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1

The influence of crystal orientations on fatigue life of single crystal cooled turbine blade  

Microsoft Academic Search

A method based on the orthotropic elastic finite element analysis (FEA) has been presented to analyze the fatigue life of cooled turbine blades made of nickel-based single crystal superalloy (SC). Special attention was put on the influence of the crystallographic orientations on the strength and fatigue life of SC cooled turbine blades. It is shown that, due to the influence

N. X. Hou; W. X. Gou; Z. X. Wen; Z. F. Yue

2008-01-01

2

Blade fatigue life assessment with application to VAWTs  

Microsoft Academic Search

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

P. S. Veers

1982-01-01

3

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

Microsoft Academic Search

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

Nobuhiro Isobe; Shuhei Nogami

2009-01-01

4

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

5

FATIGUE CHARACTERIZATION OF A VAWT BLADE MATERIAL  

Microsoft Academic Search

The fatigue analysis of Wind Energy Conversion System blades has been limited by the lack of fatigue data for typical blade materials, tncluding 6063 aluminum. an alloy commonly used for Vertical Axis Wind Turbine (VAWTI blades. This paper reports results to date of a testing program to establish a fatigue properties database for this alloy. TWO -s of fatigue response

J. A. Van; Den Avyle; H. J. Sutherland

6

Fatigue of fiberglass wind turbine blade materials.  

National Technical Information Service (NTIS)

Fatigue behavior for a variety of generic materials used in wind turbine blades has been explored. Coupon testing was carried out under constant amplitude tensile fatigue loading to beyond 10(sup 7) cycles for most materials. Unidirectional materials perf...

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

1992-01-01

7

Fatigue Evaluation of WTS-3 Wind Turbine Blade and Retention.  

National Technical Information Service (NTIS)

The WTS-3 wind turbine blade and retention computed stress levels are compared to material properties, and potentially fatigue critical areas are identified. For the blade, these are flatwise spar stresses, and blade shell flatwise stresses. It is not pos...

A. I. Gustavsson A. F. Blom

1987-01-01

8

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

9

Recrystallization and fatigue fracture of single crystal turbine blades  

Microsoft Academic Search

Two rotor blades in an aero-engine fractured during testing. The fracture mode and cause were analyzed on the basis of fracture surface observation, chemical analysis, and metallurgical structure examination. The results show that the two blades failed in the same mode – fatigue fracture caused by recrystallization. In order to find out the cause of recrystallization, simulation tests were carried

Y. H. He; X. Q. Hou; C. H. Tao; F. K. Han

2011-01-01

10

Crystallographic life model for single crystal turbine blade and validation by the miniature specimens cut from the turbine blades  

Microsoft Academic Search

Purpose – The purpose of this paper is to found a life model for the single crystal (SC) turbine blade based on the rate-dependent crystallographic plasticity theory. Design\\/methodology\\/approach – This life model has taken into consideration the creep and fatigue damages by the linear accumulation theory. A SC blade was taken from an aero-engine, which had worked for 1,000 hours,

Zhixun Wen; Naixian Hou; Baizhi Wang; Zhufeng Yue

2010-01-01

11

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

SciTech Connect

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

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

1995-12-01

12

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

Microsoft Academic Search

Nicks and dents caused by foreign object damage (FOD) in leading edges of turbine engine blades often provide crack initiation sites that may grow under high cycle fatigue (HCF) conditions and lead to reduced life. Leading edge specimens simulating the geometry of these engine blades were fabricated from STOA Ti-6Al-4V. The leading edges were then ballistically impacted with small steel

Janine C. Birkbeck

2002-01-01

13

Simulation of fatigue failure in composite axial compressor blades  

Microsoft Academic Search

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

Qubo Li; Janusz Piechna; Norbert Müeller

2011-01-01

14

High Frequency Fatigue of Turbine Blade Material.  

National Technical Information Service (NTIS)

This increased fatigue crack growth rate at elevated temperature due to high frequency loading is examined. The crack growth rate is found to depend upon major cycle stress intensity factor, hold-time and minor cycle frequency, and amplitude for a given t...

R. C. Goodman A. M. Brown

1982-01-01

15

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

16

Fatigue life prediction in composites  

Microsoft Academic Search

Because of the relatively large number of possible failure mechanisms in fibre reinforced composite materials, the prediction of fatigue life in a component is not a simple process. Several mathematical and statistical models have been proposed, but the experimental evidence to support them is limited so far. In this paper, an attempt has been made to fit experimental results to

R. J. Huston

1994-01-01

17

Fatigue life prediction using frequency response functions  

Microsoft Academic Search

This paper presents a method for fatigue-life prediction of engineering components subjected to dynamic loads. It is based on the determination of the nominal stress at the crack position using frequency response functions and this in turn enables the prediction of dynamic fatigue life under forced vibration. Stresses used for fatigue life prediction are determined via a vibration analysis. The

K. Y. Sanliturk; M. Imregun

1992-01-01

18

Ultrasonic evaluation of the effects of compressive residual stresses on aircraft engine turbine blades subjected to high cycle fatigue  

NASA Astrophysics Data System (ADS)

Experiments conducted on titanium (Ti-64) turbine blades with the LCR ultrasonic wave at 20 MHz showed significant differences in untreated blades and blades treated to increase the subsurface compressive residual stress. Group 1 showed significant differences in the treated and untreated areas, the top and bottom of the blades, high cycle fatigue and cracked and uncracked conditions. Group 2 blades showed significant difference between untreated and treated travel-times at probes located at the blade leading edge. .

Bray, Don E.; Suh, Ui; Hough, C. L. ``Mickey''

2002-05-01

19

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

SciTech Connect

This paper presents a quantitative analysis of the fatigue loads in a down wind, yaw-controlled, fixed pitch, two-bladed teetered-rotor wind turbine using proportional-integral, full-state optimal, and fuzzy logic controllers. Time-domain simulation data is generated using the EASY5x/WT software developed at the University of Texas at El Paso. The simulation data reveal that the choice of controller type, or the controller dynamics, can play a very important role in the fatigue life of a wind turbine and should be considered early in the design process of the wind turbine. In summary, the fuzzy logic controller is the most robust controller under a wide regime of wind conditions. It provides the best overall performance in terms of power regulation capability and minimum fatigue loads. The optimal controller with a full-state Kalman filter observer provides a satisfactory performance in terms of power regulation capability and loads when the operating condition is close to the design point at which the controller was optimized. It fails to regulate the power output when the actual operating point deviated too far, about 30 percent in the computer simulations, from the designed operating point. The PI controller provided satisfactory performance in power regulation. However, it produced the worst fatigue loads to the wind turbine among the three controllers.

Wu, K.C.; Guardia, R. De La [Univ. of Texas, El Paso, TX (United States). Mechanical and Industrial Engineering Dept.

1996-11-01

20

Simple method of estimating wind turbine blade fatigue at potential wind turbine sites.  

National Technical Information Service (NTIS)

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...

J. C. Barnard L. L. Wendell

1995-01-01

21

Development of a Fatigue-Life Methodology for Composite Structures Subjected to out-of-Plane Load Components.  

National Technical Information Service (NTIS)

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 configuratio...

M. Sumich K. T. Kedward

1991-01-01

22

CYCLIC FATIGUE CHARACTERISTICS OF 10%CR BLADE STEELS FOR ADVANCED STEAM TURBINE  

Microsoft Academic Search

Modified 9 ~ 12%Cr ferritic steels have been used extensively as the structural materials at the temperature up to 600oC in thermal power plants. And also the steels are excellent candidate materials for the advanced steam turbine blades in high pressure and temperature. In this paper, the low cycle fatigue (LCF) and high cycle fatigue (HCF) characteristics of the high

Jin-Ik Suk; Kuk-Cheol Kim; Byung-Hoon Kim; Jeong-Tae Kim

23

Fatigue crack initiation life prediction of railroad  

NASA Astrophysics Data System (ADS)

Study of multiaxial high-cycle fatigue initiation life prediction for railroad is done in this paper. Using ANSYS 11.0 software three dimensional elasto-plastic finite element model of rail/wheel contact is constructed and fine mesh technique in contact region is used to achieve both computational efficiency and accuracy. Stress analysis is performed and fatigue damage in railroad is evaluated numerically using multiaxial fatigue crack initiation model. Using the stress history during one loading cycle and fatigue damage model, the effects of vertical loading, material hardness material fatigue properties and wheel/rail contact situation on fatigue crack initiation life are investigated.

Tehrani, P. Hosseini; Saket, M.

2009-08-01

24

From fatigue test life to structure safe life  

NASA Astrophysics Data System (ADS)

According to Chinese military specifications a suitable fatigue life scatter factor must be used in determining aircraft safe life from fatigue test life. The relationship between the reliability and the life distribution scatter factor has been discussed. The difference between the life distribution scatter factor and the specification life scatter factor has been pointed out. The concept of spectrum variation factor has been emphasized. It is argued that the specification fatigue life scatter factor should be the product of the life distribution scatter factor and the spectrum variation factor. Determination of structure safe life from fatigue test results of used structures has also been considered. Two points are of significance: when converting used time to fatigue test life the time should be reduced instead of being increased, different specification fatigue life scatter factors should be chosen for service time and test time.

Chen, Zhiwei

1991-08-01

25

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.

2012-03-01

26

Stop drilling procedure for fatigue life improvement  

Microsoft Academic Search

This paper investigated how the stop drilling procedure improved the crack initiation life and the total fatigue life in specimens of 6061-T651 aluminium alloy and AISI 304 stainless steel. The crack initiation life was the number of fatigue cycles initiating a 0.2 mm crack at a stophole edge. The larger the stophole diameter, the longer the crack initiation and total

P. S. Song; Y. L. Shieh

2004-01-01

27

Prediction of Solder Joint Fatigue Life.  

National Technical Information Service (NTIS)

This study details the procedures used to predict the solder joint life from calculations of the joint strains and low-cycle fatigue data. The fatigue life of chip carrier/printed wiring board joints are predicted and compared to measured values. This pre...

D. G. Thompson H. D. Solomon V. Brzozowski

1988-01-01

28

Fatigue life prediction and failure mechanisms of composite materials  

Microsoft Academic Search

Fatigue life prediction and failure mechanisms of composite materials are studied based on the fatigue modulus concept and experimental results. Single-stress level fatigue life is predicted using generalized fatigue modulus degradation model and resultant strain failure criterion. Cumulative damage models defined by fatigue modulus and resultant strains are derived as functions of fatigue cycle and applied stress. This approach can

K. S. Han; W. Hwang

1992-01-01

29

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

30

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.

2012-03-01

31

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

SciTech Connect

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

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

2012-06-28

32

Predictions of solder joint fatigue life  

Microsoft Academic Search

Procedures used to predict solder-joint life from calculations of the joint strains and low-cycle fatigue data are described. The fatigue lives of chip-carrier\\/printed-wiring-board joints are predicted and compared to measured values. This prediction utilizes a finite-element analysis of the string distributions in a typical joint acted upon by an imposed displacement. These strains are then used to determine the fatigue

H. D. Solomon; V. Brzozowski; D. G. Thompson

1990-01-01

33

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

34

Quality of life in chronic fatigue syndrome  

Microsoft Academic Search

Whilst the debilitating fatigue experienced in patients suffering from Chronic Fatigue Syndrome (CFS) results in a subjective marked impairment in functioning, little research has investigated the impact of this disorder on quality of life. Forty-seven subjects with a confirmed diagnosis of CFS and 30 healthy controls were compared using the Sickness Impact Profile (SIP). A subgroup of subjects were interviewed

Robert Schweitzer; Brian Kelly; Amanda Foran; Deborah Terry; John Whiting

1995-01-01

35

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

36

Integrated Lifing Analysis of a Film-Cooled Turbine Blade.  

National Technical Information Service (NTIS)

A method to predict gas turbine component life based on engine performance analysis is demonstrated on a hot section gas turbine component. The mechanical and thermal loading of the first stage high pressure turbine rotor blade of the F100-PW-220 engine, ...

S. Woldendorp T. Tinga W. B. de Wolf W. P. Visser

2003-01-01

37

Fatigue Life Characteristics of Waterworks Pipe Welds  

NASA Astrophysics Data System (ADS)

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

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

38

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

Microsoft Academic Search

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

Stephan Issler; Eberhard Roos

2003-01-01

39

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

National Technical Information Service (NTIS)

The load spectrum unposed upon a horizontal-axis wind turbine blade is typically decomposed into two primary bending moments; flap and edgewise bending. The critical fatigue loads (stress cycles) imposed on the blade may not be on one of these axes, espec...

H. J. Sutherland

1992-01-01

40

Low-cycle fatigue of TiNi shape memory alloy and formulation of fatigue life  

SciTech Connect

The low-cycle fatigue of a TiNi shape memory alloy was investigated by the rotating-bending fatigue tests in air, in water and in silicone oil. (1) The influence of corrosion fatigue in water does not appear in the region of low-cycle fatigue. (2) The temperature rise measured through an infrared thermograph during the fatigue test in air is four times as large as that measured through a thermocouple. (3) The fatigue life at an elevated temperature in air coincides with the fatigue life at the same elevated temperature in water. (4) The shape memory processing temperature does not affect the fatigue life. (5) The fatigue equation is proposed to describe the fatigue life depending on strain amplitude, temperature and frequency. The fatigue life is estimated well by the proposed equation.

Tobushi, Hisaaki; Nakahara, Takafumi; Shimeno, Yoshirou; Hashimoto, Takahiro

2000-04-01

41

Flip chip solder joint fatigue life model investigation  

Microsoft Academic Search

In recent years, many solder fatigue models based on strain-range and energy density methods have been developed to predict the fatigue life of solder joints. The application of these fatigue models to flip chip solder joint reliability has been investigated. In this study, the solder joint fatigue life of non-underfill and underfilled flip chip on board (FCOB) assemblies was assessed

Alfred Yeo; Charles Lee; J. H. L. Pang

2002-01-01

42

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

Microsoft Academic Search

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

M. Sumich; K. T. Kedward

1991-01-01

43

Development of Stress and Lifing Criteria for Single Crystal Turbine Blades.  

National Technical Information Service (NTIS)

The stress and lifing criteria applied to turbine blades are discussed, by focusing the relevant features which make single crystal materials different from conventional alloys. The discussion basis is provided by the material data and blade finite elemen...

S. Salvano M. Stanisci E. Campo

1989-01-01

44

Fatigue Life Predictions of Notched Components: Crack Intitiation.  

National Technical Information Service (NTIS)

An approach to fatigue crack initiation analysis of notched components, consisting of life calculations based on stress and strains estimated to occur locally at the most critical notch, is presented. The fatigue life calculations take into account severa...

G. Glinka

1990-01-01

45

Shape and fatigue life prediction of chip resistor solder joints  

Microsoft Academic Search

In order to increase the fatigue life of chip resistor, it is necessary to optimize the shape of solder joints. Shape and fatigue life of chip resistor solder joint were predicted by using finite element analysis methods. Through changing the solder volume, four typical solder joint shape prediction were conducted, and three-dimensional mechanical model of fatigue life analysis was set

Guanqun Zheng; Chunqing Wang

2009-01-01

46

Analysis of Fatigue Crack Growth Mechanism and Oxidation and Fatigue Life at Elevated Temperatures.  

National Technical Information Service (NTIS)

Two quantitative models based on experimentally observed fatigue damage processes have been made: (1) a model of low cycle fatigue life based on fatigue crack growth under general-yielding cyclic loading; and (2) a model of accelerated fatigue crack growt...

H. W. Liu

1988-01-01

47

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

2012-08-17

48

Die fatigue life design and assessment via CAE simulation  

Microsoft Academic Search

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

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

2008-01-01

49

Comparative evaluation of environment induced cracking of conventional and advanced steam turbine blade steels. Part 2: Corrosion fatigue  

Microsoft Academic Search

Corrosion fatigue crack propagation rates have been determined for two steam turbine blade steels, PH13-8, a candidate steel for advanced turbines, and FV566, typical of conventional turbine blades. The testing was undertaken in simulated condensate environment, 300ppb Cl? and 300ppb SO42-, at 90°C using trapezoidal loading with a rise time of 20min to simulate two-shifting (switching on- and off-load on

A. Turnbull; S. Zhou

50

Fatigue mediates the effects of exercise on quality of life  

Microsoft Academic Search

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

Anna L. Schwartz

1999-01-01

51

Extending the Fatigue Life of Riveted Coped Stringer Connections  

Microsoft Academic Search

Fatigue cracking occurs at the copes of stringer-floorbeam connections of older, riveted steel bridges. Some cracks are quite long and raise serious questions regarding the remaining fatigue life of the subject bridges. Damage limitation methods (DLMs) have been used to increase the fatigue life of these stringers, but the effectiveness of the DLMs for these riveted connections had never been

Charles W. Roeder; Gregory MacRae; Amy Leland

2005-01-01

52

The effects of fatigue loading frequency on fatigue life of high-strength pressure vessel steels  

NASA Astrophysics Data System (ADS)

Bend specimens of high-strength pressure vessel steel were tested in bending fatigue to failure at 1.5, 15, 30, arid 75 Hz fatigue loading frequencies. In the 1.5 to 15 Hz range, there was no discernible difference in the frequency effect on fatigue life. However, in the 30 to 75 Hz range, there was a definite increase in fatigue life compared to the lower range of frequency. The average increase in fatigue over the stress range was a factor of 10 greater than the life at the lower frequency range. This factor increased at lower stresses decreased at higher stresses, but even at the highest stresses tested, the increase was significant, about 5 to 1. This indicates that the frequency effect is more effective at high-cycle fatigue and diminishes with low-cycle fatigue. A model for fatigue life deterioration caused by superimposition of loads under different frequencies is introduced.

Fujczak, Robert R.

1994-06-01

53

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

Microsoft Academic Search

A life prediction model is developed for crack nucleation and early crack growth based on fatigue, environment (oxidation),\\u000a 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).\\u000a Fatigue life predictions compare favorably with experiments in 1070 steel for a wide range of test conditions and strain-temperature\\u000a phasings. An

R. W. Neu; Huseyin Sehitoglu

1989-01-01

54

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

SciTech Connect

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

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

1999-03-04

55

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

Microsoft Academic Search

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

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

2012-01-01

56

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

57

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

Microsoft Academic Search

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

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

1997-01-01

58

Fatigue evaluation of wood laminates for the design of 100M diameter wind turbine blades.  

National Technical Information Service (NTIS)

The fatigue properties of wood laminates have been evaluated in axial tension, compression and shear. A complete constant life diagram has been constructed for Khaya ivorensis (African mahogany) from S-N curves at various R ratios. The form of S-N curves ...

P. W. Bonfield M. P. Ansell

1991-01-01

59

Prediction of residual fatigue life using nonlinear ultrasound  

Microsoft Academic Search

Prediction of fatigue life of components during service is an on-going and unsolved challenge for the NDT and structural health monitoring community. It has been demonstrated by a number of researchers that nonlinear guided waves or the acoustic nonlinear signature of fatigued cracked material provides clear signs of the progressive fatigue damage in the material, unlike linear guided waves. However,

Mikael Amura; Michele Meo

2012-01-01

60

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

61

Fatigue Life Characteristics of Waterworks Pipe Welds  

Microsoft Academic Search

The fatigue characteristic of a material or a structure is derived from fatigue tests of standard specimens. However, many test results of standard specimens are very different from those of real structures or components because of geometrical effect, surface condition and so on. In this study, fatigue tests with specimens and pipes were carried out to evaluate the fatigue characteristic

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

2006-01-01

62

Fatigue life prediction under wide band random loading  

Microsoft Academic Search

In this paper, a method for the high-cycle fatigue life prediction of components subjected to gaussian, stationary, wide band random loading is presented. It allows the user to evaluate the fatigue life of components subjected to uniaxial stress states directly from the stress power spectral density (PSD), avoiding onerous simulations in time domain. The proposed method can be applied to

G. PETRUCCI; B. ZUCCARELLO

2004-01-01

63

Thermal Fatigue Life Prediction Of Solder Joints Using Stress Analysis  

Microsoft Academic Search

The fatigue life prediction of solder joints has become one of the most important research areas in the development of reliable electronic components. In this study. elastic-creep stress analysis proposed in previous papers was carried out for the solder joints of a recently developed LSI package (ball grid array package). The results of fatigue life estimation agreed well with those

M. Mukai; T. Kawakami

1997-01-01

64

Matrix Properties Controlling Torsional Fatigue Life of Fiber Reinforced Composites.  

National Technical Information Service (NTIS)

The fatigue life of torsionally stressed N.O.L. rings can be correlated with basic properties of the matrix. In a constant maximum deformation mode, fatigue life correlates, in a nonlinear fashion, with the ultimate strain of the matrix. Performance is al...

R. E. Lavengood R. M. Anderson

1969-01-01

65

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

SciTech Connect

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, M.; Kedward, K.T.

1991-02-01

66

Creep-fatigue life prediction of in situ composite solders  

SciTech Connect

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

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

1995-12-01

67

Creep-fatigue life prediction of in situ composite solders  

NASA Astrophysics Data System (ADS)

Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. Intermetallic reinforcements of Ni3Sn4 and Cu6Sn5 are incorporated into eutectic tin-lead alloy by rapid solidification processes to form in situ composite solders. In this study, the in situ composite solders were subjected to combined creep and fatigue deformation at room temperature. Under cyclic deformation, the dominant damage mechanism of in situ composite solders is proposed to be growth of cavities. A constrained cavity growth model is applied to predict creep-fatigue life by taking into account the tensile loading component as well as the compressive loading component when reversed processes can occur. An algorithm to calculate cavity growth in each fatigue cycle is used to predict the number of fatigue cycles to failure, based on a critical cavity size of failure. Calculated lives are compared to experimental data under several fatigue histories, which include fully reversed stress-controlled fatigue, zero-tension stress-controlled fatigue, stress-controlled fatigue with tension hold time, fully reversed strain-controlled fatigue, and zero-tension straincontrolled fatigue. The model predicts the creep-fatigue lives within a factor of 2 with the incorporation of an appropriate compressive healing factor in most cases. Discrepancy between calculated lives and experimental results is discussed.

Kuo, C. G.; Sastry, S. M. L.; Jerina, K. L.

1995-12-01

68

Life prediction of fatigue crack propagation of cracked structure based on VCCT  

Microsoft Academic Search

A new method to estimate fatigue life of cracked structure is introduced in this paper. Based on the virtual crack closure technique (VCCT), the special fatigue element is developed to estimate fatigue life in conjunction with finite element analysis. The stress intensity factors are calculated within the fatigue element and the fatigue life of the element at the crack tip

Qin Qian; Chang-an Li; De Xie; Guo-qing Li

2009-01-01

69

Prestraining and its influence on subsequent fatigue life  

Microsoft Academic Search

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

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

1995-01-01

70

Equi-Biaxial Fatigue of Elastomers: the Effect of Oil Swelling on Fatigue Life  

Microsoft Academic Search

The effect of oil swelling on the fatigue life of ethylene propylene diene monomer rubber (EPDM) has been studied under conditions of equi-biaxial cycling using dynamic bubble inflation. Specimens were subjected to varying degrees of swelling in reference mineral oils and fatigued at constant engineering stress amplitudes. The reference oils used for swelling the EPDM had known aniline points, allowing

Stephen Jerrams; John Hanley; Niall M. Murphy; Ali Hassan

2008-01-01

71

Enhancing solder joint fatigue life for ball grid array packages  

Microsoft Academic Search

Solder joint fatigue failure is quite common in plastic ball grid array (BGA) packages. Accurately predicting solder joint fatigue life and developing advanced, efficient techniques of enhancing solder joint reliability are essential to package development. In this paper, a finite element model is created to simulate the thermal-mechanical behavior of solder joints in the thermal cycling environment. Darveaux's physical model

Zhou Wei; Lim Beng Kuan

2003-01-01

72

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

73

Probabilistic fatigue life prediction of metallic and composite materials  

NASA Astrophysics Data System (ADS)

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

Xiang, Yibing

74

Fatigue Life Prediction Modeling for Turbine Hot Section Materials.  

National Technical Information Service (NTIS)

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...

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

1989-01-01

75

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

SciTech Connect

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

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

1992-01-01

76

Fatigue Life Assessment of Different Steel-Based Shell Materials Under Variable Amplitude Loading  

Microsoft Academic Search

Structural components are frequently subjected to complex time histories of stress for which the prevalent mode of failure is fatigue. For reliable and cost-effective fatigue life calculations of metallic materials the systematic characterization of their fatigue behavior and the detailed understanding of basic fatigue mechanisms are of prime importance. Based on fatigue failure theories (stress-life theories such as; Goodman and

S. M. Beden; S. Abdullah; A. K. Ariffin

77

Fatigue life improvement in fatigue-aged fastener holes using the cold expansion technique  

Microsoft Academic Search

The use of cold expansion process as a life extension technique on aircraft structural joints was investigated. The primary focus was an experimental test programme consisting of open-hole and low-load transfer joint specimens made of 2024-T351 aluminium alloy and pre-fatigued to 25, 50 and 75% of the baseline fatigue life for plain holes. The FALSTAFF loading spectrum was applied. The

X. Zhang; Z. Wang

2003-01-01

78

Numerical life prediction of mechanical fatigue for hot forging tools  

Microsoft Academic Search

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

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

2009-01-01

79

Comparison of fatigue life for 3 types of manual wheelchairs  

Microsoft Academic Search

Fitzgerald SG, Cooper RA, Boninger ML, Rentschler AJ. Comparison of fatigue life for 3 types of manual wheelchairs. Arch Phys Med Rehabil 2001;82:1484-8. Objectives: To examine 3 types of manual wheelchairs[mdash ]ultralight wheelchairs (UWs), lightweight wheelchairs (LWs), and depot wheelchairs (DWs)[mdash ]and to compare the fatigue life between the wheelchair types. Design: A database of different manual wheelchairs tested according

Shirley G. Fitzgerald; Rory A. Cooper; Michael L. Boninger; Andrew J. Rentschler

2001-01-01

80

Fatigue life duration prediction for welded spots by volumetric method  

Microsoft Academic Search

The mechanical behavior of spot-welds under tensile-shear for one, three and five spot-welds is investigated in detail. Volumetric approach is applied to find fatigue life duration of welded spots. The three-dimensional finite element models for different geometries, including gap effects and non-linear features of materials are applied to obtain fatigue life. The elastic–plastic stress distribution at edge of hot spot-weld

H. Adib; J. Gilgert; G. Pluvinage

2004-01-01

81

Fatigue life of friction stir welded Al-Mg alloys  

Microsoft Academic Search

The following alloys EN- AW 5058 H321 and EN-AW 5059 H321 (Alustar) were welded by FSW (friction stir welding) method. The FSW welds showed better properties in comparison to the joints welded by the MIG method. The low-cycle fatigue life test was carried out in the symmetric cycle: in air and in 3.5% NaCl. Fatigue life of 5083 alloy welded

M. Czechowski

82

Fatigue life prediction of welded ship details  

Microsoft Academic Search

Ship structures are submitted to variable cyclic loading during navigation. The cyclic motion of waves induces variable and complex loadings in the structure, which could generate fatigue damage. Moreover, most of these metallic structures are welded assemblies. This technique generates local stress concentrations at the weld toe, which becomes a critical area regarding fatigue. In previous works, a methodology to

Carole Erny; David Thevenet; Jean-Yves Cognard; Manuel Körner

83

Development of fatigue life evaluation method using small specimen  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

84

Prestraining and its influence on subsequent fatigue life  

SciTech Connect

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, G.R.; Mcgaw, M.A.; Kalluri, S.

1995-03-01

85

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

86

Fatigue Life Characterization of Superpave Mixtures at the Virginia Smart Road. Final Contract Report.  

National Technical Information Service (NTIS)

Laboratory fatigue testing was performed on six Superpave HMA mixtures in use at the Virginia Smart Road. Evaluation of the applied strain and resulting fatigue life was performed to fit regressions to predict the fatigue performance of each mixture. Diff...

I. L. Al-Qadi S. R. Diefenderfer A. Loulizi

2005-01-01

87

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

88

Development of Fatigue Life Monitoring of Rmaf Fighter Airplanes  

Microsoft Academic Search

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

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

89

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

NASA Astrophysics Data System (ADS)

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

Endo, T.; Sakon, T.

1983-05-01

90

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

91

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

Microsoft Academic Search

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

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

2007-01-01

92

Development and evaluation of life assessment and reconditioning methods for gas turbine blading  

SciTech Connect

The blades and vanes of power generating gas turbines are critical components which can limit the turbine life. They normally subject to degradation as a result both of microstructural changes, resulting in embrittlement and creep life exhaustion and of environmental attack, leading to destruction of protective coatings (if present) and the base material itself. The aim of this program has firstly been review methods of life assessment and develop techniques for the evaluation of blade condition. These include both non destructive methods such as eddy-current testing to determine chromium depletion of the surface layers and destructive techniques such as blade sectioning and metallographic investigation. Secondly the work has been directed towards reconditioning of service-exposed blades. This part included the development of techniques for stripping used coatings, electropolishing the resulting surface to permit effective nondestructive examination of the base material and heat treatment of the base material to regenerate the mechanical properties. Either pressureless heat treatment or hot isostatic pressing can be employed depending on the condition of the blade. Material missing as a result of cracking or foreign object damage can be replaced by electrodeposition, plasma spraying, brazing or welding. These techniques have been investigated and their advantages and disadvantages demonstrated. 158 refs., 251 figs., 18 tabs.

Buergel, R.; Ebeling, W.; Ellner, J.; Fried, R.; Hoffelner, W.; Kasik, N.; Nazmy, M.; Schneider, K.; Scholz, A.; Sova, V.; Staubli, M. (ABB Asea Brown Boveri, Baden (Switzerland))

1991-06-01

93

Fatigue life prediction of solder joints.  

National Technical Information Service (NTIS)

The current status of lifetime prediction under conditions of thermomechanical creep/fatigue is reviewed. Each method is summarized and the results of the application to solder joints is shown. While each method has been applied with some success, a predi...

W. B. Jones

1991-01-01

94

Fatigue life prediction of solder joints  

Microsoft Academic Search

The current status of lifetime prediction under conditions of thermomechanical creep\\/fatigue is reviewed. Each method is summarized and the results of the application to solder joints is shown. While each method has been applied with some success, a predictive, phenomenological approach has not been developed and validated. A method which captures the response of a crack to steady-state and cycling

1991-01-01

95

Effects of initial cracks and firing environment on cannon fatigue life  

Microsoft Academic Search

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

J. H. Underwood; M. J. Audino

1999-01-01

96

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

97

Silicon nitride hybrid bearing fatigue life comparisons. Technical report  

SciTech Connect

Research to improve high-speed ball bearings for spacecraft applications has led to development of ceramic materials for bearing components, and the need to acquire sufficient fatigue life data to show the merits of various ceramic materials and fabrication processes, in comparison with the vast amount of steel bearing fatigue data acquired over many decades. In order to eliminate bias from such evaluations it is best to conduct comparative fatigue tests with steel bearings that are geometrically similar and in the same type of test rig. This report addresses some recent fatigue tests of hybrid bearings with silicon nitride (Si{sub 3}N{sub 4}) balls and Crucible Steel Company M62 steel raceways and a comparison set of all 52100 steel bearings. Results indicate that the bearings with ceramic (silicon nitride) balls are superior to the steel bearings.

Robinson, E.

1999-01-15

98

Base Oil Effects on Fatigue Life for Additive Blends as Measured on a 4Ball Fatigue Machine  

Microsoft Academic Search

As part of a study to determine the lubricant factors affecting fatigue of rolling contact bearings, the effects of base oil composition and viscosity for additive blends on the fatigue life of CVD 52100 steel balls were evaluated with a 4-ball fatigue machine. Using pure hydrocarbons as base stocks, aromatic hydrocarbons were found to not only give longer lives than

Fred G. Rounds

1977-01-01

99

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

Microsoft Academic Search

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

Paul S. Prevéy; N. Jayaraman; Michael Shepard

2007-01-01

100

Analysis of fretting fatigue in aircraft structures: Stresses, stress intensity factors, and life predictions  

NASA Astrophysics Data System (ADS)

Clamped contacts subjected to cyclic loading are prone to fretting fatigue, a mechanism of crack nucleation and propagation. In aircraft, fretting fatigue occurs at the rivet/hole interface on the fuselage skin and at the dovetail joint in engine hardware where disk and blade meet. The ability to predict the lives of such components would be a great aid in preventing failures. Finite element models appropriate for the calculation of fretting fatigue stresses and stress intensity factors are developed for two different contact geometries. In addition, several less computationally expensive numerical methods are also studied. Agreement between the various solutions is good. A severe increase in the mode I stress intensity factor near the surface is discovered in both geometries. Mode II stress intensity factors are also detailed, illustrating the complex non-proportional loading of fretting-induced cracks. A comparison is made between results obtained from actual surface profiles and those generated from prescribed surface profiles; the differences are significant. Equivalent initial flaw sizes are calculated for two different metals using an approach which ignores the effect of mode II stress intensity factors. Life predictions based on the equivalent initial flaw size approach are found to agree reasonably well with those measured in the laboratory for contact geometries similar to the rivet/hole interface. More data is needed before a judgment can be made about life correlations for the dovetail joint contact geometry. The analysis methods described throughout can be easily implemented and integrated into a system aimed at designing against fretting fatigue.

McVeigh, Pamela Alison

101

Creep Fatigue Life Prediction for Engine Hot Section Materials (Isotropic).  

National Technical Information Service (NTIS)

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...

V. Moreno D. Nissley L. J. Lin

1985-01-01

102

Complex stress state effect on fatigue life of GRP laminates  

Microsoft Academic Search

In structural applications of thin-wall, box beam constructions with composites, the effect of complex stress states is not properly taken into account in determining operational life and fatigue response in general, due either to misconceptions or lack of experimental data and theoretical models. Results from a recent research project, presented here in two parts, aim to contribute to the better

Theodore P Philippidis; Anastasios P Vassilopoulos

2002-01-01

103

Fatigue Life Prediction Modeling for Turbine Hot Section Materials.  

National Technical Information Service (NTIS)

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 h...

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

1988-01-01

104

Subjective quality of life in patients with chronic fatigue syndrome  

Microsoft Academic Search

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

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

2005-01-01

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

Thermal fatigue life prediction for solder joints with the consideration of damage evolution  

Microsoft Academic Search

Thermal fatigue of solder joints is critical to electronic package performance and service life. It is well known that the fatigue life is rather difficult to estimate because of the complex interaction between creep and fatigue of solder materials. Conventional life prediction methods such as the Coffin-Manson relation or its modifications may give erroneous results at the low strain range.

X. Zhang; S.-W. R. Lee

1998-01-01

107

A damage parameter based on fracture surface for fatigue life prediction of CSP solder joints  

Microsoft Academic Search

FEM simulation for the fatigue life of CSP solder joints with various geometries and array types under thermal cycling condition is studied. Coffin-Manson law with inelastic strain range is used to estimate the fatigue life of CSP solder joints. Therefore, the two unknown material parameters in the fatigue life model need to be determined first. Actually, the two parameters are

Lianxi Shen; Sung Yi; Jo Caers; Xiujuan Zhao; K. Zhang

2001-01-01

108

Fatigue life prediction of crankshaft repaired by twin arc spraying  

Microsoft Academic Search

This paper used Baumel Jr. and Seeger’s approach estimating fatigue parameters of 48MnV with 3Cr13 coatings. The fatigue life\\u000a of the crankshaft of a six-cylinder engine, repaired by twin arc spraying 3cr13 deposits, is respectively calculated using\\u000a different damage model such as S-N method, normal strain approaches, SWT-Bannantine approaches, shear strain approaches, and\\u000a fatemi-Socie method based on dynamical simulation and

Guo-qing Zhang; Cheng-tao Wang; Geng-qiang Pu

2005-01-01

109

Simulation work of fatigue life prediction of rubber automotive components  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

110

Fatigue life of preceramic soldered and postceramic soldered joints.  

PubMed

This research investigated the fatigue life (ie, the number of cycles of a given stress that can be sustained by a sample prior to catastrophic failure) of metal ceramic soldering. One metal ceramic alloy was joined using four postceramic solders and one preceramic solder. All specimens received appropriate heat treatment simulating ceramic application although no porcelain was applied. Five specimens were fabricated for each solder type, and a 35,000 psi (241.4 MPa) fatigue stress was applied to each solder joint during specimen testing. The test variable was the number of stress cycles required to fail each specimen. The postceramic solders exhibited significantly higher fatigue lives than did the preceramic solder. Scanning electron microscope analysis showed that the preceramic solder not only exhibited a larger grain size, but also showed micropores between these grains. PMID:7905268

Butson, T J; Nicholls, J I; Ma, T; Harper, R J

111

The Relationship Between Cancer-Related Fatigue and Patient Satisfaction with Quality of Life in Cancer  

Microsoft Academic Search

Fatigue affects a majority of patients undergoing cancer-related therapies. We conducted a study of 954 adult cancer patients presenting for treatment at our hospital between April 2001 and November 2004 to quantify the relationship between fatigue and patient satisfaction with quality of life (QoL). Fatigue was measured using the European Organization for Research and Treatment of Cancer Quality of Life

Digant Gupta; Christopher G. Lis; James F. Grutsch

2007-01-01

112

Thermal plastic strain fatigue life of the roll  

NASA Astrophysics Data System (ADS)

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

Li, Zhenzi; Huang, Xiangan; Liao, Fuchang

1992-07-01

113

Plastic stress and acoustic emission as predictors of fatigue life  

Microsoft Academic Search

The high rate of acoustic emission from AISI E4340 annealed steel when it is stressed can be used to accurately indicate the\\u000a yield stress. Predictive equations for the fatigue life of AISI E4340 annealed steel have been developed by the use of “Multiple\\u000a Classification Analysis” and “Stepwise Regression” computer programs based on an experimental study of 175 specimens. The\\u000a acoustic

L. D. Mitchell; J. R. Frederick

1970-01-01

114

Mean Stress Effects in Stress-Life and Strain-Life Fatigue  

Microsoft Academic Search

Various approaches to estimating mean stress effects on stress-life and strain-life behavior are compared with test data for engineering metals. The modified Goodman equa- tion with the ultimate tensile strength is found to be highly inaccurate, and the similar expression of Morrow using the true fracture strength is a considerable improvement. How- ever, the Morrow expression employing the fatigue strength

Norman E. Dowling

2004-01-01

115

Resistance of Welded Details under Variable Amplitude Long-Life Fatigue Loading.  

National Technical Information Service (NTIS)

This report contains the results of a study that extended the findings contained in NCHRP Report 267, 'Steel Bridge Members Under Variable Amplitude Long Life Fatigue Loading', by providing additional informtion on fatigue crack growth behavior of steel b...

J. W. Fisher A. Nussbaumer P. B. Keating B. T. Yen

1993-01-01

116

Fatigue-life prediction of SiC aluminum composite using a Weibull model  

Microsoft Academic Search

The feasibility of the acoustic emission technique in predicting the residual fatigue life of 6061-T6 aluminum matrix composite reinforced with 15vol.% SiC particulates (SiCp) is presented. Fatigue damages corresponding to 40, 60 and 80% of total fatigue life were induced at a cyclic stress amplitude. The specimens with and without fatigue damage were subjected to tensile tests. The acoustic emission

D. Shan; H. Nayeb-Hashemi

1999-01-01

117

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

118

Weighted error criterion to evaluate strain–fatigue life prediction methods  

Microsoft Academic Search

Experimental determination of strain–fatigue life curve is expensive considering the time and effort involved. Several empirical relations based on monotonic tensile properties and\\/or hardness is available for estimating strain–fatigue life properties. Existing criteria to evaluate the accuracy of these empirical relations are limited by the data points in the strain–fatigue life curve. A new criterion based on the prediction errors

K. Hariharan; Raghu V Prakash; M. Sathya Prasad

2011-01-01

119

Evaluation of low cycle fatigue life in AZ31 magnesium alloy  

Microsoft Academic Search

Magnesium alloys are attracting engineers for their practical application to structural components. Here fatigue properties, which is essential for structural use, have been examined on extruded AZ31 bar under uniaxial cyclic loading by both strain and stress controlled conditions. Adding fatigue tests with mean stresses under stress controlling conditions, fatigue life evaluation method has been discussed along with the analysis

S. Hasegawa; Y. Tsuchida; H. Yano; M. Matsui

2007-01-01

120

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

121

Microstructure-based fatigue life prediction methods for naval steel structures  

Microsoft Academic Search

The goal of the subject program has been to develop fundamental understandings of the relationships between microstructure and fatigue damage in structural steels of interest to naval applications. Quantitative descriptions of these relationships have been incorporated within practical engineering models for the prediction of fatigue life. Fatigue damage associated with microcrack nucleation and growth has been studied experimentally with S-N

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

1994-01-01

122

Precision evaluation for thermal fatigue life of power module using coupled electrical-thermal-mechanical analysis  

Microsoft Academic Search

For power module, the reliability evaluation of thermal fatigue life by power cycling has been prioritized as an important concern. Since in power cycling produces there exists non-uniform temperature distribution in the power module, coupled thermal-structure analysis is required to evaluate thermal fatigue mechanism. The thermal expansion difference between a Si chip and a substrate causes thermal fatigue. In this

Tomohiro TAKAHASHI; Qiang Yu

2010-01-01

123

Reliability evaluation of fatigue life for solder joints in chip components considering shape dispersion  

Microsoft Academic Search

This paper presents mining the worst thermal fatigue life of solder joints on chip components used in vehicle electronics. The authors proposed an isothermal fatigue test method using real size solder joints to get the fatigue properties. The Manson-Coffin's law given by this method could improve the agreement between the simulation model and experimental results. Based upon the Manson-Coffin's law

Yuji NISHIMURA; Qiang Yu; Toshiaki MARUOKA

2009-01-01

124

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

125

On the fatigue failure and life prediction for notched specimens  

Microsoft Academic Search

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

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

1998-01-01

126

Modelling low-cycle fatigue life of particulate-reinforced metal-matrix composites  

Microsoft Academic Search

A low-cycle fatigue life prediction model for particulate-reinforced metal-matrix composites (MMCs) is presented. The low-cycle fatigue behaviour of particulate-reinforced MMCs is treated as a localised damage development phenomenon activated by applied cyclic loading. The localised cyclic stress and strain concentration and fatigue damage evolution of microstructural elements within the fatigue damaged zone ahead of the crack tip are considered to

H.-Z Ding; O Hartmann; H Biermann; H Mughrabi

2002-01-01

127

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

128

Fatigue life estimation of adhesive bonded shaft joints  

Microsoft Academic Search

Fatigue tests and analytical investigation of adhesive bonded shaft joints were conducted to propose the estimation method of fatigue strength. Two kinds of adhesive bonded joints were studied: one, shaft joints connected with adhesive coupling, the other, adhesive joints of thin wall tubes to obtain standard fatigue strength. Both pulsating tensile and torsional fatigue tests were conducted with each adhesive

Makoto Imanaka; Waichiro Kishimoto; Kozo Okita; Hideaii Nakayama; Hiroyoshi Nagai

1989-01-01

129

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

PubMed Central

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

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

2010-01-01

130

Smart structure for small wind turbine blade  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

131

Influence of surface treatments on fatigue life of Al 7010 alloy  

Microsoft Academic Search

The objective of the present work is to show the influence of machining and anodizing processes on fatigue life of alloy 7010-T7451. Two different cutting conditions were employed to obtain two different initial surface roughnesses. Degreasing, pickling and anodizing were then carried out. In the as machined condition, surface roughness is clearly effective in reducing fatigue life in this material.

Majid Shahzad; Michel Chaussumier; Rémy Chieragatti; Catherine Mabru; Farhad Rezai Aria

2010-01-01

132

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

133

An evaluation of multiaxial fatigue life assessment methods for engineering components  

Microsoft Academic Search

This article deals with the problem of multiaxial fatigue life assessment of engineering components. General aspects of the critical plane damage models are discussed first. A computer-based procedure for multiaxial fatigue life assessment incorporating critical plane damage models, suitable for use in design evaluations of engineering components based on finite element analysis results, is presented and applied to correlate results

J Das; S. M Sivakumar

1999-01-01

134

Study of thermal fatigue life caused by dispersion of solder joint  

Microsoft Academic Search

The fatigue life considering dispersion of solder joints on chip resistor was investigated by experimental approach and analytical approach. The significant difference of crack propagation ratio was found each specimen by experimental approach. However, it is difficult to clarify the reasons of the difference for the fatigue life of solder joint quantitatively. So, the analytical approach that estimates not only

Kanji TAKAGI; Qiang Yu; Tadahiro SHIBUTANI; H. Miyauch; M. Shirator; Yukihiro NORO

2008-01-01

135

Solder joint fatigue life of fine pitch BGAs – impact of design and material choices  

Microsoft Academic Search

The impact of design and material choices on solder joint fatigue life for fine pitch BGA packages is characterized. Package variables included die size, package size, ball count, pitch, mold compound, and substrate material. Test board variables included thickness, pad configuration, and pad size. Three thermal cycle conditions were used.Fatigue life increased by up to 6× as die size was

Robert Darveaux; Jim Heckman; Ahmer Syed; Andrew Mawer

2000-01-01

136

Dispersion and the Worst Case of Thermal Fatigue Life of Solder Joints in Vehicle Electronic Devices  

Microsoft Academic Search

This paper presents mining the worst case of thermal fatigue life of solder joints on chip components used in vehicle electronics. Typical 36 cases with various solder shapes were examined. Thermal fatigue life including not only the crack initiation but also crack propagation was evaluated by using the finite element method. Based upon the case study's results, it was found

Toshiaki MARUOKA; Qiang Yu; T. Shibutani; H. Miyauci

2008-01-01

137

A study of factors affecting solder joint fatigue life of thermally enhanced ball grid array assemblies  

Microsoft Academic Search

In this study, a finite element study of design factors, including material constants and geometry parameters, affecting fatigue life of solder joints of a typical cavity?down Thermally Enhanced Ball Grid Array (TEBGA) assembly subjected to an accelerated temperature cycling load is performed. In order to precisely characterize the fatigue life of solder joints, the geometry profile of solder joints within

2001-01-01

138

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

Microsoft Academic Search

Self-healing polymers, based on microencapsulated dicyclopentadiene and Grubbs' catalyst embedded in the polymer matrix, are capable of responding to propagating fatigue cracks by autonomic processes that lead to higher endurance limits and life extension, or even the complete arrest of the crack growth. The amount of fatigue-life extension depends on the relative magnitude of the mechanical kinetics of crack propagation

A. S. Jones; J. D. Rule; J. S. Moore; N. R. Sottos; S. R. White

2007-01-01

139

Application of ultrasonic method in asphalt concrete testing for fatigue life estimation  

Microsoft Academic Search

This paper presents the possibilities of applying ultrasonic methods in asphalt concrete specimen testing in order to estimate fatigue life using ultrasonic characteristics of specimens. The procedures and results of testing cylinder shaped samples of both ultrasonic analysis and fatigue life testing are described. The ultrasonic method was first used in order to obtain the seismic characteristics of specimens. Then,

Mesut Tigdemir; S. Figen Kalyoncuoglu; U. Yalcin Kalyoncuoglu

2004-01-01

140

An exponential stress function for predicting fatigue strength and life due to mean stresses  

Microsoft Academic Search

An exponential stress function that relates the effect of mean stress on the fatigue strength and life is presented. This stress-based approach is based on the premise that mean stress directly affects the fatigue strength coefficient ??f, of the Basquin stress–life relation. The severity of damage depends on the relative measure of mean stress to the ultimate tensile strength of

S Kwofie

2001-01-01

141

A Methodology to Predict Fatigue Life of Cast Iron: Uniform Material Law for Cast Iron  

Microsoft Academic Search

Mechanical, physical and manufacturing properties of cast iron make it attractive for many fields of application, such as cranks and cylinder holds. As in design of all metals, fatigue life prediction is an intrinsic part of the design process of structural sections that are made of cast iron. A methodology to predict high-cycle fatigue life of cast iron is proposed.

Sinan Korkmaz

2011-01-01

142

Prediction of fatigue crack propagation life in notched members under variable amplitude loading  

SciTech Connect

One of the interesting phenomenon in the study of fatigue crack propagation under variable amplitude load cycling is the crack growth retardation that normally occurs due to the application of a periodic overload. Fatigue crack growth rate under simple variable amplitude loading sequence incorporating period overloads is studied using single edge notched specimens of AISI 304 stainless steel. Load interaction effects due to single and multiple overload have been addressed. Substantial retardation of fatigue crack growth rate is observed due to the introduction of periodic tensile overloads. Estimates of fatigue life have been obtained employing Wheeler model (using Paris and modified Paris equations) and Elber`s model. Analytical predictions are compared with experimental results. Results of these analytical fatigue life predictions show good agreement with the experimental results. Results of these analytical fatigue life predictions show good agreement with the experimental fatigue life data. Fatigue crack propagation rates also have been evaluated from the fractographic study of fatigue striations seen on the fracture surface. Good agreement was found between the experimentally observed crack growth rates and the fatigue crack growth rates determined by the fractographic studies.

Khan, Z.; Rauf, A.; Younas, M. [King Fahd Univ. of Petroleum and Minerals, Dhahran (Saudi Arabia). Mechanical Engineering Dept.

1997-06-01

143

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

NASA Astrophysics Data System (ADS)

Spectrum fatigue tests in welded steel box beam specimens were run at stress levels giving high cycle fatigue lifes. The test results and current fatigue design codes were compared. The results showed that the codes give unconservative estimations of fatigue lifes by a factor of approximately 4. The same unconservative life estimation was also shown by using a simple fracture mechanics prediction model. New design principles and other models of crack growth in this long life regime are needed. The main conclusion drawn from investigation is that using Palmgren-Miner cumulative damage rule with current design codes can give unwanted too high allowable stresses when the design life typically exceeds 10,000,000 cycles. For safe design, the use of a straight line relation between the stress range and the number of cycles to fracture extended below the constant amplitude fatigue limit, is recommended.

Dahle, Tormod; Larsson, Bertil

1992-07-01

144

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

145

Fatigue  

MedlinePLUS

... sense, fatigue is defined as a lack of energy, a subjective feeling of being tired. Fatigue also ... muscular dystrophies as muscles weaken and require greater energy to perform the same activities. Types of fatigue ...

146

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, ...

147

Fatigue life of implants made of titanium nickelide-based alloys  

NASA Astrophysics Data System (ADS)

Basic principles of predicting the fatigue life of implants of various types made from titanium nick-elide-based alloys are determined. They include an analysis of the results of preliminary clinical tests for determining the change in the implant shape during the functional displacements of a patient, the calculation of the strain from the change in the implant shape, the determination of conditions for rapid fatigue tests of implants, and the prediction of the fatigue life of the implants using the results of rapid fatigue tests of the implant material.

Kollerov, M. Yu.; Gusev, D. E.; Sharonov, A. A.; Gurtovoi, S. I.

2009-12-01

148

Influence of Asymmetrical Waveform on Low-Cycle Fatigue Life of Micro Solder Joint  

NASA Astrophysics Data System (ADS)

The effects of waveform symmetry on the low-cycle fatigue life of the Sn-3.0Ag-0.5Cu alloy have been investigated, using micro solder joint specimens with approximately the same volume of solder as is used in actual products. Focusing on crack initiation life, fatigue tests on Sn-Ag-Cu micro solder joints using asymmetrical triangular waveforms revealed no significant reduction in fatigue life. A slight reduction in fatigue life at low strain ranges caused by an increase in the fatigue ductility exponent, which is the result of a weakening microstructure due to loads applied at high temperature for long testing time, was observed. This was due to the fact that grain boundary damage, which has been reported in large-size specimens subjected to asymmetrical triangular waveforms, does not occur in Sn-Ag-Cu micro size solder joints with only a small number of crystal grain boundaries.

Kanda, Yoshihiko; Kariya, Yoshiharu

2010-02-01

149

Evaluation of Creep-Fatigue Life by Fraction of Cavity Area  

NASA Astrophysics Data System (ADS)

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

Kim, Bumjoon; Lim, Byeongsoo

150

Improving fatigue life in near-eutectic Sn Pb solders.  

National Technical Information Service (NTIS)

Due to technical advances in packaging technology, solder joint thermal shear fatigue failures pose reliability concerns and limit current packaging designs in the electronics industry. Past work has shown that thermal fatigue failures, as well as isother...

T. S. E. Summers

1991-01-01

151

Improving fatigue life in near-eutectic Sn Pb solders  

Microsoft Academic Search

Due to technical advances in packaging technology, solder joint thermal shear fatigue failures pose reliability concerns and limit current packaging designs in the electronics industry. Past work has shown that thermal fatigue failures, as well as isothermal fatigue and creep failures, in the commonly used near-eutectic Sn-Pb solders are preceded by the formation of a band of coarsened material. Examination

Summers

1991-01-01

152

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

153

Locking buttons increase fatigue life of locking plates in a segmental bone defect model.  

PubMed

BACKGROUND : Durability of plate fixation is important in delayed union. Although locking plates result in stronger constructs, it is not known if locking affects the fatigue life of a plate. Two locking screws on either side of the nonunion could decrease working length and increase strain in the plate. However, the reinforcing effect of the locking head on the plate may compensate, so that it is unclear whether locking reduces fatigue life. QUESTIONS/PURPOSES : We determined whether locking screws, compression screws, and locking buttons reduce or increase the fatigue life of a plate. METHODS : We tested fatigue life of four constructs using an eight-hole locking plate in a segmental defect model: (1) all locking screws (Locked; n = 5); (2) all compression screws (Unlocked; n = 5); (3) six compression screws with two locking buttons in the central holes (Button; n = 6); and (4) six compression screws with two open central holes (Open; n = 6). RESULTS : The Button group had the longest fatigue life (1.3 million cycles). There was no difference between the Locked and Unlocked groups. All of the constructs failed by fracture of the plates through a screw hole adjacent to the defect. CONCLUSIONS : Locking screws did not improve fatigue life, however a locking button increased the fatigue life of a locking plate in a segmental bone defect model. CLINICAL RELEVANCE : Locking buttons in holes adjacent to a defect may improve durability, which is important when delayed union is a possibility. PMID:23104045

Tompkins, Marc; Paller, David J; Moore, Douglas C; Crisco, Joseph J; Terek, Richard M

2012-10-27

154

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

Microsoft Academic Search

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

Fang Wang; Weicheng Cui

2010-01-01

155

Analysis of creep–fatigue life prediction models for nickel-based super alloys  

Microsoft Academic Search

Creep fatigue is the main damage form of engine parts operating under both cyclic mechanical and thermal loading conditions. In the present work time-dependent creep and cycle-dependent fatigue of nickel-based super alloys is discussed. Three different kinds of creep–fatigue life models are investigated for the nickel-based super alloys. Effects of temperature, loading ratio and loading hold time to material failure

Guobin Zhang; Huang Yuan; Fuqing Li

156

Fretting fatigue of single crystal/polycrystalline nickel subjected to blade/disk contact loading  

NASA Astrophysics Data System (ADS)

Two bodies are said to be in fretting contact when they are clamped together under the action of a normal force and see an oscillatory motion of small amplitudes at the contact interface due to the effect of shear force and bulk stress. The contact stresses that drive crack nucleation are very sensitive to the shape of the contacting surfaces and the coefficient of friction. To have an understanding of fretting at the contacts in engine components, it is important to simulate similar temperature, load and contact conditions in the laboratory and develop tools to analyze the contact conditions. The efforts made at simulating the temperature and load conditions typical to the engine hardware and the development of a robust mechanics based tool for life prediction are presented. The features of the rig include a combination of an efficient cooling mechanism using water and an insulation mechanism using ceramic blocks and sheets. The rig has been used to conduct an initial set of experiments using single crystal nickel (SCN) specimens and IN100 pads, and was found to function well under the operating temperature and load conditions. Crystallographic orientations contribute significantly to evaluation of the contact stress field. To perform an accurate analysis of anisotropic contact, a clear understanding of the material axes orientations must be maintained. A method for determining axes orientation using a Lauè diffraction method is described. Preliminary fractographic observations revealed that the fracture occurs along the <111> plane. Close observation of the crack initiation site revealed that the crack initiated at the edge of contact on a plane perpendicular to the contact surface.

Murthy, H.; Garcia, Daniel B.; Matlik, John F.; Farris, Thomas N.

2005-07-01

157

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

158

Prediction of fatigue crack propagation life in notched members under variable amplitude loading  

NASA Astrophysics Data System (ADS)

One of the interesting phenomenon in the study of fatigue crack propagation under variable amplitude load cycling is the crack growth retardation that normally occurs due to the application of a periodic overload. Fatigue crack growth rate under simple variable amplitude loading sequence incorporating period overloads is studied using single edge notched specimens of AISI304 stainless steel. Load interaction effects due to single and multiple overload have been addressed. Substantial retardation of fatigue crack growth rate is observed due to the introduction of periodic tensile overloads. Estimates of fatigue life have been obtained employing Wheeler model (using Paris and modified Paris equations) and Elber’s model. Analytical predictions are compared with experimental results. Results of these analytical fatigue life predictions show good agreement with the experimental fatigue life data. Fatigue crack propagation rates also have been evaluated from the fractographic study of fatigue striations seen on the fracture surface. Good agreement was found between the experimentally observed crack growth rates and the fatigue crack growth rates determined by the fractographic studies.

Khan, Z.; Rauf, A.; Younas, M.

1997-06-01

159

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

NASA Astrophysics Data System (ADS)

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

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

160

Influence of Asymmetrical Waveform on Low-Cycle Fatigue Life of Micro Solder Joint  

Microsoft Academic Search

The effects of waveform symmetry on the low-cycle fatigue life of the \\u0009Sn-3.0Ag-0.5Cu alloy have been investigated, using\\u000a micro solder joint specimens with approximately the same volume of solder as is used in actual products. Focusing on crack\\u000a initiation life, fatigue tests on Sn-Ag-Cu micro solder joints using asymmetrical triangular waveforms revealed no significant\\u000a reduction in fatigue life. A slight

Yoshihiko Kanda; Yoshiharu Kariya

2010-01-01

161

Low-cycle fatigue life of steel P92 under gradual loading  

NASA Astrophysics Data System (ADS)

The aim of the study was to determine low-cycle fatigue life characteristics of P92 steel used in the power unit components that work under the highest effort. Steel service life was determined in the tests for total fixed strain ??t ranges from 0.6 to 1.2 % and with application of two-stage sequence loading. Low-cycle fatigue tests were conducted at room temperature and at 550 °C on MTS-810 testing machine. The tests under sequence loading were carried out for two strain ranges: ??t = 0.6 and 1.2 %. Sinusoidal load cycles of a coefficient R = -1 were used. Low-cycle fatigue life characteristics were developed with consideration of loading sequence impact. It was found out the fatigue life of an element under sequence loading is strictly correlated with its history of strain, which determines the degree of material microstructure damage. Higher degree of steel damage was found in two-stage tests, in which the larger range of strain ??t = 1.2 % was used as the first one. Fractography analyses of scrap revealed the patterns of fatigue lines and bands typical for this process as well as numerous secondary cracks occurred to the boundaries of former austenite grains. Analytic method of predicting low-cycle fatigue life of an element under two-stage sequence loading is presented. For this purpose, an energy criterion for the material life developed for tests carried out in conditions of low-cycle fatigue was used.

Cie?la, M.; Junak, G.

2012-05-01

162

A fracture mechanics based fatigue life prediction for welded joints of square tubes  

Microsoft Academic Search

Square tubes of mild and low alloy steels are extensively used in vehicle structures and offshore platforms. Despite this fact the fatigue behaviour of welded nodes of these tubes is not sufficiently known, especially in thin sections.The paper presents the results of fatigue life predictions based on fracture mechanics, in non-load carrying T and also load carrying cruciform joints. The

J. M. Ferreira; A. H. Pereira; C. M. Branco

1995-01-01

163

Fatigue life prediction of welded cruciform joints using strain energy density factor approach  

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 analyzed by using the strain energy density factor (SEDF) approach. Load carrying cruciform joints were fabricated from ASTM 517 ‘F’ grade steel. Fatigue crack growth experiments were carried

V Balasubramanian; B Guha

2000-01-01

164

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

Microsoft Academic Search

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

M. R Urban

2003-01-01

165

The effect of holes quality on fatigue life of open hole  

Microsoft Academic Search

In this paper, a series of study were conducted on the effect of hole quality on the fatigue life of open holes in 2A12-T4 aircraft quality aluminum alloy. Four metrics that can define holes quality are analyzed. They are roughness, verticality, cylindricity and roundness. Firstly, open holes with different roughness were fatigue tested under constant amplitude remote tensile load and

J. Liu; X. J. Shao; Y. J. Liu; Z. F. Yue

2007-01-01

166

A fracture mechanics approach to thermal fatigue life prediction of solder joints  

Microsoft Academic Search

A life prediction approach for solder joints under thermal fatigue, based on fracture mechanics and assuming that the thermal fatigue crack propagation in solder joints is primarily controlled by the C* and the J Integrals, is presented. The approach is applied to model experiments in which surface mounted electronic components were mounted on substrates with eutectic Pb\\/Sn solder joints and

Yi-Hsin Pao

1992-01-01

167

Effects of shot peening treatment on very long life fatigue property in ductile cast irons  

Microsoft Academic Search

Rotating bending fatigue tests that covered very long life region (up to over 108), were carried out on specimens of three kinds of ductile cast iron (austempered one, ADI, pearlitic one, PDI and ferrite pearlitic one, FPDI) with shot peening (SP) treatment. Influences of the SP treatment on fracture morphology and fatigue property were investigated. It is expected that the

Yasuo Ochi; Takusaburo Hosoya; Kiyotaka Masaki; Takashi Matsumura; Takeshi Sekino

2001-01-01

168

Finite Element Based Solder Joint Fatigue Life Predictions for MLPQ Packages  

Microsoft Academic Search

The solder joint fatigue life of flip chips and ball grid array packages has been extensively studied and published. However, there are only a few published papers available on the solder joint reliability of a non-leaded, surface mounted package such as the MLPQ (Micro Leadframe Quad Package). In this paper, a non linear Darveaux's solder joint fatigue model has been

Y. S. Ng; S. K. Chin; Rosazlan

2008-01-01

169

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

Microsoft Academic Search

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

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

1999-01-01

170

Investigations on the evaluation of the residual fatigue life-time in austenitic stainless steels  

Microsoft Academic Search

In view of plant life extension of nuclear power plants, many efforts are taken to assess the structural integrity of components affected by service, such as the components of the primary circuit, but also the auxiliary and safety systems. Frequently damage in components during operation is caused by cyclic loading, due to mechanical or thermal fatigue. Fatigue damage often involves

F De Backer; V Schoss; G Maussner

2001-01-01

171

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

172

Acoustic fatigue life prediction for nonlinear structures with multiple resonant modes  

Microsoft Academic Search

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

R. N. Miles

1992-01-01

173

Fatigue life prediction based on crack propagation and acoustic emission count rates  

Microsoft Academic Search

The use of the acoustic emission technique to monitor fatigue crack propagation in steel compact tension specimens and T-section girders is described. Based on the correlations between crack propagation rates, acoustic emission count rates and stress intensity factor range procedures are suggested for predicting remaining fatigue life. It is anticipated that the experimental techniques and theoretical procedures developed will eventually

T. M. Roberts; M. Talebzadeh

2003-01-01

174

The impact of hemoglobin levels on fatigue and quality of life in cancer patients  

Microsoft Academic Search

Background: Although fatigue is a commonly reported symptom in cancer patients its etiology is still poorly understood. The objective of the present study was to investigate the relationship between hemoglobin (Hb) levels and the subjective experience of fatigue and quality of life in cancer patients with mild or no anemia undergoing chemotherapy. Patients and methods: Sixty-eight cancer patients (25 colorectal,

B. Holzner; G. Kemmler; R. Greil; M. Kopp; A. Zeimet; M. Raderer; M. Hejna; S. Zöchbauer; G. Krajnik; W. W. Fleischhacker; B. Sperner-Unterweger

2002-01-01

175

Flight Test of a Composite Multi-tubular Spar Main Rotor Blade on the AH-1G Helicopter, Volume I. Materials, Design and Test.  

National Technical Information Service (NTIS)

The objectives of this program were to design a composite main rotor blade in the multi-tubular spar configuration to be directly interchangeable (in pairs) with the production metal (540) blades on the AH-1G helicopter, have increased fatigue life, invul...

R. E. Head

1977-01-01

176

Flight Test of a Composite Multi-Tubular Spar Main Rotor Blade on the AH-1G Helicopter. Volume II. Cost Estimates and Process Specifications.  

National Technical Information Service (NTIS)

The objectives of this program were to design a composite main rotor blade in the multi-tubular spar configuration to be directly interchangeable (in pairs) with the production metal (540) blades on the AH-1G helicopter, have increased fatigue life, invul...

R. E. Head

1977-01-01

177

Prediction of fatigue crack growth and residual life using an exponential model: Part II (mode-I overload induced retardation)  

Microsoft Academic Search

Almost all load bearing components usually experience variable amplitude loading (VAL) rather than constant amplitude loading (CAL) during their service lives. A single overload cycle introduced in a con- stant amplitude fatigue loading retards fatigue crack growth and increases residual fatigue life. Although many models have been proposed on this subject, but life prediction under these complex situations is still

J. R. Mohanty; B. B. Verm; P. K. Ray

2008-01-01

178

Fatigue Life Assessment for Lead-Free Solder Joints  

Microsoft Academic Search

\\u000a The authors will indicate the basic reliability problems associated with use of lead-free solder joints. They investigated\\u000a the thermal fatigue reliability of lead-free solder joints, and focused their attention on the formation of the intermetallic\\u000a compound and its effect on the initiation and propagation of the fatigue cracks. An isothermal fatigue test method was used\\u000a to improve the efficiency of

Masaki Shiratori; Qiang Yu

179

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

180

Fatigue Life Evaluation of Changeable Message Sign Structures. Volume 2. Retrofitted Specimens.  

National Technical Information Service (NTIS)

This report outlines the research program undertaken at the Earthquake Engineering Research Center (EERC) to investigate the fatigue life of retrofitted Changeable Message Sign (CMS) structure posts. Following the failure of one CMS structure in Southern ...

J. W. Chavez A. S. Gilani A. S. Whittaker

1997-01-01

181

Finite Element Mesh Generation and Analysis of Solder Joints for Fatigue Life Predictions.  

National Technical Information Service (NTIS)

Tools for fatigue life prediction of solder joints are developed. This report consists of two parts. In Part One, the creep and plastic deformations stored in a solder joint are calculated by implementing appropriate plastic and creep constitutive models ...

N. H. Paydar Y. Tong H. U. Akay W. Boehmer

1993-01-01

182

Estimation for a Family of Life Distributions with Applications to Fatigue.  

National Technical Information Service (NTIS)

The estimation problem is studied for a new two-parameter family of life length distributions which has been previously derived from a model of fatigue crack growth. Maximum likelihood estimates of both parameters are obtained and iterative computing proc...

S. C. Saunders Z. W. Birnbaum

1968-01-01

183

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

184

Stress and Fatigue Life Modeling of Cannon Breech Closures Including Effects of Material Strength and Residual Stress.  

National Technical Information Service (NTIS)

Laboratory fatigue life results are summarized from several test series of high-strength steel cannon breech closure assemblies pressurized by rapid application of hydraulic oil. The tests were performed to determine safe fatigue lives of high-pressure co...

J. H. Underwood M. J. Glennon

2000-01-01

185

A study of creep-fatigue life prediction using an artificial neural network  

Microsoft Academic Search

In this study, using AISI 316 stainless steel, creep-fatigue tests were carried out under various test conditions (different\\u000a total strain ranges and hold times) to verify the applicability of the artificial neural network method to creep-fatigue life\\u000a prediction. Life prediction was also made by the modified Coffin-Manson method and the modified Ostegren method using 21 data\\u000a points out of a

Young Il Kwon; Byeong Soo Lim

2001-01-01

186

Load Path Sensitivity and Fatigue Life Estimation of 30CrNiMo8HH  

Microsoft Academic Search

A set of strain-controlled biaxial proportional and non-proportional tests were conducted on solid and tubular specimens of 30CrNiMo8HH steel. The effect of the phase angle on fatigue life was studied. This effect becomes noticeable when applying a 90° out-of-phase loading, reducing the fatigue life by a factor up to 5. It has been shown that the material has no additional

M. Noban; H. Jahed; E. Ibrahim; A. Ince

187

Study on Creep-Fatigue Life Prediction Using Simple High Temperature Low Cycle Fatigue Testing Machines.  

National Technical Information Service (NTIS)

The authors developed a simple high temperature low cycle fatigue testing machine for long time creep-fatigue tests and carried out experiments on two kinds of CrMoV steel forgings and 304 stainless steel. The experimental results indicate: (1) The data o...

T. Endo T. Sakon

1983-01-01

188

A new fracture mechanics method to predict the fatigue life of welded cruciform joints  

Microsoft Academic Search

The fatigue life of MIG welded cruciform joint failing from root (LOP) region was successfully predicted using new fracture mechanics equations. These equations were developed by combining Paris' law and ?Ki-endurance equation and incorporating an integral factor (Ip) obtained by integrating Paris' equation. In the numerical formulation of the equation, the initiation life (Ni) and propagation life (Np) of the

Bimalendu Guha

1995-01-01

189

Method for multiaxial fatigue life prediction using energy approaches.  

National Technical Information Service (NTIS)

Fatigue criteria based on the concept of damage energy have been proposed and evaluated with experimental fatigue data generated under uniaxial as well as biaxial loading conditions. Most of the energy-based methods utilize plastic energy of stress-strain...

K. C. Liu

1991-01-01

190

Rolling-Element Fatigue Life of Silicon Nitride Balls.  

National Technical Information Service (NTIS)

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 ...

R. J. Parker E. V. Zaretsky

1974-01-01

191

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

Microsoft Academic Search

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

D. T. Rusk; W. Hoppe

2009-01-01

192

LCF (Low Cycle Fatigue) and Crack Growth Rate of Turbine Blade Alloys in Hydrogen and Hydrogen/Steam Environments.  

National Technical Information Service (NTIS)

The low cycle fatigue (LCF) and fatigue crack growth testing of MAR-M246+Hf and PWA 1480 in high pressure hydrogen and hydrogen enriched steam at elevated temperatures are described. The PWA 1480 single crystal exhibited the best properties overall, compa...

B. A. Cowles D. P. Deluca J. R. Warren F. K. Haake

1986-01-01

193

Evaluation of tilting disc valves after fatigue life testing: preliminary results within a comparison program.  

PubMed

A fatigue life test, by accelerating the beat rate, simulates several years of virtual life of a prosthetic heart valve in a short period of time. The correlation between the in vivo life of a valve and in vitro testing expectations is as yet not well established, but reproducible test conditions yield precious information about wear and failure. The paper reports a qualitative analysis of mechanical valve wear as part of a comparison program designed to investigate the significance of fatigue testing with the ultimate aim of defining standard guidelines for these type of tests. Two tilting disc valves (29 mm) were subjected to 16 years of fatigue life simulated by means of a Rowan Ash fatigue tester (accelerated rate of 1,200 bpm). Fatigue-induced effects on valve disc and ring surfaces were observed under a monitor microscope to identify wear sites and patterns. A high speed cinematographic system was used to investigate the mechanisms responsible for the wear (wear modes). Valve closure was inspected at a 6,000 frame/s rate. Because of disc rotation during the tilting movement, the points of contact between disc and ring are distributed all around the disc edge but focally on the ring. On both sides of the disc, the surfaces present ring-like concentric grooves. After 16 years of fatigue life the valves showed neither severe wear nor alteration of their fluidodynamic behavior in the pulsatile flow test. PMID:8687299

Barbaro, V; Boccanera, G; Daniele, C; Grigioni, M; Palombo, A

1995-09-01

194

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

195

Effect of Frequency, Environment, and Temperature on Fatigue Behavior of E319 Cast Aluminum Alloy: Stress-Controlled Fatigue Life Response  

NASA Astrophysics Data System (ADS)

The fatigue stress-life (S-N) behavior of E319 cast aluminum alloy was studied by using both ultrasonic and conventional fatigue techniques in order to understand the potential effect of frequency on fatigue behavior of cast aluminum alloys. It was observed that, at the investigated temperature (20 °C, 150 °C, and 250 °C), fatigue life in air at 20 kHz is 5 to 10 times longer than that at 75 Hz. The difference in fatigue life between 20 kHz and 75 Hz is attributable to an environmental effect on fatigue crack growth rate. The effect of frequency, environment, and temperature on S-N behavior of E319 cast aluminum alloy can be predicted by use of a general version of a modified environmental superposition model. Environmental effects need to be considered when ultrasonic fatigue is used for estimating fatigue lives of aluminum alloys that are under cyclic loading at lower frequencies in service. It is possible to extrapolate ultrasonic fatigue data to conventional fatigue behavior for an E319 cast aluminum alloy based on the environmental superposition model.

Zhu, X.; Jones, J. W.; Allison, J. E.

2008-11-01

196

Cyclic Inelastic Deformation and Fatigue Life Behaviour of Notched Components.  

National Technical Information Service (NTIS)

Cyclic inelastic deformation response and fatigue notch factor are presented and discussed for two metals of contrasting stress-strain behaviour (an aluminum alloy 2024-T351 and a mild steel SAE 1015). Thin circular or elliptical notched plates fabricated...

B. N. Leis C. V. B. Gowda T. H. Topper

1974-01-01

197

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

PubMed

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

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

2011-05-18

198

Fatigue Life Prediction of Rolled AZ31 Magnesium Alloy Using AN Energy-Based Model  

NASA Astrophysics Data System (ADS)

Fatigue behavior of rolled AZ31 magnesium alloy, which shows an anisotropic deformation behavior due to the direction dependent formation of deformation twins, was investigated by carrying out stress and strain controlled fatigue tests. The anisotropy in deformation behavior introduced asymmetric stress-strain hysteresis hoops, which make it difficult to use common fatigue life prediction models, such as stress and strain-based models, and induced mean stress and/or strain even under fully-reversed conditions; the tensile mean stress and strain were found to have a harmful effect on the fatigue resistance. An energy-based model was used to describe the fatigue life behavior as strain energy density was stabilized at the early stage of fatigue life and nearly invariant through entire life. To account for the mean stress and strain effects, an elastic energy related to the mean stress and a plastic strain energy consumed by the mean strain were appropriately considered in the model. The results showed that there is good agreement between the prediction and the experimental data.

Park, Sung Hyuk; Hong, Seong-Gu; Lee, Byoung Ho; Lee, Chong Soo

199

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

200

Fatigue  

Microsoft Academic Search

Fatigue is a common complaint in patients with Parkinson’s 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

201

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

202

Development of a low-cycle fatigue life curve for 80In15Pb5Ag  

NASA Astrophysics Data System (ADS)

The purpose of this study is to develop a methodology to predict the low-cycle (large strain—from 0.1 to 0.35 strain) fatigue life of solders subject to thermal cycling. Solders are commonly used in electronic assemblies. Using thermal fatigue data measured for 80In15Pb5Ag, a low-cycle fatigue curve for 80In15Pb5Ag solder subject to thermal cycling was developed. Specifically a Coffin-Manson relationship was derived for the solder, with a high degree of correlation (see Table I), for four different failure criteria, defined in the body of the paper. This relationship, together with calculated strains in the solder joint, allows the low-cycle fatigue life of the solder joint to be predicted.

Edwards, L. K.; Nixon, W. A.; Lakes, R. S.

2000-09-01

203

Effect of shot peening on residual stress and fatigue life of a spring steel  

NASA Astrophysics Data System (ADS)

This study describes shot peening effects such as shot hardness, shot size and shot projection pressure, on the residual stress distribution and fatigue life in reversed torsion of a 60SC7 spring steel. There appears to be a correlation between the fatigue strength and the area under the residual stress distribution curve. The biggest shot shows the best fatigue life improvement. However, for a shorter time of shot peening, small hard shot showed the best performance. Moreover, the superficial residual stresses and the amount of work hardening (characterised by the width of the X-ray diffraction line) do not remain stable during fatigue cycling. Indeed they decrease and their reduction rate is a function of the cyclic stress level and an inverse function of the depth of the plastically deformed surface layer.

Farrahi, G. H.; Lebrun, J. L.; Couratin, D.

1995-02-01

204

Fatigue life assessment of load-carrying fillet-welded cruciform joints inclined to uniaxial cyclic loading  

Microsoft Academic Search

This study examines, the relationship between the direction of an applied stress cycle and the fatigue behaviour of load-carrying fillet-welded cruciform joints with weld root cracks, and presents the fatigue life assessment of the joints. Fatigue tests were performed on four sets of cruciform joints inclined at an angle of 0, 15, 30, or 45° to the normal direction of

In-Tae Kim; Shigenobu Kainuma

2005-01-01

205

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

206

Fatigue life prediction of gas metal arc welded crucifrom joints of AA7075 aluminium alloy failing from root region  

Microsoft Academic Search

Empirical relationship was developed to predict the fatigue life of gas metal arc welded (GMAW) cruciform joints failing from root region. High strength, age hardenable aluminium alloy of AA7075-T6 grade was used as the base material. The design of experiments concept was used to optimize the required number of fatigue testing experiments. Fatigue experiment was conducted in a servo hydraulic

B. RAVINDRA; T. SENTHIL KUMAR; V. BALASUBRAMANIAN

2011-01-01

207

An evaluation of shot peening, residual stress and stress relaxation on the fatigue life of AISI 4340 steel  

Microsoft Academic Search

Shot peening is a method widely used to improve the fatigue strength of materials, through the creation of a compressive residual stress field (CRSF) in their surface layers. In the present research the gain in fatigue life of AISI 4340 steel, used in landing gear, is evaluated under four shot peening conditions. Rotating bending fatigue tests were conducted and the

M. A. S. Torres; H. J. C. Voorwald

2002-01-01

208

Effect of Proportional Overloading on the Life of Low Cycle Fatigue Crack Initiation of Strain-Concentrated Member.  

National Technical Information Service (NTIS)

Investigation of the effect of proportional overloading on the life of fatigue crack initiation of low cycle symmetrical tension-compression fatigue under large peak load and tension-tension fatigue under small peak load is carried out. From the experimen...

M. H. Li Z. J. Wang

1988-01-01

209

The longitudinal relationship of hemoglobin, fatigue and quality of life in anemic cancer patients: results from five randomized clinical trials  

Microsoft Academic Search

Background: Anemia is common in cancer and has been associated with fatigue and reduced health-related quality of life (HRQOL). We report the association between hemoglobin and fatigue and the impact of reducing fatigue on several domains of HRQOL. Patients and methods: These analyses were based on five randomized trials. Patients completed the Func- tional Assessment of Cancer Therapy (FACT) Anemia

D. Cella; J. Kallich; A. McDermott; X. Xu

2004-01-01

210

Effect of solder joint geometry on the predicted fatigue life of BGA solder joints  

Microsoft Academic Search

A general computational approach to determine the effect of solder joint shape on the fatigue life is presented. Using the integrated matrix creep failure metric, a number of cases are considered wherein the solder volume, standoff height, or both, are varied and the joint life computed. Both volumetric and interface averaging of the matrix creep are considered. For non-mask defined

Ira R. Holub; James M. Pitarresi; Timothy J. Singler

1996-01-01

211

The Effect of Three Mineral Base Oils on Roller Bearing Fatigue Life  

Microsoft Academic Search

The effect of three mineral base oils on roller bearing fatigue life has been studied. Life performance tests were conducted, using a specially controlled group of 45-mm bore cylindrical roller bearings. The results indicate that base oil stock affects bearing performance. Of the highly naphthenic, naphthenic, and paraffinic mineral oils studied, bearings lubricated with the latter achieved superior lives. The

Irwin Koved

1966-01-01

212

Fatigue Tests Of Cracked Reinforced Concrete Slabs For Estimating The Service Life Of Composite Bridge Decks  

Microsoft Academic Search

A large-scale experimental program was co-sponsored by the main French owners of composite bridges in order to estimate the fatigue service life of cracked decks, as it occurs due to restrained shrinkage of concrete. The fatigue tests were carried out at the Structures Laboratory of LCPC on six transversally cracked reinforced concrete slabs largely equipped with gauges and sensors. 1.4

François Toutlemonde; Guillaume Ranc

2001-01-01

213

Fatigue life and mechanical behaviors of bearing steel by nitrogen plasma immersion ion implantation  

Microsoft Academic Search

Rolling contact fatigue (RCF) performance and mechanical characteristics of nitrogen plasma immersion ion implantation (PIII) on AISI52100 bearing steel surface has been investigated using a conventional three ball-on-rod rig. Testing investigations include optical microscopy (OM), friction and wear behavior, rolling contact fatigue life, and nano-indentation measurements. Results indicate that the rolling elements failed at the surface or near-surface layer. Moreover,

Hongxi Liu; Baoyin Tang; Langping Wang; Xiaofeng Wang; Bo Jiang

2007-01-01

214

A damage function used for prediction of low cyclic fatigue life  

Microsoft Academic Search

In this paper, the cyclic plastic strain energy is acted as damage variable and its mathematical model of transient response\\u000a is established. The nonlinear fatigue damage function is given by means of the damage mechanical method. The formula used\\u000a for prediction of low cyclic fatigue life is obtained from this damage function which takes into acount the cyclic relativity\\u000a of

Jiang Fengchun; Liu Ruitang; Liu Diankui

1999-01-01

215

High-temperature fatigue life of type 316 stainless steel containing irradiation induced helium  

Microsoft Academic Search

Specimens of 20%-cold-worked AISI type 316 stainless steel were irradiated in the High Flux Isotope Reactor (HFIR) at 550°C to a maximum damage level of 15 dpa and a transmutation produced helium level of 820 at. ppM. Fully reversed strain controlled fatigue tests were performed in a vacuum at 550°C. No significant effect of the irradiation on low-cycle fatigue life

M. L. Grossbeck; K. C. Liu

1981-01-01

216

A mechanistic model for fatigue life prediction of solder joints for electronic packages  

Microsoft Academic Search

A mechanistic model for fatigue life prediction of solder joints has been developed. The model utilized fracture mechanics theory using J-integrals and assumed the crack propagation determines the fatigue lifetime of solder joints. The model is expressed in terms of crack length ‘?’, platic strain range ??P and temperature T. Constitutive relation and crack propagation of 62Sn-36Pb-2Ag solder were tested

Soon-Bok Lee; Jin-Ki Kim

1997-01-01

217

OPTIMIZATION OF SOLDER JOINT FATIGUE LIFE USING PRODUCT MODEL-BASED ANALYSIS MODELS  

Microsoft Academic Search

Product Model-Based Analysis Models (PBAMs) have been presented as highly automated analysis modules for designer usage. Previous examples such as solder joint fatigue PBAMs have shown how explicit design-analysis associativity linkages enable seamless interfaces to solution tools (e.g., finite element analysis systems). These examples focused on using PBAMs for design verification, where a criteria such as fatigue life was checked

Selçuk Cimtalay; Russell S. Peak; Robert E. Fulton

218

Observation of static strength and fatigue life of repaired graphite\\/epoxy using a tensile coupon  

Microsoft Academic Search

The static strength and fatigue life of repaired graphite\\/epoxy laminates was observed using a tensile coupon. The lay-up of investigated laminates was [0°\\/±45°\\/90°]s. Static strength was measured from the specimens prepared by various repair techniques such as cosmetic treatment, precured-single patch, precured-double patch and cure-in-place patch methods. The strength was recovered to the extent of 60-70% of unnotched case. Fatigue

J. W. Choi; W. Hwang; H. C. Park; K. S. Han

1999-01-01

219

Finite element, critical-plane, fatigue life prediction of simple and complex contact configurations  

Microsoft Academic Search

A finite element based critical plane approach is developed incorporating the Smith–Watson–Topper (SWT) multiaxial fatigue criterion. The approach is applied to a cylinder-on-flat fretting contact to predict failure locations, crack orientations and component lifetimes. The cylinder-on-flat conditions are based on a published study on contact size effects in fretting fatigue life prediction, in which volume-averaging of theoretically predicted contact stress

Wei Siang Sum; Edward J. Williams; Sean B. Leen

2005-01-01

220

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

Microsoft Academic Search

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

S. Maekawa

1982-01-01

221

Fracture-mechanics concept offers models to help calculate fatigue life in drillpipe  

SciTech Connect

This paper is the second of two articles on drillpipe fatigue analysis, and discusses the use of concepts set forth in part 1 to address the problem of calculating fatigue life of drillpipe under known operating conditions. The study tacitly accepts the presence of crack-like defects of various types in the pipe even in the as-received condition. The paper attempts to characterize the most severe surface cracks in terms of their dimensions and location by non-destructive examination.

Kral, E.; Newlin, L.; Quan, S.S.; Sengupta, P.K.

1984-08-13

222

Monitoring fatigue life in concrete bridge deck slabs  

NASA Astrophysics Data System (ADS)

Concrete bridge deck slabs are the most common form of bridge deck construction in short and medium span bridge structures in North America. Understanding and monitoring the condition of these bridge decks is an important component of a bridge management strategy. Progressive deterioration due to fatigue occurs in concrete decks due to the large number of cycles of heavy wheels loads and normally manifests itself as the progressive growth of cracks in the top and underside of the deck slab. While some laboratory fatigue testing programs have been reported in the literature, there is very little information on proposed techniques to monitor this phenomenon. This paper discusses the issue of how fatigue monitoring may be included as part of a structural health monitoring system for bridges. The paper draws upon previously published experimental results to identify the main characteristics of fatigue damage and structural response for concrete bridge deck slabs. Several means of monitoring this response are then evaluated and monitoring methods are proposed. A specific field structure monitoring program is used to illustrate the application of the concept. The cases study examines several sensor systems and discusses the various limitations and needs in this area. The results are of interest to both the general area of structural health monitoring as well as fatigue monitoring specifically.

Newhook, J.; Limaye, V.

2007-05-01

223

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

224

Accounting for inclusions and voids allows the prediction of tensile fatigue life of bone cement.  

PubMed

Previous attempts by researchers to predict the fatigue behavior of bone cement have been capable of predicting the location of final failure in complex geometries but incapable of predicting cement fatigue life to the right order of magnitude of loading cycles. This has been attributed to a failure to model the internal defects present in bone cement and their associated stress singularities. In this study, dog-bone-shaped specimens of bone cement were micro-computed-tomography (microCT) scanned to generate computational finite element (FE) models before uniaxial tensile fatigue testing. Acoustic emission (AE) monitoring was used to locate damage events in real time during tensile fatigue tests and to facilitate a comparison with the damage predicted in FE simulations of the same tests. By tracking both acoustic emissions and predicted damage back to microCT scans, barium sulfate (BaSO(4)) agglomerates were found not to be significant in determining fatigue life (p=0.0604) of specimens. Both the experimental and numerical studies showed that diffuse damage occurred throughout the gauge length. A good linear correlation (R(2)=0.70, p=0.0252) was found between the experimental and the predicted tensile fatigue life. Although the FE models were not always able to predict the correct failure location, damage was predicted in simulations at areas identified as experiencing damage using AE monitoring. PMID:19388777

Coultrup, Oliver J; Browne, Martin; Hunt, Christopher; Taylor, Mark

2009-05-01

225

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

226

Condition monitoring techniques for composite wind turbine blades  

NASA Astrophysics Data System (ADS)

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

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

227

Estimate the thermomechanical fatigue life of two chip scale packages  

Microsoft Academic Search

In this paper, two three dimensional finite element models were developed to numerically compute the stress, total strain, plastic strain and the cumulative plastic strain of the solder joints in a microBGA and a chip scale package (CSP) under temperature cycling. These stress and strain values, along with the results of solder fatigue tests, were then used to predict the

Qizhou Yaol; Jianmin Qu; S. X. Wu

1999-01-01

228

Fatigue Life Estimation under Cumulative Cyclic Loading Conditions.  

National Technical Information Service (NTIS)

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 compres...

Kalluri M. A. McGaw G. R. Halford

1999-01-01

229

Predicting random high-cycle fatigue life with finite elements  

Microsoft Academic Search

This paper extends the classical theory of random fatigue to multiaxial stress fields, using a quadratic criterion. An equivalent uniaxial random process is constructed by combining the power spectral densities of the normal and tangential stresses according to the von Mises criterion. This process, that we call the von Mises stress, is used to evaluate the damage with a uniaxial

Andre Preumont; Vincent Piefort

1994-01-01

230

Surface Crack Growth Path and Fatigue Life Prediction Due to Repeated Rolling/Sliding Contact  

NASA Astrophysics Data System (ADS)

This paper deals with the surface crack growth path description and the fatigue life prediction due to repeated rolling/sliding contact on the elastic half-space, accompanied by frictional heat generation and crack-face pressure. The stress intensity factors are analyzed for the surface crack which is kinked in multiple times from the inclined initial main crack. The rolling/sliding contact is simulated as a Hertzian contact pressure and a frictional load with heat generation, moving with constant velocity over the surface of the half-space. Applying the maximum energy release rate criterion to each kinked angle, the crack growth path can be described, and employing a mixed mode fatigue crack growth law, the associated fatigue life also can be predicted. The effects of frictional coefficient, slide/roll ratio and crack-face pressure on the crack growth path and associated life are considered for a high carbon-chromium bearing steel (AISI52100).

Goshima, Takahito; Ishihara, Sotomi; Shimizu, Masayoshi; Yoshida, Hirokazu; Tsuchida, Yuji

231

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.

232

A simplified method for creep-fatigue life prediction for structures subjected to thermal loadings  

Microsoft Academic Search

A simplified creep-fatigue failure prevention-life prediction method (TTSDS) for pressure vessels and pipings subjected to thermal expansion-thermal transient loadings is presented. The method was constructed based on numerous SUS304 material-structure test data, and incorporates a linear cumulative damage rule with an instrinsic life reduction factor. When the TTSDS method was applied using no safety factors, good life predictions for piping

Katsumi Watashi

1995-01-01

233

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

SciTech Connect

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

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

1984-09-01

234

Fatigue  

MedlinePLUS

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

235

Cyclic fatigue life of SiAlON at room temperature  

SciTech Connect

The fatigue life of a SiAlON material was evaluated at room temperature in a rotating beam tester. No significant effect of stress level was determined. Failure origins were associated with processing and powder impurities, and consisted primarily of porosity and inclusions in the bulk material. The experimental design was such that a sufficient number of failures at each stress level would produce a good estimate of the distribution, and a test of the influence of a high stress level on fatigue life could be achieved.

Whalen, T.J.; Baer, J.R.; Trela, W.; Govila, R.K. [Ford Motor Co., Dearborn, MI (United States). Scientific Research Lab.

1996-03-01

236

Fatigue-life prediction of SiC particulate reinforced aluminum alloy 6061 matrix composite using AE stress delay concept  

Microsoft Academic Search

A study of the residual fatigue life prediction of 6061-T6 aluminum matrix composite reinforced with 15 vol % SiC particulates (SiCp) by using the acoustic emission technique and the stress delay concept has been carried out. Fatigue damages corresponding to 40, 60 and 80% of total fatigue life were stimulated at a cyclic stress amplitude. The specimens with and without

D. Shan; H. Nayeb-Hashemi

1999-01-01

237

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

SciTech Connect

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

Carek, G.A.

1987-04-01

238

Structural health monitoring of composite wind blades by fiber bragg grating  

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

239

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

NASA Astrophysics Data System (ADS)

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; Sokolov, Mikhail A.; Sham, Sam; Erdman, Donald L., III; Busby, Jeremy T.; Mo, Kun; Stubbins, James F.

2013-01-01

240

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

2013-01-01

241

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

242

Statistical models for estimating fatigue strain-life behavior of pressure boundary materials in light water reactor environments  

Microsoft Academic Search

The existing fatigue strain versus life (S-N) data for materials used in 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 have been used to estimate the probability of initiating

Jeffrey M Keisler; Omesh K Chopra; William J Shack

1996-01-01

243

Improvement of fatigue life of solder joints by thickness control of solder with wire bump technique [power modules  

Microsoft Academic Search

The solder joint between the ceramic substrate and the copper base plate is of critical importance to the reliability of the power module. An improvement of the fatigue life of the solder joint is essential to achieve a reliable module. The development of a new assembly technology for the power module improves the fatigue life of solder joints between the

Kenichi HAYASHI; Goro IZUTA; Kohei MURAKAMI; Yasumi UEGAI; H. Takao

2002-01-01

244

Fatigue life prediction analysis of surface cracked straight pipes  

Microsoft Academic Search

In piping components, for the stability assessment it is important to calculate the point of initiation of the crack and to\\u000a monitor the subsequent crack propagation behaviour. The objective of this paper is to use the finite element method backed\\u000a up with experimental results to determine the crack initiation stage and to subsequently predict the crack propagation behaviour\\u000a under fatigue

Sanjeev Saxena; N. Ramakrishnan; J. S. Chouhan

2009-01-01

245

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

246

Fatigue-life prediction methodology using small-crack theory  

Microsoft Academic Search

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 (?Keff) under constant-amplitude loading. Some modifications to the ?Keff

J. C. Newman; E. P. Phillips; M. H. Swain

1999-01-01

247

Statistical analysis of fatigue strain-life data for carbon and low-alloy steels  

SciTech Connect

The existing fatigue strain vs. life (S-N) data, foreign and domestic, for carbon and low-alloy steels used in the construction of nuclear power plant components have been compiled and categorized according to material, loading, and environmental conditions. A statistical model has been developed for estimating the effects of the various test conditions on fatigue life. 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 applying design margins for size, geometry, and surface finish to crack initiation curves estimated from the model. The significance of the effect of environment on the current Code design curve and on the proposed interim design curves for carbon and low-alloy steels presented in NUREG/CR-5999 is discussed.

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

1994-08-01

248

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

249

Fatigue behavior of 6063 aluminum alloy extrusions for wind-turbine applications  

SciTech Connect

The fatigue behavior of a 6063 aluminum alloy used in the Vertical Axis Wind Turbine (VAWT) blade extrusions was investigated under a variety of cyclic loading conditions and with different specimen geometries in order to examine the mechanisms of fatigue crack initiation and crack growth, and to provide fatigue data for use in life prediction models. The effect of open holes on fatigue crack initiation and crack growth, and on the S-N curves were investigated with plate bending. Fatigue life in plane bending was controlled by crack propagation. Hole preparation by drilling, or drilling and reaming were found to produce equivalent crack initiation behavior, and overall fatigue lives. Fatigue crack growth rates, including near-threshold behavior, were measured under LEFM conditions with compact tension specimens as a function of: heat treatment, crack plane orientation with respect to the extrusion direction, and R ratio. Low-cycle fatigue behavior and cyclic material properties were examined, and compared on the basis of material condition for extruded VAWT blade material, re-heat treated blade material and commercial 6063-T5 extruded rod. Low cyclic ductility values were observed in the extruded blade material.

Warren, A.S.

1990-01-01

250

CAE enabled methodology for die fatigue life analysis and improvement  

Microsoft Academic Search

Die performance and its service life are a non-trivial issue in metal-forming industry due to three overriding issues in this industry cluster: productivity, cost and quality are mainly dependent on it. Many factors in die life cycle from design and fabrication to downstream service all affect die performance and its service life. These factors could include die design and structure,

K. K. Tong; M. S. Yong; M. W. Fu; T. Muramatsu; C. S. Goh; S. X. Zhang

2005-01-01

251

Comparison of fatigue life for T and cruciform welded joints with different combinations of geometrical parameters  

Microsoft Academic Search

The fatigue life for T and cruciform welded joints containing different extents of lack of root penetration was calculated for different combinations of geometrical parameters, including thicknesses up to 45 mm, by integration of the Paris law and use of stress intensity factor solutions calculated previously. The effect of attachment and main plate thickness, weld leg length and initial lack

A. Khodadad Motarjemi; A. H Kokabi; F. M Burdekin

2000-01-01

252

Fatigue life prediction of load carrying cruciform joints of pressure vessel steel by statistical tools  

Microsoft Academic Search

Mathematical models have been developed to predict the fatigue life of shielded metal arc welded (SMAW) and flux cored arc welded (FCAW) cruciform joints failing from root and toe regions. High strength, quenched and tempered steel (ASTM 517 `F' grade) has been used as the base material throughout the investigation. The design of experiments (DoE) concept has been used to

V. Balasubramanian; B. Guha

2004-01-01

253

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

254

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

ERIC Educational Resources Information Center

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

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

2007-01-01

255

Power Amplifier (PA) Transistors Fatigue Life Prediction under ThermoMechanical Cyclic Loading  

Microsoft Academic Search

In this paper, a simulation procedure was established for the fatigue life prediction of transistor assembly system under thermo-mechanical cyclic loading condition. By combining non-linear finite element (FE) methodology and test data, the failure mechanisms of transistor assembly system in response to thermal cyclic loading condition were investigated. Anand material constitutive model was adopted to describe the behavior of solder

Jianjun Wang; Weiqun Peng; Wei Ren

2006-01-01

256

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

NASA Astrophysics Data System (ADS)

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

Cardick, Arthur W.; Pike, Vera J.

1994-09-01

257

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

258

Evaluation of Creep-Fatigue Life by Fraction of Cavity Area  

Microsoft Academic Search

The components of power plant such as main steam pipe and gas turbines are operated under static and cyclic load conditions. As the period of static load increases, the service life of these components decreases. Generally, the increase of cyclic load results in fatigue damage and the increase of static load period results in the metallurgical degradation by the effect

Bumjoon Kim; Byeongsoo Lim

2006-01-01

259

Effect of vibration loading on the fatigue life of part-through notched pipe  

Microsoft Academic Search

A systematic experimental and analytical study has been carried out to investigate the effect of vibration loading on the fatigue life of the piping components. Three Point bend (TPB) specimens machined from the actual pipe have been used for the evaluation of Paris constants by carrying out the experiments under vibration + cyclic and cyclic loading as per the ASTM Standard E647.

Rahul Mittal; P. K. Singh; D. M. Pukazhendi; V. Bhasin; K. K. Vaze; A. K. Ghosh

2011-01-01

260

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

National Technical Information Service (NTIS)

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 fo...

R. A. Everett

2004-01-01

261

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

Microsoft Academic Search

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

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

2008-01-01

262

State of the ART Report on Fatigue Life Evaluation of Notched Components and Welded Joints.  

National Technical Information Service (NTIS)

The evaluation of the stress intensity factor (KI) of a semieliptical surface crack initiated at a notch is discussed. The state-of-the-art of fatigue life estimates of notched components, and information on semielliptical surface cracks are reviewed. Cra...

M. Skorupa J. Prij

1985-01-01

263

CORR Insights: Locking buttons increase fatigue life of locking plates in a segmental bone defect model.  

PubMed

This CORR Insights™ is a commentary on the article "Locking Buttons Increase Fatigue Life of Locking Plates in a Segmental Bone Defect Model" by Tompkins et al. available at DOI 10.1007/s11999-012-2664-1 . PMID:23242826

Schnaser, Erik; Vallier, Heather

2012-12-14

264

A cohesive zone model for low cycle fatigue life prediction of solder joints  

Microsoft Academic Search

A cohesive zone model is proposed in this paper in an effort to predict the low cycle fatigue life of solder joints plastically deformed under cyclic loading. Damage mechanics is incorporated into the cohesive law to account for the gradual loss of stiffness and strength of solder materials under cyclic loading. The damage evolution law is assumed to be a

Q. D Yang; D. J Shim; S. M Spearing

2004-01-01

265

A new design-for-reliability approach to thermal fatigue life prediction of leadless solder joints  

Microsoft Academic Search

Summary form only given. While a tremendous amount of work has been done in leadless solder joint reliability, the detailed thermal fatigue failure mechanisms and their relations with key parameters, e.g., solder fillet, inner end geometry, and microstructure, have, however, not yet been fully understood. Also life prediction methodologies that account for the physics of failure still remain to be

Y.-H. Pao; E. Jih; R. Liu; V. Siddapureddy; X. Song; R. McMillan; J. M. Hu

1997-01-01

266

A stress relaxation model for predicting the fatigue life of leaded surface mounted solder joints  

Microsoft Academic Search

Summary form only given. A model that will allow the prediction of fatigue life for leaded SMT components has been developed. The model incorporates the fact that, as plastic creep strain occurs in a solder joint, the driving stress will decrease, resulting in a reduction of the strain rate. The temperature dependence of the creep rate has been included to

K. Felske

1990-01-01

267

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

268

Fatigue crack propagation life analysis of solder joints under thermal cyclic loading  

Microsoft Academic Search

Fatigue crack propagation life analysis of solder joints under thermal cyclic loadings was investigated by the strain energy release rate method using finite element analysis. A relationship between the crack-growth rate and the strain energy release rate was derived. Finite element simulations were carried out to investigate the effect of crack growth along the interface of solder and lead in

R. M. V. Pidaparti; X. Song

1996-01-01

269

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

270

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

Microsoft Academic Search

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

Shashwat Sinha; Somnath Ghosh

2006-01-01

271

Low Strain, Long Life Creep Fatigue of AF2-1DA and Inco 718.  

National Technical Information Service (NTIS)

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 test...

A. B. Thakker B. A. Cowles

1983-01-01

272

Effect of Persistent Slip Band (PSB) Parameters on Fatigue Life. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

An examination of PSB data pertaining to the effects of an air-excluding environment and electric current on the fatigue life of polycrystalline Cu and 316 stainless steel in rotating bending reveals that the spacing and width of the PSBs are smaller thro...

W. D. Cao H. Conrad

1992-01-01

273

Influence of wear damage on the fretting fatigue life prediction of an Al7175 alloy  

Microsoft Academic Search

This paper proposes a modification on both the Smith–Watson–Topper and the Morrow parameters concerning the prediction on fretting fatigue life, in order to take into account the wear damage. It is proposed that, besides the principal stresses involved in fretting contact (axial, normal and tangential stresses), a new parameter that is the stress concentration factor, Kt, due to the “fretting

M. Buciumeanu; I. Crudu; L. Palaghian; A. S. Miranda; F. S. Silva

2009-01-01

274

Estimation of fatigue life in metal forming tools by computer simulation  

Microsoft Academic Search

Prestressed tools for cold forging are cyclic loaded by forming loads and mainly fail by cracking due to material deterioration caused by low-cycle fatigue. The aim of the work was to investigate the applicability of damage models for prediction of location of failure and prediction of die life for cold forging tools made of PM steels. Software modules for calculation

Markus Meidert; Christian Walter; Klaus Pöhlandt

275

Random response and fatigue life of aircraft panels subjected to severe acoustic and thermal loads  

Microsoft Academic Search

The focus of this investigation is on the prediction of the fatigue life of aircraft panels subject to thermal effects and a severe random acoustic excitation. The prototypical equations for this problem, i.e. the single and double well Duffing oscillators subjected to a bandlimited white noise, are first considered. A review of some currently available spectral approaches, i.e. the Rayleigh

Bo Yang

2005-01-01

276

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

Microsoft Academic Search

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

Zhicheng Huang

2011-01-01

277

A Second-Level SAC Solder-Joint Fatigue-Life Prediction Methodology  

Microsoft Academic Search

An acceleration model is developed for relating existing second-level fatigue-life data of tin-silver-copper solder joints to untested environments. The acceleration model retains the familiar canonical form of the Norris-Landzberg equation. Model parameters are obtained through calibration with an extensive set of published empirical data. The model will find use in making rapid assessments of a product's potential solder-joint field life

Walter Dauksher

2008-01-01

278

Effect of residual stresses on fatigue crack initiation life for butt-welded joints  

Microsoft Academic Search

This investigation performs a thermal elasto-plastic analysis using finite element techniques to analyse thermomechanical behaviour and evaluate residual stresses in weldments, and develops an effective procedure by combining the finite element, strain-life methods and considerations of the residual stress effect to predict fatigue crack initiation (FCI) life in weldments. Herein, the FCI lives of butt-welded joints are forecast using the

Tso-Liang Teng; Peng-Hsiang Chang

2004-01-01

279

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

280

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

SciTech Connect

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

Syrett, B.C.; Viswanathan, R.

1982-02-01

281

Fatigue Life Prediction of Steel Bridges for Extreme Loading Using a New Damage Indicator  

NASA Astrophysics Data System (ADS)

High cycle fatigue (HCF) damage caused by normal traffic loading is one of the major modes of failures in steel bridges. During bridge service life, there are extreme loading situations such as typhoons, earthquakes which cause higher amplitude loading than normal traffic loading. Due to this reason, critical members could undergo overstress cycles in the plastic range. Therefore, such members are subjected to low cycle fatigue (LCF) during these situations while subjecting to HCF in serviceable condition. Bridges, which are not seriously damaged, generally continue to be functioned after these extreme loading situations and fatigue life estimation is required to ensure their safety. Therefore, this paper presents a new damage indicator based fatigue model to predict life of steel bridges due to combined effect of extreme and normal traffic loadings. It consists of a modified strain life curve and a strain based damage indicator. Both the strain life curve and the damage indicator are newly proposed in the study. Modified strain life curve consists of Coffin Manson relation in the LCF regime and a new strain life curve in the HCF regime. Damage variable is based on von Mises equivalent strain and modified by factors to consider effects of loading non proportionality and loading path in multiaxial stress state. The new damage indicator can capture the loading sequence effect. The proposed model is verified with experimental test results of combined HCF and LCF of three materials; S304L stainless steel, Haynes 188 (a Cobolt superalloy) and S45C steel obtained from the literature. The verification of experimental results confirms the validity of the proposed model.

Karunananda, Pallaha Athawudagedara Kamal; Ohga, Mitao; Dissanayake, Punchi Bandage Ranjith; Siriwardane, Siriwardane Arachchilage Sudath Chaminda

282

Constitutive relations and fatigue life prediction for anisotropic Al-6061-T6 rods under biaxial proportional loadings  

NASA Astrophysics Data System (ADS)

Cyclic stress-strain curves (CSSCs) and fatigue lives were obtained from fully reversed fatigue tests in strain control on two anisotropic Al-6061-T6 rods. The experiments were conducted at room temperature under three types of loading conditions: tension-compression, torsion and combined proportional tension-torsion. Based on the CSSC data, the anisotropic constitutive relations of the rods were obtained by using Hill's anisotropic plasticity theory. Yield loci and flow behavior were determined and compared with the theoretical predictions. Two anisotropic effective-stress-effective-strain criteria were evaluated. During the fatigue tests the fatigue cracking behavior of the rods was observed and found to be shear dominated. Four multiaxial fatigue life prediction models representing three different concepts were used to correlate the fatigue life data. A shear cracking model incorporated with a material anisotropy constant correlated with the test data very well. The other models, however, gave poor correlations.

Lin, Hong; Nayeb-Hashemi, Hamid; Pelloux, Regis M.

1992-07-01

283

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

284

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

285

ANALYSIS OF THE MATERIAL STRESS STATE IN THE FRETTING ZONE FOR PREDICTING LIFE UNDER CYCLIC LOADING  

Microsoft Academic Search

Fatigue damage is frequent in the site of contact between the blade root and disk in high -performance gas-turbine engines, which leads to premature fracture of a blade. The presence of contact pressure and slight relative slip on the contacting surfaces initiates the damaging processes known as fretting. This study evaluates how well some of the strain-life parameters predict fretting

G. Tsyban; P. Kurash

286

Effect of test frequency on the in vitro fatigue life of acrylic bone cement.  

PubMed

The goal of the present work was to test the hypothesis that test frequency, f, does not have a statistically significant effect on the in vitro fatigue life of an acrylic bone cement. Uniaxial constant-amplitude tension-compression fatigue tests were conducted on 12 sets of cements, covering three formulations with three very different viscosities, two different methods of mixing the cement constituents, and two values of f (1 and 10 Hz). The test results (number of fatigue stress cycles, N(f)) were analyzed using the linearized form of the three-parameter Weibull equation, allowing the values of the Weibull mean (N(WM)) to be determined for each set. Statistical analysis of the lnN(f) data, together with an examination of the N(WM) estimates, showed support for the hypothesis over the range of f used. The principal use and explanation of the present finding are presented. PMID:12504534

Lewis, Gladius; Janna, Si; Carroll, Michael

2003-03-01

287

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)); Hansen, A.C. (Utah Univ., Salt Lake City, UT (United States))

1991-12-01

288

Primary Sjögren's syndrome in Moroccan patients: characteristics, fatigue and quality of life.  

PubMed

Our aim was to evaluate fatigue and quality of life (QoL) in Moroccan patients with primary Sjögren's syndrome (PSS) and determine their correlates with disease-related parameters. Fifty-seven consecutive patients with PSS according to the American-European Consensus group (AEGG) criteria were included. Demographic, clinical, biological and immunological characteristics for all patients were collected. Xerostomia was demonstrated by histological grading of lower lip glandular biopsy. A Schirmer test was performed to measure lachrymal flow. Oral, ocular, skin, vaginal and tracheal dryness were evaluated by using a visual analogue scale (VAS). Fatigue was assessed by the Multidimensional assessment of fatigue (MAF) and the QoL by using the generic instrument: SF-36. 90% of our patients were women. The mean age of patients was 53.73 ± 7.69 years, and the mean disease duration was 5.38 ± 4.11 years. The mean oral dryness was 68.38 ± 20.29, and the mean ocular dryness was 51.91 ± 14.03. The mean total score of the MAF was 26.73 ± 8.33, and 87.5% of our patients experienced severe fatigue. Also, physical and mental domains of QoL were altered in a significant way, and the severity of fatigue had a negative impact on SF-36 scores. MAF and SF-36 scores were correlated with the delay of diagnosis, the intensity of xerostomia and the activity of joint involvement. A low socioeconomic and educational level had a negative impact on fatigue scores and QoL. Histological grading of lower lip glandular biopsy, immunological status and the severity of systemic involvement had no correlations with fatigue scores or the alteration of QoL. Patients receiving antidepressant have lesser fatigue and those receiving Methotrexate have better SF-36 scores. In our data, there was a high prevalence of fatigue in Moroccan patients with PSS associated with altered QoL. Severe fatigue and reduced QoL seem to be related to the severity of joint involvement, xerostomia and both educational and socioeconomic levels. Also, treatment with methotrexate and antidepressant seems to improve patients' living and QoL. An appropriate therapeutic intervention for depression and articular manifestations in PSS should be applied to improve patients' living. PMID:21786120

Ibn Yacoub, Yousra; Rostom, Samira; Laatiris, Assia; Hajjaj-Hassouni, Najia

2011-07-24

289

Probabilistic Modeling and Simulation of Metal Fatigue Life Prediction.  

National Technical Information Service (NTIS)

As fiscal constraints demand maximum utilization, engineers must develop more rigorous methods to predict the life limits of aircraft components Current Navy policy requires that aircraft and aircraft parts be retired before they reach 100% FLE An investi...

T. V. Heffern

2002-01-01

290

Verification of Fatigue Crack Initiation Life Prediction Results.  

National Technical Information Service (NTIS)

Crack initiation life estimates obtained with the local strain approach (LSA) and with the conventional nominal stress approach (NSA) were compared with experimental results obtained with stress block loading programs and flight simulation gust loading pr...

A. Buch

1980-01-01

291

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

PubMed

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

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

2008-02-19

292

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

SciTech Connect

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

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

2000-02-01

293

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

294

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

Microsoft Academic Search

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

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

2000-01-01

295

Small crack property of austenitic stainless steel with artificial corrosion pit in long life regime of fatigue  

Microsoft Academic Search

In order to investigate the fatigue strength in a long life regime of austenitic stainless steel with respect to the stress concentration, rotating bending fatigue tests were performed with pitted specimens (pit specimens). The Type 316NG and Type 304TP steel specimens had some artificial corrosion pits in its center. Further, in order to investigate the existence of a non-propagating crack

Kiyotaka Masaki; Yasuo Ochi; Takashi Matsumura

2006-01-01

296

Natalizumab Treatment Reduces Fatigue in Multiple Sclerosis. Results from the TYNERGY Trial; A Study in the Real Life Setting  

PubMed Central

Fatigue is a significant symptom in multiple sclerosis (MS) patients. First-generation disease modifying therapies (DMTs) are at best moderately effective to improve fatigue. Observations from small cohorts have indicated that natalizumab, an antibody targeting VLA-4, may reduce MS-related fatigue. The TYNERGY study aimed to further evaluate the effects of natalizumab treatment on MS-related fatigue. In this one-armed clinical trial including 195 MS patients, natalizumab was prescribed in a real-life setting, and a validated questionnaire, the Fatigue Scale for Motor and Cognitive functions (FSMC), was used both before and after 12 months of treatment to evaluate a possible change in the fatigue experienced by the patients. In the treated cohort all measured variables, that is, fatigue score, quality of life, sleepiness, depression, cognition, and disability progression were improved from baseline (all p values<0.0001). Walking speed as measured by the six-minute walk-test also increased at month 12 (p?=?0.0016). All patients were aware of the nature of the treatment agent, and of the study outcomes. Conclusion Natalizumab, as used in a real-life setting, might improve MS-related fatigue based on the results from this one-armed un-controlled stud. Also other parameters related to patients' quality of life seemed to improve with natalizumab treatment. Trial Registration ClinicalTrials.gov NCT00884481

Svenningsson, Anders; Falk, Eva; Celius, Elisabeth G.; Fuchs, Siegrid; Schreiber, Karen; Berko, Sara; Sun, Jennifer; Penner, Iris-Katharina; for the TYNERGY trial investigators

2013-01-01

297

Effects of material and loading variables on fatigue life of carbon and low-alloy steels in LWR environments  

SciTech Connect

The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Section III of the Code specifies fatigue design curves for structural materials. While effects of reactor coolant environments are not explicitly addressed by the design curves, test data suggest that the Code fatigue curves may not always be adequate in coolant environments. This paper reports the results of recent fatigue tests that examine the effects of steel type, strain rate, dissolved oxygen level, strain range, loading waveform, and surface morphology on the fatigue life of A106-Gr B carbon steel and A533-Gr B low-alloy steel in water.

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

1995-03-01

298

Fatigue life diagnosis of steel structures with a fatigue damage sensor  

Microsoft Academic Search

There is a growing tendency to require increased service, beyond the design life, for steel structures such as bridges, vehicles, railways, vessels and construction machinery etc. by the implementation of regular maintenance procedures. During this maintenance products are inspected at relatively short intervals and, based upon the results of inspection and diagnosis, repair and reinforcement work is carried out as

O. Muragishi

2006-01-01

299

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

Microsoft Academic Search

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

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

2009-01-01

300

Micro-Damage Evaluation and Remaining Fatigue Life Assessment with Nonlinear Vibro-Modulation Technique  

NASA Astrophysics Data System (ADS)

Assessment of structural deterioration due to in-service and environmental loads is an essential element in ensuring safety, operability and long life of various structures and structural components. We applied vibro-acoustic modulation technique to monitor material degradation at the micro/meso scale before the onset of the macro-scale fracture. The technique explores nonlinear acoustic interaction of high frequency ultrasound and low frequency structural vibration at the site of the incipient damage. It is shown that micro/meso scale degradation increases the material nonlinearity leading to modulation of the high frequency ultrasonic signal by low frequency vibration, quantified by the nonlinear acoustic Damage Index (DI). Numerous tests with hundreds of test coupons proved high sensitivity of the developed technique to micro/meso scale fatigue damage accumulation. The study further demonstrated that the remaining life of the fatigued material can be predicted using phenomenological damage accumulation rule expressed through measured Damage Index.

Donskoy, Dimitri; Chudnovsky, Alexander; Zagrai, Andrei; Golovin, Edward

2008-06-01

301

Linear Strain Theory and the Smith Method for Predicting Fatigue Life of Structures for Spectrum Type Loading.  

National Technical Information Service (NTIS)

Theoretical and test data are presented for two methods of predicting fatigue life. The first method requires preknowledge of stress concentration and nominal stress; the second requires preknowledge of neither. Both employ smooth specimen S-N curves and ...

C. R. Smith

1964-01-01

302

Prediction of the Fatigue Life of Cast Steel Containing Shrinkage Porosity  

Microsoft Academic Search

A simulation methodology for predicting the fatigue life of cast steel components with shrinkage porosity is developed and\\u000a validated through comparison with previously performed measurements. A X-ray tomography technique is used to reconstruct the\\u000a porosity distribution in 25 test specimens with average porosities ranging from 8 to 21 pct. The porosity field is imported\\u000a into finite element analysis (FEA) software to

Richard A. Hardin; Christoph Beckermann

2009-01-01

303

Surface Crack Growth Path and Fatigue Life Prediction Due to Repeated Rolling\\/Sliding Contact  

Microsoft Academic Search

This paper deals with the surface crack growth path description and the fatigue life prediction due to repeated rolling\\/sliding contact on the elastic half-space, accompanied by frictional heat generation and crack-face pressure. The stress intensity factors are analyzed for the surface crack which is kinked in multiple times from the inclined initial main crack. The rolling\\/sliding contact is simulated as

Takahito Goshima; Sotomi Ishihara; Masayoshi Shimizu; Hirokazu Yoshida; Yuji Tsuchida

2003-01-01

304

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

Microsoft Academic Search

This paper focuses on the workconducted at LaRC to evaluate the fatigue behavior of 1441 Al-Li sheet and the pressurizationfatigue life of fuselage panels using 1441 Al-Li skin.Four fuselage panels fabricated by Tupolev Design Bureau under contract to VIAM using1441 Al-Li were subjected to cyclic pressurization and depressurization to simulate flightconditions. Two panels were tested at LaRC and two were

R. Keith Bird; Dennis L. Dicus

1999-01-01

305

Flip-chip solder bump fatigue life enhanced by polymer encapsulation  

Microsoft Academic Search

Encapsulation of controlled collapse chip connection (C4) joints, using a filled epoxy resin having 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 resin along an

D. Suryanarayana; R. Hsiao; T. P. Gall; J. M. McCreary

1990-01-01

306

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

Microsoft Academic Search

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

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

2007-01-01

307

An integrated CAE system for dynamic stress and fatigue life prediction of mechanical systems  

Microsoft Academic Search

This paper presents computer simulation methodology for dynamic stress time history computation to predict the fatigue life\\u000a of machine components using flexible multi-body dynamics. A hybrid method which employes stress superposition as a function\\u000a of constraint loads and component accelerations that are predicted by flexible body dynamic simulation is utilized and implemented\\u000a using established codes. A system integration methodology for

Hong Jae Yim; Sang Beom Lee

1996-01-01

308

Finite element based fatigue life estimation of the solder joints with effect of intermetallic compound growth  

Microsoft Academic Search

This paper develops an analysis procedure to study the effects of intermetallic compound (IMC) growth on the fatigue life of 63Sn–37Pb (lead-rich)\\/96.5Sn–3.5Ag (lead-free) solder balls for flip-chip plastic ball grid array packages under thermal cycling test conditions. In this analysis procedure, the thickness of the IMC increased with the number of thermal cycles, and was determined using the growth rate

Yung-Chuan Chiou; Yi-Ming Jen; Shih-Hsiang Huang

309

CBGA solder joint thermal fatigue life estimation by a simple method  

Microsoft Academic Search

A simple analysis method was developed to determine the fatigue life of a ceramic ball grid array (CBGA) solder joint when exposed to thermal environments. The solder joint consists of a 90Pb\\/10Sn solder ball with eutectic SnPb solder on both top and bottom of the ball. A closed-form solution, based on the calculation of the equilibrium of the displacements within

T. E. Wong; C. Y. Lau; H. S. Fenger

2004-01-01

310

Universal fatigue life prediction equation for ceramic ball grid array (CBGA) packages  

Microsoft Academic Search

A traditional approach to predicting solder joint fatigue life involves finite-element simulations in combination with experimental data to develop a Coffin–Manson type predictive equation. The finite-element simulations often require good understanding of finite-element modeling, physics-based failure models, and time-, temperature-, and direction-dependent material constitutive behavior. Also, such simulations are computationally expensive and time-consuming. Microelectronic package designers often do not have

Andy Perkins; Suresh K. Sitaraman

2007-01-01

311

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

Microsoft Academic Search

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

A. B. Thakker; B. A. Cowles

1983-01-01

312

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

Microsoft Academic Search

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

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

2003-01-01

313

Primary Sjögren’s syndrome in Moroccan patients: characteristics, fatigue and quality of life  

Microsoft Academic Search

Our aim was to evaluate fatigue and quality of life (QoL) in Moroccan patients with primary Sjögren’s syndrome (PSS) and determine\\u000a their correlates with disease-related parameters. Fifty-seven consecutive patients with PSS according to the American-European\\u000a Consensus group (AEGG) criteria were included. Demographic, clinical, biological and immunological characteristics for all\\u000a patients were collected. Xerostomia was demonstrated by histological grading of lower

Yousra Ibn Yacoub; Samira Rostom; Assia Laatiris; Najia Hajjaj-Hassouni

314

Fatigue life models for SnAgCu and SnPb solder joints evaluated by experiments and simulation  

Microsoft Academic Search

In recent years, many solder fatigue models have been developed to predict the fatigue life of solder joints under thermal cycle conditions. While a variety of life prediction models have been proposed for near eutectic SnPb(Ag)-solder joints in the literature, not enough work has been reported in extending these models to lead-free soldered assemblies. The development of lie prediction models

A. Schubertt; R. Dudek; E. Auerswald; A. Gollbardt; B. Michel; H. Reichl

2003-01-01

315

A low-cycle fatigue life model of nickel-based single crystal superalloys under multiaxial stress state  

Microsoft Academic Search

The low-cycle fatigue (LCF) behavior of smooth and notched specimens of nickel-based single-crystal superalloys DD3 was studied at 620°C. Based on experimental results and finite element analysis results, a low-cycle fatigue life model has been proposed for the nickel-based single-crystal superalloys under multiaxial stress states. In the model the mean stress effect has been considered. The LCF life model is

J. S. Wan; Z. F. Yue

2005-01-01

316

Computational Materials Science and Surface Engineering Application of artificial neural network for predicting fatigue crack propagation life of aluminum alloys  

Microsoft Academic Search

Purpose: In this work, fatigue crack propagation life of 7020 T7 and 2024 T3 aluminum alloys under the influence of load ratio was predicted by using artificial neural network (ANN). Design\\/methodology\\/approach: Numerous phenomenological models have been proposed for predicting fatigue life of the components under the influence of load ratio to take into account the mean load effect. Findings: In

J. R. Mohanty; B. B. Verma; D. R. K. Parhi; P. K. Ray

317

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

2013-09-01

318

A Probabilistic Approach to Predict Thermal Fatigue Life for Ball Grid Array Solder Joints  

NASA Astrophysics Data System (ADS)

Numerous studies of the reliability of solder joints have been performed. Most life prediction models are limited to a deterministic approach. However, manufacturing induces uncertainty in the geometry parameters of solder joints, and the environmental temperature varies widely due to end-user diversity, creating uncertainties in the reliability of solder joints. In this study, a methodology for accounting for variation in the lifetime prediction for lead-free solder joints of ball grid array packages (PBGA) is demonstrated. The key aspects of the solder joint parameters and the cyclic temperature range related to reliability are involved. Probabilistic solutions of the inelastic strain range and thermal fatigue life based on the Engelmaier model are developed to determine the probability of solder joint failure. The results indicate that the standard deviation increases significantly when more random variations are involved. Using the probabilistic method, the influence of each variable on the thermal fatigue life is quantified. This information can be used to optimize product design and process validation acceptance criteria. The probabilistic approach creates the opportunity to identify the root causes of failed samples from product fatigue tests and field returns. The method can be applied to better understand how variation affects parameters of interest in an electronic package design with area array interconnections.

Wei, Helin; Wang, Kuisheng

2011-11-01

319

Vibration-induced fatigue life estimation of ball grid array packaging  

NASA Astrophysics Data System (ADS)

Vibration loading has become very important in the reliability assessment of modern electronic systems. The objective of this paper is to develop a rapid assessment methodology that can determine the solder joint fatigue life of ball grid array (BGA) and chip scale packages (CSP) under vibration loading. The current challenge is how to execute the vibration fatigue life analysis rapidly and accurately. The approach in this paper will involve global (entire printed wiring board (PWB)) and local (particular component of interest) modeling approaches. In the global model approach, the vibration response of the PWB will be determined. This global model will give us the response of the PWB at specific component locations of interest. This response is then fed into a local stress analysis for accurate assessment of the critical stresses in the solder joints of interest. The stresses are then fed into a fatigue damage model to predict the life. The goal is to retain as much accuracy and physical insight as possible while retaining computation efficiency.

Wu, Mei-Ling

2009-06-01

320

Effect of L\\/ T p ratio on fatigue life prediction of SMAW cruciform joints of ASTM 517 ‘F’ Grade steels  

Microsoft Academic Search

New fracture mechanics equations have been developed to predict the fatigue life of shielded metal arc welded (SMAW) cruciform joints of ASTM 517 ‘F’ Grade steels, containing lack of penetration (LOP) defects. These equations have been developed by combining the Paris law with the ?Ki-endurance equation The initiation life (Ni) and the propagation life (Np) of the joints were accounted

V. Balasubramanian; B. Guha

1998-01-01

321

Effect of Intermittent Overload Cycles on Thermomechanical Fatigue Life of NiTi Shape Memory Alloy Wire  

NASA Astrophysics Data System (ADS)

Effect of intermittent overload cycles on fatigue behavior of NiTi shape memory alloy wire during thermomechanical cycling (TMC) has been evaluated. Results showed that fatigue life of NiTi is enhanced when the intermittent overload is above certain minimum level. An enhancement in fatigue life by ~50 pct is observed when the overload ratio is 2.0. Accumulation of plastic strain in the material under such TMC condition is found to be relatively high compared to that of TMC with no overload cycles.

Saikrishna, C. N.; Ramaiah, K. V.; Vidyashankar, B.; Bhaumik, S. K.

2013-01-01

322

Influence of different wind profiles due to varying atmospheric stability on the fatigue life of wind turbines  

NASA Astrophysics Data System (ADS)

Offshore wind energy is being developed on a very large scale in the European seas. The objective of developing wind energy offshore is to capture greater wind speeds than are encountered onshore and as a result more energy. With this also come more challenges in the design of wind turbines due to the hostile offshore environment. Currently the standards for offshore wind turbines prescribe a site specific design for the support structures and the design for the rotor nacelle assembly according to onshore standards. Wind turbines are designed to withstand fatigue and ultimate loads. For the fatigue loading several input conditions have been prescribed, amongst which wind profile is one of them. Wind profile is represented by power law or logarithmic law as given in the standards. A neutral stability of the atmosphere is considered while obtaining the wind profile using the logarithmic law. In this paper the atmospheric stability is varied in order to estimate different wind profiles and simulations are run in Bladed to check its influence on the fatigue damage at the blade root. The variations in the atmospheric stability has been taken into account by using some typical values of Obukhov length. From steady state simulations it has been found that atmospheric stability is important for fatigue damage. The analysis showed that variation in the distribution of atmospheric stability causes large variations in the fatigue damage for different sites. Thus, it is worthwhile to carry out a full scale study using the turbulent winds and real data for wind turbine and environmental conditions.

Sathe, Ameya; Bierbooms, Wim

2007-07-01

323

Detect, troubleshoot gas-turbine blade failures  

SciTech Connect

Approximately 40% of all gas-turbine failures stem from blading problems. This article describes state-of-the-art condition monitoring technologies that can help avoid or minimize the damage, and troubleshoot failures when they occur. In today`s gas-turbine (GT) fleet, predominant blade-failure mechanism and commonly affected components include: low-cycle fatigue--compressor and turbine disks; high-cycle fatigue--compressor and turbine blades and disks, compressor stator vanes; thermal fatigue--nozzles, combustors; environmental attack, such as oxidation, sulfidation, hot corrosion, and standby corrosion--hot-section blades and stators, transition pieces, and combustors; creep damage--hot-section nozzles and blades; erosion and wear; impact overload damage; thermal aging; combined failure mechanisms, such as creep/fatigue corrosion/fatigue, oxidation/erosion, and so on. Avoiding GT blade problems requires that two conditions be met: first, and most important, the basic design has to be sound, with adequate safety factors incorporates. Second, the proper operating regime must be maintained. Properly applied, condition monitoring can help maintain the operating regime and minimize blade distress. Should blade failures occur, data captured in a monitoring program may provide valuable clues to help identify the root causes. Reviewed here are the latest GT condition monitoring techniques, as well as several case histories that illustrate their importance.

Meher-Homji, C.B. [Boyce Engineering International Inc., Houston, TX (United States)

1995-12-01

324

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

SciTech Connect

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

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

2011-11-01

325

Influence of the Inclusion Shape on the Rolling Contact Fatigue Life of Carburized Steels  

NASA Astrophysics Data System (ADS)

It has been well known that the flaking failure in rolling contact fatigue (RCF) originates from nonmetallic inclusions in steels, and their apparent size is one of the important factors affecting RCF life. However, the influence of inclusion shape on the RCF life has not been fully clarified. In this study, attention was paid to the influence of the inclusion shape on the RCF life. This was evaluated by using carburized JIS-SCM420 (SAE4320) steels that contained two different shapes of MnS—stringer type and spheroidized type—as inclusions. Sectional observations were made to investigate the relation between the occurrence of shear crack in the subsurface and the shape of MnS. It was found that the RCF life was well correlated with the length of MnS projected to the load axis, and the initiation of shear crack in subsurface was accelerated as the length of MnS increased.

Neishi, Yutaka; Makino, Taizo; Matsui, Naoki; Matsumoto, Hitoshi; Higashida, Masashi; Ambai, Hidetaka

2013-05-01

326

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

327

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

328

The surface fatigue life of contour induction hardened AISI 1552 gears  

NASA Astrophysics Data System (ADS)

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

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

1995-07-01

329

An investigation of cyclic transient behavior and implications on fatigue life estimates  

SciTech Connect

Current research focuses on proportional cyclic hardening and non-Massing behaviors. The interaction of these two hardenings can result in the traditionally observed overall softening, hardening or mixed behavior exhibited for fully reversed strain controlled fatigue tests. Proportional experiments were conducted with five materials 304 stainless steel, normalized 1070 and 1045 steels, and 7075-T6 and 6061-T6 aluminum alloys. All the materials display similar trends, but the 304 stainless steel shows the most pronounced transient behavior and will be discussed in detail. Existing algorithms for this behavior are evaluated in light of the recent experiments, and refinements to the Armstrong-Frederick class of incremental plasticity models are proposed. Modifications implemented are more extensive than the traditional variation of yield stress, and a traditional strain based memory surface is utilized to track deformation history. Implications of the deformation characteristics with regard to fatigue life estimation, especially variable amplitude loading, will be examined. The high-low step loading is utilized to illustrate the effect of transient deformation on fatigue life estimation procedures, and their relationship to the observed and modeled deformation.

Jiang, Y. [Univ. of Nevada, Reno, NV (United States). Dept. of Mechanical Engineering; Kurath, P. [Univ. of Illinois, Urbana, IL (United States)

1997-04-01

330

Unstimulated cortisol secretory activity in everyday life and its relationship with fatigue and chronic fatigue syndrome: A systematic review and subset meta-analysis.  

PubMed

The hypothalamic-pituitary-adrenal (HPA) axis is a psychoneuroendocrine regulator of the stress response and immune system, and dysfunctions have been associated with outcomes in several physical health conditions. Its end product, cortisol, is relevant to fatigue due to its role in energy metabolism. The systematic review examined the relationship between different markers of unstimulated salivary cortisol activity in everyday life in chronic fatigue syndrome (CFS) and fatigue assessed in other clinical and general populations. Search terms for the review related to salivary cortisol assessments, everyday life contexts, and fatigue. All eligible studies (n=19) were reviewed narratively in terms of associations between fatigue and assessed cortisol markers, including the cortisol awakening response (CAR), circadian profile (CP) output, and diurnal cortisol slope (DCS). Subset meta-analyses were conducted of case-control CFS studies examining group differences in three cortisol outcomes: CAR output; CAR increase; and CP output. Meta-analyses revealed an attenuation of the CAR increase within CFS compared to controls (d=-.34) but no statistically significant differences between groups for other markers. In the narrative review, total cortisol output (CAR or CP) was rarely associated with fatigue in any population; CAR increase and DCS were most relevant. Outcomes reflecting within-day change in cortisol levels (CAR increase; DCS) may be the most relevant to fatigue experience, and future research in this area should report at least one such marker. Results should be considered with caution due to heterogeneity in one meta-analysis and the small number of studies. PMID:23916911

Powell, Daniel J H; Liossi, Christina; Moss-Morris, Rona; Schlotz, Wolff

2013-08-02

331

High-temperature fatigue life of type 316 stainless steel containing irradiation induced helium  

SciTech Connect

Specimens of 20%-cold-worked AISI type 316 stainless steel were irradiated in the High Flux Isotope Reactor (HFIR) at 550/sup 0/C to a maximum damage level of 15 dpa and a transmutation produced helium level of 820 at. ppM. Fully reversed strain controlled fatigue tests were performed in a vacuum at 550/sup 0/C. No significant effect of the irradiation on low-cycle fatigue life was observed; however, the strain range of the 10/sup 7/ cycle endurance limit decreased from 0.35 to 0.30%. The relation between total strain range and number of cycles to failure was found to be ..delta..epsilon/sub T/ = 0.02N/sub f//sup -0/ /sup 12/ + N/sub f//sup -0/ /sup 6/ for N/sub f/ < 10/sup 7/ cycles.

Grossbeck, M.L.; Liu, K.C.

1981-01-01

332

Application of microcomputer to automatizing fatigue testing  

NASA Astrophysics Data System (ADS)

This paper describes how a microcomputer is applied to a blade fatigue testing system. Automatic checking and controlling of blade fatigue testing in the system are implemented with the aid of a nest-form of assembly language and high-level language. The system can also be used for fatigue testing of fuel or oil tubes.

Yang, Daman; Zhuang, Zhongliang; Lu, Qixin

1989-01-01

333

The effect of residual stress in HVOF tungsten carbide coatings on the fatigue life in bending of thermal spray coated aluminum  

NASA Astrophysics Data System (ADS)

One factor that affects the suitability of tungsten carbide (WC) coatings for wear and corrosion control applications is the fatigue life of the coated part. Coatings, whether anodized or thermal spray coated, can reduce the fatigue life of a part compared to an uncoated part. This study compares the fatigue life of uncoated and thermal spray coated 6061 Al specimens. The relation between the residual stress level in the coating and the fatigue life of the specimen is investigated. Cyclic bending tests were performed on flat, cantilever beam specimens. Applied loads placed the coating in tension. Residual stress levels for each of the coating types were determined experimentally using the modified layer removal method. Test results show that the fatigue life of WC coated specimens is directly related to the level of compressive residual stress in the coating. In some cases, the fatigue life can be increased by a factor of 35 by increasing the compressive residual stress in the coating.

McGrann, R. T. R.; Greving, D. J.; Shadley, J. R.; Rybicki, E. F.; Bodger, B. E.; Somerville, D. A.

1998-12-01

334

Fatigue life prediction of gas tungsten arc welded AISI 304L cruciform joints with different LOP sizes  

Microsoft Academic Search

Fatigue life evaluations have been carried out on gas tungsten arc welded (GTAW) load-carrying cruciform joints of AISI 304L stainless steel with lack of penetration (LOP) using conventional S-N and crack initiation-propagation (I-P) methods. The crack process normally comprises two major phases: (1) the crack initiation life (Ni): and (2) the crack propagation life (Np). The local stress-life approach is

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

2003-01-01

335

Fatigue Properties of an A356 (AlSi7Mg) Aluminium Alloy for Automotive Applications: Fatigue Life Prediction.  

National Technical Information Service (NTIS)

In the present paper a thorough study of the fatigue crack initiation mechanisms of a defect-free and a commercially cast A356 aluminum alloy are presented. Further, fatigue crack growth has been investigated in these materials. Finally an attempt to desc...

J. A. Oedegard K. Pedersen

1994-01-01

336

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

Microsoft Academic Search

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 beta extracted from acoustic (ultrasonic) harmonic generation measurements. The beta parameter for a given fatigue state is highly sensitive to

John H. Cantrell

2009-01-01

337

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

Microsoft Academic Search

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

John H. Cantrell

2009-01-01

338

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

339

Reliability analysis for low cycle fatigue life of the aeronautical engine turbine disc structure under random environment  

Microsoft Academic Search

The low cycle fatigue life (LCFL) of the aeronautical engine turbine disc structure is related to the stress–strain level of the disc applied by cyclic load and the life characteristic of the material. The randomness of the basic variables, such as applied load, working temperature, geometrical dimensions and material properties, has significant effect on the statistical properties of the stress

C. L. Liu; Z. Z. Lu; Y. L. Xu; Z. F. Yue

2005-01-01

340

Random response and fatigue life of aircraft panels subjected to severe acoustic and thermal loads  

NASA Astrophysics Data System (ADS)

The focus of this investigation is on the prediction of the fatigue life of aircraft panels subject to thermal effects and a severe random acoustic excitation. The prototypical equations for this problem, i.e. the single and double well Duffing oscillators subjected to a bandlimited white noise, are first considered. A review of some currently available spectral approaches, i.e. the Rayleigh approximation and the single spectral moment method both with and without Gaussianity correction, strongly suggests that an accurate prediction of the fatigue life for this nonlinear system requires a dedicated model. To this end, an approximation of the probability density function of the peaks of the stationary response of the Duffing oscillators is derived. This model is then used in conjunction with either a narrowband assumption or the single spectral moment methodology to yield a prediction of the fatigue life. The application of this approach to simulation data from a single/double well Duffing oscillator, as well as on the experimental response of an unbuckled panel, demonstrates the reliability of this novel approximation. Spectral approaches typically make use of the values of specific spectral moments and thus their application necessitates the availability of a reliable approximation of the power spectral density of the response considered (displacement or stress). Although of fundamental importance, the determination of the power spectrum of the response of nonlinear systems is a very difficult problem and it is only recently that successful techniques have been devised to estimate this function. Two such approaches are assessed here for the single degree of freedom Duffing oscillator and are modified to improve their accuracy and ease of use.

Yang, Bo

341

Influence of flux cored arc welded cruciform joint dimensions on fatigue life of ASTM 517 `F' grade steels  

Microsoft Academic Search

A mathematical model has been developed to predict the fatigue life of flux-cored arc-welded (FCAW) cruciform joints containing lack of penetration (LOP) defects. High strength, quenched and tempered steel (ASTM 517 `F' grade) has been used as the base material throughout the investigation. The design of experiments (DoE) concept has been used to optimize the required number of experiments. Fatigue

V Balasubramanian; B Guha

1998-01-01

342

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

Microsoft Academic Search

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

Nicole M Stroud; Clare L Minahan

2009-01-01

343

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

Microsoft Academic Search

Porosity is well known to be a potent initiator of fatigue cracks in cast aluminum alloys. This article addresses the observed\\u000a scatter in fatigue life of a cast A356-T6 aluminum-silicon alloy due to the presence of porosity. Specimens containing a controlled\\u000a amount of porosity were prepared by employing a wedge-shaped casting mold and adjusting the degassing process during casting.\\u000a High-cycle

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

2003-01-01

344

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

345

An investigation of interconnect geometry and fatigue life of ball-grid array electronic packages  

NASA Astrophysics Data System (ADS)

A model for the shapes and residual forces for an individual, axisymmetric BGA solder interconnect is developed from the basic assumption that the surface bounding the solder possesses constant mean curvature. The inputs for the model include: pad radius, stand-off height, and the volume of the solder. The model is contrasted with simpler ones to identify the combinations of parameters for which more relaxed assumptions regarding the shape of the interconnect (e.g., a cylinder, truncated sphere, or circular arc meridian) may lead to unacceptable errors when designing for the demanding requirements of aerospace applications. The parameter combinations include situations when there exists a large stand-off height in conjunction with residual tension in the interconnect and when there is considerable tension or compression in the interconnect. The errors can be especially significant if one is designing around presumed surface contact angles at the solder/pad/PCB junction. The results of this model are incorporated into a fatigue life analysis for BGA packages. In the aerospace industry the fatigue loading on the individual interconnects is Mode II shearing due to cyclic temperatures. A fracture mechanics approach is taken which accounts for this Mode II fatigue loading as well as a constant Mode I loading that is due to the residual forces arising from the surface tension within the molten interconnect. This model, which is referred to as the relative life model, is capable of demonstrating how the relative fatigue life of an interconnect can be altered as a result of a change in the residual force (and, therefore, the shape) of the interconnect. The model is capable of capturing this relationship for variable joint dimensions (i.e., volumes, stand-off heights, radii), service loading, and material constituents (i.e., solder alloys, PCBs, and IC carriers). For an array of pads of known radii, a procedure is presented for determining the optimal volumes of each solder joint so as to optimize the relative life of the entire package.

Verges, Melody Arthur

346

Fatigue life estimation of a 1D aluminum beam under mode-I loading using the electromechanical impedance technique  

NASA Astrophysics Data System (ADS)

Structures in service are often subjected to fatigue loads. Cracks would develop and lead to failure if left unnoticed after a large number of cyclic loadings. Monitoring the process of fatigue crack propagation as well as estimating the remaining useful life of a structure is thus essential to prevent catastrophe while minimizing earlier-than-required replacement. The advent of smart materials such as piezo-impedance transducers (lead zirconate titanate, PZT) has ushered in a new era of structural health monitoring (SHM) based on non-destructive evaluation (NDE). This paper presents a series of investigative studies to evaluate the feasibility of fatigue crack monitoring and estimation of remaining useful life using the electromechanical impedance (EMI) technique employing a PZT transducer. Experimental tests were conducted to study the ability of the EMI technique in monitoring fatigue crack in 1D lab-sized aluminum beams. The experimental results prove that the EMI technique is very sensitive to fatigue crack propagation. A proof-of-concept semi-analytical damage model for fatigue life estimation has been developed by incorporating the linear elastic fracture mechanics (LEFM) theory into the finite element (FE) model. The prediction of the model matches closely with the experiment, suggesting the possibility of replacing costly experiments in future.

Lim, Yee Yan; Kiong Soh, Chee

2011-12-01

347

Predicting in-service fatigue life of flexible pavements based on accelerated pavement testing  

NASA Astrophysics Data System (ADS)

Pavement performance prediction in terms of fatigue cracking and surface rutting are essential for any mechanistically-based pavement design method. Traditionally, the estimation of the expected fatigue field performance has been based on the laboratory bending beam test. Full-scale Accelerated Pavement Testing (APT) is an alternative to laboratory testing leading to advances in practice and economic savings for the evaluation of new pavement configurations, stress level related factors, new materials and design improvements. This type of testing closely simulates field conditions; however, it does not capture actual performance because of the limited ability to address long-term phenomena. The same pavement structure may exhibit different response and performance under APT than when in-service. Actual field performance is better captured by experiments such as Federal Highway Administration's Long-Term Pavement Performance (LTPP) studies. Therefore, to fully utilize the benefits of APT, there is a need for a methodology to predict the long-term performance of in-service pavement structures from the results of APT tests that will account for such differences. Three models are generally suggested to account for the difference: shift factors, statistical and mechanistic approaches. A reliability based methodology for fatigue cracking prediction is proposed in this research, through which the three models suggested previously are combined into one general approach that builds on their individual strengths to overcome some of the shortcomings when the models are applied individually. The Bias Correction Factor (BCF) should account for all quantifiable differences between the fatigue life of the pavement site under APT and in-service conditions. In addition to the Bias Correction Factor, a marginal shifty factor, M, should be included to account for the unquantifiable differences when predicting the in-service pavement fatigue life from APT. The Bias Correction Factor represents an improvement of the currently used "shift factors" since they are more general and based on laboratory testing or computer simulation. By applying the proposed methodology, APT performance results from a structure similar to an in-service structure can be used to perform four-point bending beam tests and structural analysis to obtain an accurate estimate of the necessary Bias Correction Factor to estimate in-service performance.

Guo, Runhua

348

Gender Differences in Sleep Disruption and Fatigue on Quality of Life Among Persons with Ostomies  

PubMed Central

Study Objectives: The aim of this study is to examine differences in sleep disruption and fatigue of men and women colorectal cancer (CRC) survivors with intestinal ostomies and associated health-related quality of life (HR-QOL). Methods: Participants in this cross-sectional study of long-term (> 5 years) CRC survivors received care at Kaiser Permanente. Measures included the City of Hope QOL Ostomy questionnaire with narrative comments for ostomy-related “greatest challenges.” The Short Form-36 Version 2 (SF-36v2) health survey provided physical (PCS) and mental composite scale (MCS) scores to examine generic HR-QOL. The “sleep disruption” and “fatigue” items from the ostomy questionnaire (scale from 0 to 10 with higher scores indicating better HR-QOL) were dependent variables, while independent variables included age, ethnicity, education, partnered status, body mass index, and time since surgery. Data were analyzed using chi-square for nominal variables, Student t-tests for continuous variables, and logistic regression with significance set at p < 0.05. Results: On the ostomy-specific measure, women (n = 118) compared to men (n = 168) reported more sleep disruption (p < 0.01), adjusted for age, and greater levels of fatigue (p < 0.01), adjusted for time since surgery. Women's PCS and MCS scores indicated poorer HR-QOL compared to men, and differences were clinically meaningful. Qualitative narrative comments suggested that sleep disruption could stem from ostomy-associated fear of or actual leakage during sleep. Conclusion: Although women CRC survivors with ostomies report more sleep disruption and fatigue, which is reflected in their reduced physical and mental health scores on the SF-36v2 compared to men with ostomies, their stated reasons for disrupted sleep are similar to their male counterparts. These findings can provide a foundation for gender-relevant ostomy interventions to improve sleep and HR-QOL in this patient population. Citation: Baldwin CM; Grant M; Wendel C; Hornbrook MC; Herrinton LJ; McMullen C; Krouse RS. Gender Differences in Sleep Disruption and Fatigue on Quality of Life Among Persons with Ostomies. J Clin Sleep Med 2009;5(4):335-343.

Baldwin, Carol M.; Grant, Marcia; Wendel, Christopher; Hornbrook, Mark C.; Herrinton, Lisa J.; McMullen, Carmit; Krouse, Robert S.

2009-01-01

349

Effect of casting imperfections on the fatigue life of 319-F and A356-T6 Al–Si casting alloys  

Microsoft Academic Search

Casting imperfections, such as porosity, in cast aluminum components greatly influence their fatigue properties. The effect of porosity on the fatigue life of 319-F and A356-T6 aluminum alloys was studied, where the porosity characteristics on the fracture surfaces of fatigue-tested samples were examined using SEM and image analysis. The results show that porosity has the greatest detrimental effect on fatigue

H. R. Ammar; A. M. Samuel; F. H. Samuel

2008-01-01

350

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

PubMed

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

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

2012-11-10

351

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

352

Early life stress and inflammatory mechanisms of fatigue in the Coronary Artery Risk Development in Young Adults (CARDIA) study.  

PubMed

Fatigue is highly prevalent and causes serious disruption in quality of life. Although cross-sectional studies suggest childhood adversity is associated with adulthood fatigue, longitudinal evidence of this relationship and its specific biological mechanisms have not been established. This longitudinal study examined the association between early life stress and adulthood fatigue and tested whether this association was mediated by low-grade systemic inflammation as indexed by circulating C-reactive protein (CRP) and interleukin-6 (IL-6). In the Coronary Artery Risk Development in Young Adults (CARDIA) study, a population-based longitudinal study conducted in 4 US cities, early life stress was retrospectively assessed in 2716 African-American and white adults using the Risky Families Questionnaire at Year 15 examination (2000-2001, ages 33-45 years). Fatigue as indexed by a loss of subjective vitality using the Vitality Subscale of the 12-item Short Form Health Survey was assessed at both Years 15 and 20. While CRP was measured at both Years 15 and 20, IL-6 was measured only at Year 20. Early life stress assessed at Year 15 was associated with adulthood fatigue at Year 20 after adjustment for sociodemographic characteristics, body-mass index, medication use, medical comorbidity, smoking, alcohol consumption, physical activity, current stress, pain, sleep disturbance as well as Year 15 fatigue (adjusted beta 0.047, P=0.007). However, neither CRP nor IL-6 was a significant mediator of this association. In summary, early life stress assessed in adulthood was associated with fatigue 5 years later, but this association was not mediated by low-grade systemic inflammation. PMID:22554493

Cho, Hyong Jin; Bower, Julienne E; Kiefe, Catarina I; Seeman, Teresa E; Irwin, Michael R

2012-04-25

353

Effect of tensile mean stress on fatigue behavior of single-crystal and directionally solidified superalloys  

Microsoft Academic Search

Two nickel base superalloys, single crystal PWA 1480 and directionally solidified MAR-M 246 + Hf, were studied in view of the potential usage of the former and usage of the latter as blade materials for the turbomachinery of the space shuttle main engine. The baseline zero mean stress (ZMS) fatigue life (FL) behavior of these superalloys was established, and then

S. Kalluri; M. A. Mcgaw

1990-01-01

354

Fatigue reliability of wind turbine components  

SciTech Connect

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

Veers, P.S.

1990-01-01

355

Association of fatigue and psychological distress with quality of life in patients with a previous venous thromboembolic event.  

PubMed

Health-related quality of life (QoL) has been associated with several social and medical conditions in patients with deep vein thrombosis (DVT) and pulmonary embolism (PE). To the best of our knowledge, there is no study investigating the relationship of QoL with psychological variables in this patient population. We assumed as a hypothesis an association between heightened levels of fatigue and psychological distress, as well as decreased QoL in patients with an objectively diagnosed venous thromboembolic event. Study participants were 205 consecutively enrolled out-patients (47.4 years, 54.6% men) with DVT and/or PE. Approximately 10 days before blood collection for thrombophilia work-up, QoL, fatigue, and psychological distress were assessed using the Short Form Health Survey (SF-12), the Multidimensional Fatigue Symptom Inventory Short Form (MFSI-SF) as well as the Hospitality Anxiety and Depression scale (HADS). After controlling for demographic and medical factors, fatigue (p < 0.01) but not psychological distress (p>0.05) was negatively associated with physical QoL, explaining 11.0% of the variance. Fatigue (p < 0.001) and psychological distress (p < 0.001) were significant predictors of mental QoL, explaining an additional 36.2% and 3.6% of the variance. Further analyses revealed that all subscales of the HADS (e.g. anxiety and depression) and of the MFSI-SF (e.g. general fatigue, physical fatigue, emotional fatigue, mental fatigue and vigor) were significant predictors of mental QoL. MFSI-SF subscales also predicted physical QoL. The findings suggest that fatigue and psychological distress substantially predict QoL in patients with a previous venous thromboembolic event above and beyond demographic factors. PMID:19967154

Lukas, Paul S; Krummenacher, René; Biasiutti, Franziska Demarmels; Begré, Stefan; Znoj, Hansjörg; von Känel, Roland

2009-12-01

356

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

PubMed

To design against premature mechanical failure, most implant devices such as coronary and endovascular stents are assessed on the basis of survival, i.e., if a fatigue life of 10(8) cycles is required, testing is performed to ascertain whether the device will survive 10(8) cycles under accelerated in vitro loading conditions. This is a far from satisfactory approach as the safety factors, which essentially tell you how close you are to failure, remain unknown; rather, the probability of fatigue failure should instead be assessed on the basis of testing to failure. In this work, a new damage-tolerant analysis of a cardiovascular stent is presented, where the design life is conservatively evaluated using a fracture mechanics methodology. In addition to enabling estimates of safe in vivo lifetimes to be made, this approach serves to quantify the effect of flaws in terms of their potential effect on device failure, and as such provides a rational basis for quality control. PMID:16260033

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

2005-11-02

357

Fatigue Life of Lead Free Solder BGA Joints Against Vibration Stress under High Temperature Circumstance  

NASA Astrophysics Data System (ADS)

Recently, the wave of car computerizing is surging such as electronic control unit, car navigation system, electronic toll collection system, car to car communication system, etc. The use environment of in-car devices is under combined environmental stresses such as thermal stress, vibration, and humidity. In general, the reliability of the joints of the devices is individually tested by the evaluation methods for each stress. Our main purpose of this study is to construct the evaluation method for the damages of solder joints under multiple environmental stresses. We investigated the relationship between the plastic strain caused by one cycle vibration stress calculated with FEM analysis considering the temperature dependency of the elasto-plasticity and the fatigue life obtained by the vibration experiment. We indicated the adequacy of the analysis by the correspondence of the resonance frequency of the BGA package mounting board with the experimental result. We also showed that the plastic strain concentrating position corresponded to the crack position. We clarified that the creep strain rate in the total strain was less than 1 percent. We demonstrated that we could apply the power-law equation to predict the fatigue life of the vibration stress from plastic strain rate under 80°C and 125°C as well as the room temperature.

Matsushima, Michiya; Furusawa, Takeshi; Fukuda, Kyohei; Egusa, Minoru; Yasuda, Kiyokazu; Fujimoto, Kozo

358

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

359

Fatigue life prediction of GTA welded AISI 304L cruciform joints with lack of penetration using local-stress approach  

Microsoft Academic Search

The influence of welding procedure on fatigue properties of gas tungsten arc welded (GTAW) AISI 304L load carrying cruciform joints, containing lack of penetration (LOP) has been studied using a crack initiation–propagation (I-P) method. The crack process normally comprises two major phases: (1) the crack initiation life (NI): and (2) the crack propagation life (Np). The local stress-life approach is

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

2003-01-01

360

A zero torsional stiffness twist morphing blade as a wind turbine load alleviation device  

NASA Astrophysics Data System (ADS)

This paper presents the design, analysis and realization of a zero stiffness twist morphing wind turbine blade. The morphing blade is designed to actively twist as a means of alleviating the gust loads which reduce the fatigue life of wind turbine blades. The morphing structure exploits an elastic strain energy balance within the blade to enable large twisting deformations with modest actuation requirements. While twist is introduced using the warping of the blade skin, internal pre-stressed members ensure that a constant strain energy balance is achieved throughout the deformation, resulting in a zero torsional stiffness structure. The torsional stability of the morphing blade is characterized by analysing the elastic strain energy in the device. Analytical models of the skin, the pre-stressed components and the complete blade are compared to their respective finite element models as well as experimental results. The load alleviation potential of the adaptive structure is quantified using a two-dimensional steady flow aerodynamic model which is experimentally validated with wind tunnel measurements.

Lachenal, X.; Daynes, S.; Weaver, P. M.

2013-06-01

361

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

SciTech Connect

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.

1983-04-01

362

Fatigue symptom distress and its relationship with quality of life in adult stem cell transplant survivors  

Microsoft Academic Search

Fatigue is a common problem among cancer patients, especially those who have received chemotherapy and radiation therapy. Stem cell transplant (SCT) patients are at a particular risk of persistent fatigue as they receive more aggressive therapies. This study examined the prevalence of fatigue after completion of SCT. Further, the level of fatigue symptom distress and its relationship with quality of

Suzan Fouad Abduljawad

2009-01-01

363

A New Ductility Exhaustion Model for High Temperature Low Cycle Fatigue Life Prediction of Turbine Disk Alloys  

NASA Astrophysics Data System (ADS)

Based on ductility exhaustion theory and the generalized energy-based damage parameter, a new viscosity-based life prediction model is introduced to account for the mean strain/stress effects in the low cycle fatigue regime. The loading waveform parameters and cyclic hardening effects are also incorporated within this model. It is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature low cycle fatigue conditions. In the developed model, dynamic viscosity is used to describe the flow behavior. This model provides a better prediction of Superalloy GH4133's fatigue behavior when compared to Goswami's ductility model and the generalized damage parameter. Under non-zero mean strain conditions, moreover, the proposed model provides more accurate predictions of Superalloy GH4133's fatigue behavior than that with zero mean strains.

Zhu, Shun-Peng; Huang, Hong-Zhong; Li, Haiqing; Sun, Rui; Zuo, Ming J.

2011-06-01

364

Evaluation of effects of LWR coolant environments on fatigue life of carbon and low-alloy steels  

SciTech Connect

The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Figure I-90 of Appendix I to Section III of the Code specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Recent test data indicate a significant decrease in fatigue life of carbon and low-alloy steels in LWR environments when five conditions are satisfied simultaneously, viz., applied strain range, temperature, dissolved oxygen in the water, and sulfur content of the steel are above a minimum threshold level, and the loading strain rate is below a threshold value. Only a moderate decrease in fatigue life is observed when any one of these conditions is not satisfied. This paper summarizes available data on the effects of various material and loading variables such as steel type, dissolved oxygen level, strain range, strain rate, and sulfur content on the fatigue life of carbon and low-alloy steels. The data have been analyzed to define the threshold values of the five critical parameters. Methods for estimating fatigue lives under actual loading histories are discussed.

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

1996-02-01

365

Health-related quality of life and fatigue in patients with adrenal incidentaloma.  

PubMed

The objective of the present study was to examine several dimensions of quality of life (QoL) and fatigue in patients with adrenal incidentaloma. This was a case-control study designed to analyze patient outcomes using three validated generic QoL questionnaires, EQ-5D, SF-36, and MFI-20, the results of which were compared to those obtained for age- and sex-matched controls. The study population comprised 139 consecutive patients with nonfunctioning adrenal masses (104 females, 35 males; age 59.1 ± 10.8) and 139 age- and sex-matched controls. Reduced QoL was found in patients with adrenal incidentaloma as compared to controls. Dimensions of QoL that were notably affected included mobility (P = 0.03), performance of usual activities (P = 0.002), and anxiety/depression (P = 0.04) as evaluated using the EQ-5D; physical functioning (P < 0.001), physical role (P < 0.001), general health (P < 0.001), vitality (P = 0.001), social functioning (P = 0.001), and emotional role (P < 0.001) as evaluated using the SF-36; and physical fatigue (P = 0.04) as assessed using the MFI-20 questionnaire. In addition, perceived health on a visual analogue scale was also significantly lower in patients than in controls (64.8 ± 19.2 vs. 77.1 ± 15.1; P < 0.001). Patients with adrenal incidentaloma reported reduced QoL and a higher level of physical fatigue compared to age- and sex-matched controls. This subject will benefit from further studies comparing QoL outcomes of laparoscopic adrenalectomy versus no treatment in patients with adrenal incidentaloma. PMID:21442381

Kastelan, Darko; Dzubur, Fedja; Dusek, Tina; Poljicanin, Tamara; Crncevic-Orlic, Zeljka; Kraljevic, Ivana; Solak, Mirsala; Bencevic, Tanja; Aganovic, Izet; Knezevic, Nikola; Kastelan, Zeljko; Korsic, Mirko

2011-03-26

366

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

SciTech Connect

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, D.P.

1992-01-01

367

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

368

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

369

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

370

Artificial neural networks and the effects of loading conditions on fatigue life of carbon and low-alloy steels  

SciTech Connect

The ASME Boiler and Pressure Vessel Code contains rules for the construction of nuclear power plant components. Figure 1-90 of Appendix I to Section III of the Code specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Recent test data indicate significant decreases in the fatigue lives of carbon and low-alloy steels in LWR environments when five conditions are satisfied simultaneously. When applied strain range, temperature, dissolved oxygen in the water, and sulfur content of the steel are above a minimum threshold level, and the loading strain rate is below a threshold value, environmentally assisted fatigue occurs. For this study, a data base of 1036 fatigue tests was used to train an artificial neural network (ANN). Once the optimal ANN was designed, ANN were trained and used to predict fatigue life for specified sets of loading and environmental conditions. By finding patterns and trends in the data, the ANN can find the fatigue lifetime for any set of conditions. Artificial neural networks show great potential for predicting environmentally assisted corrosion. Their main benefits are that the fit of the data is based purely on data and not on preconceptions and that the network can interpolate effects by learning trends and patterns when data are not available.

Pleune, T.T. [Argonne National Lab., IL (United States)]|[Massachusetts Institute of Technology, Cambridge, MA (United States). Nuclear Engineering Dept.; Chopra, O.K. [Argonne National Lab., IL (United States)

1996-11-01

371

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.; Yamamoto, A.; Tsubakino, H. [Himeji Inst. of Tech. (Japan)

1998-10-05

372

Fatigue life prediction of shielded metal arc welded cruciform joints containing LOP defects by a mathematical model  

Microsoft Academic Search

A new mathematical model is developed to predict the fatigue life of Shielded Metal Arc Welded (SMAW) cruciform joints containing Lack of Penetration (LOP) defect. High strength, quenched and tempered steel (ASTM 517 ‘F’ Grade) is used as the base material throughout the investigation. Four factors, five level, central composite, rotatable design matrix is used to optimise the required number

V. Balasubramanian; B. Guha

1999-01-01

373

Simulation of fatigue life of solder ball joints of an ultra-fine-pitch wafer level package  

Microsoft Academic Search

With the relentless trend towards ever increasing number of I\\/Os for IC packages, pitches of flip chip packages are becoming every smaller. With smaller pitches and smaller stand-offs, the fatigue life of solder joints are expected to decrease. It is well known that the corner solder joint which is furthest from the centre of the package (called the critical solder

B. Zhao; A. A. Tay

2003-01-01

374

Thermal fatigue life analysis and forecast of PBGA solder joints on the flexible PCB based on finite element analysis  

Microsoft Academic Search

Thermal fatigue life of PBGA (plastic ball grid array) solder joint on the FPC (flexible printed circuit) was analysed based on finite element analysis. According to symmetry theory, a quarter finite element model of 144-PIN PBGA was established. Both the stress and strain of lead and lead-free PBGA solder joints on the flexible PCB with the basic material of polyimide

Huang Chunyue

2008-01-01

375

Sensitivity study on material properties for the fatigue life prediction of solder joints under cyclic thermal loading  

Microsoft Academic Search

A computational study is presented in this paper to investigate the effect of variation in material properties on the fatigue life prediction of solder joints subjected to cyclic thermal loading. The package under investigation was a plastic quad flat pack (PQFP) with gull-wing leads. A commercial finite element code, ABAQUS, was employed to perform a two-dimensional plane stress analysis. While

Shi-Wei Ricky Lee; Xiaowu Zhang

1998-01-01

376

Optimal design and fatigue life prediction for QFN solder joints by BP Artificial Neural Networks and Genetic Algorithm  

Microsoft Academic Search

Based on the theories of Back-Propagation (BP) Artificial Neural Networks (ANN) and Genetic Algorithm (GA), combining with multiple statistical analysis method, fatigue life prediction and technological parameter optimization of QFN solder joints were studied in this paper. Firstly, correlation coefficient matrix of the swatch was gained by factor analysis; taking length and width of the pad, stand-off and the solder

Wu Zhaohua

2010-01-01

377

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

378

PREDICTION OF FATIGUE LIFE OF COLD FORGING TOOLS BY FE SIMULATION AND COMPARISON OF APPLICABILITY OF DIFFERENT DAMAGE MODELS  

Microsoft Academic Search

Tools for cold forging mainly fail due to cyclic fatigue. Tool costs can reach a significant portion of production costs and therefore meth ods to improve tool life are of high interest. However, tools are still main ly designed and optimized by the trial and error method. The purpose of the work presented is to implement damage models in a

M. Meidert; C. Walter

379

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

380

Methodology for on-line fatigue life monitoring of Indian nuclear power plant components.  

National Technical Information Service (NTIS)

Fatigue is one of the most important aging effects of nuclear power plant components. Information about accumulation of fatigue helps in assessing structural degradation of the components. This assists in-service inspection and maintenance and may also su...

N. K. Mukhopadhyay B. K. Dutta H. S. Kushawaha

1992-01-01

381

Life Prediction Model for a Nickel-base Single Crystal Superalloy DD3  

Microsoft Academic Search

The possibility of a life prediction model for nickel-base single crystal blades has been studied. The fatigue-creep (FC) and thermal fatigue-creep(TM FC) as well as creep experiments have been carried out with different hold time of DD3. The hold time and the frequency as well as the temperature range are the main factors influencing the life. An emphasis has been

Zhu-feng YUE; Zhi-guo YANG; Zhen-zhou LU

2002-01-01

382

A new finite element fatigue modeling approach for life scatter in tensile steel specimens  

Microsoft Academic Search

This paper presents the results of a finite element model developed to investigate the effects of material microstructure topology on fatigue damage evolution in dog-bone tensile specimens. The Voronoi finite element model (VFEM) developed was used to study fatigue damage evolution in AISI 4142 steel under various loading conditions. An environmental scanning electron microscope (ESEM) coupled with an Instron fatigue

Anurag Warhadpande; Behrooz Jalalahmadi; Trevor Slack; Farshid Sadeghi

2010-01-01

383

Prediction of Fatigue Life for CFRP\\/Metal Bolted Joint under Temperature Conditions  

Microsoft Academic Search

In 1997, we proposed a prediction method of fatigue failure load for polymer composite structures under an arbitrary frequency, load ratio (minimum load\\/maximum load), and temperature from the data measured by constant elongation-rate (CER) tests under various temperatures and loading rates, and by fatigue tests at a single frequency under various temperatures. In this paper, tensile CER and fatigue tests

Naoyuki Sekine; Masayuki Nakada; Yasushi Miyano; Akira Kuraishi; Stephen W. Tsai

2003-01-01

384

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

385

Chronic Stress and Fatigue-Related Quality of Life after Mild-to-Moderate Traumatic Brain Injury (TBI)  

PubMed Central

Objective To determine relationships between chronic stress, fatigue-related quality of life (QOL-F) and related covariates after mild-to-moderate traumatic brain injury (TBI). Design Observational and cross-sectional Participants A total of 84 community-dwelling individuals with mild-to-moderate TBI recruited from multiple out-patient rehabilitation clinics assessed on average 15 months after injury. Method Data were collected with self-report surveys and chart abstraction. Measures Neurofunctional Behavioral Inventory, Perceived Stress Scale-14, Impact of Events Scale, McGill Pain Short-form Scale, and modified version of the Fatigue Impact Scale. Results Fatigue-related quality of life was associated with somatic symptoms, perceived situational stress, but not with event-related stress (PTSD symptoms) related to index TBI, pre-injury demographic, or post-injury characteristics. Somatic symptoms and chronic situational stress accounted for 42% of the variance in QOL (F). Conclusions QOL (F) in community-dwelling individuals with mild-to- moderate TBI is associated with chronic situational stress and somatic symptoms. Symptom management strategies may need to include general stress management to reduce fatigue burden and improve quality of life.

Bay, Esther; de-Leon, Marita B.

2010-01-01

386

The significance of acoustic emission during stressing of TiAl-based alloys. Part II: Influence of cracks induced by pre-stressing on the fatigue life  

Microsoft Academic Search

Fully lamellar samples of Ti44Al8Nb1B have been tested in tension–tension fatigue, after being pre-stressed, in order to investigate the effect on fatigue life of the cracks which are introduced by pre-stressing. It has been found that pre-stressing samples at 0.95 of the 0.2% proof stress leads to early failure when they are fatigue-tested at stress levels of about 0.65 of

X Wu; D Hu; R Botten; M. H Loretto

2001-01-01

387

Alendronate in bone cement: fatigue life degraded by liquid, not by powder.  

PubMed

Bisphosphonates have the potential to reduce osteolysis, a phenomenon that has been postulated to play a key role in aseptic loosening of total joint replacements. Bisphosphonates may contribute to the in vivo longevity of total joint replacements. Some authors have suggested there are decreases in flexural strength and flexural modulus of the cured cement when a liquid form of disodium pamidronate is added to a commercially available acrylic bone cement (Palacos R). We proposed that it is comparatively easier to blend a bisphosphonate in powder form into an acrylic bone cement than it is when the drug is in liquid form; and that the cement's fatigue life is decreased when the bisphosphonate is added in liquid rather than in solid form. The bisphosphonate and bone cement used were alendronate sodium and Cemex XL, respectively. The fatigue tests were done using phosphate buffered saline solution at 37 degrees +/- 1 degrees C. The data supported both hypotheses. Our findings should guide orthopaedic surgeons when using bisphosphonate-impregnated acrylic bone cements in total joint replacements. Bisphosphonates are endogenous pyrophosphate analogs in which a carbon atom replaces the central oxygen atom. These therapeutic agents may be classified into nitrogen and non-nitrogen containing types. Some examples are alendronate, pamidronate, ibandronate, risedronate, etidronate, clodronate, and zoledronate. There are many targets and mechanisms of action of this family of drugs, therefore making them efficacious against diverse clinical conditions such as osteoporosis, periprosthetic bone loss subsequent to total joint replacement, tumor cell proliferation, apoptosis and angiogenesis, Charcot neuroarthropathy, rheumatoid arthritis, ankylosing spondylitis and spondyloarthropathies, and arterial calcification. It has been proposed that some bisphosphonates are effective against the mechanisms that have been suggested as being implicated in aseptic loosening of total joint replacements, these being osteoclast-mediated bone resorption and wear particle-induced osteolysis. A meta-analysis of randomized controlled trials showed that alendronate and pamidronate had beneficial effects maintaining periprosthetic bone for as much as 1 year after a total joint replacement. PMID:16446596

Lewis, Gladius; Janna, Si

2006-04-01

388

Modelling the optimum grain size on the low cycle fatigue life of a Ni based superalloy in the presence of two possible crack initiation sites  

Microsoft Academic Search

LCF experiments, in situ tensile tests and small fatigue crack growth rate measurements on different heats of Inconel 718 alloy with widely different grain sizes have been performed. A fatigue life prediction model including a transition in the crack initiation mechanism (particle\\/Stage I) is identified. This model is essentially based on Tanaka and Mura model [J Appl Mech 48 (1981)

F. Alexandre; S. Deyber; A. Pineau

2004-01-01

389

Prediction of high-cycle fatigue life reliability of aluminum cast alloy from statistical characteristics of defects at meso-scale  

Microsoft Academic Search

In this paper, a growth rate law of a small fatigue crack of an arbitrary metal and a method for predicting a size distribution of spheroidal defects cut by a specimen are proposed. And then, by combining the crack growth rate law and the prediction method for the surface defect size distribution, a method for predicting a high-cycle fatigue life

Tatsujiro Miyazaki; Hyogyoung Kang; Hiroshi Noguchi; Keisaku Ogi

2008-01-01

390

Test Method for the Fatigue Life of Layered TiB/Ti Functionally Graded Beams Subjected to Fully Reversed Bending  

NASA Astrophysics Data System (ADS)

Sonic fatigue of aircraft is characterized by fully reversed bending of components subjected to acoustic excitation. This problem is compounded in high temperature environments because solutions for acoustics which tend to result in stiff structures make thermal problems worse. Conversely solutions to the thermal problem which allow expansion often fail in the presence of high acoustic levels. Errors in fatigue life prediction in the combined environment often range from a factor of 4 to 10. This results in either heavy, overly stiff structure or premature failure. This work will test the hypothesis that the fatigue life of a layered functionally graded material (FGM) will be dominated by the failure of the stiffest outer layer. This is based on the observation that for isotropic materials the life is approximately 90% crack initiation and only 10% crack growth before failure. Four sets of cantilever specimens will be tested using an electro-mechanical shaker for base excitation. The excitation will be narrow band random around the fundamental frequency. Two sets of specimens are of uniform composition consisting of 85%TiB/Ti and two are graded specimens consisting of layers that vary from commercially pure titanium to 85%TiB/Ti. Strain vs number of cycles to failure curves will be generated with both constant amplitude sine and narrow band random around the fundamental frequency excitation. The results will be examined to compare life of the uniform material to the functionally graded material. Also to be studied will be the use of Miner's rule to predict the fatigue life of the randomly excited specimens.

Byrd, Larry; Rickerd, Greg; Wyen, Travis; Cooley, Glenn; Quast, Jeff

2008-02-01

391

Fretting fatigue of rough surfaces  

Microsoft Academic Search

This paper presents a numerical model that maps the evolution of fretting fatigue life of Hertzian rough contacting bodies in fretting wear. Effect of surface roughness parameters (i.e. root mean square, skewness and orientation) on fretting fatigue life is reported. Fretting fatigue life is calculated as the crack initiation period predicted by the Smith Watson Topper multiaxial fatigue theory. Fretting

Aditya T. Kasarekar; Farshid Sadeghi; Spyros Tseregounis

2008-01-01

392

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

Microsoft Academic Search

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

Manjoine

1994-01-01

393

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

394

Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics  

NASA Astrophysics Data System (ADS)

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

Cantrell, John H.

2009-03-01

395

A new model to predict the fatigue life of flux cored arc welded cruciform joints containing LOP defects  

Microsoft Academic Search

A mathematical model has been developed to predict the fatigue life of Flux Cored Arc Welded (FCAW) cruciform joints containing\\u000a Lack of Penetration (LOP) defect. High strength, Quenched and Tempered steel ASTM 517 ‘F’ Grade has been used as the base\\u000a material throughout the investigation. Two level, full factorial technique has been applied to design the experiments. The\\u000a model has

V. Balasubramanian; B. Guha

1998-01-01

396

Effect of cyclic frequency on the fatigue life of ASME SA106B piping steel in PWR environments  

Microsoft Academic Search

Fatigue life tests in pressurized water reactor (PWR) environments were performed on smooth and sharply notched specimens\\u000a of ASME SA-106-B piping steel at cyclic frequencies of 1.0 Hz, 0.1 Hz, and 0.017 Hz. On the basis of these tests, it was concluded\\u000a that no effect of cyclic frequency existed for smooth specimens whereas a frequency of 0.017 Hz proved to

J. B. Terrell

1988-01-01

397

A new experimental method to evaluate creep fatigue life of flip-chip solder joints with underfill  

Microsoft Academic Search

A new accelerated stress test method was developed to evaluate creep life of flip-chip solder joints with underfill. With this method, a cyclic creep test can be done simply by applying a displacement to the FR-4 printed circuit board (PCB) board in the axial direction. The creep fatigue test was performed under displacement control with real-time electrical continuity monitoring. Test

D. J. Xie

2000-01-01

398

The effect of different build-up structures on solder joint fatigue life under thermo-mechanical cyclic loading condition  

Microsoft Academic Search

A FEA-based simulation procedure was established to evaluate the effect of different build-up structures on solder joint fatigue life under thermo-mechanical cyclic loading condition. The proposed methodology can therefore be used to select dielectric materials and core materials in build-up printed wiring boards (PWB) so that a build-up PWB board with the optimized combination of dielectrics and core material may

Jianjun Wang; S. Quander

2004-01-01

399

Finite element analysis for thermal fatigue life estimation of PBGA solder joints with model validation by experimental data  

Microsoft Academic Search

A previous experimental study was conducted to characterize the thermal fatigue life of PBGA solder joints under temperature cycling condition. The thermal cycling profile was one-hour cycles with a temperature range from -40°C to 125°C. The thermal cycling test lasted up to 3,000 cycles and the Weibull characteristics were obtained. In the present study, a computational model is established for

S. W. R. Lee

2004-01-01

400

Effect of finite element modeling techniques on solder joint fatigue life prediction of flip-chip BGA packages  

Microsoft Academic Search

Solder joint fatigue life in thermal cycling has been studied for decades using the finite element method. A great variety of modeling methodologies such as global\\/local modeling (sub-modeling) and sub-structure modeling (superelement) has been developed. Many different types of constitutive equations for solder alloys, various loading assumptions, and several definitions of damage parameters have been used. However, the accuracy of

Xuejun Fan; Min Pei; Pardeep K. Bhatti

2006-01-01

401

Method for the evaluation of the service life under random loading based on the energy criterion of fatigue fracture  

Microsoft Academic Search

We propose a method aimed at the assessment of the service life of structural elements under random loads based on the energy\\u000a criterion of fatigue fracture and the model of cyclic deformation of materials after overloading. The possibility of determination\\u000a of the maximum amplitude of stresses according to the number of loading cycles prior to fracture is substantiated. The results

P. A. Fomichev

2008-01-01

402

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

Microsoft Academic Search

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

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

2007-01-01

403

Designing for Fatigue with Random Vibration Excitation.  

National Technical Information Service (NTIS)

An experimental program was conducted to determine the correlation between fatigue life values obtained by sinusoidal fatigue tests and those obtained from narrow band random fatigue tests. The fatigue tests were performed on two commonly used aluminum al...

G. W. Brown R. Ikegami

1968-01-01

404

Improvement in the fatigue life of fiber-reinforced ceramics by use of interfacial lubrication  

SciTech Connect

Continuous-fiber reinforced ceramics are potential materials for high temperature load carrying structures. Most applications involve cyclic loading. Recent work has shown that the interfacial shear stress in ceramic matrix composites decreases rapidly in the initial stages of cyclic loading. This brings up a key question. Namely can fatigue life be improved by altering the initial wear rate of the fiber/matrix interface. This letter reports such an attempt, where micro-cracked specimens were immersed in oil prior to cyclic loads, in an attempt to change the interface wear rate. A Nicalon SiC-fiber/calcium aluminosilicate matrix (SiC{sub t}/CAS-II, Corning Glass Works, Corning, NY) composite was used in the study. The composite was processed with 16 plies and had a nominal fiber content of 40 vol.%. Edge loaded specimens, similar to those used in earlier studies were machined from 6 in. x 6 in. panels with fibers parallel to the tensile loading direction. To facilitate the observation of matrix cracking, the specimens were polished along an edge (minor face) with diamond paste to a final finish of 1 {mu}m.

Soerensen, B.F.; Holmes, J.W. [Univ. of Michigan, Ann Arbor, MI (United States)

1995-05-01

405

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

Microsoft Academic Search

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

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

2009-01-01

406

Improving Fatigue Life for Aluminum Cruciform Joints by Weld Toe Grinding  

Microsoft Academic Search

Fatigue improvement by weld toe grinding for aluminum welded joints has been investigated in this paper. Fatigue tests were performed for a number of as- welded and toe-ground non-load carrying cruciform joints. Finite element analyses were carried out to further study the influence of the variation of the main weld parameters such as the weld toe angle, weld toe radius

Naiquan Ye; Torgeir Moan

407

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

Microsoft Academic Search

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

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

2003-01-01

408

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

Microsoft Academic Search

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

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

1993-01-01

409

Rolling-Element Fatigue Life of Silicon Nitride Balls Preliminary Test Results.  

National Technical Information Service (NTIS)

Hot pressed silicon nitride was evaluated as a rolling element bearing material. The five-ball fatigue tester was used to test 12.7 mm (0.500 in.) diameter balls at a maximum Hertz stress of 800,000 psi at a race temperature of 130 F. The fatigue spalls i...

R. J. Parker E. V. Zaretsky

1972-01-01

410

Elevated temperature fretting fatigue of nickel based alloys  

NASA Astrophysics Data System (ADS)

This document details the high temperature fretting fatigue of high temperature nickel based alloys common to turbine disk and blade applications. The research consists of three area of focus: Experiments are conducted to determine quantitatively the fretting fatigue lives of advanced nickel based alloys; Analytical tools are developed and used to investigate the fretting fatigue response of the material; Fractographic analysis of the experimental results is used to improve the analytical models employed in the analysis of the experiments. Sixty three fretting fatigue experiments were conducted at 649 °C using a polycrystalline Nickel specimen in contact with directionally solidified and single crystal Nickel pads. Various influences on the fretting fatigue life are investigated. Shot peened Rene' 95 had better fretting fatigue life compared to shot peened Rene' 88. Shot peening produced a 2x increase in life for Rene' 95, but only a marginal improvement in the fretting fatigue life for Rene' 88. Minor cycles in variable amplitude loading produces significant damage to the specimen. Addition of occasional overpeaks in load produces improvements in fretting fatigue life. Contact tractions and stresses are obtained through a variety of available tools. The contact tractions can be efficiently obtained for limited geometries, while FEM can provide the contact tractions for a broader class of problems, but with the cost of increased CPU requirements. Similarly, the subsurface contact stresses can be obtained using the contact tractions as a boundary condition with either a semi-analytical FFT method or FEM. It is found that to calculate contact stresses the FFT was only marginally faster than FEM. The experimental results are combined with the analysis to produce tools that are used to design against fretting fatigue. Fractographic analysis of the fracture surface indicates the nature of the fretting fatigue crack behavior. Interrupted tests were performed to analyze the crack at intermediate lives. Fretting fatigue cracks were found to have formed in less than 10% of total fretting fatigue life. In addition to the formation of the individual fretting fatigue cracks, by 10% of the total expected fretting fatigue life, the individual fretting fatigue cracks have linked together to form a through the thickness edge crack. At some point in the experiment in between 20% to 50% of total expected fretting fatigue life, the edge crack growth retards or a corner crack accelerates. The result is a corner crack forms out of the edge crack. In many experiments this corner crack is the primary crack that leads to failure. The experimental results are combined with the analytic tools to generate usefull tools for the analysis of the fretting fatigue behavior of nickel based alloys at high temperature. This analysis tool is helpfull in the design of gas turbine engines which use nickel based alloys for the turbine blades and disks.

Gean, Matthew C.

411

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

412

Low cycle fatigue  

Microsoft Academic Search

The papers contained in this volume focus on various aspects of low cycle fatigue, including cyclic deformation, crack propagation, high-temperature low cycle fatigue, microstructural defects, multiaxial and variable amplitude loading, and life prediction. Papers are presented on the low cycle fatigue of some aluminum alloys, prediction of crack growth under creep-fatigue loading conditions, high-temperature low cycle fatigue behavior and lifetime

H. D. Solomon; L. R. Kaisand; G. R. Halford; B. N. Leis

1988-01-01

413

Life prediction of different commercial dental implants as influence by uncertainties in their fatigue material properties and loading conditions.  

PubMed

Probabilistic analyses allow the effect of uncertainty in system parameters to be determined. In the literature, many researchers have investigated static loading effects on dental implants. However, the intrinsic variability and uncertainty of most of the main problem parameters are not accounted for. The objective of this research was to apply a probabilistic computational approach to predict the fatigue life of three different commercial dental implants considering the variability and uncertainty in their fatigue material properties and loading conditions. For one of the commercial dental implants, the influence of its diameter in the fatigue life performance was also studied. This stochastic technique was based on the combination of a probabilistic finite element method (PFEM) and a cumulative damage approach known as B-model. After 6 million of loading cycles, local failure probabilities of 0.3, 0.4 and 0.91 were predicted for the Lifecore, Avinent and GMI implants, respectively (diameter of 3.75mm). The influence of the diameter for the GMI implant was studied and the results predicted a local failure probability of 0.91 and 0.1 for the 3.75mm and 5mm, respectively. In all cases the highest failure probability was located at the upper screw-threads. Therefore, the probabilistic methodology proposed herein may be a useful tool for performing a qualitative comparison between different commercial dental implants. PMID:22633857

Pérez, M A

2012-05-26

414

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

415

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

416

Enhancing the damping of wind turbine rotor blades, the DAMPBLADE project  

NASA Astrophysics Data System (ADS)

A research programme enabling the development of damped wind turbine blades, having the acronym DAMPBLADE, has been supported by the EC under its 5th Framework Programme. In DAMPBLADE the following unique composite damping mechanisms were exploited aiming to increase the structural damping: tailoring of laminate damping anisotropy, damping layers and damped polymer matrices. Additional objectives of the project were the development of the missing critical analytical technologies enabling the explicit modelling of composite structural damping and a novel composite blade design capacity enabling the direct prediction of aeroelastic stability and fatigue life; the development and characterization of damped composite materials; and the evaluation of new technology via the design and fabrication of damped prototype blades and their full-scale laboratory testing. After 4 years of work a 19 m glass/polyester damped blade was designed, manufactured and tested using the know-how acquired. Modal analysis of this blade at the testing facility of CRES showed a nearly 80% increase in the damping ratio of both the first flap and lag modes compared with the earlier, standard, design practice. Copyright

Chaviaropoulos, P. K.; Politis, E. S.; Lekou, D. J.; Sørensen, N. N.; Hansen, M. H.; Bulder, B. H.; Winkelaar, D.; Lindenburg, C.; Saravanos, D. A.; Philippidis, T. P.; Galiotis, C.; Hansen, M. O. L.; Kossivas, T.

2006-01-01

417

Improvement in Surface Fatigue Life of Hardened Gears by High-Intensity Shot Peening.  

National Technical Information Service (NTIS)

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 standar...

D. P. Townsend

1992-01-01

418

Alloy design options for improvement of the thermomechanical fatigue life of solder joints.  

National Technical Information Service (NTIS)

In this paper we discuss alloy development options to improve the thermomechanical fatigue behavior of eutectic Sn-Pb solder joints. Eutectic Sn-Pb solder joins fail through the development of a heterogeneous coarsened band of recrystallized and coarsened...

D. R. Frear W. B. Jones J. W. Morris Z. Mei

1991-01-01

419

Acoustic Fatigue Life Prediction for Nonlinear Structures with Multiple Resonant Modes.  

National Technical Information Service (NTIS)

This report documents an effort to develop practical and accurate methods for estimating the fatigue lives of complex aerospace structures subjected to intense random excitations. The emphasis of the current program is to construct analytical schemes for ...

R. N. Miles

1992-01-01

420

Acoustic Fatigue Life of Adhesive Bonded Structures Subjected to Acoustic Loads.  

National Technical Information Service (NTIS)

Acoustic fatigue damage to riveted metallic structures in aircraft due to high intensity noise has been recognized as a problem and design criteria have been developed to prevent such damage. However, very little design criteria are available for bonded a...

H. F. Wolfe I. Holehouse

1984-01-01

421

Prediction of fatigue crack propagation life in notched members under variable amplitude loading  

Microsoft Academic Search

One of the interesting phenomenon in the study of fatigue crack propagation under variable amplitude load cycling is the crack\\u000a growth retardation that normally occurs due to the application of a periodic overload. Fatigue crack growth rate under simple\\u000a variable amplitude loading sequence incorporating period overloads is studied using single edge notched specimens of AISI304\\u000a stainless steel. Load interaction effects

Z. Khan; A. Rauf; M. Younas

1997-01-01

422

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

423

Alloy design options for improvement of the thermomechanical fatigue life of solder joints  

Microsoft Academic Search

In this paper we discuss alloy development options to improve the thermomechanical fatigue behavior of eutectic Sn-Pb solder joints. Eutectic Sn-Pb solder joins fail through the development of a heterogeneous coarsened band of recrystallized and coarsened Pb- and Sn-rich phases. Imposed deformation concentrates solely into this thin region, accelerating fatigue failures. To address this problem, solder alloys are currently being

D. R. Frear; W. B. Jones; J. W. Jr. Morris; Z. Mei

1991-01-01

424

Fatigue-life prediction by an order statistics treatment of acoustic-emission signals  

Microsoft Academic Search

In fatigue, both the crack-propagation rates and the cumulative acoustic-emission activity are known to be related to the\\u000a applied stress-intensity range. By considering the energy balance during crack propagation and the relation of strain energy\\u000a release to the acoustic-emission characteristics, a formal relation between acoustic emission amplitudes and initial fatigue-crack-propagation\\u000a rates has been derived. Continuous monitoring of acoustic emission during

Joseph Baram

1993-01-01

425

Fatigue Life Estimates in Woven Carbon Fabric\\/Epoxy Composites at Non-Ambient Temperatures  

Microsoft Academic Search

The influence of temperature on fatigue resistance of Plain Weave Woven CFRP isexamined. The 8-ply laminateswere obtained from epoxy resin prepreg fabric layers stacked in two different sequences, producing unidirectional [0]8 and angle plied [0, 0, 45, ?45]s orientations. The fatigue tests were carried out at ?20, 0, 24, 100 and 150°C. It wasfound that there wasno change in sequence

Rehan Khan; Z. Khan; F. Al-Sulaiman; N. Merah

2002-01-01

426

On the fatigue life prediction of CFRP laminates using the Electrical Resistance Change method  

Microsoft Academic Search

The electro-mechanical response (Electrical Resistance Change method) as a damage index of quasi-isotropic Carbon Fiber Reinforced (CFRPs) laminates under fatigue loading was investigated. The effect of dispersed Multi-Wall Carbon Nanotubes (MWCNT) into the epoxy matrix was additionally evaluated and compared with neat epoxy CFRPs. The longitudinal resistance change of the specimens was monitored throughout the fatigue experiment. Three different stress

A. Vavouliotis; A. Paipetis; V. Kostopoulos

2011-01-01

427

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

428

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

429

Assessment of low-cycle fatigue life of Sn-3.5mass%Ag-X (X=Bi or Cu) alloy by strain range partitioning approach  

NASA Astrophysics Data System (ADS)

The fatigue lives and damage mechanisms of Sn-Ag-X (X=Bi and Cu) solder alloys under creep-fatigue interaction mode have been investigated, and the adaptability of the strain partitioning approach to the creep-fatigue of these alloys was examined. Symmetrical and asymmetrical saw-tooth strain profiles components ( i.e., fast-fast, fast-slow, slow-fast and slow-slow) were employed. Application of the slow slow,strain mode did not have an effect on fatigue lives of the alloys under investigation. Transgranular fracture observed on the fracture surfaces suggests that creep damage might be cancelled under slowslow mode. The fatigue lives of all alloys were dramatically reduced under slowfast mode, which is attributed to intergranular cavitation and fracture during tensile creep flow. On the other hand, the compression creep component generated by fast-slow mode also significantly reduced the life of Sn-3.5Ag and Sn-3.5Ag-1Cu, while the component did not affect the life of Sn-3.5Ag-xBi (x=2 and 5). The four partitioned strain ranges (i.e.,p, pp, cp, and cc) versus life relationships were established in all alloys tested. Thus, it is confirmed that the creep-fatigue life of these alloys can be quantitatively predicted by the strain partitioning approach for any type of inelastic strain cycling.

Kariya, Yoshiharu; Morihata, Tomoo; Hazawa, Eisaku; Otsuka, Masahisa

2001-09-01

430

Thermal-Barrier-Coated Turbine Blade Study.  

National Technical Information Service (NTIS)

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 ...

P. A. Siemers W. B. Hillig

1981-01-01

431

Fatigue life prediction of notched components: a comparison between the theory of critical distance and the classical stress-gradient approach  

Microsoft Academic Search

Fatigue life prediction for machine components is a key factor in the industrial world and several methods can be traced in technical literature to estimate life of notched components. The paper correlates the classical stress-gradient approach, here after called support factor (SF) method, proposed by Siebel, Neuber and Petersen with the modern theory of critical distance (TCD) approach by Tanaka

Andrea Spaggiari; Davide Castagnetti; Eugenio Dragoni; Simone Bulleri

2011-01-01

432

Impact of Medical Qigong on quality of life, fatigue, mood and inflammation in cancer patients: a randomized controlled trial  

PubMed Central

Background: Substantial numbers of cancer patients use complementary medicine therapies, even without a supportive evidence base. This study aimed to evaluate in a randomized controlled trial, the use of Medical Qigong (MQ) compared with usual care to improve the quality of life (QOL) of cancer patients. Patients and methods: One hundred and sixty-two patients with a range of cancers were recruited. QOL and fatigue were measured by Functional Assessment of Cancer Therapy—General and Functional Assessment of Cancer Therapy—Fatigue, respectively, and mood status by Profile of Mood State. The inflammatory marker serum C-reactive protein (CRP) was monitored serially. Results: Regression analysis indicated that the MQ group significantly improved overall QOL (t144?=??5.761, P?fatigue (t153?=??5.621, P?

Oh, B.; Butow, P.; Mullan, B.; Clarke, S.; Beale, P.; Pavlakis, N.; Kothe, E.; Lam, L.; Rosenthal, D.

2010-01-01

433

Correlations Between the Microstructure and Fatigue Life of Near-Eutectic Sn-Ag-Cu Pb-Free Solders  

NASA Astrophysics Data System (ADS)

Relationships between the microstructure of near-eutectic Sn-Ag-Cu Pb-free solder joints and room-temperature fatigue lifetimes were studied. Correlations between the lifetimes of single Sn grained, SAC205 solder joints with the orientation of the Sn grain, and with differences in Ag3Sn and Cu6Sn5 precipitate microstructures were sought. Correlations between the number of Sn grains and fatigue life were observed. Surprisingly, it was found that Ag3Sn precipitates were highly segregated from Cu6Sn5 precipitates on a length scale of approximately 20 ?m. Furthermore, large (factor of two) variations of the Sn dendrite arm size were observed within given samples. Such variations in values of dendrite arm size within a single sample were much larger than observed variations of this parameter between individual samples. Few significant differences were observed in the average size of precipitates in different samples. Although effects of average precipitate microstructure on lifetimes were not clearly delineated, one sample showed an anomalously high number of the smallest size (30 nm to 50 nm) Ag3Sn precipitates, and this sample also exhibited a much longer lifetime than all the other samples. Thus, some evidence was presented that samples of particular orientations and precipitate microstructures can exhibit anomalous fatigue lifetimes.

Arfaei, Babak; Cotts, Eric

2009-12-01

434

Ion-bombardment effects on the fatigue life of stainless steel under simulated fusion first-wall conditions  

SciTech Connect

An experiment which uses the MITR-II 5 MW research reactor to simulate several aspects of the anticipated environment of a fusion reactor first wall is described. Pressurized tube specimens are subjected simultaneously to stress and temperature cycling, surface bombardment by energetic helium and lithium ions and bulk irradiation by high-energy neutrons. Analysis of the samples is aimed primarily at determining the behavior of the ion bombarded surface layer, which has a depth of 2.5 ..mu..m, with particular reference to possible effects on the fatigue life of the material.

Kohse, G.E.

1983-02-01

435

Fatigue, psychosocial adaptation and quality of life one year after traumatic brain injury and suspected traumatic axonal injury; evaluations of patients and relatives: A pilot study.  

PubMed

Objective: To describe fatigue and its relationship to cognition, psychosocial adjustment, quality of life (QoL), work status and relative's experiences 12 months after suspected traumatic axonal injury (TAI). Methods: Eighteen patients were assessed with the Daily Fatigue Impact Scale (D-FIS), the Barrow Neurological Institute Screen for Higher Cerebral Functions (BNIS), the European Questionnaire 5 Dimensions health-related quality of life, the Glasgow Coma Outcome Scale Extended, and the European Brain Injury Questionnaire (EBIQ) (patient and relative). Return to work was registered. Results: At 1 year, fatigue still caused great problems in daily life. Although fatigue and cognition (BNIS) did not correlate, the more fatigued patients subjectively experienced significantly more cognitive dysfunction. Although D-FIS and QoL did not correlate, most patients reported that feelings of tiredness and dullness related to having lower QoL. However, lower QoL was associated with cognitive and attention disability (BNIS), subjective perception of executive dysfunction, lack of motivation, and mood disturbances (EBIQ). Neither fatigue nor cognition associated with return to work. The general consequences of TAI showed good agreement between patients' and relatives' experiences. Conclusion: The patient's subjective experience of the impact of TAI seems to be most essential, as it is the objective reality that the patient responds to, and this should therefore be assessed and treated. PMID:24002313

Esbjörnsson, Eva; Skoglund, Thomas; Sunnerhagen, Katharina S

2013-09-01

436

Modeling and microstructure analysis of fatigue initiation life extension by reductions in microporosity  

SciTech Connect

Fatigue initiation lifetimes were demonstrated to be related to the size and density of microporosity in the midplate region for three differently processed variations of aluminum alloy 7050-T7451. Metallographic and fractographic examination of double edge notched fatigue specimens was performed to characterize microstructural inhomogeneities. A greater size and density of micropores were found for those materials that had failed at shorter fatigue lifetimes. The specific crack-initiating feature was identified for each of the known cracks. Linear elastic fracture mechanics modeling of crack initiation from each of the micropore-induced cracks showed that this could be adequately accounted for by a stress intensity factor analysis proposed by Trantina and Barishpolsky.

Elsner, J.H.; Kvam, E.P.; Grandt, A.F. Jr. [Purdue Univ., West Lafayette, IN (United States)

1997-05-01

437

Ceramic blade attachment system  

DOEpatents

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

Boyd, Gary L. (Alpine, CA)

1995-01-01

438

Ceramic blade attachment system  

DOEpatents

A retainer ring is arranged to mount turbine blades to a turbine disk so that aerodynamic forces produced by a gas turbine engine are transferred from the turbine blades to the turbine disk to cause the turbine blades and turbine disk to rotate, but so that centrifugal forces of the turbine blades resulting from the rotation of the turbine blades and turbine disk are not transferred from the turbine blades to the turbine disk. 6 figures.

Boyd, G.L.

1995-04-11

439

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

440

Effect of material, heat treatment, grinding and shot peening on contact fatigue life of carburised steels  

Microsoft Academic Search

Contact fatigue resistance has been tested in a roller to roller rig. The test simulates the conditions in a gearbox with finite slip and with impurities in the lubricant. Two case hardened alloys were included in the study, different sequences of carburising and grinding and finally additional shot peening. The tested samples were characterised with respect to residual stress, microstructure,

Mattias Widmark; Arne Melander

1999-01-01

441

Effect of Shot Peening on Surface Fatigue Life of Carburized and Hardened AISI 9310 Spur Gears.  

National Technical Information Service (NTIS)

Surface fatigue tests were conducted on two groups of AISI 9310 spur gears. Both groups were manufactured with standard ground tooth surfaces, with the second group subjected to an additional shot peening process on the gear tooth flanks. The gear pitch d...

D. P. Townsend E. V. Zaretsky

1982-01-01

442

Theory Relating the Woehler Equation to Cumulative Damage in the Distribution Fatigue Life.  

National Technical Information Service (NTIS)

A theoretical model which is able to encompass the observed fatigue growth phenomena of crack acceleration or crack deceleration, crack arrest, and crack jump at a change of load level, is proposed for the expected incremental crack growth rate under prog...

S. C. Saunders

1974-01-01

443

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

Microsoft Academic Search

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

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

2005-01-01

444

The Effect of Oil Swelling on the Fatigue Life of Elastomers Subjected to Cyclic Bubble Inflation  

Microsoft Academic Search

This paper describes the behaviour of rubber in multi-axial fatigue, with respect to oil resistance. A series of tests were carried out on EPDM specimens subjected to varying degrees of swelling. The control methodology and the loading mechanism employed in the testing of elastomers using dynamic multi-axial bubble inflation are outlined. Swollen specimens were prepared by immersing them in reference

Niall M. Murphy; John Hanley; Stephen Jerrams; Ali Hassan

2008-01-01

445

New tool-joint design boosts fatigue life of drill-pipe tubes  

Microsoft Academic Search

Fatigue failures in drill pipe are caused by cyclic bending stresses. These stresses are concentrated in the thin-wall section of the drill pipe where the thick upset blends into the tube. Drill pipe today is being subjected to higher and higher stresses with the advent of top drives, deeper wells and higher-angle holes. This condition is further agitated by a

1993-01-01

446

Thermo-fatigue life evaluation of SnAgCu solder joints in flip chip assemblies  

Microsoft Academic Search

Thermal fatigue failure, due to the fracture of solder joints which was cased by the mismatch deformation, is frequently encountered in flip chip assemblies. Unfortunately, there is no widely accepted method to evaluate the reliability of solder joints, especially for lead-free solder joints, in such assemblies up to now. The constitutive models of double power law and the hyperbolic sine

Xiaoyan Li; Zhisheng Wang

2007-01-01

447

Damage Mechanics Based Fatigue Life Prediction for 63Sn-37Pb Solder Materials.  

National Technical Information Service (NTIS)

This paper presents a method of TMF analysis based on the theory of damage mechanics to examine the fatigue damage accumulation in 63 Sn-37Pb solder. The method is developed by extending a viscoplastic damage model proposed earlier by the authors (Wei, et...

Y. Wei C. L. Chow M. K. Neilsen H. E. Fang

2000-01-01

448

Fatigue life studies on defect-free solder joints fabricated from modified reflow soldering  

Microsoft Academic Search

This paper describes the improved characteristics of defect-free solder joints fabricated through modified reflow soldering. The modified method only requires that the solder joints are split for a very short time during a conventional solder reflow. The fatigue properties and microstructure of the solder joints are critically studied. It is found that the method of splitting is effective in eliminating

D. J. Xie; Yan C. Chan; J. K. L. Lai; I. K. Hui

1996-01-01

449

Fatigue Life of High-Speed Ball Bearings with Silicon Nitride Balls.  

National Technical Information Service (NTIS)

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...

R. J. Parker E. V. Zaretsky

1974-01-01

450

Surface fatigue crack life and penetration behavior of stress concentration specimen  

Microsoft Academic Search

Surface defects in the structural members are apt to be origins of fatigue crack growth, which may cause serious failure of the whole structure. Most structural bodies have a part where stress concentration exists, such as welded joints, corner parts, etc. The analysis on the crack growth and penetration from these defects may, therefore, be one of the most important

K. W. Nam; K. Ando; N. Ogura

1995-01-01

451

Surface Fatigue Life of M50nil and AISI 9310 Spur Gears and R C Bars.  

National Technical Information Service (NTIS)

Spur gear endurance tests and rolling element surface fatigue tests were conducted to study vacuum induction melted, vacuum arc remelted (VIM-VAR) M50NiL steel for use as a gear steel in advanced aircraft applications, to determine its endurance character...

D. P. Townsend E. N. Bamberger

1991-01-01

452

A PARAMETRIC STUDY ON FATIGUE LIFE BEHAVIOR OF SPOT WELDED JOINTS  

Microsoft Academic Search

Despite the availability of other joining methods such as laser beam welding, bolted, riveted, and adhesive bonding, resistance spot welding (RSW) remains the primary method to join panels especially in automotive, railroad, and airplane structures, which contain hundreds, even thousands of spot welds. In service, mechanical components usually experience cyclic loading. This makes fatigue failure prevention the foremost design requirement.

Ahmet Hanifi ERTAS; Fazil Onder SONMEZ

453

Relationship of Exercise to Fatigue and Quality of Life in Women With Breast Cancer.  

National Technical Information Service (NTIS)

Cancer treatment-related fatigue is recognized as a significant and long-lasting problem that effects patients both physically and emotionally and influences their treatment decisions and long-term recovery. The purpose of this study is to test the direct...

A. L. Schwartz

1997-01-01

454

Remaining fatigue life prediction in the initiation regime using SAW NDE  

Microsoft Academic Search

Harmonic generation of surface acoustic waves (SAW) is shown to be a useful tool for the detection of the initiation of surface cracks during fatigue of high strength aluminum alloys. A model that relates the length and density of microcracks to the amplitude of a SAW harmonic signal is described, and an associated coefficient of generation efficiency for the second

O. Buck; W. L. Morris; M. R. James

1980-01-01

455

Eect of material uncertainties on fatigue life calculations of aircraft fuselages: a cohesive element model  

Microsoft Academic Search

The present paper deals with the eect of uncertainties on the prediction of fatigue failure of aerospace and mechanical components. Typically the design of such struc- tures has been based on costly experiments or modied versions of Paris law which are applicable to very restricted range of conditions. The present formulation em- ploys cohesive zone elements in order to resolve

P. S. Koutsourelakis; K. Kuntiyawichai; G. I. Schueller

456

The effect of cold expansion on improving the fatigue life of fastener holes  

Microsoft Academic Search

An analytical and experimental study has been completed to assess the effectiveness of a direct cold expansion technique on the fatigue strength of fastener holes. Such methods are used in the aircraft construction industry to make holes more resistant to failure but recent research findings have reported that sometimes the anticipated benefits of cold expansion are not always achieved. This

T. N. Chakherlou; J. Vogwell

2003-01-01

457

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 load–time 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 load–time

I. P. Bond; I. R. Farrow

2000-01-01

458

Predicting the fatigue life of pristine and pre-corroded friction stir welded joints  

Microsoft Academic Search

Purpose – Friction stir welding (FSW) is simple, clean and cost effective joining technology which allows high-quality joining of materials that have been traditionally troublesome to weld conventionally without distortion, cracks or voids such as high-strength aluminium alloys. Since FSW has been identified as “key technology” for primary aerospace structures, the recent FAR regulations for damage tolerance and fatigue evaluations

T. Ghidini; C. Dalle Donne; U. Alfaro Mercado

2011-01-01

459

Fatigue of a Zr-Ti-Cu-Ni-Be bulk amorphous metal: Stress/life and crack-growth behavior  

SciTech Connect

In sharp contrast to oxide glasses, bulk metallic glasses can be surprisingly ductile. For example, recent experiments on a bulk Zr{sub 41.2}Ti{sub 13.8}Cu{sub 12.5}Ni{sub 10}Be{sub 22.5} (at%) alloy have demonstrated that amorphous metals can exhibit fracture toughnesses as high as {approximately} 55 MPa {radical}m, although mechanistically this result is not understood. Recent results also show fatigue-crack growth properties comparable to that of high-strength steels and aluminum alloys. However, corresponding stress/life (S/N) behavior on smooth-bar, nominally crack-free specimens, which are traditionally used to assess total life and crack initiation characteristics, have to date not been investigated in bulk amorphous metals. Accordingly, the current study is focused on the S/N behavior of a bulk amorphous Zr-Ti-Cu-Ni-Be alloy, with the objective of examining the relationship between fatigue crack initiation and propagation in comparison to behavior in traditional crystalline alloys.

Gilbert, C.J.; Lippmann, J.M.; Ritchie, R.O. [Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering

1998-01-13

460

Effects on fatigue life of gate valves due to higher torque switch settings during operability testing  

SciTech Connect

Some motor operated valves now have higher torque switch settings due to regulatory requirements to ensure valve operability with appropriate margins at design basis conditions. Verifying operability with these settings imposes higher stem loads during periodic inservice testing. These higher test loads increase stresses in the various valve internal parts which may in turn increase the fatigue usage factors. This increased fatigue is judged to be a concern primarily in the valve disks, seats, yokes, stems, and stem nuts. Although the motor operators may also have significantly increased loading, they are being evaluated by the manufacturers and are beyond the scope of this study. Two gate valves representative of both relatively weak and strong valves commonly used in commercial nuclear applications were selected for fatigue analyses. Detailed dimensional and test data were available for both valves from previous studies at the Idaho National Engineering Laboratory. Finite element models were developed to estimate maximum stresses in the internal parts of the valves and to identity the critical areas within the valves where fatigue may be a concern. Loads were estimated using industry standard equations for calculating torque switch settings prior and subsequent to the testing requirements of USNRC Generic Letter 89--10. Test data were used to determine both; (1) the overshoot load between torque switch trip and final seating of the disk during valve closing and (2) the stem thrust required to open the valves. The ranges of peak stresses thus determined were then used to estimate the increase in the fatigue usage factors due to the higher stem thrust loads. The usages that would be accumulated by 100 base cycles plus one or eight test cycles per year over 40 and 60 years of operation were calculated.

Richins, W.D.; Snow, S.D.; Miller, G.K.; Russell, M.J.; Ware, A.G.

1995-12-01

461

The effect of music and progressive muscle relaxation on anxiety, fatigue, and quality of life in family caregivers of hospice patients.  

PubMed

The purpose of this study was to examine the effects of music, progressive muscle relaxation (PMR), and music combined with progressive muscle relaxation on the reduction of anxiety, fatigue, and improvement of quality of life in family hospice caregivers. Subjects (N = 32) were divided randomly into 4 groups: control, music only, progressive muscle relaxation only, and music combined with progressive muscle relaxation and were tested twice a week for a duration of 2 weeks. A pre and posttest measuring anxiety and fatigue was administered each session. Quality of life was measured only on the first and last session. Results of three-way mixed design ANOVA indicated no significant main effect for group. However, results revealed a significant main effect for pretest and posttest on anxiety F(1, 28) = 51.82, p < .01 and fatigue, F(1, 28) = 32.86, p < .01. Significant difference on time effect were found for both anxiety F(3, 84) = 3.53, p < .05 and fatigue F(3, 84) = 5.21, p < .01. Follow-up paired t tests used for posthoc testing were conducted to compare pre and posttest difference scores for each group separately. Statistical results indicated a significant difference in quality of life when comparing the subject sample as a whole across the four days of treatment period, F(1, 28) = 14.21, p < .01. Follow-up paired sample t test indicated that the control and PMR group exhibited a significant difference in pre and posttest quality of life scores. There was a significant correlation between anxiety and quality of life (r(32) = .75, p < .01), anxiety and fatigue (r(32) = .55, p < .01), and fatigue and quality of life (r(32) = -.53, p < .01). PMID:20635523

Choi, Yoon Kyung

2010-01-01

462

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

SciTech Connect

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

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

2006-07-01

463

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

NASA Astrophysics Data System (ADS)

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

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

1995-02-01

464

Thickness dependent fatigue life at microcrack nucleation for metal thin films on flexible substrates  

NASA Astrophysics Data System (ADS)

For polymer-supported metal thin films used in flexible electronics, the definition of the fatigue lifetime at microcrack nucleation (FLMN) should be more physically meaningful than all the previous definitions at structural instability. In this paper, the FLMN of Cu films (with thickness from 100 nm to 3.75 µm) as well as Al thin films (from 80 to 800 nm) was experimentally characterized at different strain ranges and different thicknesses by using a simple electrical resistance measurement (ERM). A significant thickness dependence was revealed for the FLMN and a similar Coffin-Manson fatigue relationship observed commonly in bulk materials was found to be still operative in both the films. Microstructural analyses were carried out to verify the feasibility of ERM correspondingly.

Sun, X. J.; Wang, C. C.; Zhang, J.; Liu, G.; Zhang, G. J.; Ding, X. D.; Zhang, G. P.; Sun, J.

2008-10-01

465

Fatigue life prediction of asphalt concrete pavement using a harmony search algorithm  

Microsoft Academic Search

This paper proposes an efficient Harmony Search (HS) algorithm for determining the material parameters of a fatigue cracking\\u000a model based on Accelerated Pavement Testing (APT). APT is preferred over typical laboratory experiments and testing because\\u000a APT can simulate field pavement performance. The main advantage of the HS heuristic algorithm is its ability to find the best\\u000a global solution of a

Youngchan Suh; Sungho Mun; Insoo Yeo

2010-01-01

466

A through-process model of an A356 brake caliper for fatigue life prediction  

Microsoft Academic Search

The demand for low-cost, high strength-to-weight ratio components continues to drive the development of aluminum alloy castings\\u000a for new applications. The automotive brake caliper, which has traditionally been made from cast iron, is one such component\\u000a where aluminum alloys are being considered. The fatigue performance of the brake caliper is an important consideration in\\u000a evaluating new designs. The use of

D. M. Maijer; Y. X. Gao; P. D. Lee; T. C. Lindley; T. Fukui

2004-01-01

467

Fatigue crack growth and life prediction of foam core sandwich composites under flexural loading  

Microsoft Academic Search

Fatigue crack growth of foam core sandwich beams loaded in flexure has been investigated. Sandwich panels were manufactured using an innovative co-injection resin transfer molding process. S2-glass fiber with epoxy resins was used as face sheets over a PVC foam core. Testing was performed in a three-point flexure mode utilizing a newly designed fixture such that the localized indentation damage

Nitin Kulkarni; Hassan Mahfuz; Shaik Jeelani; Leif A. Carlsson

2003-01-01

468

Fatigue behavior and life predictions of notched specimens made of QT and forged microalloyed steels  

Microsoft Academic Search

Fatigue behavior of notched specimens was investigated using circumferentially notched round bar and double-notched flat plate geometries, each with different stress concentration factors. Specimens were made of a commonly used vanadium-based microalloyed forging steel, in both the as-forged and quenched and tempered (QT) conditions. The effects of different notch severities and constraint conditions (i.e. plane stress versus plane strain) on

A. Fatemi; Z. Zeng; A. Plaseied

2004-01-01

469

Method of improving fatigue life of cast nickel based superalloys and composition  

Microsoft Academic Search

The invention consists of a method of producing a fine equiaxed grain structure (ASTM 2-4) in cast nickel-base superalloys which increases low cycle fatigue lives without detrimental effects on stress rupture properties to temperatures as high as 1800.degree. F. These superalloys are variations of the basic nickel-chromium matrix, hardened by gamma prime [Ni.sub.3 (Al, Ti)] but with optional additions of

Allen F. Denzine; Thomas A. Kolakowski; John F. Wallace

1978-01-01

470

Evaluation of multiaxial stress-strain models and fatigue life prediction methods under proportional loading  

Microsoft Academic Search

Multiaxial fatigue damage occurs when the principal stress directions vary during the loading induced by several independent forces, such as out-of-phase bending and torsion. Uniaxial damage models cannot be reliably applied in this case. Besides the need for multiaxial damage models, another key issue to reliably model such problems is how to calculate the elastic-plastic stresses from the multiaxial strains.

Marco Antonio Meggiolaro; Oliveira Miranda; Pontifical Catholic

471

Life extension of acoustically fatigued panels using add-on dampers  

Microsoft Academic Search

Secondary aircraft structures vibrate as a result of very high intensity pressure waves caused by engine and\\/or aerodynamic effects. This type of excitation can result in acoustically-induced cracking, also known as resonant high-cycle, acoustic or sonic fatigue. In modern military aircraft, high sound pressure levels are quite often encountered, for example, the overall sound pressure levels of the order of

W. K. Chiu; U. Siovitz; S. C. Galea; L. L. Koss

1999-01-01

472

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

Microsoft Academic Search

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

Takenobu Sakai; Keita Yasui; Shuichi Wakayama

473

Fatigue Failure of Extrusion Dies: Effect of Process Parameters and Design Features on Die Life  

Microsoft Academic Search

Analysis of die failure plays an important role in the prediction and prevention of die failure, and subsequently in improving\\u000a economics of any metal-forming process. Industrial experience has shown that fracture is the most common mode of failure in\\u000a the case of hot aluminum extrusion dies. The purpose of the present work is to implement fatigue damage models in a

S. S. Akhtar; A. F. M. Arif

2010-01-01

474

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

475

Damage repair in CMSX-4 alloy without fatigue life reduction penalty  

NASA Astrophysics Data System (ADS)

The microstructural changes in a single-crystal Ni-base superalloy, CMSX-4, that might occur during the processes of repair and recoating of hot section components for advanced gas turbines were studied. It is shown that the cellular ?/?? microstructure is formed when the material is subjected to local plastic straining, followed by the reheat treatments during the course of damage recovery. The formation of cellular microstructure in the material led to the remarkably reduced fatigue strength. In order to reduce or prevent the preceding undesirable effect resulting from cellular microstructure, a new method based on applying overlay coating technique was developed. The method is based on an idea that the alloying elements that are depleted in base alloys could be supplemented via the overlay coating. An X alloy, which contains grain boundary strengthening elements, was selected and coated on the CMSX-4 with the cellular microstructure by low-pressure plasma spraying. The fatigue tests on the coated CMSX-4 specimens demonstrated the effectiveness of the method. The observations of the crack initiation site, the fatigue fracture mode, the crack density in the cellular transformed area, and the crack propagation morphologies near the prior interface strongly supported the validity of this approach. The method is expected to build a road to a so-called damage cure (or recovery) coating.

Okazaki, Masakazu; Ohtera, Issei; Harada, Yoshio

2004-02-01

476

Comprehensive testing of Nedwind 12-Meter wind turbine blades at NREL  

SciTech Connect

This paper describes the structural testing of two NedWind 25 12-m blades at the National Renewable Energy Laboratory (NREL). The tests were conducted under the Standards, Measurement and Testing (SMT) Program in conjunction with tests conducted by four European laboratories to develop a common database of blade testing methods. All of the laboratories tested duplicate copies of blades taken from series production. Blade properties, including weight, center of gravity, natural frequencies, stiffness, and damping, were determined. Static load tests were performed at 110% of the extreme design load for strain verification. NREL performed single-axis and two-axis fatigue tests using business-as-usual testing practices. The single-axis test combined equivalent life loading for the edge and flap spectra into a single resultant load. The two-axis test applied the edge and flap components independently at a phase angle of 90{degree}. Damage areas were observed at (1) the trailing edge, which cracked near the maximum chord; (2) between the steel root collar and the composite, where circumferential cracking was noted; and (3) along the top of the spar between the 2,500-mm and 4,200-mm stations, where a notable increase in acoustic emissions was detected. NREL observed that the onset of damage occurred earlier in the single-axis test.

Larwood, S.; Musial, W.

2000-03-13

477

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

478

Decision Making of Aircraft Engine Blades Condition Based on Bispectral Analysis of the Vibroacoustical Signal  

NASA Astrophysics Data System (ADS)

In this paper the simulation of vibroacoustical signals radiated by the engine turbine at the stationary vibration excitation is carried out for situations when all turbine blades have no defects and one blade has a small fatigue crack. Bispectral analysis is used for diagnostic information processing. It demonstrates that appearance and evolution of the fatigue crack in a blade change intensity of global and local extremums of bispectral modules. The results of bispectral processing and Probability Neural Network (PNN) are used to recognize of the turbine blades condition. The efficiency factor is used for precision analysis.

Bouraou, N. I.; Protasov, A. G.; Sopilka, Yu. V.; Zazhitsky, O. V.

2005-04-01

479