coupon fatigue testing can be incorporated into the analysis allowing for life prediction and component or structural renewal rates with reasonable statistical certainty.

Zaretsky, E. V.

1985-01-01

83

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

84

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

E-print Network

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

Victoria, University of

85

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-19, 2004 ISSN: 1547-1977 * Speaker 1 #12;2 Analysis of Fatigue Life Under Complex Loading: Revisiting

Fatemi, Ali

86

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

SciTech Connect

The National Renewable Energy Laboratory (NREL) recently developed a new hybrid fatigue testing system called the Blade Resonance Excitation (B-REX) test system. The new system uses 65% less energy to test large wind turbine blades in half the time of NREL's dual-axis forced-displacement test method with lower equipment and operating costs. The B-REX is a dual-axis test system that combines resonance excitation with forced hydraulic loading to reduce the total test time required while representing the operating strains on the critical inboard blade stations more accurately than a single-axis test system. The analysis and testing required to fully implement the B-REX was significant. To control unanticipated blade motion and vibrations caused by dynamic coupling between the flap, lead-lag, and torsional directions, we needed to incorporate additional test hardware and control software. We evaluated the B-REX test system under stable operating conditions using a combination of various sensors. We then compared our results with results from the same blade, tested previously using NREL's dual-axis forced-displacement test method. Experimental results indicate that strain levels produced by the B-REX system accurately replicated the forced-displacement method. This paper describes the challenges we encountered while developing the new blade fatigue test system and the experimental results that validate its accuracy.

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

2004-12-01

87

Fatigue life of metals under cyclic loading in vacuum  

NASA Technical Reports Server (NTRS)

The effect of vacuum on the cyclic strength of metals is examined. Experimental data are presented of studies to clarify the mechanism of vacuum influence on fatigue failure. The dependence of copper and armco-iron fatigue life on vacuum level is studied. It is found that the presence of saturation on the curve of fatigue life versus vacuum level is common for the materials studied. The effect of vacuum on fatigue fracture of copper is studied over a wide range of deformations. It is shown that fatigue life increase under vacuum conditions and the observed characteristics of the fatigue fracture itself in vacuum are associated with homogenization of the plastic deformation under these conditions.

Verkin, B. I.; Lyubarskiy, I. M.; Boychuk, V. M.; Grinberg, N. M.; Alekseyev, A. I.

1974-01-01

88

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

89

How surface damage removal affects fatigue life  

NASA Technical Reports Server (NTRS)

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

Jeelani, S.; Scott, M. A.

1988-01-01

90

Development of a fatigue-life methodology for composite structures subjected to out-of-plane load components  

NASA Technical Reports Server (NTRS)

The efforts to identify and implement a fatigue life methodology applicable to demonstrate delamination failures for use in certifying composite rotor blades are presented. The RSRA/X-Wing vehicle was a proof-of-concept stopped rotor aircraft configuration which used rotor blades primarily constructed of laminated carbon fiber. Delamination of the main spar during ground testing demonstrated that significant interlaminar stresses were produced. Analysis confirmed the presence of out-of-plane load components. The wear out (residual strength) methodology and the requirements for its implementation are discussed.

Sumich, Mark; Kedward, Keith T.

1991-01-01

91

Predicting the fatigue life of asphalt concrete overlay systems  

E-print Network

for reviewing this thesis, their suggestions and advice throughout the research, and for being on my comnittee. TABLE OF CONTENTS CHAPTER I - INTRODUCTION . CHAPTER I I ? FRACTURE MECHANICS CHAPTER III - FATIGUE CRACK GROWTH CHAPTER IV ? SCHAPERY'5 THEORY... of fracture mechanics and their role in predicting the fatigue life of materials will be presented. Schapery's theory will then be presented and a review of previous research done to design asphalt mixes resistant to fatigue failure and cracking along...

Germann, Frederick P

2012-06-07

92

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

93

Nondestructive characterization of corrosion damage and fatigue life  

NASA Astrophysics Data System (ADS)

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

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

1999-01-01

94

Silicon nitride hybrid bearing fatigue life comparisons. Technical report  

Microsoft Academic Search

Research to improve high-speed ball bearings for spacecraft applications has led to development of ceramic materials for bearing components, and the need to acquire sufficient fatigue life data to show the merits of various ceramic materials and fabrication processes, in comparison with the vast amount of steel bearing fatigue data acquired over many decades. In order to eliminate bias from

1999-01-01

95

Life extension of components with high cumulative fatigue usage  

Microsoft Academic Search

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

Server

1985-01-01

96

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

97

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

98

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

99

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

100

Probabilistic fatigue life prediction of metallic and composite materials  

NASA Astrophysics Data System (ADS)

Fatigue is one of the most common failure modes for engineering structures, such as aircrafts, rotorcrafts and aviation transports. Both metallic materials and composite materials are widely used and affected by fatigue damage. Huge uncertainties arise from material properties, measurement noise, imperfect models, future anticipated loads and environmental conditions. These uncertainties are critical issues for accurate remaining useful life (RUL) prediction for engineering structures in service. Probabilistic fatigue prognosis considering various uncertainties is of great importance for structural safety. The objective of this study is to develop probabilistic fatigue life prediction models for metallic materials and composite materials. A fatigue model based on crack growth analysis and equivalent initial flaw size concept is proposed for metallic materials. Following this, the developed model is extended to include structural geometry effects (notch effect), environmental effects (corroded specimens) and manufacturing effects (shot peening effects). Due to the inhomogeneity and anisotropy, the fatigue model suitable for metallic materials cannot be directly applied to composite materials. A composite fatigue model life prediction is proposed based on a mixed-mode delamination growth model and a stiffness degradation law. After the development of deterministic fatigue models of metallic and composite materials, a general probabilistic life prediction methodology is developed. The proposed methodology combines an efficient Inverse First-Order Reliability Method (IFORM) for the uncertainty propogation in fatigue life prediction. An equivalent stresstransformation has been developed to enhance the computational efficiency under realistic random amplitude loading. A systematical reliability-based maintenance optimization framework is proposed for fatigue risk management and mitigation of engineering structures.

Xiang, Yibing

101

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

102

High Temperature Fatigue; Dwell Sensitivity and Life Prediction.  

National Technical Information Service (NTIS)

The objectives of this research were to develop knowledge to address dwell sensitivity behavior of high temperature materials and to predict dwell sensitivity and creep-fatigue life. The damage mechanisms resulting from various dwell cycles were summarize...

T. Goswami

1999-01-01

103

PROBABILISTIC FATIGUE LIFE EVALUATION OF COMPOSITE STRUCTURES  

Microsoft Academic Search

Methods and corresponding computer codes are discussed for probabilistically evaluating composite structural fracture under cyclic fatigue. The progressive fracture of a composite structure under cyclic fatigue is simulated via an innovative approach independent of stress intensity factors and fracture toughness parameters. A computer code is utilized for the simulation of composite structural damage and fracture. Structural degradation response is assessed

Levon Minnetyan; Dade Huang; Christos C. Chamis

2002-01-01

104

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

105

Light scattering diagnostics for metal fatigue detection and life estimation  

NASA Astrophysics Data System (ADS)

Metal components subjected to cyclic stress develop surface-evident defects (microcracks, slip bands, etc). Monitoring the formation and evolution of these fatigue damage precursors (FDPs) with increasing numbers of cycles can be an effective tool for determining the fatigue state of the component, which can be used in remaining fatigue life prognostics. In this paper a laser scanning technique for FDP detection is described and experimental results from examination of specimens of several metal types are presented. This technique is based on scanning a focused laser beam over the specimen surface and detecting variations in the characteristics of the scattered light signal. These variations can indicate the presence of surface abnormalities and therefore can be associated with fatigue damage formation. Particular patterns of spatial, angular, and optical characteristics can be used to identify and discriminate many types of FDP, which can provide a means to enhance the accuracy of surface defect frequency estimates and to eliminate the false counts that typically occur on surfaces in uncontrolled environments. Experiments during fatigue testing in the laboratory have shown that the technique can produce a defect frequency estimate that relates well to remaining fatigue life, but previous experiments showed large "plateau" regions, in which the slow defect frequency change made life estimation difficult. New data collection and analysis techniques have therefore been developed, and new experiments have been performed to test the ability of this modified approach to improve the utility of defect frequency measurements over the whole of fatigue life.

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

2005-08-01

106

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

107

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

108

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

109

Spectrum fatigue data in comparison to design curves in the long life regime  

Microsoft Academic Search

Spectrum fatigue tests in welded steel box beam specimens were run at stress levels giving high cycle fatigue lifes. The test results and current fatigue design codes were compared. The results showed that the codes give unconservative estimations of fatigue lifes by a factor of approximately 4. The same unconservative life estimation was also shown by using a simple fracture

Tormod Dahle; Bertil Larsson

1992-01-01

110

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

111

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

112

Study on creep-fatigue life prediction using simple high temperature low cycle fatigue testing machines  

NASA Astrophysics Data System (ADS)

A simple high temperature low cycle fatigue testing machine for long time creep fatigue tests was developed and experiments on two kinds of CrMoV steel forgings and 304 stainless steel were carried out. The experimental results indicate: (1) the data obtained by long hold time tests deviate remarkably from the linear damage fraction rule. (2) Creep rupture ductility seems to be one of important factors for creep fatigue life after long time. (3) In the case of materials the creep rupture ductility makes a remarkable change with time.

Endo, T.; Sakon, T.

1983-05-01

113

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

Microsoft Academic Search

A cursory analysis of the stress history of wind turbine blades indicates that a single stress level at each wind speed does not adequately describe the blade stress history. A statistical description is required. Blade stress data collected from the DOE\\/ALCOA Low Cost experimental turbines indicate that the Rayleigh probability density function adequately describes the distribution of vibratory stresses at

Veers

1981-01-01

114

Physical fitness, fatigue, and quality of life after liver transplantation  

Microsoft Academic Search

Fatigue is often experienced after liver transplantation. The aims of this cross-sectional study were to assess physical fitness\\u000a (cardiorespiratory fitness, neuromuscular fitness, body composition) in liver transplant recipients and to explore whether\\u000a physical fitness is related to severity of fatigue. In addition, we explored the relationship between physical fitness and\\u000a health-related quality of life. Included were 18 patients 1–5 years after

Berbke T. J. van Ginneken; Rita J. G. van den Berg-Emons; Geert Kazemier; Herold J. Metselaar; Hugo W. Tilanus; Henk J. Stam

2007-01-01

115

Reliability-based reassessment of corrosion fatigue life  

Microsoft Academic Search

A reliability-based evaluation approach for pitting corrosion fatigue damage which combines analytical estimation and nondestructive inspection is developed in this paper. First, a mechanics-based probabilistic life model for the corrosion fatigue on the surface of a lap sheet is established and then a reassessment approach is developed after in-service inspection. The reliability of the NDI technique is quantified through a

Ruoxue Zhang; Sankaran Mahadevan

2001-01-01

116

Fatigue life analysis and experimental verification of coronary stent  

Microsoft Academic Search

A computational and experimental method on biomechanics of stent is presented to analyze the stress distribution of different\\u000a phases and evaluate the fatigue life according to Goodman criteria. As a result, the maximum stress and alternating stress\\u000a were always located at the curvature area of rings, the fatigue bands in the experiment also verified the computation rationality.\\u000a Matching between the

Jianjun Li; Qiyi Luo; Zhiyong Xie; Yu Li; Yanjun Zeng

2010-01-01

117

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

118

Fatigue life of silicon nitride balls  

Microsoft Academic Search

Because its specific weight is 40 percent that of steel, silicon nitride has been considered as a rolling element material in very high speed ball and roller bearings. Furthermore, similar to steel components, hot pressed silicon nitride rolling components, when properly manufactured, have demonstrated the capacity to fail in a non-catastrophic manner, i.e., fatigue of the rolling contact surfaces. In

A. T. Galbato; R. T. Cundill; T. A. Harris

1992-01-01

119

Effects of initial cracks and firing environment on cannon fatigue life  

Microsoft Academic Search

A case-study description is given of laboratory fatigue life tests of a US Army 155 mm inner diameter cannon tube, performed in the early 1990s. Measured fatigue lives and results from stress and fracture mechanics analyses are used to determine the effects of service conditions on the safe fatigue life of the cannon tube. Fatigue failure in the laboratory tests

J. H. Underwood; M. J. Audino

1999-01-01

120

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

121

Prediction of residual fatigue life from NDE of corroded components  

NASA Astrophysics Data System (ADS)

A study was performed to determine how effectively the structural integrity of corroded aircraft components may be predicted from nondestructive evaluation (NDE) of test specimens. Al 2024 specimens were corroded under a wide range of conditions to achieve a range of corrosion morphologies, including a mix of pitting, intergranular, and general corrosion. The specimens were then examined using ultrasonic testing (UT), white light interference microscopy (WLIM), and microradiography to quantify the corrosion damage level and provide inputs to a life prediction model. Image analysis was used to extract metrics to describe the damage state. Finally, the corroded specimens were fatigued to failure. The resulting data was used to obtain a correlation between the NDE metrics and the residual fatigue life. This was accomplished by both multiple linear regression (MLR) and artificial neural networks (ANNs). A good correlation was achieved by MLR. ANNs also fit the experimental data well, with a slightly lower mean square error. However, for the more heavily damaged specimens, the ANN systematically over-predicted the residual life. Both the MLR model and the ANN model indicate a similar dependence of the fatigue life on the NDE metrics. While there are several important metrics that can be extracted from UT and WLIM, the correlation with microradiography metrics was weak. The focus of this work is to provide an empirical methodology for quantifying the effects of corrosion damage on fatigue life in situations where deterministic or analytical approaches, such as those based on linear elastic fracture mechanics are not well suited.

Shell, Eric Brian

122

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

E-print Network

The fatigue life of a Steel Catenary Riser (SCR) near its touch-down zone is substantially affected by its interaction with the seabed. Hence, accurate estimate of its fatigue life requires the understanding and realistic modeling of the interaction...

Nakhaee, Ali

2011-02-22

123

Cyclic rate-dependent fatigue life in reactor water  

SciTech Connect

The study of crack growth rates in mildly aggressive environments such as reactor water clearly demonstrates an important sensitivity to crack tip strain rate during the tensile portion of cyclic loadings. Moreover, the effects of strain rate interact directly with mean stress influences in such environments. Current safe-life analysis methods are based on fatigue data obtained in air and do not address strain rate sensitivity issues. In the present work strain rate sensitivities are quantified and used with environmental crack growth rate data to produce theoretical S-N fatigue data which explicitly include mean stress and strain rate (or cyclic rate) effects on crack growth rates in reactor water. Results are presented for several cases of loading rise time and mean stress level. Some combinations of these variables are observed to significantly reduce S-N fatigue life relative to that for air environments, while other combinations do not.

O`Donnell, T.P.; O`Donnell, W.J. [O`Donnell Consulting Engineers, Pittsburgh, PA (United States)

1995-12-31

124

Surface Fatigue Life of Contour Induction Hardened AISI 1552 Gears.  

National Technical Information Service (NTIS)

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 ...

D. P. Townsend, A. Turza, M. Chaplin

1995-01-01

125

Torsional fatigue life prediction method for DRAM module  

Microsoft Academic Search

In this study, shear strain controlled torsional test method was developed for torsional fatigue life prediction of DRAM module. The maximum principal strain and its direction was measured using rosette gage during module inserting user environment, and it was verified that shear strain was the dominant driving factor for solder joint failure. Apart from other studies where torsional tests were

Yeo Hoon Yoon; Yong ho Ko; Ho jung Moon; Se Young Yang

2007-01-01

126

Effect of Interference Fits on Roller Bearing Fatigue Life  

Microsoft Academic Search

An analysis was performed to determine the effects of inner-ring speed and press fits on roller bearing fatigue life. 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 and load, and were applied to a conventional roller

Harold H. Coe; Erwin V. Zaretsky

1987-01-01

127

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

128

Cold expansion and interference for extending the fatigue life of multi-layer metal joints  

Microsoft Academic Search

The influences of both hole cold expansion and interference-fit fasteners for extending the fatigue life of multilayer aluminum alloy joint specimens under variable amplitude loading have been examined experimentally. Improvements in fatigue life were markedly dependent on the degree of load transfer in the specimen joint. The cold expansion of fastener holes enhanced fatigue life in low load transfer joints

J. M. Finney

1993-01-01

129

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

130

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

131

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

132

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

Microsoft Academic Search

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

Paul S. Prevéy; N. Jayaraman; Michael Shepard

2007-01-01

133

The effect of tensile strength on the fatigue life of spot-welded sheet steels  

SciTech Connect

Tensile-shear spot-weld specimens were tested to determine the effect of base-metal tensile properties on fatigue life. Four sheet thicknesses (t) were investigated. Base-metal yield strength ranged between 186 and 757 MPa (27 and 110 ksi). Results showed that fatigue life was independent of base-metal strength for lives greater than 10/sup 4/ cycles. At shorter lives, fatigue performance improved with increasing base-metal strength. For a given cyclic load range, fatigue life increased at all lives with increasing sheet thickness. (t). Fatigue results from both this and a previous study were used to develop a spot-weld fatigue design curve.

Davidson, J.A.; Imhof, E.J. Jr.

1984-01-01

134

A simulation of corrosion fatigue life distribution in low alloy steel  

NASA Astrophysics Data System (ADS)

A Monte Carlo simulation of corrosion fatigue life distributions was conducted in a low alloy steel, SNCM439, by assuming that the scatter of fatigue life resulted from the variation in the growth characteristics of corrosion pits and fatigue cracks. The parameters used in the simulation were obtained experimentally. The results showed that the experimental distributions were expressed satisfactorily by the simulation in which the parameters obtained from fatigue tests at the same stress were used. Therefore, it is concluded that corrosion fatigue life distribution can be predicted by a Monte Carlo simulation taking account of the statistical properties in the growth processes of corrosion pits and fatigue cracks.

Nakajima, Masaki; Kunieda, Hisashi; Tokaji, Keiro

1992-07-01

135

Tension fatigue analysis and life prediction for composite laminates  

NASA Technical Reports Server (NTRS)

A tension fatigue life prediction methodology for composite laminates is presented. Tension fatigue tests were conducted on quasi-isotropic and orthotropic glass epoxy, graphite epoxy, and glass/graphite epoxy hybrid laminates. Edge delamination onset data were used to generate plots of strain energy release rate as a function of cycles to delamination onset. These plots were then used along with strain energy release rate analyses of delaminations initiating at matrix cracks to predict local delamination onset. Stiffness loss was measured experimentally to account for the accumulation of matrix cracks and for delamination growth. Fatigue failure was predicted by comparing the increase in global strain resulting from stiffness loss to the decrease in laminate failure strain resulting from delaminations forming at matrix cracks through the laminate thickness. Good agreement between measured and predicted lives indicated that the through-thickness damage accumulation model can accurately describe fatigue failure for laminates where the delamination onset behavior in fatigue is well characterized, and stiffness loss can be monitored in real time to account for damage growth.

Obrien, T. K.; Rigamonti, M.; Zanotti, C.

1988-01-01

136

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

137

Test evaluation of a laminated wood wind turbine blade concept  

NASA Technical Reports Server (NTRS)

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

Faddoul, J. R.

1981-01-01

138

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

139

Robust optimization of the Life of turbine blades an automated approach  

E-print Network

. OPTIONS, OptionsMatlab and OptionsNSGA2_RSM are optimization packages developed in Southampton with provenRobust optimization of the Life of turbine blades ­ an automated approach UTC for Computational-objective CAD and optimization based robust design tools that allow for uncertainties in the manufacturing

Sóbester, András

140

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

141

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

Microsoft Academic Search

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

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

1987-01-01

142

Storage tank design and fatigue life  

Microsoft Academic Search

High-viscosity hydrocarbons sometimes require heating to 500 F to be discharged from storage tanks. To give minimum guidance for temperature ranges for certain grades of steels, American Petroleum Institute Standard 650, Appendix M, considers yield strength reduction to increase shell thicknesses and elastic modulus reduction to increase the effective maximum alternating stress amplitude and lower the cycle life. But guidelines

1982-01-01

143

Effect of magnetic treatment on fatigue life of AISI 4140 steel  

Microsoft Academic Search

The effect of magnetic field with different intensities on fatigue life of AISI 4140 steel has been investigated. For this purpose, unnotched and notched specimens were prepared from AISI 4140 steel. It was obtained that when the magnetic field especially was applied to the specimens at the stage of fatigue crack initiation, the fatigue life improved by reason of delaying

Ayhan Çelik; A. Fatih Yetim; Akgün Alsaran; Mehmet Karakan

2005-01-01

144

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

E-print Network

of premature failure. Cyclic fatigue failure is particularly important as the heart beats, and henceBiomaterials 27 (2006) 1988­2000 Fatigue and life prediction for cobalt-chromium stents: A fracture.e., if a fatigue life of 108 cycles is required, testing is performed to ascertain whether the device will survive

Ritchie, Robert

145

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

E-print Network

Modeling cyclic ratcheting based fatigue life of HSLA steels using crystal plasticity FEM; Cyclic ratcheting; Nucleation cycles; Total fatigue life 1. Introduction High strength low alloy (HSLA, the understanding of cyclic deformation and fatigue behavior of HSLA steels is of high technological relevance

Ghosh, Somnath

146

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

E-print Network

Life extension of self-healing polymers with rapidly growing fatigue cracks A. S. Jones1,*, J. D embedded in the polymer matrix, are capable of responding to propagating fatigue cracks by autonomic growth. The amount of fatigue-life extension depends on the relative magnitude of the mechanical kinetics

Sottos, Nancy R.

147

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

E-print Network

Fatigue-Life Computational Analysis for the Self-Expanding Endovascular Nitinol Stents M. Grujicic to the fatigue-induced damage since over its expected ten-year life span, the stent will normally experience 370 and fluid-structure interaction finite element computational methods are combined with the advanced fatigue

Grujicic, Mica

148

MODELING OF THE FATIGUE LIFE OF ADHESIVELY-BONDED FRP JOINTS WITH GENETIC  

E-print Network

MODELING OF THE FATIGUE LIFE OF ADHESIVELY- BONDED FRP JOINTS WITH GENETIC PROGRAMMING Anastasios P life of adhesively-bonded FRP joints subjected to tensile fatigue loading under different environmental INTRODUCTION The effect of the environment on the fatigue behavior of adhesively-bonded joints has formed

Fernandez, Thomas

149

Influence of surface roughness skewness on rolling contact fatigue life  

NASA Astrophysics Data System (ADS)

This paper evaluates the effects of randomly distributed small indentations, or pits, on the lubricating properties when operating under these mixed or boundary lubrication conditions. Rings and needle rollers were textured with randomly distributed small indentations, or pits, for evaluation. Skewness (Sk) was used as a measure of surface finish to characterize the degree to which the material of these modified parts was above the mean line, a positive value, or below the mean line, a negative value. Fatigue life tests were conducted on these rolling elements, whose skewness ranged from -1.2 to -2.0, under mixed or boundary lubrication conditions. Test results showed rolling bearing fatigue life to increase with a decrease in skewness as related to the depth, width, and distribution of the surface indentations, or pits, on the parts.

Akamatsu, Yoshinobu; Tsushima, Noriyuki; Goto, Toshihide; Hibi, Kenji

1992-10-01

150

Life design of high-temperature turbine blades with minimum cooling requirements  

NASA Astrophysics Data System (ADS)

The problem of minimizing fuel requirements for the air cooling of gas turbine blades, while providing for a specified service life, is stated and solved for a dual-mode engine. It is shown that, for a multimode engine, the problem should be solved by using nonlinear programming methods. It is further shown that fuel consumption for blade cooling can be minimized only by controlling air flow rate with allowance for the operation mode. Recommendations concerning practical applications of the results of the study are given.

Nagoga, G. P.; Tseitlin, V. I.; Balter, V. P.

151

Effects of Low Speed on Roller Bearing Fatigue Life©  

Microsoft Academic Search

Two test series were conducted to study the effect of low speed and high load on the rolling-element fatigue life of 30 mm and 40 mm bore cylindrical roller bearings at inner race speeds from 19 to 3725 rpm and lubricant film parameter Lambda (?) ratios from 0.03 to 1.2. Maximum Hertz stress ranged from 2.24 to 4.2 GPa (325

John R. Miller; Yoshinobu Akamatsu

1997-01-01

152

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

153

Effect on interference fits on roller bearing fatigue life  

NASA Technical Reports Server (NTRS)

An analysis was performed to determine the effects of inner-ring speed and press fits on roller bearing fatigue life. 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 and load, and were applied to a conventional roller bearing life analysis. The effect of mean stress was determined using Goodman diagram approach. Hoop stresses caused by press fits and centrifugal force can reduce bearing life by as much as 90 percent. Use of a Goodman diagram predicts life reductions of 20 to 30 percent. The depth of the maximum shear stress remains virtually unchanged.

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

1986-01-01

154

Effect of interference fits on roller bearing fatigue life  

NASA Technical Reports Server (NTRS)

An analysis was performed to determine the effects of inner-ring speed and press fits on roller bearing fatigue life. 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 and load, and were applied to a conventional roller bearing life analysis. The effect of mean stress was determined using Goodman diagram approach. Hoop stresses caused by press fits and centrifugal force can reduce bearing life by as much as 90 percent. Use of a Goodman diagram predicts life reduction of 20 to 30 percent. The depth of the maximum shear stress remains virtually unchanged.

Coe, Harold H.; Zaretsky, Erwin V.

1987-01-01

155

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 Department of Biology, Hamilton College, Clinton, NY, USA a r t i c l e i n f o Article history: Received 14 t In Southwest Asia, sickle blades first appear early in the sequence of the transition to agriculture

Kohler, Tim A.

156

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

157

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

158

Energy models for fatigue life estimation under uniaxial random loading. Part II: Verification of the model  

Microsoft Academic Search

The paper concerns verification of the energy model for the fatigue life determination under the uniaxial random and variable-amplitude stress state. Application of the energy parameter for the fatigue life calculation using the algorithmic method under the random and variable-amplitude uniaxial tension–compression proves that most results of the fatigue life calculation are included in the scatter band with the coefficient

Tadeusz ?agoda

2001-01-01

159

Prediction of the Fatigue Life of Cast Steel Containing Shrinkage Porosity  

E-print Network

Prediction of the Fatigue Life of Cast Steel Containing Shrinkage Porosity RICHARD A. HARDIN and CHRISTOPH BECKERMANN A simulation methodology for predicting the fatigue life of cast steel components life of steel castings containing porosity. For ease of use in standard design practice, commonly used

Beckermann, Christoph

160

Life assessment for a gas turbine blade under creep conditions based on continuum fracture mechanics  

Microsoft Academic Search

Based on the semi-analytic finite element method and relationships of the continuum fracture mechanics, a numerical investigation\\u000a on the creep and extension of the continuum fracture zone in a gas turbine blade is performed. The value of life prior to\\u000a the formation of a crack-like defect and applicability limits of the relationships of continuum fracture mechanics are determined.

V. A. Bazhenov; A. I. Gulyar; S. O. Piskunov; A. A. Shkryl’

2006-01-01

161

Statistical fatigue properties of SCM435 steel in ultra-long-life regime based on JSMS database on fatigue strength of metallic materials  

Microsoft Academic Search

In reliability assessment of mechanical structures in the long period, it is important to clarify the fatigue characteristics in such a long sequence of cyclic loading. Thus, ultra-long life fatigue properties of SCM435 steel were experimentally examined in rotating bending. In addition, high cycle fatigue data of the same kind of steels were extracted from the database on fatigue strength

Tatsuo Sakai; Takashi Sakai; Kenji Okada; Machiko Furuichi; Izuru Nishikawa; Atsushi Sugeta

2006-01-01

162

Fatigue  

MedlinePLUS

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

163

Lubricant and additive effects on spur gear fatigue life  

NASA Technical Reports Server (NTRS)

Spur gear endurance tests were conducted with six lubricants using a single lot of consumable-electrode vacuum melted (CVM) AISI 9310 spur gears. The sixth lubricants was divided into four batches each of which had a different additive content. Lubricant tested with a phosphorus-type load carrying additive showed a statistically significant improvement in life over lubricants without this type of additive. The presence of sulfur type antiwear additives in the lubricant did not appear to affect the surface fatigue life of the gears. No statistical difference in life was produced with those lubricants of different base stocks but with similar viscosity, pressure-viscosity coefficients and antiwar additives. Gears tested with a 0.1 wt pct sulfur and 0.1 wt pct phosphorus EP additives in the lubricant had reactive films that were 200 to 400 (0.8 to 1.6 microns) thick.

Townsend, D. P.; Zaretsky, E. V.; Scibbe, H. W.

1986-01-01

164

Lubricant and additive effects on spur gear fatigue life  

NASA Technical Reports Server (NTRS)

Spur gear endurance tests were conducted with six lubricants using a single lot of consumable-electrode vacuum melted (CVM) AISI 9310 spur gears. The sixth lubricant was divided into four batches each of which had a different additive content. Lubricants tested with a phosphorus-type load carrying additive showed a statistically significant improvement in life over lubricants without this type of additive. The presence of sulfur type antiwear additives in the lubricant did not appear to affect the surface fatigue life of the gears. No statistical difference in life was produced with those lubricants of different base stocks but with similar viscosity, pressure-viscosity coefficients and antiwear additives. Gears tested with a 0.1 wt % sulfur and 0.1 wt % phosphorus EP additives in the lubricant had reactive films that were 200 to 400 (0.8 to 1.6 microns) thick.

Townsend, D. P.; Zaretsky, E. V.; Scibbe, H. W.

1985-01-01

165

Trauma, stressful life events and depression predict HIV-related fatigue  

Microsoft Academic Search

Despite the fact that fatigue is a common and debilitating symptom among HIV-infected persons, we know little about the predictors of fatigue in this population. The goal of this cross-sectional study was to examine the effects of early childhood trauma, recent stressful life events and depression on intensity and impairment of fatigue in HIV, over and above demographic factors and

J. Leserman; J. Barroso; B. W. Pence; N. Salahuddin; J. L. Harmon

2008-01-01

166

In vitro fatigue behavior of human dentin with implications for life prediction  

E-print Network

: Although human dentin is known to be suscep- tible to failure under repetitive cyclic fatigue loading the paucity of fatigue data through a systematic investigation of the effects of prolonged cyclical loadingIn vitro fatigue behavior of human dentin with implications for life prediction R. K. Nalla,1 V

Ritchie, Robert

167

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

168

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

169

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

170

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

171

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

172

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

173

Fatigue life of organic fiber/epoxy pressure vessels  

NASA Technical Reports Server (NTRS)

The cyclic fatigue life of 10.2-cm-diam cylindrical pressure vessels has been studied. The vessels were made of an organic fiber/epoxy composite. To determine the typical strength distribution of the vessels, 25 of them were internally pressurized until they burst. Twenty-five vessels were then tested under sinusoidal cycling at 1 Hz between 4% and 91% of the mean burst strength. An additional twenty-five vessels were tested between 4% and 91% with a rectangular pressure pulse at 1/3 Hz. A limited number of vessels were tested for stress rupture at the 91% level. Cyclic life was found to depend on time at peak load as well as the number of stress cycles.

Hamstad, M. A.; Chiao, T. T.; Patterson, R. G.

1975-01-01

174

NASALIFE - Component Fatigue and Creep Life Prediction Program  

NASA Technical Reports Server (NTRS)

NASALIFE is a life prediction program for propulsion system components made of ceramic matrix composites (CMC) under cyclic thermo-mechanical loading and creep rupture conditions. Although the primary focus was for CMC components, the underlying methodologies are equally applicable to other material systems as well. The program references empirical data for low cycle fatigue (LCF), creep rupture, and static material properties as part of the life prediction process. Multiaxial stresses are accommodated by Von Mises based methods and a Walker model is used to address mean stress effects. Varying loads are reduced by the Rainflow counting method or a peak counting type method. Lastly, damage due to cyclic loading and creep is combined with Minor's Rule to determine damage due to cyclic loading, damage due to creep, and the total damage per mission and the number of potential missions the component can provide before failure.

Gyekenyesi, John Z.; Murthy, Pappu L. N.; Mital, Subodh K.

2014-01-01

175

Rainflow counting algorithm for the LIFE2 fatigue analysis code  

NASA Astrophysics Data System (ADS)

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. A set of numerical algorithms are described that were 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.

Schluter, L. L.; Sutherland, H. J.

176

On the sonic fatigue life estimation of skin structures at room and elevated temperatures  

NASA Astrophysics Data System (ADS)

Fighter/trainer empennages and STOL (Short Take-Off and Landing) aircraft flap systems are subjected to severe acoustic pressure levels as high as 150-170 dB. As a result, acoustic fatigue has become one of the major factors in design. Empennages and flap systems are also subject to high temperatures and thus the influence of thermal buckling on fatigue life must be taken into consideration. To estimate the sonic fatigue life of skin structures, combined use is made of the Monte Carlo method of non-linear panel response analysis and local stress-strain simulations with rheological models. Calculations were conducted and comparison of the results with experimental data shows that the method estimates the sonic fatigue life accurately when adequate values of fatigue notch factors are chosen. Example calculations with thermal as well as static pressure effects were also carried out and the effect of thermal buckling on sonic fatigue life is clarified.

Maekawa, S.

1982-01-01

177

A high fatigue life prediction methodology under constant amplitude multiaxial proportional loadings  

Microsoft Academic Search

The main aim of this study is to propose a method for prediction of the fatigue-life for different materials subjected to constant amplitude multiaxial proportional loading. The paper presents a method to solve a high-cycle-fatigue problem using linear elastic analysis via Ansys software. A computing program of the fatigue life prediction methodology was developed. This program uses both Ansys and

H. Guechichi; S. Benkabouche; A. Amrouche; M. Benkhettab

2011-01-01

178

Feasibility study of pultruded blades for wind turbine rotors  

SciTech Connect

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

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

2000-02-28

179

A Model of the Fatigue Life Distribution of Composite Laminates Based on Their Static Strength Distribution  

Microsoft Academic Search

The reasons of the static strength dispersion and the fatigue life dispersion of composite laminates are analyzed in this article. It is concluded that the inner original defects, which derived from the manufacturing process of composite laminates, are the common and major reason of causing the random distributions of the static strength and the fatigue life. And there is a

Wu Fuqiang; Yao Weixing

2008-01-01

180

Fatigue Life Properties and Availability of Proof Testing in Ceramics-Coated Glass  

NASA Astrophysics Data System (ADS)

The long-term durability of high-performance ceramics-coated glass should be appropriately evaluated prior to their practical applications. Fatigue properties of such materials should be clarified to ensure the long-term durability. In this work, a borosilicate glass was coated with alumina or silicon carbide thin films by sputtering method. Fatigue tests of coated glass were conducted under three-point bending. It was clarified that the fatigue life was elongated by coating ceramic thin films on glass and the fatigue life distribution in glass coated with thicker films shifted toward longer life region. Proof testing was carried out for coated glass specimens to remove specimens having lower fatigue lives. It was suggested that proof testing for fatigue of ceramics-coated glass was effective as a screening procedure which can remove weaker specimens by static pre-loading before fatigue tests. In correlating average fatigue lives, fatigue resistance strength was introduced as the average bending strength divided by the applied maximum stress. It was revealed that the average fatigue lives of every coated glass, including average lives after proof testing, were well correlated by a power function of the fatigue resistance strength and its modified parameter, irrespective of film material and thickness and also applied stress level.

Hoshide, Toshihiko; Shimizu, Shohei; Tanaka, Motoki

2014-03-01

181

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

182

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, ...

183

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 ...

184

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

185

Fatigue Life Prediction of a Hoop-Wrapped Composite CNG Cylinder Containing Surface Flaw  

E-print Network

Abstract — In recent years many experimental and numerical studies have been conducted on the fatigue behaviour of CNG storage pressure vessels. The main objective of these studies is to estimate the total fatigue life, which consists of two parts: i) Life till crack nucleation and ii) Crack growth life. Although fatigue evaluation methods for metal cylinders are widely covered in literature including the ASME Boiler and Pressure Vessel Code, comprehensive approaches for fatigue evaluation of composite-reinforced pressure vessels are very few. This paper calculates the fatigue life till crack nucleation for a steel-lined hoop wrapped composite pressure vessel containing a surface flaw (notch) using strain-life approach. Firstly, static stress analysis taking into account the non-linear material behaviour of steel liner was performed using finite element method to provide input for the fatigue analysis. Then fatigue analysis was carried out by applying a cyclic pressure inside the pre-stressed cylinder using strain-life approach, and the results obtained by the numerical simulations are discussed. The approach associated with these calculations can be used to study the effect of various material and geometry parameters on the fatigue life of the pressure vessel.

Kumar Agrawal; Surendra Kumar

186

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

187

Effect of orientation and extrusion welds on the fatigue life of an Al–Mg–Si–Mn alloy  

Microsoft Academic Search

The effect of specimen orientation and extrusion weld (seam and charge) on the fatigue life of specimens from a hollow AA6082 alloy extrusion profile have been characterized in the form of S–N curves. Specimen orientation with respect to the extrusion direction has a large effect on fatigue life. Transverse specimens exhibit only a fraction of the high cycle fatigue life

N. Nanninga; C. White; T. Furu; O. Anderson; R. Dickson

2008-01-01

188

Development of a 3D Biological method for fatigue life based optimisation and its application to structural shape design  

Microsoft Academic Search

Damage tolerance design philosophy assumes that numerous cracks can be present at various arbitrary locations in a structure, which makes fatigue life based shape optimisation very computationally intensive. As a result, there have been limited applications of fatigue life based optimisation. To address this, the paper presents a gradient-less 3D Biological algorithm that uses fatigue life as the design objective

R. Das; R. Jones

2009-01-01

189

Stress and fatigue life monitoring of high temperature bearing elements based on the solution of inverse conduction problem  

Microsoft Academic Search

The stress and fatigue life monitoring of high temperature bearing elements is of great significance for the safe and economic operation of thermal power plant. The calculation of temperature distribution is the fundamental of the stress and fatigue life analysis. In order to improve the precision of the temperature distribution, a method for stress and fatigue life analysis of boiler

Li Bin; Wang Song-ling; Yang Dong

2008-01-01

190

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

191

Transverse Tension Fatigue Life Characterization Through Flexure Testing of Composite Materials  

NASA Technical Reports Server (NTRS)

The transverse tension fatigue life of S2/8552 glass-epoxy and IM7/8552 carbon-epoxy was characterized using flexure tests of 90-degree laminates loaded in 3-point and 4-point bending. The influence of specimen polishing and specimen configuration on transverse tension fatigue life was examined using the glass-epoxy laminates. Results showed that 90-degree bend specimens with polished machined edges and polished tension-side surfaces, where bending failures where observed, had lower fatigue lives than unpolished specimens when cyclically loaded at equal stress levels. The influence of specimen thickness and the utility of a Weibull scaling law was examined using the carbon-epoxy laminates. The influence of test frequency on fatigue results was also documented for the 4-point bending configuration. A Weibull scaling law was used to predict the 4-point bending fatigue lives from the 3-point bending curve fit and vice-versa. Scaling was performed based on maximum cyclic stress level as well as fatigue life. The scaling laws based on stress level shifted the curve fit S-N characterizations in the desired direction, however, the magnitude of the shift was not adequate to accurately predict the fatigue lives. Furthermore, the scaling law based on fatigue life shifted the curve fit S-N characterizations in the opposite direction from measured values. Therefore, these scaling laws were not adequate for obtaining accurate predictions of the transverse tension fatigue lives.

OBrien, T. Kevin; Chawan, Arun D.; Krueger, Ronald; Paris, Isabelle

2001-01-01

192

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

193

On the engineering approach to estimating the parameters in an improved crack growth rate model for fatigue life prediction  

Microsoft Academic Search

Metal structures in ships and offshore platforms are subjected to complex loading histories and one of the most significant failure modes is fatigue. Accurate prediction of the fatigue life of marine structures is very important for both safe and economic design and operation. It has been realised that fatigue crack propagation theory can provide a more rational basis for fatigue

Fang Wang; Weicheng Cui

2010-01-01

194

Fatigue life prediction in AlMgSi1 lap joint weldments  

Microsoft Academic Search

The fatigue behaviour of an AlMgSi1 alloy lap welded joint and the improvement in fatigue strength due to post-weld heat treatment were investigated. Two series of fatigue tests were performed: one in as-welded specimens and another in heat-treated specimens. The prediction of crack initiation life under a plane strain condition was made based on the local strain approach using Morrow's

J. A. M Pinho da Cruz; J. D. M Costa; L. F. P Borrego; J. A. M Ferreira

2000-01-01

195

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

196

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

197

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

198

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

199

Ultrasonic attenuation as an indicator of fatigue life of graphite/epoxy fiber composite  

NASA Technical Reports Server (NTRS)

The narrow band ultrasonic longitudinal wave velocity and attenuation were measured as a function of the transfiber compression-compression fatigue of unidirectional graphite/epoxy composites. No change in velocity was detected at any point in fatigue life. For specimens fatigued at 80% of static strength, there was generally a 5% to 10% increase in attenuation, however, this increase does not appear to be a satisfactory indicator of fatigue life. On the other hand, there appears to be a correlation between initial attenuation (measured prior to cycling) and cycles to fracture. Initial attenuation as measured at 1.5 MHz and 2.0 MHz appears to be a good indicator of relative fatigue life.

Williams, J. H., Jr.; Doll, B.

1979-01-01

200

Strain Energy Approach for Axial and Torsional Fatigue Life Prediction in Aged NiCrMoV Steels  

NASA Astrophysics Data System (ADS)

Axial and torsional low cycle fatigue tests were performed for NiCrMoV steels serviced low-pressure turbine rotor of nuclear power plant. The results were used to evaluate multiaxial fatigue life models including Tresca, von Mises and Brown and Miller's critical plane. The fatigue life predicted by the multiaxial fatigue models didn't correspond with the experimental results in small strain range. We proposed the total strain energy density model to predict torsional fatigue life from axial fatigue data. The total strain energy density model was found to best correlate the experimental data with predictions being within a factor of 2.

Song, Gee Wook; Hyun, Jung Seob; Ha, Jeong Soo

201

Probabilistic Distribution of Fatigue Crack Growth Life Considering Effect of Crack Coalescence  

NASA Astrophysics Data System (ADS)

The studies of probabilistic distribution of fatigue crack growth life (or the fatigue fracture probability) have been reported. However, some studies have concluded that each crack grows independently, without crack coalescence; while others indicate the defects should be treated as 2-dimensional cracks. In this study, a method to predict the probabilistic distribution of fatigue crack growth life that considers crack coalescence of the surface crack at the welded line is presented, and the influence of several parameters on the life distribution is discussed.

Yoon, Han-Yong; Lee, Sang-Chan

202

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

203

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

E-print Network

, which does not. The applicability of Miner's linear damage rule for predicting fatigue lives of variable that Miner's linear damage rule was not applicable under those conditions. A rainflow filtering process hasFatigue life analysis and predictions for NR and SBR under variable amplitude and multiaxial

Fatemi, Ali

204

Effects of carburization on expected fatigue life of alloys steel shafts  

Microsoft Academic Search

The motivation of this work is to improve fatigue life of the alloys steel power transmission shafts of the palm oil screw press machines in a Malaysia palm oil company. In order to improve daily productions of the palm oil, a high extraction efficiency of the machine with bigger crushing forces are required. Consequently, the failures due to torsional fatigue

T. M. Loganathan; J. Purbolaksono; J. I. Inayat-Hussain; N. Wahab

2011-01-01

205

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

206

Assessment of existing steel structures. A guideline for estimation of the remaining fatigue life  

Microsoft Academic Search

In many countries and regions, traffic infrastructure projects suffer from low funding. The budget is tight for new infrastructure building and, thus, the importance of inspection, maintenance and assessment of the existing traffic infrastructure increases. A new fatigue assessment guideline for the estimation of the remaining fatigue life of steel bridges has been written by technical committee 6 of the

Rosemarie Helmerich; Bertram Kühn; Alain Nussbaumer

2007-01-01

207

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

E-print Network

Modulus Tests and Tensile Tests .............................28 Section 3.4 Rockwell Hardness Testing fabrication, material characteristics, statistical analysis of fatigue testing results, a comparison of material selection in the fatigue life of HSS Y-joints. All fabrication of components, besides the test

Foley, Christopher M.

208

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

National Technical Information Service (NTIS)

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

M. C. Cherry

1995-01-01

209

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

210

Description of a computerized method for predicting thermal fatigue life of metals  

NASA Technical Reports Server (NTRS)

A computer program is described which can be used to predict the thermal fatigue life of metals and structural components from conventional metal properties. A unique feature of TFLIFE is that it calculates lives according to several different failure criteria for the same input data. These criteria are surface crack initiation, interior crack initiation, and complete fracture of both unnotched and notched fatigue specimens. Sample output tables are shown, together with results for two typical problems: (1) Thermal-mechanical fatigue of bar specimens of the tantalum alloy T-111, and (2) thermal-stress fatigue of wedge specimens of the nickel alloy B-1900.

Spera, D. A.; Cox, E. C.

1975-01-01

211

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

212

Research on Fatigue Life of the Automobile Differential Case  

Microsoft Academic Search

Basing on the fatigue breaking of the differential case of the drive axle with the material of nodular graphite cast iron, the fatigue analysis is made. According to the criterion of `Q\\/T 543-1999 Drive Axle Bench Test Standard', with the fatigue software FEMFAT 4.7D, the research on the cumulative damage and endurance limit safety factors in differential case is studied

Yu Xianzhong; Chen Xuedong; Huang Pinghui; Jie Gang

2010-01-01

213

Fatigue Life Prediction of an Intermetallic Matrix Composite at Elevated Temperatures.  

National Technical Information Service (NTIS)

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 t...

P. A. Bartolotta

1991-01-01

214

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

215

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

216

Tensile, Fracture, Fatigue Life, and Fatigue Crack Growth Rate Behavior of Structural Materials for the ITER Magnets: The European Contribution  

SciTech Connect

Fatigue crack growth rates (FCGR) are determined for R ratios between 0.1 - 0.7 at 7 K for three full-size Mock-up Models of the ITER Toroidal Field coil case produced by modified Type 316LN alloys. A representative forged block of Model 3 is additionally manufactured to determine its improved spatial tensile properties and compare it to former Model 3 data. From the new candidate jacket materials, developed for the ITER Central Solenoid coil, a batch is investigated to assess the fatigue life behavior at 7 K. Furthermore, the 4 K test facility, a 630 kN load capacity hydraulic machine has been used to allow fatigue life investigations under four point bending of the full-size jackets with artificial surface flaws. Cyclic life results have been assessed for the heat affected zone, weld, and base metal. The results are used in the fatigue analysis of the coil. Residual stresses resulting from jacket welding have been determined using two different techniques. First by distortion measurements of sliced pieces of the weld section and secondly by neutron diffraction measurements. In addition, tensile and fracture tests have been performed at 7 K with Al 7075, a candidate alloy for the pre-compression system of the CS coil.

Nyilas, A. [Forschungszentrum Karlsruhe, ITP, Karlsruhe (Germany); Nikbin, K. [Imperial College of Science, Technology and Medicine (United Kingdom); Portone, A.; Sborchia, C. [EFDA Close Support Unit, Garching (Germany)

2004-06-28

217

Tensile, Fracture, Fatigue Life, and Fatigue Crack Growth Rate Behavior of Structural Materials for the ITER Magnets: The European Contribution  

NASA Astrophysics Data System (ADS)

Fatigue crack growth rates (FCGR) are determined for R ratios between 0.1 - 0.7 at 7 K for three full-size Mock-up Models of the ITER Toroidal Field coil case produced by modified Type 316LN alloys. A representative forged block of Model 3 is additionally manufactured to determine its improved spatial tensile properties and compare it to former Model 3 data. From the new candidate jacket materials, developed for the ITER Central Solenoid coil, a batch is investigated to assess the fatigue life behavior at 7 K. Furthermore, the 4 K test facility, a 630 kN load capacity hydraulic machine has been used to allow fatigue life investigations under four point bending of the full-size jackets with artificial surface flaws. Cyclic life results have been assessed for the heat affected zone, weld, and base metal. The results are used in the fatigue analysis of the coil. Residual stresses resulting from jacket welding have been determined using two different techniques. First by distortion measurements of sliced pieces of the weld section and secondly by neutron diffraction measurements. In addition, tensile and fracture tests have been performed at 7 K with Al 7075, a candidate alloy for the pre-compression system of the CS coil.

Nyilas, A.; Nikbin, K.; Portone, A.; Sborchia, C.

2004-06-01

218

What roles do team climate, roster control, and work life conflict play in shiftworkers' fatigue longitudinally?  

PubMed

The study aimed to examine shiftworkers fatigue and the longitudinal relationships that impact on fatigue such as team climate, work life conflict, control of shifts and shift type in shift working nurses. We used a quantitative survey methodology and analysed data with a moderated hierarchical multiple regression. After matching across two time periods 18 months apart, the sample consisted of 166 nurses from one Australian hospital. Of these nurses, 61 worked two rotating day shifts (morning & afternoon/evening) and 105 were rotating shiftworkers who worked three shifts (morning afternoon/evening and nights). The findings suggest that control over shift scheduling can have significant effects on fatigue for both two-shift and three-shift workers. A significant negative relationship between positive team climate and fatigue was moderated by shift type. At both Time 1 and Time 2, work life conflict was the strongest predictor of concurrent fatigue, but over time it was not. PMID:24210672

Pisarski, Anne; Barbour, Jennifer P

2014-05-01

219

Study on creep-fatigue life prediction using simple high temperature low cycle fatigue testing machines  

Microsoft Academic Search

A simple high temperature low cycle fatigue testing machine for long time creep fatigue tests was developed and experiments on two kinds of CrMoV steel forgings and 304 stainless steel were carried out. The experimental results indicate: (1) the data obtained by long hold time tests deviate remarkably from the linear damage fraction rule. (2) Creep rupture ductility seems to

T. Endo; T. Sakon

1983-01-01

220

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

221

Fatigue life prediction of dentin-adhesive interface using micromechanical stress analysis  

PubMed Central

Objectives The objective of this work was to develop a methodology for the prediction of fatigue life of the dentin-adhesive (d-a) interface. Methods At the micro-scale, the d-a interface is composed of dissimilar material components. Under global loading, these components experience different local stress amplitudes. The overall fatigue life of the d-a interface is, therefore, determined by the material component that has the shortest fatigue life under local stresses. Multiple 3d finite element (FE) models were developed to determine the stress distribution within the d-a interface by considering variations in micro-scale geometry, material composition and boundary conditions. The results from these models were analyzed to obtain the local stress concentrations within each d-a interface component. By combining the local stress concentrations and experimentally determined stress versus number of cycle to failure (S-N) curves for the different material components, the overall fatigue life of the d-a interface was predicted. Results The fatigue life was found to be a function of the applied loading amplitude, boundary conditions, microstructure and the mechanical properties of the material components of the d-a interface. In addition, it was found that the overall fatigue life of the d-a interface is not determined by the weakest material component. In many cases, the overall fatigue life was determined by the adhesive although exposed collagen was the weakest material component. Comparison of the predicted results with experimental data from the literature showed both qualitative and quantitative agreement. Significance The methodology developed for fatigue life prediction can provide insight into the mechanisms that control degradation of the bond formed at the d-a interface. PMID:21700326

Singh, Viraj; Misra, Anil; Marangos, Orestes; Park, Jonggu; Ye, Qiang; Kieweg, Sarah L; Spencer, Paulette

2011-01-01

222

Transverse tension fatigue life characterization through flexure testing of composite materials  

Microsoft Academic Search

The transverse tension fatigue life of S2\\/8552 glass–epoxy and IM7\\/8552 carbon–epoxy was characterized using flexure tests of 90-degree laminates loaded in 3-point and 4-point bending. The influence of specimen polishing and specimen configuration on transverse tension fatigue life was examined using the glass–epoxy laminates. Results showed that 90-degree flexure specimens with polished machined edges and polished tension-side surfaces had lower

T. Kevin O'Brien; Arun D Chawan; Ronald Krueger; Isabelle L Paris

2002-01-01

223

Variations in Gas-Turbine Blade Life and Cost due to Compressor Fouling - A Thermoeconomic Approach  

Microsoft Academic Search

The connection between gas turbine compressor fouling and expander blade lifetime is studied in a simplified manner for a gas turbine operating in a combined cycle with a constant power output. It is shown how blade materials and compressor fouling rate affect the blade lifetime, and with this background, based on a thermoeconomic approach, the economic aspects of compressor washing

Kristin JORDAL; Mohsen ASSADI; Magnus GENRUP

2002-01-01

224

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

Microsoft Academic Search

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

D. T. Rusk; W. Hoppe

2009-01-01

225

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

226

Increasing fatigue life of weld repaired rotating elements  

SciTech Connect

The paper discusses the use of controlled shot peening to regain the fatigue strength lost on rotating elements due to welding during original manufacture, welding used for salvaging expensive components due to mishaps during final machining, and weld repair after years of successful service. Weld repair of rotating components is becoming more popular due to improved welding techniques and non-destructive testing capabilities. Confidence in weld repair has further been heightened by the ability to regain the fatigue strength lost by welding and actually raise the fatigue strength close to that of the original homogeneous metal.

Welsch, W.

1998-07-01

227

Microstructure-based fatigue life prediction methods for naval steel structures  

NASA Astrophysics Data System (ADS)

The goal of the subject program has been to develop fundamental understandings of the relationships between microstructure and fatigue damage in structural steels of interest to naval applications. Quantitative descriptions of these relationships have been incorporated within practical engineering models for the prediction of fatigue life. Fatigue damage associated with microcrack nucleation and growth has been studied experimentally with S-N fatigue specimens of HSLA-80 steel. Some microstructures were modified with appropriate heat treatments, and the effects of microstructure on microcrack nucleation and growth have been characterized. Microstructural scaling laws have been developed and verified for both fatigue crack growth (FCG) and smooth specimen total life in a wide range of steels. The effects of microstructure on FCG have been described by a dimensionless microstructural parameter which is defined in terms of stress, fatigue ductility, dislocation cell size, and dislocation barrier spacing. FCG data from large and small flaws have been critically compared on the basis of engineering models for FCG rates, and the implications of this comparison for engineering fatigue life prediction are explored. A probabilistic treatment of the micromechanical scaling laws for FCG has been derived, permitting a direct evaluation of the relationship between microstructural variation and variability in FCG rates.

McClung, R. C.; Chan, K. S.; Davidson, D. L.; Torng, T. Y.

1994-09-01

228

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

229

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

230

A comparison of reliability and conventional estimation of safe fatigue life and safe inspection intervals  

NASA Technical Reports Server (NTRS)

Both the conventional and reliability analyses for determining safe fatigue life are predicted on a population having a specified (usually log normal) distribution of life to collapse under a fatigue test load. Under a random service load spectrum, random occurrences of load larger than the fatigue test load may confront and cause collapse of structures which are weakened, though not yet to the fatigue test load. These collapses are included in reliability but excluded in conventional analysis. The theory of risk determination by each method is given, and several reasonably typical examples have been worked out, in which it transpires that if one excludes collapse through exceedance of the uncracked strength, the reliability and conventional analyses gave virtually identical probabilities of failure or survival.

Hooke, F. H.

1972-01-01

231

Evaluation of the probability distribution of pitting corrosion fatigue life in aircraft materials  

NASA Astrophysics Data System (ADS)

Corrosion and fatigue properties of aircraft materials are known to have a considerable scatter due to the random nature of materials, loading, and environmental conditions. A probabilistic approach for predicting the pitting corrosion fatigue life has been investigated which captures the effect of the interaction of the cyclic load and corrosive environment and all stages of the corrosion fatigue process (i.e. the pit nucleation and growth, pit-crack transition, short- and long-crack propagation). The probabilistic model investigated considers the uncertainties in the initial pit size, corrosion pitting current, and material properties due to the scatter found in the experimental data. Monte Carlo simulations were performed to define the failure probability distribution. Predicted cumulative distribution functions of fatigue life agreed reasonably well with the existing experimental data.

Qingyuan, Wang; Kawagoishi, N.; Chen, Q.; Pidaparti, R. M.

2003-06-01

232

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

233

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

E-print Network

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

Meyer, Christian

234

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

235

Evaluation of the EHL film thickness and extreme pressure additives on gear surface fatigue life  

NASA Astrophysics Data System (ADS)

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

1994-07-01

236

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

237

Fatigue-Life Prediction Methodology Using Small-Crack Theory  

NASA Technical Reports Server (NTRS)

This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using 'small-crack theory' for various materials and loading conditions. Crack-tip constraint factors, to account for three-dimensional state-of-stress effects, were selected to correlate large-crack growth rate data as a function of the effective-stress-intensity factor range (delta K(eff)) under constant-amplitude loading. Some modifications to the delta k(eff)-rate relations were needed in the near-threshold regime to fit measured small-crack growth rate behavior and fatigue endurance limits. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens made of two aluminum alloys and a steel under constant-amplitude and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks for the aluminum alloys and steel for edge-notched specimens. An equivalent-initial-flaw-size concept was used to calculate fatigue lives in other cases. Results from the tests and analyses agreed well.

Newmann, James C., Jr.; Phillips, Edward P.; Swain, M. H.

1997-01-01

238

Mechanisms of high-strength structural materials fatigue failure in ultra-wide life region  

Microsoft Academic Search

For attractive technical applications such as cars and trains, the durability sought for some components is between 108 and 1010 cycles. However, only few experimental results beyond 107 cycles are available. The S–N curve in the ultra-wide life region must be determined in order to guarantee the real fatigue strength and safe life of components. This paper presents a study

František Nový; Marián ?in?ala; Peter Kopas; Otakar Bok?vka

2007-01-01

239

Effect of specimen orientation and extrusion welds on the fatigue life of an AA6063 alloy  

Microsoft Academic Search

The effect of specimen orientation and extrusion seam welds on the fatigue life of specimens milled from a hollow AA6063 aluminum alloy extrusion profile have been characterized in the form of S–N curves. The fatigue behavior of the fully recrystallized AA6063 alloy reported here is compared to previously reported results on a partially recrystallized AA6082 extruded aluminum alloy [Nanninga N,

N. Nanninga; C. White; O. Mills; J. Lukowski

2010-01-01

240

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

241

Fatigue Life Study of Bogie Framework Welding Seam by Finite Element Analysis Method  

Microsoft Academic Search

Using adaptive grid algorithm method, framework and its weld seam are meshed by manual method, fillet is instead of the corner\\u000a of weld seam and the needed finite element model of a bogie framework and weld-seam are built. Based on the miner theory of\\u000a cumulative fatigue damage and S-N curve modified, the strength and fatigue life distribution contours for welding

Pingqing Fan; Xintian Liu; Bo Zhao

242

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

243

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

244

Detection and Influence of Shrinkage Pores and Nonmetallic Inclusions on Fatigue Life of Cast Aluminum Alloys  

NASA Astrophysics Data System (ADS)

In the current study, test bars of cast aluminum alloys EN AC-AlSi8Cu3 and EN AC-AlSi7Mg0.3 were produced with a defined amounts of shrinkage pores and oxides. For this purpose, a permanent mold with heating and cooling devices for the generation of pores was constructed. The oxides were produced by contaminating the melt. The specimens and their corresponding defect distributions were examined and quantified by X-ray computer tomography (CT) and quantitative metallography, respectively. A special test algorithm for the simultaneous image analyses of pores and oxides was developed. Fatigue tests were conducted on the defective samples. It was found that the presence of shrinkage pores lowers the fatigue strength, and only few oxide inclusions were found to initiate fatigue cracks when shrinkage pores are present. The results show that the pore volume is not sufficient to characterize the influence of shrinkage pores on fatigue life. A parametric model for the calculation of fatigue life based on the pore parameters obtained from CT scans was implemented. The model accounts for the combined impact of pore location, size, and shape on fatigue life reduction.

Tijani, Yakub; Heinrietz, André; Stets, Wolfram; Voigt, Patrick

2013-12-01

245

Hold-time effects on the fatigue life of CuCrZr alloys for fusion applications  

Microsoft Academic Search

The fatigue and creep–fatigue response of copper alloys is of interest due to the cyclic thermal–mechanical loading processes a fusion first wall will experience during operation. Creep–fatigue experiments were performed on a CuCrZr alloy with an overaged heat treatment at room temperature to determine the effects on fatigue life of a 10s hold period applied at the maximum tension and

Xianglin Wu; Xiao Pan; Bachu N. Singh; Meimei Li; James F. Stubbins

2007-01-01

246

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

247

A CHARACTERISTIC PLANE METHOD FOR MULTIAXIAL FATIGUE LIFE PREDICTION  

Microsoft Academic Search

This paper proposes a new multiaxial fatigue damage model based on a characteristic plane approach. The characteristic plane in the proposed model is defined as the material plane on which the damage caused by the cyclic hydrostatic strain amplitude is minimized to zero. The characteristic plane in the proposed model depends not only on the stress state but also on

Y. Liu; S. Mahadevan

248

Probabilistic Fatigue Life Analysis of High Density Electronics Packaging  

NASA Technical Reports Server (NTRS)

The fatigue of thin film metal interconnections in high density electronics packaging subjected to thermal cycling has been evaluated using a probabilistic fracture mechanics methodology. This probabilistic methodology includes characterization of thin film stress using an experimentally calibrated finite element model and simulation of flaw growth in the thin films using a stochastic crack growth model.

Moore, N. R.; Kolawa, E. A.; Sutharshana, S.; Newlin, L. E.; Creager, M.

1996-01-01

249

Improvement of fatigue life of an aluminum alloy by overstressing  

NASA Technical Reports Server (NTRS)

Fatigue tests were made on some 1.375-inch-diameter and 0.300-inch diameter specimens of a 17S-T aluminum alloy rod. One test of a large specimen was run continuously to failure at a maximum stress of 22,000 pounds per square inch. In two other tests of large specimens, thin surface layers were removed periodically until failure occurred. The same nominal maximum stress of 22,000 pounds per square inch was used throughout the two tests and the load on the fatigue machine was lowered accordingly after the removal of each surface layer. As each test progressed the stress in the metal of the final surface area therefore was increased after the removal of each surface layer. Because of the stresses used, this metal was overstressed, that is, stressed above its endurance limit. All the remaining specimens were subjected to similar over- stressing conditions but no metal was removed and a low initial stress was increased periodically to a final maximum value of 22,000 pounds per square inch as each test progressed. It was found that the fatigue resistance of 17S-T aluminum alloy can be increased by moderate overstressing. Apparently the increase in fatigue lift obtained in the tests of specimens from which layers were removed was the result of overstressing rather than from the removal of damaged surface layers.

STRICKLEY G W

1942-01-01

250

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

251

Predicted effect of dynamic load on pitting fatigue life for low-contact-ratio spur gears  

NASA Technical Reports Server (NTRS)

How dynamic load affects the surface pitting fatigue life of external spur gears was predicted by using the NASA computer program TELSGE. Parametric studies were performed over a range of various gear parameters modeling low-contact-ratio involute spur gears. In general, gear life predictions based on dynamic loads differed significantly from those based on static loads, with the predictions being strongly influenced by the maximum dynamic load during contact. Gear mesh operating speed strongly affected predicted dynamic load and life. Meshes operating at a resonant speed or one-half the resonant speed had significantly shorter lives. Dynamic life factors for gear surface pitting fatigue were developed on the basis of the parametric studies. In general, meshes with higher contact ratios had higher dynamic life factors than meshes with lower contact ratios. A design chart was developed for hand calculations of dynamic life factors.

Lewicki, David G.

1986-01-01

252

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

253

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

254

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

255

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

256

The effect of cryogenic treatment on the fatigue life of chrome silicon steel compression springs  

NASA Astrophysics Data System (ADS)

The purpose of this dissertation is to explore the effect of cryogenic treatment on the fatigue life of compression springs. Product manufacturers are constantly searching for ways to make their products last longer. This dissertation addresses three questions: (1) What is the effect of cryogenic treatment on the fatigue life of chrome silicon steel compression springs? Does the life increase, decrease, or remain the same? (2) What is the effect of cryogenic treatment on the Percent Load Loss (Stress Relaxation) of chrome silicon steel compression springs? (3) What are the possible changes in the material that cause these effects? The following tests were carried out; wire tensile test, hardness test, chemical analysis, residual stress, retained austenite, lattice parameter, force vs. deflection, percent load loss (stress relaxation), fatigue, microstructures, and eta carbides. This research produced a number of key findings: (1) The cryogenically treated springs had a longer cycle life and a higher endurance limit than the untreated springs. (2) The percent load loss (stress relaxation) of the cryogenically treated springs was similar to the untreated springs. (3) The cryogenically treated springs had a higher compressive residual stress at the surface than the untreated springs. The conclusions of this research are that the cryogenic treatment of chrome silicon steel compression springs led to an increase in compressive residual stress on the wire surface, which in turn led to an increase in fatigue life and a higher endurance limit. A recommended future study would be to compare cryogenically treated springs to shot peened springs.

Smith, Debra Lynn

257

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

258

Fatigue, fracture, and life prediction criteria for composite materials in magnets  

SciTech Connect

An explosively-bonded copper/Inconel 718/copper laminate conductor was proposed to withstand the severe face compression stresses in the central core of the Alcator C-MOD tokamak toroidal field (TF) magnet. Due to the severe duty of the TF magnet, it is critical that an accurate estimate of useful life be determined. As part of the effort to formulate an appropriate life prediction, fatigue crack growth experiments were performed on the laminate as well as its components. Metallographic evaluation of the laminate interface revealed many shear bands in the Inconel 718. Shear bands and shear band cracks were produced in the Inconel 718 as a result of the explosion bonding process. These shear bands were shown to have a detrimental effect on the crack growth behavior of the laminate, by significantly reducing the load carrying capability of the reinforcement layer and providing for easy crack propagation paths. Fatigue crack growth rate was found not only to be dependent on temperature but also on orientation. Fatigue cracks grew faster in directions which contained shear bands in the plane of the propagating crack. Fractography showed crack advancement by fatigue cracking in the Inconel 718 and ductile tearing of the copper at the interface. However, further away from the interfaces, the copper exhibited fatigue striations indicating that cracks were now propagating by fatigue. Laminate life prediction results showed a strong dependence on shear band orientation, and exhibited little variation between room temperature and 77{degree}K. Predicted life of this laminate was lower when the crack propagation was along a shear band than when crack propagation was across the shear bands. Shear bands appear to have a dominating effect on crack growth behavior.

Wong, F.M.G.

1990-06-01

259

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

260

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

261

Effect of Surface Roughness on Fatigue Life of Notched Carbon Steel  

E-print Network

Abstract — The effects of surface roughness on the fatigue life of carbon steel have been investigated. Rotational bending specimens have been machined and tested in fatigue. Specimens with surface roughness changed by emery papers (Grit #600, #400, #100) were prepared. The fatigue experiments were carried out at room temperature, applying a fully reversed cyclic load with the frequency of 50Hz, with mean stress equal to zero (R =-1), on a cantilever rotating-bending fatigue testing machine. The stress ratio was kept constant throughout the experiment. Regarding the effect of surface roughness, the number of cycles to failure of finer specimens was a little bigger than those of the courser specimens. Morphological observation on fracture surface of specimens was done using Optical and Scanning Electron Microscope (SEM). The result shows the number of possible fatigue crack initiation sites of courser specimen are higher compare to finer one. In addition, the specimens were broken in transgranular fracture. Index Term — Surface roughness, fatigue limit, carbon steel, fracture surface, transgranular fracture.

N. A. Alang; N. A. Razak; A. K. Miskam; Pahang Darul Makmur

262

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

263

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

E-print Network

of dollars each year for the railroad industry in terms of maintenance and inspection. Since a large number of these bridges are steel and their service life is typically governed by fatigue of welded details, it is important to determine the interactions...

Soape, Jack

2012-07-16

264

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

265

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

Microsoft Academic Search

This paper develops a plastic ratcheting based fatigue failure model for HSLA steels from a combination of results from experiments and finite element simulations using crystal plasticity constitutive relations. It predicts the nucleation of major cracks in the microstructure in ratcheting. Subsequently, the total life is limited by the growth of ductile fracture in the microstructure, which is factored in

Shashwat Sinha; Somnath Ghosh

2006-01-01

266

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

267

Drilled ball bearings - An approach to extending bearing fatigue life at high speeds  

NASA Technical Reports Server (NTRS)

Reducing the mass of the rolling elements in ball bearings causes a reduction of centrifugal forces and thereby extends bearing fatigue life. Ball mass is reduced by drilling a concentric hole through each ball. Concentricity and finish of the drilled hole can be closely controlled and the balls accurately balanced.

Anderson, W. J.; Coe, H. H.

1970-01-01

268

Bearing Fatigue Life Tests in Advanced Base Oil and Grease for Space Applications  

Microsoft Academic Search

Two synthetic base oils (815Z and 2001A) and two greases (601EF and R2000) used for space applications have been studied at ground level. Rheological tests were performed in order to characterize the behavior of each of the base oils versus the pressure and the temperature. Next, the effect of base oils and greases on ball bearing fatigue life was carried

Nobuyoshi Ohno; Hidekazu Komiya; Sobahan Mia; Shigeki Morita; Naoki Satoh; Shingo Obara

2008-01-01

269

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

270

Research on fatigue life of the casting crane's girder by using damnification limits design method  

Microsoft Academic Search

By using ANSYS to carry out finite element analysis, combining the results of the analysis and the theory of fracture mechanics, and making use of damnification limits design method based on the theory of fracture mechanics, the thesis gave a certain type of casting crane girder for example to analyze its fatigue life. It provided some theory basis and reference

Zhicheng Huang

2011-01-01

271

Safe fatigue life of steel towers under the action of wind vibrations  

Microsoft Academic Search

The problem of definition of the service life for high-rise steel tower installations is solved, depending on the fatigue damage accumulated in members or sections. This problem is important for towers and most communication systems, wind turbine supports and others, because for this type of structure wind load is regarded as the main load. The analysis of damage in most

M. A. Mikitarenko; A. V. Perelmuter

1998-01-01

272

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

273

Fatigue and life prediction for cobalt-chromium stents: A fracture mechanics analysis  

Microsoft Academic Search

To design against premature mechanical failure, most implant devices such as coronary and endovascular stents are assessed on the basis of survival, i.e., if a fatigue life of 108 cycles is required, testing is performed to ascertain whether the device will survive 108 cycles under accelerated in vitro loading conditions. This is a far from satisfactory approach as the safety

Ramesh V. Marrey; Robert Burgermeister; Randy B. Grishaber; R. O. Ritchie

2006-01-01

274

A theoretical study of the effect of weld geometry parameters on fatigue crack propagation life  

Microsoft Academic Search

In the present work, the effect of important butt weld geometry parameters e.g. tip radius of undercut at weld toe, weld toe radius, flank angle, plate thickness and edge preparation angle, and the effect of initial crack geometry on the fatigue crack propagation life have been studied by using Linear Elastic Fracture Mechanics (LEFM), Finite Element Analysis (FEA) and superposition

T. Ninh Nguyen; M. A. Wahab

1995-01-01

275

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

276

The surface fatigue life of contour induction hardened AISI 1552 gears  

Microsoft Academic Search

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,

Dennis P. Townsend; Alan Turza; Mike Chaplin

1995-01-01

277

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

SciTech Connect

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

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

1984-09-01

278

A Multiaxial Low Cycle Fatigue Life Prediction Model for Both Proportional and Non-proportional Loading Conditions  

NASA Astrophysics Data System (ADS)

This paper has presented a life prediction model in the field of multiaxial low-cycle fatigue. The proposed model is generally applied for constant amplitude multiaxial proportional and non-proportional loading. Depending upon applied strain path the equivalent strain varies within a cycle. Equivalent average strain amplitude is considered as fatigue damage parameter in the proposed model. The model has requirement of only two material constants and no other tuning parameters. The model is examined by the proportional and non-proportional low-cycle fatigue life experimental data for eight different types of materials. The model is successfully correlated with multiaxial fatigue lives of eight different materials.

Paul, Surajit Kumar

2014-09-01

279

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

280

A two-parameter analysis of S– N fatigue life using ? ? and ? max  

Microsoft Academic Search

The effect of the load ratio, R, or the mean-stress on fatigue life has been recognized for more than a hundred years. In considering the mean-stress effects in the stress-life (S–N) approach, research efforts have been mostly concentrated in establishing correlating functions in terms of the flow stress or yield stress or the ultimate tensile stress, etc., by taking, say,

K. Sadananda; S. Sarkar; D. Kujawski; A. K. Vasudevan

2009-01-01

281

Profiled Roller Stress/Fatigue Life Analysis Methodology and Establishment of an Appropriate Stress/Life Exponent  

NASA Technical Reports Server (NTRS)

The objective of this work was to determine the three dimensional volumetric stress field, surface pressure distribution and actual contact area between a 0.50" square roller with different crown profiles and a flat raceway surface using Finite Element Analysis. The 3-dimensional stress field data was used in conjunction with several bearing fatigue life theories to extract appropriate values for stress-life exponents. Also, results of the FEA runs were used to evaluate the laminated roller model presently used for stress and life prediction.

1997-01-01

282

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

283

Fatigue life prediction using a new moving window regression method  

NASA Astrophysics Data System (ADS)

A simple method to assess the safety of metallic structures in the presence of crack-like defects is considered. Linear regression techniques are used to fit fatigue-crack growth (FCG) laws of exponential type with respect to the number of cycles, in FCG experimental results. A moving window regression method is used to accurately predict whether or not the critical crack length region is reached. The probability of fast failure at any time (number of cycles) is formulated in terms of a characteristics defect size exceeding a critical value. The concept of conditional probability of failure is also employed here in order to evaluate the failure rate used in reliability practice. As an illustrative example, an analytical closed-form solution for the failure probability of structures is presented and evaluated using experimental FCG data.

Stavrakakis, G. S.; Pouliezos, A.

1991-07-01

284

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

285

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

286

Excitation, response, and fatigue life estimation methods for the structural design of externally blown flaps  

NASA Technical Reports Server (NTRS)

Means for predicting the fluctuating pressures acting on externally blown flap surfaces are developed on the basis of generalizations derived from non-dimensionalized empirical data. Approaches for estimation of the fatigue lives of skin-stringer and honeycomb-core sandwich flap structures are derived from vibration response analyses and panel fatigue data. Approximate expressions for fluctuating pressures, structural response, and fatigue life are combined to reveal the important parametric dependences. The two-dimensional equations of motion of multi-element flap systems are derived in general form, so that they can be specialized readily for any particular system. An introduction is presented of an approach to characterizing the excitation pressures and structural responses which makes use of space-time spectral concepts and promises to provide useful insights, as well as experimental and analytical savings.

Ungar, E. E.; Chandiramani, K. L.; Barger, J. E.

1972-01-01

287

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

288

The Relationships Between Fatigue, Quality of Life, and Family Impact Among Children With Special Health Care Needs  

PubMed Central

Objective?To examine the relationships among pediatric fatigue, health-related quality of life (HRQOL), and family impact among children with special health care needs (CSHCNs), specifically whether HRQOL mediates the influence of fatigue on family impact.?Methods?266 caregivers of CSHCNs were studied. The Pediatric Quality of Life Inventory Multidimensional Fatigue Scale, Pediatric Quality of Life Inventory Generic Scale, and Impact on Family Scale were used to measure fatigue, HRQOL, and family impact, respectively. Linear regressions were used to analyze the designated relationships; path analyses were performed to quantify the mediating effects of HRQOL on fatigue–family impact relationship.?Results?Although greater fatigue was associated with family impact (p < .05), the association was not significant after accounting for HRQOL. Path analyses indicated the direct effect of fatigue on family impact was not significant (p > .05), whereas physical and emotional functioning significantly mediated the fatigue–family impact relationship (p < .001).?Conclusion?Fatigue is related to family impact among CSHCNs, acting through the impairment in HRQOL. PMID:23584707

Anderson, Mary; Gandhi, Pranav; Tuli, Sanjeev; Krull, Kevin; Lai, Jin-Shei; Nackashi, John; Shenkman, Elizabeth

2013-01-01

289

Modeling thermomechanical fatigue life of high-temperature titanium alloy IMI 834  

SciTech Connect

A microcrack propagation model was developed to predict thermomechanical fatigue (TMF) life of high-temperature titanium alloy IMI 834 from isothermal data. Pure fatigue damage, which is assumed to evolve independent of time, is correlated using the cyclic J integral. For test temperatures exceeding about 600 C, oxygen-induced embrittlement of the material ahead of the advancing crack tip is the dominating environmental effect. To model the contribution of this damage mechanism to fatigue crack growth, extensive use of metallographic measurements was made. Comparisons between stress-free annealed samples and fatigued specimens revealed that oxygen uptake is strongly enhanced by cyclic plastic straining. In fatigue tests with a temperature below about 500 C, the contribution of oxidation was found to be negligible, and the detrimental environmental effect was attributed to the reaction of water vapor with freshly exposed material at the crack tip. Both environmental degradation mechanisms contributed to damage evolution only in out-of-phase TMF tests, and thus, this loading mode is most detrimental. Electron microscopy revealed that cyclic stress-strain response and crack initiation mechanisms are affected by the change from planar dislocation slip to a more wavy type as test temperature is increased. The predictive capabilities of the model are shown to result from the close correlation with the microstructural observations.

Maier, H.J.; Teteruk, R.G.; Christ, H.J.

2000-02-01

290

An intriguing design concept to enhance the pulsatile fatigue life of self-expanding stents.  

PubMed

Intravascular stenting has emerged as the primary treatment for vascular diseases and has received great attention from the medical community since its introduction two decades ago. The endovascular self-expanding stent is used to treat peripheral artery diseases; however, once implanted, these stents suffer from various cyclic motions caused by pulsatile blood pressure and daily activities. Due to this challenging environment, fatigue performance has become a critical issue for stent design. In this paper, a simple yet intriguing concept of stent design aimed at enhancing pulsatile fatigue life is investigated. The concept of this design is to shift the highly concentrated stresses/strains away from the crown and re-distribute them along the stress-free bar arm by tapering its strut width. Finite element models were developed to evaluate the mechanical integrity and pulsatile fatigue resistance of the stent to various loading conditions. Results show that the fatigue safety factor jumped to 2.5-3.0 times that of the standard stent with constant strut width. This is astonishing considering that the stent profile and scaffolding were not compromised. The findings of this paper provide an excellent approach to the optimization of future stent design to greatly improve stent fatigue performance. PMID:24045977

Hsiao, Hao-Ming; Yin, Ming-Ting

2014-02-01

291

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

292

Fatigue Life Recovery in Corroded Aluminium Alloys Using Bonded Composite Reinforcements  

NASA Astrophysics Data System (ADS)

Bonded composite reinforcements, such as boron/epoxy or carbon/epoxy, are becoming widely used to repair fatigue or stress corrosion cracks in aluminium alloy aircraft components. They also have considerable potential as repairs for corrosion damage, although the non-discrete nature of corrosion damage is a considerable complication. This paper describes studies on bonded repairs of two types of typical corrosion damage, both of which cause a dramatic reduction in fatigue life: a) relatively severe exfoliation and b) relatively minor pitting. Both studies are based on earlier Australian experimental studies on the structural significance of corrosion. In the studies described in this paper, other than the standard surface treatment used to attach the reinforcement no attempt was made to remove the corrosion damage. It is concluded that bonded repairs can provide useful fatigue life recovery even with serious exfoliation damage; however, such repairs should be regarded only as a temporary measure. For permanent and far more effective repairs most of the damage should be removed (ground-out) prior to reinforcement. In contrast, with minor pitting, greater than full life recovery is feasible. This observation also leads to the conclusion that bonded repairs will be tolerant of minor pitting inadvertently left after grind-out. Strain reduction by the reinforcement, as expected, is the major contributor to life extension. However, in the case of minor pitting environmental isolation by the adhesive is probably highly beneficial. Residual stresses in the metal resulting from the composite reinforcement causes some loss in patching efficiency.

Baker, Alan A.

2006-05-01

293

Field telemetry testing of long-arc, low-pressure turbine blading  

SciTech Connect

The next-to-last stage blades in Southern California Edison's Huntington Beach Station, Unit No. 2, LP turbine were retrofitted with long arc shrouds and continuous floating tiewires. The EPRI funded BLADE was used to perform a finite element analysis of the blades for the purpose of predicting operating stresses, natural frequencies, and fatigue life. A commercial finite element code, ANSYS, was also used to provide a comparison and assist in the development of a long-arc modeling capability in BLADE. A rotating telemetry test and impact modal test was performed on the LP turbine to provide data for comparison with the finite element predictions. This report documents the results of the analyses and tests performed. An assessment of the accuracy of the present version of the BLADE code in predicting low pressure turbine blade fatigue is provided. The turbine test and modal tests were successful in providing a limited amount of data for the ongoing verification of the BLADE code. The analysis results indicate the need for further refinements to BLADE in order to accurately predict the dynamics of long-arc grouping. The improvements are currently being made under EPRI project RP1865-7.

Burton, W. (Stress Technology, Inc., Rochester, NY (United States))

1992-01-01

294

Probabilistic Life Assessment Method of Low Cycle Fatigue for Power Plant Components  

NASA Astrophysics Data System (ADS)

This study focuses on the probabilistic analysis method to the determination of low cycle fatigue life for power plant components. The analysis incorporates standard life assessment modeling techniques used in the determination analysis of the low cycle fatigue. The probabilistic life assessment is developed to increase the reliability of life assessment. A probabilistic life assessment procedure can provide the engineer with the probability of structural failure as a function of operating time given the uncertainties in the input data. The probabilistic life assessment involves some uncertainties, for example, initial crack size, aspect ratio, crack initiation time, crack location, structural geometry, material properties, and loading condition, and a triangle distribution function is used for random variable generation. The resulting information provides the engineer with an assessment of the probability of structural failure. This information can form the basis of inspection planning and retirement-for-cause decisions. This study forms basis of the probabilistic life assessment technique and will be extended to other damage mechanisms.

Kang, Myung Soo

295

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

SciTech Connect

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

Syrett, B.C.; Viswanathan, R.

1982-02-01

296

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

Microsoft Academic Search

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

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

2009-01-01

297

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

298

The Effect of Drive Signal Limiting on High Cycle Fatigue Life Analysis  

NASA Technical Reports Server (NTRS)

It is common practice to assume a Gaussian distribution of both the input acceleration and the response when modeling random vibration tests. In the laboratory, however, shaker controllers often limit the drive signal to prevent high amplitude peaks. The high amplitudes may either be truncated at a given level (socalled brick wall limiting or abrupt clipping), or compressed (soft limiting), resulting in drive signals which are no longer Gaussian. The paper first introduces several methods for limiting a drive signal, including brick wall limiting and compression. The limited signal is then passed through a linear time-invariant system representing a device under test. High cycle fatigue life predictions are subsequently made using spectral fatigue and rainflow cycle counting schemes. The life predictions are compared with those obtained from unclipped input signals. Some guidelines are provided to help the test engineer decide how clipping should be applied under different test scenarios.

Kihm, Frederic; Rizzi, Stephen A.

2014-01-01

299

An analytical life prediction model for the crack propagation occurring in contact fatigue failure  

NASA Astrophysics Data System (ADS)

This analysis develops a three-dimensional analytical model for the crack propagation phase of the surface pitting failure process. An initiated pre-pitting crack is simulated as a semicircular inclined planar surface crack in a half-space. The cyclic contact fatigue loading is approximated by a repetitious Hertzian line loading moving quasi-statically across the half-space surface with both normal and shear components. Three-dimensional fracture mechanics is utilized to determine the three modes of stress intensity factors around the crack front. A mixed mode fatigue crack growth law is employed to estimate both crack growth geometry and crack propagation life. Numerical results are presented for a 45 degree inclined crack and for the 20 to 30 degree shallow crack angle which is experimentally observed. Life estimates from the present calculations are in line with previous experimental measurements.

Hanson, M. T.; Keer, L. M.

1992-07-01

300

Weld tool travel speed effects on fatigue life of friction stir welds in 5083 aluminium  

Microsoft Academic Search

This paper reports the results of a study into the influence of weld tool travel speed (in the range 80–200 mm\\/min) on the occurrence of ‘onion-skin’ forging-type defects (similar to the root defects known as ‘kissing bonds’) in single pass friction stir (SP FS) welds, and on the effect of these defects on fatigue crack initiation and overall life. Results

M. N James; D. G Hattingh; G. R Bradley

2003-01-01

301

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

Microsoft Academic Search

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

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

2010-01-01

302

The Study on Surface Roughness and Fatigue Life of Fastener Holes for 7075 Al Alloy  

Microsoft Academic Search

The aim of investigation is to analyze the effects of conventional drilling processes with multiple step and Winslow(one-step compound process) on the surface roughness and fatigue life of fastener holes drilled on 7075-7351 Al alloy for aircraft assembly. The Surface topography was tested and observed by using advanced detection devices. We found that the Ra value produced by multi-step drilling

Pei Xu-ming; Li Hao; Liu Jie; Zhang Duan-qin

2010-01-01

303

Influence of shot peening on the fatigue life of laser hardened 17-4PH steel  

Microsoft Academic Search

In order to improve the fatigue life of 17-4PH steel after laser hardening treatment, shot peening and dual shot peening treatments were performed on laser hardened 17-4PH steel in this paper. Characteristic changes of the roughness, hardness and residual stress distribution in three typical areas were discussed in order to gain a better understanding about the shot peening influence on

Zhou Wang; Chuanhai Jiang; Xiaoyan Gan; Yanhua Chen; Vincent Ji

2011-01-01

304

Fatigue life analysis of wheels on guideway vehicle using multibody dynamics  

Microsoft Academic Search

A guideway vehicle is used in automobile, semiconductor and LCD manufacturing industries to transport products efficiently.\\u000a Since the operating speed of the guideway vehicle should be increased for maximum productivity, the weight of the vehicle\\u000a has to be reduced, and this weight reduction may cause a failure of a part in the system. Therefore, the estimation of the\\u000a fatigue life

Soo-Ho Lee; Tae-Won Park; Joong-Kyung Park; Ji-Won Yoon; Kab-Jin Jun; Sung-Pil Jung

2009-01-01

305

Simulating the Residual Stress in an A356 Automotive Wheel and Its Impact on Fatigue Life  

Microsoft Academic Search

Keeping the weight of unsprung rotating components low is critical for fuel efficiency in automobiles; therefore, cast aluminum\\u000a alloys are the current material of choice for wheels. However, pores formed during solidification can combine with residual\\u000a stresses and in-service loads to reduce the fatigue life of this safety critical part. In this study, a model of the residual\\u000a stresses arising

P. Li; D. M. Maijer; T. C. Lindley; P. D. Lee

2007-01-01

306

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

307

The effect of higher harmonic forces on fatigue life of marine risers  

NASA Astrophysics Data System (ADS)

Higher harmonic responses measured in flexible riser model tests conducted within the Norwegian Deepwater Programme (NDP) are studied to evaluate the effect of higher harmonics of force on the fatigue life of risers. A large third-harmonic contribution and sometimes a fifth-harmonic are observed for the majority of test cases. Since existing methods of fatigue life estimation account for the effect of hydrodynamic forces only at the frequency of vortex shedding, a new methodology is introduced which takes into account the influence of the higher harmonic components: First, a new response reconstruction technique is used to reconstruct the entire span-wise riser motion in both the cross-flow and in-line directions based on measurements at specific points along the length. Then, a force database obtained from forced in-line and cross-flow motions of rigid cylinders is used to estimate the higher harmonic components of the force along the entire riser length. A significant decrease in fatigue life is obtained when the higher harmonic components of the fluid forces are considered.

Modarres-Sadeghi, Y.; Mukundan, H.; Dahl, J. M.; Hover, F. S.; Triantafyllou, M. S.

2010-01-01

308

Fatigue life parameter for type 304 stainless steel under biaxial-tensile loading at elevated temperature  

SciTech Connect

This paper describes a damage parameter for predicting fatigue life under biaxial-tensile loadings. Several studies have focused in the past on the situations where the in-plane biaxial stress ratio is negative; however, little attention has been paid for the cases involving both principal stresses in tension. A new testing method is used to carry out biaxial fatigue tests, at room and 427 C, on Type 304 stainless steel for different positive values of the stress ratio. In the experimental procedure, a disk-shaped specimen was used in connection with a spatial-arms mechanism which converts the uniaxial force generated by a conventional testing machine to radial forces extending the disk specimen. A modified virtual strain energy parameter is then suggested to normalize fatigue data obtained under a wide range of stress states. The proposed parameter accounts for the mean stress and the mean strain effects in an explicit form. In addition, the COD equivalent stress and strain concepts are adopted to account for the stress state biaxiality. The predictions of the proposed parameter are compared with the obtained experimental data and the correlation between the applied stress states and the experimental fatigue lives is discussed.

Zouani, A.; Bui-Quoc, T.; Bernard, M. [Ecole Polytechnique de Montreal (Canada). Dept. of Mechanical Engineering

1999-07-01

309

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

310

Fatigue criterion to system design, life and reliability: A primer  

NASA Technical Reports Server (NTRS)

A method for estimating a component's design survivability by incorporating finite element analysis and probabilistic material properties was developed. The method evaluates design parameters through direct comparisons of component survivability expressed in terms of Weibull parameters. The analysis was applied to a rotating disk with mounting bolt holes. The highest probability of failure occurred at, or near, the maximum shear stress region of the bolt holes. Distribution of material failure as a function of Weibull slope affects the probability of survival. Where Weibull parameters are unknown for a rotating disk, it may be permissible to assume Weibull parameters, as well as the stress-life exponent, in order to determine the qualitative effect of disk speed on the probability of survival.

Zaretsky, Erwin V.

1992-01-01

311

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

312

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

313

The surface fatigue life of contour induction hardened AISI 1552 gears  

NASA Astrophysics Data System (ADS)

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

1995-07-01

314

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

315

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

316

Deep surface rolling for fatigue life enhancement of laser clad aircraft aluminium alloy  

NASA Astrophysics Data System (ADS)

Deep surface rolling can introduce deep compressive residual stresses into the surface of aircraft metallic structure to extend its fatigue life. To develop cost-effective aircraft structural repair technologies such as laser cladding, deep surface rolling was considered as an advanced post-repair surface enhancement technology. In this study, aluminium alloy 7075-T651 specimens with a blend-out region were first repaired using laser cladding technology. The surface of the laser cladding region was then treated by deep surface rolling. Fatigue testing was subsequently conducted for the laser clad, deep surface rolled and post-heat treated laser clad specimens. It was found that deep surface rolling can significantly improve the fatigue life in comparison with the laser clad baseline repair. In addition, three dimensional residual stresses were measured using neutron diffraction techniques. The results demonstrate that beneficial compressive residual stresses induced by deep surface rolling can reach considerable depths (more than 1.0 mm) below the laser clad surface.

Zhuang, W.; Liu, Q.; Djugum, R.; Sharp, P. K.; Paradowska, A.

2014-11-01

317

Study of an engineering method for fatigue life estimation and safety evaluation of well drilling string  

SciTech Connect

In this paper, an engineering method for calculating the loading capacity, predicting the residual life, making the safety evaluation of drilling pipe and connection joint based on fracture mechanics was presented. The stress intensity factors K{sub I}, K{sub II} and K{sub III} at the critical sections were calculated by means of 3D FEM, then the fracture toughness J{sub c} under mixed mode loading of drilling pipe steel 37Mn5 and 4340 was obtained. In addition, the tests of fatigue crack initiation under different stress concentration state and fatigue crack growth performance of the same steel were carried out, and corresponding expressive formulae were researched.

Deng Zengjie; Zhang Yi; Li Helin [China National Petroleum Corp., Xi`an, Shaanxi (China). Tubular Goods Research Center; Li Zhonghua [Xi`an Jiaotong Univ., Xi`an, Shaanxi (China)

1995-12-31

318

Cellular and Molecular Life Sciences REVIEW Fatigue in neuromuscular disorders: focus on Guillain–Barré  

E-print Network

Ó The Author(s) 2009. This article is published with open access at Springerlink.com Abstract Fatigue accounts for an important part of the burden experienced by patients with neuromuscular disorders. Substantial high prevalence rates of fatigue are reported in a wide range of neuromuscular disorders, such as Guillain–Barré syndrome and Pompe disease. Fatigue can be subdivided into experienced fatigue and physiological fatigue. Physiological fatigue in turn can be of central or peripheral origin. Peripheral fatigue is an important contributor to fatigue in neuromuscular disorders, but in reaction to neuromuscular disease fatigue of central origin can be an important protective mechanism to restrict further damage. In most cases, severity of fatigue seems to be related with disease severity, possibly with the exception of fatigue occurring in a monophasic disorder like Guillain–Barré syndrome. Treatment of fatigue in neuromuscular disease starts with symptomatic treatment of the underlying disease. When symptoms of fatigue J. M. de Vries (&)

Pompe Disease; P. A. Van Doorn; J. B. J. Bussmann; P. A. Van Doorn

319

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

320

Improvement of Work Ability, Quality of Life, and Fatigue in Patients With Rheumatoid Arthritis Treated With Adalimumab  

Microsoft Academic Search

Objective: To assess the effect of 12-month treatment with adalimumab on work ability, quality of life, and fatigue in patients with active rheumatoid arthritis ( RA). Methods: One hundred twenty-six patients with active RA started treatment with adalimumab. Primary outcome measurements were work ability, assessed by the first item of the Work Ability Index, quality of life, assessed by the

Marieke M. J. Herenius; Jan L. Hoving; Judith K. Sluiter; Hennie G. Raterman; Willem F. Lems; Ben A. C. Dijkmans; Paul Peter Tak; Mike T. Nurmohamed; Alexandre E. Voskuyl; Monique H. W. Frings-Dresen

2010-01-01

321

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

322

Statistical investigation of the fatigue life based on small-crack growth law  

NASA Astrophysics Data System (ADS)

Rotating bending fatigue tests were carried out on specimens of a 5052 Al alloy with two small blind holes, in order to investigate the distribution characteristics of the fatigue crack growth life based on the small-crack growth law dl/dN = C1(sigma super n sub a)l. The crack growth rate in each specimen was determined uniquely by (sigma super n sub a)l, therefore the crack growth life can be predicted by the small-crack growth law. On the assumption that the value of n is a fixed one and the value of C1 is a random variable, the distribution of the crack growth rate can be evaluated through the value of C3 in the relationship dl/dN = (C3)l. C3 follows a Weibull distribution approximately. The calculated distribution of the crack growth life based on the small-crack growth law and the distribution of C3 is in good agreement with the experimental results.

Kawagoishi, Norio; Nisitani, Hironobu; Goto, Masahiro; Toyohiro, Toshinobu; Kitayama, Satoshi

1993-01-01

323

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

324

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

325

The relationship between extrusion die line roughness and high cycle fatigue life of an AA6082 alloy  

Microsoft Academic Search

The effect of surface finish on the fatigue life of hollow extruded AA6082 was studied by comparing results from specimens with as-extruded surfaces to results from specimens with polished surfaces. Extrusion die lines are the main contributor to surface roughening, and since die lines are parallel to the extrusion direction, distinct variations exist between fatigue lives of as-extruded specimens taken

N. Nanninga; C. White

2009-01-01

326

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

Microsoft Academic Search

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

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

2008-01-01

327

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

328

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

329

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

330

An investigation of the reduction in tensile strength and fatigue life of pre-corroded 7075-T6 aluminum alloy  

NASA Astrophysics Data System (ADS)

In aging aircraft, the synergetic interaction between corrosion and fatigue has been shown to reduce the life expectancy of aluminum alloys. The objective of this study was to quantify the effects of corrosion, in terms of mass loss per unit area, on the static strength and fatigue life of 7075-T6 aluminum alloy. This was an experimental study in which test specimens were corroded in a laboratory environment. The corrosion process was accelerated by use of a corrosion cell. Test specimens were cut from flat sheets of aluminum and covered with masking material to restrict corrosion to a confined area. After testing, the fatigue life, ultimate tensile strength (UTS), and hardness of the specimens were observed to drop significantly with small amounts of corrosion. After the initial decrease, the UTS was observed to decrease linearly with increasing corrosion levels. The fatigue life of the specimens decreased in an inverse exponential fashion as mass loss per unit area increased. The hardness values of the corroded surfaces were also observed to drop. The topology of the pits and the related subsurface damage produced areas of high stress concentration resulting in the immediate reduction of UTS and fatigue life of the specimens. Subsurface corrosion damage was responsible for the reduction in hardness.

Obert, B.; Ngo, K.; Hashemi, J.; Ekwaro-Osire, S.; Sivam, T. P.

2000-08-01

331

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

332

Low Cycle Fatigue Behavior of 316LN Stainless Steel Alloyed with Varying Nitrogen Content. Part II: Fatigue Life and Fracture Behavior  

NASA Astrophysics Data System (ADS)

Influence of nitrogen content on low cycle fatigue life and fracture behavior of 316LN stainless steel (SS) alloyed with 0.07 to 0.22 wt pct nitrogen is presented in this paper over a range of total strain amplitudes ( ±0.25 to 1.0 pct) in the temperature range from 773 K to 873 K (500 °C to 600 °C). The combined effect of nitrogen and strain amplitude on fatigue life is observed to be complex i.e., fatigue life either decreases/increases with increase in nitrogen content or saturates/peaks at 0.14 wt pct N depending on strain amplitude and temperature. Coffin-Manson plots (CMPs) revealed both single-slope and dual-slope strain-life curves depending on the test temperature and nitrogen content. 316LN SS containing 0.07 and 0.22 wt pct N showed nearly single-slope CMP at all test temperatures, while 316LN SS with 0.11 and 0.14 wt pct N exhibited marked dual-slope behavior at 773 K (500 °C) that changes to single-slope behavior at 873 K (600 °C). The changes in slope of CMP are found to be in good correlation with deformation substructural changes.

Prasad Reddy, G. V.; Sandhya, R.; Sankaran, S.; Mathew, M. D.

2014-10-01

333

Life prediction of thermomechanical fatigue using total strain version of strainrange partitioning (SRP): A proposal  

NASA Technical Reports Server (NTRS)

A method is proposed (without experimental verification) for extending the total strain version of Strainrange Partitioning (TS-SRP) to predict the lives of thermomechanical fatigue (TMF) cycles. The principal feature of TS SRP is the determination of the time-temperature-waveshape dependent elastic strainrange versus life lines that are added subsequently to the classical inelastic strainrange versus life lines to form the total strainrange versus life relations. The procedure is based on a derived relation between failure and flow behavior. Failure behavior is represented by conventional SRP inelastic strainrange versus cyclic life relations, while flow behavior is captured in terms of the cyclic stress-strain response characteristics. Stress-strain response is calculated from simple equations developed from approximations to more complex cyclic constitutive models. For applications to TMF life prediction, a new testing technique, bithermal cycling, is proposed as a means for generating the inelastic strainrange versus life relations. Flow relations for use in predicting TMF lives would normally be obtained from approximations to complex thermomechanical constitutive models. Bithermal flow testing is also proposed as an alternative to thermomechanical flow testing at low strainranges where the hysteresis loop is difficult to analyze.

Saltsman, James F.; Halford, Gary R.

1988-01-01

334

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

335

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

336

Thermal Fatigue Life of Glidcop Al-15 High-Heat-Load Components  

NASA Astrophysics Data System (ADS)

Shanghai Synchrotron Radiation Facility (SSRF) is a third-generation of synchrotron radiation light source and is presently under construction as a large scale national scientific project in China. Depending on the outstanding thermal and mechanical performance, Glidcop Al-15, a dispersion strengthened copper alloy, is chosen to serve for the high-heat-load components at beam line front end in SSRF. Present study is to investigate the thermal fatigue lives of critical SSRF components. A nonlinear finite element method (FEM) is used to simulate the nonlinear three dimensional stress-strain fields of the critical component-Mask2 at SSRF beam line. The method consists of transient temperature analyses followed by elastic-plastic stress analyses. Then, a critical plane approach is used to predict the thermal fatigue life of mask2. The critical plane approach is appropriate for estimating service life of critical SSRF components since the results are in good consistent with the experimental ones taken at the Advanced Photon Source (APS).

Jin, J. F.; Xiao, W. L.; Chen, H. B.

2010-05-01

337

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

338

Microstructures and fatigue life of SnAgCu solder joints bearing Nano-Al particles in QFP devices  

NASA Astrophysics Data System (ADS)

Microstructures and fatigue life of SnAgCu and SnAgCu bearing nano-Al particles in QFP (Quad flat package) devices were investigated, respectively. Results show that the addition of nano-Al particles into SnAgCu solder can refine the microstructures of matrix microstructure. Moreover, the nano-Al particles present in the solder matrix, act as obstacles which can create a back stress, resisting the motion of dislocations. In QFP device, it is found that the addition of nano-Al particles can increase the fatigue life by 32% compared with the SnAgCu solder joints during thermal cycling loading.

Zhang, Liang; Fan, Xi-ying; Guo, Yong-huan; He, Cheng-wen

2014-05-01

339

A high temperature fatigue life prediction computer code based on the total strain version of StrainRange Partitioning (SRP)  

NASA Technical Reports Server (NTRS)

A recently developed high-temperature fatigue life prediction computer code is presented and an example of its usage given. The code discussed is based on the Total Strain version of Strainrange Partitioning (TS-SRP). Included in this code are procedures for characterizing the creep-fatigue durability behavior of an alloy according to TS-SRP guidelines and predicting cyclic life for complex cycle types for both isothermal and thermomechanical conditions. A reasonably extensive materials properties database is included with the code.

Mcgaw, Michael A.; Saltsman, James F.

1993-01-01

340

Fatigue reliability of wind turbine components  

SciTech Connect

Fatigue life estimates for wind turbine components can be extremely variable due to both inherently random and uncertain parameters. A structural reliability analysis is used to qualify the probability that the fatigue life will fall short of a selected target. Reliability analysis also produces measures of the relative importance of the various sources of uncertainty and the sensitivity of the reliability to each input parameter. The process of obtaining reliability estimates is briefly outlined. An example fatigue reliability calculation for a blade joint is formulated; reliability estimates, importance factors, and sensitivities are produced. Guidance in selecting distribution functions for the random variables used to model the random and uncertain parameters is also provided. 5 refs., 9 figs., 1 tab.

Veers, P.S.

1990-01-01

341

The effect of porosity and gamma-gamma' eutectic content on the low cycle fatigue behavior of hydrogen-charged PWA-1480  

NASA Technical Reports Server (NTRS)

Single crystal superalloys such as PWA 1480 are considered for turbopump blades in the main engines of the space shuttle. As fatigue resistance in a hydrogen environment is a key issue in this application, a study of the effect of porosity and gamma-gamma' eutectic content on the fatigue life of a hydrogen-charged PWA 1480 was performed. Porosity and eutectic were linked to fatigue initiation, and therefore reduction of either of both may be one means to improve fatigue life of PWA 1480 when hydrogen is present.

Gayda, John; Dreshfield, Robert L.; Gabb, Timothy P.

1991-01-01

342

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

343

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

344

Multidisciplinary Design Optimization for Glass-Fiber Epoxy-Matrix Composite 5 MW Horizontal-Axis Wind-Turbine Blades  

NASA Astrophysics Data System (ADS)

A multi-disciplinary design-optimization procedure has been introduced and used for the development of cost-effective glass-fiber reinforced epoxy-matrix composite 5 MW horizontal-axis wind-turbine (HAWT) blades. The turbine-blade cost-effectiveness has been defined using the cost of energy (CoE), i.e., a ratio of the three-blade HAWT rotor development/fabrication cost and the associated annual energy production. To assess the annual energy production as a function of the blade design and operating conditions, an aerodynamics-based computational analysis had to be employed. As far as the turbine blade cost is concerned, it is assessed for a given aerodynamic design by separately computing the blade mass and the associated blade-mass/size-dependent production cost. For each aerodynamic design analyzed, a structural finite element-based and a post-processing life-cycle assessment analyses were employed in order to determine a minimal blade mass which ensures that the functional requirements pertaining to the quasi-static strength of the blade, fatigue-controlled blade durability and blade stiffness are satisfied. To determine the turbine-blade production cost (for the currently prevailing fabrication process, the wet lay-up) available data regarding the industry manufacturing experience were combined with the attendant blade mass, surface area, and the duration of the assumed production run. The work clearly revealed the challenges associated with simultaneously satisfying the strength, durability and stiffness requirements while maintaining a high level of wind-energy capture efficiency and a lower production cost.

Grujicic, M.; Arakere, G.; Pandurangan, B.; Sellappan, V.; Vallejo, A.; Ozen, M.

2010-11-01

345

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

346

Improvement in surface fatigue life of hardened gears by high-intensity shot peening  

NASA Technical Reports Server (NTRS)

Two groups of carburized, hardened, and ground spur gears that were manufactured from the same heat vacuum induction melted vacuum arc melted (VIM VAR) AISI 9310 steel were endurance tested for surface fatigue. Both groups were manufactured with a standard ground 16 rms surface finish. One group was subjected to a shot peening (SP) intensity of 7 to 9A, and the second group was subjected to a SP intensity of 15 to 17A. All gears were honed after SP to a surface finish of 16 rms. The gear pitch diameter was 8.89 cm. Test conditions were a maximum Hertz stress of 1.71 GPa, a gear temperature of 350 K, and a speed of 10000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The following results were obtained: The 10 pct. surface fatigue (pitting) life of the high intensity (15 to 17A) SPed gears was 2.15 times that of the medium intensity (7 to 9A) SPed gears, the same as that calculated from measured residual stress at a depth of 127 microns. The measured residual stress for the high intensity SPed gears was 57 pct. higher than that for the medium intensity SPed gears at a depth of 127 microns and 540 pct. higher at a depth of 51 microns.

Townsend, Dennis P.

1992-01-01

347

Improvement in surface fatigue life of hardened gears by high-intensity shot peening  

NASA Astrophysics Data System (ADS)

Two groups of carburized, hardened, and ground spur gears that were manufactured from the same heat vacuum induction melted vacuum arc melted (VIM VAR) AISI 9310 steel were endurance tested for surface fatigue. Both groups were manufactured with a standard ground 16 rms surface finish. One group was subjected to a shot peening (SP) intensity of 7 to 9A, and the second group was subjected to a SP intensity of 15 to 17A. All gears were honed after SP to a surface finish of 16 rms. The gear pitch diameter was 8.89 cm. Test conditions were a maximum Hertz stress of 1.71 GPa, a gear temperature of 350 K, and a speed of 10000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The following results were obtained: The 10 pct. surface fatigue (pitting) life of the high intensity (15 to 17A) SPed gears was 2.15 times that of the medium intensity (7 to 9A) SPed gears, the same as that calculated from measured residual stress at a depth of 127 microns. The measured residual stress for the high intensity SPed gears was 57 pct. higher than that for the medium intensity SPed gears at a depth of 127 microns and 540 pct. higher at a depth of 51 microns.

Townsend, Dennis P.

1992-04-01

348

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

349

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

350

Creep Cavity Growth Model for Creep-Fatigue Life Prediction of a Unidirectional W/Cu Composite.  

National Technical Information Service (NTIS)

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...

Y. Kim, M. J. Verrilli, G. R. Halford

1992-01-01

351

Optimising FSW process parameters to minimise defects and maximise fatigue life in 5083-H321 aluminium alloy  

Microsoft Academic Search

This paper presents a systematic approach to optimising FSW process parameters (tool rotational speed and feed rate) through consideration of frictional power input. Frictional power governs the tensile strength and the fatigue life in this 5083-H321 alloy through its effect on plastic flow processes in the thermo-mechanically affected zone (TMAZ) of the weld. Although, a close relationship therefore exists between

H. Lombard; D. G. Hattingh; A. Steuwer; M. N. James

2008-01-01

352

Study on the turbine vane and blade for a 1500 C class industrial gas turbine  

NASA Astrophysics Data System (ADS)

This paper describes the summary of a three-year development program for the first-stage stationary vane and rotating blade for the next generation, 1500 C class, high-efficiency gas turbine. In such a high-temperature gas turbine, the first turbine vane and blade are the most important hot parts. Full-coverage film cooling (FCFC) is adopted for the cooling scheme, and directionally solidified (DS) nickel base superalloy and thermal barrier coating (TBC) will be used to prolong the creep and thermal fatigue life. The concept of the cooling configuration, fundamental cascade test results, and material test results will be presented.

Amagasa, S.; Shimomura, K.; Kadowaki, M.; Takeishi, K.; Kawai, H.; Aoki, S.; Aoyama, K.

1994-07-01

353

Surface fatigue life of CBN and vitreous ground carburized and hardened AISI 9310 spur gears  

NASA Technical Reports Server (NTRS)

Spur gear surface endurance tests were conducted to investigate CBN ground AISI 9310 spur gears for use in aircraft applications, to determine their endurance characteristics and to compare the results with the endurance of standard vitreous ground AISI 9310 spur gears. Tests were conducted with VIM-VAR AISI 9310 carburized and hardened gears that were finish ground with either CBN or vitreous grinding methods. Test conditions were an inlet oil temeprature of 320 K (116 F), an outlet oil temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. The CBN ground gears exhibited a surface fatigue life that was slightly better than the vitreous ground gears. The subsurface residual stress of the CBN ground gears was approximately the same as that for the standard vitreous ground gears for the CBN grinding method used.

Townsend, Dennis P.; Patel, P. R.

1988-01-01

354

Fatigue life estimation program for Part 23 airplanes, `AFS.FOR`  

SciTech Connect

The purpose of this paper is to introduce to the general aviation industry a computer program which estimates the safe fatigue life of any Federal Aviation Regulation (FAR) Part 23 airplane. The algorithm uses the methodology (Miner`s Linear Cumulative Damage Theory) and the various data presented in the Federal Aviation Administration (FAA) Report No. AFS-120-73-2, dated May 1973. The program is written in FORTRAN 77 language and is executable on a desk top personal computer. The program prompts the user for the input data needed and provides a variety of options for its intended use. The program is envisaged to be released through issuance of a FAA report, which will contain the appropriate comments, instructions, warnings and limitations.

Kaul, S.K.

1993-12-31

355

Life prediction of expulsion bladders through fatigue test and fold strain analysis.  

NASA Technical Reports Server (NTRS)

Consideration of the problem of reducing the probability of mechanical failure of bladder systems used for the expulsion of propellants into liquid rocket engines. It is shown that individual local folds in collapsing bladders can be classified into single and double folds, specifiable by nondimensional geometrical parameters which directly define the maximum strains at these folds. From these maximum strains the number of collapse/inflation cycles to failure can be obtained from low-cycle fatigue data experimentally determined for the bladder material of interest. Cycle life data are presented in terms of true maximum strain for four metals, two plastics, and two elastomers. It is found that double folds give rise to much more severe folding strains than do simple folds.

Chu, H. N.; Unterberg, W.

1972-01-01

356

Health-related quality of life in chronic fatigue syndrome: predictors of physical functioning and psychological distress.  

PubMed

This study investigated health-related quality of life (HRQoL; physical functioning and psychological distress) in an Australian chronic fatigue syndrome (CFS) population. The aims of the study were to compare HRQoL in those with CFS to the normal population, and to investigate the extent to which sociodemographic (age, gender, partner status, education), illness-related (illness duration, symptom frequency), and fatigue severity (physical, mental) variables predicted HRQoL. A total of 139 people meeting CFS criteria completed questionnaires. HRQoL was assessed using standardised measures of distress and physical functioning. Compared with norms, those with CFS obtained significantly lower scores on all physical functioning areas, whereas 63% of participants reported clinically significant psychological distress. Hierarchical regression analyses indicated that physical fatigue severity and symptom frequency were the strongest predictors of deficits in physical domain HRQoL. Physical HRQoL outcomes were also predicted by mental fatigue severity, older age, and female gender. All predictors were unrelated to psychological distress apart from weak positive associations with physical fatigue and symptom frequency. Results identify a potent set of predictors of HRQoL and show that CFS has a pervasive negative impact on quality of life, particularly physical and psychological functioning. PMID:18350466

Lowry, Timothy J; Pakenham, Kenneth I

2008-03-01

357

Impact of Poststroke Fatigue on Health-Related Quality of Life of Nigerian Stroke Survivors  

PubMed Central

Background and Purpose A stroke event is often characterized by a number of debilitating consequences that may impact negatively on the health-related quality of life (HRQL) of survivors. This study examined the impact of poststroke fatigue (PSF), a persistent and prevalent stroke consequence, on HRQL of Nigerian stroke survivors. Methods One hundred stroke survivors were recruited from the physiotherapy outpatient departments of two tertiary hospitals in Northern Nigeria. The Fatigue Severity Scale and Health-Related Quality of Life in Stroke Patients-26 were respectively used to assess PSF and HRQL. The independent impact of PSF on overall and domain-specific HRQL was examined using hierarchical regression analyses. Results Mean age of the stroke survivors was 55.32 years (SD 13.9 years). The majority were males (66%), had suffered ischemic stroke (70%) and presented with moderately severe disability (42%). After controlling for demographic and stroke-related variables, PSF was found to be significantly and independently associated with all the domains of HRQL albeit at varying degrees. While the influence of PSF on the emotional domain was the most pronounced and uniquely contributed to 15% of the variance in the domain, its influence on the cognitive domain was the least prominent. PSF also solely accounted for 9% of the variation in overall HRQL with higher levels of PSF related with lower HRQL. Conclusions Being a potentially treatable condition, PSF's significant impact on HRQL has implications for successful stroke care and rehabilitation. For instance, addressing PSF through appropriate interventions may assist in enhancing HRQL of stroke survivors. PMID:25328879

Adamu, Abdulbaqi

2014-01-01

358

Fatigue and malaise” as a quality-of-life indicator in small-cell lung cancer patients  

Microsoft Academic Search

Fatigue and malaise” (FM) is a frequent, non-specific symptom of cancer patients caused by the disease, its treatment and psychological distress. Since comprehensive quality of life assessment is often not feasible in multicentre clinical trials, short, but clinically relevant, quality of life indicators have to be defined. In a representative subsample of 127 patients in a phase-III randomized small-cell lung

Christoph Hiirny; Jiirg Bernhard; Rudolf Joss; Ernst Schatzmann; Franco Cavalli; Kurt Brunner; Pierre Alberto; Hans-Jörg Senn; Urs Metzger

1993-01-01

359

Surface fatigue life of M50NiL and AISI 9310 spur gears and R C bars  

NASA Technical Reports Server (NTRS)

Spur gear endurance tests and rolling element surface fatigue tests were conducted to study vacuum induction melted, vacuum arc remelted (VIM-VAR) M50NiL steel for use as a gear steel in advanced aircraft applications, to determine its endurance characteristics, and to compare the results with those for standard VAR and VIM-VAR AISI 9310 gear material. Tests were conducted with spur gears and rolling contact bars manufactured from VIM-VAR M50NiL and VAR and VIM-VAR AISI 9310. The gear pitch diameter was 8.9 cm. Gear test conditions were an inlet oil temperature of 320 K, and outlet oil temperature of 350 K, a maximum Hertz stress of 1.71 GPa, and a speed of 10000 rpm. Bench rolling element fatigue tests were conducted at ambient temperatures with a bar speed of 12,500 rpm and a maximum Hertz stress of 4.83 GPa. The VIM-VAR M50NiL gears had a surface fatigue life that was 4.5 and 11.5 times that for VIM-VAR and VAR AISI 9310 gears, respectively. The surface fatigue life of the VIM-VAR M50NiL rolling contact bars was 13.2 and 21.6 times that for the VIM-VAR and VAR AISI 9310, respectively. The VIM-VAR M50NiL material was shown to have good resistance to fracture through a fatigue spall and superior fatigue life to both other gears.

Townsend, Dennis P.; Bamberger, Eric N.

1991-01-01

360

FULL-SCALE BLADE TESTING ENHANCED BY ACOUSTIC EMISSION MONITORING  

Microsoft Academic Search

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

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

361

A study of rolling-contact fatigue of bearing steel coated with physical vapor deposition TiN films: Coating response to cyclic contact stress and physical mechanisms underlying coating effect on the fatigue life  

Microsoft Academic Search

The effect of physical vapor deposition (PVD) TiN coatings of different thicknesses on the rolling-contact fatigue (RCF) life of coated specimens is studied experimentally. Based on the results of conventional three-ball-on-rod testing, the optimum film thickness is found to be about 0.75 ?m. Thinner coatings do not significantly affect the fatigue life, while much thicker ones have a negative effect

I. A. Polonsky; T. P. Chang; L. M. Keer; W. D. Sproul

1998-01-01

362

Grain boundary oxidation and an analysis of the effects of pre-oxidation on subsequent fatigue 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.

1986-01-01

363

Tensile, Fracture, Fatigue Life, and Fatigue Crack Growth Rate Behavior of Structural Materials for the ITER Magnets: The European Contribution  

Microsoft Academic Search

Fatigue crack growth rates (FCGR) are determined for R ratios between 0.1 - 0.7 at 7 K for three full-size Mock-up Models of the ITER Toroidal Field coil case produced by modified Type 316LN alloys. A representative forged block of Model 3 is additionally manufactured to determine its improved spatial tensile properties and compare it to former Model 3 data.

A. Nyilas; K. Nikbin; A. Portone; C. Sborchia

2004-01-01

364

Rolling-element fatigue life of silicon nitride balls. [as compared to that of steel, ceramic, and cermet materials  

NASA Technical Reports Server (NTRS)

The five-ball fatigue tester was used to evaluate silicon nitride as a rolling-element bearing material. Results indicate that hot-pressed silicon nitride running against steel may be expected to yield fatigue lives comparable to or greater than those of bearing quality steel running against steel at stress levels typical rolling-element bearing application. The fatigue life of hot-pressed silicon nitride is considerably greater than that of any ceramic or cermet tested. Computer analysis indicates that there is no improvement in the lives of 120-mm-bore angular--contact ball bearings of the same geometry operating at DN values from 2 to 4 million where hot-pressed silicon nitride balls are used in place of steel balls.

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

1974-01-01

365

Displacement measurement on specimens subjected to non-Gaussian random vibrations in fatigue life tests  

NASA Astrophysics Data System (ADS)

High-cycle fatigue life tests conducted using controlled random vibrations are commonly used to evaluate failure in components and structures. In most cases, a Gaussian distribution of both the input vibration and the stress response is assumed, while real-life loads may be non-Gaussian causing the response to be non-Gaussian as well. Generating non-Gaussian drive signals with high kurtosis and a given power spectral density, however, does not always guarantee that the stress response will actually be non-Gaussian, because this depends on the adherence of the tested system to the Central Limit Theorem. On the other side, suitable measurement methods need to be developed in order to estimate the stress amplitude response at critical failure locations, and therefore to evaluate and select input loads. In this paper, a simple test rig with a notched cantilevered specimen was developed to measure the response and examine the kurtosis values in the case of stationary Gaussian, stationary non-Gaussian, and non-stationary non-Gaussian excitation signals. The Laser Doppler Vibrometry (LDV) technique was used for the first time in this type of test, to estimate the specimen stress amplitude response in terms of differential displacement at the notch section ends. A method based on the use of accelerometers to correct for the occasional signal drops occurring during the experiment is described and the results are discussed with respect to the ability of the test procedure to evaluate the output signal.

Troncossi, M.; Di Sante, R.; Rivola, A.

2014-05-01

366

Fatigue Life Prediction in Rapid Die Casting - Preliminary Work in View of Current Research  

SciTech Connect

Numerical simulation technique as a prediction tool is slowly adopted in metal casting industry for predicting design modelling solidification analysis. The reasons for this activity is found in the need to further enhance the geometrical design and mechanical properties of the tool design and the correct prediction methodology to fulfil industrial needs. The present state of numerical simulation capabilities in rapid die casting technologies is reviewed and the failure mode mechanisms of thermal fatigue, aimed at developing a numerical simulation with a systematic design guidance for predicting the thermal cyclic loading analysis and improvement is presented along with several other methods. The economic benefits of a numerical simulation technique in die casting are limited to tool life time, mechanical properties and design guidance. The extensive computer capabilities of a numerical simulation with a systematic design guidance methodology are exploited to provide a solution for flexible design, mechanical properties and mould life time. Related research carried out worldwide by different organisations and academic institutions are discussed.

Chuan Huat Ng [Faculty of Mechanical and Manufacturing Engineering (FKMP), Kolej Universiti Teknologi Tun Hussein Onn (KUiTTHO), P.O.Box 101, 86400 Parit Raja, Batu Pahat, Johor (Malaysia); Grote, Karl-Heinrich [Institut fuer Maschinenkonstruktion, Lehrstuhl Konstruktionstechnik, Otto-von-Guericke University Magdeburg, Universitaetsplatz 2, 39106 Magdeburg (Germany); Baehr, Ruediger [Institut fuer Fertigungstechnik und Qualitaetssicherung, Ur und Umformtechnik, Otto-von-Guericke University Magdeburg, Universitaetsplatz 2, 39106 Magdeburg (Germany)

2007-05-17

367

Finite element analysis of sucker rod couplings with guidelines for improving fatigue life  

SciTech Connect

The response of a variety of sucker rod couplings to an applied axial load was simulated using axisymmetric finite element models. The calculations investigated three sucker rod sizes and various combinations of the slimhole, Spiralock, and Flexbar modifications to the coupling. In addition, the effect of various make-ups (assembly tightness) on the performance of coupling was investigated. An axial load was applied to the sucker rod ranging from {minus}5 ksi to 40 ksi, encompassing three load cycles identified on a modified Goodman diagram as acceptable for indefinite service life of the sucker rods. The simulations of the various coupling geometries and make-ups were evaluated with respect to how well they accomplish the two primary objectives of preloading threaded couplings: (1) to lock the threaded coupling together so that it will not loosen and eventually uncouple, and (2) to improve the fatigue resistance of the threaded connection by reducing the stress amplitude in the coupling when subjected to cyclic loading. Perhaps the most significant finding in this study was the characterization of the coupling parameters which affect two stress measures. The mean hydrostatic stress, which determines the permissible effective alternating stress, is a function of the coupling make-up. Whereas, the alternating effective stress is a function of the relative stiffnesses of the pin and box sections of the coupling and, as long as the coupling does not separate, is unaffected by the amount of circumferential displacement applied during make-up. The results of this study suggest approaches for improving the fatigue resistance of sucker rod couplings.

Hoffman, E.L. [Sandia National Labs., Albuquerque, NM (United States). Engineering and Structural Mechanics Div.

1997-09-01

368

Neural network fatigue life prediction in steel i-beams using mathematically modeled acoustic emission data  

NASA Astrophysics Data System (ADS)

The purpose of this research is to predict fatigue cracking in metal beams using mathematically modeled acoustic emission (AE) data. The AE data was collected from nine samples of steel Ibeam that were subjected to three-point bending caused by cyclic loading. The data gathered during these tests were filtered in order to remove long duration hits, multiple hit data, and obvious outliers. Based on the duration, energy, amplitude, and average frequency of the AE hits, the filtered data were classified into the various failure mechanisms of metals using NeuralWorksRTM Professional II/Plus software based self-organizing map (SOM) neural network. The parameters from mathematically modeled AE failure mechanism data were used to predict plastic deformation data. Amplitude data from classified plastic deformation data is mathematically modeled herein using bounded Johnson distributions and Weibull distribution. A backpropagation neural network (BPNN) is generated using MATLABRTM. This BPNN is able to predict the number of cycles that ultimately cause the steel I-beams to fail via five different models of plastic deformation data. These five models are data without any mathematical modeling and four which are mathematically modeled using three methods of bounded Johnson distribution (Slifker and Shapiro, Mage and Linearization) and Weibull distribution. Currently, the best method is the Linearization method that has prediction error not more than 17%. Multiple linear regression (MLR) analysis is also performed on the four sets of mathematically modeled plastic deformation data as named above using the bounded Johnson and Weibull shape parameters. The MLR gives the best prediction for the Linearized method which has a prediction error not more than 2%. The final conclusion made is that both BPNN and MLR are excellent tools for accurate fatigue life cycle prediction.

Selvadorai, Prathikshen N.

369

The Relationship between Qi Deficiency, Cancer-related Fatigue and Quality of Life in Cancer Patients  

PubMed Central

Background: Qi (? qì) refers to the vital energy of the body in Traditional Chinese medicines (TCM). Qi deficiency (?? qì x?) is the most common symptom in cancer patients according to the concept of TCM. We hypothesized that cancer patients with Qi deficiency suffer from poor quality of life (QOL) and fatigue. Method: Among the 256 registered cancer patients screened at our outpatient clinic, a total of 198 were enrolled. The inclusion criteria were (1) age between 18 and 70 years, (2) cancer diagnosis confirmed by the professional physician, (3) being Chinese, and (4) Eastern Cooperative Oncology Group (ECOG) performance status rating (PSR) ? 3. The major outcome is the difference in QOL score in cancer patients with and without Qi deficiency. Results: The initial results showed statistically significant differences in WHO-QOL scores in physical, psychological, and social domains between the groups with and without Qi deficiency as well as the groups with and without cancerrelated fatigue (CRF). All patients with CRF present were also diagnosed as Qi deficient. In addition, among the patients with no CRF, 39.9% (69/173) were diagnosed as suffering from Qi deficiency, which led to poor QOL. Conclusions: The present study showed statistically significant difference in WHO-QOL scores in physical, psychological, and social domains between the groups with and without Qi deficiency as well as the groups with and without CRF. Cancer patients diagnosed with Qi deficiency or CRF have poor QOL. The concept of Qi deficiency in TCM might be applied to cancer health care. PMID:24716125

Hsu, Chung-Hua; Lee, Chia-Jung; Chien, Tsai-Ju; Lin, Che-Pin; Chen, Chien-Hung; Yuen, Mei-Jen; Lai, Yuen-Liang

2012-01-01

370

Vibration of axial turbomachinery blades: Measurement and fluid-structure interactions  

NASA Astrophysics Data System (ADS)

The focus of this dissertation is on turbomachinery blade vibration measurements and unsteady fluid-structure interactions. Vibration of turbomachinery blades are critical to jet engine durability and performance. The combined high natural frequency of the vibrations and long service life of modern jet engines can result in high cycle fatigue. There are two main topics discussed in this dissertation. The first topic of this dissertation is the investigation of unsteady fluid-structure interactions an isolated compressor blade in transonic flow. This was preferred as a simpler alternative to a cascade of blades. Note that the boundary conditions of an single vibrating blade are much simpler than those for a vibrating cascade, and so a more clear understanding of the fundamental interactions are provided with the simple setup. New insights were obtained regarding aerodynamic damping and "quasi-steady" blade vibrations in transonic flow. The second topic of this dissertation discusses the development and application of a novel blade vibration measurement technique. Accurate blade vibration measurements are critical in product aero-mechanical design validation and can be difficult to obtain. This measurement technique, termed Blade Image Velocimetry, provides an alternative to the current measurement methods which is both easy to implement and can have the potential to exceed the current accuracy of Blade Tip Timing. The theory of measurement and uncertainty analysis and benchtop validation measurements will be presented. This will be followed by the application of the measurement technique to a high speed axial compressor rotor. Tip deflections as low as 8mum were resolved by the measurement technique at a rotor tip speed of 350 m/s.

Mikrut, Paul Louis

371

Field Measurement of the Acoustic Nonlinearity Parameter in Turbine Blades  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

372

Application of two creep fatigue life models for the prediction of elevated temperature crack initiation of a nickel base alloy  

NASA Technical Reports Server (NTRS)

Cyclic Damage Accumulation (CDA) and Total Strain-Strain Range Partitioning (TS-SRP) models for predicting the creep-fatigue crack initiation life of high temperature alloys are presented. The models differ in their fundamental assumptions regarding the controlling parameters for fatigue crack initiation and in the amount of data required to determine model constants. The CDA model represents a ductility exhaustion approach and uses stress quantities to calculate the cyclic fatigue damage. The TS-SRP model is based on the use of total mechanical strain and earlier concepts of the Strain Range Partitioning Method. Both models were applied to a well controlled fatigue data set at a high temperature nickel base alloy, B1900 + Hf, tested at 1600 F and 1800 F. The tests were divided into a baseline data set required to determine model constants and a verification data set for evaluation of the predictive capability of the models. Both models correlated the baseline data set to within factors of two in life, and predicted the verification data set to within a factor of three or better. In addition, sample calculations to demonstrate the application of each model and discusions of the predictive capabilities and areas requiring further development are presented.

Moreno, V.; Nissley, D. M.; Halford, G. R.; Saltsman, J. F.

1985-01-01

373

FLAPS (Fatigue Life Analysis Programs): Computer Programs to Predict Cyclic Life Using the Total Strain Version of Strainrange Partitioning and Other Life Prediction Methods. Users' Manual and Example Problems, Version 1.0  

NASA Technical Reports Server (NTRS)

This manual presents computer programs FLAPS for characterizing and predicting fatigue and creep-fatigue resistance of metallic materials in the high-temperature, long-life regime for isothermal and nonisothermal fatigue. The programs use the Total Strain version of Strainrange Partitioning (TS-SRP), and several other life prediction methods described in this manual. The user should be thoroughly familiar with the TS-SRP and these life prediction methods before attempting to use any of these programs. Improper understanding can lead to incorrect use of the method and erroneous life predictions. An extensive database has also been developed in a parallel effort. The database is probably the largest source of high-temperature, creep-fatigue test data available in the public domain and can be used with other life-prediction methods as well. This users' manual, software, and database are all in the public domain and can be obtained by contacting the author. The Compact Disk (CD) accompanying this manual contains an executable file for the FLAPS program, two datasets required for the example problems in the manual, and the creep-fatigue data in a format compatible with these programs.

Arya, Vinod K.; Halford, Gary R. (Technical Monitor)

2003-01-01

374

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

SciTech Connect

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

Galib Abumeri; Frank Abdi (PhD)

2012-02-16

375

Adhesive and Protective Characteristics of Ceramic Coating A-417 and Its Effect on Engine Life of Forged Refractaloy-26 (AMS 5760) and Cast Stellite 21 (AMS 5385) Turbine Blades  

NASA Technical Reports Server (NTRS)

The adhesive and protective characteristics of National Bureau of Standards Coating A-417 were investigated, as well as the effect of the coating on the life of forged Refractaloy 26 and cast Stellite 21 turbine blades. Coated and uncoated blades were run in a full-scale J33-9 engine and were subjected to simulated service operations consisting of consecutive 20-minute cycles (15 min at rated speed and approximately 5 min at idle). The ceramic coating adhered well to Refractaloy 26 and Stellite 21 turbine blades operated at 1500 degrees F. The coating also prevented corrosion of the Refractaloy 26, a corrosion-sensitive nickel-base alloy, and of the Stellite 21, a relatively corrosion-resistant cobalt-base alloy. Although the coating prevented corrosion of both alloys, it had no apparent effect on blade life.

Garrett, Floyd B; Gyorgak, Charles A

1953-01-01

376

Effect of Seawater on the Fatigue Life and Failure Distribution of Flood-Lubricated Angular Contact Ball Bearings  

Microsoft Academic Search

Reductions in rolling contact fatigue life as high as 80 percent were observed during flood-lubricated angular-contact ball bearing studies when 1 percent by volume of seawater was added to various lubricants as a contaminant. The lubricants investigated were of different chemical and physical classes and included mineral oils, triaryl phosphate, and two recently developed mineral-oil-base sea-water-emulsifying hydraulic fluids of different

I. M. Felsen; R. W. McQuaid; J. A. Marzani

1972-01-01

377

Analysis of the effect of cold-working of rivet holes on the fatigue life of an aluminum alloy  

Microsoft Academic Search

An experimental and analytical program was carried out to assess the effect of cold-working by hole expansion on the fatigue life of Alclad 2024-T3 aluminium alloy. The magnitude of the residual stresses introduced into the specimens due to cold expansion was evaluated by an X-ray diffraction procedure. Specimens containing non-cold-worked and cold-worked holes were tested under cyclic loading at an

P. F. P. de Matos; A. J. McEvily; P. M. G. P. Moreira

2007-01-01

378

Designs of temperature loads on the fatigue life analysis of lead-free solder in IC packages  

Microsoft Academic Search

Firstly, finite element analysis software (ANSYS) is used to investigate the accumulated creep strain range and accumulated creep stain energy density properties of lead-free solder (95.5Sn-3.9Ag-0.6Cu) in IC packages under the temperature cyclic loading by the Garofalo-Arrhenius hyperbolic sine law. Then the Taguchi method is further used to analyze the effects of IC package models on the fatigue life subjected

W. R. Jong; H. C. Tsai; C. C. Lau

2009-01-01

379

Variations in gear fatigue life for different wind turbine braking strategies  

SciTech Connect

A large number of gearbox failures have occurred in the wind industry in a relatively short period, many because service loads were underestimated. High-torque transients that occur during starting and stopping are difficult to predict and may be overlooked in specifying gearbox design. Although these events comprise a small portion of total load cycles, they can be the most damaging. The severity of these loads varies dramatically with the specific configuration of the wind turbine. The large number of failures in Danish-designed Micon 65 wind turbines prompted this investigation. The high-speed and low-speed shaft torques were measured on a two-stage helical gearbox of a single Micon 65 turbine. Transient events and normal running loads were combined statistically to obtain a typical annual load spectrum. The pitting and bending fatigue lives of the gear teeth were calculated by using Miner's rule for four different high-speed shaft brake configurations. Each breaking scenario was run for both a high- and a low-turbulence normal operating load spectrum. The analysis showed increases in gear life by up to a factor of 25 when the standard high-speed shaft brake is replaced with a dynamic brake or modified with a damper. 9 refs., 9 figs., 3 tabs.

McNiff, B.P. (Second Wind, Inc., Somerville, MA (USA)); Musial, W.D. (Solar Energy Research Inst., Golden, CO (USA)); Errichello, R. (GEARTECH, Albany, CA (USA))

1991-06-01

380

Fatigue life improvement of AISI 304L cruciform welded joints by cryogenic treatment  

Microsoft Academic Search

Existing theories and reported practical experience show that cryogenic processing greatly increases abrasion resistance and contact fatigue resistance of some metals and alloys. In the present work, an attempt has been made to investigate the effect of cryogenic treatment on the axial fatigue performance of fillet welded cruciform joints of AISI 304L stainless steel, which failed in the weld metal.

P Johan Singh; B Guha; D. R. G Achar

2003-01-01

381

Low cycle fatigue crack initiation life assessment of HY-100 undermatched weld  

Microsoft Academic Search

An evaluation is conducted of several approaches to the prediction of low cycle fatigue crack initiation in HY-100 welds of an undermatched weldment. FEM analyses and experiments using various types of low cycle fatigue specimens were conducted and their results were compared with the results of such theoretical algorithms as Neuber's rule. A two-surface cyclic plasticity algorithm was implanted in

K. Wang; R. Shah; D. Yuan; M. J. Kleinosky

1993-01-01

382

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

Microsoft Academic Search

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

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

1992-01-01

383

Cement fatigue and HPHT well integrity with application to life of well prediction  

E-print Network

on stress levels and number of cycles. There have been a lot of research and experimental investigations on the mechanism of fatigue failure of concrete structures but the fatigue behavior of oil well cement is still relatively unknown to engineers. Research...

Ugwu, Ignatius Obinna

2009-05-15

384

High-temperature fatigue in metals - A brief review of life prediction methods developed at the Lewis Research Center of NASA  

NASA Technical Reports Server (NTRS)

The presentation focuses primarily on the progress we at NASA Lewis Research Center have made. The understanding of the phenomenological processes of high temperature fatigue of metals for the purpose of calculating lives of turbine engine hot section components is discussed. Improved understanding resulted in the development of accurate and physically correct life prediction methods such as Strain-Range partitioning for calculating creep fatigue interactions and the Double Linear Damage Rule for predicting potentially severe interactions between high and low cycle fatigue. Examples of other life prediction methods are also discussed. Previously announced in STAR as A83-12159

Halford, G. R.

1983-01-01

385

Turbofan blade stresses induced by the flow distortion of a VTOL inlet at high angles of attack  

NASA Technical Reports Server (NTRS)

A 51-cm-diameter turbofan with a tilt-nacelle VTOL inlet was tested in the Lewis Research Center's 9- by 15-Ft Low Speed Wind Tunnel at velocities up to 72 m/s and angles of attack up to 120 deg. Fan-blade vibratory stress levels were investigated over a full aircraft operating range. These stresses were due to inlet air flow distortion resulting from (1) internal flow separation in the inlet, and (2) ingestion of the exterior nacelle wake. Stress levels are presented, along with an estimated safe operating envelope, based on infinite blade fatigue life.

Williams, R. C.; Diedrich, J. H.; Shaw, R. J.

1983-01-01

386

Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics  

NASA Technical Reports Server (NTRS)

Safe-life and damage-tolerant design philosophies of high performance structures have driven the development of various methods to evaluate nondestructively the accumulation of damage in such structures resulting from cyclic loading. Although many techniques have proven useful, none has been able to provide an unambiguous, quantitative assessment of damage accumulation at each stage of fatigue from the virgin state to fracture. A method based on nonlinear acoustics is shown to provide such a means to assess the state of metal fatigue. The salient features of an analytical model are presented of the microelastic-plastic nonlinearities resulting from the interaction of an acoustic wave with fatigue-generated dislocation substructures and cracks that predictably evolve during the metal fatigue process. The interaction is quantified by the material (acoustic) nonlinearity parameter extracted from acoustic harmonic generation measurements. The parameters typically increase monotonically by several hundred percent over the fatigue life of the metal, thus providing a unique measure of the state of fatigue. Application of the model to aluminum alloy 2024-T4, 410Cb stainless steel, and IN100 nickel-base superalloy specimens fatigued using different loading conditions yields good agreement between theory and experiment. Application of the model and measurement technique to the on-site inspection of steam turbine blades is discussed.

Cantrell, John H., Jr.

2008-01-01

387

Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics  

NASA Astrophysics Data System (ADS)

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

Cantrell, John H.

2009-03-01

388

Structural health monitoring of wind turbine blades : SE 265 Final Project.  

SciTech Connect

ACME Wind Turbine Corporation has contacted our dynamic analysis firm regarding structural health monitoring of their wind turbine blades. ACME has had several failures in previous years. Examples are shown in Figure 1. These failures have resulted in economic loss for the company due to down time of the turbines (lost revenue) and repair costs. Blade failures can occur in several modes, which may depend on the type of construction and load history. Cracking and delamination are some typical modes of blade failure. ACME warranties its turbines and wishes to decrease the number of blade failures they have to repair and replace. The company wishes to implement a real time structural health monitoring system in order to better understand when blade replacement is necessary. Because of warranty costs incurred to date, ACME is interested in either changing the warranty period for the blades in question or predicting imminent failure before it occurs. ACME's current practice is to increase the number of physical inspections when blades are approaching the end of their fatigue lives. Implementation of an in situ monitoring system would eliminate or greatly reduce the need for such physical inspections. Another benefit of such a monitoring system is that the life of any given component could be extended since real conditions would be monitored. The SHM system designed for ACME must be able to operate while the wind turbine is in service. This means that wireless communication options will likely be implemented. Because blade failures occur due to cyclic stresses in the blade material, the sensing system will focus on monitoring strain at various points.

Barkley, W. C. (Walter C.); Jacobs, Laura D.; Rutherford, A. C. (Amanda C.); Puckett, Anthony

2006-03-23

389

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

Microsoft Academic Search

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

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

2008-01-01

390

Low cycle fatigue crack initiation life assessment of HY-100 undermatched weld  

SciTech Connect

An evaluation is conducted of several approaches to the prediction of low cycle fatigue crack initiation in HY-100 welds of an undermatched weldment. FEM analyses and experiments using various types of low cycle fatigue specimens were conducted and their results were compared with the results of such theoretical algorithms as Neuber's rule. A two-surface cyclic plasticity algorithm was implanted in a FEM code's user subroutine in order to simulate the material's cyclic stress-strain behavior under cyclic loading conditions; fatigue tests ranging from small, standard smooth specimens to notched cylindrical specimens with notch constraint were conducted for HY-100. 11 refs.

Wang, K.; Shah, R.; Yuan, D.; Kleinosky, M.J.

1993-01-01

391

Inversion of the strain-life and strain-stress relationships for use in metal fatigue analysis  

NASA Technical Reports Server (NTRS)

The paper presents closed-form solutions (collocation method and spline-function method) for the constants of the cyclic fatigue life equation so that they can be easily incorporated into cumulative damage analysis. The collocation method involves conformity with the experimental curve at specific life values. The spline-function method is such that the basic life relation is expressed as a two-part function, one applicable at strains above the transition strain (strain at intersection of elastic and plastic lines), the other below. An illustrative example is treated by both methods. It is shown that while the collocation representation has the advantage of simplicity of form, the spline-function representation can be made more accurate over a wider life range, and is simpler to use.

Manson, S. S.

1979-01-01

392

Cyclic Strain Resistance, Stress Response, Fatigue Life, and Fracture Behavior of High Strength Low Alloy Steel 300 M  

NASA Astrophysics Data System (ADS)

The focus of this technical manuscript is a record of the specific role of microstructure and test specimen orientation on cyclic stress response, cyclic strain resistance, and cyclic stress versus strain response, deformation and fracture behavior of alloy steel 300 M. The cyclic strain amplitude-controlled fatigue properties of this ultra-high strength alloy steel revealed a linear trend for the variation of log elastic strain amplitude with log reversals-to-failure, and log plastic strain amplitude with log reversals-to-failure for both longitudinal and transverse orientations. Test specimens of the longitudinal orientation showed only a marginal improvement over the transverse orientation at equivalent values of plastic strain amplitude. Cyclic stress response revealed a combination of initial hardening for the first few cycles followed by gradual softening for a large portion of fatigue life before culminating in rapid softening prior to catastrophic failure by fracture. Fracture characteristics of test specimens of this alloy steel were different at both the macroscopic and fine microscopic levels over the entire range of cyclic strain amplitudes examined. Both macroscopic and fine microscopic observations revealed fracture to be a combination of both brittle and ductile mechanisms. The underlying mechanisms governing stress response, deformation characteristics, fatigue life, and final fracture behavior are presented and discussed in light of the competing and mutually interactive influences of test specimen orientation, intrinsic microstructural effects, deformation characteristics of the microstructural constituents, cyclic strain amplitude, and response stress.

Manigandan, K.; Srivatsan, T. S.; Tammana, Deepthi; Poorgangi, Behrang; Vasudevan, Vijay K.

2014-05-01

393

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

SciTech Connect

This paper uses two high-cycle fatigue data bases, US blade materials and one for European materials the service lifetime of a wind turbine blade sit WISPER load spectrum for northern European sit 19921 and the WISPER protocol load spectrum farm sites. The US data base, developed by Mandell, et al. (1995), contains over 2200 data points that were obtained using coupon testing procedures. These data are used to construct a Goodman diagram that is suitable for analyzing wind turbine blades. This result is compared to the Goodman diagram derived from the European fatigue data base FACT. The LIFE2 fatigue analysis code for wind turbines is then used to predict the service lifetime of a turbine blade subjected to the two loading histories. The results of this study indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a US wind farm site; i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a US wind farm site. Further, the analyses demonstrate that the European and the US fatigue material data bases are in general agreement for the prediction of tensile failures. However, for compressive failures, the two data bases are significantly different, with the US data base predicting significantly shorter service lifetimes than the European data base.

Sutherland, H.J.

1996-02-01

394

The Effect of Intravenous Vitamin C on Cancer- and Chemotherapy-Related Fatigue and Quality of Life  

PubMed Central

Cancer patients commonly experience a number of symptoms of disease progression and the side-effects of radiation therapy and adjuvant chemotherapy, which adversely impact on their quality of life (QOL). Fatigue is one of the most common and debilitating symptom reported by cancer patients and can affect QOL more than pain. Several recent studies have indicated that intravenous (IV) vitamin C alleviates a number of cancer- and chemotherapy-related symptoms, such as fatigue, insomnia, loss of appetite, nausea, and pain. Improvements in physical, role, cognitive, emotional, and social functioning, as well as an improvement in overall health, were also observed. In this mini review, we briefly cover the methods commonly used to assess health-related QOL in cancer patients, and describe the few recent studies examining the effects of IV vitamin C on cancer- and chemotherapy-related QOL. We discuss potential mechanisms that might explain an improvement in QOL and also considerations for future studies. PMID:25360419

Carr, Anitra C.; Vissers, Margreet C. M.; Cook, John S.

2014-01-01

395

Application of fracture mechanics and half-cycle theory to the prediction of fatigue life of aerospace structural components  

NASA Technical Reports Server (NTRS)

The service life of aircraft structural components undergoing random stress cycling was analyzed by the application of fracture mechanics. The initial crack sizes at the critical stress points for the fatigue crack growth analysis were established through proof load tests. The fatigue crack growth rates for random stress cycles were calculated using the half-cycle method. A new equation was developed for calculating the number of remaining flights for the structural components. The number of remaining flights predicted by the new equation is much lower than that predicted by the conventional equation. This report describes the application of fracture mechanics and the half-cycle method to calculate the number of remaining flights for aircraft structural components.

Ko, William L.

1989-01-01

396

Fatigue life prediction and experiment research for composite laminates with circular hole  

Microsoft Academic Search

Based on the fatigue prediction model of exponential function and Whitney-Nuismer(WN) criterion of static strength for the\\u000a composite material laminate with a circular hole, the stress correct factor (?) was put forward and a new fatigue prediction\\u000a model for composite material laminate was set up. T300\\/KH304, which is recently studied and is a high capability composite\\u000a material, was used as

Hong-yu Qi; Wei-dong Wen; Lian-wen Xun

2004-01-01

397

Low cycle fatigue  

NASA Technical Reports Server (NTRS)

The papers contained in this volume focus on various aspects of low cycle fatigue, including cyclic deformation, crack propagation, high-temperature low cycle fatigue, microstructural defects, multiaxial and variable amplitude loading, and life prediction. Papers are presented on the low cycle fatigue of some aluminum alloys, prediction of crack growth under creep-fatigue loading conditions, high-temperature low cycle fatigue behavior and lifetime prediction of a nickel-base ODS alloy, and an integrated approach to creep-fatigue life prediction. Other topics discussed include thermal fatigue testing of coated monocrystalline superalloys, low cycle fatigue of Al-Mg-Si alloys, and the effect of superimposed stresses at high frequency on low cycle fatigue.

Solomon, H. D. (editor); Kaisand, L. R. (editor); Halford, G. R. (editor); Leis, B. N. (editor)

1988-01-01

398

Panel resonant behavior of wind turbine blades.  

SciTech Connect

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

Paquette, Joshua A.; Griffith, Daniel Todd

2010-03-01

399

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

NASA Astrophysics Data System (ADS)

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

Magadanz, Christine M.

400

Risk assessment of Cumberland unit 2 L-O blades  

SciTech Connect

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

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

1996-12-31

401

On the functional degradation of binary titanium-tantalum high-temperature shape memory alloys — A new concept for fatigue life extension  

NASA Astrophysics Data System (ADS)

High-temperature shape memory alloys are promising candidates for actuator applications at elevated temperatures. Ternary nickel-titanium-based alloys either contain noble metals which are very expensive, or suffer from poor workability. Titanium-tantalum shape memory alloys represent a promising alternative if one can avoid the cyclic degradation due to the formation of the omega phase. The current study investigates the functional fatigue behavior of Ti-Ta and introduces a new concept providing for pronounced fatigue life extension.

Niendorf, T.; Krooß, P.; Batyrsina, E.; Paulsen, A.; Frenzel, J.; Eggeler, G.; Maier, H. J.

2014-05-01

402

Effect of Application of Short and Long Holds on Fatigue Life of Modified 9Cr-1Mo Steel Weld Joint  

NASA Astrophysics Data System (ADS)

Modified 9Cr-1Mo steel is a heat-treatable steel and hence the microstructure is temperature sensitive. During welding, the weld joint (WJ) is exposed to various temperatures resulting in a complex heterogeneous microstructure across the weld joint, such as the weld metal, heat-affected zone (HAZ) (consisting of coarse-grained HAZ, fine-grained HAZ, and intercritical HAZ), and the unaffected base metal of varying mechanical properties. The overall creep-fatigue interaction (CFI) response of the WJ is hence due to a complex interplay between various factors such as surface oxides and stress relaxation (SR) occurring in each microstructural zone. It has been demonstrated that SR occurring during application of hold in a CFI cycle is an important parameter that controls fatigue life. Creep-fatigue damage in a cavitation-resistant material such as modified 9Cr-1Mo steel base metal is accommodated in the form of microstructural degradation. However, due to the complex heterogeneous microstructure across the weld joint, SR will be different in different microstructural zones. Hence, the damage is accommodated in the form of preferential coarsening of the substructure, cavity formation around the coarsened carbides, and new surface formation such as cracks in the soft heat-affected zone.

Shankar, Vani; Mariappan, K.; Sandhya, R.; Mathew, M. D.; Jayakumar, T.

2013-11-01

403

A Practical Method for Determining the Corten-Dolan Exponent and Its Application to Fatigue Life Prediction  

NASA Astrophysics Data System (ADS)

Based on the derivation and calculation of the Corten-Dolan exponent d, a practical method of determining its value is proposed. This exponent depends not only upon the materials, but also upon the load spectrums. Therefore its value is obtained by a function which decreases with increasing stress amplitude. This exponent was investigated through analysis of fatigue damage evolution to determine its parameters. The proposed method has been effectively proved by experimental data from literature. Utilization of the modified Corten-Dolan's model significantly improves its life prediction capability when compared to the conventional model where that exponent was assumed to be constant.

Zhu, Shun-Peng; Huang, Hong-Zhong; Liu, Yu; He, Li-Ping; Liao, Qiang

2012-06-01

404

Mitigation of edgewise vibrations in wind turbine blades by means of roller dampers  

NASA Astrophysics Data System (ADS)

Edgewise vibrations in wind turbine blades are lightly damped, and large amplitude vibrations induced by the turbulence may significantly shorten the fatigue life of the blade. This paper investigates the performance of roller dampers for mitigation of edgewise vibrations in rotating wind turbine blades. Normally, the centrifugal acceleration of the rotating blade can reach to a magnitude of 7-8g, which makes it possible to use this kind of damper with a relatively small mass ratio for suppressing edgewise vibrations effectively. The parameters of the damper to be optimized are the mass ratio, the frequency ratio, the coefficient of rolling friction and the position of the damper in the blade. The optimization of these parameters has been carried out on a reduced 2-DOF nonlinear model of the rotating wind turbine blade equipped with a roller damper in terms of a ball or a cylinder, ignoring the coupling with other degrees of freedom of the wind turbine. The edgewise modal loading on the blade has been calculated from a more sophisticated 13-DOF aeroelastic wind turbine model with due consideration to the indicated couplings, the turbulence and the aerodynamic damping. Various turbulence intensities and mean wind speeds have been considered to evaluate the effectiveness of the roller damper in reducing edgewise vibrations when the working conditions of the wind turbine are changed. Further, the optimized roller damper is incorporated into the 13-DOF wind turbine model to verify the application of the decoupled optimization. The results indicate that the proposed damper can effectively improve the structural response of wind turbine blades.

Zhang, Zili; Li, Jie; Nielsen, Søren R. K.; Basu, Biswajit

2014-10-01

405

Counterrotating aircraft propulsor blades  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

406

Failure of gas turbine blades  

Microsoft Academic Search

The first-stage blades of a gas turbine had suffered a severe deterioration after around 10500h service. The expected service life was 40000h. Failure analysis (visual observations, studies by optical microscopy, scanning electron microscopy (SEM), SEM back-scattered electron (SEM-BSE), EDX, X-ray diffraction (XRD) and dimensional metrology) has been carried out. Blades, manufactured in the nickel superalloy CMSX-4, lost the protective coatings

J. M Gallardo; J. A Rodr??guez; E. J Herrera

2002-01-01

407

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

Microsoft Academic Search

The objective of this study was to compare the durability of crankshafts from two competing manufacturing processes, as well as to perform dynamic load and stress analysis, and optimization. The crankshafts used in the study were forged steel and ductile cast iron from a one-cylinder gasoline engine. Strain-controlled monotonic and fatigue tests as well as impact tests were performed on

JONATHAN WILLIAMS; FARZIN MONTAZERSADGH; ALI FATEMI

2007-01-01

408

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

Microsoft Academic Search

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

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

2009-01-01

409

Fatigue Life Improvement for Cruciform Welded Joint by Mechanical Surface Treatment using Hammer Peening and UNSM  

NASA Astrophysics Data System (ADS)

For the improvement of fatigue strength of welded structures, mechanical post treatments have been applied in various industrial fields and have in most cases been founded to give substantial increases in their fatigue lives. These methods, generally, consist of the modification of weld toe geometry and the introduction of compressive residual stresses. In mechanical surface treatments, e.g. PHP (pneumatic hammer peening) and UNSM (ultrasonic nano-crystal surface modification), the weld profile is modified due to remove or reduce minute crack-like flaws, and compressive residual stresses are also induced. In this study, a pneumatic hammer peening procedure and a UNSM device were introduced, and a quantitative measure of fatigue strength improvement was performed. The fatigue strength at 2 × 106 cycles of hammer-peened and UNSM treated on a non-load carrying cruciform welded joint shows 220 and 260MPa, respectively, which are more than two times higher than that of as-welded specimen. Especially, the surface layer in the vicinity weld toe treated by the UNSM provides nano-crystal structure created by an ultrasonic cold forging and introduces very high welding residual stress in compression.

Han, Seung-Ho; Han, Jeong-Woo; Nam, Yong-Yun; Cho, In-Ho

410

Fatigue life extension of notches in AISI 304L weldments using deep cryogenic treatment  

Microsoft Academic Search

The fatigue crack initiation lives of notches in AISI 304L austenitic stainless steel weldments were improved after the deep cryogenic treatment of specimens at liquid nitrogen temperature (?185 °C). During this treatment, a significant change in microstructure is developed. Strain induced martensitic transformation occurs. During this transformation, the weld metal expands. This expansion relieves the tensile residual stresses and induces

P. Johan Singh; S. L. Mannan; T. Jayakumar; D. R. G. Achar

2005-01-01

411

Environment enhanced fatigue crack propagation in metals: Inputs to fracture mechanics life prediction models  

NASA Technical Reports Server (NTRS)

This report is a critical review of both environment-enhanced fatigue crack propagation data and the predictive capabilities of crack growth rate models. This information provides the necessary foundation for incorporating environmental effects in NASA FLAGRO and will better enable predictions of aerospace component fatigue lives. The review presents extensive literature data on 'stress corrosion cracking and corrosion fatigue.' The linear elastic fracture mechanics approach, based on stress intensity range (Delta(K)) similitude with microscopic crack propagation threshold and growth rates, provides a basis for these data. Results are presented showing enhanced growth rates for gases (viz., H2 and H2O) and electrolytes (e.g. NaCl and H2O) in aerospace alloys including: C-Mn and heat treated alloy steels, aluminum alloys, nickel-based superalloys, and titanium alloys. Environment causes purely time-dependent accelerated fatigue crack growth above the monotonic load cracking threshold (KIEAC) and promotes cycle-time dependent cracking below (KIEAC). These phenomenon are discussed in terms of hydrogen embrittlement, dissolution, and film rupture crack tip damage mechanisms.

Gangloff, Richard P.; Kim, Sang-Shik

1993-01-01

412

Improvement in surface fatigue life of hardened gears by high-intensity shot peening  

Microsoft Academic Search

Two groups of carburized, hardened, and ground spur gears that were manufactured from the same heat vacuum induction melted vacuum arc melted (VIM VAR) AISI 9310 steel were endurance tested for surface fatigue. Both groups were manufactured with a standard ground 16 rms surface finish. One group was subjected to a shot peening (SP) intensity of 7 to 9A, and

Dennis P. Townsend

1992-01-01

413

Acoustic Emission Monitoring of Small Wind Turbine Blades  

Microsoft Academic Search

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

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

2002-01-01

414

Relation of Engine Turbine-blade Life to Stress-rupture Properties of the Alloys, Stellite 21, Hastelloy B, Cast S-816, Forged S-816, X-40, Nimonic 80, Refractaloy 26, N-155, and Inconel X  

NASA Technical Reports Server (NTRS)

An investigation was conducted to relate the engine performance of the heat-resistant alloys, Stellite 21, Hastelloy B, cast S-816, forged S-816, X-40, Nimonic 80, Refractory 26, N-155, and Iconel X to their stress-rupture properties. The engine test consisted of the repetition of a 20-minute cycle, 15 minutes at rated speed and approximately 5 minutes at idle. The results of the investigation indicated a direct correlation between stress-rupture life and blade life for the relatively low-strength alloys. The stress-rupture life and blade life for the relatively high-strength alloys did not correlate because of the effects of the vibratory stresses and the corrosive-gas atmosphere.

Garrett, F B; Yaker, C

1951-01-01

415

Optimization of rotor blades for combined structural, dynamic, and aerodynamic properties  

NASA Technical Reports Server (NTRS)

Optimal helicopter blade design with computer-based mathematical programming has received more and more attention in recent years. Most of the research has focused on optimum dynamic characteristics of rotor blades to reduce vehicle vibration. There is also work on optimization of aerodynamic performance and on composite structural design. This research has greatly increased our understanding of helicopter optimum design in each of these aspects. Helicopter design is an inherently multidisciplinary process involving strong interactions among various disciplines which can appropriately include aerodynamics; dynamics, both flight dynamics and structural dynamics; aeroelasticity: vibrations and stability; and even acoustics. Therefore, the helicopter design process must satisfy manifold requirements related to the aforementioned diverse disciplines. In our present work, we attempt to combine several of these important effects in a unified manner. First, we design a blade with optimum aerodynamic performance by proper layout of blade planform and spanwise twist. Second, the blade is designed to have natural frequencies that are placed away from integer multiples of the rotor speed for a good dynamic characteristics. Third, the structure is made as light as possible with sufficient rotational inertia to allow for autorotational landing, with safe stress margins and flight fatigue life at each cross-section, and with aeroelastical stability and low vibrations. Finally, a unified optimization refines the solution.

He, Cheng-Jian; Peters, David A.

1990-01-01

416

Optimal placement of piezoelectric plates for active vibration control of gas turbine blades: experimental results  

NASA Astrophysics Data System (ADS)

It is well known that the gas turbine blade vibrations can give rise to catastrophic failures and a reduction of the blades life because of fatigue related phenomena[1]-[3] . In last two decades, the adoption of piezoelectric elements, has received considerable attention by many researcher for its potential applicability to different areas of mechanical, aerospace, aeronautical and civil engineering. Recently, a number of studies of blades vibration control via piezoelectric plates and patches have been reported[4]-[6] . It was reported that the use of piezoelectric elements can be very effective in actively controlling vibrations. In one of their previous contributions[7] , the authors of the present manuscript studied a model to control the blade vibrations by piezoelectric elements and validated their results using a multi-physics finite elements package (COMSOL) and results from the literature. An optimal placement method of piezoelectric plate has been developed and applied to different loading scenarios for realistic configurations encountered in gas turbine blades. It has been demonstrated that the optimal placement depends on the spectrum of the load, so that segmented piezoelectric patches have been considered and, for different loads, an optimal combination of sequential and/or parallel actuation and control of the segments has been studied. In this paper, an experimental investigation carried out by the authors using a simplified beam configuration is reported and discussed. The test results obtained by the investigators are then compared with the numerical predictions [7] .

Botta, F.; Marx, N.; Gentili, S.; Schwingshackl, C. W.; Di Mare, L.; Cerri, G.; Dini, D.

2012-04-01

417

Notched fatigue of single crystal PWA 1480 at turbine attachment temperatures  

NASA Technical Reports Server (NTRS)

The focus is on the lower temperature, uncoated and notched features of gas turbine blades. Constitutive and fatigue life prediction models applicable to these regions are being developed. Fatigue results are presented which were obtained thus far. Fatigue tests are being conducted on PWA 1480 single crystal material using smooth strain controlled specimens and three different notched specimens. Isothermal fatigue tests were conducted at 1200, 1400, and 1600 F. The bulk of the tests were conducted at 1200 F. The strain controlled tests were conducted at 0.4 percent per second strain rate and the notched tests were cycled at 1.0 cycle per second. A clear orientation dependence is observed in the smooth strain controlled fatigue results. The fatigue lifes of the thin, mild notched specimens agree fairly well with this smooth data when elastic stress range is used as a correlating parameter. Finite element analyses were used to calculate notch stresses. Fatigue testing will continue to further explore the trends observed thus far. Constitutive and life prediction models are being developed.

Meyer, T. G.; Nissley, D. M.; Swanson, G. A.

1989-01-01

418

Cyclic Hardening Behaviors and Reduction in Fatigue Life of Type 316LN Austenitic Stainless Steel in 310 deg. C Low Oxygen-Containing Water  

SciTech Connect

Low cycle fatigue tests were conducted to investigate the cyclic behavior and the fatigue life of type 316LN stainless steel (SS) at various strain rates in 310 deg. C low oxygen-containing water. The strain rates were 0.008, 0.04, and 0.4%/s, and the applied strain amplitude was varied from 0.4 to 1.0%. The dissolved oxygen concentration of the test water was maintained below 1 ppb. The test material in 310 deg. C low oxygen-containing water experienced a primary hardening, followed by a softening. From our data, we confirm the occurrence of the dynamic strain aging (DSA), and finally it can be considered that the primary hardening was brought about by the DSA. The secondary hardening was observed distinctly for 0.4%/s and 0.4%. The improvement of fatigue resistance and the secondary hardening occurred under the same loading condition. Therefore, the improvement of fatigue resistance may be related to the occurrence of the secondary hardening. When the secondary hardening occurs, intense slip bands are replaced by the corduroy structure. The corduroy structure can induce retardation of crack initiation, and ultimately the fatigue resistance is improved. Comparative study between the fatigue life generated in the current study and some prediction models was performed to evaluate the reliability of our data. (authors)

Hyunchul Cho; Byoung Koo Kim; Changheuil Jang; In Sup Kim; Seung Mo Hong [Korea Advanced Institute of Science and Technology (Korea, Republic of)

2006-07-01

419

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

E-print Network

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

420

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

E-print Network

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

421

Fatigue crack initiation life prediction in high strength structural steel welded joints  

NASA Astrophysics Data System (ADS)

The local approach method is used to calculate the fatigue crack initiation/early crack growth lives (N(i)) in high strength structural steel weldments. Weld-toe geometries, welding residual stresses and HAZ (heat affected zone) cyclic mechanical properties are taken into account in the N(i) estimation procedure. Fatigue crack initiation lives are calculated from either a Basquin type or a Manson-Coffin type equation. The local (HAZ) stress and strain amplitudes and the local mean stress are determined from an analysis based on the Neuber rule and the Molski-Glinka energy approach. The accuracy of the different methods is evaluated and discussed. Finally the previous methods are used with HAZ cyclic mechanical properties estimated from hardness measurements.

Tricoteaux, A.; Fardoun, F.; Degallaix, S.; Sauvage, F.

1995-02-01

422

Case histories involving fatigue and fracture mechanics; Proceedings of the Symposium, Charleston, SC, Mar. 21, 22, 1985  

NASA Technical Reports Server (NTRS)

Papers are presented on cracking at nozzle corners in the nuclear pressure vessel industry, applied fracture mechanics for assessing defect significance in a crude oil pipeline, failure analysis of a large wind-tunnel compressor blade, analysis of a compressor-wheel failure, and preventing fracture by inspection and analysis. Consideration is also given to the fatigue crack growth predictions of welded aircraft structures containing flaws in the residual stress field, the fatigue and fracture mechanics analysis of a compression loaded aircraft structure, fracture of an aircraft horizontal stabilizer, fatigue life analysis of fuel tank skins under combined loads, and aircraft structural maintenance recommendations based on fracture mechanics analysis. Additional papers discuss an analysis of two metal-forming die failures, an analysis of a failed saw arbor, and the role of fracture mechanics in assessing the effect on fatigue life of design changes in welded fabrications.

Hudson, C. Michael (editor); Rich, Thomas P. (editor)

1986-01-01

423

Application of Single Crystal Failure Criteria: Theory and Turbine Blade Case Study  

NASA Technical Reports Server (NTRS)

The orientation of the single crystal material within a structural component is known to affect the strength and life of the part. The first stage blade of the High Pressure Fuel Turbopump (HPFTP)/ Alternative Turbopump Development (ATD), of the Space Shuttle Main Engine (SSME) was used to study the effects of secondary axis'orientation angles on the failure rate of the blade. A new failure criterion was developed based on normal and shear strains on the primary crystallographic planes. The criterion was verified using low cycle fatigue (LCF) specimen data and a finite element model of the test specimens. The criterion was then used to study ATD/HPFTP first stage blade failure events. A detailed ANSYS finite element model of the blade was used to calculate the failure parameter for the different crystallographic orientations. A total of 297 cases were run to cover a wide range of acceptable orientations within the blade. Those orientations are related to the base crystallographic coordinate system that was created in the ANSYS finite element model. Contour plots of the criterion as a function of orientation for the blade tip and attachment were obtained. Results of the analysis revealed a 40% increase in the failure parameter due to changing of the primary and secondary axes of material orientations. A comparison between failure criterion predictions and actual engine test data was then conducted. The engine test data comes from two ATD/HPFTP builds (units F3- 4B and F6-5D), which were ground tested on the SSME at the Stennis Space Center in Mississippi. Both units experienced cracking of the airfoil tips in multiple blades, but only a few cracks grew all the way across the wall of the hollow core airfoil.

Sayyah, Tarek; Swanson, Gregory R.; Schonberg, W. P.

1999-01-01

424

Ali Fatemi -University of Toledo All Rights Reserved Chapter 2Fatigue Design Methods 1 FATIGUE DESIGN METHODS  

E-print Network

­Fatigue Design Methods 9 FATIGUE DESIGN CRITERIA (CONT'D) Safe-Life Design The practice of designing design. The safe life must include a margin for the scatter of fatigue results and for other unknown Methods 2 FATIGUE DESIGN METHODS STRATEGIES IN FATIGUE DESIGN FATIGUE DESIGN CRITERIA ANALYSIS

Fatemi, Ali

425

Fatigue of cold-work tool steels: Effect of heat treatment and carbide morphology on fatigue crack formation, life, and fracture surface observations  

Microsoft Academic Search

The fatigue properties of two types of cold-work tool steels tempered at various temperatures were evaluated. The microstructure\\u000a and fracture surface morphology were correlated to the fatigue behavior. Cold-work tool steels using this study were a conventional\\u000a tool steel (JIS SKD11; 1.4C-11Cr-0.8Mo-0.2V) and its modified steel (M-SKD11; 0.8C-8Cr-2Mo-0.5V). The fatigue strength of\\u000a the M-SKD11 steel increased 20 pct over that

Kenzo Fukaura; Yoshihiko Yokoyama; Daien Yokoi; Nobuhiro Tsujii; Kanji Ono

2004-01-01

426

Discs low cycle fatigue life predictions for gas turbine engines in CSFR by using fractographic information  

Microsoft Academic Search

Besides the conventional SL (Safe Life) philosophy for disk cyclic life predictions, the DT (Damage Tolerance) philosophy starts to be used in connection with the RFC (Retirement for Cause) strategy. The present paper is aimed especially at the certification demonstrations proofs. The use of advanced life prediction approaches is quite dependent on a reliable NDIT (Nondestructive Inspection Technique). Therefore the

Jiri Statecny; Jan Drexler; Antonin Janak

1991-01-01

427

Overview of the fatigue/fracture/life prediction working group program at the Lewis Research Center  

NASA Technical Reports Server (NTRS)

The objective is to develop and verify constitutive and life prediction models for materials typically used in hot gas path components of reusable space propulsion systems over the range of relevant operative environments. The efforts were concentrated on the development of crack initiation life prediction methods and on the development of cyclic crack propagation and fracture life prediction methods.

Mcgaw, Michael A.

1991-01-01

428

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

NASA Technical Reports Server (NTRS)

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

Eggert, W. S.

1982-01-01

429

Fatigue life prediction for a carbon fiber reinforced resin composite subjected to reversed cycle loading  

SciTech Connect

A study has been made of the fatigue behavior of an intermediate modulus Toray T800 carbon fiber/resin laminate with a [({+-}45,O{sub 2}){sub 2}]{sub s} lay-up. While in sequences of all-tension blocks, a linear damage law was found to be appropriate, in all compression or mixed tension-compression modes a linear law was no longer valid. An analysis of data from 2-block loading tests shows the potential of a power law of cumulative damage for describing behavior in reversed loading.

Adam, T.; Gathercole, N.; Harris, B.; Reiter, H. [Univ. of Bath (United Kingdom). Dept. of Materials Science

1993-12-31

430

Physical activity and quality of life in multiple sclerosis: Intermediary roles of disability, fatigue, mood, pain, self-efficacy and social support  

Microsoft Academic Search

Physical activity has been associated with a small improvement in quality of life (QOL) among those with multiple sclerosis (MS). This relationship may be indirect and operate through factors such as disability, fatigue, mood, pain, self-efficacy and social support. The present study examined variables that might account for the relationship between physical activity and QOL in a sample (N = 292) of

Robert W. Motl; Edward McAuley; Erin M. Snook; Rachael C. Gliottoni

2009-01-01

431

Perceived work ability, quality of life, and fatigue in patients with rheumatoid arthritis after a 6-month course of TNF inhibitors: prospective intervention study and partial economic evaluation  

Microsoft Academic Search

Objective: The objective of this exploratory study was to evaluate the effects and costs of a 6-month course of tumour necrosis factor (TNF) inhibitors on work ability, quality of life, and fatigue in patients with rheumatoid arthritis (RA). Methods: In this prospective single-arm intervention study 59 consecutive patients of working age with established RA were recruited from an outpatient clinic

J. L. Hoving; G. M. Bartelds; J. K. Sluiter; K. Sadiraj; I. Groot; W. F. Lems; B. A. C. Dijkmans; C. A. Wijbrandts; P. P. Tak; M. T. Nurmohamed; A. E. Voskuyl; M. H. W. Frings-Dresen

2009-01-01

432

Exercise therapy and cognitive behavioural therapy to improve fatigue, daily activity performance and quality of life in Postpoliomyelitis Syndrome: the protocol of the FACTS2PPS trial  

Microsoft Academic Search

BACKGROUND: Postpoliomyelitis Syndrome (PPS) is a complex of late onset neuromuscular symptoms with new or increased muscle weakness and muscle fatigability as key symptoms. Main clinical complaints are severe fatigue, deterioration in functional abilities and health related quality of life. Rehabilitation management is the mainstay of treatment. Two different therapeutic interventions may be prescribed (1) exercise therapy or (2) cognitive

Fieke S Koopman; Anita Beelen; Karin H Gerrits; Gijs Bleijenberg; Tineke A Abma; Marianne de Visser; Frans Nollet

2010-01-01

433

Comparison of pitting fatigue life of ausforged and standard forged AISI M-50 and AISI 9310 spur gears  

NASA Technical Reports Server (NTRS)

Standard forged and ausforged spur gears made of vacuum-induction-melted, consumable-electrode, vacuum-arc-remelted AISI M-50 steel were tested under conditions that produced fatigue pitting. The gears were 8.89 cm (3.5 in.) in pitch diameter and had tip relief. The M-50 standard forged and ausforged test results were compared with each other. They were then compared with results for machined vacuum-arc-remelted AISI 9310 gears tested under identical conditions. Both types of M-50 gears had lives approximately five times that of the 9310 gears. The life at which 10 percent of the M-50 ausforged gears failed was slightly less than that at which the M-50 standard forged gears failed. The ausforged gears had a slightly greater tendency to fail by tooth fracture than did the standard forged gears, most likely because of the better forging and grain flow pattern of standard forged gears.

Townsend, D. P.; Bamberger, E. N.; Zaretsky, E. V.

1975-01-01

434

Application of a thermal fatigue life prediction model to high-temperature aerospace alloys B1900 + Hf and Haynes 188  

NASA Technical Reports Server (NTRS)

The results of the application of a newly proposed thermomechanical fatigue (TMF) life prediction method to a series of laboratory TMF results on two high-temperature aerospace engine alloys are presented. The method, referred to as TMF/TS-SRP, is based on three relatively recent developments: the total strain version of the method of Strain Range Partitioning (TS-SRP), the bithermal testing technique for characterizing TMF behavior, and advanced viscoplastic constitutive models. The high-temperature data reported in a companion publication are used to evaluate the constants in the model and to provide the TMF verification data to check its accuracy. Predicted lives are in agreement with the experimental lives to within a factor of approximately 2.

Halford, G. R.; Salisman, J. F.; Verrilli, M. J.; Arya, V.

1992-01-01

435

An assessment of the role of near-threshold crack growth in high-cycle-fatigue life prediction of aerospace titanium alloys under turbine engine spectra  

Microsoft Academic Search

Increasingly accurate life prediction models are required to utilize the full capability of current and future advanced materials\\u000a in gas turbine engines. Of particular recent interest are predictions of the lifetimes of engine airfoil materials that experience\\u000a significant intervals of high-frequency, high-cycle fatigue (HCF). Conventional life management practices for HCF in the turbine\\u000a engine industry have been based principally on

J. M. Larsen; B. D. Worth; C. G. Annis; F. K. Haake

1989-01-01

436

Ceramic blade attachment system  

DOEpatents

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

Boyd, Gary L. (Alpine, CA)

1995-01-01

437

Growian rotor blades: Production development, construction and test  

NASA Technical Reports Server (NTRS)

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

Thiele, H. M.

1984-01-01

438

Viscoelastic Vibration Dampers for Turbomachine Blades  

NASA Technical Reports Server (NTRS)

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

Nguyen, Nhan

2003-01-01