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

Fatigue life variability and reliability analysis of a wind turbine blade  

NASA Astrophysics Data System (ADS)

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

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

2

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

3

Blade fatigue life assessment with application to VAWTs  

NASA Astrophysics Data System (ADS)

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

Veers, P. S.

1982-05-01

4

FATIGUE LIFE AND RESIDUAL STRESSES IN COLD ROLLED PROPELLER BLADES  

Microsoft Academic Search

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

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

5

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

6

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

SciTech Connect

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

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

1997-01-01

7

Fatigue strength and life of compressor blades for marine gas turbine engines  

Microsoft Academic Search

An experimental procedure has been developed for the investigation of fatigue and crack growth resistance of materials and\\u000a real compressor blades. Methods for the determination of stress intensity factors in specimens and in blades with cracks have\\u000a been justified. Investigations have been performed on the influence of manufacturing residual stresses and surface defects\\u000a in the form of simulators of dents,

V. T. Troshchenko; A. V. Prokopenko

1999-01-01

8

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

9

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

Microsoft Academic Search

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

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

2011-01-01

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 analysis and testing of wind turbine blades  

NASA Astrophysics Data System (ADS)

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

Greaves, Peter Robert

12

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

13

Fatigue Failure of Space Shuttle Main Engine Turbine Blades  

NASA Technical Reports Server (NTRS)

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

Swanson, Gregrory R.; Arakere, Nagaraj K.

2000-01-01

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

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

16

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

17

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

NASA Technical Reports Server (NTRS)

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

Arakere, Nagaraj K.; Swanson, Gregory R.

2000-01-01

18

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

SciTech Connect

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

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

2014-09-01

19

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

Microsoft Academic Search

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

Paul S. Prevy; N. Jayaraman; Ravi Ravindranath

20

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

21

Fatigue Failure Analysis of Small Wooden Wind Turbine Blade  

E-print Network

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

Maldhure S. S; Dr. Kharde Y. R

22

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

23

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 Meller

2011-01-01

24

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

Microsoft Academic Search

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

A. J. Scalzo

1992-01-01

25

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

Microsoft Academic Search

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

M. Reihanian; K. Sherafatnia; M. Sajjadnejad

2011-01-01

26

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

NASA Astrophysics Data System (ADS)

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

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

1987-08-01

27

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

NASA Astrophysics Data System (ADS)

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

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

28

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

E-print Network

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

29

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

E-print Network

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

30

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

31

Nitinol Fatigue Life for Variable Strain Amplitude Fatigue  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

32

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

33

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

34

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

NASA Technical Reports Server (NTRS)

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

Janetzke, D. C.

1983-01-01

35

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

36

Neural Network Would Estimate Fatigue Life  

NASA Technical Reports Server (NTRS)

Processor learns mappings between sequences of loads and fatigue damage. Data processor built around neural network provides real-time estimates of fatigue life of simple mechanical components. Intended to be forerunner of more-advanced processors that estimates remaining lives of components stressed near their mechanical and thermal limits in turbine engines and other complicated, high-performance machinery. Real-time estimates of accumulated fatigue damage and remaining life before mechanical failure useful in scheduling maintenance and controlling operation to extend overall life of machinery.

Merrill, W.; Troudet, T.

1993-01-01

37

Strength and Fatigue Life of Wire Rope  

Microsoft Academic Search

A method is presented that predicts the fatigue life of a large diameter wire rope, from test data for small diameter rope. Dimensional analysis and the technique of interpolation and extrapolation are employed. The method is applied first to study size effects on the breaking strength of wire ropes and then to predict fatigue strength. Results are compared with experimental

Chi-Hui Chien; Raymond A. LeClair; George A. Costello

1988-01-01

38

Full-scale fatigue tests of CX-100 wind turbine blades. Part I: testing  

NASA Astrophysics Data System (ADS)

This paper overviews the test setup and experimental methods for structural health monitoring (SHM) of two 9-meter CX-100 wind turbine blades that underwent fatigue loading at the National Renewable Energy Laboratory's (NREL) National Wind Technology Center (NWTC). The first blade was a pristine blade, which was manufactured to standard specifications for the CX-100 design. The second blade was manufactured for the University of Massachusetts, Lowell with intentional simulated defects within the fabric layup. Each blade was instrumented with piezoelectric transducers, accelerometers, acoustic emission sensors, and foil strain gauges. The blades underwent harmonic excitation at their first natural frequency using the Universal Resonant Excitation (UREX) system at NREL. Blades were initially excited at 25% of their design load, and then with steadily increasing loads until each blade reached failure. Data from the sensors were collected between and during fatigue loading sessions. The data were measured over multi-scale frequency ranges using a variety of acquisition equipment, including off-the-shelf systems and specially designed hardware developed at Los Alamos National Laboratory (LANL). The hardware systems were evaluated for their aptness in data collection for effective application of SHM methods to the blades. The results of this assessment will inform the selection of acquisition hardware and sensor types to be deployed on a CX-100 flight test to be conducted in collaboration with Sandia National Laboratory at the U.S. Department of Agriculture's (USDA) Conservation and Production Research Laboratory (CPRL) in Bushland, Texas.

Farinholt, Kevin M.; Taylor, Stuart G.; Park, Gyuhae; Ammerman, Curtt M.

2012-04-01

39

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

SciTech Connect

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

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

1995-06-01

40

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

41

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

42

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

43

Considerations concerning fatigue life of metal matrix composites  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

44

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

45

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

46

Fatigue life estimation under complex loading  

NASA Astrophysics Data System (ADS)

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

Tian, Dingshuan; Wu, Fumin

1991-02-01

47

Predicting fatigue life of metal bellows  

NASA Technical Reports Server (NTRS)

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

Daniels, C. M.

1968-01-01

48

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

SciTech Connect

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

Beattie, A.G.

1997-01-01

49

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

NASA Astrophysics Data System (ADS)

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

Reiso, M.; Muskulus, M.

2014-12-01

50

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

51

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

52

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

53

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-19, 2004 ISSN: 1547-1977 * Speaker 1 #12;2 Analysis of Fatigue Life Under Complex Loading: Revisiting An early study by Cadwell, Merrill, Sloman, and Yost reports fatigue lives under several combinations

Fatemi, Ali

54

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

55

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

56

Low cycle fatigue behavior of Ti-Mn alloys: Fatigue life  

NASA Astrophysics Data System (ADS)

The effect of morphology, particle size, ? grain size and volume fraction of ?, from 0.025 to 1.0, on the low cycle fatigue life of ? -? Ti-Mn alloys, have been studied under total strain control. In general, Widmansttten plus grain boundary (W+GB) ? structures show shorter fatigue lives than equiaxed (E) ? structures, and this has been ascribed to the formation of much larger surface cracks and ease of transfer of slip from ? to ?. For E? structures, fatigue life increases with decreasing ? particle size and when the alloy is single phase ? fatigue life increases with decreasing grain size. At high total strains the nearly all ? alloy had the longest fatigue life and at lower strains the ? alloy, with the higher yield strength, had the longest fatigue life. Fatigue life was correlated with strain hardening. The nearly all ? alloy which had the highest strain hardening, over the plastic strains encountered, had the highest fatigue life, while the ? alloy, with the lowest strain hardening, had the lowest fatigue life. For a portion of the fatigue life curves, it was found that as the average Baushinger strain (ABS) increased, the Coffin-Manson exponent c decreased. The results are discussed.

Saleh, Y.; Margolin, H.

1982-07-01

57

Spot welds fatigue life prediction with cyclic strain range  

Microsoft Academic Search

Even though spot welds have been used widely in automotive manufacturing for years, fatigue life prediction methods for estimating life have been based on welds connecting sheets of the same thickness. A validated fatigue life prediction method for spot welds connecting sheets of different thicknesses has yet to be published. In this study, the stresses and strains at the notch

Ning Pan; Sheri Sheppard

2002-01-01

58

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

59

Weld detail fatigue life improvement techniques. Part 1: review  

Microsoft Academic Search

Fatigue cracks in fabricated steel structures often occur at welded joints where stress concentrations due to the joint geometry are relatively high. In many cases the fatigue performance can be improved by employing good detail design practices. However, when this is not practicable, or is not sufficient, fatigue life improvement techniques which rely on improving the stress field in and

K. J. Kirkhope; R. Bell; L. Caron; R. I. Basu; K.-T. Ma

1999-01-01

60

Effects of cavitation on high-cycle fatigue life  

SciTech Connect

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

Majumdar, S.

1985-09-01

61

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

62

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

63

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

64

Fatigue life of automotive rubber jounce bumper  

NASA Astrophysics Data System (ADS)

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

Sidhu, R. S.; Ali, Aidy

2010-05-01

65

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

66

Airframe structural optimization for maximum fatigue life  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

67

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

NASA Astrophysics Data System (ADS)

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

Xu, Jinlong; Dong, Yongkang; Li, Hui

2014-03-01

68

Effect of surface irregularities on bellows fatigue life  

NASA Technical Reports Server (NTRS)

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

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

1968-01-01

69

Extension of Life Time of Welded Fatigue Loaded Structures  

Microsoft Academic Search

Summary. At the University of Braunschweig the effects of ultrasonic peening (UP) and shot peening on the fatigue life and fatigue strength of new and existing wind energy plants have been investigated. The test results demonstrate that UP is an effective and practical means to extend their service life.

Thomas Ummenhofer; Imke Weich; Thomas Nitschke-Pagel

70

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

PubMed

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

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

2012-09-01

71

Effect of spectral shape on acoustic fatigue life estimates  

NASA Astrophysics Data System (ADS)

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

Miles, R. N.

1992-03-01

72

Effect of spectral shape on acoustic fatigue life estimates  

NASA Technical Reports Server (NTRS)

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

Miles, R. N.

1992-01-01

73

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

74

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

75

Fatigue life prediction of composite laminates by FEA simulation method  

Microsoft Academic Search

This paper is to simulate the fatigue damage evolution in composite laminates and predict fatigue life of the laminates with different lay-up sequences on the basis of the fatigue characteristics of longitudinal, transverse and in-plane shear directions by finite element analysis (FEA) method. In FEA model, considering the scatter of the materials properties, each element was assigned with different materials

Wei Lian; Weixing Yao

2010-01-01

76

Development of an improved method of consolidating fatigue life data  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

77

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

E-print Network

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

Victoria, University of

78

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

E-print Network

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

79

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

80

Residual fatigue life estimation using a nonlinear ultrasound modulation method  

NASA Astrophysics Data System (ADS)

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

Piero Malfense Fierro, Gian; Meo, Michele

2015-02-01

81

A strategy for the estimation of the fatigue life of notched components under random multaxial fatigue  

E-print Network

A strategy for the estimation of the fatigue life of notched components under random multaxial fatigue G. Cailletaud1, T. Herbland1, B. Melnikov2, A. Musienko2, S. Quilici1 1MINES ParisTech, Centre des) to determine the stress­strain response in stress concentration zones for components submitted to complex

Boyer, Edmond

82

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

83

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

84

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

NASA Astrophysics Data System (ADS)

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

Zhao, Lihui; Zheng, Songlin; Feng, Jinzhi

2014-11-01

85

Predicting mooring system fatigue life by probabilistic methods  

SciTech Connect

Failure of moored structures from accumulated fatigue damage in shackles, connecting links, chain and wire rope components is common. When systems will be deployed for long periods, it is especially important to determine at the design, inspection and maintenance stages the fatigue damage. Since slack moored structures behave in a highly nonlinear manner, commonly used fatigue analysis procedures are normally inadequate. This paper reviews present probablistic fatigue analysis methods, and provides a means for incorporating nonlinear mooring behavior into analysis and design to predict accumulated damage and remaining service life. The procedures presented are general, and they are also applicable to ship and buoy moorings, offshore terminals, and guyed and tension leg platforms.

Saders, D.R.; Dominguez, R.F.; Ho, K.C.; Lai, N.W.

1983-05-01

86

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

87

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

88

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

NASA Astrophysics Data System (ADS)

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

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

89

A comparison of fatigue life prediction methodologies for rotorcraft  

NASA Technical Reports Server (NTRS)

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

Everett, R. A., Jr.

1990-01-01

90

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

91

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

92

Robust optimization of the Life of turbine blades an automated approach  

E-print Network

individually, the designer can choose an arbitrary number of control points which when moved would affectRobust optimization of the Life of turbine blades ­ an automated approach UTC for Computational complex workflows. The aim of this sequence is to manipulate the shape and position of the blade core

Sóbester, András

93

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

NASA Astrophysics Data System (ADS)

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

Neu, R. W.; Sehitoglu, Huseyin

1989-09-01

94

a Study on the Fretting Fatigue Life of Zircaloy Alloys  

NASA Astrophysics Data System (ADS)

Studies on the strength and fatigue life of machines and structures have been conducted in accordance with the development of modern industries. In particular, fine and repetitive cyclic damage occurring in contact regions has been known to have an impact on fretting fatigue fractures. The main component of zircaloy alloy is Zr, and it possesses good mechanical characteristics at high temperatures. This alloy is used in the fuel rod material of nuclear power plants because of its excellent resistance. In this paper, the effect of the fretting damage on the fatigue behavior of the zircaloy alloy is studied. Further, various types of mechanical tests such as tension and plain fatigue tests are performed. Fretting fatigue tests are performed with a flat-flat contact configuration using a bridge-type contact pad and plate-type specimen. Through these experiments, it is found that the fretting fatigue strength decreases by about 80% as compared to the plain fatigue strength. Oblique cracks are observed in the initial stage of the fretting fatigue, in which damaged areas are found. These results can be used as the basic data for the structural integrity evaluation of corrosion-resisting alloys considering the fretting damages.

Kwon, Jae-Do; Park, Dae-Kyu; Woo, Seung-Wan; Chai, Young-Suck

95

Prediction of the fatigue life of pneumatic tires  

Microsoft Academic Search

A method of the prediction of the fatigue life for parts of pneumatic tires based on the computation of the stress-strain\\u000a state of the stress concentration areas in a rubber matrix and the self-heating temperature by means of the finite-element\\u000a method and experimental fatigue curves for rubbercord composites has been developed. Multiple tensile tests of single-layer\\u000a rubber-cord samples with a

S. L. Sokolov

2010-01-01

96

Fatigue life prediction modeling for turbine hot section materials  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

97

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

98

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

99

Fatigue life predictions using fracture mechanics methods  

Microsoft Academic Search

In the present work, a simple engineering approach which is based on a relatively solid background and which is checked against fatigue test data for various test conditions was developed: it may provide a practical and reliable basis for the analysis of structures under in-service loading conditions, in the presence of previous corrosion attack, or in the presence of a

T. Ghidini; C. Dalle Donne

2009-01-01

100

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

101

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

102

Fatigue Life Prediction of Two-Stroke Free Piston Engine Mounting Using Frequency Response Approach  

Microsoft Academic Search

This paper describes a vibration fatigue analysis techniques to predict the fatigue life using the frequency response approach. The life prediction results are useful for improving the component design at a very early development stage. The finite element modeling and frequency response analysis have been performed using the finite element analysis software. In addition, the fatigue life prediction was carried

M. M. Rahman; A. K. Ariffin; N. Jamaludin

2008-01-01

103

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

E-print Network

High-Cycle Constant Amplitude Fatigue Life Variability of Welded Round HSS Y-Joints By John L 2003 #12;i Preface The variability in fatigue life estimates for welded pipe joints commonly found. The primary goal of this thesis was to quantify the variability in the fatigue life of welded round HSS Y

Foley, Christopher M.

104

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

105

Effect of spectral shape on acoustic fatigue life estimates  

Microsoft Academic Search

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

R. N. Miles

1992-01-01

106

A mesoscopic approach for fatigue life prediction under multiaxial loading  

Microsoft Academic Search

This paper deals with the presentation of a high cycle multiaxial fatigue life prediction method for metallic materials. By means of the mesoscopic approach introduced by Dang Van and developed by Papadopoulos, accumulated plastic strain due to external loading is estimated at a scale on the order of a grain or a few grains. Its evaluation requires the use of

Franck Morel; Narayanaswami Ranganathan; Jean Petit; Andr Bignonnet

1999-01-01

107

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

108

Fatigue life analysis of a turboprop reduction gearbox  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

109

Fatigue life analysis of a turboprop reduction gearbox  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

110

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

111

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

112

S. Chataigner, L. Dieng, K. Guiot, M. Grasset 1 IMPROVING WELDED JOINT FATIGUE LIFE USING SHOT  

E-print Network

S. Chataigner, L. Dieng, K. Guiot, M. Grasset 1 IMPROVING WELDED JOINT FATIGUE LIFE USING SHOT the fatigue life expectancy of welded steel joints in civil engineering structures. It includes both numerical. It is therefore10 momentous to lead research works on the fatigue of welded joints and the existing strengthening

Paris-Sud XI, Université de

113

ENGINEERING JOURNAL / FIRST QUARTER / 2006 / 57 Fatigue Life Prediction and Variability of  

E-print Network

of the present effort is to contribute to the process of un- derstanding the fatigue life variability of welded and synthesis to follow. A large amount of experimental research in fatigue perfor- mance of welded CHSENGINEERING JOURNAL / FIRST QUARTER / 2006 / 57 Fatigue Life Prediction and Variability of New

Foley, Christopher M.

114

Fatigue life estimation under complex loading  

Microsoft Academic Search

The cyclic property of aluminum alloy sheet LY12-CZ is quantitatively reported using accumulated plastic hysteresis energy under cyclic loading as the damage criterion. Nonlinearity of damage accumulation with cycle number under cyclic loading is demonstrated. The formula used to calculate instantaneous plastic strain energy is derived. The total dissipated plastic strain energy for the whole life period is calculated and

Dingshuan Tian; Fumin Wu

1991-01-01

115

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

SciTech Connect

Recently, the blade fatigue testing capabilities at NREL were upgraded from single-axis to two-axis loading. To implement this, several practical challenges were addressed, as hardware complexity increased dramatically with two actuators applying the loads at right angles to each other. A custom bellcrank was designed and implemented to minimize the load angle errors and to prevent actuator side loading. The control system was upgraded to accept load and displacement feedback from two actuators. The inherent long strokes uniquely associated with wind turbine blade-tests required substantial real-time corrections for both the control and data systems. A custom data acquisition and control system was developed using a National Instruments LabVIEW platform that interfaces with proprietary servo-hydraulic software developed by MTS Corporation. Before testing, the program is run under quasi-static (slow speed) conditions and iterates to determine the correct operational control parameters for the controller, taking into consideration geometry, test speed, and phase angle errors between the two actuators. Comparisons are made between single-axis and two-axis test loads using actual test load data and load uncertainties are qualitatively described. To date, two fatigue tests have been completed and another is currently ongoing using NREL's two-axis capability.

Hughes, S. D.; Musial, W. D. [National Renewable Energy Lab., Golden, CO (US); Stensland, T. [Stensland Technologies (US)

1999-09-09

116

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

117

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

118

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

119

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

Microsoft Academic Search

An energy based fatigue life prediction framework has been developed for calculation of remaining fatigue life of in service\\u000a gas turbine materials. The purpose of the life prediction framework is to account aging effect caused by cyclic loadings on\\u000a fatigue strength of gas turbine engines structural components which are usually designed for very long life. Previous studies\\u000a indicate the total

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

2011-01-01

120

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

121

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

122

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

123

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 elastic modulus. For plasticity/creep interaction conditions (PC and CP) two more pairs of stress strain parameters must be ascertained.

Berkovits, A.; Nadiv, S.

1988-01-01

124

The Effect of Geometry on Fatigue Life for Bellows  

NASA Astrophysics Data System (ADS)

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

Kim, Jinbong

125

Effects of cyclic stress distribution models on fatigue life predictions  

NASA Astrophysics Data System (ADS)

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

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

1994-10-01

126

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

127

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

Microsoft Academic Search

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

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

2001-01-01

128

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

Microsoft Academic Search

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

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

2011-01-01

129

Accumulative damage near crack tip for welded bridge members: fatigue life determination  

Microsoft Academic Search

The behavior of crack growth for the fatigue damage accumulation near tip where damage is most severe is analyzed. Fatigue life is assessed for the welded members of bridges under traffic loading. Two parts are considered. They consist of the development of a fatigue damage accumulation model for welded bridge members and a method for calculating the stress intensity factor

Z. X. Li; T. H. T. Chan; T. Q. Zhou

2005-01-01

130

Estimating the Fatigue Life of Wire Rope with a Stochastic Approach  

NASA Astrophysics Data System (ADS)

A method for estimating the fatigue life of wire ropes for elevators was developed. It is based on the assumption that the fatigue life of a wire rope is determined by the fretting-fatigue life of the wires from which the rope was made. Estimates done on a sample wire rope with this method are consistent with experimental measurements. The method of estimation involves four steps. First, a finite-element analysis is conducted to estimate the pressure between the wires. To take into account the behavior of the whole wire rope and each wire in the stress analysis, a zooming analysis is conducted. Second, a fretting-fatigue test on the wires is conducted to construct a fretting-fatigue database for them. Third, the fatigue life of each wire is estimated from the pressures between the wires and data from the fretting fatigue database. Finally, the fatigue life of the wire rope is estimated from the fretting-fatigue life of the individual wires. The rope's fatigue life estimated with this new method revealed some important findings: (1) the inner wires break earlier than the outer wires, and (2) the residual strength of the wire rope decreases rapidly after decreasing to 80% of the initial residual strength.

Sasaki, Koji; Iwakura, Shota; Takahashi, Tatsuhiko; Moriya, Toshiyuki; Furukawa, Ippei

131

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

132

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

133

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

134

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

135

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

136

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

SciTech Connect

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

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

2011-06-01

137

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

138

Fatigue Life Methodology for Tapered Composite Flexbeam Laminates  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

139

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

140

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

141

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

142

Effects of metal removal and residual stress on the contact fatigue life of railway wheels  

Microsoft Academic Search

Damage often occurs on the surface of railway wheel by the wheelrail contact fatigue. Since the wheel failure may result in the derailment causing detrimental loss of life and property, the damaged surface should be removed prior to wheel failure. The increase or decrease of contact fatigue life by the metal removal of the contact surface was shown by many

Jung Won Seo; Byeong Choon Goo; Jae Boong Choi; Young Jin Kim

2008-01-01

143

An experimental investigation of wear and fatigue life reduction of boundary lubricated spherical roller thrust bearings  

Microsoft Academic Search

Wear and fatigue life reduction in boundary lubricated spherical roller thrust bearings has been investigated. Previously presented results from measurements show that there is a significant change in the washer profile due to wear. This change in surface profile greatly affects the fatigue-life of the bearings. A fractional factor experiment series was used to study how the contacting surfaces of

U. Olofsson

1997-01-01

144

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

SciTech Connect

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

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

2011-05-31

145

High cycle fatigue life prediction of cold forging tools based on workpiece material property  

Microsoft Academic Search

The present investigation is focused on high cycle fatigue life prediction based on material property of the workpiece. A new approach based on industrial tool life data was introduced for estimation of fatigue properties of the tool material. The effect of the strength coefficient K and strain hardening exponent n of four different workpiece materials was included in the local

M. A. Saroosh; H.-C. Lee; Y.-T. Im; S.-W. Choi; D.-L. Lee

2007-01-01

146

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

147

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

NASA Astrophysics Data System (ADS)

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

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

148

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

149

Effect of orientation and extrusion welds on the fatigue life of an AlMgSiMn 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 SN 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

150

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 ...

151

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, ...

152

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

Microsoft Academic Search

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

Wei Duan; Zhangqi Wang

2010-01-01

153

Effect of lubricant extreme pressure additives on rolling element fatigue life  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

154

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

155

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

156

Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life  

NASA Technical Reports Server (NTRS)

Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061.

Vlcek, Brian L.; Zaretsky, Erwin V.; Hendricks, Robert C.

2012-01-01

157

Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life  

NASA Technical Reports Server (NTRS)

Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061.

Vlcek, Brian L.; Zaretsky, Erwin V.; Hendricks, Robert C.

2008-01-01

158

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

159

Grain boundary oxidation and its effects on high temperature fatigue life  

NASA Technical Reports Server (NTRS)

Fatigue lives at elevated temperatures are often shortened by creep and/or oxidation. Creep causes grain boundary void nucleation and grain boundary cavitation. Grain boundary voids and cavities will accelerate fatigue crack nucleation and propagation, and thereby shorten fatigue life. The functional relationships between the damage rate of fatigue crack nucleation and propagation and the kinetic process of oxygen diffusion depend on the detailed physical processes. The kinetics of grain boundary oxidation penetration was investigated. The statistical distribution of grain boundary penetration depth was analyzed. Its effect on high temperature fatigue life are discussed. A model of intermittent micro-ruptures of grain boundary oxide was proposed for high temperature fatigue crack growth. The details of these studies are reported.

Liu, H. W.; Oshida, Yoshiki

1986-01-01

160

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

161

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

162

A strain rate ratio approach for assessing creep-fatigue life of 63Sn37Pb solder under shear loading  

Microsoft Academic Search

This paper studies creep-fatigue life prediction under shear loading by making extensive torsion creep-fatigue experiments using four kinds of strain waves. The linear damage rule, the strain range partitioning method, the frequency modified fatigue life and the ductility exhaustion model were applied to the experimental data, but no methods accurately predicted the creep-fatigue life. A new method based on the

Masao Sakane; Hiroki Yamamoto

2000-01-01

163

Subjective quality of life in patients with chronic fatigue syndrome.  

PubMed

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

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

2005-02-01

164

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 25C. 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

165

Probabilistic micromechanical modeling of fatigue-life variability in an ?+? Ti alloy  

NASA Astrophysics Data System (ADS)

The fatigue-life variability in an ?+? Ti alloy (Ti-6Al-4V) has been examined through a probabilistic micromechanical model that treats the crack-initiation and growth processes at the grain-size level. First, a physics-based crack-initiation model is described. This is followed by a summary of a physics-based fatigue-crack-growth model. The combined model is applied to predict the variability of crack initiation and growth lives due to microstructural variations in Ti-6Al-4V. Finally, possible fatigue mechanisms or scenarios that can lead to the worst-case fatigue life are elucidated via probabilistic modeling of the fatigue-crack-initiation process, the driving force of the grain-sized cracks, as well as the intrinsic (closure-free) threshold and the closure-affected threshold of the small cracks. In the absence of preexisting cracks, the worst-case total fatigue life is obtained when two conditions are met: (1) the crack size at initiation is on the order of 1 to 2 times the grain size, and (2) the driving force (applied ?K) exceeds the intrinsic threshold of the small cracks. The probabilistic results are also used to elucidate the conditions for the occurrence of dual fatigue limits in high-cycle fatigue (HCF) or giga-cycle fatigue.

Chan, Kwai S.; Enright, Michael P.

2005-10-01

166

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 25C. 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

167

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

168

Computational Mechanics of Fatigue and Life Predictions for Composite Materials and Structures  

E-print Network

are introduced to model the fatigue damage. The degradation of material response under cyclic loading initiation, propaga- tion and overall structural failure under cyclic loading. When applying the CDM based1 Computational Mechanics of Fatigue and Life Predictions for Composite Materials and Structures

Fish, Jacob

169

Weld detail fatigue life improvement techniques. Part 2: application to ship structures  

Microsoft Academic Search

This paper provides guidance on the application of the burr grinding, TIG dressing and hammer peening techniques for improving the fatigue life of welded ship details. These techniques are considered to have the most potential for ship structure details. The guidance covers the types of applications and details that the treatments can be applied to, the degree of fatigue strength

K. J Kirkhope; R Bell; L Caron; R. I Basu; K.-T Ma

1999-01-01

170

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

171

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

172

Fatigue life assessment of top tensioned risers under vortex-induced vibrations  

NASA Astrophysics Data System (ADS)

The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal flowing fluid on the riser is analyzed in the time domain. The long-term stress histories of the riser under VIVs are calculated and the mean stresses, the number of stress cycles and amplitudes are determined by the rainflow counting method. The Palmgren-Miner rule for cumulative damage theory with a specified S-N curve is used to estimate the fatigue life of the riser. The corresponding numerical programs numerical simulation of vortex-induced vibrations (NSVIV) which can be used to calculate the VIV response and fatigue life of the riser are compiled. Finally the influences of the risers parameters such as flexural rigidity, top tension and internal flow velocity on the fatigue life of the riser are analyzed in detail and some conclusions are drawn.

Li, Xiaomin; Guo, Haiyan; Meng, Fanshun

2010-03-01

173

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.... Values of the Parameters Used in Schapery's Theory Fatigue-Crack-Growth Cal cul ations Based on Experimental Results. Fatigue-Crack-Growth Calculations Based on Schapery's Theory . Horizontal Shift Factor (aT) Calculations for AC-5 Asphalt. Reduced...

Germann, Frederick P

1979-01-01

174

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

PubMed Central

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

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

2013-01-01

175

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

176

Fatigue life under variable-amplitude loading according to the cycle-counting and spectral methods  

Microsoft Academic Search

We compare the values for the fatigue life of 12010.3 steel determined experimentally under variable-amplitude tension-compression\\u000a and calculated by two methods in time and frequency ranges. The first method is based on the schematization of the loading\\u000a history and uses the rainflow algorithm. The fatigue life was calculated according to the Serensen-Kogaev linear hypothesis\\u000a of damage accumulation wit the use

E. Macha; T. ?agoda; A. Nies?ony; D. Kardas

2006-01-01

177

Multiaxial fatigue life prediction of kiln roller under axis line deflection  

Microsoft Academic Search

This paper investigates the multiaxial fatigue life of the roller in rolling contact with wheels with respect to axis line\\u000a deflection. The multiaxial fatigue criteria proposed by Wang and Brown, together with the rainflow counting method and Miner-Palmgrens\\u000a rule, are applied to the cumulative damage estimation and life prediction. As the axis line deflection of overlong kilns generally\\u000a results in

Yi-ping Shen; Song-lai Wang; Xue-jun Li; B. S. Dhillon

2010-01-01

178

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

179

Fatigue Life Analysis of Tapered Hybrid Composite Flexbeams  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

180

Thermal-barrier-coated turbine blade study  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

181

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

PubMed

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

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

2014-06-19

182

Fatigue-life assessment and validation techniques for metallic vascular implants.  

PubMed

Vascular implants, such as cardiac valve prostheses, stents, and other devices are often subjected to complex loading conditions in vivo, which can include pulsatile pressure cycling, bending, torsion, tension, and compression, among others. At an average of 72 heartbeats per minute, pulsatile loading alone produces approximately 40-million cycles per year. With design lives of 10-15 years, fatigue performance assessment and validation of these devices are critical for the designer, as mechanical failure can have serious consequences. Historically, various fatigue life assessment approaches have been used to validate endovascular device fatigue performance, including durability testing, stress/strain-life analysis, and damage tolerance-based analysis. This paper explores the merits and shortcomings of each of these design approaches, and provides recommendations for fatigue-life validation of endovascular implants. PMID:19875165

James, Brad A; Sire, Robert A

2010-01-01

183

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

184

Ultrasonic harmonic generation from fatigue-induced dislocation substructures in planar slip metals and assessment of remaining fatigue life  

NASA Astrophysics Data System (ADS)

An analytical model is presented of the microelastic-plastic nonlinearities resulting from the interactions of a stress perturbation with dislocation substructures and cracks that evolve during cyclic fatigue of planar slip metals. The interactions are quantified by a material nonlinearity parameter ? extracted from acoustic (ultrasonic) harmonic generation measurements. The ? parameter for a given fatigue state is highly sensitive to the volume fractions of active persistent Luders bands (PLBs) and PLB internal stresses, as well as to the densities, loop lengths, and dipole heights of the dislocation monopoles and dipoles that form the PLBs. The ? parameter is predicted to increase monotonically with the increase in the hardness of the metal during cyclic loading, thus allowing an unambiguous assessment of the remaining life of the material. The model is applied to the calculation of ? as a function of percent full fatigue life of IN100 nickel-base superalloy. The theoretical predictions are in good agreement with experimental measurements reported in the literature of IN100 samples fatigued in strain-controlled, low cycle, fully reversed loading.

Cantrell, John H.

2009-11-01

185

Multiaxial Fatigue Life Prediction for Steels Based on Some Simple Approximations  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

186

Fatigue Life Prediction for Porosity-Containing Cast 319-T7 Aluminum Alloy  

NASA Astrophysics Data System (ADS)

In this study, the linear elastic fracture mechanics (LEFM) approach, including use of the equivalent initial flaw size (EIFS) concept and fatigue crack propagation (FCP) rates, da/ dN, as a function of either ? K or ? K eff, was used to predict the fatigue life of a porosity-containing 319-T7 specimen. The uniaxial fatigue tests were conducted on a 319-T7 specimen at a stress ratio ( R) of -1. For the LEFM-based fatigue life prediction, da/ dN-? K data were obtained for the 319-T7 specimen at R = 0.1. The shape and the size of the porosity were analyzed based on the fractographic and the micrographic analyses for each fatigued specimen. The LEFM concept, including the use of the EIFS value, back-calculated by using da/ dN-? K eff data, successfully predicts the porosity-affected stress vs the number of cycles to failure (S-N) fatigue behavior of cast 319-T7 specimens. The LEFM models presently available for predicting the fatigue life of porosity-containing alloys were evaluated and a simple modification was proposed based on extensive fractographic analysis results.

Jang, Younghwan; Jeong, Youin; Yoon, Chongho; Kim, Sangshik

2009-05-01

187

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

188

Fatigue in patients with spondyloarthritis associates with disease activity, quality of life and inflammatory bowel symptoms.  

PubMed

The study aimed to assess the severity of fatigue in patients with axial spondyloarthritis (AxSpA), to assess the performance of two different fatigue measures in AxSpA, and to examine disease variables which may influence the severity of fatigue. Fatigue was examined among 67 patients with AxSpA using two measures: the fatigue Visual Analogue Scale (VAS) from the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and the Multidimensional Assessment of Fatigue (MAF) score. These measures were tested for convergent validity using linear regression analysis. Correlations between fatigue measured using both questionnaires, and key disease variables was examined using the following assessments: BASDAI, Bath Ankylosing Spondylitis Functional Index (BASFI), Ankylosing Spondylitis Quality of Life (ASQoL) questionnaire, spondyloarthritis modification of the Dudley Inflammatory Bowel Symptom Questionnaire (DISQ) and pain VAS. Human leucocyte antigen (HLA) B27 and CRP were performed and followed by physical examination, Bath AS Metrology Index (BASMI) and Ankylosing Spondylitis Disease Activity Score (ASDAS). Correlations were assessed using multivariate regression analysis. Mean (SD) fatigue measured by MAF (range 0-50) was 24.7 (11.5) and 5.14 (2.47) on the BASDAI VAS fatigue item (range 0-10). The MAF scores and BASDAI VAS fatigue were strongly correlated (r?=?0.71, P?fatigue measures was consistently noted with DISQ bowel symptom scores. MAF fatigue scores were most strongly associated with poorer ASQoL in multivariate models and mediated the effects of BASFI functioning, ASDAS disease activity and HLA-B27 status that were apparent in multivariate models. Patients with AxSpA experience substantial fatigue, which is associated with poorer quality of life. Fatigue VAS and MAF scores were strongly correlated. Factors most strongly associated with fatigue were disease activity and inflammatory bowel symptoms. PMID:24322832

Stebbings, Simon M; Treharne, Gareth J; Jenks, Katey; Highton, John

2014-10-01

189

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

190

Fatigue in sarcoidosis and exercise tolerance, dyspnea, and quality of life.  

PubMed

Fatigue is one of the major symptoms reported by sarcoidosis patients. The relationship between fatigue and clinical course of sarcoidosis remains unclear. The aim of the study was to evaluate the relationship between fatigue and lung function tests, exercise tolerance, dyspnea, and quality of life among sarcoidosis patients. One hundred eleven sarcoidosis patients completed the following questionnaires: Fatigue and Assessment Scale (FAS), Quality of Life Scale (SF-36), and dyspnea scales: Medical Research Council Questionnaire, Baseline Dyspnea Index, and Oxygen Cost Diagram. Clinical parameters (FVC, FEV1, DLCO, VO2, and VO2/AT, and work load) were derived from the patients' medical files. The exercise tolerance was the only clinical parameter associated with fatigue (Max. Work Load -0.65, VO2 -0.42, VO2/AT -0.51). No correlations were found between FAS and spirometry or diffusing tolerance. Fatigue correlated with all dyspnea domains by means of (r values ranging from 0.47 to 0.77 in multivariate regression analysis) and with quality of life in SF-36 questionnaire (r values ranging from -0.33 to -0.83). We conclude that FAS seems a reliable and valid indicator of dyspnea level, quality of life, and exercise tolerance in sarcoidosis patients. PMID:25298259

Jastrz?bski, D; Ziora, D; Lubecki, M; Ziele?nik, K; Maksymiak, M; Hanzel, J; Pocz?tek, A; Kolczy?ska, A; Nguyen Thi, L; Zebrowska, A; Kozielski, J

2015-01-01

191

Fatigue  

Microsoft Academic Search

Fatigue is a common complaint in patients with Parkinsons disease (PD). More than half of all patients with PD rank fatigue\\u000a among their three worst symptoms. Fatigue has been variously hypothesized to be caused by dysfunction of the striato-thalamo-cortical\\u000a loop, abnormalities in the hypothalamic-pituitary-adrenal axis, inflammatory processes, and neurotransmitter abnormalities\\u000a within the central nervous system. However, there is no firm

Carol Ewing Garber; Joseph H. Friedman

192

Fatigue  

Microsoft Academic Search

Fatigue is a highly prevalent, complex and poorly delineated symptom, which occurs before, during and after treatment for\\u000a cancer. Difficulties in establishing a case definition of cancer-related fatigue have resulted in an absence of reliable and\\u000a valid epidemiological data, and confound investigation into the etiology and pathogenesis of this problem. Among the possible\\u000a predisposing and perpetuating factors underlying fatigue are

Michael J. Fisch

193

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

194

Effect of weld geometry on the fatigue life of non-load-carrying fillet welded cruciform joints  

Microsoft Academic Search

In the present study, the effect of weld geometry on the fatigue life of non-load-carrying fillet welded cruciform joints was experimentally investigated. The weld geometry of the cruciform specimens was intentionally varied, and fatigue tests were carried out on various weld geometry configurations. The configurations included weld flank angle, weld toe radius and weld throat thickness. Constant amplitude fatigue tests

Chin-Hyung Lee; Kyong-Ho Chang; Gab-Chul Jang; Chan-Young Lee

2009-01-01

195

The Effect of Corner Radii and Part Orientation on Fatigue Life of Closed-Forging Die  

NASA Astrophysics Data System (ADS)

An approach to optimal design of cold forging die is presented in this paper. The closed forging of the Universal joint was generated using three-dimensional CAD modeling software namely Solid works and analysis of stress and fatigue life were carried out. This study focused on the effects of corner radius of the die and part orientations to fatigue life of the die. The forging load is obtained by using Simplified Slab Method. The result indicate that corner radius and part orientation gives significant effect to reduction of stress on the die, thus increase the service life of the die.

Abdullah, A. B.; Ling, K. S.; Samad, Z.; Sahudin, S.

196

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

NASA Technical Reports Server (NTRS)

A computer program called TFLIFE is described which can be used to predict the thermal fatigue life of metals and structural components from conventional metal properties. This program is used as a subroutine with a main program supplied by the user. The main program calculates input cycles of temperature and total strain for TFLIFE which then calculates a stress cycle, creep and plastic strain damage, and cyclic life. 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. Results are presented for two typical problems: thermal-mechanical fatigue of bar specimens of the tantalum alloy T-111 and thermal-stress fatigue of wedge specimens of the nickel alloy B-1900. The computer program is now ready for more extensive evaluation on structural components and additional laboratory specimens.

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

1975-01-01

197

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

198

Fatigue life prediction of an intermetallic matrix composite at elevated temperatures  

NASA Technical Reports Server (NTRS)

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

Bartolotta, P. A.

1991-01-01

199

Fatigue reliability of wind turbine components  

NASA Astrophysics Data System (ADS)

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

Veers, P. S.

200

Roller-burnishing to improve fatigue life in beta-titanium alloys  

SciTech Connect

The possibilities for using roller-burnishing to improve fatigue behavior in the beta titanium alloys Ti-3Al-8V-6Cr-4Mo-4Zr (Beta C) and Ti-10V-2Fe-3Al (10-2-3) are examined. While roller burnishing does not significantly increase the endurance limit in Beta C, fatigue lifetimes at high cyclic stresses can be increased by up to one order of magnitude. In 10-2-3, the endurance limit can be increased by roughly 100 MPa, while fatigue life at high cyclic stresses is only marginally improved.

Berg, A.; Drechsler, A.; Wagner, L.

1999-07-01

201

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

202

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

203

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

SciTech Connect

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

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

1992-01-01

204

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

Microsoft Academic Search

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

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

1999-01-01

205

A stress invariant based spectral method to estimate fatigue life under multiaxial random loading  

Microsoft Academic Search

The present paper aims to propose a frequency-domain formulation of a stress invariant based multiaxial fatigue criterion, called Projection by Projection (PbP) approach, suitable for estimating fatigue life in presence of complex multiaxial loadings. The new proposed spectral method is first validated with experimental data from the literature, concerning bending-torsion random loading, showing a general accuracy. Numerical simulations are next

A. Cristofori; D. Benasciutti; R. Tovo

2011-01-01

206

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 SN 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

207

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

208

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

NASA Astrophysics Data System (ADS)

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

Colin, Julie

209

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

210

Dynamic loads in Francis runners and their impact on fatigue life  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

211

Probability Analysis of Static Frequency and Dynamic Frequency of Steam Turbine Blade Based on RBF Neural Network and Monte Carlo Simulation  

Microsoft Academic Search

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

Wei Duan; Zhang-Qi Wang

2007-01-01

212

A hybrid model for fatigue life estimation of polymer matrix composites  

NASA Astrophysics Data System (ADS)

A major limitation of current fatigue life prediction methods for polymer matrix composite laminates is that they rely on empirical S-N data. In contrast to fatigue life prediction methods for metals which are based on physical crack growth models, the heart of fatigue life models for composites is empirical S-N data for each specific material system and specific loading conditions. This implies that the physical nature and processes responsible for tensile fatigue are not well understood. In this work a mechanism-based approach is used to model the damage growth and failure of uniaxial polymer matrix composites under uni-axial tension-tension fatigue loading. The model consists of three parts: an initial damage model, a damage growth model, and a tensile failure model. The damage growth portion of the model is based on fracture mechanics at the fiber/matrix level. The tensile failure model is based on a chain of bundles failure theory originally proposed for predicting the static strength of unidirectional laminates using fiber strength distributions. The tensile fatigue life prediction model developed in this work uses static tensile strength data and basic material properties to calculate the strength degradation due to fiber-matrix damage growth caused by fatigue loading and does not use any experimental S-N data. The output of the model is the probability of failure under tensile fatigue loading for a specified peak load level. Experimental data is used to validate and refine the model and good correlation between the model and experimental data has been shown. The principal contribution of this work is a hybrid-mechanistic model for analyzing and predicting the tension-tension fatigue life behavior of uniaxial polymer matrix composites. This model represents the very foundation to build upon a comprehensive model for fatigue. It demonstrates the validity of the ideas as they apply to uniaxial laminates that may in turn be used to apply to more complex laminates. Additionally, because the model is mechanism based it can be used for evaluation of the effects of constituent property changes such as matrix stiffness and toughness, or environmental conditions such as temperature and moisture.

Uleck, Kevin R.

213

EFFECT OF LASER GLAZING PROCESS ON RAIL CONTACT FATIGUE LIFE  

Microsoft Academic Search

????? . Rail fatigue is a major problem for railroad industry. It can lead to catastrophic derailment causing loss of lives and great financial loss. A new technology has recently been developed at Argonne National Laboratory (ANL) showed desirable results. This technology involves the use of laser to treat (glaze) the gage side of the rail. Treating steel rails by

S. Aldajah

214

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

215

Improve the fatigue life of titanium alloys; Part 1  

Microsoft Academic Search

Heat treatment and mechanical surface treatments of titanium alloys interact in unique ways to allow tailoring of surface microstructures for specific applications. Part 1 of this two-part review discusses the properties of titanium alloys in their various microstructural phases, and Part 2 will describe novel methods for improving fatigue performance by combining mechanical and thermal treatments. Microstructural modification by thermomechanical

L. Wagner; J. K. Gregory

1994-01-01

216

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

NASA Technical Reports Server (NTRS)

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

Jeelani, S.; Collins, M. R.

1988-01-01

217

Fatigue Life of Cold Expanded Fastener Holes at Short Edge Margins  

Microsoft Academic Search

\\u000a The fatigue life of cold-expanded fastener holes with short edge margins was studied on aluminum 7075-T6 specimens with straight\\u000a open holes. The study was done in two parts: experimentally and through finite element analysis. The experiments measured\\u000a the total fatigue life and crack growth, and the results from the finite element analysis consisted of tangential residual\\u000a stress profiles.\\u000a \\u000a \\u000a The experiments

G. M. Vallires; D. L. DuQuesnay

218

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

NASA Astrophysics Data System (ADS)

Structural integrity is the science and technology of the margin between safety and disaster. Proper evaluation of the structural integrity and fatigue life of any structure (aircraft, ship, railways, bridges, gas and oil transmission pipelines, etc.) is important to ensure the public safety, environmental protection, and economical consideration. Catastrophic failure of any structure can be avoided if structural integrity is assessed and necessary precaution is taken appropriately. Structural integrity includes tasks in many areas, such as structural analysis, failure analysis, nondestructive testing, corrosion, fatigue and creep analysis, metallurgy and materials, fracture mechanics, fatigue life assessment, welding metallurgy, development of repairing technologies, structural monitoring and instrumentation etc. In this research fatigue life assessment of welded and weld-repaired joints is studied both in numerically and experimentally. A new approach for the simulation of fatigue crack growth in two elastic materials has been developed and specifically, the concept has been applied to butt-welded joint in a straight plate and in tubular joints. In the proposed method, the formation of new surface is represented by an interface element based on the interface potential energy. This method overcomes the limitation of crack growth at an artificial rate of one element length per cycle. In this method the crack propagates only when the applied load reaches the critical bonding strength. The predicted results compares well with experimental results. The Gas Metal Arc welding processes has been simulated to predict post-weld distortion, residual stresses and development of restraining forces in a butt-welded joint. The effect of welding defects and bi-axial interaction of a circular porosity and a solidification crack on fatigue crack propagation life of butt-welded joints has also been investigated. After a weld has been repaired, the specimen was tested in a universal testing machine in order to determine fatigue crack propagation life. The fatigue crack propagation life of weld-repaired specimens was compared to un-welded and as-welded specimens. At the end of fatigue test, samples were cut from the fracture surfaces of typical welded and weld-repaired specimens and are examined under Scanning Electron Microscope (SEM) and characteristics features from these micrographs are explained.

Alam, Mohammad Shah

2005-11-01

219

Fatigue life prediction of welded structures containing non-planar flaws using Quality Category under non-constant amplitude loading  

Microsoft Academic Search

The prediction of fatigue life is important for welded structures. A new fatigue life prediction method of welded structures containing non-planar flaws was developed in this article. The new method is based on the Quality Category of PD6493 and Miner's liner damage rule. It accounts for the maximum height or width of slag inclusions, and the percentage of projected area

Jin Xing; Q. P. Zhong; Y. J. Hong; J. F. Tian

1998-01-01

220

Analysing the influences of weld size on fatigue life prediction of FCAW cruciform joints by strain energy concept  

Microsoft Academic Search

The effect of weld size on fatigue life of flux cored arc welded (FCAW) cruciform joints containing lack of penetration (LOP) defect has been analysed by using the strain energy density factor (SEDF) concept. Moreover, new fracture mechanics equations have been developed to predict the fatigue life of the cruciform joints. Load carrying cruciform joints were fabricated from ASTM 517

V Balasubramanian; B Guha

1999-01-01

221

Fatigue  

MedlinePLUS

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

222

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

223

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

2011-12-01

224

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

225

Reliability prediction of the fatigue life of a crankshaft  

Microsoft Academic Search

Crankshaft, the core element of the engine of a vehicle, transforms the translational motion generated by combustion to rotational\\u000a motion. Its failure will cause serious damage to the engine so its reliability verification must be performed. In this study,\\u000a the S-N data of the bending fatigue limit of a crankshaft are derived. To evaluate the reliability of the crankshaft, reliability

Do-Hyun Jung; Hong-Jin Kim; Young-Shik Pyoun; Alisher Gafurov; Gue-Cheol Choi; Jong-Mo Ahn

2009-01-01

226

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

227

Noncontact monitoring of surface-wave nonlinearity for predicting the remaining life of fatigued steels  

NASA Astrophysics Data System (ADS)

A nonlinear acoustic measurement is studied for fatigue damage monitoring. An electromagnetic acoustic transducer (EMAT) magnetostrictively couples to a surface-shear-wave resonance along the circumference of a rod specimen during rotating bending fatigue of carbon steels. Excitation of the EMAT at half of the resonance frequency caused the standing wave to contain only the second-harmonic component, which was received by the same EMAT to determine the second-harmonic amplitude. Thus measured surface-wave nonlinearity always showed two distinct peaks at 60% and 85% of the total life. We attribute the earlier peak to crack nucleation and growth, and the later peak to an increase of free dislocations associated with crack extension in the final stage. This noncontact resonance-EMAT measurement can monitor the evolution of the surface-shear-wave nonlinearity throughout the metal's fatigue life and detect the pertinent precursors of the eventual failure.

Ogi, Hirotsugu; Hirao, Masahiko; Aoki, Shinji

2001-07-01

228

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

229

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

230

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

231

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

232

A computational tool for the life prediction of GFRP laminates under irregular complex stress states: Influence of the fatigue failure criterion  

Microsoft Academic Search

A new computational tool for the fatigue life prediction of composite materials, designated CCfatigue, is presented in this paper. This new software has been developed based on a well-established phenomenological fatigue life prediction methodology. It is capable of performing the calculations necessary to estimate the fatigue life of composite materials under complex cyclic stress states of variable amplitude. Although the

Anastasios P. Vassilopoulos; Roohollah Sarfaraz; Behzad D. Manshadi; Thomas Keller

2010-01-01

233

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

Microsoft Academic Search

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

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

1996-01-01

234

Fatigue life prediction based on natural frequency changes for spot welds under random loading  

Microsoft Academic Search

Fatigue tests were carried out on tensile-shear spot-welded specimens under random loading; at the same time, natural frequencies at different life stages were measured. Test results were compared with that under constant amplitude loading. The relationship between damage and natural frequency change ratio established under constant amplitude loading is here modified. The nonlinear damage evolution equation was established using the

Rui-Jie Wang; De-Guang Shang

2009-01-01

235

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

236

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

237

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

238

A critical plane approach for life prediction of high cycle fatigue under multiaxial variable amplitude loading  

Microsoft Academic Search

In this paper, a new life prediction method for high cycle multiaxial fatigue of metallic materials is presented. It is based on a local approach introduced by Dang Van and developed by Papadopoulos, where accumulated plastic strain due to external loading is estimated at a scale of the order of a few grains. Its evaluation requires the use of a

F. Morel

2000-01-01

239

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

Microsoft Academic Search

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

Mohammad Shah Alam

2005-01-01

240

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 with shrinkage porosity is developed and validated through comparison with previously performed measure- ments. A X-ray tomography technique is used to reconstruct the porosity distribution in 25 test specimens

Beckermann, Christoph

241

A Fatigue Life Comparison of Two-Row Tapered Roller Bearings and Spherical Roller Bearings  

Microsoft Academic Search

Tests were run to compare the fatigue life of two-row tapered roller bearings to that of spherical roller bearings. Both bearing types had an outer diameter of 110 mm with the spherical roller bearing having a 22 percent larger dynamic radial load rating than the tapered roller bearings. All tests were run at 165 percent of the respective two-row dynamic

Harry Zantopulos; Joel Z. Russell

1999-01-01

242

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

243

Fatigue life of cold-forging dies with various values of hardness  

Microsoft Academic Search

Four selected die materials commonly used in the cold-forging process were examined in the present study to obtain the relationship between the hardness and the die fatigue life. The die materials were first heat-treated by a developed process to obtain different values of hardness, while the ductility was retained at a favorable level. The material properties of these die materials

Yi-Che Lee; Fuh-Kuo Chen

2001-01-01

244

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

Microsoft Academic Search

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

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

2007-01-01

245

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

Microsoft Academic Search

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

Hong Tang

2008-01-01

246

Effect of surface treatments on the fatigue life of titanium for biomedical applications  

Microsoft Academic Search

Many surface treatments that are used in cementless and endosseous implants modify the topography and the roughness to increase the implant-bone contact area and thus favor bio-mechanical anchorage, shortening the period of osseointegration. Nevertheless, the effects that the surface treatments can have on the fatigue life of the material are not generally considered. In this sense, the superficial condition of

L. Pazos; P. Corengia; H. Svoboda

2010-01-01

247

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

E-print Network

- expandable stents, which are manufactured primarily from austenitic stainless steel (e.g., AISI 316L.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

Ritchie, Robert

248

Impact of temperature cycle profile on fatigue life of solder joints  

Microsoft Academic Search

In this paper the influence of the temperature cycle time history profile on the fatigue life of ball grid array (BGA) solder joints is studied. Temperature time history in a Pentium processor laptop computer was measured for a three-month period by means of thermocouples placed inside the computer. In addition, Pentium BGA packages were subjected to industry standard temperature cycles

Terry Dishongh; Cemal Basaran; Alexander N. Cartwright; Ying Zhao; Heng Liu

2002-01-01

249

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

250

Effect of UIT on Fatigue Life in Web-Gusset Welded Joints  

NASA Astrophysics Data System (ADS)

Ultrasonic impact treatment (UIT), which is a peening method, is usually used as a post-weld treatment in order to improve the fatigue strength of welded joints. In this study, fatigue tests were carried out on web-gusset welded joints treated by UIT and the results were compared with the fatigue lives of as-welded joints in order to examine the effects of UIT on the fatigue lives of welded joints. The fatigue lives of web-gusset welded joints treated by UIT increased to more than ten times those of as-welded joints. The introduction of compressive residual stress, relaxation of stress concentration at a weld toe, and refinement of grains under the weld toes were considered as possible reasons for the improvement in fatigue life caused by UIT. Residual stress near weld toes was measured using the X-ray diffraction method. The stress concentration factor at the weld toes was analyzed using the finite element method (FEM). The grain size under the weld toes was measured using electron backscatter diffraction pattern (EBSD) analysis.

Togasaki, Yu; Tsuji, Hirokazu; Honda, Takashi; Sasaki, Tetsuya; Yamaguchi, Atsushi

251

The effects of sheet spacing on the fatigue life of spotwelded joints  

NASA Astrophysics Data System (ADS)

While investigating the fatigue strength of spot-welded joints, the effects of sheet spacing or gap amounts between sheet joints may be considered as one of the most important parameters on the fatigue life duration of the joints. The main goal of the present work is to study the influence of sheet spacing on the fatigue life of 5083-O aluminium alloy spot welded tensile-shear joints. The amounts of sheet spacing are the average values over three measurements of photograph observation of the cut-off surfaces from the nugget centre of the spot-welded joints. The amounts of gap distances between spot weld sheet joints for three different electrode clamping force levels were 0.09mm, 0.11mm and 0.13mm, respectively. The values of notch strength reduction factors have been obtained at all levels of applied loads based on volumetric approach. The fatigue lives of spot welded joints have been obtained according to the volumetric method using the notch strength reduction factors and the available smooth S-N curve of 5083-O aluminium alloy sheets. The results based on the volumetric approach have been compared with the experimental fatigue test data and there is good agreement between numerical predictions and experimental results.

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

2010-06-01

252

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

NASA Technical Reports Server (NTRS)

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

Jones, David J.; Kurath, Peter

1988-01-01

253

The Role of Fatigue Variability in Life Prediction of an ?+? Titanium Alloy  

NASA Astrophysics Data System (ADS)

The fatigue life variability of the ?+? titanium alloy, Ti-6Al-2Sn-4Zr-6Mo increased with decreasing stress level. The variability in life was found to be due to segregation of lives due to two failure mechanisms. A bimodal cumulative distribution model was shown to accurately describe the combined failure modes. The nominal failure processes for the two regimes were similar, with crack nucleation occurring in equiaxed ?p particles, irrespective of life or stress level. However the variability in life was not controlled by the size of the crack-nucleating ?p, but rather by the ability of the material to distribute deformation and avoid early crack nucleation.

Jha, S. K.; Larsen, J. M.; Rosenberger, A. H.

2004-06-01

254

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

255

Scatter in fatigue life due to effects of porosity in cast A356-T6 aluminum-silicon alloys  

NASA Astrophysics Data System (ADS)

Porosity is well known to be a potent initiator of fatigue cracks in cast aluminum alloys. This article addresses the observed scatter in fatigue life of a cast A356-T6 aluminum-silicon alloy due to the presence of porosity. Specimens containing a controlled amount of porosity were prepared by employing a wedge-shaped casting mold and adjusting the degassing process during casting. High-cycle fatigue tests were conducted under fixed stress conditions on a series of specimens with controlled microstructures (especially, the secondary dendrite-arm spacing), and the degree of scatter in the results was assessed. Stochastically, such scatter was found to be adequately characterized by a three-parameter Weibull distribution function. Large pores at or close to the specimen surface were found to be responsible for crack initiation in all fatigue-test specimens, and the resultant fatigue life was related to the initiating pore size through a relationship based on the rate of small-fatigue-crack propagation. With respect to the probabilities for the pores of various sizes and locations to initiate a fatigue crack, a statistical model was developed to establish the relationship between the porosity population and the resultant scatter in fatigue life. The modeling predictions are in agreement with the experimental results. Moreover, Monte-Carlo simulation based on this model demonstrated that the average pore size, pore density, and standard deviation of the pore sizes, together with the specimen size and geometry, are all of consequence regarding scatter in fatigue life.

Yi, J. Z.; Gao, Y. X.; Lee, P. D.; Flower, H. M.; Lindley, T. C.

2003-09-01

256

Fatigue  

MedlinePLUS

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

257

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

SciTech Connect

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

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

1995-09-01

258

Microstructure-based fatigue life prediction for cast A356-T6 aluminum-silicon alloys  

NASA Astrophysics Data System (ADS)

Fatigue life prediction and optimization is becoming a critical issue affecting the structural applications of cast aluminum-silicon alloys in the aerospace and automobile industries. In this study, a range of microstructure and porosity populations in A356 alloy was created by controlling the casting conditions and by applying a subsequent hot isostatic pressing (hipping) treatment. The microstructure and defects introduced during the processing were then quantitatively characterized, and their effects on the fatigue performance were examined through both experiment and modeling. The results indicated that whenever a pore is present at or near the surface, it initiates fatigue failure. In the absence of large pores, a microcell consisting of ?-Al dendrites and associated Si particles was found to be responsible for crack initiation. Crack initiation life was quantitatively assessed using a local plastic strain accumulation model. Moreover, the subsequent crack growth from either a pore or a microcell was found to follow a small-crack propagation law. Based on experimental observation and finite-element analysis, a unified model incorporating both the initiation and small crack growth stages was developed to quantitatively predict the dependency of fatigue life on the microstructure and porosity. Good agreement was obtained between the model and experiment.

Yi, J. Z.; Gao, Y. X.; Lee, P. D.; Lindley, T. C.

2006-04-01

259

Effects of weld profile and undercut on fatigue crack propagation life of thin-walled cruciform joint  

Microsoft Academic Search

Fatigue may occur in undercarriages and support systems of trailers, haymakers, graders and swing-ploughs made up of thin-walled tubular sections with wall thicknesses less than 4 mm. Little research has been done on the fatigue of thin-walled tubular sections below 4 mm thickness. The weld profile and weld undercut may affect the fatigue crack propagation life of welded joints especially

F. R. Mashiri; X. L. Zhao; P. Grundy

2001-01-01

260

A reliability assessment method in strain-based fatigue life analysis  

SciTech Connect

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

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

1996-12-01

261

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

NASA Technical Reports Server (NTRS)

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

Gyekenyesi, Andrew L.

1998-01-01

262

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

263

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

264

Extra-corporeal life support, transradial thrombus aspiration and stenting, percutaneous blade and balloon atrioseptostomy, all as a bridge to heart transplantation to save one life.  

PubMed

In patients with cardiogenic shock, the Extra-Corporeal Life Support (ECLS) has been shown to be lives saving. But, in some situations, it proves inadequate for the discharge of the left heart. Several device-based techniques have been proposed to decompress the left side either surgically or percutaneously, each of them with the proper potential risks and complications. One technique, the percutaneous blade and balloon atrioseptostomy that requires transseptal catheter based experience and consists of creating an atrial septal defect (ASD) could be an elegant technique as an "add on" to the classic assistance making together a bridge to partial recovery or to heart transplantation. Herein, we present a case of an adult patient who presented with inaugural resistant cardiac arrest with a thrombotic occlusion of the left anterior descending artery (LAD) who required Extra-Corporeal Life Support, thrombus aspiration, stenting of the culprit lesion, and percutaneous blade and balloon atrioseptostomy to bridge "safely" to the heart transplantation. PMID:22480784

Dahdouh, Ziad; Roule, Vincent; Sabatier, Rmi; Lognon, Thrse; Labombarda, Fabien; Pellissier, Arnaud; Belin, Annette; Ivascau, Calin; Buklas, Dimitrios; Massetti, Massimo; Grollier, Gilles

2012-01-01

265

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

Microsoft Academic Search

This research aims to develop the methods and understanding needed to incorporate time and loading variable dependent environmental effects on fatigue crack propagation (FCP) into computerized fatigue life prediction codes such as NASA FLAGRO (NASGRO). In particular, the effect of loading frequency on FCP rates in alpha + beta titanium alloys exposed to an aqueous chloride solution is investigated. The

Richey

1995-01-01

266

Influences of welding processes on fatigue life of cruciform joints of pressure vessel grade steels containing LOP defects  

Microsoft Academic Search

The influences of two welding processes, namely, shielded metal arc welding (SMAW) and flux cored arc welding (FCAW), on fatigue life of cruciform joints, containing lack of penetration (LOP) defects, have been studied. Load carrying cruciform joints were fabricated from high strength, quenched and tempered steels of pressure vessel (ASTM 517 F) grade. Fatigue crack growth experiments were carried out

V Balasubramanian; B Guha

2000-01-01

267

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

E-print Network

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

Meyer, Christian

268

Fatigue Fracture Behavior of High-Strength Steel in Super Long Life Range  

NASA Astrophysics Data System (ADS)

Long term cantilever-type rotational bending fatigue tests of up to 109 cycles were carried out on high carbon chromium bearing steel, SUJ2. The fatigue fracture behavior of SUJ2 in the super long life range was discussed based on scanning electron microscope observations and fracture mechanics. Fatigue failure occurred when the number of cycles exceeded 107. In the super long life range, the fish-eye-type fracture and the subsurface-type fracture were observed. In the fish-eye-type fracture, the stress intensity factor calculated from the area of the facet region was independent of the number of cycles to failure and was almost constant at 5.4MPa m1/2. In the subsurface-type fracture, high carbon segregation was observed at the crack initiation area. The stress intensity factor for the carbon segregation area was close to 5.0MPam1/2. Pure fatigue crack was initiated from the area outside the facet region or the high carbon segregation area.

Murakami, Ri-Ichi; Yonekura, Daisuke; Ni, Zhengdong

269

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

PubMed

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

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

2014-01-01

270

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

271

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

272

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

273

Blade Manufacturing Improvement: Remote Blade Manufacturing Demonstration  

SciTech Connect

The objective of this program was to investigate manufacturing improvements for wind turbine blades. The program included a series of test activities to evaluate the strength, deflection, performance, and loading characteristics of the prototype blades. The original contract was extended in order to continue development of several key blade technologies identified in the project. The objective of the remote build task was to demonstrate the concept of manufacturing wind turbine blades at a temporary manufacturing facility in a rural environment. TPI Composites successfully completed a remote manufacturing demonstration in which four blades were fabricated. The remote demonstration used a manufacturing approach which relied upon material ''kits'' that were organized in the factory and shipped to the site. Manufacturing blades at the wind plant site presents serious logistics difficulties and does not appear to be the best approach. A better method appears to be regional manufacturing facilities, which will eliminate most of the transportation cost, without incurring the logistical problems associated with fabrication directly onsite. With this approach the remote facilities would use commonly available industrial infrastructure such as enclosed workbays, overhead cranes, and paved staging areas. Additional fatigue testing of the M20 root stud design was completed with good results. This design provides adhesive bond strength under fatigue loading that exceeds that of the fastener. A new thru-stud bonding concept was developed for the M30 stud design. This approach offers several manufacturing advantages; however, the test results were inconclusive.

ASHWILL, THOMAS D.

2003-05-01

274

Fatigue life under non-Gaussian random loading from various models  

Microsoft Academic Search

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

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

2004-01-01

275

Fatigue life assessment of top tensioned risers under vortex-induced vibrations  

Microsoft Academic Search

The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal\\u000a flowing fluid on the riser is analyzed in the time domain. The long-term stress histories of the riser under VIVs are calculated\\u000a and the mean stresses, the number of stress cycles and amplitudes are determined by the rainflow counting method. The Palmgren-Miner

Xiaomin Li; Haiyan Guo; Fanshun Meng

2010-01-01

276

An approach to fatigue life modeling in titanium-matrix composites  

Microsoft Academic Search

A review of the procedures developed by the author and his colleagues over the last several years for predicting elevated-temperature fatigue life of metal-matrix composites is presented. Modeling approaches involve concepts of both linear and non-linear summation of damage from cycle-dependent as well as time-dependent mechanisms. The analyses, further, treat the micromechanical stresses in the constituents as parameters in the

Theodore Nicholas

1995-01-01

277

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

278

Fatigue life of a plate with an arbitrary-shaped concentrator under low-cycle plane loading  

Microsoft Academic Search

A technique and an algorithm for calculating fatigue life of a plate with a concentrator under complex loading in the low-cycle\\u000a fatigue region are presented and the life of the plate with different shape concentrators is considered. The local stress\\u000a strain state is investigated in the framework of plane loading using the finite element method with the aid of the

A. T. Ponomarev; V. G. Stopkevich; E. V. Korobeinikov

2010-01-01

279

Helicopter rotor blade design for minimum vibration  

NASA Technical Reports Server (NTRS)

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

Taylor, R. B.

1984-01-01

280

Relationship between Defect Size and Fatigue Life Distributions in Al-7 Pct Si-Mg Alloy Castings  

NASA Astrophysics Data System (ADS)

A new method for predicting the variability in fatigue life of castings was developed by combining the size distribution for the fatigue-initiating defects and a fatigue life model based on the Paris-Erdo?an law for crack propagation. Two datasets for the fatigue-initiating defects in Al-7 pct Si-Mg alloy castings, reported previously in the literature, were used to demonstrate that (1) the size of fatigue-initiating defects follow the Gumbel distribution; (2) the crack propagation model developed previously provides respectable fits to experimental data; and (3) the method developed in the present study expresses the variability in both datasets, almost as well as the lognormal distribution and better than the Weibull distribution.

Tiryakio?lu, Murat

2009-07-01

281

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

282

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

PubMed

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

Silva, Matthew J; Touhey, Daniel C

2007-02-01

283

Surface topography and fatigue life of rolling contact bearings  

SciTech Connect

The contact stresses of bearings were analyzed by a micro-macrocontact model in which the macrocontact was elastic, and the microcontact was elastic-plastic. Subsurface stress maps were calculated far real contact surfaces, by including roughness, waviness, and profile. The predicted subsurface stress maps display the local stress levels for various elastohydrodynamic lubrication (EHL) film thicknesses and show why enhanced-finish bearings have longer lives than the standard-finish bearings. It is believed that the present approach provides an alternative to the empirical methods that are used for predicting life under thin-film EHL conditions. 18 refs.

Zhou, R.S. (Timken Co., Canton, OH (United States))

1993-07-01

284

Integrated actuation system for individual control of helicopter rotor blades  

NASA Astrophysics Data System (ADS)

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

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

1996-05-01

285

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 chamber liners were fabricated of copper or copper alloy and contained milled coolant channels. The chambers were completed by means of an electroformed nickel closeout. The oxidant/fuel ratio for the liquid oxygen and gaseous hydrogen propellants was 6.0. 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 lives were much shorter than were predicted by an analytical structural analysis computer program used in conjunction with fatigue life data from isothermal test specimens, due to the uneven distribution of Zr in the chamber material.

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

1976-01-01

286

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

287

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

288

A comprehensive energy approach to predict fatigue life in CuAlBe shape memory alloy  

NASA Astrophysics Data System (ADS)

Stabilized dissipated energy is an effective parameter on the fatigue life of shape memory alloys (SMAs). In this study, a formula is proposed to directly evaluate the stabilized dissipated energy for different values of the maximum and minimum applied stresses, as well as the loading frequency, under cyclic tensile loadings. To this aim, a one-dimensional fully coupled thermomechanical constitutive model and a cycle-dependent phase diagram are employed to predict the uniaxial stress-strain response of an SMA in a specified cycle, including the stabilized one, with no need of obtaining the responses of the previous cycles. An enhanced phase diagram in which different slopes are defined for the start and finish of a backward transformation strip is also proposed to enable the capture of gradual transformations in a CuAlBe shape memory alloy. It is shown that the present approach is capable of reproducing the experimental responses of CuAlBe specimens under cyclic tensile loadings. An explicit formula is further presented to predict the fatigue life of CuAlBe as a function of the maximum and minimum applied stresses as well as the loading frequency. Fatigue tests are also carried out, and this formula is verified against the empirically predicted number of cycles for failure.

Sameallah, S.; Legrand, V.; Saint-Sulpice, L.; Kadkhodaei, M.; Arbab Chirani, S.

2015-02-01

289

A generalized fitting technique for the LIFE2 fatigue analysis code  

SciTech Connect

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

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

1996-08-01

290

Factors affecting quality of life and fatigue in patients with leukemia under chemotherapy  

PubMed Central

Background: The goal of treating chronic diseases, including hematologic malignancies, is to increase patients life span and to improve their capabilities as much as possible; so that patients could maintain an appropriate level of quality of life (QoL) and continue their lives. Most studies performed to evaluate the treatment of various diseases were mostly focused on the increase of life expectancy regardless of the QoL and treatment issues. Furthermore, fatigue is one of the most common and distressing side effects of cancer and treatments related to it, which can affect a patient's QoL, and be followed by many problems. This study was designed and implemented with the aim to determine the factors affecting the QoL and fatigue in patients with leukemia undergoing chemotherapy. Materials and Methods: This was a cross-sectional correlation descriptive-analytical study. One hundred and fifteen patients with leukemia referred to Sayyed-Al-Shohada Hospital were enrolled in the study through convenient sampling method. To collect data, a three-part questionnaire was used: The first part was related to demographic characteristics and disease-related data and the second part was the fatigue check list and the third part was the Short-Form 36 Health Survey (SF-36) related to QoL. The data were analyzed after collection and coding through Software SPSS version 18 and descriptive and analytical statistics (analysis of variance test, independent t test, Pearson's and Spearman's correlation coefficient) with 95% confidence interval. Results: The results showed that there was a significant correlation between QoL in Physical Component Summary with gender (P = 0.03), educational level (P = 0.09), and marital status (P = 0.004), Also there was a significant correlation between QoL in Mental Component Summary with educational level (P = 0.01) and economic status (P = 0.02). Findings showed that there was a significant correlation between fatigue and marital status (P = 0.005). But statistically there was no significant correlation between demographic variables such as age, educational level, and employment status with patients fatigue. Spearman correlation coefficient showed that there was a significant correlation between fatigues with pain (P = 0.005). Also findings revealed the statistically significant correlation between fatigues with economic status (P = 0.003). Conclusion: According to the present results, it seems that some demographic factors affect QoL and significant relationship exists between them. Fatigue in patients with leukemia dramatically affects their QoL. Therefore, it is important for medical staff to pay attention to demographics and fatigue in leukemic patients in order to improve their QoL and help them to organize their activities to promote health and QoL. PMID:25077157

Musarezaie, Amir; Khaledi, Firuz; Esfahani, Homayoon Naji; Ghaleghasemi, Tahere Momeni

2014-01-01

291

Determination of Some Parameters for Fatigue Life in Welded Joints Using Fracture Mechanics Method  

NASA Astrophysics Data System (ADS)

In this work, the parameters stress intensity factor (SIF), initial and final crack lengths ( a i and a f), crack growth parameters ( C and m), and fatigue strength (FAT) are investigated. The determination of initial crack length seems to be the most serious factor in fatigue life and strength calculations for welded joints. A fracture mechanics approach was used in these calculations based on SIF which was calculated with the finite element method (FEM). The weld toe crack was determined to be equal to 0.1 mm, whereas the weld root crack's length was varied depending on the degree of the weld penetration. These initial crack length values are applicable for all types of joints which have the same crack phenomenon. As based on the above calculated parameters, the new limits of FAT for new geometries which are not listed yet in recommendations can be calculated according to the current approach.

Al-Mukhtar, A. M.; Biermann, H.; Hbner, P.; Henkel, S.

2010-12-01

292

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

NASA Technical Reports Server (NTRS)

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

Jadaan, Osama

2001-01-01

293

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

SciTech Connect

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

Richey, E. III

1995-10-01

294

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

295

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

296

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

297

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

SciTech Connect

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

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

2007-03-21

298

Effect of weld geometric profile on fatigue life of cruciform welds made by laser\\/GMAW processes  

Microsoft Academic Search

The effect of weld geometric profile on fatigue life of laser-welded HSLA-65 steel is evaluated. Presented are results of cruciform-shaped fatigue specimens with varying weld profiles loaded cyclically in axial tensioncompression. Specimens with a nearly circular-weld profile were created at 133cm\\/min, as part of this effort, with a hybrid laser gas-metal-arc welding GMAW (L\\/GMAW) process. The ability of the laser-welding

V. Caccese; P. A. Blomquist; K. A. Berube; S. R. Webber; N. J. Orozco

2006-01-01

299

Rationale for the design characteristics of fatigue resistance and service life of elements of railway rolling stock  

Microsoft Academic Search

The approaches to the assessment of fatigue resistance of bearing structures of railway rolling stock in accordance with existing\\u000a regulations are considered. On the basis of theoretical and experimental studies, the need is shown to supplement evaluations\\u000a of fatigue resistance with calculations for durability (service life). The main methods of calculation on durability are described,\\u000a and recommendations for their use

N. A. Makhutov; V. S. Kossov; E. S. Oganyan; N. F. Krasyukov; B. B. Bunin; T. M. Ponomareva

2010-01-01

300

Effects of Spot Diameter and Sheets Thickness on Fatigue Life of Spot Welded Structure based on FEA Approach  

Microsoft Academic Search

This study presents the effect of the spot weld and sheets thickness on the fatigue life of the of the spot-weld joints to predict the lifetime and location of the weakest spot-welds due to the variable amplitude loading conditions. A simple model was used to illustrate the technique of spot-weld fatigue analysis. Finite element model and analysis were carried out

M. M. Rahman; A. B. Rosli; M. M. Noor; M. S. M. Sani; J. M. Julie

2009-01-01

301

Improvement of fatigue life of electrical discharge machined AISI D2 tool steel by TiN coating  

Microsoft Academic Search

This work presents the effects of titanium nitride (TiN) coating by physical vapor deposition (PVD) on the fatigue life of AISI D2 tool steel, which was electrical discharge machined (EDM) at various machining parameters, such as pulse current and pulse-on duration. Surface hardness, surface roughness, residual stress and fatigue strength were measured. Experimental results indicate that EDM treatment has a

Y. H. Guu; H. Hocheng

2001-01-01

302

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

303

CARES/Life Ceramics Durability Evaluation Software Enhanced for Cyclic Fatigue  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

304

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

305

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

306

Dynamic stall on wind turbine blades  

SciTech Connect

Dynamic loads must be predicted accurately in order to estimate the fatigue life of wind turbines operating in turbulent environments. Dynamic stall contributes to increased dynamic loads during normal operation of all types of horizontal-axis wind turbine (HAWTs). This report illustrates how dynamic stall varies throughout the blade span of a 10 m HAWT during yawed and unyawed operating conditions. Lift, drag, and pitching moment coefficients during dynamics stall are discussed. Resulting dynamic loads are presented, and the effects of dynamic stall on yaw loads are demonstrated using a yaw loads dynamic analysis (YAWDYN). 12 refs., 22 figs., 1 tab.

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

1991-12-01

307

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

308

Acoustic study of dislocation rearrangement at later stages of fatigue: Noncontact prediction of remaining life  

NASA Astrophysics Data System (ADS)

This study is devoted to clarifying the mechanism of the surface-shear-wave attenuation peak observed during rotating bending fatigue of carbon steels. We have developed electromagnetic acoustic resonance to make a contactless monitoring of the attenuation throughout the fatigue test. The attenuation peak occurs at a fixed fraction to lifetime, being independent of the bending stress (0.49-1.20 of the yield stresses) and the carbon content (0.22-0.45 mass %). Low-temperature heat treatment reduces the peak attenuation back to the previous value, which indicates a dominant contribution of dislocations. Microstructure observations with transmission electron microscopy, surface crack study with replicas and the acoustic measurements show that a large-scale change occurs in the dislocation structure (persistent slip bands to cells) at the attenuation peak and that it is triggered by the inward growth of cracks. This change is completed in a short time, a few percent of the total lifetime. The acoustic-resonance technique can be an important means for the exact prediction of the remaining life of fatigued steels.

Ogi, Hirotsugu; Minami, Yoshikiyo; Hirao, Masahiko

2002-02-01

309

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

310

Interference fits and stress-corrosion failure. [aircraft parts fatigue life analysis  

NASA Technical Reports Server (NTRS)

It is pointed out that any proper design of interference fit fastener, interference fit bushings, or stress coining processes should consider both the stress-corrosion susceptibility and fatigue-life improvement together. Investigations leading to such a methodology are discussed. A service failure analysis of actual aircraft parts is considered along with the stress-corrosion susceptibility of cold-working interference fit bushings. The optimum design of the amount of interference is considered, giving attention to stress formulas and aspects of design methodology.

Hanagud, S.; Carter, A. E.

1976-01-01

311

A review of the Workshop on Fatigue Life Methodologies for Wind Turbines  

NASA Astrophysics Data System (ADS)

From March 31 - April 1, 1993, Sandia National Laboratories (SNL) and the National Renewable Energy Laboratory (NREL) hosted a workshop entitled 'Fatigue Life Methodologies.' The purpose of this workshop was to bring together a representative panel of experts to discuss the prediction and measurement of infrequent events that contribute significantly to the damage of wind turbine components. The diverse backgrounds of the participants yielded discussions that covered a wide range of research and design activities from many varying viewpoints. Consensus was not reached on most of the questions raised at the workshop; however, the workshop laid the foundation for a program that now knows what questions must be answered.

Sutherland, H. J.; Butterfield, C. P.

312

Creep fatigue life prediction for engine hot section materials (isotropic): Fourth year progress review  

NASA Technical Reports Server (NTRS)

As gas turbine technology continues to advance, the need for advanced life prediction methods for hot section components is becoming more and more evident. The complex local strain and temperature histories at critical locations must be accurately interpreted to account for the effects of various damage mechanisms (such as fatigue, creep, and oxidation) and their possible interactions. As part of the overall NASA HOST effort, this program is designed to investigate these fundamental damage processes, identify modeling strategies, and develop practical models which can be used to guide the early design and development of new engines and to increase the durability of existing engines.

Nelson, Richard S.; Schoendorf, John F.

1986-01-01

313

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

314

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

NASA Technical Reports Server (NTRS)

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

Wirsching, P. H.

1981-01-01

315

Prediction of fatigue life of high-heat-load componentsmade of oxygen-free copper by comparing with Glidcop.  

PubMed

Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep-fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep-fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment. PMID:23254657

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

2013-01-01

316

Prediction of fatigue life of high-heat-load componentsmade of oxygen-free copper by comparing with Glidcop  

PubMed Central

Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creepfatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creepfatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment. PMID:23254657

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

2013-01-01

317

Oxidation and the Effects of High Temperature Exposures on Notched Fatigue Life of an Advanced Powder Metallurgy Disk Superalloy  

NASA Technical Reports Server (NTRS)

Oxidation and the effects of high temperature exposures on notched fatigue life were considered for a powder metallurgy processed supersolvus heat-treated ME3 disk superalloy. The isothermal static oxidation response at 704 C, 760 C, and 815 C was consistent with other chromia forming nickel-based superalloys: a TiO2-Cr2O3 external oxide formed with a branched Al2O3 internal subscale that extended into a recrystallized - dissolution layer. These surface changes can potentially impact disk durability, making layer growth rates important. Growth of the external scales and dissolution layers followed a cubic rate law, while Al2O3 subscales followed a parabolic rate law. Cr- rich M23C6 carbides at the grain boundaries dissolved to help sustain Cr2O3 growth to depths about 12 times thicker than the scale. The effect of prior exposures was examined through notched low cycle fatigue tests performed to failure in air at 704 C. Prior exposures led to pronounced debits of up to 99 % in fatigue life, where fatigue life decreased inversely with exposure time. Exposures that produced roughly equivalent 1 m thick external scales at the various isotherms showed statistically equivalent fatigue lives, establishing that surface damage drives fatigue debit, not exposure temperature. Fractographic evaluation indicated the failure mode for the pre-exposed specimens involved surface crack initiations that shifted with exposure from predominately single intergranular initiations with transgranular propagation to multi-initiations from the cracked external oxide with intergranular propagation. Weakened grain boundaries at the surface resulting from the M23C6 carbide dissolution are partially responsible for the intergranular cracking. Removing the scale and subscale while leaving a layer where M23C6 carbides were dissolved did not lead to a significant fatigue life improvement, however, also removing the M23C6 carbide dissolution layer led to nearly full recovery of life, with a transgranular initiation typical to that observed in unexposed specimens.

Sudbrack, Chantal K.; Draper, Susan L.; Gorman, Timothy T.; Telesman, Jack; Gab, Timothy P.; Hull, David R.

2012-01-01

318

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

319

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

E-print Network

of prehistoric sickle blades. 2. Sickle blades and archaeological context in Southwest Asia Recent evidence from the Southern Levant in Southwest Asia (Fig. 1) links several inventions associated with cereal cultivation. These inventions are likely im

Kohler, Tim A.

320

Application of fracture mechanics and half-cycle method to the prediction of fatigue life of B-52 aircraft pylon components  

NASA Technical Reports Server (NTRS)

Stress intensity levels at various parts of the NASA B-52 carrier aircraft pylon were examined for the case when the pylon store was the space shuttle solid rocket booster drop test vehicle. Eight critical stress points were selected for the pylon fatigue analysis. Using fracture mechanics and the half-cycle theory (directly or indirectly) for the calculations of fatigue-crack growth ,the remaining fatigue life (number of flights left) was estimated for each critical part. It was found that the two rear hooks had relatively short fatigue life and that the front hook had the shortest fatigue life of all the parts analyzed. The rest of the pylon parts were found to be noncritical because of their extremely long fatigue life associated with the low operational stress levels.

Ko, W. L.; Carter, A. L.; Totton, W. W.; Ficke, J. M.

1989-01-01

321

Effect of the dimensions of the alpha- and beta-phases on the fatigue life of titanium alloys  

Microsoft Academic Search

1.The cyclic life of (a+)-titanium alloys depends on the size of the -transformed phase. The maximum fatigue life has the VT6 alloy whose structure contains the smallest -transformed phase.2.The volume percentage of the initial a-phase and -transformed phase as well as the dimensions of the a-phase have no effect on the cyclic life of (a+)-titanium alloys.

T. V. Bazaikina; O. V. Ivanova; L. P. Laricheva; A. N. Romanov; Yu. K. Shtovba

1990-01-01

322

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

SciTech Connect

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. [CAS Key Laboratory Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2010-05-21

323

Investigation of Bearing Fatigue Damage Life Prediction Using Oil Debris Monitoring  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

324

An equivalent strain/Coffin-Manson approach to multiaxial fatigue and life prediction in superelastic Nitinol medical devices.  

PubMed

Medical devices, particularly endovascular stents, manufactured from superelastic Nitinol, a near-equiatomic alloy of Ni and Ti, are subjected to complex mixed-mode loading conditions in vivo, including axial tension and compression, radial compression, pulsatile, bending and torsion. Fatigue lifetime prediction methodologies for Nitinol, however, are invariably based on uniaxial loading and thus fall short of accurately predicting the safe lifetime of stents under the complex multiaxial loading conditions experienced physiologically. While there is a considerable body of research documented on the cyclic fatigue of Nitinol in uniaxial tension or bending, there remains an almost total lack of comprehensive fatigue lifetime data for other loading conditions, such as torsion and tension/torsion. In this work, thin-walled Nitinol tubes were cycled in torsion at various mean and alternating strains to investigate the fatigue life behavior of Nitinol and results compared to equivalent fatigue data collected under uniaxial tensile/bending loads. Using these strain-life results for various loading modes and an equivalent referential (Lagrangian) strain approach, a strategy for normalizing these data is presented. Based on this strategy, a fatigue lifetime prediction model for the multiaxial loading of Nitinol is presented utilizing a modified Coffin-Manson approach where the number of cycles to failure is related to the equivalent alternating transformation strain. PMID:21531019

Runciman, Amanda; Xu, David; Pelton, Alan R; Ritchie, Robert O

2011-08-01

325

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

SciTech Connect

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, M.A.; Saltsman, J.F.

1993-10-01

326

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

327

A method for predicting the fatigue life of pre-corroded 2024-T3 aluminum from breaking load tests  

NASA Astrophysics Data System (ADS)

Characterization of material properties is necessary for design purposes and has been a topic of research for many years. Over the last several decades, much progress has been made in identifying metrics to describe fracture mechanics properties and developing procedures to measure the appropriate values. However, in the context of design, there has not been as much success in quantifying the susceptibility of a material to corrosion damage and its subsequent impact on material behavior in the framework of fracture mechanics. A natural next step in understanding the effects of corrosion damage was to develop a link between standard material test procedures and fatigue life in the presence of corrosion. Simply stated, the goal of this investigation was to formulate a cheaper and quicker method for assessing the consequences of corrosion on remaining fatigue life. For this study, breaking load specimens and fatigue specimens of a single nominal gage (0.063?) of aluminum alloy 2024-T3 were exposed to three levels of corrosion. The breaking load specimens were taken from three different material lots, and the fatigue tests were carried out at three stress levels. All failed specimens, both breaking load and fatigue specimens, were examined to characterize the damage state(s) and failure mechanism(s). Correlations between breaking load results and fatigue life results in the presence of corrosion damage were developed using a fracture mechanics foundation and the observed mechanisms of failure. Where breaking load tests showed a decrease in strength due to increased corrosion exposure, the corresponding set of fatigue tests showed a decrease in life. And where breaking load tests from different specimen orientations exhibited similar levels of strength, the corresponding set of fatigue specimens showed similar lives. The spread from shortest to longest fatigue lives among the different corrosion conditions decreased at the higher stress levels. Life predictions based on breaking load data were generally shorter than the experimental lives by an average of 20%. The life prediction methodology developed from this investigation is a very valuable tool for the purpose of assessing material substitution for aircraft designers, alloy differentiation for manufacturers, or inspection intervals and aircraft retirement schedules for aircraft in service.

Gruenberg, Karl Martin

328

Low strain, long life creep fatigue of AF2-1DA and INCO 718  

NASA Technical Reports Server (NTRS)

Two aircraft turbine disk alloys, GATORIZED AF2-DA and INCO 718 were evaluated for their low strain long life creep-fatigue behavior. Static (tensile and creep rupture) and cyclic properties of both alloys were characterized. The cntrolled strain LCF tests were conducted at 760 C (1400 F) and 649 C (1200 F) for AF2-1DA and INCO 718, respectively. Hold times were varied for tensile, compressive and tensile/compressive strain dwell (relaxation) tests. Stress (creep) hold behavior of AF2-1DA was also evaluated. Generally, INCO 718 exhibited more pronounced reduction in cyclic life due to hold than AF2-1DA. The percent reduction in life for both alloys for strain dwell tests was greater at low strain ranges (longer life regime). Changing hold time from 0 to 0.5, 2.0 and 15.0 min. resulted in corresponding reductions in life. The continuous cycle and cyclic/dwell initiation failure mechanism was predominantly transgranular for AF2-1DA and intergranular for INCO 718.

Thakker, A. B.; Cowles, B. A.

1983-01-01

329

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, Jrgen; Cikalova, Ulana; Hillmann, Susanne; Meyendorf, Norbert; Hoffmann, Jochen

2013-01-01

330

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

331

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

332

Analysis of aeroelastic loads and their contributions to fatigue damage  

NASA Astrophysics Data System (ADS)

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

Bergami, L.; Gaunaa, M.

2014-12-01

333

Creep-Fatigue Life Prediction and Reliability Analysis of P91 Steel Based on Applied Mechanical Work Density  

NASA Astrophysics Data System (ADS)

A creep-fatigue (CF) life prediction model and its simplified expression were developed based on the applied mechanical work density (AMWD). The foundation of this model was an integration of N- S curve. Comparisons of the model predicted fatigue lifetimes with the experimental data of load-controlled CF tests on P91 base metal and welded metal at 848 K from the reference were made and apparently illustrated that the model predictions were in a good agreement with the experimental fatigue lifetimes. In addition, the curve of the numbers of cycles to failure versus AMWD at the associated probability was deduced. A reliability model was constructed by combining the curve and the simplified life prediction model.

Ji, D. M.; Shen, M.-H. H.; Wang, D. X.; Ren, J. X.

2015-01-01

334

The Effect of Weld Profile and Geometries of Butt Weld Joints on Fatigue Life Under Cyclic Tensile Loading  

NASA Astrophysics Data System (ADS)

The fatigue life of welded joint was calculated based on numerical integration of simple Paris' law and a reliable solution of the stress intensity factor (SIF). The initial crack length ( a i) was assumed to be equal to 0.1 mm in case of weld toe. This length was satisfactory for different butt joints geometries. The comparisons with the available data from standards and literature were demonstrated. It was shown numerically that the machining of weld reinforcements will increase the fatigue life. The increase of plate thickness decreases the fatigue strength (FAT) and the number of cycles to failure when using the proportional scaling of crack length. The validation processes of the current calculations have been shown. Therefore, it can be concluded that it will prevent the unnecessary waste of time consumed to carry out the experiments.

Al-Mukhtar, A. M.; Biermann, H.; Hbner, P.; Henkel, S.

2011-11-01

335

Simulated Bladed MMC Disk LCF Validation  

NASA Technical Reports Server (NTRS)

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

Merrick, H. F.; Costen, M.

1998-01-01

336

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

337

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

338

Fatigue life calculation of desuperheater for solving pipe cracking issue using finite element method (FEM) software  

NASA Astrophysics Data System (ADS)

Desuperheater assembly experiences thermal cycling in operation by design. During power plant's start up, load change and shut down, thermal gradient is highest. Desuperheater should be able to handle rapid ramp up or ramp down of temperature in these operations. With "hump style" two nozzle desuperheater, cracks were appearing in the pipe after only few cycles of operation. From the field data, it was clear that desuperheater is not able to handle disproportionate thermal expansion happening in the assembly during temperature ramp up and ramp down in operation and leading to cracks appearing in the piping. Growth of thermal fatigue crack is influenced by several factors including geometry, severity of thermal stress and applied mechanical load. This paper seeks to determine cause of failure of two nozzle "hump style" desuperheater using Finite Element Method (FEM) simulation technique. Thermal stress simulation and fatigue life calculation were performed using commercial FEA software "ANSYS" [from Ansys Inc, USA]. Simulation result showed that very high thermal stress is developing in the region where cracks are seen in the field. From simulation results, it is also clear that variable thermal expansion of two nozzle studs is creating high stress at the water manifold junction. A simple and viable solution is suggested by increasing the length of the manifold which solved the cracking issues in the pipe.

Kumar, Aravinda; Singh, Jeetendra Kumar; Mohan, K.

2012-06-01

339

Crack-growth analysis code for assessing fatigue life of 2219 T851 aluminium specimens under aircraft structure service spectra  

Microsoft Academic Search

A new crack growth analysis code for assessing crack growth curve and fatigue life of specimens subjected to aircraft structure service spectra is proposed. It makes use of the strip plastic zone approximation to include material hardening effect by means of yield stress variations along the path of prospective crack growth. Calculation of degree of plastification has been made manageable

Sp. G. Pantelakis; Al. Th. Kermanidis; P. G. Daglaras

1997-01-01

340

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

341

STRESS ANALYSIS OF HEAVY DUTY TRUCK CHASSIS AS A PRELIMINARY DATA FOR ITS FATIGUE LIFE PREDICTION USING FEM  

Microsoft Academic Search

This paper presents the stress analysis of heavy duty truck chassis. The stress analysis is important in fatigue study and life prediction of components to determine the critical point which has the highest stress. The analysis was done for a truck model by utilizing a commercial finite element packaged ABAQUS. The model has a length of 12.35 m and width

Roslan Abd Rahman; Mohd Nasir Tamin; Ojo Kurdi

2008-01-01

342

Influences of post weld heat treatment on fatigue life prediction of strength mis-matched HSLA steel welds  

Microsoft Academic Search

Welding of High Strength Low Alloy Steels (HSLA) involve usage of low, even and high strength filler materials (electrodes) than the parent material depending on the application of the welded structures and the availability of the filler materials. In the present investigation, the influences of post weld heat treatment (PWHT) on fatigue life prediction of under matched (UM), even matched

S. Ravi; V. Balasubramanian; S. Nemat Nasser

2005-01-01

343

IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 25, NO. 3, AUGUST 2002 433 Impact of Temperature Cycle Profile on Fatigue Life  

E-print Network

Cycle Profile on Fatigue Life of Solder Joints Terry Dishongh, Cemal Basaran, Alexander N. Cartwright joints under thermal cycling has been studied extensively, Basaran et al. [1], [2] presents an extensive is with Intel Corporation, Hillsboro, OR 97124-6497 USA. C. Basaran, A. N. Cartwright, and H. Liu

Cartwright, Alexander N.

344

Influence of Interfacial Bond Strength on Fatigue Life and ThermoMechanical Behavior of a Particulate Composite: An Experimental Study  

Microsoft Academic Search

Experimental studies conducted on a particular cast acrylic composite demonstrate the significant influence of the interfacial bond strength between filler particles and the polymer matrix on the fatigue life, and mechanical properties. The composite studied in this project is composed of a ductile matrix, which is lightly cross-linked poly-methyl methacrylate (PMMA) and hard, brittle alumina trihydrate (ATH) agglomerate particle filler.

C. Basaran; S. Nie; C. S. Hutchins; H. Ergun

2008-01-01

345

Successful Solutions to SSME/AT Development Turbine Blade Distress  

NASA Technical Reports Server (NTRS)

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

Montgomery, Stuart K.

1999-01-01

346

Effect of sulfur on rolling contact fatigue life of high-manganese precipitation-hardening austenitic steel  

SciTech Connect

For mechanical components used in high magnetic flux such as bearings and shafts that undergo cyclic stress, materials require low permeability with high strength, hardness, appropriate machinability, and good fatigue properties. Although it is implied that low permeability and machinability will be achieved by a selection of sulfurized austenitic ({gamma}) steel grades, effect of manganese sulfide (MnS) on fatigue properties of such grades especially for bearing applications is not clarified. For high-carbon chromium bearing steels, the effect of MnS on rolling contact fatigue life of the steels containing sulfur less than 0.03% are discussed. In these studies, the effect of MnS is not clearly determined whether it is beneficial or harmful to contact fatigue lives of the steels. However, effect of MnS under higher sulfur content, i.e., 0.10%, on the fatigue properties of {gamma} steel has not been studied. In this paper, the effect of sulfur on rolling contact fatigue properties of vanadium added {gamma} steel, 10Cr-6Ni-8Mn-1.6V-0.6C, was investigated focusing on microstructural change in connection with MnS particles.

Haruna, Y. [Sanyo Special Steel Co., Ltd., Himeji (Japan). Technological Research Lab.] [Sanyo Special Steel Co., Ltd., Himeji (Japan). Technological Research Lab.; Yamamoto, A.; Tsubakino, H. [Himeji Inst. of Tech. (Japan)] [Himeji Inst. of Tech. (Japan)

1998-10-05

347

Influence of surface treatments on fatigue life of a two-stroke free piston linear engine component using random loading  

Microsoft Academic Search

This paper describes the finite element (FE) analysis technique to predict fatigue life using the narrow band frequency response\\u000a approach. The life prediction results are useful for improving the component design methodology at the very early development\\u000a stage. The approach is found to be suitable for a periodic loading but requires very large time records to accurately describe\\u000a random loading

M. M. Rahman; A. K. Ariffin; N. Jamaludin; C. H. C. Haron

2006-01-01

348

User`s guide for the frequency domain algorithms in the LIFE2 fatigue analysis code  

SciTech Connect

The LIFE2 computer code is a fatigue/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. However, many structural analysis techniques yield frequency-domain stress spectra and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the analysis of this class of data, a Fourier analysis is used to transform a frequency-domain spectrum to an equivalent time series suitable for rainflow counting by other modules in the code. This paper describes the algorithms incorporated into the code and their numerical implementation. Example problems are used to illustrate typical inputs and outputs.

Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States); Linker, R.L. [New Mexico Engineering Research Inst., Albuquerque, NM (United States)

1993-10-01

349

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

350

Fatigue life of anti-friction bearings subjected to cyclic loading  

SciTech Connect

Cyclic loading is defined as external loading that varies within the revolution of a bearing and is repeated for every revolution. The cyclicly varying loads may consist of a series of discrete loads that occur in a repeating pattern or a continuously varying force or a combination of these. A simple example of cyclic loading is a single cylinder, double acting piston pump in which the force on the bearings reverse every 180/sup 0/ of a revolution; as a result, the same half of the rotating bearing race passes under the load twice in a single revolution. More complex patterns of cyclic loads occur in rotary engines, fuel injection pumps, nutating engines, etc. The paper presents the theoretical relationships and methods that predict the effect of cyclic loading on the fatigue life of anti-friction bearings. An example problem solved with the aid of a special analysis program illustrates the results from these methods.

Dominik, W.K.

1986-01-01

351

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

352

Fatigue modeling for small wind systems: basic theory  

SciTech Connect

This report discusses the theory of fatigue as applied to horizontal-axis wind systems and reviews current techniques for predicting fatigue loads and fatigue life. Wind systems are subjected to a complex and diverse variety of loads, ranging from simple gravity and centrifugal loads to complex and random wind loads. The categories of loads described here include transient, periodic, and control-induced loads, as well as loads induced by severe aeroelastic instabilities. Within these categories, load types include centrifugal, aerodynamic thrust and torque, parked rotor survival loads, gravity loads, gyroscopic loads, and aerodynamic loads induced by crossflow or yaw motion. Control systems can impose loads whenever they are activated. Catastrophic failure can result from severe aeroelastically-induced loads caused by flutter. Techniques available for predicting fatigue loads include various aerodynamic performance codes (such as PROP) and simplified methods for calculating the convection of the vortex wake. MOSTAB, an aeroelasticity computer code, treats all major load sources. Results using this code are shown to be fairly comparable to experimental data in the case of a rigid-bladed wind system. Fatigue life of a machine component can be predicted during design by several techniques, including the strength-of-materials method, the fatigue curve method, and the fatigue event method. The theories of Miner, Manson, and Corten-Dolan can be used to predict fatigue life based on test data and operational experience. A fatigue research project to be performed at Rocky Flats will attempt to resolve whether any of these theories or a combination of theories can be used with an acceptable degree of accuracy in predicting fatigue loads and life for wind systems. An appendix to the report provides sample calculations of fatigue load magnitudes made using available methods.

Waldon, C.A.; Hansen, A.C.

1983-06-01

353

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

354

Improvement of Fatigue Life of a Holed Specimen of Aluminum-Alloy 2024-T3 by Indentation and Hole Expansion  

NASA Astrophysics Data System (ADS)

A method of improving the fatigue life and crack growth behavior of a center holed specimen was investigated. Local plastic deformation was applied around the hole by indentation to achieve the purpose. A series of fatigue tests was conducted on aluminum-alloy 2024-T3. Push-pull tests were performed under a stress ratio of R= -1 and a frequency of 10Hz. The observations of the crack initiation and growth were performed with a microscope, and hardness around the hole was measured by Vickers hardness testing machine. In the present study, the longest fatigue life was observed in the case of an indentation specimen with the highest load. The indentation was performed on both sides of the hole edges. The crack growth rate was decreased by indentation or expansion of the material around the hole. From the experimental results, it is found that the fatigue life and crack growth behavior of a holed or notched specimen can be improved by a simple technical method that is related to the local plastic working.

Shafiul Ferdous, Md.; Makabe, Chobin; Miyazaki, Tatsujiro; Hattori, Nobusuke

355

Combining Turbine Blade-Strike and Life Cycle Models to Assess Mitigation Strategies for Fish Passing Dams  

SciTech Connect

Combining the two models produced a rapid, cost effective tool for assessing dam passage impacts to fish populations and prioritizing among mitigation strategies for conserving fish stocks in regulated rivers. Estimated mortality of juvenile and adult Atlantic salmon (Salmo salar) and sea trout (S. trutta) passing turbines at two dams in northern Sweden was significantly higher for Kaplan turbines compared to Francis turbines, and for adult fish compared to juveniles based on blade strike models. Mean probability of mortality ranged from 6.7% for salmon smolts passing Francis turbines to >100% for adult salmon passing Kaplan turbines. Life cycle modeling allowed benefits to be assessed for three alternatives that mitigated this mortality. Salmon population responses varied considerably among alternatives and rivers: growth rates improved as much as 17.9%, female escapements increased up to 669%, and more than 1,300 additional female salmon were produced in one case. Protecting both smolts and adults provided benefits, and in one river, mitigating turbine mortality alone was estimated to have met the production capacity of the available habitat.

Ferguson, John W.; Ploskey, Gene R.; Leonardsson, Kjell; Zabel, Richard W.; Lundqvist, Hans

2008-08-01

356

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

357

Review of time-dependent fatigue behavior and life prediction for 2 1/4 Cr-1 Mo steel. [LMFBR  

SciTech Connect

Available data on creep-fatigue life and fracture behavior of 2 1/4 Cr-1 Mo steel are reviewed. Whereas creep-fatigue interaction is important for Type 304 stainless steel, oxidation effects appear to dominate the time-dependent fatigue behavior of 2 1/4 Cr-1 Mo steel. Four of the currently available predictive methods - the Linear Damage Rule, Frequency Separation Equation, Strain Range Partitioning Equation, and Damage Rate Equation - are evaluated for their predictive capability. Variations in the parameters for the various predictive methods with temperature, heat of material, heat treatment, and environment are investigated. Relative trends in the lives predicted by the various methods as functions of test duration, waveshape, etc., are discussed. The predictive methods will need modification in order to account for oxidation and aging effects in the 2 1/4 Cr-1 Mo steel. Future tests that will emphasize the difference between the various predictive methods are proposed.

Booker, M.K.; Majumdar, S.

1982-01-01

358

Axial-thrust responses due to a gas turbine's rotor blade distortions  

NASA Astrophysics Data System (ADS)

The axial thrust imposed on the shaft of a gas turbine depends upon its rotor blade inlet inclination to the turbine's axial direction: this inclination can change due to the distortions resulting from fouling, aging, tip rubbing, erosion, thermal-fatigue cracks, and corrosion. Relevant influential parameters for an operational gas turbine were measured. Theoretical predictions for the behavior of the same turbine were obtained from computer simulations. The results of both measurements and theoretical predictions were compared and showed qualitative correspondence. The rotor blade profile distortions result in significant increases in the axial thrust on the compressor, which adversely affects the gas turbine's thermodynamic performance, reliability, and operational life.

Lebele-Alawa, B. T.

2010-11-01

359

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

360

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

361

NASALife-Component Fatigue and Creep Life Prediction Program and Illustrative Examples  

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 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. Lastly, damage due to cyclic loading (Miner s rule) and creep are combined to determine the total damage per mission and the number of missions the component can survive before failure are calculated. Illustration of code usage is provided through example problem of a CMC turbine stator vane made of melt-infiltrated, silicon carbide fiber-reinforced, silicon carbide matrix composite (MI SiC/SiC)

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

2005-01-01

362

The role of competing mechanisms in the fatigue-life variability of a titanium and gamma-TiAl alloy  

NASA Astrophysics Data System (ADS)

The variability in fatigue lives of an ?+? titanium alloy (Ti-6Al-2Sn-4Zr-6Mo) and a ?-TiAl-based alloy in stress vs. life space resulted from superposition of variability associated with two separate mechanisms. The mean lives of the two mechanisms diverged with decreasing stress level, giving rise to the variability. A life-prediction methodology based on the variability in the worst-case mechanism is suggested. The potential for reducing uncertainty and increasing the utilization of the useful life as compared to more traditional approaches is discussed.

Jha, S. K.; Larsen, J. M.; Rosenberger, A. H.

2005-09-01

363

Fracture mechanics characterization of welds: Fatigue life analysis of notches at welds: J(sub Ic) fracture toughness tests for weld metal  

Microsoft Academic Search

In this report two methods of fracture analysis of welds will be emphasized, one addressing fatigue life testing and analysis of notches at welds, and the other addressing the final fracture of the welded component and the fracture toughness tests used to characterize final fracture. These fatigue and fracture methods will be described by referring to recent work from the

John H. Underwood

1995-01-01

364

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

365

Biaxial Fatigue Life Predicted by Crack Growth Analysis in Various Material Microstructures Modeled by Voronoi-Polygons  

NASA Astrophysics Data System (ADS)

Fatigue life is affected by the crack growth behavior that depends on the material microstructure as well as the stress biaxiality. By considering such effects on crack growth, a numerical procedure for predicting failure life in biaxial fatigue of materials with different microstructures was proposed in this study. Such a procedure will be helpful in the material design for higher performance of fatigue resistance in a material. The microstructure of a material was first modeled using Voronoi-polygons, and the crack initiation was analyzed as the result of slip-band formation in individual grains in the modeled microstructure. In the analysis, stress states in individual grains were randomized so that the average stress state should be equivalent to the bulk stress state. An algorithm for the crack growth analysis was established as a competition between the crack-coalescence growth and the propagation as a single crack. The failure life was statistically predicted based on the crack growth behavior simulated for 40 distinct microstructural configurations, which were generated by randomizing shapes of Voronoi-polygons for the same material. By applying the proposed procedure, simulations were conducted for experimental conditions of fatigue tests, which had been conducted under axial, torsional, and combined loading modes using circumferentially notched specimens of pure copper, medium carbon steel, and (? + ?) and ? titanium alloys. In this case, 40 different failure-lives were obtained for each combination of material and loading mode. It was revealed that the failure lives observed in experiments were almost covered by the life-ranges between the minimum and the maximum lives given in simulation. Statistical characteristics in simulated life-distributions were investigated using Weibull distribution function and its related statistical parameters.

Hoshide, Toshihiko

2011-12-01

366

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

367

Strainrange partitioning - A total strain range version. [for creep fatigue life prediction by summing inelastic and elastic strain-range-life relations for two Ni base superalloys  

NASA Technical Reports Server (NTRS)

Procedures are presented for expressing the Strainrange Partitioning (SRP) method for creep fatigue life prediction in terms of total strain range. Inelastic and elastic strain-range - life relations are summed to give total strain-range - life relations. The life components due to inelastic strains are dealt with using conventional SRP procedures while the life components due to elastic strains are expressed as families of time-dependent terms for each type of SRP cycle. Cyclic constitutive material behavior plays an important role in establishing the elastic strain-range life relations as well as the partitioning of the inelastic strains. To apply the approach, however, it is not necessary to have to determine the magnitude of the inelastic strain range. The total strain SRP approach is evaluated and verified using two nickel base superalloys, AF2-1DA and Rene 95. Excellent agreement is demonstrated between observed and predicted cyclic lifetimes with 70 to 80 percent of the predicted lives falling within factors of two of the observed lives. The total strain-range SRP approach should be of considerable practical value to designers who are faced with creep-fatigue problems for which the inelastic strains cannot be calculated with sufficient accuracy to make reliable life predictions by the conventional inelastic strain range SRP approach.

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

1983-01-01

368

Deformation, Failure, and Fatigue Life of SiC/Ti-15-3 Laminates Accurately Predicted by MAC/GMC  

NASA Technical Reports Server (NTRS)

NASA Glenn Research Center's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) (ref.1) has been extended to enable fully coupled macro-micro deformation, failure, and fatigue life predictions for advanced metal matrix, ceramic matrix, and polymer matrix composites. Because of the multiaxial nature of the code's underlying micromechanics model, GMC--which allows the incorporation of complex local inelastic constitutive models--MAC/GMC finds its most important application in metal matrix composites, like the SiC/Ti-15-3 composite examined here. Furthermore, since GMC predicts the microscale fields within each constituent of the composite material, submodels for local effects such as fiber breakage, interfacial debonding, and matrix fatigue damage can and have been built into MAC/GMC. The present application of MAC/GMC highlights the combination of these features, which has enabled the accurate modeling of the deformation, failure, and life of titanium matrix composites.

Bednarcyk, Brett A.; Arnold, Steven M.

2002-01-01

369

Improvement of the fatigue life of titanium alloys for biomedical devices through microstructural control.  

PubMed

A limited number of reports exist regarding the systematic investigation or comparison of the fatigue strength of titanium alloys for medical devices, including plain, fretting and notch fatigue, for improvement through various treatments and processes, with respect to related microstructures. This article focuses on the changes and improvements in fatigue strength of newly developed beta-type and practically used alpha + beta-titanium alloys for medical devices through heat treatments, thermomechanical treatments and surface modifications. PMID:20583885

Niinomi, Mitsuo; Akahori, Toshikazu

2010-07-01

370

A state-of-the-art review on fatigue life prediction methods for metal structures  

Microsoft Academic Search

Metals are the most widely used materials in engineering structures, and one of the most common failure modes of metal structures\\u000a is fatigue failure. Although metal fatigue has been studied for more than 160 years, many problems still remain unsolved.\\u000a In this article, a state-of-the-art review of metal fatigue is carried out, with particular emphasis on the latest developments\\u000a in

Weicheng Cui

2002-01-01

371

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

372

Demonstrating the Effect of Particle Impact Dampers on the Random Vibration Response and Fatigue Life of Printed Wiring Assemblies  

NASA Technical Reports Server (NTRS)

In a recent experimental study, small Particle Impact Dampers (PID) were bonded directly to the surface of printed circuit board (PCB) or printed wiring assemblies (PWA), reducing the random vibration response and increasing the fatigue life. This study provides data verifying practicality of this approach. The measured peak strain and acceleration response of the fundamental out of plane bending mode was significantly attenuated by adding a PID device. Attenuation of this mode is most relevant to the fatigue life of a PWA because the local relative displacements between the board and the supported components, which ultimately cause fatigue failures of the electrical leads of the board-mounted components are dominated by this mode. Applying PID damping at the board-level of assembly provides mitigation with a very small mass impact, especially as compared to isolation at an avionics box or shelf level of assembly. When compared with other mitigation techniques at the PWA level (board thickness, stiffeners, constrained layer damping), a compact PID device has the additional advantage of not needing to be an integral part of the design. A PID can simply be bonded to heritage or commercial off the shelf (COTS) hardware to facilitate its use in environments beyond which it was originally qualified. Finite element analysis and test results show that the beneficial effect is not localized and that the attenuation is not due to the simple addition of mass. No significant, detrimental reduction in frequency was observed. Side-by-side life testing of damped and un-damped boards at two different thicknesses (0.070" and 0.090") has shown that the addition of a PID was much more significant to the fatigue life than increasing the thickness. High speed video, accelerometer, and strain measurements have been collected to correlate with analytical results.

Knight, Brent; Montgomery, Randall; Geist, David; Hunt, Ron; LaVerde, Bruce; Towner, Robert

2013-01-01

373

The Effect of Weld Profile and Geometries of Butt Weld Joints on Fatigue Life Under Cyclic Tensile Loading  

Microsoft Academic Search

The fatigue life of welded joint was calculated based on numerical integration of simple Paris law and a reliable solution\\u000a of the stress intensity factor (SIF). The initial crack length (a\\u000a i) was assumed to be equal to 0.1mm in case of weld toe. This length was satisfactory for different butt joints geometries.\\u000a The comparisons with the available data from

A. M. Al-Mukhtar; H. Biermann; P. Hbner; S. Henkel

374

Prediction of fatigue life and estimation of its reliability on the parts of an air suspension system  

Microsoft Academic Search

Air suspension systems have been implemented in various commercial vehicles, such as buses and special purpose trucks, because\\u000a of the comfortable ride and easy height control. An evaluation of the durability of vehicle parts has been required for service\\u000a life and safety starting in the early stages of design. The cyclic load applied to the vehicle can cause fatigue failure

K. J. Jun; T. W. Park; S. H. Lee; S. P. Jung; J. W. Yoon

2008-01-01

375

Health-related quality of life, fatigue, and depression under low-dose IFN-? therapy in melanoma patients.  

PubMed

Adjuvant melanoma treatment with interferon-? (IFN-?) has proven to be accompanied by several side effects and to decrease patients' health-related quality of life (HRQOL), fatigue and depression being essential factors at that. Although a large body of evidence exists for HRQOL under IFN-? therapy, we now specifically address this topic combining the HRQOL survey in the first months of IFN-? low-dose treatment with a structured assessment of relevant neuropsychiatric side effects, fatigue and depression, with specific validated assessment tools. The present study is a longitudinal observational study assessing fatigue, depression, and HRQOL with specific assessment tools at 3 assessment points over 6 months. The IFN-? treatment group consisted of 48 patients with current IFN-? therapy (3 MU 3 times weekly) from a consecutively recruited melanoma collective and compared with a parallelized nontreatment group (n=48) in routine clinical practice. A descriptive analysis and generalized linear models were applied to compare the groups. Physical fatigue increased significantly within the first months of IFN-? treatment, whereas cognitive and emotional fatigue and depression symptoms did not show this increase. The hypothesis of a significant deterioration of HRQOL after IFN-? initiation was not confirmed. The treatment group did, however, show a different course of global HRQOL than the comparison group, with a significant improvement in the nontreatment group. Patients under low-dose IFN-? therapy primarily suffer from physical side effects, mainly physical fatigue, in the early phases of treatment. The HRQOL improvement evident in the nontreatment group was not observed in the IFN-? group. PMID:25304729

Reuter, Katrin; Albrecht, Karoline; Seelig, Harald; Meiss, Frank; Mauch, Cornelia; Kreuzberg, Nicole; Nashan, Dorothe

2014-01-01

376

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

377

Fatigue handbook: Offshore steel structures  

SciTech Connect

The contents of this book are: Overview of Offshore Steel Structures; Loads on Ocean Structures; Fracture Mechanics As a Tool in Fatigue Analysis; Basic Fatigue Properties of Welded Joints; Significance of Defects; Improving the Fatigue Strength of Welded Joints; Effects of Marine Environment and Cathodic Protection on Fatigue of Structural Steels Fatigue of Tubular Joints; Unstable Fracture; Fatigue Life Calculations; and Fatigue in Building Codes Background and Applications.

Almarnaess, A.

1985-01-01

378

Fatigue life simulation of a rear tow hook assembly of a passenger car  

Microsoft Academic Search

A comparison between laboratory test data on fatigue crack nucleation in a rear tow hook pin assembly of passenger vehicle and a computational methodology using commercial package software is presented. Fatigue damage is determined using local material response, measured during experimental tests. Experiments were performed simulating the actual conditions in the customer environment. Stress and strain were experimentally measured by

C. L. Petracconi; S. E. Ferreira; E. S. Palma

2010-01-01

379

Fatigue Life Prediction Criterion for MicroNanoscale Single-Crystal Silicon Structures  

Microsoft Academic Search

This paper describes fatigue damage evaluation for micro-nanoscale single-crystal silicon (SCS) structures toward the reliable design of microelectromechanical systems subjected to fluctuating stresses. The fatigue tests, by using atomic force microscope (AFM), nanoindentation tester, and specially developed uniaxial tensile tester, have been conducted under tensile and bending deformation modes for investigating the effects of specimen size, frequency, temperature, and deformation

Takahiro Namazu; Yoshitada Isono

2009-01-01

380

Temporal scaling in fatigue life of materials and incorporation of temporal events in Paris's law  

NASA Astrophysics Data System (ADS)

Temporal scaling in mechanical strength of materials is vital for long-term effects such as fatigue. The fatigue crack length ? is related to the change in the stress intensity factor ?K by the omnipresent Paris's law, which works well for cyclic fatigue of specific frequency and amplitude. The paper considers time scaling in fatigue and through it incorporates the effects of temporal events such as unexpected or accidental loads, impact loads, and rare events such as earthquake loads. This is achieved by theoretically incorporating the effects of delta-function type loads into fatigue. Since the time-scale decomposition of such a load contains information at all scales, the theoretical framework is easily extended to include general types of loads.

Frantziskonis, George N.

2013-04-01

381

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

382

Brief summary of the evolution of high-temperature creep-fatigue life prediction models for crack initiation  

NASA Technical Reports Server (NTRS)

The evolution of high-temperature, creep-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940's. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-temperature fatigue life prediction methods by providing a background from which choices can be made. The need for high-temperature, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-temperature, high-pressure boilers and steam turbines, nuclear reactors, high-temperature forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the 'build-em and bust-em' approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed. These include thermal-structural finite element and boundary element analyses, advanced constitutive stress-strain-temperature-time relations, and creep-fatigue-environmental models for crack initiation and propagation. The high-temperature durability methods that have evolved for calculating high-temperature fatigue crack initiation lives of structural engineering materials are addressed. Only a few of the methods were refined to the point of being directly useable in design. Recently, two of the methods were transcribed into computer software for use with personal computers.

Halford, Gary R.

1993-01-01

383

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

384

Brief summary of the evolution of high-temperature creep-fatigue life prediction models for crack initiation  

SciTech Connect

The evolution of high-temperature, creep-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940`s. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material`s crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-temperature fatigue life prediction methods by providing a background from which choices can be made. The need for high-temperature, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-temperature, high-pressure boilers and steam turbines, nuclear reactors, high-temperature forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the `build-em and bust-em` approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed.

Halford, G.R.

1993-10-01

385

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

386

The Relationships Between Microstructure, Tensile Properties and Fatigue Life in Ti-5Al-5V-5Mo-3Cr-0.4Fe (Ti-5553)  

NASA Astrophysics Data System (ADS)

beta-titanium alloys are being increasingly used in airframes as a way to decrease the weight of the aircraft. As a result of this movement, Ti-5Al-5V-5Mo-3Cr-0.4Fe (Timetal 555), a high-strength beta titanium alloy, is being used on the current generation of landing gear. This alloy features good combinations of strength, ductility, toughness and fatigue life in alpha+beta processed conditions, but little is known about beta-processed conditions. Recent work by the Center for the Accelerated Maturation of Materials (CAMM) research group at The Ohio State University has improved the tensile property knowledge base for beta-processed conditions in this alloy, and this thesis augments the aforementioned development with description of how microstructure affects fatigue life. In this work, beta-processed microstructures have been produced in a Gleeble(TM) thermomechanical simulator and subsequently characterized with a combination of electron and optical microscopy techniques. Four-point bending fatigue tests have been carried out on the material to characterize fatigue life. All the microstructural conditions have been fatigue tested with the maximum test stress equal to 90% of the measured yield strength. The subsequent results from tensile tests, fatigue tests, and microstructural quantification have been analyzed using Bayesian neural networks in an attempt to predict fatigue life using microstructural and tensile inputs. Good correlation has been developed between lifetime predictions and experimental results using microstructure and tensile inputs. Trained Bayesian neural networks have also been used in a predictive fashion to explore functional dependencies between these inputs and fatigue life. In this work, one section discusses the thermal treatments that led to the observed microstructures, and the possible sequence of precipitation that led to these microstructures. The thesis then describes the implications of microstructure on fatigue life and implications of tensile properties on fatigue life. Several additional experiments are then described that highlight possible causes for the observed dependence of microstructure on fatigue life, including fractographic evidence to provide support of microstructural dependencies.

Foltz, John W., IV

387

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

388

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

389

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

390

Rolling Contact Fatigue Life of Steel Rollers Treated by Cavitation Peening and Shot Peening  

NASA Astrophysics Data System (ADS)

The purpose of this study is to investigate the influence of peening on the rolling contact fatigue (RCF) life of steel rollers. First, steel rollers were treated by three types of peenings to ensure the same surface roughness of peened rollers. One is the cavitation peening (CP) used a cavitating jet in water with an injection pressure of 30 MPa, and the others are the fine particle peening (FPP) with a shot diameter of 0.1 mm and the normal shot peening (NSP) with a shot diameter of 0.3 mm. The surface hardness and the surface compressive residual stress of the steel rollers were increased by all the peenings. In particular, they were most increased by the FPP. On the other hand, the work-hardened depth due to the CP and the NSP was larger than that due to the FPP. As a result of the RCF tests, the RCF lives of the steel rollers were improved by all the peenings, and they were most improved by the NSP. Judging from the pmax - N curves and the [A(?y/?3 HV)]max - N curves, the improvement in RCF lives due to the FPP depended heavily on the increase in surface hardness due to that, and the effects of the CP and the NSP on the RCF were equivalent under the same surface roughness and the same surface hardness. It follows from these that the surface treatment condition should be selected according to the rolling contact conditions and the failure modes of machine elements.

Seki, Masanori; Soyama, Hitoshi; Kobayashi, Yuji; Gowa, Daisuke; Fujii, Masahiro

391

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

392

A design-centered approach in developing Al-Si-based light-weight alloys with enhanced fatigue life and strength  

NASA Astrophysics Data System (ADS)

Material heterogeneities and discontinuities such as porosity, second phase particles, and other defects at meso/micro/nano scales, determine fatigue life, strength, and fracture behavior of aluminum castings. In order to achieve better performance of these alloys, a design-centered computer-aided renovative approach is proposed. Here, the term design-centered is used to distinguish the new approach from the traditional trial-and-error design approach by formulating a clear objective, offering a scientific foundation, and developing a computer-aided effective tool for the alloy development. A criterion for tailoring child microstructure, obtained by parent microstructure through statistical correlation, is proposed for the fatigue design at the initial stage. A dislocations pileup model has been developed. This dislocation model, combined with an optimization analysis, provides an analytical-based solution on a small scale for silicon particles and dendrite cells to enhance both fatigue performance and strength for pore-controlled castings. It can also be used to further tailor microstructures. In addition, a conceptual damage sensitivity map for fatigue life design is proposed. In this map there are critical pore sizes, above which fatigue life is controlled by pores; otherwise it is controlled by other mechanisms such as silicon particles and dendrite cells. In the latter case, the proposed criteria and the dislocation model are the foundations of a guideline in the design-centered approach to maximize both the fatigue life and strength of Al-Si-based light-weight alloy.

Fan, Jinghong; Hao, Su

2004-01-01

393

PREDICTION OF LOW-CYCLE FATIGUE-LIFE BY ACOUSTIC EMISSION. PART 1: 2024-T3 ALUMINUM ALLOY PART 2: ALCLAD 7075-T6/ ALUMINUM ALLOY  

SciTech Connect

Low-cycle fatigue tests were conducted by tension-compression until rupture, on a 2024-T3 aluminum alloy sheet. Initial crack sizes and orientations in the fatigue specimens were found to be randomly distributed. Acoustic emission was continuously monitored during the tests. Every few hundred cycles, the acoustic signal having the highest peak-amplitude, was recorded as an extremal event for the elapsed period. This high peak-amplitude is related to a fast crack propagation rate through a phenomenological relationship. The extremal peakamplitudes are shown by an ordered statistics treatment, to be extremally distributed. The statistical treatment enables the prediction of the number of cycles left until failure. Predictions performed a-posteriori based on results gained early in each fatigue test are in good agreement with actual fatigue lives. The amplitude distribution analysis of the acoustic signals emitted during cyclic stress appears to be a promising nondestructive method of predicting fatigue life.

Baram, J.; Rosen, M.

1980-05-01

394

PREDICTION OF FATIGUE LIFE AND CRACK PATH IN GENERIC 2D STRUCTURAL COMPONENTS UNDER COMPLEX LOADING  

Microsoft Academic Search

A reliable and cost effective two-phase methodology is proposed to predict crack propagation in generic two-dimensional structural components under complex fatigue loading. First, the fatigue crack path and its stress intensity factors are calculated in a specialized finite element software, using small crack increments. At each crack propagation step, the mesh is automatically redefined based on a self-adaptive strategy that

Oliveira Miranda; Luiz Fernando Martha; Tulio N. Bittencourt

395

Impact of Fatigue on Quality of Life in Patients with Parkinson's Disease  

Microsoft Academic Search

Abstract Fatigue is frequent ,and ,important ,in the ,lives of Parkinsons disease (PD) patients. It is multidimensional, with physical and mental aspects. The aim of our ,study was ,to explore ,the impact ,of fatigue ,on quality oflife for PD patients. The sample ,consisted of 175 PD patients from Eastern Slovakia (52% males, mean age 68.29.2, mean disease duration 7.46.7). The

Eva Havlikova; Jaroslav Rosenberger; Iveta Nagyova; Berrie Middel; Tatiana Dubayova; Zuzana Gdovinova; Jitse P. van Dijk; Johan W. Groothoff

396

Fatigue Life Prediction of Spot-Welded Structures: A Finite Element Analysis Approach  

Microsoft Academic Search

This paper presents the technique of the fatigue analysis of spot-weld joints to predict the lifetime and location of the weakest spot-welds due to the imposed loading conditions. A simple model was used to illustrate the technique of spot-weld fatigue analysis. Finite element model and analysis were carried out utilizing the finite element analysis commercial codes. Linear elastic finite element

M. M. Rahman; Rosli A. Bakar; M. M. Noor

397

An investigation into the effect of various surface treatments on fatigue life of a tool steel  

Microsoft Academic Search

The effects of nitriding, nitrocarburizing and shot peening on fatigue behavior of AISI D3 cold work tool steel were investigated. Five batches of fatigue specimens were manufactured according to the ASTM E466-96 standard. All specimens were quenched and tempered to a hardness of 50HRC. One group of specimens was shot peened with an Almen intensity of 16 A, one group

G. H. Farrahi; H. Ghadbeigi

2006-01-01

398

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.; Kroo, P.; Batyrsina, E.; Paulsen, A.; Frenzel, J.; Eggeler, G.; Maier, H. J.

2014-05-01

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

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

401

Creep-fatigue interaction in aircraft gas turbine components by simulation and testing at scaled temperatures  

NASA Astrophysics Data System (ADS)

Advanced gas turbine engines, which use hot section airfoil cooling, present a wide range of design problems. The frequencies of applied loads and the natural frequencies of the blade also are important since they have significant effects on failure of the component due to fatigue phenomenon. Due to high temperature environment the thermal creep and fatigue are quite severe. One-dimensional creep model, using ANSYS has been formulated in order to predict the creep life of a gas turbine engine blade. Innovative mathematical models for the prediction of the operating life of aircraft components, specifically gas turbine blades, which are subjected to creep-fatigue at high temperatures, are proposed. The components are modeled by FEM, mathematically, and using similitude principles. Three models have been suggested and evaluated numerically and experimentally. Using FEM method for natural frequencies causes phenomena such as curve veering which is studied in more detail. The simulation studies on the life-limiting modes of failure, as well as estimating the expected lifetime of the blade, using the proposed models have been carried out. Although the scale model approach has been used for quite some time, the thermal scaling has been used in this study for the first time. The only thermal studies in literature using scaling for structures is by NASA in which materials of both the prototype and the model are the same, but in the present study materials also are different. The finite element method is employed to model the structure. Because of stress redistribution due to the creep process, it is necessary to include a full inelastic creep step in the finite element formulation. Otherwise over-conservative creep life predictions will be estimated if only the initial elastic stresses are considered. The experimental investigations are carried out in order to validate the models. The main contributions in the thesis are: (1) Using similitude theory for life prediction of components in general, and specifically using thermal scaling for the first time for prototype and model with two different materials. (2) Developing 1-D creep ANSYS macro to study creep effects to get meaningful results for industrial applications of gas turbine blade. (3) Analyzing the curve veering and flattening phenomena in rotating blade at thermal environment, using Lagrange-Bhat method. (4) Simple constitutive models in creep-fatigue interaction are proposed that can predict the lifetime in complicated situations of creep-fatigue, using the pure creep and pure fatigue test data.

Sabour, Mohammad Hossein

402

Turbine blade tip durability analysis  

NASA Technical Reports Server (NTRS)

An air-cooled turbine blade from an aircraft gas turbine engine chosen for its history of cracking was subjected to advanced analytical and life-prediction techniques. The utility of advanced structural analysis techniques and advanced life-prediction techniques in the life assessment of hot section components are verified. Three dimensional heat transfer and stress analyses were applied to the turbine blade mission cycle and the results were input into advanced life-prediction theories. Shortcut analytical techniques were developed. The proposed life-prediction theories are evaluated.

Mcknight, R. L.; Laflen, J. H.; Spamer, G. T.

1981-01-01

403

Quality of life, fatigue and local response of patients with unstable spinal bone metastases under radiation therapy - a prospective trial  

PubMed Central

Background To evaluate the local response according to stability after radiotherapy (RT) with a special focus on quality-of-life (QoL), fatigue, pain and emotional distress in patients with unstable spinal bone metastases. Methods In this prospective trial, 30 patients were treated from September 2011 until March 2013. The stability of osteolytic metastases in the thoracic and lumbar spine was evaluated on the basis of the Taneichi-score after three and six months. EORTC QLQ-BM22, EORTC QLQ-FA13, and QSC-R10 were assessed at baseline, and three months after RT. Results After 3months, 25% (n?=?6) and after 6months 33.3% (n?=?8) were classified as stable. QoL, fatigue, and emotional distress showed no difference over the course. The pain response 3months after RT showed a significant difference (p?fatigue, and emotional distress. Trial registration Clinical trial identifier NCT01409720. PMID:24917420

2014-01-01

404

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

405

Fatigue strain-life behavior of carbon and low-alloy steels, austenitic stainless steels, and Alloy 600 in LWR environments  

SciTech Connect

The existing fatigue strain vs. life (S-N) data, foreign and domestic, for carbon and low-alloy steels, austenitic stainless steels, and Alloy 600 used in the construction of nuclear power plant components have been compiled and categorized according to material, loading, and environmental conditions. Statistical models have been developed for estimating the effects of the various service conditions on the fatigue life of these materials. The results of a rigorous statistical analysis have been used to estimate the probability of initiating a fatigue crack. Data in the literature were reviewed to evaluate the effects of size, geometry, and surface finish of a component on its fatigue life. The fatigue S-N curves for components have been determined by adjusting the probability distribution curves for smooth test specimens for the effect of mean stress and applying design margins to account for the uncertainties due to component size/geometry and surface finish. The significance of the effect of environment on the current Code design curve and on the proposed interim design curves published in NUREG/CR-5999 is discussed. Estimations of the probability of fatigue cracking in sample components from BWRs and PWRs are presented.

Keisler, J.; Chopra, O.K.; Shack, W.J. [Argonne National Lab., IL (United States)

1995-08-01

406

Dynamic characteristics of single crystal SSME blades  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

407

Piezoelectric Vibration Damping Study for Rotating Composite Fan Blades  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

408

Life prediction technologies for aeronautical propulsion systems  

NASA Technical Reports Server (NTRS)

Fatigue and fracture problems continue to occur in aeronautical gas turbine engines. Components whose useful life is limited by these failure modes include turbine hot-section blades, vanes, and disks. Safety considerations dictate that catastrophic failures be avoided, while economic considerations dictate that catastrophic failures be avoided, while economic considerations dictate that noncatastrophic failures occur as infrequently as possible. Therefore, the decision in design is making the tradeoff between engine performance and durability. LeRC has contributed to the aeropropulsion industry in the area of life prediction technology for over 30 years, developing creep and fatigue life prediction methodologies for hot-section materials. At the present time, emphasis is being placed on the development of methods capable of handling both thermal and mechanical fatigue under severe environments. Recent accomplishments include the development of more accurate creep-fatigue life prediction methods such as the total strain version of LeRC's strain-range partitioning (SRP) and the HOST-developed cyclic damage accumulation (CDA) model. Other examples include the development of a more accurate cumulative fatigue damage rule - the double damage curve approach (DDCA), which provides greatly improved accuracy in comparison with usual cumulative fatigue design rules. Other accomplishments in the area of high-temperature fatigue crack growth may also be mentioned. Finally, we are looking to the future and are beginning to do research on the advanced methods which will be required for development of advanced materials and propulsion systems over the next 10-20 years.

Mcgaw, Michael A.

1990-01-01

409

Compassion fatigue in nurses  

Microsoft Academic Search

Compassion fatigue, trigger situations, and coping strategies were investigated in hospital and home care nurses. The Professional Quality of Life Scale measured compassion fatigue, compassion satisfaction, and burnout. Narrative questions elicited trigger situations and coping strategies. Compassion fatigue scores were significantly different between nurses who worked 8- or 12-hour shifts. Fifteen percent of the participants had scores indicating risk of

Elizabeth A. Yoder

2010-01-01

410

Fatigue life prediction for a vessel sailing the North Atlantic route  

Microsoft Academic Search

A method for calculating the wave load induced fatigue damage accumulated by a vessel sailing along the North Atlantic route (NAr) is presented. This method is based on the PalmgrenMiner additive rule and the rainflow cycle (RFC) count. For simplicity, the load the vessel experiences is assumed to be proportional to the encountered significant wave height process, Hs. The asymptotically

Anastassia Baxevani; Igor Rychlik

2007-01-01

411

Fatigue life prediction under complex loading for XAS\\/914 CFRP incorporating a mechanical fastener  

Microsoft Academic Search

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

I. P. Bond; I. R. Farrow

2000-01-01

412

Advanced methodology for assessing distribution characteristics of Paris equation coefficients to improve fatigue life prediction  

Microsoft Academic Search

This paper offers a methodology for coping with information loss following consolida- tion of data on fatigue crack propagation rates derived from different experiments. It is customary, both in the literature and in standardization, to consolidate results of several experiments conducted under similar conditions, using identical materials. This reduces the ability to implement a probabilistic fracture mechanics approach in order

Y. R ABINOWICZ; I. ROMAN; Y. R ITOV

2008-01-01

413

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

Microsoft Academic Search

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

Julie Colin

2010-01-01

414

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

415

A mathematical model for the evaluation of amplitude of hemoglobin fluctuations in elderly anemic patients affected by myelodysplastic syndromes: correlation with quality of life and fatigue.  

PubMed

Therapy with RBC transfusions and rHuEPO for management of anemia in patients with myelodysplastic syndromes causes recurrent fluctuations in hemoglobin levels. The purpose of this study was to elaborate a mathematical model for the interpretation of hemoglobin fluctuations and to correlate the resulting numerical parameter (Variaglobin Index) with quality of life and fatigue. In 32 myelodysplastic patients, lower amplitude of the Variaglobin Index was found significantly correlated with a better quality of life and less fatigue. The mathematical model proposed here makes it easy to monitor anemia in myelodysplastic patients and to adjust therapy accordingly. PMID:16814382

Caocci, Giovanni; Baccoli, Roberto; Ledda, Antonio; Littera, Roberto; La Nasa, Giorgio

2007-02-01

416

Bimodal processing of titanium steam turbine blades  

Microsoft Academic Search

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

Rust

1985-01-01

417

Effect of grinding on the fatigue life of titanium alloy (5 Al-2.5 Sn) under dry and wet conditions  

NASA Technical Reports Server (NTRS)

The principal factors in the performance of aerospace materials are strength-to-weight ratio, fatigue life, fracture toughness, survivability and, of course, reliability. Machining processes and, in particular, grinding under adverse conditions have been found to cause damage to surface integrity and affect the residual stress distribution in the surface and subsurface region. These effects have a direct bearing on the fatigue life. In this investigation the effects of grinding conditions on the fatigue life of Titanium 5 Al-2.5Sn were studied. This alloy is used in ground form in the manufacturing of some critical components in the space shuttle's main engine. It is essential that materials for such applications be properly characterized for use in severe service conditions. Flat sub-size specimens 0.1 inch thick were ground on a surface grinding machine equipped with a variable speed motor at speeds of 2000 to 6000 rpm using SiC wheels of grit sizes 60 and 120. The grinding parameters used in this investigation were chosen from a separate study. The ground specimens were then fatigued at a selected stress and the resulting lives were compared with that of the virgin material. The surfaces of the specimens were examined under a scanning electron microscope, and the roughness and hardness were measured using a standard profilometer and microhardness tester, respectively. The fatigue life of the ground specimens was found to decrease with the increase in speed for both dry and wet conditions. The fatigue life of specimens ground under wet conditions showed a significant increase at the wheel speed of 2000 rpm for both the grit sizes and thereafter decreased with increase profilometry, microhardness measurements and scanning electron microscopic examination.

Rangaswamy, Partha; Terutung, Hendra; Jeelani, Shaik

1989-01-01

418

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

419

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

420

Fatigue life of a Nd:YAG laser-welded metal ceramic alloy.  

PubMed

Fifteen laser-welded Olympia alloy samples were divided into three groups of five samples each, with different gap distances between the welded halves. The first group was welded with a 0.0-mm gap distance. The second and third groups had Olympia shims placed in 0.3- and 1.0-mm gaps, respectively, prior to laser welding. Each of the samples was tested to failure in load fatigue at 30 Hz in a fatigue testing device using an applied stress of 35,000 psi (241.4 MPa). The means and standard deviations for the number of cycles required to produce fatigue failure for each group was 494,618 +/- 118,311 cycles for the group welded with 0.0-mm gap distance, and 242,741 +/- 44,623 and 232,021 +/- 55,877 cycles for the 0.3- and 1.0-mm specimens, respectively. A one-way analysis of variance showed that the 0.0-mm gap specimens had the greatest number of cycles to failure (P < or = 0.05). There was no significant difference between the other two groups. With the exception of two specimens that failed at the weld center, all failures occurred at the edge of the weld. PMID:9495162

Lee, W V; Nicholls, J I; Butson, T J; Daly, C H

1997-01-01

421

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

422

Influence function method for fracture mechanics and residual fatigue life analysis of cracked components under complex stress fields. Technical report 2  

Microsoft Academic Search

The development and application of an influence function method for calculating stress intensity factors and residual fatigue life for two- and three-dimensional structures with complex stress fields and geometries are reviewed. Through elastic superposition, the method properly accounts for redistribution of stress as the crack grows through the structure. The analytical methods utilized and the computer programs necessary for computation

Besuner

1975-01-01

423

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

424

What about me? Avoiding fatigue and gaining personal time in the work to leisure transition in work-life balance initiatives  

Microsoft Academic Search

Fatigue and overwork are problems experienced by numerous employees in many industry sectors. Focusing on improving work-life balance can frame the problem of long work hours to resolve working time duration issues. Flexible work options through re-organising working time arrangements is key to developing an organisational response for delivering work-life balance and usually involves changing the internal structure of work

Kerry A Brown; Sharine Ling; Lisa M Bradley; Helen Lingard; Keith Townsend

2012-01-01

425

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

426

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

427

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

E-print Network

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

428

Influence of electroless nickel-phosphorus deposits on the corrosion-fatigue life of notched and unnotched samples of an AISI 1045 steel  

SciTech Connect

Electroless nickel-phosphorus deposits of approximately 10% phosphorus and about 20 {micro}m thickness are shown either to have no effect or sometimes to increase the corrosion-fatigue properties of a quenched and tempered AISI 1045 steel in the stress amplitude range of 481 to 687 MPa, in the presence of an aqueous solution of 3% sodium chloride. Such an increase is produced when the stress amplitude is below 516 MPa. For the notched specimens, no substantial differences are found between the fatigue life of the coated and uncoated specimens.

Chitty, J.A.; Pertuz, A.; Puchi, E.S. [Central Univ. of Venezuela, Caracas (Venezuela)] [Central Univ. of Venezuela, Caracas (Venezuela); Hintermann, H. [Univ. of Neuchatel (Switzerland). Dept. of Mechanical Engineering] [Univ. of Neuchatel (Switzerland). Dept. of Mechanical Engineering

1999-02-01

429

Evaluation of the Fatigue Life of High-Strength Low-Alloy Steel Girth Welds in Aqueous Saline Environments with Varying Carbon Dioxide Partial Pressures  

NASA Astrophysics Data System (ADS)

High-strength low-alloy steel girth weld specimens were subjected to fatigue tests in saline environments saturated with different carbon dioxide partial pressures. As expected, results show that increases in gas concentration initially affect fatigue life adversely, but when higher partial pressures are associated with low stresses, a reduction in the negative impact of environmental conditions is seen. This may be related to a competition between corrosion rates and mechanisms of crack initiation and propagation. Data is presented with the aim of contributing toward the establishment of a database of results in literature which may lead to better understanding of the phenomena involved through association of these with ongoing research.

Lemos, M.; Kwietniewski, C.; Clarke, T.; Joia, C. J. B.; Altenhofen, A.

2012-07-01

430

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

Microsoft Academic Search

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

In-Kyung Sung

2006-01-01

431

Bimodal processing of titanium steam turbine blades  

SciTech Connect

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

Rust, T.M.

1985-10-01

432

Quality of life in multiple sclerosis (MS) and role of fatigue, depression, anxiety, and stress: A bicenter study from north of Iran  

PubMed Central

Background: Although studies have demonstrated significant negative relationships between quality of life (QOL), fatigue, and the most common psychological symptoms (depression, anxiety, stress), the main ambiguity of previous studies on QOL is in the relative importance of these predictors. Also, there is lack of adequate knowledge about the actual contribution of each of them in the prediction of QOL dimensions. Thus, the main objective of this study is to assess the role of fatigue, depression, anxiety, and stress in relation to QOL of multiple sclerosis (MS) patients. Materials and Methods: One hundred and sixty-two MS patients completed the questionnaire on demographic variables, and then they were evaluated by the Persian versions of Short-Form Health Survey Questionnaire (SF