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Sample records for high-cycle fatigue life

  1. A method for calculation of finite fatigue life under multiaxial loading in high-cycle domain

    Directory of Open Access Journals (Sweden)

    M. Malnati

    2014-04-01

    Full Text Available A method for fatigue life assessment in high-cycle domain under multiaxial loading is presented in this paper. This approach allows fatigue assessment under any kind of load history, without limitations. The methodology lies on the construction - at a macroscopic level - of an indicator in the form of a set of cycles, representing plasticity that can arise at mesoscopic level throughout fatigue process. During the advancement of the loading history new cycles are created and a continuous evaluation of the damage is made.

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

    Science.gov (United States)

    Kihm, Frederic; Rizzi, Stephen A.

    2014-01-01

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

  3. Very high cycle fatigue life of 2.25Cr-1Mo steel at room and high temperatures

    International Nuclear Information System (INIS)

    An ultrasonic fatigue testing machine was developed to obtain the very high cycle fatigue life at elevated temperature for safety and reliability of structural components in the faster breeder reactor (FBR). This testing machine consists of an amplifier, booster, horn and equipments such as system controller and data acquisition. The test specimen is attached at the end of the horn. The electric power generated in the amplifier is transformed into the mechanical vibration in the converter and is magnified in the booster and horn. The developed ultrasonic fatigue testing machine enables to carry out the fatigue test at 20kHz so that it can perform the very high cycle fatigue test within a very shorter time as compared with the regular fatigue testing machines such as a hydraulic fatigue testing machine. This study carried out very high cycle fatigue tests using type STBA 24, the steel for tube in boiler and heat exchanger, at room and elevated (673K) temperatures by the developed testing and conventional hydraulic testing machines, and obtained the fatigue lives. This paper also described the cracks observed on specimen surface of fatigued specimen and discussed the very high cycle fatigue strength properties. It was confirmed that the fatigue data obtained by the ultrasonic fatigue testing machine are continuous and compatible with the results obtained by the hydraulic tension-compression testing machine. Fatigue lives more than 106 cycles at room and high temperatures can be predicted conservatively by the best fit design curve employed in the nuclear power plant design. (author)

  4. Crack propagation mechanism and life prediction for very-high-cycle fatigue of a structural steel in different environmental medias

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    Guian Qian

    2013-07-01

    Full Text Available The influence of environmental medias on crack propagation of a structural steel at high and very-high-cycle fatigue (VHCF regimes is investigated based on the fatigue tests performed in air, water and 3.5% NaCl aqueous solution. Crack propagation mechanisms due to different crack driving forces are investigated in terms of fracture mechanics. A model is proposed to study the relationship between fatigue life, applied stress and material property in different environmental medias, which reflects the variation of fatigue life with the applied stress, grain size, inclusion size and material yield stress in high cycle and VHCF regimes. The model prediction is in good agreement with experimental observations.

  5. Expansion of high-cycle fatigue life data and investigation of mean stress effect of stainless steel for light water reactor piping

    International Nuclear Information System (INIS)

    Establishment of a life evaluation method for structural components is essential for the rational operation and maintenance of LWR plants during their operating period. In this study, high-cycle fatigue tests for austenitic stainless steel SUS316NG, which is one of the representative structural materials of LWR piping, were conducted at 288degC, and fatigue data beyond 108 cycles were obtained. Results were summarized as follows; 1. SUS316NG showed notable cyclic hardening following cyclic softening. Additional mean stress increased mean strain, while it slightly decreased strain amplitude. 2. Fatigue tests with a constant amplitude less than a certain level ran out over 108 cycles. This suggested that SUS316NG has fatigue limit at 288degC. 3. Superposed mean stress did not decrease fatigue life. Correction of the effect of mean stress on fatigue life provided in the present design code seemed to be too conservative. (author)

  6. Fatigue characteristics of bearing steel in very high cycle fatigue

    International Nuclear Information System (INIS)

    Very high cycle fatigue (VHCF) tests were carried out to find the fatigue characteristics of a super-long life range by using a cantilever type rotational bending fatigue test machine on three kinds of specimens in bearing steel which were quenched and tempered in air (A: non-shot peened and B: shot peened after heat treatment) and under vacuum environment(C: non-shot peened) in this study. S-N curves obtained from the VHCF tests of the B and C specimens tend to come down again in the super-long life (109 cycles) range due to fish-eye type cracking, while most of the A and B specimens were fractured by surface defects such as scratches and slip lines. This duplex S-N behavior of bearing steel has to be reviewed by the change of the fracture modes

  7. Very High Cycle Fatigue Failure Analysis and Life Prediction of Cr-Ni-W Gear Steel Based on Crack Initiation and Growth Behaviors

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    Hailong Deng

    2015-12-01

    Full Text Available The unexpected failures of structural materials in very high cycle fatigue (VHCF regime have been a critical issue in modern engineering design. In this study, the VHCF property of a Cr-Ni-W gear steel was experimentally investigated under axial loading with the stress ratio of R = ?1, and a life prediction model associated with crack initiation and growth behaviors was proposed. Results show that the Cr-Ni-W gear steel exhibits the constantly decreasing S-N property without traditional fatigue limit, and the fatigue strength corresponding to 109 cycles is around 485 MPa. The inclusion-fine granular area (FGA-fisheye induced failure becomes the main failure mechanism in the VHCF regime, and the local stress around the inclusion play a key role. By using the finite element analysis of representative volume element, the local stress tends to increase with the increase of elastic modulus difference between inclusion and matrix. The predicted crack initiation life occupies the majority of total fatigue life, while the predicted crack growth life is only accounts for a tiny fraction. In view of the good agreement between the predicted and experimental results, the proposed VHCF life prediction model involving crack initiation and growth can be acceptable for inclusion-FGA-fisheye induced failure.

  8. High-cycle fatigue properties of structural materials for FBR (I). The study on the high-cycles fatigue properties of SUS304 at elevated temperature

    International Nuclear Information System (INIS)

    Fatigue fractures caused by high-cycle fatigue with thermal-striping or flow induced vibration have been occurred recently. For this reason, the importance of high-cycle fatigue life evaluation has been recognized. In this study, the high-cycle fatigue behavior was evaluated based on the results of high-cycle fatigue test up to 108 cycles at elevated temperature on Type 304 stainless steel, and the effect of notch on the high-cycle fatigue lives were investigated, too. The tests were carried out at 500degC under a load control mode with frequency set at 30Hz. The results obtained from this study are as follows. (1) The date of high-cycle fatigue properties were obtained in the range below 108 cycles at 500degC. (2) It is considered that the fatigue limit exists from the examination results in the range up to 108 cycles on smooth fatigue specimen. The internal fatigue fracture wasn't observed in the high-cycle region. (3) The fatigue lives increased with decreasing stress range below 108 cycles on notch specimen. The fatigue lives that calculated from the specimen shape were conservatively evaluated at 108 cycles. (4) Fracture that affect of stationary crack was observed near the crack initiation point on the notch specimen in the high-cycle region. (author)

  9. Study on dominant mechanism of high-cycle fatigue life in 6061-T6 aluminum alloy through microanalyses of microstructurally small cracks

    International Nuclear Information System (INIS)

    The mechanism controlling the fatigue life of a precipitation-hardened AlMgSi alloy (6061-T6) at a high-cycle fatigue (HCF) regime of over 107 cycles was investigated in detail. It was found that over 90% of the total fatigue life was occupied by the growth process of a microstructurally small crack at relatively low stress amplitude. The small crack was often found to be arrested and halted for a long period (more than 106 cycles) before it began to grow again, which resulted in a significantly slow growth process. The small crack was then analyzed not only by the conventional fractography but also by the cross-sectional observation of the crack tip region using a focused ion beam and transmission electron microscopy. These observations, supplemented also by a grain orientation analysis using electron backscattered diffraction, explicitly revealed the following points: (i) the small crack growth observed on the specimen surface is primarily related to facet-type cracking that occurs exclusively at the specimen surface; (ii) the growth direction of the small crack has strong anisotropy (i.e. surface-induced growth); (iii) the facet-type cracking is related to the formation of persistent fine slip bands that accompany no structural change of the matrix. On the basis of these results, the micromechanism of small crack growth and its relation to the concept of fatigue limit at the HCF regime is discussed in detail.

  10. Development of a probabilistic model for the prediction of fatigue life in the very high cycle fatigue (VHCF range based on inclusion population

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    Kolyshkin A.

    2014-06-01

    Full Text Available The VHCF behaviour of metallic materials containing microstructural defects such as non-metallic inclusions is determined by the size and distribution of the damage dominating defects. In the present paper, the size and location of about 60.000 inclusions measured on the longitudinal and transversal cross sections of AISI 304 sheet form a database for the probabilistic determination of failure-relevant inclusion distribution in fatigue specimens and their corresponding fatigue lifes. By applying the method of Murakami et al. the biggest measured inclusions were used in order to predict the size of failure-relevant inclusions in the fatigue specimens. The location of the crack initiating inclusions was defined based on the modeled inclusion population and the stress distribution in the fatigue specimen, using the probabilistic Monte Carlo framework. Reasonable agreement was obtained between modeling and experimental results.

  11. Torsional fatigue behaviour and damage mechanisms in the very high cycle regime

    OpenAIRE

    E. Bayraktar; Xue, H.; F. Ayari; C. Bathias

    2010-01-01

    Purpose: of this paper: Many engineering components operate under combined torsion and axial cyclic loading conditions, which can result in fatigue fracture after a very long life regime of fatigue. This fatigue regime were carried out beyond 109 loading cycles called very high cycle fatigue (VHCF) to understand the fatigue properties and damage mechanisms of materials.Design/methodology/approach: Torsional fatigue tests were conducted using a 20 kHz frequency ultrasonic fatigue testing devic...

  12. High cycle fatigue of austenitic stainless steels

    International Nuclear Information System (INIS)

    This study concerns the evaluation of material data to be used in LMFBR design codes. High cycle fatigue properties of three austenitic stainless steels are evaluated: type AISI 316 (UKAEA tests), type AISI 316L (CEA tests) and type AISI 304 (Interatom tests). The data on these steels comprised some 550 data points from 14 casts. This data set covered a wide range of testing parameters: temperature from 20-6250C, frequency from 1-20 000 Hz, constant amplitude and random fatigue loading, with and without mean stress, etc. However, the testing conditions chosen by the three partners differed considerably because they had been fixed independently and not harmonized prior to the tests. This created considerable difficulties for the evaluations. Experimental procedures and statistical treatments used for the three subsets of data are described and discussed. Results are presented in tables and graphs. Although it is often difficult to single out the influence of each parameter due to the different testing conditions, several interesting conclusions can be drawn: The HCF properties of the three steels are consistent with the 0.2% proof stress, the fatigue limit being larger than the latter at temperatures above 5500C. The type 304 steel has lower tensile properties than the two other steels and hence also lower HCF properties. Parameters which clearly have a significant effect of HCF behaviour are mean stress or R-ratio (less in the non-endurance region than in the endurance region), temperature, cast or product. Other parameters have probably a weak or no effect but it is difficult to conclude due to insufficient data: environment, specimen orientation, frequency, specimen geometry

  13. High-cycle fatigue properties of structural materials for FBR (2). High-cycle fatigue tests of 316FR steel at elevated temperature. Interim report

    International Nuclear Information System (INIS)

    In liquid metal cooled Fast Reactors (LMFBRs), thermal fluctuation due to fluid mixing induces high-cycle fatigue damages on structural materials. Such a cyclic thermal stress is estimated to repeat approximately from 108 to 109 cycles during a plant service period. Therefore, it is essential to investigate the fatigue property in a very-high cycle region. In this study, high-cycle fatigue tests at 550degC, 600degC, and 650degC under strain controlled conditions were carried out for the 316FR steel. The following results are obtained until now. (1) Adopting experimental techniques using laser level meter, high-cycle fatigue tests were performed at elevated temperature in the repetition frequency of 10-60 Hz, and the high cycle fatigue fracture data up to 107 cycle regions were obtained. (2) The number of cycles to failure observed in the high-cycle fatigue tests up to 107 cycle regions was larger than that calculated from simple extrapolation of average fatigue failure formula given in the material strength standard (DDS) for a design. Moreover, these lives were also conservative in comparison with those estimated from the high-cycle fatigue failure formula given by KOM-MSS WG. (3) The influence of frequency on fatigue life was not almost significant in the range from 0.1 to 60Hz. In contrast, the influence of temperature on fatigue life was observed. (4) The fisheye fracture was observed in the high-cycle fatigue test specimens failure in 107 cycle regions. (author)

  14. Effects of a high mean stress on the high cycle fatigue life of PWA 1480 and correlation of data by linear elastic fracture mechanics

    Science.gov (United States)

    Majumdar, S.; Kwasny, R.

    1985-01-01

    High-cycle fatigue tests using 5-mm-diameter smooth specimens were performed on the single crystal alloy PWA 1480 (001 axis) at 70F (room temperature) in air and at 100F (538C) in vacuum (10 to the -6 power torr). Tests were conducted at zero mean stress as well as at high tensile mean stress. The results indicate that, although a tensile mean stress, in general, reduces life, the reduction in fatigue strength, for a given mean stress at a life of one million cycles, is much less than what is predicted by the usual linear Goodman plot. Further, the material appears to be significantly more resistant to mean stress effects at 1000F than at 70F. Metallographic examinations of failed specimens indicate that failures in all cases are initiated from micropores of sizes of the order of 30 to 40 microns. Since the macroscopic stress-strain response in all cases was observed to be linear elastic, linear elastic fracture mechanics (LEFM) analyses were carried out to determine the crack growth curves of the material assuming that crack initiation from a micropore (a sub o = 40 microns) occurs very early in life. The results indicate that the calculated crack growth rates at an R (defined as the ratio between minimum stress to maximum stress) value of zero are approximately the same at 70F as at 1000F. However, the calculated crack growth rates at other R ratios, both positive and negative, tend to be higher at 70F than at 1000F. Calculated threshold effects at large R values tend to be independent of temperature in the temperature regime studied. They are relatively constant with increasing R ratio up to a value of about 0.6, beyond which the calculated threshold stress intensity factor range decreases rapidly with increasing R ratios.

  15. High cycle fatigue behaviour of extruded Magnesium alloys containing Neodymium

    OpenAIRE

    Nascimento Silva Ferri, Ligia

    2014-01-01

    In the present work the high cycle fatigue behaviour and quasi-static mechanical properties of extruded profiles of newly designed magnesium alloys containing rare earth element, Nd were investigated. The study mainly concerned the damage mechanisms under dynamic loading in the high cycle fatigue regime. The different damage mechanisms, interactions among them as well as their association with microstructural features (i.e. crystallographic texture, precipitates and grain size), which have a ...

  16. Initiation and propagation life distributions of fatigue cracks and the life evaluation in high cycle fatigue of ADI; ADI zai no ko cycle hiro kiretsu hassei shinten jumyo bunpu tokusei to jumyo hyoka

    Energy Technology Data Exchange (ETDEWEB)

    Ochi, Y.; Ishii, A. [University of Electro Communications, Tokyo (Japan); Ogata, T. [Hitachi Metals, Ltd., Tokyo (Japan); Kubota, M. [Kyushu University, Fukuoka (Japan). Faculty of Engineering

    1997-10-15

    Rotating bending fatigue tests were carried out on austempered ductile cast iron (ADI) in order to investigate the statistical properties of life distributions of crack initiation and propagation, and also the evaluation of fatigue life. The results are summarized as follows: (1) The size of crack initiation sites of the material was represented by a Weibull distribution without regarding to the kinds of crack initiation sites such as microshrinkage and graphite grain. The crack initiation life scattered widely, but the scatter became much smaller as soon as the cracks grew. (2) The crack propagation life Nac which was defined as the minimum crack propagation rate showed lower scatter than the crack initation life. (3) The fatigue life of the material was evaluated well by Nac and the propagation rate after Nac. It was clear that the fatigue life of ductile cast iron was goverened by the scatter of Nac. 8 refs., 13 figs., 4 tabs.

  17. High-cycle Fatigue Properties of Alloy718 Base Metal and Electron Beam Welded Joint

    Science.gov (United States)

    Ono, Yoshinori; Yuri, Tetsumi; Nagashima, Nobuo; Sumiyoshi, Hideshi; Ogata, Toshio; Nagao, Naoki

    High-cycle fatigue properties of Alloy 718 plate and its electron beam (EB) welded joint were investigated at 293 K and 77 K under uniaxial loading. At 293 K, the high-cycle fatigue strength of the EB welded joint with the post heat treatment exhibited somewhat lower values than that of the base metal. The fatigue strengths of both samples basically increased at 77 K. However, in longer life region, the EB welded joint fractured from a blow hole formed in the welded zone, resulting in almost the same fatigue strength at 107 cycles as that at 293 K.

  18. Estimation of the Plain High-Cycle Fatigue Propagation Resistance in Steels

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    Mirco D. Chapetti

    2002-06-01

    Full Text Available In this work a method to estimate the high cyclic fatigue propagation life of steel specimens under constant loading is presented. This method is based in experimental evidence that the fatigue limit represents the threshold stress for the propagation of nucleated cracks, so that both the fatigue limit and the fatigue resistance depend on the effective resistance of the microstructural barriers that have to be overcome by the nucleated cracks. It is proposed also, that in those cases where the number of cycles that is necessary for the nucleation of the cracks can be neglected, the fatigue crack propagation life can be taken as an estimation of the total fatigue life. The high cycle fatigue propagation life of a structural steel of the type JIS 10C is estimated.

  19. Estimation of the Plain High-Cycle Fatigue Propagation Resistance in Steels

    Scientific Electronic Library Online (English)

    Mirco D., Chapetti.

    2002-06-01

    Full Text Available In this work a method to estimate the high cyclic fatigue propagation life of steel specimens under constant loading is presented. This method is based in experimental evidence that the fatigue limit represents the threshold stress for the propagation of nucleated cracks, so that both the fatigue li [...] mit and the fatigue resistance depend on the effective resistance of the microstructural barriers that have to be overcome by the nucleated cracks. It is proposed also, that in those cases where the number of cycles that is necessary for the nucleation of the cracks can be neglected, the fatigue crack propagation life can be taken as an estimation of the total fatigue life. The high cycle fatigue propagation life of a structural steel of the type JIS 10C is estimated.

  20. MODELS OF FATIGUE LIFE CURVES IN FATIGUE LIFE CALCULATIONS OF MACHINE ELEMENTS EXAMPLES OF RESEARCH

    OpenAIRE

    Grzegorz SZALA; Bogdan LIGAJ

    2014-01-01

    In the paper there was attempted to analyse models of fatigue life curves possible to apply in calculations of fatigue life of machine elements. The analysis was limited to fatigue life curves in stress approach enabling cyclic stresses from the range of low cycle fatigue (LCF), high cycle fatigue (HCF), fatigue limit (FL) and giga cycle fatigue (GCF) appearing in the loading spectrum at the same time. Chosen models of the analysed fatigue live curves will be illustrated with test results of ...

  1. High cycle thermal fatigue crack initiation behavior of type 304 stainless steel in pure water

    International Nuclear Information System (INIS)

    In order to maintain the integrity of engineering plants, it is necessary to evaluate the thermal fatigue life of certain structures. While low cycle thermal fatigue behavior has been widely studied in the past, high cycle thermal fatigue behavior has not been studied due to some difficulties with experiment. In this paper, an apparatus for performing high cycle thermal fatigue tests in pure water is described. High and low temperature water is continuously supplied into each passage in an autoclave, so that the surface of a revolving cylindrical specimen in the autoclave suffers from revolution synchronized thermal fatigue. The beat transfer coefficients between the water and the metal surface were considerably high. These were 50,000--70,OOOW/m 2K for the thermal cycle frequency less than 5Hz and 70,000--120,000W/m2K for the thermal cycle frequency higher than 5Hz. A high stress amplitude can therefore be obtained at a high thermal cycle frequency by the high heat transfer coefficient. Thermal fatigue cracks were observed in specimens under the testing conditions of fictitious stress amplitudes over 290MPa in Type 304 stainless steel. The thermal fatigue limit is therefore considered to be around 290MPa. The number of cycles to crack initiation agreed with that for the mechanical fatigue when the fictitious stress amplitudes were identical. It is considered that the thermal fatigue crack initiation life can be predicted from the mechanical fatigue crack initiation life

  2. A New Multiaxial High-Cycle Fatigue Criterion Based on the Critical Plane for Ductile and Brittle Materials

    Science.gov (United States)

    Wang, Cong; Shang, De-Guang; Wang, Xiao-Wei

    2015-02-01

    An improved high-cycle multiaxial fatigue criterion based on the critical plane was proposed in this paper. The critical plane was defined as the plane of maximum shear stress (MSS) in the proposed multiaxial fatigue criterion, which is different from the traditional critical plane based on the MSS amplitude. The proposed criterion was extended as a fatigue life prediction model that can be applicable for ductile and brittle materials. The fatigue life prediction model based on the proposed high-cycle multiaxial fatigue criterion was validated with experimental results obtained from the test of 7075-T651 aluminum alloy and some references.

  3. High-cycle fatigue strength of a pultruded composite material

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    L. Vergani

    2009-01-01

    Full Text Available Dealing with composites in polymeric matrix, the pultruded ones are among the more suitable for large production rates and volumes. For this reason, their use is increasing also in structural applications in civil and mechanical engineering. However, their use is still limited by the partial knowledge of their fatigue behaviour; in many applications it is, indeed, required a duration of many millions of cycles, while most of the data that can be found in literature refer to a maximum number of cycles equal to 3 millions. In this paper a pultruded composite used for manufacturing structural beams is considered and its mechanical behaviour characterized by means of static and high-cycle fatigue tests. The results allowed to determine the S-N curve of the material and to assess the existence of a fatigue limit. Observations at the scanning electronic microscope (SEM allowed to evaluate the damage mechanisms involved in the static and fatigue failure of the material.

  4. High-cycle fatigue of IN 713LC.

    Czech Academy of Sciences Publication Activity Database

    Kunz, Ludvk; Luk, Petr; Mintch, Rastislav; Kone?n, R.

    Brno : VUTIUM Brno, 2008 - (Pokluda, J.; Luk, P.; andera, P.; Dlouh, I.), s. 945-951 ISBN 978-80-214-3692-3. [ECF17 - European Conference on Fracture /17./. Brno (CZ), 02.09.2008-05.09.2008] R&D Projects: GA MPO FT-TA4/023 Institutional research plan: CEZ:AV0Z20410507 Keywords : Inconel 713LC * high cycle fatigue * casting defects * largest extreme value statistic Subject RIV: JG - Metallurgy

  5. Competition between microstructure and defect in multiaxial high cycle fatigue

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    F. Morel

    2015-07-01

    Full Text Available This study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion on the experimental and predicted fatigue strength of a 316 stainless steel containing artificial defect.

  6. Effects of HTGR helium on the high cycle fatigue of structural materials

    International Nuclear Information System (INIS)

    High cycle fatigue tests have been conducted on Incoloy 800H and Hastelloy X in air and in HTGR helium environments containing low and high levels of moisture. For the helium environments, a higher mositure level usually gives a lower fatigue strength. For air, however, the strength is usually much lower than those for helium. For long test times at higher test temperatures, the fatigue strengths for Incoloy 800H often show a large decrease, and the fatigue limits are much lower than those anticipated from low cycle tests. Optical and scanning electron microscope observations were made to correlate fatigue life with surface and bulk microstructural changes in the material during test. Oxide scale cracking and spallation, surface recrystallization and intergranular attack appear to contribute to losses in fatigue strength

  7. The high cycle thermal fatigue cracking, a problem bond to the structure

    International Nuclear Information System (INIS)

    High cycle thermal fatigue cracking is explained through the arrest of cracks initiated at surface, in the thickness of the component. On some components of nuclear power plants the configuration of crack network is explained through the sign of weld residual stress. We show also that local residual stresses are dependent on second derivative of temperature field. Far from the weld we explain the presence of crack network under high compressive stress for stainless steels by detrimental effect of pre-hardening on fatigue life in strain control and we conclude that shot peening may be detrimental in thermal fatigue. (author)

  8. Torsional fatigue behaviour and damage mechanisms in the very high cycle regime

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    E. Bayraktar

    2010-06-01

    Full Text Available Purpose: of this paper: Many engineering components operate under combined torsion and axial cyclic loading conditions, which can result in fatigue fracture after a very long life regime of fatigue. This fatigue regime were carried out beyond 109 loading cycles called very high cycle fatigue (VHCF to understand the fatigue properties and damage mechanisms of materials.Design/methodology/approach: Torsional fatigue tests were conducted using a 20 kHz frequency ultrasonic fatigue testing device. The results obtained were compared to those of the conventional torsional fatigue test machine operated at 35 Hz to observe any discrepancy in results due to frequency effects between two experiments.Findings: All the fatigue tests were done up to 1010 cycles at room temperature. Damage mechanisms in torsional fatigues such as crack initiation and propagation in different modes were studied by imaging the samples in a Scanning Electron Microscope (SEM. The results of the two kinds of material show that the stress vs. number of cycle curves (S-N curves display a considerable decrease in fatigue strength beyond 107 cycles.Research limitations/implications: Each test, the strain of specimen in the gage length must be calibrated with a strain gage bonded to the gage section. This is a critical point of this study. The results are very sensitive to the calibration system. Control of the displacement and the output of the power supply are made continuously by computer and recorded the magnitude of the strain in the specimen.Practical implications: torsional fatigue tests has been investigated in the very high cycle fatigue (VHCF range for two kinds of alloys used very largely in automotive engine components. Based on the test results and analyses presented in this paper, practical applications are being actually carried out in the automotive industry essentially in France.Originality/value: Ultrasonic fatigue damage (VHCF >109 in VHCF is originally different from classical fatigue (up to 106 by typical internal fish eye formation. Additionally, fatigue crack of all the fractured specimens for the 2-AS5U3G-Y35 specimens initiated at the surface of the specimens. Fatigue fracture surfaces of AISI52100 steel specimens show a typical scorpion-shaped formation, which was considerably different from the fatigue fracture specimen subjected to axial cyclic loading, which exhibited the fish-eye formation.

  9. High-cycle fatigue behavior of ultrafine-grained austenitic stainless and TWIP steels

    Energy Technology Data Exchange (ETDEWEB)

    Hamada, A.S. [Materials Engineering Laboratory (4KOMT), Box 4200, University of Oulu, 90014 Oulu (Finland); Metallurgical and Materials Engineering Department, Faculty of Petroleum and Mining Engineering, Suez Canal University, Box 43721, Suez (Egypt); Karjalainen, L.P., E-mail: pentti.karjalainen@oulu.fi [Materials Engineering Laboratory (4KOMT), Box 4200, University of Oulu, 90014 Oulu (Finland)

    2010-08-20

    High-cycle fatigue behavior of ultrafine-grained (UFG) 17Cr-7Ni Type 301LN austenitic stainless and high-Mn Fe-22Mn-0.6C TWIP steels were investigated in a reversed plane bending fatigue and compared to the behavior of steels with conventional coarse grain (CG) size. Optical, scanning and transmission electron microscopy were used to examine fatigue damage mechanisms. Testing showed that the fatigue limits leading to fatigue life beyond 4 x 10{sup 6} cycles were about 630 MPa for 301LN while being 560 MPa for TWIP steel, and being 0.59 and 0.5 of the tensile strength respectively. The CG counterparts were measured to have the fatigue limits of 350 and 400 MPa. The primary damage caused by fatigue took place by grain boundary cracking in UFG 301LN, while slip band cracking occurred in CG 301LN. However, in the case of TWIP steel, the fatigue damage mechanism is similar in spite of the grain size. In the course of cycling neither the formation of a martensite structure nor mechanical twinning occurs, but intense slip bands are created with extrusions and intrusions. Fatigue crack initiates preferentially on grain and twin boundaries, and especially in the intersection sites of slip bands and boundaries.

  10. High cycle fatigue of 2.25Cr-1Mo steel at elevated temperatures

    International Nuclear Information System (INIS)

    Information on the elevated temperature, long life (> 105 cycles to failure) fatigue resistance of pressure vessel and piping alloys is needed to properly design structural components subjected to low amplitude cyclic loadings at high temperatures. The high cycle fatigue resistance of annealed 2 1/4 Cr-1Mo steel has been evaluated in air at temperatures up to 5380C. A design fatigue curve has been developed for temperatures 0C, and a design fatigue curve has been developed for 5380C maximum temperature. These curves are for strain rates >= 4 x 10-3 sec-1, more long life fatigue data are needed for applications at lower strain rates. The effect of tensile mean stress on fatigue life has been evaluated. Design fatigue curve corrections for maximum effect of mean stress appear to be adequate at 0C, but they may not be satisfactory at higher temperatures. The present experimental work was limited to constant amplitude cycling and a crack initiation failure criterion. (author)

  11. MODELS OF FATIGUE LIFE CURVES IN FATIGUE LIFE CALCULATIONS OF MACHINE ELEMENTS EXAMPLES OF RESEARCH

    Directory of Open Access Journals (Sweden)

    Grzegorz SZALA

    2014-03-01

    Full Text Available In the paper there was attempted to analyse models of fatigue life curves possible to apply in calculations of fatigue life of machine elements. The analysis was limited to fatigue life curves in stress approach enabling cyclic stresses from the range of low cycle fatigue (LCF, high cycle fatigue (HCF, fatigue limit (FL and giga cycle fatigue (GCF appearing in the loading spectrum at the same time. Chosen models of the analysed fatigue live curves will be illustrated with test results of steel and aluminium alloys.

  12. Fatigue behaviour and failure analysis of IN 713LC in high-cycle fatigue region.

    Czech Academy of Sciences Publication Activity Database

    Mintch, R.; Kunz, Ludvk; Bok?vka, O.

    2009-01-01

    Ro?. 16, 3a (2009), s. 37-40. ISSN 1335-0803 R&D Projects: GA MPO FT-TA4/023 Institutional research plan: CEZ:AV0Z20410507 Keywords : Ni base superalloy * casting defect * high-cycle fatigue Subject RIV: JG - Metallurgy

  13. Fatigue behaviour of ultrafine-grained copper in very high cycle fatigue regime.

    Czech Academy of Sciences Publication Activity Database

    Kunz, Ludvk; Luk, Petr; Bok?vka, O.

    2008-01-01

    Ro?. 15, ?. 4 (2008), s. 1-5. ISSN 1335-0803 R&D Projects: GA Mk(CZ) 1P05ME804 Institutional research plan : CEZ:AV0Z20410507 Keywords : very high cycle fatigue * ultrafine-grained structure * ECAP * Copper Subject RIV: JG - Metallurgy

  14. Al-Li alloy AA2198's very high cycle fatigue crack initiation mechanism and its fatigue thermal effect

    Science.gov (United States)

    Xu, Luopeng; Cao, Xiaojian; Chen, Yu; Wang, Qingyuan

    2015-10-01

    AA2198 alloy is one of the third generation Al-Li alloys which have low density, high elastic modulus, high specific strength and specific stiffness. Compared With the previous two generation Al-Li alloys, the third generation alloys have much improved in alloys strength, corrosion resistance and weldable characteristic. For these advantages, the third generation Al-Li alloys are used as aircraft structures, such as C919 aviation airplane manufactured by China and Russia next generation aviation airplane--MS-21. As we know, the aircraft structures are usually subjected to more than 108 cycles fatigue life during 20-30 years of service, however, there is few reported paper about the third generation Al-Li alloys' very high cycle fatigue(VHCF) which is more than 108 cycles fatigue. The VHCF experiment of AA2198 have been carried out. The two different initiation mechanisms of fatigue fracture have been found in VHCF. The cracks can initiate from the interior of the testing material with lower stress amplitude and more than 108 cycles fatigue life, or from the surface or subsurface of material which is the dominant reason of fatigue failures. During the experiment, the infrared technology is used to monitor the VHCF thermal effect. With the increase of the stress, the temperature of sample is also rising up, increasing about 15 C for every 10Mpa. The theoretical thermal analysis is also carried out.

  15. Low cycle fatigue: high cycle fatigue damage accumulation in a 304L austenitic stainless steel

    International Nuclear Information System (INIS)

    The aim of this study was to evaluate the consequences of a Low Cycle Fatigue pre-damage on the subsequent fatigue limit of a 304L stainless steel. The effects of hardening and severe roughness (grinding) have also been investigated. In a first set of tests, the evolution of the surface damage induced by the different LCF pre-cycling was characterized. This has permitted to identify mechanisms and kinetics of damage in the plastic domain for different surface conditions. Then, pre-damaged samples were tested in the High Cycle Fatigue domain in order to establish the fatigue limits associated with each level of pre-damage. Results evidence that, in the case of polished samples, an important number of cycles is required to initiate surface cracks ant then to affect the fatigue limit of the material but, in the case of ground samples, a few number of cycles is sufficient to initiate cracks and to critically decrease the fatigue limit. The fatigue limit of pre-damaged samples can be estimated using the stress intensity factor threshold. Moreover, this detrimental effect of severe surface conditions is enhanced when fatigue tests are performed under a positive mean stress (author)

  16. Effects of loading condition on very-high-cycle fatigue behaviour and dominant variable analysis

    Science.gov (United States)

    Lei, ZhengQiang; Xie, JiJia; Sun, ChengQi; Hong, YouShi

    2014-01-01

    The specimens of a high carbon chromium steel were quenched and tempered at 150C, 180C and 300C. Such specimens were tested via rotating bending and a push-pull type of axial loading to investigate the influences of loading condition on the behaviour of very-high-cycle fatigue (VHCF). Experimental results show the different influences of inclusion size on the fatigue life for the two loading conditions. Predominant factors and mechanism for the fine-granular-area (FGA) of crack origin were discussed. In addition, a reliability analysis based on a modified Tanaka-Mura model was carried out to evaluate the sensitivity of inclusion size, stress, and ? K FGA to the life of VHCF crack initiation.

  17. Effect of severe shot peening on ultra-high-cycle fatigue of a low-alloy steel

    International Nuclear Information System (INIS)

    Highlights: • Severe shot peening was applied to obtain a nanostructured surface of 50Crmo4 steel. • An nanocrystalline structured is generated by severe shot peening. • Ultra-high-cycle fatigue test results show the remarkable effect of severe shot peening. • The results were discussed in the light the surface modifications induced by SSP. - Abstract: It is well known that shot peening is able to increase the fatigue strength and endurance of metal parts, especially with a steep stress gradient due to a notch. This positive effect is mainly put into relation with the ability of this treatment to induce a compressive residual stress state in the surface layer of material and to cause surface work hardening. Recently the application of severe shot peening (shot peening performed with severe treatment parameters) showed the ability to obtain more a remarkable improvement of the high cycle fatigue strength of steels. In this paper severe shot peening is applied to the steel 50CrMo4 and its effect in the ultra-high cycle fatigue regime is investigated. Roughness, microhardness, X-ray diffraction residual stress analysis and crystallite size measurement as well as scanning electron microscopy (SEM) observations were used for characterizing the severely deformed layer. Tension–compression high frequency fatigue tests were carried out to evaluate the effect of the applied treatment on fatigue life in the ultra-high cycle region. Fracture surface analysis by using SEM was performed with aim to investigate the mechanism of fatigue crack initiation and propagation. Results show an unexpected significant fatigue strength increase in the ultra-high cycle region after SSP surface treatment and are discussed in the light of the residual stress profile and crystallite size

  18. Notch size effects on high cycle fatigue limit stress of Udimet 720

    International Nuclear Information System (INIS)

    Notch size effects on the high cycle fatigue (HCF) limit stress of Ni-base superalloy Udimet 720 were investigated on cylindrical specimens with three notch sizes of the same stress concentration factor Kt=2.74. The HCF limit stress corresponding to a life of 106 cycles was experimentally determined at a stress ratio of 0.1 and a frequency of 25 Hz at room temperature. The stresses were calculated using finite element analysis (FEA) and the specimens analyzed using scanning electron microscopy (SEM). Test results show that at the same Kt value, notch size can slightly affect the HCF limit stress of U720 when notch root plasticity occurs. FEA and SEM results reveal that the notch size effects are influenced by a complicated combination of the stress and plastic strain fields at the notch tip, the nominal stress, and the effects of prior plastic deformation on fatigue crack initiation

  19. Notch size effects on high cycle fatigue limit stress of Udimet 720

    Energy Technology Data Exchange (ETDEWEB)

    Ren Weiju; Nicholas, Theodore

    2003-09-25

    Notch size effects on the high cycle fatigue (HCF) limit stress of Ni-base superalloy Udimet 720 were investigated on cylindrical specimens with three notch sizes of the same stress concentration factor K{sub t}=2.74. The HCF limit stress corresponding to a life of 10{sup 6} cycles was experimentally determined at a stress ratio of 0.1 and a frequency of 25 Hz at room temperature. The stresses were calculated using finite element analysis (FEA) and the specimens analyzed using scanning electron microscopy (SEM). Test results show that at the same K{sub t} value, notch size can slightly affect the HCF limit stress of U720 when notch root plasticity occurs. FEA and SEM results reveal that the notch size effects are influenced by a complicated combination of the stress and plastic strain fields at the notch tip, the nominal stress, and the effects of prior plastic deformation on fatigue crack initiation.

  20. Microstructural aspects of duplex steel during high cycle and very high cycle fatigue

    Energy Technology Data Exchange (ETDEWEB)

    Knobbe, H; Koester, P; Christ, H-J [Institut fuer Werkstofftechnik, Universitaet Siegen, Paul-Bonatz-Strasse 9-11, D-57068 Siegen (Germany); Krupp, U [Fakultaet Ingenieurwissenschaften und Informatik, Fachhochschule Osnabrueck, Albrechtstrasse 30, D-49076 Osnabrueck (Germany); Fritzen, C-P, E-mail: helge.knobbe@uni-siegen.d [Institut fuer Mechanik und Regelungstechnik - Mechatronik, Universitaet Siegen, Paul-Bonatz-Strasse 9-11, D-57068 Siegen (Germany)

    2010-07-01

    Fatigue experiments were conducted up to N=10{sup 8} cycles on a duplex stainless steel. The investigations revealed important information: (i) most of the slip markings on {l_brace}111{r_brace}-slip planes form during the early stage of fatigue ({approx}10{sup 4}), although many grains stay active in developing more and/or longer slip bands (investigations with SEM/EBSD). It was found that the damage in these grains often has its origin at grain or phase boundaries, growing into the interior of the grains; (ii) in most of the recrystallisation twins slip markings are present in all parts of the grain leading to the assumption that just tilted grain boundaries are not very effective as microstructural barriers. In cases where the twin grain boundary is favorably oriented, it even can promote microcrack initiation; (iii) phase boundaries are most effective in restricting dislocation movement to the softer austenite, since no evidence of growing fatigue damage was found in ferritic grains. These findings lead to the conclusion that for the material studied an endurance limit exists despite occurring plastic deformation. This behaviour is a consequence of the barrier effect induced by phase boundaries against short crack propagation and holds true as long as no inclusions are present.

  1. Microstructural aspects of duplex steel during high cycle and very high cycle fatigue

    International Nuclear Information System (INIS)

    Fatigue experiments were conducted up to N=108 cycles on a duplex stainless steel. The investigations revealed important information: (i) most of the slip markings on {111}-slip planes form during the early stage of fatigue (?104), although many grains stay active in developing more and/or longer slip bands (investigations with SEM/EBSD). It was found that the damage in these grains often has its origin at grain or phase boundaries, growing into the interior of the grains; (ii) in most of the recrystallisation twins slip markings are present in all parts of the grain leading to the assumption that just tilted grain boundaries are not very effective as microstructural barriers. In cases where the twin grain boundary is favorably oriented, it even can promote microcrack initiation; (iii) phase boundaries are most effective in restricting dislocation movement to the softer austenite, since no evidence of growing fatigue damage was found in ferritic grains. These findings lead to the conclusion that for the material studied an endurance limit exists despite occurring plastic deformation. This behaviour is a consequence of the barrier effect induced by phase boundaries against short crack propagation and holds true as long as no inclusions are present.

  2. Development of a high cycle vibration fatigue diagnostic system with non-contact vibration sensing

    Energy Technology Data Exchange (ETDEWEB)

    Yoshitsugu, Nekomoto; Satoshi, Kiriyama; Moritatsu, Nishimura [Mitsubishi Heavy Industries Ltd., Tokyo (Japan); Kenji, Matsumoto [Japan Power Engineering and Inspection Corporation (Japan); Eiji, O' shima [Tokyo Institute of Technology (Japan)

    2001-07-01

    Nuclear power plants have a large number of pipes. Of these small-diameter pipe branches in particular are often damaged due to high-cycle fatigue. In order to ensure the reliability of a plant it is important to detect the fatigues in pipe branches at an early stage and to develop the technology to predict and diagnose the advancement of fatigue. Further, in order to carry out the diagnosis of the piping system effectively during operation, non-contact evaluation is useful. Hence, we have developed a 'high-cycle fatigue diagnostic system with non-contact vibration sensing', where the vibration of the pipe branch is measured using a non-contact sensor. Since the contents of the developed sensor technology has already been reported, this paper mainly describes the newly developed high-cycle fatigue diagnostic system. (authors)

  3. Fatigue behavior of titanium Ti-4Al-2V rods under high cycle loading

    International Nuclear Information System (INIS)

    The high cycle fatigue behavior of titanium alloy Ti-4Al-2V rods at room temperature was evaluated. The common high cycle fatigue (HCF) tests with group specimen and the up-and-down tests were performed under bending and rotating loadings at room temperature in air environment. The experimental data were analyzed and the S-N curve and P-S-N curve were plotted, and the fracture morphology is analyzed by SEM. The results show that Ti-4Al-2V rods have good resistance to high cycle fatigue and the value of ?-1(107) is about the same with that of the corresponding equation. The fracture morphology of Ti-4Al-2V specimen after fatigue failure presents typical characteristics with three areas of fatigue crack initiation,growth and rupture. (authors)

  4. Comparative study to evaluate remaining life in steel SAE 8620 under high cycle fatigue; Estudo comparativo para avaliar vida restante em aco SAE 8620, quando submetido a fadiga de alto-ciclo

    Energy Technology Data Exchange (ETDEWEB)

    Mansur, Tanius Rodrigues; Pinto, Joao Mario Andrade [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN), Belo Horizonte, MG (Brazil); Palma, Ernani Sales; Alvarenga Junior, Alvaro [Pontificia Univ. Catolica de Minas Gerais, MG (Brazil); Colosimo, Enrico A. [Minas Gerais Univ., Belo Horizonte, MG (Brazil)

    2002-07-01

    Life of metallic structures is often governed by processes of fatigue, caused by either vibration or by the application of cyclic, periodic or not, load. Most of the life is related to a sequence of processes during which slip bands, localized strain, damages and begin and they grow until the nucleation of some macroscopic crack. To evaluate the life of structural components (from now on refereed as components) related to fatigue, several proposed models some linear and others not. This paper presents a comparison among some of them, for the steel SAE 8620. (author)

  5. Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl

    Science.gov (United States)

    Lerch, Brad; Draper, Sue; Pereira, J. Mike

    2002-01-01

    High cycle fatigue strength testing of gamma TiAl by the step test method is investigated. A design of experiments was implemented to determine if the coaxing effect occurred during testing. Since coaxing was not observed, step testing was deemed a suitable method to define the fatigue strength at 106 cycles.

  6. High cycle fatigue of austenitic stainless steels under random loading

    International Nuclear Information System (INIS)

    To investigate reactor components, load control random fatigue tests were performed at 3000C and 5500C, on specimens from austenitic stainless steels plates in the transverse orientation. Random solicitations are produced on closed loop servo-hydraulic machines by a mini computer which generates random load sequence by the use of reduced Markovian matrix. The method has the advantage of taking into account the mean load for each cycle. The solicitations generated are those of a stationary gaussian process. Fatigue tests have been mainly performed in the endurance region of fatigue curve, with scattering determination using stair case method. Experimental results have been analysed aiming at determining design curves for components calculations, depending on irregularity factor and temperature. Analysis in term of mean square root fatigue limit calculation, shows that random loading gives more damage than constant amplitude loading. Damage calculations following Miner rule have been made using the probability density function for the case where the irregularity factor is nearest to 100 %. The Miner rule is too conservative for our results. A method using design curves including random loading effects with irregularity factor as an indexing parameter is proposed

  7. Effect of rare earth elements on high cycle fatigue behavior of AZ91 alloy

    Energy Technology Data Exchange (ETDEWEB)

    Mokhtarishirazabad, M., E-mail: mehdi-mokhtari@hotmail.com [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Boutorabi, S.M.A. [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Azadi, M.; Nikravan, M. [Irankhodro Powertrain Company (IPCO), Tehran (Iran, Islamic Republic of)

    2013-12-10

    This article investigates effects of adding rare earth elements (RE) into a magnesiumaluminumzinc alloy (the AZ91 alloy) on its high cycle fatigue (HCF) behavior. For this purpose, AZ91 and AZ91+1% RE (AZE911) alloys were gravity casted in a metallic die. RE elements were added to the AZ91 alloy in the form of mischmetals. Microscopic evaluations with the scanning electron microscopy (SEM) and mechanical tests include tensile, hardness and HCF behaviors, were performed on prepared samples. Rotary bending fatigue tests were carried out at a stress ratio (R) of ?1 and a frequency of 125 Hz, at the room temperature, in the air. The microscopic investigation demonstrates that the addition of 1% RE elements leads to the formation of Al{sub 11}RE{sub 3} intermetallic particles which is associated to the reduction of ?-(Mg{sub 17}Al{sub 12}) phases. Results of mechanical experiments suggest a negligible effect of adding 1% RE elements on mechanical properties of the AZ91 alloy. Curves of stress-life (SN) shows an increase in the fatigue strength at 10{sup 5} cycles, from 10010 MPa to 13510 MPa, when RE elements were added to the AZ91 alloy.

  8. Effect of rare earth elements on high cycle fatigue behavior of AZ91 alloy

    International Nuclear Information System (INIS)

    This article investigates effects of adding rare earth elements (RE) into a magnesiumaluminumzinc alloy (the AZ91 alloy) on its high cycle fatigue (HCF) behavior. For this purpose, AZ91 and AZ91+1% RE (AZE911) alloys were gravity casted in a metallic die. RE elements were added to the AZ91 alloy in the form of mischmetals. Microscopic evaluations with the scanning electron microscopy (SEM) and mechanical tests include tensile, hardness and HCF behaviors, were performed on prepared samples. Rotary bending fatigue tests were carried out at a stress ratio (R) of ?1 and a frequency of 125 Hz, at the room temperature, in the air. The microscopic investigation demonstrates that the addition of 1% RE elements leads to the formation of Al11RE3 intermetallic particles which is associated to the reduction of ?-(Mg17Al12) phases. Results of mechanical experiments suggest a negligible effect of adding 1% RE elements on mechanical properties of the AZ91 alloy. Curves of stress-life (SN) shows an increase in the fatigue strength at 105 cycles, from 10010 MPa to 13510 MPa, when RE elements were added to the AZ91 alloy

  9. A New High-Speed, High-Cycle, Gear-Tooth Bending Fatigue Test Capability

    Science.gov (United States)

    Stringer, David B.; Dykas, Brian D.; LaBerge, Kelsen E.; Zakrajsek, Andrew J.; Handschuh, Robert F.

    2011-01-01

    A new high-speed test capability for determining the high cycle bending-fatigue characteristics of gear teeth has been developed. Experiments were performed in the test facility using a standard spur gear test specimens designed for use in NASA Glenn s drive system test facilities. These tests varied in load condition and cycle-rate. The cycle-rate varied from 50 to 1000 Hz. The loads varied from high-stress, low-cycle loads to near infinite life conditions. Over 100 tests were conducted using AISI 9310 steel spur gear specimen. These results were then compared to previous data in the literature for correlation. Additionally, a cycle-rate sensitivity analysis was conducted by grouping the results according to cycle-rate and comparing the data sets. Methods used to study and verify load-path and facility dynamics are also discussed.

  10. Very high cycle fatigue behaviour of as-extruded AZ31, AZ80, and ZK60 magnesium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Novy, Frantisek; Skorik, Viktor [Zilina Univ. (Slovakia). Dept. of Materials Engineering; Janecek, Milos [Charles Univ., Prague (Czech Republic). Dept. of Physics of Materials; Mueller, Julia; Wagner, Lothar [Technische Univ. Clausthal, Clausthal-Zellerfeld (Germany). Inst. of Materials Science and Technology

    2009-03-15

    The very high cycle fatigue properties of extruded AZ31, AZ80, and ZK60 magnesium alloys were investigated. Fatigue tests were performed at ultrasonic cyclic frequency and at a load ratio of R = -1 at ambient temperature using smooth electropolished specimens. Fatigue failures were observed at lifetimes above 10{sup 9} cycles. The fatigue life was found to increase with decreasing stress amplitude. The fracture surfaces and fracture profiles of selected specimens cycled until failure were examined. The purpose of the study was to determine the role of the microstructure on the fatigue crack nucleation and growth. Furthermore, the fatigue properties were discussed on the basis of microstructure and the presence of inclusions which are known as crack initiation sites. In AZ31 and AZ80 alloys only surface-induced fatigue cracks were observed. On the other hand, in the ZK60 alloy both surface- and interior-induced fatigue cracks were observed. Both mechanisms operate in the ZK60 also at a lifetime of around 10{sup 1}0 cycles. Interior-induced fatigue cracks were accompanied by clear fish-eye marks on the fracture surfaces of the ZK60 alloy. (orig.)

  11. Effectiveness of the modified fatigue criteria for biaxial loading of notched specimen in high-cycle region.

    Czech Academy of Sciences Publication Activity Database

    Major, t?pn; Hublovsk, .; Kocour, Vladimr; Valach, Jaroslav

    Vol. 732. Zrich : Trans Tech Publications, 2015 - (Polach, P.), s. 63-70 ISBN 978-3-03835-413-0. ISSN 1660-9336. [EAN 2014. Conference on experimental stress analysis. /52./. Marinsk Lzn? (CZ), 02.06.2014-05.06.2014] Institutional support: RVO:68378297 Keywords : notched specimen * multiaxial criteria * biaxial loading * fatigue life * bending-torsion loading * high-cycle loading Subject RIV: JM - Building Engineering http://www.scientific.net/AMM.732.63

  12. Influence of mechanical surface treatments on the high cycle fatigue performance of TIMETAL 54M

    International Nuclear Information System (INIS)

    Research highlights: → Effect of mean stress and environmental sensitivities on high cycle fatigue (HCF) performance in TIMETAL 54M compared to Ti-6Al-4V. → TIMETAL 54M shows normal mean stress sensitivity but Ti-6Al-4V shows anomalous mean stress. → Both alloys are sensitive to air environment. → HCF performance of TIMETAL 54 M was enhanced after shot peening and ball-burnishing but deteriorated in Ti-6Al-4V. - Abstract: TIMETAL 54M (in the following Ti-54M) is a newly developed (α + β) titanium alloy with nominal composition Ti-5Al-4V-0.6Mo-0.4Fe. The alloy can provide a cost benefit over Ti-6Al-4V due to improved machinability and formability. These attractive properties might be a driving force for replacing Ti-6Al-4V in many aircraft as well as biomedical applications. Since HCF performance is one of the most important requirements for these applications, it is essential to improve this property by microstructural optimization and by mechanical surface treatments such as shot peening or ball burnishing. The latter improvement is mainly the result of induced near-surface severe plastic deformation which results in work-hardening and the generation of compressive residual stresses that retard fatigue crack propagation. The main aim of the present study was to investigate the potential fatigue life improvements in Ti-54M due to shot peening and ball-burnishing. The process-induced residual stresses and stress-depth profiles were determined by energy-dispersive X-ray diffraction (ED) of synchrotron radiation with the beam energy of 10-80 keV. Results on Ti-54M and Ti-6Al-4V will be compared and correlated with the mean stress and environmental sensitivities of the fatigue strengths in the microstructures.

  13. High cycle fatigue crack propagation resistance and fracture toughness in ship steels (Short Communication

    Directory of Open Access Journals (Sweden)

    R.S. Tripathi

    2001-04-01

    Full Text Available In this paper, two grades of steel, viz., plain carbon steel and low alloy steel used in naval ships have been selected for studies on high cycle fatigue, crack propagation, stress intensity and crack opening displacement (COD. Specimen for high cycle fatigue was prepared as per IS: 1608. High cycle fatigue was carried out up to 50,000 cycles at 1000 kgfto 2000 kgfloads. Up to 2000 kgfloads, both the materials were observed within elastic zones. A number of paran1eters, including stress, strain and strain range, which indicate elastic behaviour of steels, have been considered. Low alloy steel specimen was prepared as per ASTM standard: E-399 and subjected to 5,00,000 cycles. Crack propagation, COD, stress intensity, load-cycle variations, load-COD relation, and other related paran1eters have been studied using a modem universal testing machine with state-of-the-art technology

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1995-12-01

    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.

  15. The role of high cycle fatigue (HCF) onset in Francis runner reliability

    International Nuclear Information System (INIS)

    High Cycle Fatigue (HCF) plays an important role in Francis runner reliability. This paper presents a model in which reliability is defined as the probability of not exceeding a threshold above which HCF contributes to crack propagation. In the context of combined Low Cycle Fatigue (LCF) and HCF loading, the Kitagawa diagram is used as the limit state threshold for reliability. The reliability problem is solved using First-Order Reliability Methods (FORM). A study case is proposed using in situ measured strains and operational data. All the parameters of the reliability problem are based either on observed data or on typical design specifications. From the results obtained, we observed that the uncertainty around the defect size and the HCF stress range play an important role in reliability. At the same time, we observed that expected values for the LCF stress range and the number of LCF cycles have a significant influence on life assessment, but the uncertainty around these values could be neglected in the reliability assessment.

  16. High-Cycle Fatigue Properties at Cryogenic Temperatures in INCONEL 718

    International Nuclear Information System (INIS)

    High-cycle fatigue properties at 4 K, 20 K, 77 K and 293 K were investigated in forged-INCONEL 718 nickel-based superalloy with a mean gamma (?) grain size of 25 ?m. In the present material, plate-like delta phase precipitated at ? grain boundaries and niobium (Nb)-enriched MC type carbides precipitated coarsely throughout the specimens. The 0.2% proof stress and the tensile strength of this alloy increased with decreasing temperature, without decreasing elongation or reduction of area. High-cycle fatigue strengths also increased with decreasing temperature although the fatigue limit at each temperature didn't appear even around 107 cycles. Fatigue cracks initiated near the specimen surface and formed faceted structures around crack initiation sites. Fatigue cracks predominantly initiated from coarse Nb-enriched carbides and faceted structures mainly corresponded to these carbides. In lower stress amplitude tests, however, facets were formed through transgranular crack initiation and growth. These kinds of distinctive crack initiation behavior seem to lower the high-cycle fatigue strength below room temperature in the present material

  17. High cycle fatigue of nickel-based superalloy MAR-M 247 at high temperatures.

    Czech Academy of Sciences Publication Activity Database

    md, Miroslav; Kunz, Ludvk; Huta?, Pavel; Hrb?ek, K.

    Amsterdam : Elsevier, 2014 - (Gulagliano, M.; Vergani, L.), s. 329-332 ISSN 1877-7058. - (Procedia Engineering. 74). [ICMFM 2014 International Colloquium on Mechanical Fatigue of Metals /17./. Verbania (IT), 25.06.2014-27.06.2014] R&D Projects: GA MPO FR-TI4/030; GA Mk(CZ) EE2.3.20.0214 Institutional support: RVO:68081723 Keywords : High cycle fatigue * Superalloy * MAR-M 247 * High temperature * Fracture surface * S-N curve Subject RIV: JL - Materials Fatigue , Friction Mechanics

  18. Two scale damage model and related numerical issues for thermo-mechanical high cycle fatigue

    International Nuclear Information System (INIS)

    On the idea that fatigue damage is localized at the microscopic scale, a scale smaller than the mesoscopic one of the Representative Volume Element (RVE), a three-dimensional two scale damage model has been proposed for High Cycle Fatigue applications. It is extended here to aniso-thermal cases and then to thermo-mechanical fatigue. The modeling consists in the micro-mechanics analysis of a weak micro-inclusion subjected to plasticity and damage embedded in an elastic meso-element (the RVE of continuum mechanics). The consideration of plasticity coupled with damage equations at micro-scale, altogether with Eshelby-Kroner localization law, allows to compute the value of microscopic damage up to failure for any kind of loading, 1D or 3D, cyclic or random, isothermal or aniso-thermal, mechanical, thermal or thermo-mechanical. A robust numerical scheme is proposed in order to make the computations fast. A post-processor for damage and fatigue (DAMAGE-2005) has been developed. It applies to complex thermo-mechanical loadings. Examples of the representation by the two scale damage model of physical phenomena related to High Cycle Fatigue are given such as the mean stress effect, the non-linear accumulation of damage. Examples of thermal and thermo-mechanical fatigue as well as complex applications on real size testing structure subjected to thermo-mechanical fatigue are detailed. (authors)

  19. Biaxial high cycle fatigue: experimental investigation and two-scale damage model

    International Nuclear Information System (INIS)

    This research thesis first describes the multi-axial fatigue phenomenon in the cases of mechanical and complex loadings, discusses multi-axial fatigue criteria, and presents the approach of fatigue by incremental damage mechanics. Then, it reports an experimental investigation of fatigue crack initiation under biaxial polycyclic fatigue in 304L austenitic stainless steel and in titanium alloy. The author presents a probabilistic two-scale damage model, and then reports the assessment of multi-axial fatigue life by means of this model

  20. Fatigue of Austempered Ductile Iron with Two Strength Grades in Very High Cycle Regime

    Science.gov (United States)

    Zhang, Jiwang; Li, Wei; Song, Qingpeng; Zhang, Ning; Lu, Liantao

    2016-01-01

    In this study, Austempered ductile irons (ADIs) with two different strength grades were produced and the fatigue properties were measured at 109 cycles. The results show that the S-N curves give a typical step-wise shape and there is no fatigue limit in the very high cycle fatigue regime. The two grades ADI have the similar fracture behaviors and fatigue failure can initiate from defects at specimen surface and subsurface zone. On the fracture surfaces of some specimens, the `granular-bright-facet' area with rich carbon distribution is observed in the vicinity of the defect. The microstructure affects the crack behaviors at the early propagation stage. The ADI with upper and lower bainite shows higher fatigue strength compared with the ADI with coarse upper bainite.

  1. High-Cycle Fatigue Resistance of Si-Mo Ductile Cast Iron as Affected by Temperature and Strain Rate

    Science.gov (United States)

    Matteis, Paolo; Scavino, Giorgio; Castello, Alessandro; Firrao, Donato

    2015-09-01

    Silicon-molybdenum ductile cast irons are used to fabricate exhaust manifolds of internal combustion engines of large series cars, where the maximum pointwise temperature at full engine load may be higher than 973 K (700 C). In this application, high-temperature oxidation and thermo-mechanical fatigue (the latter being caused by the engine start and stop and by the variation of its power output) have been the subject of several studies and are well known, whereas little attention has been devoted to the high-cycle fatigue, arising from the engine vibration. Therefore, the mechanical behavior of Si-Mo cast iron is studied here by means of stress-life fatigue tests up to 10 million cycles, at temperatures gradually increasing up to 973 K (700 C). The mechanical characterization is completed by tensile and compressive tests and ensuing fractographic examinations; the mechanical test results are correlated with the cast iron microstructure and heat treatment.

  2. Experimental study on properties of high cycle thermal fatigue. Outline and test plan of high cycle fatigue test equipment on sodium

    International Nuclear Information System (INIS)

    At a nuclear power plant, where fluids of high and low temperature flow into each other, it is necessary to prevent structural failure damage caused by high cycle thermal fatigue (thermal striping phenomenon). High cycle fatigue test equipment on thermal can be develop by modifying the thermal transient test facility for structure (TTS) in order to clarify the effect of temperature fluctuation induced by the thermal striping phenomenon on crack initiation and their propagation behavior. The test equipment has the following characteristic. (1) Fluid is controlled by a circulation pump, and by continuously changing the flow quantity ratio of high and low temperature Sodium, sinusoidal temperature fluctuations at various period of the test samples can be taken. (2) Mixing is done by the jet flow mix, thus it can generate axisymmetric temperature fluctuations by accelerating the mixing process of high and low temperature Sodium. (3) It can also control the temperature fluctuation, in which short and long term changes are superimposed. (4) Because the test sample cylinder is hollow, analysis of thermal stress and data from crack initiation to crack propagation can easily be obtained. Sinusoidal temperature fluctuations, random temperature fluctuations, and strength testing of the weld zone by test samples made of stainless steel are planned in the next stage. (author)

  3. Effects of load ratio, R, and test temperature on high cycle fatigue behavior of nano-structured Al4Y4NiX alloy composites

    International Nuclear Information System (INIS)

    Nanostructured Al4Y4NiX composites created by extruding atomized amorphous powders at different extrusion ratios were tested under high cycle bending fatigue at load ratios, R=0.1, 0.33 and ?1 at room temperature, 149 C and 260 C. Increasing the extrusion ratio generally improved the fatigue life and the fatigue limits were well in excess of that obtained on conventional aluminum alloys at all temperatures tested. The fatigue limits obtained in this work were also compared to previously reported values for a nanostructured composite AlGdNiFe alloy produced via similar means.

  4. Estimation of High Cycle Thermal Fatigue Caused by Mixing Flow at RHR System (II)

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sun-ki; Lee, Sang-kook [Korea Electric Power Research Institute, Taejon (Korea, Republic of)

    2006-07-01

    In the case of nuclear power plant, thermal fatigue occurs in the piping system because of temperature change accompanied with plant operations. Therefore pipe and instrument are designed not to exceed fatigue limit. But damage is happening in piping system by thermal fatigue that is not considered at design (for example, abnormal movement at surge line of Torjan, crack at safety injection line of Farley unit 2 and Tihange unit 1, crack at RHR system of Genkai unit 1 and Civaux unit 1 etc). Root cause of these damages is explained by the thermal stratification and thermal cycling, thermal striping phenomena. In this paper, integrity assessment of high cycle thermal fatigue were carried out about the heat exchange out let of residual heat removal system (RHR system) of operating domestic PWR nuclear power plants, which is the high temperature coolant mixing region.

  5. Experimental investigation of high cycle thermal fatigue in a T-junction piping system

    Energy Technology Data Exchange (ETDEWEB)

    Selvam, P. Karthick; Kulenovic, Rudi; Laurien, Eckart [Stuttgart Univ. (Germany). Inst. of Nuclear Technology and Energy Systems (IKE)

    2015-10-15

    High cycle thermal fatigue damage of structure in the vicinity of T-junction piping systems in nuclear power plants is of importance. Mixing of coolant streams at significant temperature differences causes thermal fluctuations near piping wall leading to gradual thermal degradation. Flow mixing in a T-junction is performed. The determined factors result in bending stresses being imposed on the piping system ('Banana effect').

  6. Avoiding thermal striping damage: Experimentally-based design procedures for high-cycle thermal fatigue

    International Nuclear Information System (INIS)

    In the coolant circuits of a liquid metal cooled reactor (LMR), where there is turbulent mixing of coolant streams at different temperatures, there are temperature fluctuations in the fluid. If an item of the reactor structure is immersed in this fluid it will, because of the good heat transfer from the flowing liquid metal, experience surface temperature fluctuations which will induce dynamic surface strains. It is necessary to design the reactor so that these temperature fluctuations do not, over the life of the plant, cause damage. The purpose of this paper is to describe design procedures to prevent damage of this type. Two such procedures are given, one to prevent the initiation of defects in a nominally defect-free structure or to allow initiation only at the end of the component life, and the other to prevent significant growth of undetectable pre-existing defects of the order of 0.2 to 0.4 mm in depth. Experimental validation of these procedures is described, and the way they can be applied in practice is indicated. To set the scene the paper starts with a brief summary of cases in which damage of this type, or the need to avoid such damage, have had important effects on reactor operation. Structural damage caused by high-cycle thermal fatigue has had a significant adverse influence on the operation of LMRs on several occasions. It is necessary to eliminate the risk of such damage at the design stage. In the absence of detailed knowledge of the temperature history to which it will be subject, an LMR structure can be designed so that, if it is initially free of defects more than 0.1 mm deep, no such defects will be initiated by high-cycle fatigue. This can be done by ensuring that the maximum source temperature difference in the liquid metal is less than a limiting value, which depends on temperature. The limit is very low, however, and likely to be restrictive. This method, by virtue of its safety margin, takes into account pre-existing surface crack-like defects up to 0.1 mm deep. If the surface temperature-time history for points on the component is known, the procedure allows the calculation of allowable surface temperature amplitudes such that crack initiation will not occur before the end of the component life. This imposes a less restrictive limit, but it still might be 65 K for a life of 300,000 hours. It is also dependent on the nature of the surface temperature fluctuations, in particular the infrequent large fluctuations. In practice it is difficult to ensure that a structure as built is free from defects greater than 0.1 mm deep, and it has to be recognised that such defects may grow under the imposed thermal loading. A procedure based on limited crack growth and arrest at a depth of about 0.5 mm has been developed. It requires a knowledge of the maximum surface temperature amplitude and the frequency spectrum if the fluctuations, as well as the stress state of the component and the postulated crack shape. For a nominally unstressed structure this procedure is less restrictive and can give allowable amplitudes (though a design safety factor is not included). Detailed information on the temperature fluctuations can in principle be obtained from measurements on the plant or in a liquid metal rig, but it has been shown that if the modelling is correct an air model can provide reliable and conservative information, and can provide it more quickly and economically

  7. An Investigation of High-Cycle Fatigue Models for Metallic Structures Exhibiting Snap-Through Response

    Science.gov (United States)

    Przekop, Adam; Rizzi, Stephen A.; Sweitzer, Karl A.

    2007-01-01

    A study is undertaken to develop a methodology for determining the suitability of various high-cycle fatigue models for metallic structures subjected to combined thermal-acoustic loadings. Two features of this problem differentiate it from the fatigue of structures subject to acoustic loading alone. Potentially large mean stresses associated with the thermally pre- and post-buckled states require models capable of handling those conditions. Snap-through motion between multiple post-buckled equilibrium positions introduces very high alternating stress. The thermal-acoustic time history response of a clamped aluminum beam structure with geometric and material nonlinearities is determined via numerical simulation. A cumulative damage model is employed using a rainflow cycle counting scheme and fatigue estimates are made for 2024-T3 aluminum using various non-zero mean fatigue models, including Walker, Morrow, Morrow with true fracture strength, and MMPDS. A baseline zero-mean model is additionally considered. It is shown that for this material, the Walker model produces the most conservative fatigue estimates when the stress response has a tensile mean introduced by geometric nonlinearity, but remains in the linear elastic range. However, when the loading level is sufficiently high to produce plasticity, the response becomes more fully reversed and the baseline, Morrow, and Morrow with true fracture strength models produce the most conservative fatigue estimates.

  8. Study of high cycle fatigue of PVD surface-modified austempered ductile iron

    Energy Technology Data Exchange (ETDEWEB)

    Feng, H.P.; Lee, S.C.; Hsu, C.H.; Ho, J.M. [Tatung Inst. of Technol., Taipei (Taiwan, Province of China). Dept. of Mater. Eng.

    1999-05-25

    Austempered ductile iron (ADI) is made from ductile iron by an austempering treatment, and its main microstructure is ausferrite that is composed of acicular ferrite and high carbon austenite. The purpose of this experiment is to investigate the influence of different coating layers and the size of casting (mass effect) on the high-cycle fatigue properties of ADI. Specimens in two casting sizes of the same chemical composition were subjected to a high-toughness austempering treatment, then coated with TiN or TiCN hard films by a physical vapor deposition (PVD) process. The results showed that the fatigue limit of the small casting size ADI is 292 MPa for ADI coated with TiN and 306 MPa for ADI coated with TiCN, which are 16% and 22%, respectively, higher than that of the ADI without coating (251 MPa). For the large casting size ADI, the fatigue limits are 200, 214 and 217 MPa for ADI without coating, ADI coated with TiN and ADI coated with TiCN, respectively. ADI coated with TiN and with TiCN are 7% and 9% better than the uncoated. Thus, it is concluded that TiN and TiCN coatings by PVD can improve the high-cycle fatigue strength of ADI. This is due to the high surface hardness and possibly the ADI surface compressive residual stress as well. For the small casting size ADI, TiCN-coated specimens have a bit higher fatigue strengths and this might be attributed to the higher hardness of TiCN than TiN films. As to the effect of mass, it is found that the small casting size has better fatigue properties and benefits more from the coating films. This could have stemmed from the higher nodule count and its associated benefits in thinner castings. (orig.) 24 refs.

  9. High-cycle fatigue behavior of Ti-5Al-2.5Sn ELI alloy forging at low temperatures

    International Nuclear Information System (INIS)

    High-cycle fatigue properties of Ti-5Al-2.5Sn Extra Low Interstitial (ELI) alloy forging were investigated at low temperatures. The high-cycle fatigue strength at low temperatures of this alloy was relatively low compared with that at ambient temperature. The crystallographic orientation of a facet formed at a fatigue crack initiation site was determined by electron backscatter diffraction (EBSD) method in scanning electron microscope (SEM) to understand the fatigue crack initiation mechanism and discuss on the low fatigue strength at low temperature. Furthermore, in terms of the practical use of this alloy, the effect of the stress ratio (or mean stress) on the high-cycle fatigue properties was evaluated using the modified Goodman diagram

  10. Thermally Induced Ultra High Cycle Fatigue of Copper Alloys of the High Gradient Accelerating Structures

    CERN Document Server

    Heikkinen, Samuli; Wuensch, Walter

    2010-01-01

    In order to keep the overall length of the compact linear collider (CLIC), currently being studied at the European Organization for Nuclear Research (CERN), within reasonable limits, i.e. less than 50 km, an accelerating gradient above 100 MV/m is required. This imposes considerable demands on the materials of the accelerating structures. The internal surfaces of these core components of a linear accelerator are exposed to pulsed radio frequency (RF) currents resulting in cyclic thermal stresses expected to cause surface damage by fatigue. The designed lifetime of CLIC is 20 years, which results in a number of thermal stress cycles of the order of 2.33•1010. Since no fatigue data existed in the literature for CLIC parameter space, a set of three complementary experiments were initiated: ultra high cycle mechanical fatigue by ultrasound, low cycle fatigue by pulsed laser irradiation and low cycle thermal fatigue by high power microwaves, each test representing a subset of the original problem. High conductiv...

  11. Damage estimates for European and U.S.sites using the U.S. high-cycle fatigue data base

    Energy Technology Data Exchange (ETDEWEB)

    Sutherland, H.J. [Wind Energy Technology, Sandia National Lab., Albuquerque, NM (United States)

    1996-09-01

    This paper uses two high-cycle fatigue data bases, one for typical U.S. blade materials and one for European materials, to analyze the service lifetime of a wind turbine blade subjected to the WISPER load spectrum for northern European sites and the WISPER protocol load spectrum for U.S. wind farm sites. The U.S. data base contains over 2200 data points that were obtained using coupon testing procedures. These data are used to construct a Goodman diagram that is suitable for analyzing wind turbine blades. This result is compared to the Goodman diagram derived from the European fatigue data base FACT. The LIFE2 fatigue analysis code for wind turbines is then used to predict the service lifetime of a turbine blade subjected to the two loading histories. The results of this study indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a U.S. wind farm site, i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a U.S. wind farm site. Further, the analysis demonstrate that the European and the U.S. fatigue material data bases are in general agreement for the prediction of tensile failures. However, for compressive failures, the two data bases are significantly different, with the U.S. data base predicting significantly shorter service lifetimes than the European data base. (au) 14 refs.

  12. Simulation of Delamination Under High Cycle Fatigue in Composite Materials Using Cohesive Models

    Science.gov (United States)

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

    2006-01-01

    A new thermodynamically consistent damage model is proposed for the simulation of high-cycle fatigue crack growth. The basis for the formulation is an interfacial degradation law that links Fracture Mechanics and Damage Mechanics to relate the evolution of the damage variable, d, with the crack growth rate da/dN. The damage state is a function of the loading conditions (R and (Delta)G) as well as the experimentally-determined crack growth rates for the material. The formulation ensures that the experimental results can be reproduced by the analysis without the need of additional adjustment parameters.

  13. Development of a high cycle vibration fatigue diagnostic system with non-contact vibration sensing

    International Nuclear Information System (INIS)

    In nuclear power plants, it is very important to foresee occurring events with in-operation -inspection (IOI) since the foreseeing makes plant maintenance more speedy and reliable. Moreover, information on plant condition under operating would make period of in-service inspection (ISI) shorter because maintenance plan can be made effectively using the information. In this study, a high cycle fatigue diagnostic system is being developed applying to especially pipe branches with small diameter under in-operating condition, which are in the radioactive areas of PWR plants and hard to access. This paper presents a concept of the in-operating diagnostic system and current status of developing sensing systems. (author)

  14. High-cycle fatigue characteristics of weldable steel for light-water reactors

    Energy Technology Data Exchange (ETDEWEB)

    Klesnil, M.; Polak, J.; Obrtlik, K. (Ceskoslovenska Akademie Ved, Brno. Ustav Fyzikalni Metalurgie); Troshchenko, V.T.; Mishchenko, Yu.I.; Khamaza, L.A. (AN Ukrainskoj SSR, Kiev. Inst. Problem Prochnosti)

    1982-11-01

    Czechoslovak and Soviet 15Kh2NMFA steel was used for running fatigue tests at temperatures of 20, 350 and 400 degC in the high-cycle range with various loading regimes. The results show that at the given temperatures in this type of steel a cyclic softening occurs. The fatigue characteristics were measured with great dispersion of results, but within this dispersion they are almost identical for various steels at the same temperature. Increased temperature results in the decrease in the amplitude of cyclic deformation stress and in the increase in the amplitude of plastic deformation. The diversity in the values of cyclic plasticity and stress response measured in the given mode may be explained by the lower level of softening and the non-homogeneous cyclic plastic deformation of material under the given constant conditions.

  15. High-cycle fatigue characteristics of weldable steel for light-water reactors

    International Nuclear Information System (INIS)

    Czechoslovak and Soviet 15Kh2NMFA steel was used for running fatigue tests at temperatures of 20, 350 and 400 degC in the high-cycle range with various loading regimes. The results show that at the given temperatures in this type of steel a cyclic softening occurs. The fatigue characteristics were measured with great dispersion of results, but within this dispersion they are almost identical for various steels at the same temperature. Increased temperature results in the decrease in the amplitude of cyclic deformation stress and in the increase in the amplitude of plastic deformation. The diversity in the values of cyclic plasticity and stress response measured in the given mode may be explained by the lower level of softening and the non-homogeneous cyclic plastic deformation of material under the given constant conditions. (J.B.)

  16. High Cycle Fatigue Crack Initiation Study of Case Blade Alloy Rene 125

    Science.gov (United States)

    Kantzos, P.; Gayda, J.; Miner, R. V.; Telesman, J.; Dickerson, P.

    2000-01-01

    This study was conducted in order to investigate and document the high cycle fatigue crack initiation characteristics of blade alloy Rene 125 as cast by three commercially available processes. This alloy is typically used in turbine blade applications. It is currently being considered as a candidate alloy for high T3 compressor airfoil applications. This effort is part of NASA's Advanced Subsonic Technology (AST) program which aims to develop improved capabilities for the next generation subsonic gas turbine engine for commercial carriers. Wrought alloys, which are customarily used for airfoils in the compressor, cannot meet the property goals at the higher compressor exit temperatures that would be required for advanced ultra-high bypass engines. As a result cast alloys are currently being considered for such applications. Traditional blade materials such as Rene 125 have the high temperature capabilities required for such applications. However, the implementation of cast alloys in compressor airfoil applications where airfoils are typically much thinner does raise some issues of concern such as thin wall castability, casting cleaningness, and susceptibility to high-cycle fatigue (HCF) loading.

  17. Very high cycle regime fatigue of thin walled tubes made from austenitic stainless steel

    DEFF Research Database (Denmark)

    Carstensen, J.V.; Mayer, H.

    2002-01-01

    Fatigue life data of cold worked tubes (diameter 4 mm, wall thicknesses 0.25 and 0.30 mm) of an austenitic stainless steel, AISI 904 L, were measured in the regime ranging from 2 105 to 1010 cycles to failure. The influence of the loading frequency was investigated as data were obtained in conventional rotating bending at 160 and 200 Hz and in ultrasonic axial loading at 20 kHz. Above 5 106 cycles the fatigue lifetimes found with both methods were comparable. The results show that the slope of the SN curve significantly decreases beyond 108 cycles. Fracture surfaces were examined using scanning electron microscopy. Fatigue cracks initiate at the surface and no significant influence from frequency or from loading modes on fatigue crack initiation and growth is visible.

  18. Very high cycle regime fatigue of thin walled tubes made from austenitic stainless steel

    DEFF Research Database (Denmark)

    Carstensen, J.V.; Mayer, H.; Brndsted, P.

    Fatigue life data of cold worked tubes (diameter 4 mm, wall thicknesses 0.25 and 0.30 mm) of an austenitic stainless steel, AISI 904 L, were measured in the regime ranging from 2 105 to 1010 cycles to failure. The influence of the loading frequency was investigated as data were obtained in...... conventional rotating bending at 160 and 200 Hz and in ultrasonic axial loading at 20 kHz. Above 5 106 cycles the fatigue lifetimes found with both methods were comparable. The results show that the slope of the SN curve significantly decreases beyond 108 cycles. Fracture surfaces were examined using...... scanning electron microscopy. Fatigue cracks initiate at the surface and no significant influence from frequency or from loading modes on fatigue crack initiation and growth is visible....

  19. Effect of thermo-mechanical loading histories on fatigue crack growth behavior and the threshold in SUS 316 and SCM 440 steels. For prevention of high cycle thermal fatigue failures

    International Nuclear Information System (INIS)

    High cycle thermal fatigue failure of pipes induced by fluid temperature change is one of the interdisciplinary issues to be concerned for long term structural reliability of high temperature components in energy systems. In order to explore advanced life assessment methods to prevent the failure, fatigue crack propagation tests were carried out in a low alloy steel and an austenitic stainless steel under typical thermal and thermo-mechanical histories. Special attention was paid to both the effect of thermo-mechanical loading history on the fatigue crack threshold, as well as to the applicability of continuum fracture mechanics treatment to small or short cracks. It was shown experimentally that the crack-based remaining fatigue life evaluation provided more reasonable assessment than the traditional method based on the semi-empirical law in terms of 'usage factor' for high cycle thermal fatigue failure that is employed in JSME Standard, S017. The crack propagation analysis based on continuum fracture mechanics was almost successfully applied to the small fatigue cracks of which size was comparable to a few times of material grain size. It was also shown the thermo-mechanical histories introduced unique effects to the prior fatigue crack wake, resulting in occasional change in the fatigue crack threshold. (author)

  20. Mean stress effects on high-cycle fatigue of Alloy 718

    International Nuclear Information System (INIS)

    This report covers an investigation of the effects of tensile mean stress on the high-cycle fatigue properties of Alloy 718. Three test temperatures (24, 427, and 649 degree C) were employed, and there were tests in both strain and load control. Results were compared with three different models: linear Modified-Goodman, Peterson cubic, and stress-strain parameter. The linear Modified-Goodman model gave good correlation with actual test data for low and moderate mean stress values, but the stress-strain parameter showed excellent correlation over the entire range of possible mean stresses and therefore is recommended for predicting mean stress effects of Alloy 718. 13 refs., 12 figs

  1. Very-High-Cycle-Fatigue of in-service air-engine blades, compressor and turbine

    Science.gov (United States)

    Shanyavskiy, A. A.

    2014-01-01

    In-service Very-High-Cycle-Fatigue (VHCF) regime of compressor vane and turbine rotor blades of the Al-based alloy VD-17 and superalloy GS6K, respectively, was considered. Surface crack origination occurred at the lifetime more than 1500 hours for vanes and after 550 hours for turbine blades. Performed fractographic investigations have shown that subsurface crack origination in vanes took place inspite of corrosion pittings on the blade surface. This material behavior reflected lifetime limit that was reached by the criterion VHCF. In superalloy GS6K subsurface fatigue cracking took place with the appearance of flat facet. This phenomenon was discussed and compared with specimens cracking of the same superalloy but prepared by the powder technology. In turbine blades VHCF regime appeared because of resonance of blades under the influenced gas stream. Both cases of compressor-vanes and turbine blades in-service cracking were discussed with crack growth period and stress equivalent estimations. Recommendations to continue aircrafts airworthiness were made for in-service blades.

  2. Comparison of the very high cycle fatigue behaviors of INCONEL 718 with different loading frequencies

    Science.gov (United States)

    Zhang, YangYang; Duan, Zheng; Shi, HuiJi

    2013-03-01

    In order to clarify the differences of very high cycle fatigue (VHCF) behavior of nickel based superalloy IN718 with different loading frequencies, stress-controlled fatigue tests were carried out by using ultrasonic testing method (20 KHz) and rotary bending testing method (52.5 Hz), both at room temperatures, to establish stress versus cycles to failure (S-N) relationships. Results disclosed that cycles to failure at a given stress level increased with an increase of the applied frequency, i.e., the higher frequency produced an upper shift of the S-N curves. Fractographic analysis suggested that crack initiation and propagation behaviors had large differences: cracks in low-frequency tests preferentially initiated from multiple sources on the specimen surface, while in high-frequency tests, cracks mostly originated from a unique source of subsurface inclusions. Subsequently, frequency-involved modeling was proposed, based on the damage accumulation theory, which could well illustrate qualitatively those comparisons due to different loading frequencies.

  3. Laser High-Cycle Thermal Fatigue of Pulse Detonation Engine Combustor Materials Tested

    Science.gov (United States)

    Zhu, Dong-Ming; Fox, Dennis S.; Miller, Robert A.

    2001-01-01

    Pulse detonation engines (PDE's) have received increasing attention for future aerospace propulsion applications. Because the PDE is designed for a high-frequency, intermittent detonation combustion process, extremely high gas temperatures and pressures can be realized under the nearly constant-volume combustion environment. The PDE's can potentially achieve higher thermodynamic cycle efficiency and thrust density in comparison to traditional constant-pressure combustion gas turbine engines (ref. 1). However, the development of these engines requires robust design of the engine components that must endure harsh detonation environments. In particular, the detonation combustor chamber, which is designed to sustain and confine the detonation combustion process, will experience high pressure and temperature pulses with very short durations (refs. 2 and 3). Therefore, it is of great importance to evaluate PDE combustor materials and components under simulated engine temperatures and stress conditions in the laboratory. In this study, a high-cycle thermal fatigue test rig was established at the NASA Glenn Research Center using a 1.5-kW CO2 laser. The high-power laser, operating in the pulsed mode, can be controlled at various pulse energy levels and waveform distributions. The enhanced laser pulses can be used to mimic the time-dependent temperature and pressure waves encountered in a pulsed detonation engine. Under the enhanced laser pulse condition, a maximum 7.5-kW peak power with a duration of approximately 0.1 to 0.2 msec (a spike) can be achieved, followed by a plateau region that has about one-fifth of the maximum power level with several milliseconds duration. The laser thermal fatigue rig has also been developed to adopt flat and rotating tubular specimen configurations for the simulated engine tests. More sophisticated laser optic systems can be used to simulate the spatial distributions of the temperature and shock waves in the engine. Pulse laser high-cycle thermal fatigue behavior has been investigated on a flat Haynes 188 alloy specimen, under the test condition of 30-Hz cycle frequency (33-msec pulse period and 10-msec pulse width including a 0.2-msec pulse spike; ref. 4). Temperature distributions were calculated with one-dimensional finite difference models. The calculations show that that the 0.2-msec pulse spike can cause an additional 40 C temperature fluctuation with an interaction depth of 0.08 mm near the specimen surface region. This temperature swing will be superimposed onto the temperature swing of 80 C that is induced by the 10-msec laser pulse near the 0.53-mm-deep surface interaction region.

  4. Additive manufactured AlSi10Mg samples using Selective Laser Melting (SLM): Microstructure, high cycle fatigue, and fracture behavior

    OpenAIRE

    Brandl, E.; Heckenberger, U.; Holzinger, V.; Buchbinder, D.

    2012-01-01

    In order to produce serial parts via additive layer manufacturing, the fatigue performance can be a critical attribute. In this paper, the microstructure, high cycle fatigue (HCF), and fracture behavior of additive manufactured AlSi10Mg samples are investigated. The samples were manufactured by a particular powder-bed process called Selective Laser Melting (SLM) and machined afterwards. 91 samples were manufactured without (30C) and with heating (300C) of the building platform and in differ...

  5. A rapid method for generation of a Haigh diagram for high cycle fatigue

    International Nuclear Information System (INIS)

    A rapid test method is described for generating data points for a Haigh diagram for Ti-6Al-4V at a constant life of 107 cycles at room temperature. It involves subjecting specimens to loading blocks of 107 fatigue cycles and progressively increasing the load until failure occurs. An equivalent stress is obtained for each test specimen for plotting on the Haigh diagram. The method is applied to tests conducted at stress ratios (ratio of minimum to maximum stress) from R = -1 to R = 0.9. The validity of the method is confirmed by comparing data with those obtained using the conventional S-N interpolation approach at values of R = 0.1, 0.5, and 0.8. The rapid testing technique is then extended to the generation of a Haigh diagram for the same material subjected to prior low cycle fatigue (LCF) for 10% of its LCF life. No degradation of the fatigue limit is observed from subsequent HCF testing using the rapid testing technique

  6. Simulation of delamination growth under high cycle fatigue using cohesive zone models

    Scientific Electronic Library Online (English)

    Pedro P., Camanho; Albert, Turon; Josep, Costa.

    2008-01-01

    Full Text Available Este artigo apresenta um modelo coesivo para simular a delaminagem de materiais compsitos sob fadiga de altos ciclos. O modelo constitutivo proposto relaciona a evoluo da varivel de dano, d, com a velocidade de crescimento da delaminagem, da/dN. O modelo coesivo implementado no cdigo de eleme [...] ntos finitos ABAQUS e utilizado na simulao de provetes fabricados em carbono-epoxy carregados ciclicamente em modo I, modo II e modo misto I e II. O modelo validado comparando as suas previses com resultados experimentais. Abstract in english A cohesive zone model is proposed for the simulation of delamination growth in composite materials under high-cycle fatigue loading. The basis for the formulation is an interfacial constitutive law that links fracture mechanics and damage mechanics relating the evolution of the damage variable, d, w [...] ith the crack growth rate, da/dN. The cohesive zone model is implemented in ABAQUS finite element code and used in the simulation of carbon-epoxy test specimens cyclically loaded in mode I, mode II and mixed-mode I and II. The accuracy of the model is assessed by comparing the predictions with experimental data.

  7. Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, High-Cycle and Low-Cycle Mechanical Fatigue, Creep and Thermal Fatigue Effects

    Science.gov (United States)

    Bast, Callie C.; Boyce, Lola

    1995-01-01

    The development of methodology for a probabilistic material strength degradation is described. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep and thermal fatigue. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing predictions of high-cycle mechanical fatigue and high temperature effects with experiments are presented. Results from this limited verification study strongly supported that material degradation can be represented by randomized multifactor interaction models.

  8. Investigation of effect of pre-strain on very high-cycle fatigue strength of austenitic stainless steels

    International Nuclear Information System (INIS)

    This paper describes the effect of large pre-strain on very high cycle fatigue strength of austenitic stainless steels that are widely used in nuclear power plants. Fatigue tests were carried out on strain-hardened specimens. The material served in this study was type SUS316NG. Up to 20% pre-strain was introduced to the materials, and the materials were mechanically machined into hourglass shaped smooth specimens. Some specimens were pre-strained after machining. Experiments were conducted in ultrasonic and rotating-bending fatigue testing machines. The S-N curves obtained in this study show that an increase in the magnitude of the pre-strain increases the fatigue strength of the material and this relationship is independent of the type of the pre-strain of tension or compression. Although all specimens fractured by the surface initiated fatigue cracks, one specimen fractured by an internal origin. However, this internal fracture did not cause a sudden drop in fatigue strength of type SUS316NG. Vickers hardness tests were carried out to ascertain the relationship between fatigue strength and hardness of the pre-strained materials. It was found that the increase in the fatigue limit of the pre-strained materials strongly depended on the hardness derived from an indentation size equal to the scale of stage I fatigue cracks. (author)

  9. Application of in situ thermography for evaluating the high-cycle and very high-cycle fatigue behaviour of cast aluminium alloy AlSi7Mg (T6).

    Science.gov (United States)

    Krewerth, D; Weidner, A; Biermann, H

    2013-12-01

    The present paper illustrates the application of infrared thermal measurements for the investigation of crack initiation point and crack propagation in the high-cycle and the very high-cycle fatigue range of cast AlSi7Mg alloy (A356). The influence of casting defects, their location, size and amount was studied both by fractography and thermography. Besides internal and surface fatigue crack initiation as a further crack initiation type multiple fatigue crack initiation was observed via in situ thermography which can be well correlated with the results from fractography obtained by SEM investigations. In addition, crack propagation was studied by the development of the temperature measured via thermography. Moreover, the frequency influence on high-cycle fatigue behaviour was investigated. The presented results demonstrate well that the combination of fractography and thermography can give a significant contribution to the knowledge of crack initiation and propagation in the VHCF regime. PMID:23541962

  10. Micro-scale testing and micromechanical modelling for high cycle fatigue of CoCr stent material.

    Science.gov (United States)

    Sweeney, C A; O'Brien, B; Dunne, F P E; McHugh, P E; Leen, S B

    2015-06-01

    This paper presents a framework of experimental testing and crystal plasticity micromechanics for high cycle fatigue (HCF) of micro-scale L605 CoCr stent material. Micro-scale specimens, representative of stent struts, are manufactured via laser micro-machining and electro-polishing from biomedical grade CoCr alloy foil. Crystal plasticity models of the micro-specimens are developed using a length scale-dependent, strain-gradient constitutive model and a phenomenological (power-law) constitutive model, calibrated from monotonic and cyclic plasticity test data. Experimental microstructural characterisation of the grain morphology and precipitate distributions is used as input for the polycrystalline finite element (FE) morphologies. Two microstructure-sensitive fatigue indicator parameters are applied, using local and non-local (grain-averaged) implementations, for the phenomenological and length scale-dependent models, respectively, to predict fatigue crack initiation (FCI) in the HCF experiments. PMID:25817609

  11. High cycle fatigue and threshold behaviour of powder metallurgical Mo and Mo-alloys

    International Nuclear Information System (INIS)

    A detailed characterization of the room temperature fatigue properties of powder metallurgical Mo, Mo-W and Ti-Zr-Mo (TZM) alloys is presented. In particular the factors affecting fatigue crack nucleation and growth behaviour are described. Fatigue tests were carried out by conventional rotating-bending and compared with results from a time-saving 20 kHz resonance push-pull test method. Fatigue strength data were determined by a statistical evaluation of test results from a sufficiently large number of specimens. The results show an increase in fatigue strength with alloying additions. Fatigue cracks were observed nucleating at highly localized slip bands at the specimen surface with the fatigue crack zones comprising only a small fraction of the total specimen cross-section. Fatigue crack growth rates at low stress intensities and threshold stress intensity values for crack growth were determined for a stress ratio of R = -1 using a 20 kHz resonance test method. These latter values were found to be sensitively dependent on microstructure, composition and processing history. (author)

  12. The Effect of Ballistic Impacts on the High Cycle Fatigue Properties of Ti-48Al-2Nb-2Cr (at.%)

    Science.gov (United States)

    Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Austin, C. M.; Erdman, O.

    2000-01-01

    The ability of gamma - TiAl to withstand potential foreign and/or domestic object damage is a technical risk to the implementation of gamma - TiAl in low pressure turbine (LPT) blade applications. The overall purpose of the present study was to determine the influence of ballistic impact damage on the high cycle fatigue strength of gamma - TiAl simulated LPT blades. Impact and specimen variables included ballistic impact energy, projectile hardness, impact temperature, impact location, and leading edge thickness. The level of damage induced by the ballistic impacting was studied and quantified on both the impact (front) and backside of the specimens. Multiple linear regression was used to model the cracking and fatigue response as a function of the impact variables. Of the impact variables studied, impact energy had the largest influence on the response of gamma - TiAl to ballistic impacting. Backside crack length was the best predictor of remnant fatigue strength for low energy impacts (gamma - TiAl samples displayed a classical mean stress dependence on the fatigue strength. For the fatigue design stresses of a 6th stage LPT blade in a GE90 engine, a Ti-48Al-2Nb-2Cr LPT blade would survive an impact of normal service conditions.

  13. The effect of HVOF sprayed coatings on the elevated temperature high cycle fatigue behavior of a martensitic stainless steel

    International Nuclear Information System (INIS)

    This study reports the influence of three High Velocity Oxy-Fuel (HVOF) applied coatings on the high cycle fatigue resistance of a martensitic stainless steel substrate at room and elevated temperatures. It was found that chromium carbide and tungsten carbide coated specimens exhibited significantly lower fatigue capability compared to the substrate material at elevated temperatures while IN625 coated specimens exhibited a small beneficial effect. An attempt is made to explain the observed behavior in terms of elastic modulus mismatch, thermal expansion mismatch, residual stress and coating/substrate properties. It is concluded that coated metallic components must be analyzed as composite structures and that data generated for design properties must be performed on specimens which represent the geometry and characteristics of intended component

  14. High cycle fatigue behavior of Fe-Cr-Mn-C and Ni-Mo-Al aligned eutectics

    Energy Technology Data Exchange (ETDEWEB)

    Miyahara, Y. (Komatsu Ltd., Osaka (Japan)); Stoloff, N.S. (Materials Engineering Dept., Rensselaer Polytechnic Inst., Troy, NY (United States))

    1991-12-30

    High cycle fatigue tests were conducted on an Fe-Cr-Mn-C eutectic alloy at 500, 650 and 800degC and on an Ni-Al-Mo eutectic (AG-170) at 500 and 650degC. Fractographic observations were also conducted on fractured samples. The fatigue strength of the Fe-Cr-Mn-C eutectic decreased with increasing temperature while that of AG-170 exhibited almost no perceivable difference with temperature change. A remarkably high value of {Delta}{sigma}{sub 10}{sup 7}/{sigma}{sub UTS} was obtained for AG-170 (UTS, ultimate tensile strength). Crack initiation sites were found to be prior broken fibers for the Fe-Cr-Mn-C eutectic and an unidentified faceted particle for AG-170. (orig.).

  15. Duplex S-N fatigue curves: statistical distribution of the transition fatigue life

    Directory of Open Access Journals (Sweden)

    D.S. Paolino

    2014-10-01

    Full Text Available In recent years, very-high-cycle fatigue (VHCF behavior of metallic materials has become a major point of interest for researchers and industries. The needs of specific industrial fields (aerospace, mechanical and energy industry for structural components with increasingly large fatigue lives, up to 1010 cycles (gigacycle fatigue, requested for a more detailed investigation on the experimental properties of materials in the VHCF regime. Gigacycle fatigue tests are commonly performed using resonance fatigue testing machines with a loading frequency of 20 kHz (ultrasonic tests. Experimental results showed that failure is due to cracks which nucleate at the specimen surface if the stress amplitude is above the conventional fatigue limit (surface nucleation and that failure is generally due to cracks which nucleate from inclusions or internal defects (internal nucleation when specimens are subjected to stress amplitudes below the conventional fatigue limit. Following the experimental evidence, the Authors recently proposed a new statistical model for the complete description of SN curves both in the high-cycle-fatigue (HCF and in the VHCF fatigue regions (Duplex S-N curves. The model differentiates between the two failure modes (surface and internal nucleation, according to the estimated distribution of the random transition stress (corresponding to the conventional fatigue limit. No assumption is made about the statistical distribution of the number of cycles at which the transition between surface and internal nucleation occurs (i.e., the transition fatigue life. In the present paper, the statistical distribution of the transition fatigue life is obtained, according to the statistical model proposed. The resulting distribution depends on the distance between the HCF and the VHCF regions and on the distribution of the random transition stress. The estimated distribution can be effectively used to predict, with a specified confidence level, the number of cycles for which an internal nucleation may probabilistically occur in a VHCF test and it is also informative for properly choosing the end of HCF tests in terms of number of cycles. A numerical example, based on experimental datasets taken from the literature, is provided.

  16. Study on high cycle thermal fatigue in mixing tee. Evaluation of transfer characteristics of temperature fluctuation from fluid to structure

    International Nuclear Information System (INIS)

    Thermal striping is observed at a point where hot and cold fluids are mixing. Evaluation of high cycle thermal fatigue on structural components is a significant issue for the reactor safety design. Japan Atomic Energy Agency (JAEA) has conducted experimental and numerical investigations to establish a quantitative evaluation method of high cycle thermal fatigue in a sodium-cooled fast reactor, based on the nature of the phenomena. A water experiment WATLON (as Water Experiment of Fluid Mixing in T-pipe with Long Cycle Fluctuation) has been conducted to clarify the thermal striping phenomena in a mixing tee area. In this study, water experiments WATLON were carried out to clarify the unsteady behavior of heat transfer under wall jet condition. In experiments, heat transfer coefficients between fluid and wall in the mixing region were obtained from temperature measurements using thermocouples (movable tree type in fluid and embedded type in wall). To clarify the relation between the local velocity and the wall temperature, those were measured simultaneously by the Particle Image Velocimetry (PIV) and the thermocouple measurement, respectively. Sampling time of the velocity by the PIV and the temperature by the thermocouple were synchronized in the measurement. The experimental results showed that the heat transfer coefficient was 2?6 time larger than the reference value predicted by the Dittus-Boelter correlation in straight pipes and was increased as the local velocity near the wall. A CD-ROM is attached as an appendix. (J.P.N.)

  17. Thermal mixing in T-junction piping system concerned with high-cycle thermal fatigue in structure

    International Nuclear Information System (INIS)

    In Japan Atomic Energy Agency (JAEA), a numerical simulation code 'MUGTHES' has been developed to investigate thermal striping phenomena caused by turbulence mixing of fluids in different temperature and to provide transient data for an evaluation method of high-cycle thermal fatigue. MUGTHES adopts Large Eddy Simulation (LES) approach to predict unsteady phenomena in thermal mixing and employs boundary fitted coordinate system to be applied to complex geometry in a power reactor. Numerical simulation of thermal striping phenomena in a T-junction piping system (T-pipe) is conducted. Boundary condition for the simulation is chosen from an existing water experiment in JAEA, named as WATLON experiment. In the numerical simulation, standard Smagorinsky model is employed as eddy viscosity model with the model coefficient of 0.14 (=Cs). Numerical results of MUGTHES are verified by the comparisons with experimental results of velocity and temperature. Through the numerical simulation in the T-pipe, applicability of MUGTHES to the thermal striping phenomena is confirmed and the characteristic large-scale eddy structure which dominates thermal mixing and may cause high-cycle thermal fatigue is revealed. (author)

  18. A Simulation Method for High-Cycle Fatigue-Driven Delamination using a Cohesive Zone Model

    DEFF Research Database (Denmark)

    Bak, Brian Lau Verndal; Turon, A.; Lindgaard, Esben; Lund, Erik

    2015-01-01

    function of the energy release rate for the crack growth rate during cyclic loading. The J-integral has been applied to determine the energy release rate. Unlike other cohesive fatigue methods, the proposed method depends only on quasi-static properties and Paris' law parameters without relying on...

  19. Influence of surface finish on the high cycle fatigue behavior of a 304L austenitic stainless steel

    International Nuclear Information System (INIS)

    This work has dealt with the influence of surface finish on the high cycle fatigue behavior of a 304L. The role played by roughness, surface hardening and residual stresses has been particularly described. First part of this study has consisted of the production of several surface finishes. These latter were obtained by turning, grinding, mechanical polishing and sandblasting. The obtained surfaces were then characterised in terms of roughness, hardening, microstructure and residual stresses. Fatigue tests were finally conducted under various stress ratios or mean stresses at two temperatures (25 C and 300 C). Results clearly evidenced an effect of the surface integrity on the fatigue resistance of the 304L. This influence is nevertheless more pronounced at ambient temperature and for a positive mean stress. For all explored testing conditions, the lowest endurance limit was obtained for ground specimens whereas polished samples exhibited the best fatigue strength. Results also cleared out a detrimental influence of a positive mean stress in the case of specimens having surface defaults of a great acuity. The study of the relative effect of each of the surface parameter, under a positive stress ratio and at the ambient temperature, showed that roughness profile and surface hardening are the two more influential factors. The role of the residual stresses remains negligible due to their rapid relaxation during the application of the first cycles of fatigue. The estimation of the initiation and propagation periods showed that mechanisms differed as a function of the applied stress ratio. Crack propagation is governed by the parameter DK at a positive stress ratio and by Dep/2 in the case of tension-compression tests. (author)

  20. Prediction of three-dimensional crack propagation paths taking high cycle fatigue into account

    Directory of Open Access Journals (Sweden)

    Guido Dhondt

    2016-01-01

    Full Text Available Engine components are usually subject to complex loading patterns such as mixed-mode Low Cycle Fatigue Loading due to maneuvering. In practice, this LCF Loading has to be superimposed by High Cyclic Fatigue Loading caused by vibrations. The changes brought along by HCF are twofold: first, the vibrational cycles which are superposed on the LCF mission increase the maximum loading of the mission and may alter the principal stress planes. Secondly, the HCF cycles themselves have to be evaluated on their own, assuring that no crack propagation occurs. Indeed, the vibrational frequency is usually so high that propagation leads to immediate failure. In the present paper it is explained how these two effects can be taken care of in a standard LCF crack propagation procedure. The method is illustrated by applying the Finite Element based crack propagation software CRACKTRACER3D on an engine blade.

  1. Deformation mechanisms induced under high cycle fatigue tests in a metastable austenitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Roa, J.J., E-mail: joan.josep.roa@upc.edu [CIEFMA-Departament de Cincia dels Materials i Enginyeria Metallrgica, ETSEIB, Universitat Politcnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain); CRnE, Campus Diagonal Sud, Edificio C, Universitat Politcnica de Catalunya, C/ Pascual i Vila 15, 08028 Barcelona (Spain); Fargas, G. [CIEFMA-Departament de Cincia dels Materials i Enginyeria Metallrgica, ETSEIB, Universitat Politcnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain); Jimnez-Piqu, E. [CIEFMA-Departament de Cincia dels Materials i Enginyeria Metallrgica, ETSEIB, Universitat Politcnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain); CRnE, Campus Diagonal Sud, Edificio C, Universitat Politcnica de Catalunya, C/ Pascual i Vila 15, 08028 Barcelona (Spain); Mateo, A. [CIEFMA-Departament de Cincia dels Materials i Enginyeria Metallrgica, ETSEIB, Universitat Politcnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain)

    2014-03-01

    Advanced techniques were used to study the deformation mechanisms induced by fatigue tests in a metastable austenitic stainless steel AISI 301LN. Observations by Atomic Force Microscopy were carried out to study the evolution of a pre-existing martensite platelet at increasing number of cycles. The sub-superficial deformation mechanisms of the austenitic grains were studied considering the cross-section microstructure obtained by Focused Ion Beam and analysed by Scanning Electron Microscopy and Transmission Electron Microscopy. The results revealed no deformation surrounding the pre-existing martensitic platelet during fatigue tests, only the growth on height was observed. Martensite formation was associated with shear bands on austenite, mainly in the {111} plane, and with the activation of the other intersecting austenite {111}?110? slip system. Furthermore, transmission electron microscopy results showed that the nucleation of ?-martensite follows a two stages phase transformation (?{sub fcc}??{sub hcp}??'{sub bcc})

  2. Deformation mechanisms induced under high cycle fatigue tests in a metastable austenitic stainless steel

    International Nuclear Information System (INIS)

    Advanced techniques were used to study the deformation mechanisms induced by fatigue tests in a metastable austenitic stainless steel AISI 301LN. Observations by Atomic Force Microscopy were carried out to study the evolution of a pre-existing martensite platelet at increasing number of cycles. The sub-superficial deformation mechanisms of the austenitic grains were studied considering the cross-section microstructure obtained by Focused Ion Beam and analysed by Scanning Electron Microscopy and Transmission Electron Microscopy. The results revealed no deformation surrounding the pre-existing martensitic platelet during fatigue tests, only the growth on height was observed. Martensite formation was associated with shear bands on austenite, mainly in the {111} plane, and with the activation of the other intersecting austenite {111}?110? slip system. Furthermore, transmission electron microscopy results showed that the nucleation of ?-martensite follows a two stages phase transformation (?fcc??hcp??'bcc)

  3. Very High Cycle Fatigue Behavior of Riblet Structured High Strength Aluminium Alloy Thin Sheets

    OpenAIRE

    Stille, Sebastian

    2015-01-01

    Fatigue testing was performed on two age hardened high strength aluminum alloys(AA 2024 T351 and AA 7075 T6) at ultrasonic frequencies of around 20 kHz in fullyreversed axial loading (R = 1). Tests were carried out on flat and riblet structuredthin sheets in order to evaluate their usability for a novel technique for aerodynamicdrag reduction as well as for gaining further insight into the relevant degradationand failure mechanisms. The studied riblets were of semi-circular geometry andprodu...

  4. How to deal with very high cycle fatigue (VHCF) effects in practical applications?

    Energy Technology Data Exchange (ETDEWEB)

    Bacher-Hoechst, Manfred; Issler, Stephan [Robert Bosch GmbH, Stuttgart (Germany). Corporate Research and Advance Engineering, Materials and Process Engineering Metals

    2012-07-01

    Fatigue designing of high-stressed engine components is a key factor for reliable power train systems in automotive industry. In this context load assumptions are very important since this is attended with a pre-designing of important machine elements. Load analyses are usually performed by using experimental methods since the accuracy of load simulations are often not precise enough. An example for VHCF problems occurs in modern high pressure pumps for gasoline direct injection systems, which have load spectra with a large amount of cycles up to 10{sup 9} including a very powerful shape of the spectra. At the same time it is necessary to consider the properties of fuels in service since they might affect the fatigue strength significantly. For example, ethanol-based gasoline fuels are used in a lot of countries worldwide and especially their additives may lead to significant corrosion fatigue effects. In addition, it is well known that material inclusions play an important role for the VHCF behaviour especially for high-strength steels. This paper deals with possibilities to avoid VHCF problems of components in service to maintain reliable systems. (orig.)

  5. Deformation behaviour and fracture of Ni-base single crystals at simultaneous action of high-cycle fatigue and creep.

    Czech Academy of Sciences Publication Activity Database

    Kunz, Ludvk; Luk, Petr

    2007-01-01

    Ro?. 14, ?. 2 (2007), s. 15-20. ISSN 1335-0803 R&D Projects: GA ?R GA106/05/2112 Institutional research plan: CEZ:AV0Z20410507 Keywords : CMSX-4 * CM186LC * Fatigue life * Constant lifetime diagram Subject RIV: JG - Metallurgy

  6. Very high cycle fatigue behavior of riblet structured high strength aluminum alloy thin sheets

    OpenAIRE

    Stille, Sebastian

    2015-01-01

    Fatigue testing was performed on two age hardened high strength aluminum alloys (AA 2024 T351 and AA 7075 T6) at ultrasonic frequencies of around 20 kHz in fully reversed axial loading (R = -1). Tests were carried out on flat and riblet structured thin sheets in order to evaluate their usability for a novel technique for aerodynamicdrag reduction as well as for gaining further insight into the relevant degradation and failure mechanisms. The studied riblets were of semi-circular geometry and ...

  7. Design and realization of a multisamples rotating high cycle fatigue machine

    Directory of Open Access Journals (Sweden)

    Massimo Martorelli

    2012-10-01

    Full Text Available In this work the design and the technical characteristic of a Moore rotating bending machine are presented. The machine has been realized at the University of Cassino in order to run tests on multiple specimens at different temperature. The user can choose independently the load and the temperature for each specimen. The machine has been designed to produce in short time a several numbers of data of materials fatigue strength at low costs. The machine is in assembling step at the Laboratory of Industrial Design of the University of Cassino.

  8. Influence of Microstructural Inhomogeneity and Residual Stress on Very High Cycle Fatigue Property of Clean Spring Steel

    Science.gov (United States)

    Li, Wei; Sakai, Tatsuo; Wang, Ping

    2013-09-01

    The present study investigated the very high cycle fatigue (VHCF) properties of a spring steel SUP7-T386 under the conditions of surface grinding and electro-polishing by performing the axial loading test at a stress ratio of -1. The influence of the microstructural inhomogeneity (MI) generated in the process of heat treatment and the residual stress induced by surface grinding on the VHCF properties was discussed. This steel with surface grinding exhibits the continuously descending S-N characteristics, corresponding to the surface flaw-induced failure at high stress level and the interior flaw-induced failure at low stress level. Otherwise, with surface electro-polishing, it exhibits continuously descending S-N characteristics with lower fatigue strength, but only corresponding to the surface flaw-induced failure even at low stress level. Compared with the evaluated maximum inclusion size of about 11.5 ?m, the larger MI size and the compressive residual stress play a key role in determining fatigue failure mechanism of this steel under axial loading in the VHCF regime. From the viewpoint of fracture mechanics, MI-induced crack growth behavior belongs to the category of small crack growth, and threshold stress intensity factors controlling surface and interior crack growth are evaluated to be 2.85 and 2.51 MPa m1/2, respectively. The predicted maximum MI size of about 27.6 ?m can be well used to evaluate surface and interior fatigue limit of this steel under axial loading in the VHCF regime, combined with the correction of residual stress.

  9. Effect of secondary flow generated in 90-degree bend upon high-cycle thermal fatigue in a mixing tee

    International Nuclear Information System (INIS)

    In nuclear power plants, there are many T-junctions at which different temperature fluids are mixed. When the fluids with different temperature are mixed, temperature fluctuation in fluids reachs wall and high-cycle heat fatigue occurs. Depending on amplitude and frequency of temperature fluctuation, it could lead to pipe rupture accident at worst. In addition, in case of the T-junction with 90-degree bend at upstream, there is higher risk for pipe rupture accident due to secondary flow which arises in the 90-degree bend. In this study, the effects of temperature fluctuation above the T-junction in case of different distance of 90-degree bend outlet to the T-junction are investigated. (author)

  10. High-cycle metal fatigue under multiaxial loading damage accumulation models applied to an industrial structure

    International Nuclear Information System (INIS)

    Some components in French nuclear power plants are submitted to thermo-mechanical loadings during their lifetime. Thermal fatigue cracking (striping) is observed in the mixing zones of the reactor in some areas of the residual heat removal system (RHR). Edge cracks located on the internal surface of the pipe are observed essentially near weld tips but also far from the weld. Crack initiation has been related in a qualitative way to the thermal fluctuation and to the detrimental effects of residual weld stress and surface finishing. The aim is to simulate the damage accumulation for two industrial structures : a mock-up of a RHR and the RHR itself. For that we used two endurance limit criteria for multiaxial loading : MATAKE and DANG VAN both based on the concept of critical plane. We extend these models to damage accumulation and constant or variable amplitude loading. Furthermore, in these models we have introduced a new parameter to take into account an initial hardening. These criteria have been implemented in Code-Aster the structural analysis finite element code of EDF [http://www.code-aster.org]. Finite Element simulations are carried out on a RHR structure and an experimental T-piece, denoted FATHER, in which cold water and hot water are mixed. In our computations the thermal loading used results from a thermo-hydraulic calculation realized at EDF R and D [1,2]. For the moment there is no guaranty about the validity of thermal loading, but we consider that it is sufficiently realistic to be employed. From the comparison of the numerical results we conclude that the damage is at least three times more important with models extended to variable amplitude than with those extended to constant amplitude. Furthermore when we compare the largest fatigue damage obtained with a variable amplitude criterion in which the pre-hardening coefficient is equal to 1.25, with a constant amplitude criterion the ratio is about ten. (authors)

  11. High cycle fatigue behavior of as-cast Mg96.34Gd2.5Zn1Zr0.16 alloy fabricated by semi-continuous casting

    International Nuclear Information System (INIS)

    This article presents the tension–compression high cycle fatigue behavior of as-cast Mg96.34Gd2.5Zn1Zr0.16 alloy produced by semi-continuous casting at ambient temperature. The relationship between stress amplitude and cycles to failure is established, which indicates that fatigue strength of this alloy is approximately 105±8 MPa. Fracture surface of specimens were examined using a scanning electron microscope, indicating that the fatigue cracks all initiate from the oxides located at the surface. Different from other cast Mg alloys, there exist two kinds of unique fatigue morphologies at the fatigue propagation region, which consists of fine steps. Meanwhile, there is a fatigue life gap between 105 and 107 cycles on the S–N curve, which probably demonstrates that the growth rate of the fatigue cracks of as-cast Mg96.34Gd2.5Zn1Zr0.16 alloy is relatively large, and once the fatigue cracks form, the samples could fails in less than 105 cycles

  12. A constitutive high cycle fatigue damage model - based on the interaction between microplasticity and local damage

    Energy Technology Data Exchange (ETDEWEB)

    Flaceliere, L. [Futurscope (France); Morel, F.; Dragon, A.

    2006-07-01

    This paper presents a new model that accounts, on a local scale, for the coupling between plasticity due to gliding in shear bands and damage occurring when the accumulated plastic strain has reached a threshold value. The irreversible thermodynamics with internal state variables is employed to keep a middle way between extensive description of plastic and damage flow and application of accessibility requirements. Plasticity and damage are governed by their proper complementary rules (yield functions and potentials). At the same time, a coupling occurs between the damage variable and the hardening parameters. A large experimental database relative to the fatigue behavior of a mild steel C36 submitted to different loading modes (tension, torsion, combined proportional tension and torsion) proves the efficiency of such a model. The prediciton of Woehler curves for cyclic complex stress states can be readily done, but the main feature of this approach is to ensure a clear link between mesoscopic parameters like the hardening behavior of individual grains and the subsequent local damage.

  13. High Cycle Thermal Fatigue Analysis for a Mixing Tee in Safety Injection and Shutdown Cooling System of SKN Unit 3 and 4 Power Plant

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Kyeong Jin; Lee, Dong Jae; Kim, Dae Soo; Huh, Man Gil [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2011-05-15

    Safety Injection and Shutdown Cooling system (SISC) in a nuclear power plant has an important role of core cooling during plant shutdown and on emergency conditions. A heat exchanger on the SISC removes the heat energy generated in the reactor core during shutdown cooling event. Mixing tee placed on downstream of the heat exchanger designates a Tshaped branch connection where the hot flow passed through the by-pass line mixes with the flow passed through the heat exchanger, and due to the characteristics of fluid with bad heat conductivity, the flow develops a mixing zone in a distance from the mixing tee. The pipe wall in the mixing zone experiences the thermal oscillation of high cycle, and therefore is in a state of the high cycle thermal fatigue loadings. In this work, performed is the high cycle thermal fatigue analysis for a mixing tee under the prescribed thermal loadings in a mixing zone. Using the evaluation guide established by JSME, JSME S017- 2003 which has evaluation procedure composing of the four steps, we evaluate the fatigue integrity of the mixing tee of which the results show that the mixing tee satisfies the fatigue integrity in the last step (fourth) of four steps of evaluation procedure where the fatigue usage factor, U was calculated and then compared with the well known criterion, U<1. Representative results of the fatigue analysis are also discussed

  14. Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

    Science.gov (United States)

    Forman, R. G.; Zanganeh, M.

    2014-01-01

    This paper describes the results of a research program conducted to improve the understanding of fatigue crack growth rate behavior in the threshold growth rate region and to answer a question on the validity of threshold region test data. The validity question relates to the view held by some experimentalists that using the ASTM load shedding test method does not produce valid threshold test results and material properties. The question involves the fanning behavior observed in threshold region of da/dN plots for some materials in which the low R-ratio data fans out from the high R-ratio data. This fanning behavior or elevation of threshold values in the low R-ratio tests is generally assumed to be caused by an increase in crack closure in the low R-ratio tests. Also, the increase in crack closure is assumed by some experimentalists to result from using the ASTM load shedding test procedure. The belief is that this procedure induces load history effects which cause remote closure from plasticity and/or roughness changes in the surface morphology. However, experimental studies performed by the authors have shown that the increase in crack closure is a result of extensive crack tip bifurcations that can occur in some materials, particularly in aluminum alloys, when the crack tip cyclic yield zone size becomes less than the grain size of the alloy. This behavior is related to the high stacking fault energy (SFE) property of aluminum alloys which results in easier slip characteristics. Therefore, the fanning behavior which occurs in aluminum alloys is a function of intrinsic dislocation property of the alloy, and therefore, the fanned data does represent the true threshold properties of the material. However, for the corrosion sensitive steel alloys tested in laboratory air, the occurrence of fanning results from fretting corrosion at the crack tips, and these results should not be considered to be representative of valid threshold properties because the fanning is eliminated when testing is performed in dry air.

  15. Low cycle fatigue: high cycle fatigue damage accumulation in a 304L austenitic stainless steel; Endommagement et cumul de dommage en fatigue dans le domaine de l'endurance limitee d'un acier inoxydable austenitique 304L

    Energy Technology Data Exchange (ETDEWEB)

    Lehericy, Y

    2007-05-15

    The aim of this study was to evaluate the consequences of a Low Cycle Fatigue pre-damage on the subsequent fatigue limit of a 304L stainless steel. The effects of hardening and severe roughness (grinding) have also been investigated. In a first set of tests, the evolution of the surface damage induced by the different LCF pre-cycling was characterized. This has permitted to identify mechanisms and kinetics of damage in the plastic domain for different surface conditions. Then, pre-damaged samples were tested in the High Cycle Fatigue domain in order to establish the fatigue limits associated with each level of pre-damage. Results evidence that, in the case of polished samples, an important number of cycles is required to initiate surface cracks ant then to affect the fatigue limit of the material but, in the case of ground samples, a few number of cycles is sufficient to initiate cracks and to critically decrease the fatigue limit. The fatigue limit of pre-damaged samples can be estimated using the stress intensity factor threshold. Moreover, this detrimental effect of severe surface conditions is enhanced when fatigue tests are performed under a positive mean stress (author)

  16. Generation of stationary Gaussian processes and extreme value distributions for high-cycle fatigue models - application to tidal stream Turbines

    Scientific Electronic Library Online (English)

    M., Suptille; E., Pagnacco; L., Khalij; J. E. Souza de, Cursi; J., Brossard.

    Full Text Available The operating environment of tidal stream turbines is random due to the variability of the sea flow (turbulence, wake, tide, streams, among others). This yields complex time-varying random loadings, making it necessary to deal with high cycle multiaxial fatigue when designing such structures. It is [...] thus required to apprehend extreme value distributions of stress states, assuming they are stationary multivariate Gaussian processes. This work focus on such distributions, addressing their numerical simulation with an analytical description. For that, we first focused on generating one-dimensional Gaussian processes, considering a band-limited white noise in both the narrow-band and the wide-band cases. We then fitted the resulting extreme value distributions with GEV distributions. We secondly extended the generation method to the correlated two-dimensional case, in which the joint extreme value distribution can be obtained from the associated margins. Finally, an example of application related to tidal stream turbines introduces a Bretschneider spectrum, whose shape is commonly encountered in the field of hydrology. Comparing the empirical calculations with the GEV fits for the extreme value distributions shows a very well agreement between the results.

  17. On the effect of deep-rolling and laser-peening on the stress-controlled low- and high-cycle fatigue behavior of Ti-6Al-4V at elevated temperatures up to 550?C

    Energy Technology Data Exchange (ETDEWEB)

    Ritchie, IAltenberger, RKNalla, YSano LWagner, RO

    2012-04-01

    The effect of surface treatment on the stress/life fatigue behavior of a titanium Ti-6Al-4V turbine fan blade alloy is investigated in the regime of 102 to 106 cycles to failure under fully reversed stress-controlled isothermal push-pull loading between 25? and 550?C at a frequency of 5 Hz. Specifically, the fatigue behavior was examined in specimens in the deep-rolled and laser-shock peened surface conditions, and compared to results on samples in the untreated (machined and stress annealed) condition. Although the fatigue resistance of the Ti-6Al-4V alloy declined with increasing test temperature regardless of surface condition, deep-rolling and laser-shock peening surface treatments were found to extend the fatigue lives by factors of more than 30 and 5-10, respectively, in the high-cycle and low-cycle fatigue regimes at temperatures as high as 550?C. At these temperatures, compressive residual stresses are essentially relaxed; however, it is the presence of near-surface work hardened layers, with a nanocystalline structure in the case of deep-rolling and dense dislocation tangles in the case of laser-shock peening, which remain fairly stable even after cycling at 450?-550?C, that provide the basis for the beneficial role of mechanical surface treatments on the fatigue strength of Ti-6Al-4V at elevated temperatures.

  18. Fatigue life prediction for 316 stainless steel. Case of superimposed and repeated two-step stress

    International Nuclear Information System (INIS)

    In this study, applicability of linear-cumulative damage rule was investigated for variable loading of high-cycle fatigue for Type 316 stainless steel. Push-pull fatigue tests were conducted in ambient air and room temperature by controlling stress amplitude. Two types variable loading were tested. Repeated two-step tests were conducted in order to assess the effect of loading history by crack on fatigue life. And superimposed tests were also conducted to investigate applicability for linear-cumulative damage rule. As a result, effect of loading history by crack was not confirmed in repeated two-step test. However, fatigue life for superimposed wave decreased by change of crack opening range. It was concluded that considering safety factor, a linear-cumulative damage rule almost applicable to thermal fatigue. (author)

  19. Experimental study of cyclic creep and high-cycle fatigue of welded joints of St3 steel by the DIC technique

    Science.gov (United States)

    Kibitkin, Vladimir V.; Solodushkin, Andrey I.; Pleshanov, Vasily S.

    2015-10-01

    In the paper the mechanisms of plastic deformation and fracture of welded joints of steel St3 were investigated at high-cycle fatigue and cyclic creep by the digital image correlation (DIC) technique. The evolution of strain rate is studied for the following regions: base metal, HAZ, and fusion zone. This strain rate evolution can be considered as a mechanical response of material. Three stages of deformation evolution are shown: deformation hardening (I), fatigue crack initiation (II), and the last stage is related to main crack (III). Two criteria are offered to evaluate the current mechanical state of welded joints.

  20. Impact of hydrogen on the high cycle fatigue behaviour of Inconel 718 in asymmetric push-pull mode at room temperature

    OpenAIRE

    Bruchhausen, M.; Fischer, B; Ruiz, A.; Gonzalez Sanchez, Sergio; Hhner, P.; Soller, S.

    2014-01-01

    The influence of hydrogen on the high cycle fatigue (HCF) behaviour of Inconel 718 has been studied at room temperature in asymmetric pushpull mode using an ultrasonic HCF test rig. Fatigue tests have been carried out in gaseous hydrogen (GH2) and in Ar at a pressure of 30 MPa. Oscillating stresses with amplitudes (?a) up to 450 MPa and mean stresses (?m) up to 600 MPa have been applied. For a given ?a and ?m, the lifetime in Ar is generally longer than in GH2, which is explained by a hydrog...

  1. Fatigue maps and multistage life prediction methods

    Energy Technology Data Exchange (ETDEWEB)

    Pratesi, F.; Zonfrillo, G.; Del Puglia, A. (Dipt. di Meccanica e Tecnologie Industriali, Univ. Florence (Italy))

    1992-04-01

    Various methods have been recently developed for life prediction under creep-fatigue conditions. This study is concerned with continuous damage models. In particular, a model developed at ONERA, which evaluates the creep and fatigue contributions separately and which sums the corresponding differential damage, has been used for fitting the high-temperature experimental data for IN 738 test bars. The data were taken both from the literature and from our own tests. In addition, it was found that the model can also be used to derive schematic fatigue maps. Following the introduction of Ashby maps for creep, several other maps have been proposed for fatigue. However, the task for fatigue maps is more difficult to define. This work presents a discussion of the whole problem, a review of existing proposals, and some indicative maps that have been obtained for IN 100. Even though the approach appears to be promising for outlining approximate fatigue maps, metallographic observations are still a necessary complement for mapping single domains where given microstructural mechanisms are predominant. (orig.).

  2. Fatigue maps and multistage life prediction methods

    International Nuclear Information System (INIS)

    Various methods have been recently developed for life prediction under creep-fatigue conditions. This study is concerned with continuous damage models. In particular, a model developed at ONERA, which evaluates the creep and fatigue contributions separately and which sums the corresponding differential damage, has been used for fitting the high-temperature experimental data for IN 738 test bars. The data were taken both from the literature and from our own tests. In addition, it was found that the model can also be used to derive schematic fatigue maps. Following the introduction of Ashby maps for creep, several other maps have been proposed for fatigue. However, the task for fatigue maps is more difficult to define. This work presents a discussion of the whole problem, a review of existing proposals, and some indicative maps that have been obtained for IN 100. Even though the approach appears to be promising for outlining approximate fatigue maps, metallographic observations are still a necessary complement for mapping single domains where given microstructural mechanisms are predominant. (orig.)

  3. Simulation of irreversible damage accumulation in the very high cycle fatigue (VHCF) regime using the boundary element method

    International Nuclear Information System (INIS)

    Many components have to withstand a very high number of loading cycles due to high frequency or long product life. In this regime, the period of fatigue crack initiation and thus the localization of plastic deformation play an important role. Metastable austenitic stainless steel (AISI304) that is investigated in this study shows localization of plastic deformation in bands of intense slip. In order to provide a physically-based understanding of the relevant damage mechanisms under VHCF condition, simulation of irreversible damage accumulation in slip bands is performed. For this purpose, a microstructural simulation model is proposed which accounts for the damage mechanisms in slip bands documented by experimental results. The model describes the damage accumulation through formation of slip bands, sliding and multiplication of dislocations and the amount of irreversibility of such mechanisms in case of VHCF relevant loading conditions. The implementation of the simulation model into a numerical method allows the investigation of the damage accumulation in a real microstructure simulated on the basis of metallographic analysis. The numerical method used in this study is the two-dimensional (2-D) boundary element method which is based on two integral equations: the displacement and the stress boundary integral equation. Fundamental solutions within these integral equations represent anisotropic elastic behavior. By using this method, a 2-D microstructure can be reproduced that considers orientations as well as individual anisotropic elastic properties in each grain. Contours of shear stresses along most critical slip systems are compared with images of slip band formation at the surface of fatigued specimens provided by scanning electron microscopy (SEM). Results show that simulation of slip bands is in good agreement with experimental observations and that plastic deformation in slip bands has a high impact on shear stresses at grain boundaries acting as possible crack origin in the fully austenitic material condition. In contrast to most other publications in the field of fatigue simulation the present paper tackles the problem of modeling cyclic slip irreversibility and gives an insight into its effect on the microstructural damage evolution

  4. Simulation of irreversible damage accumulation in the very high cycle fatigue (VHCF) regime using the boundary element method

    Energy Technology Data Exchange (ETDEWEB)

    Hilgendorff, P.-M., E-mail: philipp.hilgendorff@uni-siegen.de [Institut fr Mechanik und RegelungstechnikMechatronik, Universitt Siegen, Siegen 57068 (Germany); Grigorescu, A. [Institut fr Werkstofftechnik, Universitt Siegen, Siegen 57068 (Germany); Zimmermann, M. [Institut fr Werkstoffwissenschaft, Technische Universitt Dresden, 01062 Dresden (Germany); Fritzen, C.-P. [Institut fr Mechanik und RegelungstechnikMechatronik, Universitt Siegen, Siegen 57068 (Germany); Christ, H.-J. [Institut fr Werkstofftechnik, Universitt Siegen, Siegen 57068 (Germany)

    2013-07-15

    Many components have to withstand a very high number of loading cycles due to high frequency or long product life. In this regime, the period of fatigue crack initiation and thus the localization of plastic deformation play an important role. Metastable austenitic stainless steel (AISI304) that is investigated in this study shows localization of plastic deformation in bands of intense slip. In order to provide a physically-based understanding of the relevant damage mechanisms under VHCF condition, simulation of irreversible damage accumulation in slip bands is performed. For this purpose, a microstructural simulation model is proposed which accounts for the damage mechanisms in slip bands documented by experimental results. The model describes the damage accumulation through formation of slip bands, sliding and multiplication of dislocations and the amount of irreversibility of such mechanisms in case of VHCF relevant loading conditions. The implementation of the simulation model into a numerical method allows the investigation of the damage accumulation in a real microstructure simulated on the basis of metallographic analysis. The numerical method used in this study is the two-dimensional (2-D) boundary element method which is based on two integral equations: the displacement and the stress boundary integral equation. Fundamental solutions within these integral equations represent anisotropic elastic behavior. By using this method, a 2-D microstructure can be reproduced that considers orientations as well as individual anisotropic elastic properties in each grain. Contours of shear stresses along most critical slip systems are compared with images of slip band formation at the surface of fatigued specimens provided by scanning electron microscopy (SEM). Results show that simulation of slip bands is in good agreement with experimental observations and that plastic deformation in slip bands has a high impact on shear stresses at grain boundaries acting as possible crack origin in the fully austenitic material condition. In contrast to most other publications in the field of fatigue simulation the present paper tackles the problem of modeling cyclic slip irreversibility and gives an insight into its effect on the microstructural damage evolution.

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

    Science.gov (United States)

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

    2000-01-01

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

  6. High-Strength Bolt Corrosion Fatigue Life Model and Application

    OpenAIRE

    Wang Hui-li; Qin Si-feng

    2014-01-01

    The corrosion fatigue performance of high-strength bolt was studied. Based on the fracture mechanics theory and the Gerberich-Chen formula, the high-strength bolt corrosion fracture crack model and the fatigue life model were established. The high-strength bolt crack depth and the fatigue life under corrosion environment were quantitatively analyzed. The factors affecting high-strength bolt corrosion fatigue life were discussed. The result showed that the high-strength bolt corrosion fracture...

  7. Effect of strain-induced martensitic transformation on high cycle fatigue behavior in cyclically-prestrained type 304

    International Nuclear Information System (INIS)

    The effects of the cyclic prestrain on the fatigue behavior in type 304 austenitic stainless steel were investigated. Rotating bending fatigue tests have been performed in laboratory air using the specimens subjected to ±5% cyclic prestrain at room temperature (R.T.) and -5°C. Martensitic phase volume fraction of the prestrained specimen at -5°C was 48% and larger than 3.8% at R.T. The prestrained specimens exhibited higher fatigue strengths than the as-received ones, and larger volume fraction of martensitic phase resulted in the higher fatigue limit. EBSD analysis revealed that the martensitic phases were more uniformly distributed in the austenitic matrix in the cyclically-prestrained specimens than in the monotonically-prestrained ones. Fatigue crack initiation from inclusion was observed only in the cyclically-prestrained specimens at -5°C. High volume fraction and uniform distribution of martensitic phase induced the transition of crack initiation mechanism and led to the higher fatigue limit. In type 304 stainless steel with high volume fraction of strain-induced martensitic phase, the prediction of fatigue limit based on Vickers hardness could give unconservative results. (author)

  8. Fatigue Life of Superalloy Haynes 188 in Hydrogen

    Science.gov (United States)

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

    2012-08-01

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

  9. Mean stress effect under Multi-Axial High Cycle Fatigue loading for cast A356-T6 alloy

    Directory of Open Access Journals (Sweden)

    Houria M. Iben

    2014-06-01

    The obtained results show clearly that: (i the mean stress has detrimental, it is more significant in tension, lesser in tension-torsion case and slightly in torsion tests. (ii The improved DSG criterion describes very well the trend of the fatigue limit as a function of defect size and SDAS.

  10. Fatigue life of automotive rubber jounce bumper

    Energy Technology Data Exchange (ETDEWEB)

    Sidhu, R S [Automotive Engineering Unit, Institute of Advanced Technology, University Putra Malaysia, 43400, UPM Serdang, Selangor (Malaysia); Ali, Aidy, E-mail: aidy@eng.upm.edu.my [Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM, Serdang Selangor (Malaysia)

    2010-05-15

    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.

  11. Fatigue life of automotive rubber jounce bumper

    International Nuclear Information System (INIS)

    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.

  12. Towards a unified fatigue life prediction method for marine structures

    CERN Document Server

    Cui, Weicheng; Wang, Fang

    2014-01-01

    In order to apply the damage tolerance design philosophy to design marine structures, accurate prediction of fatigue crack growth under service conditions is required. Now, more and more people have realized that only a fatigue life prediction method based on fatigue crack propagation (FCP) theory has the potential to explain various fatigue phenomena observed. In this book, the issues leading towards the development of a unified fatigue life prediction (UFLP) method based on FCP theory are addressed. Based on the philosophy of the UFLP method, the current inconsistency between fatigue design and inspection of marine structures could be resolved. This book presents the state-of-the-art and recent advances, including those by the authors, in fatigue studies. It is designed to lead the future directions and to provide a useful tool in many practical applications. It is intended to address to engineers, naval architects, research staff, professionals and graduates engaged in fatigue prevention design and survey ...

  13. Mean stress effect under Multi-Axial High Cycle Fatigue loading for cast A356-T6 alloy

    OpenAIRE

    Houria M. Iben; Nadot Y.; Fathallah R.; Roy M.J.; Maijer D.M.

    2014-01-01

    Mechanical engineers are submitted to the antagonistic criteria when designing security components, such as, used in aeronautic, automotive and industrial components. They have to look for solutions leading to have as less as possible the weight, cost and in the same time as more as possible the security under complex and severe conditions of use. They consider fatigue to be the most common mechanism which causes components fail. In this context, cast A356-T6, which presents a good casting pr...

  14. A study at understanding the mechanisms governing the high cycle fatigue and final fracture behavior of the titanium alloy: Ti-4Al-2.5V

    International Nuclear Information System (INIS)

    In this research paper, the cyclic stress amplitude-controlled high cycle fatigue properties and fracture behavior of a titanium alloy are presented and discussed. The material chosen for this study is a Ti-Al-V-Fe-O2 alloy that is marketed under the trade name ATI 425TM. This alloy was initially developed and put forth for use as a ballistic material but through the last few years it gained in stature for use in other areas due to a healthy combination of physical and mechanical properties. Test specimens were prepared, in conformance with the ASTM E-8 standard, from the as-received sheet stock, which was cold rolled and mill annealed, with the rolling direction both parallel (longitudinal) and perpendicular (transverse) to the length of the sheet. The test specimens were cyclically deformed at three different load ratios (R = 0.1, R = 0.3 and R = 0.033) and the cycles-to-failure (Nf) was recorded. The fatigue fracture surfaces were examined in a scanning electron microscope to examine the macroscopic fracture mode, the intrinsic features on the fatigue fracture surface and the role of magnitude of applied stress-microstructural feature interactions in governing failure.

  15. Microstructure characteristics and temperature-dependent high cycle fatigue behavior of advanced 9% Cr/CrMoV dissimilarly welded joint

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Qingjun [Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240 (China); Lu, Fenggui, E-mail: Lfg119@sjtu.edu.cn [Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240 (China); Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, Shanghai 200072 (China); Cui, Haichao [Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240 (China); Ding, Yuming; Liu, Xia [Shanghai Turbine Plant of Shanghai Electric Power Generation Equipment Co. Ltd., Shanghai 200240 (China); Gao, Yulai, E-mail: ylgao@shu.edu.cn [Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, Shanghai 200072 (China)

    2014-10-06

    Advanced 9% Cr and CrMoV steels chosen as candidate materials are first welded by narrow-gap submerged arc welding (NG-SAW) to fabricate the heavy section rotor. The present work focuses on studying the high-cycle fatigue (HCF) behavior of advanced 9% Cr/CrMoV dissimilarly welded joint at different temperatures. Conditional fatigue strength of this dissimilarly welded joint was obtained by HCF tests at room temperature (RT), 400 °C and 470 °C. It was observed that the failure occurred at the side of CrMoV base metal (BM), weld metal (WM) and heat affected zone (HAZ) of CrMoV side over 5×10{sup 7} cycles for the specimens tested at RT, 400 °C and 470 °C. The detailed microstructures of BMs, WMs and HAZs as well as fracture appearance were observed by optical microscopy (OM) and scanning electron microscopy (SEM). Precipitation and aggregation of carbides along the grain boundaries were clearly detected with the increase of temperature, which brought a negative effect on the fatigue properties. It is interesting to note that the inclusion size leading to crack initiation became smaller for the HCF test at higher temperature. Therefore, reduction in the inclusion size in a welded joint helps to improve the HCF performance at high temperature.

  16. Fatigue criterion to system design, life and reliability

    Science.gov (United States)

    Zaretsky, E. V.

    1985-01-01

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

  17. Fracture Mechanics Prediction of Fatigue Life of Aluminum Highway Bridges

    DEFF Research Database (Denmark)

    Rom, Sren; Agerskov, Henning

    2015-01-01

    Fracture mechanics prediction of the fatigue life of aluminum highway bridges under random loading is studied. The fatigue life of welded joints has been determined from fracture mechanics analyses and the results obtained have been compared with results from experimental investigations. The...... fatigue life of welded plate specimens has been investigated. Both the fracture mechanics analyses and the fatigue tests have been carried out using load histories, which correspond to one week's traffic loading, determined by means of strain gauge measurements on the deck structure of the Far Bridges in...

  18. Fatigue life and damage evolution of martensitic steels for low-pressure steam turbine blades in the VHCF regime

    International Nuclear Information System (INIS)

    Low-pressure steam turbine blades are usually made of martensitic steels with Cr contents between 9 and 12%, which combine good corrosion resistance, high mechanical strength and sufficient ductility. The inhomogeneous flow field behind the vanes generates high-frequency oscillations above 1 kHz. In addition, the blades with lengths up to 1.5 m are operated at rotational speeds up to 3000 rpm, resulting in large centrifugal forces leading to the superposition of extremely high mean stresses. Also resonance oscillations during start-up and shutdown cannot be completely excluded. Currently, the components are designed using high safety factors against S-N curves with an assumed asymptotic fatigue limit above 107 load cycles. Nevertheless, fatigue cracks are observed even at high number of cycles, starting from the blade root without pre-damage by erosion or steam droplet impingement. While fatigue failure usually occurs at the surface, fatigue cracks at very high number of cycles (> 108) initiate at oxides or intermetallic inclusions below the surface. This transition between both failure mechanisms in the Very High-Cycle Fatigue (VHCF) regime is in the focus of numerous current research activities, because numbers of cycles above 108 can be attained in a viable period of time using the recently developed high-frequency testing techniques operated at 20 kHz. Also for wind turbines, gas turbines, bearings, springs, etc. VHCF issues become increasingly important. Within this work, the fatigue life and damage behavior of a martensitic Cr-steel during fatigue loading with and without high mean stresses at number of cycles to failure above 108 was analyzed. On the one hand, the studies gave insights into the relation between fatigue life and fatigue damage evolution of the investigated group of high-strength steels in the very high cycle fatigue regime (up to 2109). In particular, the influence of high mean stresses on the VHCF behavior (fracture origin, crack growth, fatigue life) which was not investigated in detail before is studied and the crack initiation and propagation mechanisms are analyzed by electron microscopy (SEM, TEM / FIB). With this, the work contributes to the reliable design of future low-pressure steam turbines. The results show that in particular non-metallic inclusions in the steel cause fracture by fatigue cracks initiated in the volume under very high cycle fatigue conditions. This fatigue behavior can be described very well by means of fracture mechanics approaches over a wide range of load ratios.

  19. Effect of equal channel angular pressing on microstructure, texture, and high-cycle fatigue performance of wrought magnesium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, Julia; Yi Sangbong; Wagner, Lothar [Clausthal Univ. of Tech., Inst. of Materials Science and Engineering, Clausthal-Zellerfeld (Germany); Janecek, Milos [Charles Univ., Dept. of Physics of Materials, Prague (Czech Republic); Cizek, Jakub [Charles Univ. Prague, Dept. of Low Temperature Physics, Prague (Czech Republic)

    2009-06-15

    The magnesium alloys AZ80 und ZK60 received from Dead Sea Magnesium in as-cast conditions were extruded at T = 350 C using an extrusion ratio of ER = 22. The extruded bars were severely plastically deformed by equal channel angular pressing (ECAP). Multiple ECAP processing up to 8 passes was done. The ECAP-induced changes in grain size and grain size distribution were measured by transmission electron microscopy while changes in dislocation density and crystallographic textures were determined by positron annihilation spectroscopy and X-ray diffraction analysis, respectively. The strain induced by ECAP was found to influence the microstructural characteristics, in particular the grain size, the dislocation density, and the crystallographic texture, which in turn enhance (or deteriorate) the mechanical or fatigue response of both alloys. (orig.)

  20. High compressive pre-strains reduce the bending fatigue life of nitinol wire.

    Science.gov (United States)

    Gupta, Shikha; Pelton, Alan R; Weaver, Jason D; Gong, Xiao-Yan; Nagaraja, Srinidhi

    2015-04-01

    Prior to implantation, Nitinol-based transcatheter endovascular devices are subject to a complex thermo-mechanical pre-strain associated with constraint onto a delivery catheter, device sterilization, and final deployment. Though such large thermo-mechanical excursions are known to impact the microstructural and mechanical properties of Nitinol, their effect on fatigue properties is still not well understood. The present study investigated the effects of large thermo-mechanical pre-strains on the fatigue of pseudoelastic Nitinol wire using fully reversed rotary bend fatigue (RBF) experiments. Electropolished Nitinol wires were subjected to a 0%, 8% or 10% bending pre-strain and RBF testing at 0.3-1.5% strain amplitudes for up to 10(8) cycles. The imposition of 8% or 10% bending pre-strain resulted in residual set in the wire. Large pre-strains also significantly reduced the fatigue life of Nitinol wires below 0.8% strain amplitude. While 0% and 8% pre-strain wires exhibited distinct low-cycle and high-cycle fatigue regions, reaching run out at 10(8) cycles at 0.6% and 0.4% strain amplitude, respectively, 10% pre-strain wires continued to fracture at less than 10(5) cycles, even at 0.3% strain amplitude. Furthermore, over 70% fatigue cracks were found to initiate on the compressive pre-strain surface in pre-strained wires. In light of the texture-dependent tension-compression asymmetry in Nitinol, this reduction in fatigue life and preferential crack initiation in pre-strained wires is thought to be attributed to compressive pre-strain-induced plasticity and tensile residual stresses as well as the formation of martensite variants. Despite differences in fatigue life, SEM revealed that the size, shape and morphology of the fatigue fracture surfaces were comparable across the pre-strain levels. Further, the mechanisms underlying fatigue were found to be similar; despite large differences in cycles to failure across strain amplitudes and pre-strain levels, cracks initiated from surface inclusions in nearly all wires. Compressive pre-strain-induced damage may accelerate such crack initiation, thereby reducing fatigue life. The results of the present study indicate that large compressive pre-strains are detrimental to the fatigue properties of Nitinol, and, taken together, the findings underscore the importance of accounting for thermo-mechanical history in the design and testing of wire-based percutaneous implants. PMID:25625888

  1. Effect of spectral shape on acoustic fatigue life estimates

    Science.gov (United States)

    Miles, R. N.

    1992-03-01

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

  2. Fatigue life characterization for piezoelectric macrofiber composites

    International Nuclear Information System (INIS)

    In an effort to aid the investigation into lightweight and reliable materials for actuator design, a study was developed to characterize the temperature-dependent lifetime performance of a piezoelectric macrofiber composite (MFC). MFCs are thin rectangular patches of polyimide film, epoxy and a single layer of rectangular lead zirconium titanate (PZT) fibers. In this study, the useful life of the MFC is characterized to determine the effect of temperature on the performance of the composite as it is fatigued by cyclic piezoelectric excitation. The test specimen consists of the MFC laminated to a cantilevered stainless steel beam. Beam strain and tip displacement measurements are used as a basis for determining the performance of the MFC as it is cyclically actuated under various operating temperatures. The temperature of the beam laminate is held constant and then cycled to failure, or 250 million cycles, in order to determine the useful life of the MFC over a temperature range from ? 15 to 145?C. The results of the experiments show a strong temperature dependence of the operational life for the MFC. Damage inside the composite was identified through in situ visual inspection and during post-test microstructural observation; however, no degradation in operational performance was identified as it was cyclically actuated up to the point of failure, regardless of temperature or actuation cycle number. (paper)

  3. Fatigue life characterization for piezoelectric macrofiber composites

    Science.gov (United States)

    Henslee, Isaac A.; Miller, David A.; Tempero, Tyler

    2012-10-01

    In an effort to aid the investigation into lightweight and reliable materials for actuator design, a study was developed to characterize the temperature-dependent lifetime performance of a piezoelectric macrofiber composite (MFC). MFCs are thin rectangular patches of polyimide film, epoxy and a single layer of rectangular lead zirconium titanate (PZT) fibers. In this study, the useful life of the MFC is characterized to determine the effect of temperature on the performance of the composite as it is fatigued by cyclic piezoelectric excitation. The test specimen consists of the MFC laminated to a cantilevered stainless steel beam. Beam strain and tip displacement measurements are used as a basis for determining the performance of the MFC as it is cyclically actuated under various operating temperatures. The temperature of the beam laminate is held constant and then cycled to failure, or 250 million cycles, in order to determine the useful life of the MFC over a temperature range from - 15 to 145?C. The results of the experiments show a strong temperature dependence of the operational life for the MFC. Damage inside the composite was identified through in situ visual inspection and during post-test microstructural observation; however, no degradation in operational performance was identified as it was cyclically actuated up to the point of failure, regardless of temperature or actuation cycle number.

  4. Life prediction of creep fatigue at very high temperatures

    International Nuclear Information System (INIS)

    Life prediction methods of creep fatigue were investigated to consider applications to Hastelloy XRs at very high temperatures where materials would be damaged severely by creep deformation. The ductility exhaustion rule, coupled with a creep constitutive equation consisting of primary and secondary stages, showed a good prediction of creep-fatigue life as well as the damage-rate equations. The strain range partitioning method was also discussed regarding its possibility for life prediction. The results of these methods were compared with the time fraction rule in conjunction with the Miner's rule. In these experiments, creep tests were done under constant stress condition in air, and low-cycle fatigue tests were carried out with and without a dwell period in vacuum. Creep-fatigue damage was evaluated in the life of low-cycle fatigue tests with a dwell period. All specimens were fabricated from the same hot-rolled plates to reduce scatter in different heat treatments. (author)

  5. Fatigue and quality of life in pediatric multiple sclerosis.

    Science.gov (United States)

    MacAllister, William S; Christodoulou, Christopher; Troxell, Regina; Milazzo, Maria; Block, Pamela; Preston, Thomas E; Bender, Heidi A; Belman, Anita; Krupp, Lauren B

    2009-12-01

    Fatigue and quality of life are significant concerns in adult multiple sclerosis (MS) but little is known about these factors in pediatric MS. The present investigation evaluates fatigue and quality of life in 51 pediatric MS patients to determine the rate of fatigue and reduced quality of life and assesses the relations between these variables and clinical factors. Fatigue and quality of life were assessed by self- and parent-report via the PedsQL Multidimensional Fatigue Scale and the PedsQL Quality of Life Scale. One-sample t-tests determined if scores were below published data for healthy individuals. Moreover, scores falling one standard deviation from norms were considered mildly affected, with severe difficulties being defined as scores falling two or more standard deviations from norms. Associations between self- and parent-reported difficulties and clinical factors were examined via Pearson correlation analyses. In comparison with healthy samples, pediatric MS patients reported greater difficulties with respect to fatigue, sleep, cognition, physical limitations, and academics. In addition to significant difficulties on these factors, parents reported problems with respect to emotional functioning, and tended to report greater fatigue, sleep, and cognitive difficulties than were self-reported. Expanded Disability Status Scale score was the only neurologic variable significantly related to fatigue or quality of life scores. Fatigue was significantly correlated with reports of sleep difficulties, cognitive problems, and quality of life variables. These findings suggest that fatigue and poorer quality of life is a clear concern in pediatric MS, and is related to overall physical disability. PMID:19965517

  6. On line fatigue life monitoring methodology for power plant components

    International Nuclear Information System (INIS)

    Fatigue is one of the most important ageing effects of power plant components. Information about fatigue helps in assessing structural degradation of the components and so assists in planning in-service inspection and maintenance. It may also support the future life extension programme of a power plant. In the present paper, the development of a methodology for on line fatigue life monitoring using available plant instrumentation is presented. The Green's function technique is used to convert plant data to stress-time data. Using a rainflow cycle counting method, stress-time data are analysed and the fatigue usage factor is computed from the material fatigue curve. Various codes are developed to generate Green's functions, to convert plant data to stress-time data, to find the fatigue usage factor and to display fatigue information. Using the developed codes, information about the fatigue life of various components of a power plant can be updated, stored and displayed interactively by plant operators. Three different case studies are reported in the present paper. These are the fatigue analyses of a thick pipe, of a nozzle connected to a pressure vessel and of a reducer connecting a heat exchanger to its piping system. (Author)

  7. Fatigue tests and life estimation of Incoloy alloy 908

    International Nuclear Information System (INIS)

    Incoloy reg-sign alloy 908* is a candidate conduit material for Nb3Sn cable-in-conduit superconductors. The conduit is expected to experience cyclic loads at 4 K. Fatigue fracture of the conduit is one possible failure mode. So far, fatigue life has been estimated from fatigue crack growth data, which provide conservative results. The more traditional practice of life estimation using S-N curves has not been done for alloy 908 due to a lack of data at room and cryogenic temperatures. This paper presents a series of fatigue test results in response to this need. Tests were performed in reversed bending, rotating bending, and uniaxial fatigue machines. The test matrix included different heat treatments, two load ratios (R=-1 and 0.1), two temperatures (298 and 77 K), and two orientations (longitudinal and transverse). As expected, there is a semi-log linear relation between the applied stress and fatigue life above an applied stress (e.g., 310 MPa for tests at 298 K and R=-1). Below this stress the curves show an endurance limit. The aged and cold-worked materials have longer fatigue lives and higher endurance limits than the others. Different orientations have no apparent effect on life. Cryogenic temperature results in a much high fatigue life than room temperature. A higher tensile mean stress gives shorter fatigue life. It was also found that the fatigue lives of the reversed bending specimens were of the same order as those of the uniaxial test specimens, but were only half the lives of the rotating bending specimens for given stresses. A sample application of the S-N data is discussed

  8. Carbide factor predicts rolling-element bearing fatigue life

    Science.gov (United States)

    Chevalier, J. L.; Zaretsky, E. V.

    1973-01-01

    Analysis was made to determine correlation between number and size of carbide particles and rolling-element fatigue. Correlation was established, and carbide factor was derived that can be used to predict fatigue life more effectively than such variables as heat treatment, chemical composition, and hardening mechanism.

  9. Fatigue life prediction of pedicle screw for spinal surgery.

    Czech Academy of Sciences Publication Activity Database

    Major, t?pn; Kocour, Vladimr

    Ferrara : University of Ferrara, 2015. s. 94 ISBN N. [International Conference on Crack Paths (CP 2015) /5./. 16.08.2015-18.08.2015, Ferrara] Institutional support: RVO:68378297 Keywords : pedicle-screw * titan alloy * fatigue life * finite element analysis Subject RIV: JL - Materials Fatigue, Friction Mechanics http://www.gruppofrattura.it/events/CP2015/index.html#682

  10. Application of multistage life prediction methods to fretting fatigue interactions

    International Nuclear Information System (INIS)

    This paper reports the application field of the multistage prediction model extended to fretting- fatigue interaction. The model was used to achieve a preliminary evaluation of the reduction in fatigue life induced by fretting conditions in a case-hardening steel. Satisfactory agreement with experimental data was found without considering any effects on the propagation stage

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

    Science.gov (United States)

    Zhao, Lihui; Zheng, Songlin; Feng, Jinzhi

    2014-11-01

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

  12. The role of microtexture on the faceted fracture morphology in Ti-6Al-4V subjected to high-cycle fatigue

    International Nuclear Information System (INIS)

    Microtextured regions (or macrozones) are commonly reported in titanium alloys and are believed to be related to fatigue life. Here, fractographic investigations are conducted on bimodal Ti-6Al-4V plate, including transmission electron microscopy to determine the mechanism of fatigue facet formation and electron backscattered diffraction to examine the underlying macrozone structures. It is found that macrozones oriented with their c-axis close to the loading direction are responsible for facet formation, and that the facets are associated with basal slip. Microtextured regions with c-axis orientations near-perpendicular to the loading direction are believed to act as barriers to faceted crack growth, based on the change in crack morphology as the crack crosses a macrozone boundary. The variant selection occurring during the transformation of the retained beta appears to favour a common orientation with the surrounding primary alpha grains, contributing to the size of the macrozones and therefore to the extent of the observed faceted regions.

  13. An investigation on fatigue life of borided AISI 1010 steel

    Directory of Open Access Journals (Sweden)

    O.N. Celik

    2009-01-01

    Full Text Available Purpose: This study aims to investigate the fatigue life of box borided AISI 1010 steel materials.Design/methodology/approach: Fatigue specimens firstly have been prepared according to ASTM E466-96 standard and normalized. Then their surfaces have been cleaned by polishing. Boriding heat treatment has been applied in solid media with the help of Ekabor2 powder. Specimens have been borided at 1173-1223-1273 and 1323 K temperatures for 2-4 and 6 hours respectively. Fatigue tests have been made in rotating-bend test device. Separate S-N diagram has been formed for each boriding condition and then their results were compared with the results of the specimens on which any heat treatment has not been made.Findings: As a result it has been seen that boriding has no positive effect on fatigue life of AISI 1010 steel materials. And also it has been determined that fatigue life of the materials on which boriding heat treatment applied, decreases in between 14 %-55 %.Research limitations/implications: It can be noted that the reasons of short fatigue life determination are the boride layers much higher hardness than the substrate materials, and the micro cracks existed between boride phases formed onto the surface.Originality/value: The investigations on fatigue life of borided AISI 1010 steel were made.

  14. Fatigue life and microstructure of ODS steels.

    Czech Academy of Sciences Publication Activity Database

    Kub?na, Ivo; Kruml, Tom

    2013-01-01

    Ro?. 103, SI (2013), s. 39-47. ISSN 0013-7944 R&D Projects: GA Mk(CZ) ED1.1.00/02.0068; GA ?R(CZ) GA106/09/1954 Institutional support: RVO:68081723 Keywords : ODS steels * Fatigue * Surface evolution * Crack nucleation mechanisms Subject RIV: JL - Materials Fatigue , Friction Mechanics Impact factor: 1.662, year: 2013

  15. Fatigue Life of High-Strength Steel Offshore Tubular Joints

    DEFF Research Database (Denmark)

    Petersen, Rasmus Ingomar; Agerskov, Henning; Lopez Martinez, Luis

    1996-01-01

    amplitude fatigue test results showed shorter fatigue lives in variable amplitude loading than should be expected from the linear fatigue damage accumulation formula. Furthermore, the fatigue tests on high-strength steel tubular joints showed slightly longer fatigue lives than those obtained in......In the present investigation, the fatigue life of tubular joints in offshore steel structures is studied. Two test series on full-scale tubular joints have been carried through. One series was on joints in conventional offshore structural steel, and the other series was on joints in high......-strength steel with a yield stress of 820-830 MPa and with high weldability and toughness properties. The test specimens of both series had the same geometry. The present report concentrates on the results obtained in the investigation on the high-strength steel tubular joints.The test specimens were fabricated...

  16. Enhanced Prediction of Gear Tooth Surface Fatigue Life Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Sentient will develop an enhanced prediction of gear tooth surface fatigue life with rigorous analysis of the tribological phenomena that contribute to pitting...

  17. Fatigue life prediction in woven carbon fabric polyester composites

    International Nuclear Information System (INIS)

    An analytical model, based on stiffness degradation during fatigue loading, which has been used for fatigue life predictions in the Fiber Reinforced Plastics (FRP), is employed to examine its validity to the fatigue life predictions in the Woven Fabric Reinforced Plastics. The rate of stiffness degradation (dE/dN) has been obtained from the constant amplitude fatigue testing of 8-ply coupons made from prepreg plain-weave woven carbon-carbon fabric having a polyester resin as the matrix material. The test coupons had three different ply stacking sequences, namely, the unidirectional (0)8,and two off axis plied (0,0,+45,-45)s, and (+45,-45,0,0)s orientations. The estimated fatigue lives obtained from the damage rate function dD/dN, which in turn was a function of the stiffness degradation rate dE/dN, were compared with the experimentally observed fatigue life data. It is shown that the stiffness degradation model provides reasonably good correlation between the analytically determined fatigue lives and the experimentally observed fatigue for the plain-weave woven Carbon-Carbon Fabric Reinforced Plastic Composites. (author)

  18. Numerical life prediction of mechanical fatigue for hot forging tools

    OpenAIRE

    Mocellin, Katia; Ferraro, Matthieu; Velay, Vincent; Log, Roland E.; Rezai-Aria, Farhad

    2009-01-01

    In the forging industry, tools represent an important part in term of production and costs. Enhancing their life cycle is then a challenging issue. Several mechanical and thermal mechanisms are responsible for hot forging tools damage such as wear, thermal and mechanical fatigue. This work will be focused only on the mechanical fatigue life prediction for hot forging tools. Both experimental data analysis and numerical simulation will be discussed in this paper. The aim is to perform qualitat...

  19. Studies of Microtexture and Its Effect on Tensile and High-Cycle Fatigue Properties of Laser-Powder-Deposited INCONEL 718

    Science.gov (United States)

    Qi, Huan; Azer, Magdi; Deal, Andrew

    2012-11-01

    The current work studies the microstructure, texture, and mechanical properties of INCONEL 718 alloy (IN718) produced by laser direct metal deposition. The grain microstructure exhibits an alternative distribution of banded fine and coarse grain zones as a result of the rastering scanning pattern. The effects of the anisotropic crystallographic texture on the tensile and high-cycle fatigue (HCF) properties at room temperature are investigated. Tensile test results showed that the tensile strength of laser-deposited IN718 after direct aging or solution heat treatment is equivalent to the minimum-forged IN718 properties. The transverse direction (relative to the laser scanning direction) produces >10 pct stiffer modulus of elasticity but 3 to 6 pct less tensile strength compared to the longitudinal direction due to the preferential alignment of grains having and directions parallel to the tensile loading direction. Laser-deposited IN718 with good metallurgical integrity showed equivalent HCF properties compared to the direct-aged wrought IN718, which can be attributed to the banded grain size variation and cyclic change of inclining grain orientations resulted from alternating rastering deposition path.

  20. Studies on fatigue life enhancement of pre-fatigued spring steel specimens using laser shock peening

    International Nuclear Information System (INIS)

    Highlights: • Laser peening significantly extended fatigue life of pre-fatigued spring steel. • Increase in fatigue life of laser peened specimens was more than 15 times. • Black PVC tape is an effective coating for laser peening of ground surfaces. • Repeat peening repaired local surface melted regions on laser peened surface. • Technique is effective for life extension of in-service automobile parts. - Abstract: SAE 9260 spring steel specimens after enduring 50% of their mean fatigue life were subjected to laser shock peening using an in-house developed 2.5 J/7 ns pulsed Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser for studying their fatigue life enhancement. In the investigated range of process parameters, laser shock peening resulted in the extension of fatigue life of these partly fatigue damaged specimens by more than 15 times. Contributing factors for the enhanced fatigue life of laser peened specimens are: about 400 μm thick compressed surface layer with magnitude of surface stress in the range of −600 to −700 MPa, about 20% increase in surface hardness and unaltered surface finish. For laser peening of ground steel surface, an adhesive-backed black polyvinyl chloride (PVC) tape has been found to be a superior sacrificial coating than conventionally used black paint. The effect of repeated laser peening treatment was studied to repair locally surface melted regions and the treatment has been found to be effective in re-establishing desired compressive stress pattern on the erstwhile tensile-stressed surface

  1. Low and high cycle fatigue behaviour of steel-X6CRNI1811 (Type 304 SS) in air and flowing sodium

    International Nuclear Information System (INIS)

    Strain controlled LCF-tests were performed on X6CrNi1811 steel (Type 304 SS) in air and flowing sodium in a non-isothermal sodium loop. The results measured at 550 deg. C in an upstream position of the sodium loop show an increase in fatigue life in the strain range from about 1.5% to 0.4% for the base material in the as-received condition while the welded joints remain unaffected by the environment. The LCF-behaviour of base material specimens tested at 500 deg. C in a downstream position after a prior pre-exposure to sodium (4058 h, 500 deg. C) is also improved in comparison to parallel specimens tested in air with comparable thermal aging. Load controlled HCF-tests performed on X6CrNi1811 steel at 550 deg. C show a significant increase in fatigue life in the low cycle region (Nsub(f)6 cycles) and a higher endurance limit for the base material in sodium but no influence of the environment is indicated for the welded joints. (author)

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

    Science.gov (United States)

    Neu, R. W.; Sehitoglu, Huseyin

    1989-09-01

    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.

  3. An investigation on fatigue life of borided AISI 1010 steel

    OpenAIRE

    O.N. Celik; H. Gasan; M. Ulutan; Saygin, M

    2009-01-01

    Purpose: This study aims to investigate the fatigue life of box borided AISI 1010 steel materials.Design/methodology/approach: Fatigue specimens firstly have been prepared according to ASTM E466-96 standard and normalized. Then their surfaces have been cleaned by polishing. Boriding heat treatment has been applied in solid media with the help of Ekabor2 powder. Specimens have been borided at 1173-1223-1273 and 1323 K temperatures for 2-4 and 6 hours respectively. Fatigue tests have been made ...

  4. Fatigue life assessment under multiaxial variable amplitude loading

    International Nuclear Information System (INIS)

    A variable amplitude multiaxial fatigue life prediction method is presented in this paper. It is based on a stress as input data are the stress tensor histories which may be calculated by FEM analysis or measured directly on the structure during the service loading. The different steps of he method are first presented then its experimental validation is realized for log and finite fatigue lives through biaxial variable amplitude loading tests using cruciform steel samples. (authors). 9 refs., 7 figs

  5. An improved method for estimating fatigue life under combined stress.

    Czech Academy of Sciences Publication Activity Database

    Balda, Miroslav; Svoboda, Jaroslav; Frhlich, Vladislav

    2007-01-01

    Ro?. 1, ?. 1 (2007), s. 1-10. ISSN 1802-680X. [Applied and Computational Mechanics 2007. Ne?tiny, 05.11.2007 - 07.11.2007] R&D Projects: GA ?R GA101/05/0199 Institutional research plan: CEZ:AV0Z20760514 Keywords : multiaxial fatigue * life- time estimation * nonlinear least squares Subject RIV: JL - Materials Fatigue, Friction Mechanics

  6. Bayesian inference model for fatigue life of laminated composites

    DEFF Research Database (Denmark)

    Dimitrov, Nikolay Krasimirov; Kiureghian, Armen Der; Berggreen, Christian

    2016-01-01

    A probabilistic model for estimating the fatigue life of laminated composite plates is developed. The model is based on lamina-level input data, making it possible to predict fatigue properties for a wide range of laminate configurations. Model parameters are estimated by Bayesian inference. The...... reference data used consists of constant-amplitude cycle test results for four laminates with different layup configurations. The paper describes the modeling techniques and the parameter estimation procedure, supported by an illustrative application....

  7. Effects of pre-working and dynamic strain aging on high cycle fatigue fracture of a stainless steel SUS316NG at 300degC

    International Nuclear Information System (INIS)

    In order to obtain information about relationships between fatigue strength of a SUS316NG austenitic stainless steel and hardening behavior due to dynamic strain aging during fatigue tests, rotating bending fatigue tests were carried out at 300degC for notched specimens for stress concentration factors being less than 2.0 and for burnished hourglass type specimens. As for the notched specimens, fatigue fracture occurred before the specimens hardened enough during fatigue tests and the fatigue strengths did not reach the expected values from fatigue strengths of notched specimens for stress concentration factor being greater than 2.0. As for the burnished specimens, the specimen surfaces hardened enough previously to fatigue test but the fatigue strength also did not reach the expected value. Internal fracture occurred for burnished specimens and fish-eye patterns were observed on the fracture surfaces. (author)

  8. Fatigue Life and Cyclic Softening Behavior of JLF-1 Steel

    International Nuclear Information System (INIS)

    Development of reactor materials and blankets is a critical issue for early realization of fusion energy. A reduced-activation ferritic/martensitic steel, JLF-1, is considered as one of the candidate alloys for the first wall application of fusion reactor. In this paper, the low cycle fatigue (LCF) properties of JLF-1 steel were studied from room temperature (RT) to 873 K in a vacuum condition using engineering size cylinder specimens with 8 mm in diameter. The fatigue life at elevated temperature was almost as same as that at RT when the life was plotted against the total strain range. But when the life was plotted against the plastic strain range, the fatigue life curves for RT, 673 K and 873 K of JLF-1 were on different lines. This phenomenon were also observed in F82H and modified 9Cr-1Mo. Cyclic softening was observed in fatigue test at elevated temperature. The cyclic stress-strain curve can be obtained from the fatigue stress-strain hysteresis curves around half life. The cyclic yield point was lower than the static one, especially at 873 K. That means the cyclic softening is a design issue at elevated temperature, which will reduce the design margin significantly.The experiments of thermal history simulating the LCF test (annealing) were performed at 673 K and 873 K in vacuum.The temperature and cyclic deformation effects on microstructure will be observed by TEM. (author)

  9. Fracture Mechanics Prediction of Fatigue Life of Aluminum Highway Bridges

    DEFF Research Database (Denmark)

    Rom, Sren; Agerskov, Henning

    2015-01-01

    Fracture mechanics prediction of the fatigue life of aluminum highway bridges under random loading is studied. The fatigue life of welded joints has been determined from fracture mechanics analyses and the results obtained have been compared with results from experimental investigations. The fatigue life of welded plate specimens has been investigated. Both the fracture mechanics analyses and the fatigue tests have been carried out using load histories, which correspond to one week's traffic loading, determined by means of strain gauge measurements on the deck structure of the Far Bridges in Denmark. The results obtained from the fracture mechanics analyses show a significant difference between constant amplitude and variable amplitude results. Both the fracture mechanics analyses and the results of the fatigue tests carried out indicate that Miner's rule, which is normally used in the design against fatigue in aluminum bridges, may give results which are unconservative. Furthermore, it was in both investigations found that the validity of the results obtained from Miner's rule will depend on the distribution of the load history in tension and compression.

  10. Fatigue life prediction modeling for turbine hot section materials

    Science.gov (United States)

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

    1989-01-01

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

  11. A methodology to evaluate the fatigue life of flexible pipes

    Energy Technology Data Exchange (ETDEWEB)

    Sousa, Fernando J.M. de; Sousa, Jose Renato M. de; Siqueira, Marcos Q. de; Sagrilo, Luis V.S. [Coordenacao dos Programas de Pos-graduacao em Engenharia (COPPE/UFRJ), Rio de Janeiro, RJ (Brazil); Lemos, Carlos Alberto D. de [Petroleo Brasileiro S.A. (PETROBRAS), Rio de Janeiro, RJ (Brazil)

    2009-07-01

    This paper focus on a methodology to perform the fatigue analysis of flexible pipes. This methodology employs functions that convert forces and moments obtained in global analyses into stresses. The stresses are then processed by well-known cycle counting methods, and S-N curves evaluate the damage at several points in the pipe cross-section. Palmgren-Miner linear damage hypothesis is assumed in order to calculate the accumulated fatigue damage. A parametric study on the fatigue life of a flexible pipe employing this methodology is presented. The main points addressed in the study are the influence of friction between layers in the results, the importance of evaluating the fatigue life in various points of the pipe cross-section and the effect of different mean stress levels. The obtained results suggest that the consideration of friction effects strongly influences the fatigue life of flexible risers and these effects have to be accounted both in the global and local analyses of the riser. Moreover, mean stress effects are also significant and at least 8 equally spaced wires in each analyzed section of the riser must be considered in fatigue analyses. (author)

  12. Fatigue life and initiation mechanisms in wrought Inconel 718 DA for different microstructures

    OpenAIRE

    Abikchi, Meriem; Billot, Thomas; Crpin, Jrome; Longuet, Arnaud; Mary, Caroline; Morgeneyer, Thilo F.; Pineau, Andr

    2013-01-01

    Wrought Inconel 718 DA superalloy disk zones present a wide range of behavior in fatigue life due to the variability of the microstructure. In order to link the effect of the forging conditions and achieved microstructure to the fatigue life, two microstructures have been tested in fatigue. Fatigue tests under strain control were performed at 450C. Grain size distributions and phase distributions were characterized in the specimens and related to fatigue failure initiation modes. Fatigue cra...

  13. Fatigue life of the casting-magnesium alloy AZ91

    International Nuclear Information System (INIS)

    The cyclic deformation behaviour of the die-casting magnesium alloy AZ91 was investigated at constant total strain amplitudes between 1.4 x 10-3 and 2 x 10-2 at room temperature (20 C) and at 130 C. At low total strain amplitudes, a weak cyclic softening at the beginning of the fatigue tests is followed by cyclic hardening, whereas at high total strain amplitudes a strong cyclic hardening occurs throughout. The fatigue lives at 130 C are slightly longer at high strain amplitudes but shorter at low strain amplitudes than at room temperature. The fatigue life data for both temperatures can be described well by the laws of Manson-Coffin and Basquin. The microstructural investigations performed show the strong influence of several microstructural features on the initiation and propagation of fatigue cracks. In order to understand the fatigue crack propagation behaviour, fatigue tests were interrupted at certain numbers of cycles in order to make replicas of the surface of the samples. It could be verified that crack propagation occurs mainly by the coalescence of smaller cracks. Furthermore, unloading tests, performed within a closed cycle, were carried out in order to capture the changes of stiffness (compliance) during a closed cycle with the aim to ascertain the damage evolution occurring during the fatigue tests and to determine the stresses at which the cracks open and close. Finally, two-step fatigue tests were carried out with the objective to quantify deviations from the linear damage rule (LDR) of Palmgren and Miner. The results obtained in this study will be used to formulate a microstructurally based life-prediction concept for single-step as well as for two-step fatigue loading. (orig.)

  14. Fatigue Life of Extended Hollobolt Connection in Concrete Filled Tube

    Directory of Open Access Journals (Sweden)

    Norashidah Abd Rahman

    2013-12-01

    Full Text Available Studies on the performance of blind bolt connections have been carried out by many researchers. A number of recent studies of new blind bolted connection system have been proposed. The system uses the so called Extended Hollobolt fastener to connect the concrete filled tubular columns. The strength performance of this system has been investigated under both monotonic and cyclic loading. However, the performance of such connections under fatigue loading is still unknown. Therefore, a study to investigate the fatigue performance of Extended Hollobolt was proposed. The main objective of this study is to provide a better understanding of the fatigue life of the proposed blind bolt, consequently provides the design guidance for Extended Hollobolt connection in concrete filled tube. A number of tests were conducted to determine the effect of the frequency and the level of stress range loading on the behaviour of the Extended Hollobolt. The tests were used grade 8.8 bolts subjected to tension. Results show that the frequencies between 0.2 Hz to 5 Hz does affect fatigue life and the stress-range versus fatigue life behaviour of Extended Hollobolt follows the expected pattern of behaviour of standard bolts. The test results of Extended Hollobolt under different stress range then further compared to the normative regulation Eurocode 3. The fatigue life or behaviour of Extended Hollobolt is found to be higher than the theoretical curve of Eurocode 3. Meanwhile, the failure mode of Extended Hollobolt is similar to the standard bolt which is a very positive outcome for blind bolt. However, fatigue life for standard bolt appears to be higher.

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

    Science.gov (United States)

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

    2012-11-01

    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.

  16. Deformation heterogeneities and their role in life-limiting fatigue failures in a two-phase titanium alloy

    International Nuclear Information System (INIS)

    Fatigue crack-initiation sites in Ti–6Al–2Sn–4Zr–6Mo (Ti–6–2–4–6), an α + β titanium alloy used in turbine engine applications, were characterized with emphasis on distinguishing the microstructural neighborhoods and mechanisms that produce the life-limiting failures vs. those that promote the mean-lifetime behavior. The characterization methods included quantitative tilt fractography, focused ion beam milling across crack-initiation facets, and electron backscattered diffraction analysis. The motivation for discerning between the life-limiting and the mean-dominating crack-initiation microstructural neighborhoods stemmed from the previously developed understanding that the mean and the life-limiting behaviors respond differently to stress level (and many other variables), leading to an increasing separation between the two subpopulations as the stress level is decreased, thereby increasing the variability in lifetime. The different rates of response of the two behaviors was found to arise because the life-limiting mechanism was dominated by the crack-growth lifetime, with microstructural-scale crack-initiation occurring within the first few fatigue cycles, whereas the mean behavior was increasingly dominated by the crack-initiation lifetime as the stress level was decreased. Representative specimens for 2-D characterization of crack-initiation neighborhoods were selected from life-limiting and mean-dominating populations generated by fatigue tests on a duplex α + β phase microstructure of Ti–6–2–4–6 under a narrow range of applied stress amplitudes. A compilation of data on the crack-initiation facet and the neighborhood of the faceted grain from multiple specimens pointed to at least four categories of critical microstructural configurations, each representing a set of necessary (but perhaps not sufficient) conditions for crack-initiation in this alloy. Based on this characterization, a hypothesis for the life-limiting fatigue behavior is presented. The hypothesis invokes the concept of hierarchy of fatigue deformation heterogeneities, which is suggested to develop within the first few fatigue cycles. The deformation heterogeneity is suggested to be linked to the underlying randomness and hierarchy in the microstructural arrangements. This hypothesis appears to explain the occurrence of crack-growth-lifetime-dominated, life-limiting failures in the regime of high-cycle fatigue, as shown in this study, and suggests a probability of occurrence of such failures even in the very-high-cycle fatigue regime, although with diminishing probability as the stress level is decreased

  17. The effect of plasma electrolytic oxidation on the mean stress sensitivity of the fatigue life of the 6082 aluminum alloy

    Science.gov (United States)

    Winter, L.; Morgenstern, R.; Hockauf, K.; Lampke, T.

    2016-03-01

    In this work the mean stress influence on the high cycle fatigue behavior of the plasma electrolytic oxidized (PEO) 6082 aluminum alloy (AlSi1MgMn) is investigated. The present study is focused on the fatigue life time and the susceptibility of fatigue-induced cracking of the oxide coating and their dependence on the applied mean stress. Systematic work is done comparing conditions with and without PEO treatment, which have been tested using three different load ratios. For the uncoated substrate the cycles to failure show a significant dependence on the mean stress, which is typical for aluminum alloys. With increased load ratio and therefore increased mean stress, the fatigue strength decreases. The investigation confirms the well-known effect of PEO treatment on the fatigue life: The fatigue strength is significantly reduced by the PEO process, compared to the uncoated substrate. However, also the mean stress sensitivity of the fatigue performance is reduced. The fatigue limit is not influenced by an increasing mean stress for the PEO treated conditions. This effect is firstly shown in these findings and no explanation for this effect can be found in literature. Supposedly the internal compressive stresses and the micro-cracks in the oxide film have a direct influence on the crack initiation and growth from the oxide film through the interface and in the substrate. Contrary to these findings, the susceptibility of fatigue-induced cracking of the oxide coating is influenced by the load ratio. At tension-tension loading a large number of cracks, which grow partially just in the aluminum substrate, are present. With decreasing load ratio to alternating tension-compression stresses, the crack number and length increases and shattering of the oxide film is more pronounced due to the additional effective compressive part of the load cycle.

  18. Development of generic creep-fatigue life prediction models

    International Nuclear Information System (INIS)

    This paper presents a data bank that was compiled from published and unpublished sources. Using these data, low cycle fatigue curves were generated under a range of test conditions showing the effect of test parameters on the Coffin-Manson behavior of steel alloys. Phenomenological methods of creep-fatigue life prediction are summarized in a table showing number of material parameters required by each method and type of tests needed to generate such parameters. Applicability of viscosity method was assessed with creep-fatigue data on 1Cr-Mo-V, 2.25Cr-Mo and 9Cr-1Mo steels. Generic equations have been developed in this paper to predict the creep-fatigue life of high temperature materials. Several new multivariate equations were developed to predict the creep-fatigue life of following alloy groups; (1) Cr-Mo steels, (2) stainless steels and (3) generic materials involving the materials from the following alloy groups, solder, copper, steels, titanium, tantalum and nickel-based alloys. Statistical analyses were performed in terms of coefficient of correlation (R2) and normal distribution plots and recommended these methods in the design of components operating at high temperatures

  19. Study the Effect of Cooling Rate on Fatigue Strength and Fatigue Life of Heated Carbon Steel Bars

    OpenAIRE

    Ali S. Yasir

    2013-01-01

    The fatigue failure is the reason of (90%) of mechanical failures. This work tries improving the fatigue strength and increasing the fatigue life for steel bars that used in concrete reinforcing. Tensile test were done to find the mechanical properties of steel bar. The heating over critical temperature (AC3) and cooling by different cooling rates were done for steel bars, and tested this samples by tensile and fatigue tests. The tensile test results show increasing in yield and tensile stren...

  20. Cyclic rate-dependent fatigue life in reactor water

    International Nuclear Information System (INIS)

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

  1. Fatigue life of ablation-cast 6061-T6 components

    Energy Technology Data Exchange (ETDEWEB)

    Tiryakioglu, Murat, E-mail: m.tiryakioglu@unf.edu [School of Engineering. University of North Florida, Jacksonville, FL 32224 (United States); Eason, Paul D. [School of Engineering. University of North Florida, Jacksonville, FL 32224 (United States); Campbell, John [Department of Metallurgy and Materials, University of Birmingham, Edgbaston B15 2TT (United Kingdom)

    2013-01-01

    The fatigue life of 6061-T6 alloy, normally used in its wrought form, was investigated in this study in cast form from parts produced by the new ablation casting process. All specimens were excised from military castings. Unidirectional tensile test results yielded elongation values comparable to forgings and extrusions. A total of 39 fatigue specimens were tested by the rotating cantilever beam technique at five maximum stress levels. Moreover nine specimens excised from a forging were also tested for comparison. Results revealed that the fatigue life of ablation-cast 6061-T6 (i) follows a three-parameter Weibull distribution, and (ii) is comparable to data from the 6061 forging and is superior to conventionally cast Al-7% Si-Mg alloy castings published in the literature. Analysis of the fracture surfaces of ablation-cast 6061-T6 via scanning electron microscopy showed the existence of fracture surface facets and multiple cracks propagating in different directions.

  2. Multi-Axial Damage Index and Accumulation Model for Predicting Fatigue Life of CMC Materials Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The fatigue life of CMCs must be well characterized for the safe and reliable use of these materials as integrated TPS components. Existing fatigue life prediction...

  3. Fatigue life assessment of free spanning pipelines containing corrosion defects

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, Rita de Kassia D.; Campello, Georga C.; Matt, Cyntia G. da Costa; Benjamin, Adilson C.; Franciss, Ricardo [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES)

    2009-12-19

    The free spanning pipelines assessment is a highlighted issue to be considered during the project and maintenance of the submarine pipelines. It is required to evaluate the fatigue life and the maximum stress due to VIV (Vortex Induced Vibration) as well as wave forces when applicable in case of shallow water. The code DNV-RP-F105 (2006) presents a methodology to calculate the fatigue life for free spanning pipelines. Such methodology however considers the pipe with no kind of defects. Nevertheless, sometimes corrosion defects are detected in periodic inspections and therefore their effects need to be taken into account in the fatigue life evaluation. The purpose of this paper thus is to present a procedure to assess the influence of the corrosion defects in the fatigue life of free spanning pipelines. Some FE analyses were performed to determine the stress concentrate factor (SCF) of the corrosion defects, which were used as input in the methodology presented in the code DNV-RP-F105 (2006). Curves of damage and so lifetime have been generated as function of the span length and water depth. As a practical application, this methodology was applied to a sub sea pipeline with several corrosion defects, localized in shallow water offshore Brazil. (author)

  4. Evaluation of Environmental Effects on Fatigue Life of Piping

    International Nuclear Information System (INIS)

    This paper calculates the expected probabilities of fatigue failures and associated core damage frequencies at a 40-year and 60-year plant life for a sample of components from five PWR and BWR plants. These calculations were made possible by the development of an enhanced version of the pc-PRAISE probabilistic fracture mechanics code

  5. Investigations on selection of method to fit lab-test fatigue life curve

    International Nuclear Information System (INIS)

    The scatter of fatigue life is a factor considered for fitting lab-test fatigue life curves. By leading into diversity coefficient CR, the rule of selection of method to fit lab-test fatigue life curve was established with the value of maximum CR correspond to kinds of S/N the experiment used. Lab-test fatigue life data was fitted to curves according to the rule, and it indicates that the rule can improve the curve fitting. (authors)

  6. Simulation work of fatigue life prediction of rubber automotive components

    Energy Technology Data Exchange (ETDEWEB)

    Samad, M S A [Automotive Engineering Unit, Institute of Advanced Technology, University Putra Malaysia, 43400, UPM Serdang, Selangor (Malaysia); Ali, Aidy, E-mail: aidy@eng.upm.edu.my [Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM, Serdang Selangor (Malaysia)

    2010-05-15

    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.

  7. Simulation work of fatigue life prediction of rubber automotive components

    International Nuclear Information System (INIS)

    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.

  8. Finite Element Analysis of the Fatigue Life for the Connecting Rod Remanufacturing

    Directory of Open Access Journals (Sweden)

    Cheng Gang

    2013-01-01

    Full Text Available One important technical issue is whether the residual fatigue life of products meeting the needs of its next life cycle.This study analyzes the failure mechanism of the connecting rod, establishes its three dimensional model, uses dynamic simulation software ADAMS to calculate its time-load spectrum of the connecting rod; uses finite element analysis software ANSYS to get local stress-strain distribution; uses the traditional anti-fatigue methods to calculate the condition limited fatigue strength and then based on Miner fatigue damage theory and the stress of the connecting rod to make analysis, finally, uses Goodman fatigue theory to get fatigue strength and to estimate its total fatigue life, combined with its historical service time to predict its residual fatigue life. Provide reliable data to support how to calculate the residual fatigue life of these parts.

  9. Fatigue of vanadium--hydrogen alloys

    International Nuclear Information System (INIS)

    The fatigue behavior of unalloyed V, a V-H solid solution, and alloys containing H in excess of the room temperature solubility limit was investigated. It was found that hydrogen contents near and above the room temperature solubility limit increase the high cycle fatigue life, but decrease low cycle life of polycrystalline vanadium. Changes in endurance limit with hydrides may be a consequence of decreased cyclic strain hardening coefficient, n'. 132 ppM hydrogen in solution has only a slightly beneficial effect on stress controlled fatigue life and essentially no effect on low cycle fatigue life. Unalloyed vanadium exhibits profuse striations, while hydrides produce cleavage cracks in fatigued samples

  10. Damage assessment of low-cycle fatigue by crack growth prediction. Fatigue life under cyclic thermal stress

    International Nuclear Information System (INIS)

    The number of cycles to failure of specimens in fatigue tests can be estimated by predicting crack growth. Under a cyclic thermal stress caused by fluctuation of fluid temperature, due to the stress gradient in the thickness direction, the estimated fatigue life differs from that estimated for mechanical fatigue tests. In this paper, the influence of crack growth under cyclic thermal loading on the fatigue life was investigated. First, the thermal stress was derived by superposing analytical solutions, and then, the stress intensity factor was obtained by the weight function method. It was shown that the thermal stress depended not on the rate of the fluid temperature change but on the rise time, and the magnitude of the stress was increased as the rise time was decreased. The stress intensity factor under the cyclic thermal stress was smaller than that under the uniform stress distribution. The change in the stress intensity factor with the crack depth was almost the same regardless of the rise time. The estimated fatigue life under the cyclic thermal loading could be 1.6 times longer than that under the uniform stress distribution. The critical size for the fatigue life determination was assumed to be 3 mm for fatigue test specimens of 10 mm diameter. By evaluating the critical size by structural integrity analyses, the fatigue life was increased and the effect of the critical size on the fatigue life was more pronounced for the cyclic thermal stress. (author)

  11. Damage assessment of low-cycle fatigue by crack growth prediction. Fatigue life under cyclic thermal stress

    International Nuclear Information System (INIS)

    The number of cycles to failure of specimens in fatigue tests can be estimated by predicting crack growth. Under a cyclic thermal stress caused by fluctuation of fluid temperature, due to the stress gradient in the thickness direction, the estimated fatigue life differs from that estimated for mechanical fatigue tests. In this paper, the influence of crack growth under cyclic thermal loading on the fatigue life was investigated. First, the thermal stress was derived by superposing analytical solutions, and then, the stress intensity factor was obtained by the weight function method. It was shown that the thermal stress depended not on the rate of the fluid temperature change but on the rise time, and the magnitude of the stress was increased as the rise time was decreased. The stress intensity factor under the cyclic thermal stress was smaller than that under the uniform stress distribution. The change in the stress intensity factor with the crack depth did not depend on the heat transfer coefficient and only slightly depended on the rise time. The estimated fatigue life under the cyclic thermal loading could be 1.6 times longer than that under the uniform stress distribution. The critical size for the fatigue life determination was assumed to be 3 mm for fatigue test specimens of 10 mm diameter. By evaluating the critical size by structural integrity analyses, the fatigue life was increased and the effect of the critical size on the fatigue life was more pronounced for the cyclic thermal stress. (author)

  12. A frequency domain approach for estimating multiaxial random fatigue life

    Energy Technology Data Exchange (ETDEWEB)

    Bacher-Hoechst, M. [Robert Bosch GmbH, Corporate Sector Research and Advance Engineering, Schwieberdingen (Germany); Sonsino, C.M. [Fraunhofer Institute for Structural Durability and System Reliability LBF, Darmstadt (Germany); Nguyen, N.

    2011-10-15

    This paper presents a probabilistic method for fatigue life estimation within the frequency domain for structural elements subjected to multiaxial random loadings. Multivariate Monte Carlo Simulation is used to account for the correlation between the stress components and their different probability of occurrence and, moreover, enables stochastics during damage analysis to be allowed for and, at the same time, uses any suitable, material dependent multiaxial fatigue criterion known from the time domain. Comparison of the evaluated fatigue damage with experimental results from vibration tests on a demonstrator, chosen from common application fields in the automobile industry, shows good correlation. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Fatigue life prediction of autofrettage tubes using actual material behaviour

    International Nuclear Information System (INIS)

    There is a profound Bauschinger effect in the behaviour of high-strength steels used in autofrettaged tubes. This has led to development of methods capable of considering experimentally obtained (actual) material behaviour in residual stress calculations. The extension of these methods to life calculations is presented here. To estimate the life of autofrettaged tubes with a longitudinal surface crack emanating from the bore more accurately, instead of using idealized models, the experimental loading-unloading stress-strain behaviour is employed. The resulting stresses are then used to calculate stress intensity factors by the weight function method as input to fatigue life determination. Fatigue lives obtained using the actual material behaviour are then compared with the results of frequently used ideal models including those considering Bauschinger effect factors and strain hardening in unloading. Using standard fatigue crack growth relationships, life of the vessel is then calculated based on recommended initial and final crack length. It is shown that the life gain due to autofrettage above 70% overstrain is considerable

  14. Fatigue life prediction of autofrettage tubes using actual material behaviour

    Energy Technology Data Exchange (ETDEWEB)

    Jahed, Hamid [Mechanical Engineering Department, University of Waterloo, 200 University Ave West, Waterloo, Ont., N2L 3G1 (Canada)]. E-mail: hjahedmo@uwaterloo.ca; Farshi, Behrooz [Mechanical Engineering Department, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of); Hosseini, Mohammad [Mechanical Engineering Department, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of)

    2006-10-15

    There is a profound Bauschinger effect in the behaviour of high-strength steels used in autofrettaged tubes. This has led to development of methods capable of considering experimentally obtained (actual) material behaviour in residual stress calculations. The extension of these methods to life calculations is presented here. To estimate the life of autofrettaged tubes with a longitudinal surface crack emanating from the bore more accurately, instead of using idealized models, the experimental loading-unloading stress-strain behaviour is employed. The resulting stresses are then used to calculate stress intensity factors by the weight function method as input to fatigue life determination. Fatigue lives obtained using the actual material behaviour are then compared with the results of frequently used ideal models including those considering Bauschinger effect factors and strain hardening in unloading. Using standard fatigue crack growth relationships, life of the vessel is then calculated based on recommended initial and final crack length. It is shown that the life gain due to autofrettage above 70% overstrain is considerable.

  15. Fatigue Life Prediction of the Keel Structure of A Tsunami Buoy Using Spectral Fatigue Analysis Method

    Directory of Open Access Journals (Sweden)

    Angga Yustiawan

    2013-04-01

    Full Text Available One of the components of the Indonesia Tsunami Early Warning System (InaTEWS is a surface buoy. The surface buoy is exposed to dynamic and random loadings while operating at sea, particularly due to waves. Because of the cyclic nature of the wave load, this may result in a fatigue damage of the keel structure, which connects the mooringline with the buoy hull. The operating location of the buoy is off the Java South Coast at the coordinate (10.3998 S, 108.3417 E. To determine the stress transfer function, model tests were performed, measuring the buoy motions and the stress at the mooring line. A spectral fatigue analysis method is applied for the purpose of estimating the fatigue life of the keel structure. Utilizing the model-test results, the S-N curve obtained in a previous study and the wave data at the buoy location, it is found that the fatigue life of the keel structure is approximately 11 years.

  16. Simplified fatigue life analysis for traction drive contacts

    Science.gov (United States)

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

    1980-01-01

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

  17. Numerical calculation of bending fatigue life of thin-rim spur gears

    OpenAIRE

    Kramberger, Janez; raml, Matja; Potr?, Iztok; Flaker, Joe

    2012-01-01

    Mechanical elements subjected to cyclic loading have to be designed against fatigue. The main goal of the presented analysis was to determine the the bending fatigue life prediction of thin rim spur gears. The service life is divided into the initiation phase of the damage accumulation and the crack growth, resprcitively. The analysis has been performed usig FEM and BEM. The continuum mechanics approach is used for the prediction of the fatigue life initiation phase, where the basic fatigue m...

  18. Time-dependent fatigue--phenomenology and life prediction

    International Nuclear Information System (INIS)

    The time-dependent fatigue behavior of materials used or considered for use in present and advanced systems for power generation is outlined. A picture is first presented to show how basic mechanisms and phenomenological information relate to the performance of the component under consideration through the so-called local strain approach. By this means life prediction criteria and design rules can be formulated utilizing laboratory test information which is directly translated to predicting the performance of a component. The body of phenomenological information relative to time-dependent fatigue is reviewed. Included are effects of strain range, strain rate and frequency, environment and wave shape, all of which are shown to be important in developing both an understanding and design base for time dependent fatigue. Using this information, some of the current methods being considered for the life prediction of components are reviewed. These include the current ASME code case, frequency-modified fatigue equations, strain range partitioning, the damage function method, frequency separation and damage rate equations. From this review, it is hoped that a better perspective on future directions for basic material science at high temperature can be achieved

  19. Thermomechanical Fatigue of Ductile Cast Iron and Its Life Prediction

    Science.gov (United States)

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

    2015-06-01

    Thermomechanical fatigue (TMF) behaviors of ductile cast iron (DCI) were investigated under out-of-phase (OP), in-phase (IP), and constrained strain-control conditions with temperature hold in various temperature ranges: 573 K to 1073 K, 723 K to 1073 K, and 433 K to 873 K (300 C to 800 C, 450 C to 800 C, and 160 C to 600 C). The integrated creep-fatigue theory (ICFT) model was incorporated into the finite element method to simulate the hysteresis behavior and predict the TMF life of DCI under those test conditions. With the consideration of four deformation/damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement, (iii) creep, and (iv) oxidation, as revealed from the previous study on low cycle fatigue of the material, the model delineates the contributions of these physical mechanisms in the asymmetrical hysteresis behavior and the damage accumulation process leading to final TMF failure. This study shows that the ICFT model can simulate the stress-strain response and life of DCI under complex TMF loading profiles (OP and IP, and constrained with temperature hold).

  20. Impact of Fatigue and Disability on Quality of Life in Multiple Sclerosis

    Directory of Open Access Journals (Sweden)

    ztrk, A.

    2005-01-01

    Full Text Available Purpose: To investigate the impact of fatigue and disability on the quality of life in 70 multiple sclerosis (MS patients. Material and Methods: Quality of Life was assessed using the Functional Assessment of MS (FAMS. Disability was assessed using the Kurtzkes expanded disability status scale (EDSS and fatigue was quantified using the fatigue severity scale (FSS. Results: Fatigue groups (MSF had more impaired scores than nonfatigue groups (MSNF (p<0,05. Fatigue and disability were significantly associated with FAMS total and subgroups (p<0,05. Conclusion: Fatigue and disability have an effect on the quality of life.

  1. High cycles fatigue damage of CFRP plates clamped by bolts for axial coupling joint with off-set angle during rotation

    Science.gov (United States)

    Ooka, Kazuaki; Okubo, Kazuya; Fujii, Toru; Umeda, Shinichi; Fujii, Masayuki; Sugiyama, Tetsuya

    2014-03-01

    This study discussed the change of residual fracture torque and the fatigue damage process of thin CFRP plates clamped by bolts for axial coupling joint, in which flexible deformation was allowed in the direction of off-set angle by the deflection of the CFRP plates while effective stiffness was obtained in rotational direction. Mechanically laminated 4 layers of the CFRP plates were repeatedly deflected during the rotation of axial coupling, when two axes were jointed with 3 degree of off-set angle, in which number of revolution was 1,800 rpm (30Hz of loading frequency). At first, the fracture morphology of specimen and the residual fracture torque was investigated after 1.0107 cycles of repeated revolutions. The reduction ratio of spring constant was also determined by simple bending test after the fatigue. The residual fracture torque of the joint was determined on the rotational test machine after 1.0107 cycles of fatigue. After rotations of cyclic fatigue, fiber breaking and wear of matrix were observed around the fixed parts compressed by washers for setting bolts. The reduction of spring constant of the CFRP plates was caused by the initiation of cyclic fatigue damages around the fixed parts, when the axial coupling joint was rotated with off-set angle. It was found that residual fracture torque of the joint was related with the specific fatigue damage of the CFRP observed in this study.

  2. On Fatigue Life Under Stationary Gaussian Random Loads (A)

    DEFF Research Database (Denmark)

    Talreja, R.

    1973-01-01

    Power spectra are taken to represent stationary Gaussian random loads. Location, scale, and shape parameters are defined for power spectra and proposed as a convenient set of load parameters for random loads. The center frequency of a power spectrum, defined as its weighted average frequency, is proposed as a measure of fatigue life. A servohydraulic closed loop testing machine is used to load specimens of carbon steel under six different power spectral shapes. Test results are utilized to evalu...

  3. Fatigue life of layered metallic and ceramic plasma sprayed coatings.

    Czech Academy of Sciences Publication Activity Database

    Kov?k, O.; Hauild, P.; Siegl, J.; Mat?j?ek, Ji?; Davydov, V.

    2014-01-01

    Ro?. 3, July (2014), s. 586-591. ISSN 2211-8128. [European Conference on Fracture (ECF20)/20./. Trondheim, 30.06.2014-04.07.2014] R&D Projects: GA ?R(CZ) GAP108/12/1872 Institutional support: RVO:61389021 Keywords : functionally graded materials * fatigue life * neutron diffraction * grit blasting Subject RIV: JK - Corrosion ; Surface Treatment of Materials http://www.sciencedirect.com/science/article/pii/S2211812814000984#

  4. Cyclic behaviour and fatigue life prediction in welded aluminium joints

    International Nuclear Information System (INIS)

    The paper gives an overall state-of-the-art view of international attempts to find a solution, describes cyclic stress-strain behavior for the different zones of aluminium weldments, as stated above, states results from a recent research program of the Versuchsanstalt Stahl, Holz, und Steine in Karlsruhe and gives a step by step model for the calculation procedure of fatigue life. (orig.) 891 RW/orig. 892 RKD

  5. Comparison between tensile, stiffness and fatigue life tests results

    OpenAIRE

    Silva, Hugo Manuel Ribeiro Dias da; Pais, Jorge C.; Pereira, Paulo A. A.

    2003-01-01

    A laboratory mechanical test is being implemented in the University of Minho to evaluate the asphalt-aggregate interaction. This test measures the tensile properties of the bituminous mixture in the interface between the asphalt and the aggregates. By using the tensile test it is intended to observe how the asphalt-aggregate interaction influences the mechanical properties of the bituminous mixtures, namely, stiffness modulus and fatigue life. The tensile test results must have a good correla...

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

    International Nuclear Information System (INIS)

    Fatigue life prediction and evaluation are very important in design procedure to assure the safety and reliability of the rubber components. Fatigue lifetime prediction methodology of the rubber component was proposed by incorporating the finite element analysis and fatigue damage parameter from fatigue test. Finite element analysis of rubber component was performed based on a hyper-elastic material model determined from material test. The Green-Lagrange strain at the critical location determined from the finite element method was used to evaluate the fatigue damage parameter of the natural rubber. Fatigue life of rubber components was predicted by using the fatigue damage parameter at the critical location. Predicted fatigue life of the rubber component agreed fairly well with the experimental fatigue lives

  7. Fatigue life and fatigue crack growth of the ods nickel-base superalloy PM 1000

    International Nuclear Information System (INIS)

    Fatigue crack growth (FCG) and fatigue life (LCF and HCF) of the oxide dispersion strengthened (ODS) nickel-base superalloy PM 1000 have been studied at 850 oC on strongly textured bar (GAR=10) and sheet material (GAR=4). Specimens were prepared with their axis parallel to the and (sheet only) directions, resp. The fatigue tests were performed under total strain control in the LCF regime and under stress control for HW and FCG testing. In the HW range, shorter lives were observed with specimens as compared to ones. The opposite is true in the LCF range where longer lives are found in -specimens. In fatigue crack growth studies, the threshold values obtained for FCG in direction are higher than those of direction. This finding is in accordance with the orientation dependence of Young's modulus and strength level. In order to evaluate the potential of additional ?'-hardening, PM 3030 has been included into our investigations. At 850 oC, a coarse elongated grained variant (GAR>100 showed much better HW properties than PM 1000. (author)

  8. The Study on Fatigue Experiment and Reliability Life of Submarine Pipeline Steel

    OpenAIRE

    Yan Yifei; Shao Bing; Liu Jinkun; Cheng Lufeng

    2013-01-01

    The aim of the fatigue experiment study is to solve the fatigue fracture problem of X70 submarine tubing when it is under the scouring effect of offshore current. The multilevel fatigue experiments are carried out following the internation (GB4337-84) recommended method. The standard round bar fatigue specimen was made by the material of submarine pipeline steel. The fatigue life of submarine pipeline steel in different survival probability and P-S-N curve were achieved. According to reliabil...

  9. Estimation of fatigue life for I-beam structure of wind turbine blade

    International Nuclear Information System (INIS)

    The research of fatigue analysis is based on the purpose that prevents the fatigue failure as estimate the material strength and structure stability. In this paper, the fatigue life is analyzed for I-beam which used as spar part in the wind turbine blade. To estimate the fatigue life, I-beam structure is modeled by MSC.Patran and the static analysis is performed by MSC.Nastran. All of the geometric information and conditions are based on DOE/MSU data base to compare the fatigue life between the proposed fatigue analysis method and the test result. The proposed fatigue analysis is used least square method to get regression curve form the S-N data. Moreover, the coefficient of determination method is used to ensure how accuracy it has. In addition, the Goodman method is used to consider the mean stress effect for evaluating more accuracy fatigue life. The proposed analysis program is accomplished by Fortran code.

  10. Selected issues concerning calculations and experimental tests of transport means construction elements fatigue life

    Directory of Open Access Journals (Sweden)

    Bogdan LIGAJ

    2014-12-01

    Full Text Available Development of an algorithm of fatigue life of structural components of road and rail vehicles as well as sea vessels and aircrafts involves three groups of activities connected with: development of fatigue load spectra on the basis measurement of service loads, determination of the construction material fatigue properties and a selection of the best hypothesis for estimating the fatigue damage to be used for a phenomenological description of the fatigue process. The above listed groups of problems include the main causes of differences that occur between the calculation results and the results of fatigue life experimental tests. Evaluation of these differences is the main goal of this article.

  11. Fatigue, mood and quality of life improve in MS patients after progressive resistance training

    DEFF Research Database (Denmark)

    Dalgas, U; Stenager, E; Jakobsen, J; Petersen, T; Hansen, H J; Knudsen, C; Overgaard, K; Ingemann-Hansen, T

    2010-01-01

    Fatigue occurs in the majority of multiple sclerosis patients and therapeutic possibilities are few. Fatigue, mood and quality of life were studied in patients with multiple sclerosis following progressive resistance training leading to improvement of muscular strength and functional capacity. Fatigue (Fatigue Severity Scale, FSS), mood (Major Depression Inventory, MDI) and quality of life (physical and mental component scores, PCS and MCS, of SF36) were scored at start, end and follow-up of a r...

  12. Casting defects and high temperature fatigue life of IN 713LC superalloy.

    Czech Academy of Sciences Publication Activity Database

    Kunz, Ludvk; Luk, Petr; Kone?n, R.; Fintov, S.

    2012-01-01

    Ro?. 41, AUG (2012), s. 47-51. ISSN 0142-1123 R&D Projects: GA MPO(CZ) FR-TI3/055; GA Mk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : IN 713LC * High-cycle fatigue * casting defects * hot isostatic pressing * extreme value statistics Subject RIV: JL - Materials Fatigue , Friction Mechanics Impact factor: 1.976, year: 2012

  13. Life extension of components with high cumulative fatigue usage

    International Nuclear Information System (INIS)

    The current ASME Boiler and Pressure Vessel Code fatigue design approach has significant margins of safety as evidenced by fatigue data from full-scale vessels. In order to extend the qualification (life) of components which have reached the Code design usage limit of unity, improved criteria are needed which address crack initiation and propagation separately such that safe operation of these components is assured. The fatigue crack initiation phase is composed of two processes: initial microcracking of internal particles or accumulation of local strain (cyclic slip) creating discontinuities which form microcracks, and the growth of the microcracks, and the growth of the microcracks in a noncontinuum manner. The microcracks which initiate will eventually grow to a size in which continuum mechanics apply, and fracture mechanics concepts can be employed. The later propagation to failure of a component is also composed of two parts, continuum crack growth in a stable manner and eventual unstable fracture of the remaining ligament of material. This paper reviews the current status of technology in assessing initiation and propagation relative to the current design Code and suggests areas of improvement to cover extended life of high usage factor components

  14. Corrosion fatigue behavior and life prediction method under changing temperature condition

    International Nuclear Information System (INIS)

    Axially strain controlled low cycle fatigue tests of a carbon steel in oxygenated high temperature water were carried out under changing temperature conditions. Two patterns of triangular wave were selected for temperature cycling. One was in-phase pattern synchronizing with strain cycling and the other was an out-of-phase pattern in which temperature was changed in anti-phase to the strain cycling. The fatigue life under changing temperature condition was in the range of the fatigue life under various constant temperature within the range of the changing temperature. The fatigue life of in-phase pattern was equivalent to that of out-of-phase pattern. The corrosion fatigue life prediction method was proposed for changing temperature condition, and was based on the assumption that the fatigue damage increased in linear proportion to increment of strain during cycling. The fatigue life predicted by this method was in good agreement with the test results

  15. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibs, Jan Behrend; Agerskov, Henning

    test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical...... analytical fatigue lives. Both the analytical and experimental results obtained show that the Miner rule may give quite unconservative predictions of the fatigue life for the types of stochastic loading studied....... determination of the fatigue life is included. Furthermore, the results obtained in studies of the various parameters that have an influence on the fatigue life, are given. A very good agreement between experimental and analytical results is obtained, when the crack closure model is used in determination of the...

  16. Fatigue life prediction of pedicle screw for spinal surgery

    Directory of Open Access Journals (Sweden)

    . Major

    2016-02-01

    Full Text Available This paper is dedicated to fatigue estimation of implants for spinal surgery. This article deals especially with special case of hollow pedicle screw. Implant systems utilizing specially designed spinal instrumentation are often used in these surgical procedures. The most common surgical procedure is spinal fusion, also known as spondylodesis, is a surgical technique used to join two or more vertebra. Implants are subjected to many loading cycles during their life, especially in the case of other degenerative changes in the skeleton, there are often changes in loading conditions, which often cannot be accurately determined. These changes often lead to further bending load in the thread. Hollow screws studied in this work show higher fatigue resistance than other types of implants.

  17. Service life determination for a fatigue-limited Class 1 piping component

    International Nuclear Information System (INIS)

    The design fatigue life assessment of an ASME Class 1 piping component typically has a significant safety margin. Methods containing varying degrees of detail may be used to develop the component's fatigue usage factor. This paper presents the technical bases used to establish a more realistic fatigue life for a piping component which was nearing its calculated design fatigue limit. The original design basis methodology was superseded by a more detailed inelastic evaluation to demonstrate structural integrity and determine the revised component fatigue life. An effective design cycle curve was developed to assess future fatigue damage, and for tracking ongoing fatigue accumulation. In addition, the existing transient tracking procedure was updated to take into account the actual transient severity for all future fatigue-significant events

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

    International Nuclear Information System (INIS)

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

  19. Life extension of components with high cumulative fatigue usage

    International Nuclear Information System (INIS)

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

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

    OpenAIRE

    Nijssen, R.P.L.

    2006-01-01

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

  1. Fatigue life prediction for a cold worked T316 stainless steel

    International Nuclear Information System (INIS)

    Permanent damage curves of initiation-life and propagation-life which predict the fatigue life of specimens of a cold-worked type 316 stainless steel under complex strain-range histories were generated by a limited test program. Analysis of the test data showed that fatigue damage is not linear throughout life and that propagation life is longer than initiation-life at high strain ranges but is shorter at low strain ranges. If permanent damage has been initiated by prior history and/or fabrication, propagation to a given life can occur at a lower strain range than that estimated from the fatigue curves for constant CSR. (author)

  2. In-situ fatigue life prognosis for composite laminates based on stiffness degradation

    Data.gov (United States)

    National Aeronautics and Space Administration — In this paper, a real-time composite fatigue life prognosis framework is proposed. The proposed methodology combines Bayesian inference, piezoelectric sensor...

  3. Fatigue and Quality of Life of Women Undergoing Chemotherapy or Radiotherapy for Breast Cancer

    OpenAIRE

    Winnie K.W. SO; Gene Marsh; W.M. Ling

    2009-01-01

    OBJECTIVE To examine fatigue and quality of life (QOL) in breast cancer patients undergoing chemotherapy or radiotherapy.METHODS A self-report survey derived from the Chinese version of Brief Fatigue Inventory, the Functional Assessment of Chronic Illness Therapy for Breast Cancer, and the Medical Outcomes Study Social Support Survey. Descriptive statistics was used to examine the intensity of fatigue and the prevalence of severe fatigue. Multivariate analysis of variance was used to de...

  4. Fatigue Life Characterization of Superpave Mixtures at the Virginia Smart Road

    OpenAIRE

    Al-Qadi, Imad L.; Diefenderfer, Stacey D.; Loulizi, Amara

    2005-01-01

    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. Differences in fatigue performance due to field and laboratory production and compaction methods were investigated. Also, in-situ mixtures were compared to mixtures produced accurately from the job mix formula to determine if changes occurring be...

  5. Structural health monitoring of wind towers: residual fatigue life estimation

    International Nuclear Information System (INIS)

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

  6. Thermal fatigue of pipes induced by fluid temperature change. Effect of multiaxial pre-loading on fatigue strength

    International Nuclear Information System (INIS)

    This study investigates an effect of pre-inelastic multiaxial loading on failure lives in a followed high cycle fatigue test for SUS316 steel. In the multiaxial low cycle fatigue test for the pre-loading, two types of strain paths were employed which are a push-pull straining and a circle straining. The circle straining is the non-proportional loading in which axial strain ε and shear strain γ has 90 degree phase difference. Using the specimen fatigued in the pre-loading test, high cycle fatigue test was conducted by a rotating bending fatigue testing machine. Based on the obtained results, property of fatigue life in high cycle fatigue which received pre-loading under non-proportional loading is discussed. (author)

  7. Finite Element Based Fatigue Life Prediction of Cylinder Head for Two-Stroke Linear Engine Using Stress-Life Approach

    OpenAIRE

    Rahman, M. M .; A.K. Ariffin; S.Abdullah; M.M. Noor; R. A. Bakar; Maleque, M.A.

    2008-01-01

    This study describes the finite element based fatigue life prediction of cylinder head for a two-stroke free piston linear engine subjected to variable amplitude loading, applicable to electric power generation. A set of aluminum alloys, cast iron and forged steel for cylinder head are considered in this study. The finite element modeling and analysis were performed utilizing the finite element analysis codes. The fatigue life analysis was carried out using finite element based fatigue ...

  8. Rainflow counting algorithm for the LIFE2 fatigue analysis code

    Science.gov (United States)

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

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

  9. NASALIFE - Component Fatigue and Creep Life Prediction Program

    Science.gov (United States)

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

    2014-01-01

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

  10. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibs, Jan Behrend; Agerskov, Henning

    1996-01-01

    Fatigue in steel structures subjected to stochastic loading is studied. Of special interest is the problem of fatigue damage accumulation and in this connection, a comparison between experimental results and results obtained using fracture mechanics. Fatigue test results obtained for welded plate test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical determination of the fatigue life is included. Furthermore, the results obtained in studies of the various parameters that have an influence on the fatigue life, are given. A very good agreement between experimental and analytical results is obtained, when the crack closure model is used in determination of the analytical fatigue lives. Both the analytical and experimental results obtained show that the Miner rule may give quite unconservative predictions of the fatigue life for the types of stochastic loading studied.

  11. Fatigue life and damage evolution of martensitic steels for low-pressure steam turbine blades in the VHCF regime; Lebensdauer und Schaedigungsentwicklung martensitischer Staehle fuer Niederdruck-Dampfturbinenschaufeln bei Ermuedungsbeanspruchung im VHCF-Bereich

    Energy Technology Data Exchange (ETDEWEB)

    Kovacs, Stephan

    2014-07-01

    Low-pressure steam turbine blades are usually made of martensitic steels with Cr contents between 9 and 12%, which combine good corrosion resistance, high mechanical strength and sufficient ductility. The inhomogeneous flow field behind the vanes generates high-frequency oscillations above 1 kHz. In addition, the blades with lengths up to 1.5 m are operated at rotational speeds up to 3000 rpm, resulting in large centrifugal forces leading to the superposition of extremely high mean stresses. Also resonance oscillations during start-up and shutdown cannot be completely excluded. Currently, the components are designed using high safety factors against S-N curves with an assumed asymptotic fatigue limit above 107 load cycles. Nevertheless, fatigue cracks are observed even at high number of cycles, starting from the blade root without pre-damage by erosion or steam droplet impingement. While fatigue failure usually occurs at the surface, fatigue cracks at very high number of cycles (> 108) initiate at oxides or intermetallic inclusions below the surface. This transition between both failure mechanisms in the Very High-Cycle Fatigue (VHCF) regime is in the focus of numerous current research activities, because numbers of cycles above 108 can be attained in a viable period of time using the recently developed high-frequency testing techniques operated at 20 kHz. Also for wind turbines, gas turbines, bearings, springs, etc. VHCF issues become increasingly important. Within this work, the fatigue life and damage behavior of a martensitic Cr-steel during fatigue loading with and without high mean stresses at number of cycles to failure above 108 was analyzed. On the one hand, the studies gave insights into the relation between fatigue life and fatigue damage evolution of the investigated group of high-strength steels in the very high cycle fatigue regime (up to 2109). In particular, the influence of high mean stresses on the VHCF behavior (fracture origin, crack growth, fatigue life) which was not investigated in detail before is studied and the crack initiation and propagation mechanisms are analyzed by electron microscopy (SEM, TEM / FIB). With this, the work contributes to the reliable design of future low-pressure steam turbines. The results show that in particular non-metallic inclusions in the steel cause fracture by fatigue cracks initiated in the volume under very high cycle fatigue conditions. This fatigue behavior can be described very well by means of fracture mechanics approaches over a wide range of load ratios.

  12. Creep-fatigue life prediction method using Diercks equation for Cr-Mo steel

    International Nuclear Information System (INIS)

    For dealing with the situation that creep-fatigue life properties of materials do not exist, a development of the simple method to predict creep-fatigue life properties is necessary. A method to predict the creep-fatigue life properties of Cr-Mo steels is proposed on the basis of D. Diercks equation which correlates the creep-fatigue lifes of SUS 304 steels under various temperatures, strain ranges, strain rates and hold times. The accuracy of the proposed method was compared with that of the existing methods. The following results were obtained. (1) Fatigue strength and creep rupture strength of Cr-Mo steel are different from those of SUS 304 steel. Therefore in order to apply Diercks equation to creep-fatigue prediction for Cr-Mo steel, the difference of fatigue strength was found to be corrected by fatigue life ratio of both steels and the difference of creep rupture strength was found to be corrected by the equivalent temperature corresponding to equal strength of both steels. (2) Creep-fatigue life can be predicted by the modified Diercks equation within a factor of 2 which is nearly as precise as the accuracy of strain range partitioning method. Required test and analysis procedure of this method are not so complicated as strain range partitioning method. (author)

  13. Statistical analysis of manufacturing defects on fatigue life of wind turbine casted Component

    DEFF Research Database (Denmark)

    Rafsanjani, Hesam Mirzaei; Srensen, John Dalsgaard; Mukherjee, Krishnendu; Fster, Sren; Sturlason, Asger

    2014-01-01

    Wind turbine components experience heavily variable loads during its lifetime and fatigue failure is a main failure mode of casted components during their design working life. The fatigue life is highly dependent on the microstructure (grain size and graphite form and size), number, type, locatio...

  14. Use of Strain-life Models with Wavelet Bump Extraction (WBE fro Prediction Fatigue Damage

    Directory of Open Access Journals (Sweden)

    John R. Yates

    2008-08-01

    Full Text Available This paper presents the use of strain-life fatigue damage models to observe the cycle sequence effects in the wavelet-based fatigue data editing algorithm. This algorithm is called Wavelet Bump Extraction (WBE, which was developed to produce a shortened signal by extracting fatigue damaging events from the original signal with the retention of the original cycle sequences. Current industrial practice uses the Plamgren-Miner linear damage rule to predict the fatigue life or fatigue damage under variable amplitude(VA loadings. Using VA loadings, however, this rule does not have load interaction accountability in the analysis. Thus, a more suitable approach has been identified for predicting fatigue damage od VA loadings, i.e. the Effective Strain Damage (ESD model. In this study, the cycle sequence effect observation was implemented in both analytical and experimental works using the WBE extracted VA loadings. The study includes the comparison between the experimental and the anlytical (using four strain-life fatigue damage models: Coffin-Manson, Morrow, Smith-Watson-Topper and ESD fatigue damage. The smallest average in the fatigue damage difference was found when using the ESD strain-life model, suggesting the suitability of the model for analysing VA fatigue technique.

  15. Comparing Fatigue Life Estimations of Composite Wind Turbine Blades using different Fatigue Analysis Tools

    DEFF Research Database (Denmark)

    Ardila, Oscar Gerardo Castro; Lennie, Matthew; Branner, Kim; Pechlivanoglou, George; Nayeri, Christian; Paschereit, Christian Oliver

    2015-01-01

    In this paper, fatigue lifetime prediction of NREL 5MW reference wind turbine is presented. The fatigue response of materials used in selected blade cross sections was obtained by applying macroscopic fatigue approaches and assuming uniaxial stress states. Power production and parked load cases suggested by the IEC 61400-1 standard were studied employing different load time intervals and by using two novel fatigue tools called ALBdeS and BECAS+F. The aeroelastic loads were defined thought aeroel...

  16. Fatigue life under random load history derived from exceedance curves using different algorithms

    Science.gov (United States)

    Prakash, Raghu V.; Sunder, R.

    1993-07-01

    Low cycle fatigue life and crack growth rates were analytically estimated for random load sequences, generated from three combat aircraft load exceedance curves using different algorithms, including simulated rainflow cycle count, extreme-to-extreme excursions, upper to lower bound excursions and unrestricted peak-trough excursions. Also, the response of a fatigue meter to a random load sequence was simulated. Fatigue damage for the different load histories was computed using material constants for an Al-Cu alloy. Computed fatigue damage was relatively insensitive to the algorithm used for load sequence generation from combat aircraft load exceedance curves. Fatigue meter data based damage estimates were, however, sometimes unconservative.

  17. Fatigue life estimation of welded components considering welding residual stress relaxation and its mean stress effect

    International Nuclear Information System (INIS)

    The fatigue life of welded joints is sensitive to welding residual stress and complexity of their geometric shapes. To predict the fatigue life more reasonably, the effects of welding residual stress and its relaxation on their fatigue strengths should be considered quantitatively, which are often regarded to be equivalent to the effects of mean stresses by external loads. The hot-spot stress concept should be also adopted which can reduce the dependence of fatigue strengths for various welding details. Considering the factors mentioned above, a fatigue life prediction model using the modified Goodman's diagram was proposed. In this model, an equivalent stress was introduced which is composed of the mean stress based on the hot-spot stress concept and the relaxed welding residual stress. From the verification of the proposed model to real welding details, it is proved that this model can be applied to predict reasonably their fatigue lives

  18. Shape-Simplification Analysis Model for Fatigue Life Prediction of Casting Products Considering Internal Defects

    International Nuclear Information System (INIS)

    Internal defects are a major concern in the casting process because they have a significant influence on the strength and fatigue life of casting products. In general, they cause stress concentration and can be a starting point of cracks. Therefore, it is important to understand the effects of internal defects on mechanical properties such as fatigue life. In this study, fatigue experiments on tensile specimens with internal defects were performed. The internal defects in the casting product were scanned by an industrial CT scanner, and its shape was simplified by ellipsoidal primitives for the structural and fatigue analysis. The analysis results were compared with experimental results for casting products with internal defects. It was demonstrated that it is possible to consider internal defects of casting products in stress and fatigue analysis. The proposed method provides a tool for the prediction of the fatigue life of casting products and the investigation of the effects of internal defects on mechanical performance

  19. Assessment of Fatigue Life for High-temperature Pipeline Welds by Non-destructive Method

    International Nuclear Information System (INIS)

    The objective of this study is to estimate the feasibility of X-ray diffraction method application for fatigue life assessment of the high-temperature pipeline steel such as main steam pipe, reheater pipe and header etc. in power plant. In this study, X-ray diffraction tests using various types of specimen simulated low cycle fatigue damage were performed in order to analyze fatigue properties when fatigue damage conditions become various stages such as l/4, 1/2 and 3/4 of fatigue life, respectively As a result of X-ray diffraction tests for specimens simulated fatigue damages, we conformed that the variation of the full width at half maximum intensity decreased in proportion to the increase of fatigue life ratio. And also, the ratio of the full width at half maximum intensity due to fatigue damage has linear relationship with fatigue life ratio algebraically. From this relationships, it was suggested that direct expectation of the life consumption rate was feasible.

  20. Fatigue life assessment for pipeline welds by x-ray diffraction technique

    International Nuclear Information System (INIS)

    The objective of this study is to estimate the feasibility of X-ray diffraction method application for fatigue life assessment of the high-temperature pipeline steel such as main steam pipe, re-heater pipe and header etc. in power plant. In this study, X-ray diffraction tests using various types of specimen simulated low cycle fatigue damage were performed in order to analyze fatigue properties when fatigue damage conditions become various stages such as 1/4, l/2 and 3/4 of fatigue life, respectively. As a result off-ray diffraction tests for specimens simulated fatigue damages, we conformed that the variation of the full width at half maximum intensity decreased in proportion to the increase of fatigue life ratio. And also, He ratio of the full width at half maximum intensity due to fatigue damage has linear relationship with fatigue life ratio algebraically. From this relationship, it was suggested that direct expectation of the life consumption rate was feasible.

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

    Directory of Open Access Journals (Sweden)

    M.M. Rahman

    2008-01-01

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

  2. Statistical analysis of manufacturing defects on fatigue life of wind turbine casted Component

    DEFF Research Database (Denmark)

    Rafsanjani, Hesam Mirzaei; Srensen, John Dalsgaard; Mukherjee, Krishnendu; Fster, Sren; Sturlason, Asger

    2014-01-01

    Wind turbine components experience heavily variable loads during its lifetime and fatigue failure is a main failure mode of casted components during their design working life. The fatigue life is highly dependent on the microstructure (grain size and graphite form and size), number, type, location...... and size of defects in the casted components and is therefore rather uncertain and needs to be described by stochastic models. Uncertainties related to such defects influence prediction of the fatigue strengths and are therefore important in modelling and assessment of the reliability of wind turbine...... fatigue life, namely LogNormal and Weibull distributions. The statistical analyses are performed using the Maximum Likelihood Method and the statistical uncertainty is estimated. Further, stochastic models for the fatigue life obtained from the statistical analyses are used for illustration to assess the...

  3. Probabilistic assessment of fatigue life including statistical uncertainties in the S-N curve

    International Nuclear Information System (INIS)

    A probabilistic framework is set up to assess the fatigue life of components of nuclear power plants. It intends to incorporate all kinds of uncertainties such as those appearing in the specimen fatigue life, design sub-factor, mechanical model and applied loading. This paper details the first step, which corresponds to the statistical treatment of the fatigue specimen test data. The specimen fatigue life at stress amplitude S is represented by a lognormal random variable whose mean and standard deviation depend on S. This characterization is then used to compute the random fatigue life of a component submitted to a single kind of cycles. Precisely the mean and coefficient of variation of this quantity are studied, as well as the reliability associated with the (deterministic) design value. (author)

  4. Study on fatigue life evaluation of structural component based on crack growth criterion

    International Nuclear Information System (INIS)

    As one of the practical application of fracture mechanics, fatigue life evaluation method based on crack growth criterion has been diffusing in various field of technology in order to determine the rational and reliable life of structural components. The fatigue life by this method is evaluated based on the fatigue crack growth analysis from defects, while many problems, such as the influence of residual stress on the crack growth behavior, the effect of overloading, and evaluation method for multiple surface cracks, are not sufficiently solved yet. In this paper, the above problems are treated, and based on some exprimental data some simple mehtods for fatigue life evaluation are proposed regarding the above problems. Verification of the proposed methods are shown in the paper by comparing with some experimental results, and the applicability of the proposed method is also examined by the fatigue test of pipes with cracks in the inner surface. (author)

  5. Uncertainty Analysis in Fatigue Life Prediction of Gas Turbine Blades Using Bayesian Inference

    Science.gov (United States)

    Li, Yan-Feng; Zhu, Shun-Peng; Li, Jing; Peng, Weiwen; Huang, Hong-Zhong

    2015-12-01

    This paper investigates Bayesian model selection for fatigue life estimation of gas turbine blades considering model uncertainty and parameter uncertainty. Fatigue life estimation of gas turbine blades is a critical issue for the operation and health management of modern aircraft engines. Since lots of life prediction models have been presented to predict the fatigue life of gas turbine blades, model uncertainty and model selection among these models have consequently become an important issue in the lifecycle management of turbine blades. In this paper, fatigue life estimation is carried out by considering model uncertainty and parameter uncertainty simultaneously. It is formulated as the joint posterior distribution of a fatigue life prediction model and its model parameters using Bayesian inference method. Bayes factor is incorporated to implement the model selection with the quantified model uncertainty. Markov Chain Monte Carlo method is used to facilitate the calculation. A pictorial framework and a step-by-step procedure of the Bayesian inference method for fatigue life estimation considering model uncertainty are presented. Fatigue life estimation of a gas turbine blade is implemented to demonstrate the proposed method.

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

    Science.gov (United States)

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

    2012-01-01

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

  7. Fatigue life evaluation method of austenitic stainless steel in PWR water

    International Nuclear Information System (INIS)

    It is known that the fatigue life in elevated temperature water is substantially reduced compared with that in the air. The fatigue life reduction has been investigated experimentally in EFT project of Japan Nuclear Energy Safety Organization (JNES) to evaluate the environmental effect on fatigue life. Many tests have been done for carbon, low alloy, stainless steels and nickel-based alloy under the various conditions. In this paper, the results of the stainless steel in simulated PWR water environments were reported. Fatigue life tests in simulated PWR environments were carried out and the effect of key parameters on fatigue life reduction was examined. The materials used in this study were base and weld metal of austenitic stainless steel SS316, weld metal of SS304 and the base and aged metal of the duplex stainless steel SCS14A. In order to evaluate the effects of stain amplitude, strain rate, strain ratio, temperature, aging, water flow rate and strain holding time, many fatigue tests were examined. In transient condition in an actual plant, however, such parameters as temperature and strain rate are not constant. In order to evaluate fatigue damage in actual plant on the basis of experimental results under constant temperature and strain rate condition, the modified rate approach method was developed. Various kinds of transient have to be taken into account of in actual plant fatigue evaluation, and stress cycle of several ranges of amplitude has to be considered in assessing damage from fatigue. Generally, cumulative usage factor is applied in this type of evaluation. In this study, in order to confirm the applicability of modified rate approach method together with cumulative usage factor, fatigue tests were carried out by combining stress cycle blocks of different strain amplitude levels, in which strain rate changes in response to temperature in a simulated PWR water environment. Consequently, fatigue life could be evaluated with an accuracy of factor of 3 by modified rate approach method. (authors)

  8. Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

    OpenAIRE

    Mitrovi?, Radivoje; Atanasovska, Ivana; MOM?ILOVI?, Dejan; Vuherer, Toma

    2015-01-01

    This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaftflange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values ...

  9. Aspects of fatigue life in thermal barrier coatings

    Energy Technology Data Exchange (ETDEWEB)

    Brodin, H.

    2001-08-01

    Thermal barrier coatings (TBC) are applied on hot components in airborne and land based gas turbines when higher turbine inlet temperature, meaning better thermal efficiency, is desired. The TBC is mainly applied to protect underlying material from high temperatures, but also serves as a protection from the aggressive corrosive environment. Plasma sprayed coatings are often duplex TBC's with an outer ceramic top coat (TC) made from partially stabilised zirconia - ZrO{sub 2} + 6-8% Y{sub 2}O{sub 3}. Below the top coat there is a metallic bond coat (BC). The BC is normally a MCrAlX coating (M=Ni, Co, Fe... and X=Y, Hf, Si ... ). In gas turbine components exposed to elevated temperatures nickel-based superalloys are commonly adopted as load carrying components. In the investigations performed here a commercial wrought Ni-base alloy Haynes 230 has been used as substrate for the TBC. As BC a NiCoCrAlY serves as a reference material and in all cases 7% Yttria PS zirconia has been used. Phase development and failure mechanisms in APS TBC during service-like conditions, have been evaluated in the present study. This is done by combinations of thermal cycling and low cycle fatigue tests. The aim is to achieve better knowledge regarding how, when and why thermal barrier coatings fail. As a final outcome of the project a model capable of predicting fatigue life of a given component will help engineers and designers of land based gas turbines for power generation to better optimise TBC's. In the investigations it is seen that TBC life is strongly influenced by oxidation of the BC and interdiffusion between BC and the substrate. The bond coat is known to oxidise with time at high temperature. The initial oxide found during testing is alumina. With increased time at high temperature Al is depleted from the bond coat due to inter-diffusion and oxidation. Oxides others than alumina start to form when the Al content is reduced below a critical limit. It is here believed that spinel appears when the Al content is lowered below 2 w/o in the bond coat. Here it was shown that a faster growing oxide, rich in Ni, Cr and Co forms at the interface. Al depletion is also linked to BC phases. Initially the bond coat is a {gamma}/{beta}-material possibly with very fine dispersed {gamma}. Simultaneously with Al-depletion the {beta}-phase is found to disappear. This occurs simultaneously with the formation of spinel. However, oxidation is not only a disadvantage. Low cycle fatigue tests reveal that oxide streaks within the bond coat will slow down crack growth due to crack deflection and crack branching. Therefore benefit of or damage from oxide growth on crack initiation and propagation is dependent on crack mode, spalling of the ceramic TC or growth of 'classic' cracks perpendicular to the surface. From the observations conclusions are drawn regarding fatigue behaviour of TBC systems. The basic idea is that all cracks leading to failure initiate in the thermally grown oxide. Following the initiation, they can, however, grow to form either delamination cracks leading to top coat spallation or cracks transverse to the surface leading to component failure.

  10. Development of a methodology for on line fatigue life monitoring of nuclear power plant components

    International Nuclear Information System (INIS)

    A methodology has been developed for on line fatigue life monitoring of nuclear power plant components. Green's function technique is used to convert plant data to stress time data. Rainflow cycle counting method is used to compute the fatigue usage factor from stress time history by using material fatigue data. An interactive user friendly graphics code has been developed for updating the stored data and also for retrieving relevant informations by plant operators. (author)

  11. Probabilistic fatigue life of balsa cored sandwich composites subjected to transverse shear

    DEFF Research Database (Denmark)

    Dimitrov, Nikolay Krasimirov; Berggreen, Christian

    2015-01-01

    A probabilistic fatigue life model for end-grain balsa cored sandwich composites subjectedto transverse shear is proposed. The model is calibrated to measured three-pointbending constant-amplitude fatigue test data using the maximum likelihood method. Some possible applications of the probabilistic model are obtaining characteristic SNcurves corresponding to a given survival probability, and calibrating partial safety factorsfor material fatigue. The latter is demonstrated by a calibration perf...

  12. Fatigue, Physical Function and Quality of Life in Relation to Disease Activity in Established Rheumatoid Arthritis

    OpenAIRE

    Barman A; Chatterjee A.; Das KM; Mandal PK; Ghosh A; Ballav A

    2010-01-01

    Objectives: This study was intended to find out therelationship of fatigue, functional disability and Health-Related Quality Of Life (HRQOL) with disease activityin adult patients with active rheumatoid arthritis (RA)and to observe the effect of rehabilitation programme onthese parameters.Material and Methods: 106 patients participated and 96completed the study. Disease Activity Score-28 (DAS-28), visual analogue scale for pain and fatigue,Multidimensional Assessment of Fatigue Scale (MAF),He...

  13. Fatigue service life of transversally cracked reinforced concrete slabs representative of composite bridge decks

    OpenAIRE

    TOUTLEMONDE, F

    2001-01-01

    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 carcked decks, as it occurs due to restrained shrinkage of concrete. The fatigue tests were carried out at LCPC on six instrumented transversally cracked reinforced concrete slabs. 1,4 to 12 million cycles were applied representing more than 100 years of heavy motorway traffic. The onset of fatigue failure of lower transverse reinforcing bars app...

  14. Comparing Fatigue Life Estimations of Composite Wind Turbine Blades using different Fatigue Analysis Tools

    DEFF Research Database (Denmark)

    Ardila, Oscar Gerardo Castro; Lennie, Matthew

    2015-01-01

    In this paper, fatigue lifetime prediction of NREL 5MW reference wind turbine is presented. The fatigue response of materials used in selected blade cross sections was obtained by applying macroscopic fatigue approaches and assuming uniaxial stress states. Power production and parked load cases suggested by the IEC 61400-1 standard were studied employing different load time intervals and by using two novel fatigue tools called ALBdeS and BECAS+F. The aeroelastic loads were defined thought aeroelastic simulations performed with both FAST and HAWC2 tools. The stress spectra at each layer were calculated employing laminated composite theory and beam cross section methods. The Palmgren-Miner linear damage rule was used to calculate the accumulation damage. The theoretical results produced by both fatigue tools proved a prominent effect of analysed design load conditions on the estimated lifetime of the wind turbine blades and are good starting points for future fatigue analysis using other methods.

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

    Science.gov (United States)

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

    2013-02-01

    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.

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

    Science.gov (United States)

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

    2014-01-01

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

  17. Residual stress evaluation and fatigue life prediction in the welded joint by X-ray diffraction

    International Nuclear Information System (INIS)

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

  18. Residual stress evaluation and fatigue life prediction in the welded joint by X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Keun Bong [Korea Electric Power Research Institute, Daejeon (Korea, Republic of); Kim, Jae Hoon [Chungnam National University, Daejeon (Korea, Republic of)

    2009-07-01

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

  19. Surface characterization and influence of anodizing process on fatigue life of Al 7050 alloy

    International Nuclear Information System (INIS)

    Highlights: ? We studied the effect of surface treatments on fatigue behaviour of 7050 alloy. ? Dissolution of constituent particles in pickling solution result in pits formation. ? Decrease is fatigue life caused by anodization is small. ? Multi-site cracks initiation has been observed for pickled and anodized specimens. -- Abstract: The present study investigates the influence of anodizing process on fatigue life of aluminium alloy 7050-T7451 by performing axial fatigue tests at stress ratio 'R' of 0.1. Effects of pre-treatments like degreasing and pickling employed prior to anodizing on fatigue life were studied. The post-exposure surface observations were made by scanning electron microscope (SEM) to characterize the effect of each treatment before fatigue testing. The surface observations have revealed that degreasing did not change the surface topography while pickling solution resulted in the formation of pits at the surface. Energy dispersive spectroscopy (EDS) was used to identify those constituent particles which were responsible for the pits formation. These pits are of primary concern with respect to accelerated fatigue crack initiation and subsequent anodic coating formation. The fatigue test results have shown that pickling process was detrimental in reducing the fatigue life significantly while less decrease has been observed for anodized specimens. Analyses of fracture surfaces of pickled specimens have revealed that the process completely changed the crack initiation mechanisms as compared to non-treated specimens and the crack initiation started at the pits. For most of the anodized specimens, fatigue cracks still initiated at the pits with very few cracks initiated from anodic coating. The decrease in fatigue life for pickled and anodized specimens as compared to bare condition has been attributed to decrease in initiation period and multi-site crack initiations. Multi-site crack initiation has resulted in rougher fractured surfaces for the pickled and anodized specimens as compare to bare specimens tested at same stress levels.

  20. Low-cycle fatigue life of steel P92 under gradual loading

    Science.gov (United States)

    Cie?la, M.; Junak, G.

    2012-05-01

    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.

  1. Low-cycle fatigue life of steel P92 under gradual loading

    International Nuclear Information System (INIS)

    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.

  2. The Relation between Fatigue Severity with Psychological Symptoms and Quality of Life in Multiple Sclerosis

    Directory of Open Access Journals (Sweden)

    Ghasem Salehpoor

    2012-09-01

    Full Text Available Background: Fatigue is one of the most common and disabling symptoms of multiple sclerosis (MS disease. Since fatigue can cause a great deal of problems it create can cause a variety of psychological symptoms particularly depression, anxiety and stress as well, that quality of daily lives, endanger. Thus, the objective of this study was to determine the relation between fatigue severity and psychological symptoms and quality of life in patients with MS.Materials and Methods: In this descriptive-correlational study, 76 patients with MS with a mean age of 34.029.42 (16-58 year, a member of Guilan province MS association, were selected consecutively. At first, all patients completed the questionnaire of demographic information, and then they were evaluated by the Fatigue Severity Scale (Fatigue Severity Scale, depression, anxiety, Stress Scale (depression, anxiety, stress scale-21 and Quality of Life questionnaire (Short Form-36. Results: Correlational analyses indicated a significant association between fatigue severity and patient's age, depression, anxiety and stress (p<0.05 and quality of life (p<0.01, While there were no significant relations between fatigue severity and duration of MS. The results of multiple stepwise regression analysis showed that only the factor of quality of life as a selected variable in final model could explain 27% of the shared variance of fatigue severity results (p=0.002.Conclusion: The findings showed that regardless of other variables, the levels of quality of life are predictor of fatigue severity in patients with MS. Therefore it is suggested in these patients psychotherapy based on improvement of quality of life for decrease of the levels of fatigue be set as the central aim of psychological interventions.

  3. MS quality of life, depression, and fatigue improve after mindfulness training: A randomized trial

    OpenAIRE

    Grossman, P.; Kappos, L; Gensicke, H.; D'Souza, M.; Mohr, D C; Penner, I K; Steiner, C.

    2010-01-01

    Objective: Health-related quality of life (HRQOL) is often much reduced among individuals with multiple sclerosis (MS), and incidences of depression, fatigue, and anxiety are high. We examined effects of a mindfulness-based intervention (MBI) compared to usual care (UC) upon HRQOL, depression, and fatigue among adults with relapsing-remitting or secondary progressive MS.

  4. Fatigue Life Analysis of Tapered Hybrid Composite Flexbeams

    Science.gov (United States)

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

    2002-01-01

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

  5. Evaluation of creep-fatigue life prediction methods for low-carbon/nitrogen-added SUS316

    International Nuclear Information System (INIS)

    Low-carbon/medium nitrogen 316 stainless steel called 316FR is a principal candidate for the high-temperature structural materials of a demonstration fast reactor plant. Because creep-fatigue damage is a dominant failure mechanism of the high-temperature materials subjected to thermal cycles, it is important to establish a reliable creep-fatigue life prediction method for this steel. Long-term creep tests and strain-controlled creep-fatigue tests have been conducted at various conditions for two different heats of the steel. In the constant load creep tests, both materials showed similar creep rupture strength but different ductility. The material with lower ductility exhibited shorter life under creep-fatigue loading conditions and correlation of creep-fatigue life with rupture ductility, rather than rupture strength, was made clear. Two kinds of creep-fatigue life prediction methods, i.e. time fraction rule and ductility exhaustion method were applied to predict the creep-fatigue life. Accurate description of stress relaxation behavior was achieved by an addition of 'viscous' strain to conventional creep strain and only the latter of which was assumed to contribute to creep damage in the application of ductility exhaustion method. The current version of the ductility exhaustion method was found to have very good accuracy in creep-fatigue life prediction, while the time fraction rule overpredicted creep-fatigue life as large as a factor of 30. To make a reliable estimation of the creep damage in actual components, use of ductility exhaustion method is strongly recommended. (author)

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

    International Nuclear Information System (INIS)

    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

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

    Science.gov (United States)

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

    2004-06-01

    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.

  8. Finite Element Based Fatigue Life Prediction of Cylinder Head for Two-Stroke Linear Engine Using Stress-Life Approach

    Directory of Open Access Journals (Sweden)

    M.M. Rahman

    2008-01-01

    Full Text Available This study describes the finite element based fatigue life prediction of cylinder head for a two-stroke free piston linear engine subjected to variable amplitude loading, applicable to electric power generation. A set of aluminum alloys, cast iron and forged steel for cylinder head are considered in this study. The finite element modeling and analysis were performed utilizing the finite element analysis codes. The fatigue life analysis was carried out using finite element based fatigue analysis commercial codes. Fatigue stress-life approach was used when the piston is subjected to variable amplitude at different loading conditions. The effects of mean stress and sensitivity analysis on fatigue life are discussed. From the results, it was shown that the Goodman mean stress correction method is predicted more conservative (minimum life results. It was found to differ significantly the compressive and tensile mean stresses. The compressive mean stress are beneficial however tensile mean stress detrimental to the fatigue life. The effect of materials and components S-N was also investigated and not found to give any large advantages, however the effect of certainty of survival was found to give noticeable advantages and it concluded that the 99.9% are fond to be design criteria. The proposed technique is capable of determining premature products failure phenomena.

  9. Impact of Radiotherapy Treatment on Jordanian Cancer Patients Quality of Life and Fatigue

    Directory of Open Access Journals (Sweden)

    Kholoud Abu Obead

    2013-11-01

    Full Text Available Background: The distressing treatment of cancer whether chemotherapy or radiotherapy is associated with fatigue and has negative impact on patient quality of life (QOL. Objectives: The purposes of this study were to examine the impact of radiotherapy treatment on Jordanian cancer patients QOL and fatigue, and to explore the relationship between fatigue and QOL. Methods: One group quasi-experimental correlational design was used with 82 patients who had been diagnosed with cancer and required radiotherapy treatment. QOL was measured using the Functional Assessment of Cancer Therapy-General (FACT-G. Fatigue was measured using Piper Fatigue Scale (PFS. Data were collected over a period of three months, and analyzed using Pearson Product Moment Correlation, descriptive statistics and paired-sample t-test. Results: Significant differences were found between pre- and post- radiotherapy QOL mean total scores (t=19.3, df=79, P<0.05, as well as physical, emotional, sexual, and functional wellbeing dimensions. Statistically significant differences were found between pre- and post- radiotherapy fatigue mean total scores (t=-8.95, df=79, P<0.05, as well as on behavioral, affective, sensory, and cognitive dimensions of PFS. Quality of life total scores correlated significantly and negatively with total fatigue scores (P<0.01. Conclusions: Exposure of cancer patient to radiotherapy treatment increased their fatigue level and decreased their QOL. Nurses should assess cancer patients before, during, and after their treatment to design proper interventions to reduce fatigue and enhance QOL.

  10. Fatigue, Physical Function and Quality of Life in Relation to Disease Activity in Established Rheumatoid Arthritis

    Directory of Open Access Journals (Sweden)

    Barman A

    2010-04-01

    Full Text Available Objectives: This study was intended to find out therelationship of fatigue, functional disability and Health-Related Quality Of Life (HRQOL with disease activityin adult patients with active rheumatoid arthritis (RAand to observe the effect of rehabilitation programme onthese parameters.Material and Methods: 106 patients participated and 96completed the study. Disease Activity Score-28 (DAS-28, visual analogue scale for pain and fatigue,Multidimensional Assessment of Fatigue Scale (MAF,Health Assessment Questionnaire (HAQ, AmericanCollege of Rheumatology revised criteria for functionalstatus classification, World Health Organization QualityOf Life instrument (WHOQOL-BREF wereadministered. A comprehensive rehabilitation programmecomprising pharmacologic and non-pharmacologic therapywas continued for 6 months.Results: Mean VAS fatigue, DAS28 & HAQ scores were45.68, 5.14 and 1.16 respectively. Significant correlation(Pearsons r =0.82, p<0.05; r=0.75, p<0.05; r=0.85,p=<0.05 between the disease activity and the value ofthe VAS Fatigue, Global Fatigue (MAF and HAQ scorerespectively and inverse co-relation between quality oflife (QOL domain scores and disease activity wereobserved. Similar results were also found in the final visit.Comprehensive rehabilitation reduced the disease activity,fatigue, functional disability and improved QOL.Conclusion: High fatigue level, disability, pain anddecreased QOL characterized RA disease activity.Reduction of DAS, Fatigue, HAQ scores with treatmentimproved QOL.

  11. The effects of fibre architecture on fatigue life-time of composite materials

    DEFF Research Database (Denmark)

    Hansen, Jens Zangenberg; Østergaard, Rasmus

    reinforced composites used for the main laminate of a wind turbine rotor blade, the problem addressed in the present work is the effect of the fibre and fabric architecture on the fatigue life-time under tension-tension loading. Fatigue of composite materials has been a central research topic for the last...... real material samples and numerical simulations. Experimental fatigue tests identify, quantify, and analyse the cause of failure. Different configurations of the fibre architecture are investigated in order to determine and understand the tension-tension fatigue failure mechanisms. A numerical study is...... analyses identify and explain the onset of tension fatigue failure. It is documented that improvements of the fibre architecture and specimen design are needed in order to provide next generation of fatigue resistant composite materials for wind turbine rotor blades....

  12. Fatigue life analysis of die forged railway axle manufactured from C30 steel

    Directory of Open Access Journals (Sweden)

    Libor Trko

    2014-06-01

    Full Text Available With respect to the manufacturing process, different parts of one structural component can have different fatigue properties. In this study, the fatigue life of arailway axle manufactured from C30 steel by die forging is evaluated in the part of the axle bolster and axle body. According to the fatigue test results obtained at high frequency tension - compression fatigue tests (f ? 20 kHz, R=-1, T=205C, due to the higher level of work hardening of the axle bolster, the fatigue strength of material in this part is significantly higher than in the axle body. Different fatigue strength of these parts were observed despite the fact, that results of static tensile tests did not proved any important differences in the ultimate tensile strength, yield point and elongation.

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

    Science.gov (United States)

    Li, Xiaomin; Guo, Haiyan; Meng, Fanshun

    2010-03-01

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

  14. Extreme Environment Damage Index and Accumulation Model for CMC Laminate Fatigue Life Prediction Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Materials Research & Design (MR&D) is proposing in the SBIR Phase II an effort to develop a tool for predicting the fatigue life of C/SiC composite...

  15. Fatigue life prediction of magnetorheological elastomers subjected to dynamic equi-biaxial cyclic loading

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Yanfen, E-mail: yanfen.zhou@mydit.ie [Centre for Elastomer Research, Focas Research Institute, Dublin Institute of Technology, Dublin 8 (Ireland); Jerrams, Stephen [Centre for Elastomer Research, Focas Research Institute, Dublin Institute of Technology, Dublin 8 (Ireland); Betts, Anthony [Applied Electrochemistry Group, Focas Research Institute, Dublin Institute of Technology, Dublin 8 (Ireland); Chen, Lin [Beijing Aeronautical Science and Technology Research Institute, Commercial Aircraft Corporation of China (China)

    2014-08-01

    Prediction of fatigue life is of great significance in ensuring that dynamically loaded rubber components exhibit safety and reliability in service. In this text, the dynamic equi-biaxial fatigue behaviour of magnetorheological elastomer (MREs) using a bubble inflation method is described. Whler (SN) curves for both isotropic and anisotropic MREs were produced by subjecting the compounds to cycling over a range of stress amplitudes (?{sub a}) between 0.75MPa and 1.4MPa. Changes in physical properties, including variation in stressstrain relations and complex modulus (E*) during the fatigue process were analysed. It was found that the complex modulus of MRE samples decreased throughout the entire fatigue test and failure took place at a limiting value of approximately 1.228MPa4.38% for isotropic MREs and 1.29510.33% for anisotropic MREs. It was also determined that a dynamic stored energy criterion can be used as a plausible predictor in determining the fatigue life of MREs. - Highlights: The first Whler curves for MREs subjected to equi-biaxial loading were presented. Anisotropic MREs exhibited higher fatigue resistance than isotropic MREs. There is a limiting value of complex modulus (E*) at which fatigue failure will occur. The dynamic stored energy criterion can be used as a fatigue life predictor.

  16. Fatigue life prediction of magnetorheological elastomers subjected to dynamic equi-biaxial cyclic loading

    International Nuclear Information System (INIS)

    Prediction of fatigue life is of great significance in ensuring that dynamically loaded rubber components exhibit safety and reliability in service. In this text, the dynamic equi-biaxial fatigue behaviour of magnetorheological elastomer (MREs) using a bubble inflation method is described. Wöhler (S–N) curves for both isotropic and anisotropic MREs were produced by subjecting the compounds to cycling over a range of stress amplitudes (σa) between 0.75 MPa and 1.4 MPa. Changes in physical properties, including variation in stress–strain relations and complex modulus (E*) during the fatigue process were analysed. It was found that the complex modulus of MRE samples decreased throughout the entire fatigue test and failure took place at a limiting value of approximately 1.228MPa ± 4.38% for isotropic MREs and 1.295 ± 10.33% for anisotropic MREs. It was also determined that a dynamic stored energy criterion can be used as a plausible predictor in determining the fatigue life of MREs. - Highlights: • The first Wöhler curves for MREs subjected to equi-biaxial loading were presented. • Anisotropic MREs exhibited higher fatigue resistance than isotropic MREs. • There is a limiting value of complex modulus (E*) at which fatigue failure will occur. • The dynamic stored energy criterion can be used as a fatigue life predictor

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

    Science.gov (United States)

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

    2009-07-01

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

  18. A Comparative Study on Fatigue Life Optimization of the Intersection between a Longitudinal and a Webframe

    DEFF Research Database (Denmark)

    Birk-Srensen, Martin

    1996-01-01

    The connection between longitudinals and transverse web frames, is a weak point in the fatigue strength of a ship structure. Moreover it is very expensive to repair fatigue damages in these intersections, and a fatigue analysis for a specific detail was therefore carried out in order to seek to improve the design. A new improved slot for the longitudinal intersection in the web plate is found on the basis of a shape optimization of the conventional slot. The new slot has an unique shape (tongue form) resulting in a stress relaxation around the slot. Both the conventional and the new slot structure were analyzed by FEM followed by fatigue life calculations and subsequently compared. The overall expected fatigue life for the shape optimized slot will increase by approximately 12 %. The results were compared with an another study concerning a slot for a T-longitudinal.

  19. Modeling the effects of control systems of wind turbine fatigue life

    Energy Technology Data Exchange (ETDEWEB)

    Pierce, K.G.; Laino, D.J. [Univ. of Utah, Salt Lake City, UT (United States)

    1996-12-31

    In this study we look at the effect on fatigue life of two types of control systems. First, we investigate the Micon 65, an upwind, three bladed turbine with a simple yaw control system. Results indicate that increased fatigue damage to the blade root can be attributed to continuous operation at significant yaw error allowed by the control system. Next, we model a two-bladed teetered rotor turbine using three different control systems to adjust flap deflections. The first two limit peak power output, the third limits peak power and cyclic power output over the entire range of operation. Results for simulations conducted both with and without active control are compared to determine how active control affects fatigue life. Improvement in fatigue lifetimes were seen for all control schemes, with increasing fatigue lifetime corresponding to increased flap deflection activity. 13 refs., 6 figs., 2 tabs.

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

    OpenAIRE

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

    2006-01-01

    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 and the chemical kinetics of healing. As the healing kinetics are accele...

  1. Span Length Variance Effect on the Fatigue Life of FRP Bridge Deck

    OpenAIRE

    Ki-Tae Park; Young-Jun Yu; Hyunseop Shin

    2013-01-01

    Fiber reinforced composite materials have the merits of light weight and durability for bridge deck and are estimated to be superior in economy to conventional deck materials considering the life-cycle cost of bridge. In this study, fatigue tests were conducted for the span lengths of 2.0?m and 2.5?m in order to investigate the change trend of fatigue characteristics of composite material deck according to the change in the span length. The result showed that the fatigue life rapidly reduces ...

  2. Fatigue Life of High Performance Grout in Dry and Wet Environment for Wind Turbine Grouted Connections

    DEFF Research Database (Denmark)

    Sørensen, Eigil V.

    fatigue life of a high performance cement based grout was tested by dynamic compressive loading of cylindrical specimens at varying levels of cyclic frequency and load. The fatigue tests were performed in two series, one with the specimens tested in air and one with the specimens submerged in water during...... the test. The fatigue life of the grout, in terms of the number of cycles to failure, was found to be significantly shorter when tested in water than when tested in air, particularly at low frequency....

  3. Fatigue life prediction under variable amplitude axialtorsion loading using maximum damage parameter range method

    International Nuclear Information System (INIS)

    This article deals with the problem of multiaxial fatigue life assessment under variable amplitude axialtorsion loading. A maximum damage parameter range (MDPR) reversal counting method is proposed to predict fatigue life under variable amplitude multiaxial loading. First, a multiaxial fatigue damage parameter is selected for a given multiaxial loading time history. Then, a damage parameter range time history can be calculated. Finally, based on the MDPR method, fatigue life can be predicted by correlating with multiaxial fatigue damage model and the MinerPalmgren damage rule. The proposed method is evaluated with experimental data of the 7050-T7451 aluminum alloy and En15R steel under variable amplitude multiaxial loading. The results demonstrated that the proposed method can provide satisfactory prediction. -- Highlights: A maximum damage parameter range (MDPR) reversal counting method is proposed. Fatigue damage parameter will be directly defined as cycle counting parameter. Based on MDPR method, a fatigue life prediction procedure is proposed. The detailed algorithm is proposed. The proposed method can provide satisfactory prediction

  4. Fatigue failure by in-line flow-induced vibration. Fatigue crack detection and fatigue life evaluation

    International Nuclear Information System (INIS)

    The phenomenon of fatigue failure due to In-line flow-induced vibration has been investigated. In the experimental program an induced-vibration experimental set-up involving water flow was developed. This apparatus was used to produce fatigue failure resulting from In-line flow-induced vibration. The fatigue test cylinders were made of medium carbon steel. A small hole was drilled onto the test cylinder surface to localize the fatigue cracking process. A strain histogram recorder was used to acquire the service strain histogram and also to detect any variation in natural frequency. The cumulative fatigue damage, D, as defined by the Modified Miner Rule, was determined by using the strain histogram of the early portion of the test record. The value of D was close to unity in the case of In-line vibration. In contrast, the value of D obtained in a previous investigation for the case of the Cross-flow vibration ranged approximately from 0.2 to 0.8. (author)

  5. Room temperature creep-fatigue response of selected copper alloys for high heat flux applications

    DEFF Research Database (Denmark)

    Li, M.; Singh, B.N.; Stubbins, J.F.

    2004-01-01

    Two copper alloys, dispersion-strengthened CuAl25 and precipitation-hardened CuCrZr, were examined under fatigue and fatigue with hold time loading conditions. Tests were carried out at room temperature and hold times were imposed at maximum tensile and maximum compressive strains. It was found that hold times could be damaging even at room temperature, well below temperatures typically associated with creep. Hold times resulted in shorter fatigue lives in the high cycle fatigue, long life regim...

  6. A methodology for on line fatigue life monitoring : rainflow cycle counting method

    International Nuclear Information System (INIS)

    Green's function technique is used in on line fatigue life monitoring to convert plant data to stress versus time data. This technique converts plant data most efficiently to stress versus time data. To compute the fatigue usage factor the actual number of cycles experienced by the component is to be found out from stress versus time data. Using material fatigue properties the fatigue usage factor is to be computed from the number of cycles. Generally the stress response is very irregular in nature. To convert an irregular stress history to stress frequency spectra rainflow cycle counting method is used. This method is proved to be superior to other counting methods and yields best fatigue estimates. A code has been developed which computes the number of cycles experienced by the component from stress time history using rainflow cycle counting method. This postprocessor also computes the accumulated fatigue usage factor from material fatigue properties. The present report describes the development of a code to compute fatigue usage factor using rainflow cycle counting technique and presents a real life case study. (author). 10 refs., 10 figs

  7. Effect of Defects Distribution on Fatigue Life of Wind Turbine Components

    DEFF Research Database (Denmark)

    Rafsanjani, Hesam Mirzaei; Srensen, John Dalsgaard

    2015-01-01

    The reliability of the component of a wind turbine is often highly dependent on defects introduced during the manufacturing process. In this paper a stochastic model is proposed for modeling these defects and the influence on the fatigue life is considered. Basically the defects assumed distributed by a Poisson process / field where the defects form clusters that consist of a parent defect and related defects around the parent defect. The fatigue life is dependent on the number, type, location and size of the defects in the component and is therefore quite uncertain and needs to be described by stochastic models. In this paper, the Poisson distribution for modeling of defects of component are considered and the surface and sub-surface defects categorized. Furthermore, a model to estimate the probability of failure by fatigue due to the defects is proposed. Moreover, the relation between defect distribution and fatigue life of component explained.

  8. Fatigue life research for the push chain of shearing machine based on ANSYS

    International Nuclear Information System (INIS)

    Combined with the theories of fatigue life prediction, according to the empirical formula S-N curve of parts was estimated, Splitting the push chain of shearing machine into a model of chain axles and external chain plates and a model of inner sleeves and inner chain plates, by using the fatigue analysis module of ANSYS software stress, the fatigue life of the push chain has been analyzed. Stress and fatigue life nephogram of inner sleeve. chain axle, inner chain plate, and external chain plate have also been obtained in this paper. As a result, the area near the hole of chain plate is the vulnerable part of the push chain, and external chain plate can only bear 73594 times of pressure. while inner chain plate can bear 212430 times of pressure. (authors)

  9. FATIGUE LIFE EVALUATION OF SUSPENSION KNUCKLE USING MULTIBODY SIMULATION TECHNIQUE

    OpenAIRE

    A.G.A. Rahman; Rahman, M. M .; M Kamal

    2012-01-01

    Suspension is part of automotive systems, providing both vehicle control and passenger comfort. The knuckle is an important part within the suspension system, constantly encountering the cyclic loads subjecting it to fatigue failure. This paper presents an evaluation of the fatigue characteristics of a knuckle using multibody simulation (MBS) techniques. Load time history extracted from the MBS is used for stress analysis. An actual road profile of road bumps was used as the input to MBS. The...

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

    Science.gov (United States)

    Everett, Richard A., Jr.

    2004-01-01

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

  11. Influence of initial heat treatment on the fatigue life of austenitic FeNi alloy

    Directory of Open Access Journals (Sweden)

    K.J. Ducki

    2008-02-01

    Full Text Available Purpose: The paper addresses the problem of determining the dependence between initial heat treatment of anaustenitic FeNi alloy and its mechanical properties and fatigue life at room temperature.Design/methodology/approach: For the investigated FeNi alloy after solution heat treatment, two variantsof specimen ageing were applied for comparison, i.e. typical single-stage ageing and novel two-stage ageing.Specimens that underwent heat treatment were subjected to a static tensile test and low-cycle fatigue tests (LCF,carried out at room temperature.Findings: It has been found that, the specimens of FeNi alloy after two-stage ageing are distinguished by higherstrength properties with a little lower plastic properties. In a case of low-cycle fatigue tests, specimens after singlestageageing were characterized by higher fatigue life. Lower fatigue life of the alloy after two-stage ageing canbe explained by increased brittleness of material in boundary areas.Practical implications: The fatigue life results obtained in LCF conditions can be used in predicting theduration of operation of products made out of FeNi alloy at room temperature.Originality/value: The significance of the applied ageing variants effect on the mechanical properties andfatigue life of the tested austenitic FeNi alloy is shown in the paper.

  12. Low cycle fatigue life of two nickel-base casting alloys in a hydrogen environment

    International Nuclear Information System (INIS)

    Results of low cycle fatigue tests on alloy Mar-M-246 and Inconel 713 are presented. Based on the limited data, it was concluded that the Mar-M-246 material had a cyclic life in hydrogen that averaged three times higher than the alloy 713LC material for similar strain ranges. The hydrogen environment reduced life for both materials. The life reduction was more than an order of magnitude for the 713LC material. Porosity content of the cast specimens was as expected and was an important factor governing low cycle fatigue life

  13. Effects of microstructural inclusions on fatigue life of polyether ether ketone (PEEK).

    Science.gov (United States)

    Simsiriwong, Jutima; Shrestha, Rakish; Shamsaei, Nima; Lugo, Marcos; Moser, Robert D

    2015-11-01

    In this study, the effects of microstructural inclusions on fatigue life of polyether ether ketone (PEEK) was investigated. Due to the versatility of its material properties, the semi-crystralline PEEK polymer has been increasingly adopted in a wide range of applications particularly as a biomaterial for orthopedic, trauma, and spinal implants. To obtain the cyclic behavior of PEEK, uniaxial fully-reversed strain-controlled fatigue tests were conducted at ambient temperature and at 0.02 mm/mm to 0.04 mm/mm strain amplitudes. The microstructure of PEEK was obtained using the optical and the scanning electron microscope (SEM) to determine the microstructural inclusion properties in PEEK specimen such as inclusion size, type, and nearest neighbor distance. SEM analysis was also conducted on the fracture surface of fatigue specimens to observe microstructural inclusions that served as the crack incubation sites. Based on the experimental strain-life results and the observed microstructure of fatigue specimens, a microstructure-sensitive fatigue model was used to predict the fatigue life of PEEK that includes both crack incubation and small crack growth regimes. Results show that the employed model is applicable to capture microstructural effects on fatigue behavior of PEEK. PMID:26301567

  14. Analysis of Impact Fatigue Life for Valve Leaves in Small Hermetic Reciprocating Compressors

    Directory of Open Access Journals (Sweden)

    Dong Zhang

    2013-07-01

    Full Text Available Impact fatigue life of valve leaves has great influence on energy saving performance and lifetime of small hermetic reciprocating compressors. This paper presented a test system that intended to analysis and evaluate of impact fatigue life of valve leaves used in small hermetic reciprocating compressors. Firstly, an incentive system was designed to simulate real work condition for valve leaf. Then, a data acquisition system was built to collect the sound signal while valve leaf was being under test. Simultaneously, the system could control the working state of incentive system so that test could be terminated automatically once fatigue was detected. Finally, fatigue detection system was designed to detect fatigue of valve leaf. Fatigue detection was the key point of this test system. Fast Fourier Transform (FFT and Wavelet Packet Transform (WPT were applied to analyze sound signal, both of which were effective in detecting the damage through analyzing. Facts showed that the test system provided a feasible approach to evaluate impact fatigue life for valve leaf manufacturing.

  15. Fatigue failure by in-line flow-induced vibration and fatigue life evaluation

    International Nuclear Information System (INIS)

    The phenomenon of fatigue failure due to In-line flow-induced vibration has been investigated. In the experimental program an induced-vibration experimental set-up involving water flow was developed. This apparatus was used to produce fatigue failure resulting from In-line flow-induced vibration. The fatigue specimens were made of a medium carbon steel. A small hole was drilled into the specimen surface to localize the fatigue cracking process. A strain histogram recorder (Mini Rainflow Corder, MRC) was used to acquire the service strain histogram and also to detect any variations in natural frequency. The cumulative fatigue damage, D, as defined by the Modified Miner Rule, was determined by using the strain histogram of the early portion of the test record. The value of D was almost unity in the case of In-line vibration. In contrast, the value of D obtained in a previous investigation for the case of the Cross-flow vibration ranged approximately from 0.2 to 0.8. (author)

  16. Fatigue

    Science.gov (United States)

    ... sleep. Fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of not caring ... and drink plenty of water throughout the day. Exercise regularly. Learn better ways to relax. Try yoga ...

  17. Time and frequency domain models for multiaxial fatigue life estimation under random loading

    Directory of Open Access Journals (Sweden)

    Andrea Carpinteri

    2015-07-01

    Full Text Available Engineering structures and components are often subjected to random fatigue loading produced, for example, by wind turbulences, marine waves and vibrations. The methods available in the literature for fatigue assessment under random loading are formulated in time domain or, alternatively, in frequency domain. The former methods require the knowledge of the loading time history, and a large number of experimental tests/numerical simulations is needed to obtain statistically reliable results. The latter methods are generally more advantageous with respect to the time domain ones, allowing a rapid fatigue damage evaluation. In the present paper, a multiaxial criterion formulated in the frequency-domain is presented to estimate the fatigue lives of smooth metallic structures subjected to combined bending and torsion random loading. A comparison in terms of fatigue life prediction by employing a time domain methods, previously proposed by the authors, is also performed.

  18. A methodology for on-line fatigue life monitoring of Indian nuclear power plant components

    International Nuclear Information System (INIS)

    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 support future life extension program of a plant. In the present report a methodology is being proposed for monitoring on line fatigue life of nuclear power plant components using available plant instrumentations. Major factors affecting fatigue life of a nuclear power plant components are the fluctuations of temperature, pressure and flow rate. Green's function technique is used in on line fatigue monitoring as computation time is much less than finite element method. A code has been developed which computes temperature and stress Green's functions in 2-D and axisymmetric structure by finite element method due to unit change in various fluid parameters. A post processor has also been developed which computes the temperature and stress responses using corresponding Green's functions and actual fluctuation in fluid parameters. In this post processor, the multiple site problem is solved by superimposing single site Green's function technique. It is also shown that Green's function technique is best suited for on line fatigue life monitoring of nuclear power plant components. (author). 6 refs., 43 figs

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

    Science.gov (United States)

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

    2013-07-01

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

  20. Quality of life in multiple sclerosis association with clinical features, fatigue and depressive syndrome

    Directory of Open Access Journals (Sweden)

    ?abuz-Roszak, Beata

    2013-06-01

    Full Text Available Introduction. The aim of the study was to assess the health related quality of life in patients suffering from multiple sclerosis (MS in association with clinical features, fatigue and depressive symptoms. Methods. The examined group consisted of 61 patients (45 women and 16 men in the mean age of 38.611.4. The mean duration of disease was 7.16.1 years. The control group consisted of 30 healthy volunteers. The following questionnaires were used: EuroQol (EQ5D with visual scale EuroQol-VAS, Modified Impact Fatigue Scale (MIFS and Beck Depression Inventory (BDI. Results. The quality of life in the examined group of MS patients was significantly lower in comparison to the control group. Results of EQ-5D and EQ-VAS were influenced by age, disease course, level of disability and carried treatment. Statistically significant association was also found between results of the questionnaires assessing quality of life and either fatigue or depressive symptoms. Conclusion. The used questionnaires confirmed that quality of life in patients with MS is significantly worse, especially in the older people with secondary progressive course of the disease, more disable and not treated. Presence of fatigue and depressive symptoms influenced the self-assessment of quality of life. Complex care of MS patient should consider diagnosis and treatment of fatigue and depression which could improve their quality of life.

  1. The effects of fibre architecture on fatigue life-time of composite materials

    DEFF Research Database (Denmark)

    Hansen, Jens Zangenberg

    2013-01-01

    Wind turbine rotor blades are among the largest composite structures manufactured of fibre reinforced polymer. During the service life of a wind turbine rotor blade, it is subjected to cyclic loading that potentially can lead to material failure, also known as fatigue. With reference to glass fibre reinforced composites used for the main laminate of a wind turbine rotor blade, the problem addressed in the present work is the effect of the fibre and fabric architecture on the fatigue life-time under tension-tension loading. Fatigue of composite materials has been a central research topic for the last decades; however, a clear answer to what causes the material to degrade, has not been given yet. Even for the simplest kind of fibre reinforced composites, the axially loaded unidirectional material, the fatigue failure modes are complex, and require advanced experimental techniques and characterisation methodologies in order to be assessed. Furthermore, numerical evaluation and predictions of the fatigue damage evolution are decisive in order to make future improvements. The present work is focused around two central themes: fibre architecture and fatigue failure. The fibre architecture is characterised using real material samples and numerical simulations. Experimental fatigue tests identify, quantify, and analyse the cause of failure. Different configurations of the fibre architecture are investigated in order to determine and understand the tension-tension fatigue failure mechanisms. A numerical study is used to examine the onset of fatigue failure. Topics treated include: experimental fatigue investigations, scanning electron microscopy, numerical simulations, advanced measurements techniques (micro computed tomography and thermovision), design of test specimens and preforms, and advanced materials characterisation. The results of the present work show that the fibre radii distribution has limited effect on the fibre architecture. This raises the question of which fibre radii distribution ensures optimum mechanical properties, damage tolerance, and fatigue performance. The experimental fatigue results and analyses identify and explain the onset of tension fatigue failure. It is documented that improvements of the fibre architecture and specimen design are needed in order to provide next generation of fatigue resistant composite materials for wind turbine rotor blades.

  2. A comparison of some methods to estimate the fatigue life of plain dents

    Energy Technology Data Exchange (ETDEWEB)

    Martins, Ricardo R.; Noronha Junior, Dauro B. [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil)

    2009-12-19

    This paper describes a method under development at PETROBRAS R and D Center (CENPES) to estimate the fatigue life of plain dents. This method uses the API Publication 1156 as a base to estimate the fatigue life of dome shaped plain dents and the Pipeline Defect Assessment Manual (PDAM) approach to take into account the uncertainty inherent in the fatigue phenomenon. CENPES method, an empirical and a semi-empirical method available in the literature were employed to estimate the fatigue lives of 10 plain dents specimens of Year 1 of an ongoing test program carried out by BMT Fleet Technology Limited, with the support of the Pipeline Research Council International (PRCI). The results obtained with the different methods are presented and compared. Furthermore some details are given on the numerical methodology proposed by PETROBRAS that have been used to describe the behavior of plain dents. (author)

  3. Fatigue life estimates for a notched member in a corrosive environment

    International Nuclear Information System (INIS)

    It is often assumed that the effects of an aggressive environment can be included in fatigue life estimation procedures by determining the material properties in the environment and at the frequency of interest. An analytical and experimental program was conducted to confirm or refute this assumption. Automotive grade aluminum alloy, 5454-H32, in 3 percent NaCl solution and laboratory environment was selected for this study. A simple model where the total fatigue life is the summation of the portion where fatigue damage is best described by the notch strain field, and the portion where nominal stress and crack length dominate damage assessment, was used to estimate fatigue lives for center notched plates. Smooth cylindrical specimens were employed to determine the material properties for initiation

  4. Elliptical exercise improves fatigue ratings and quality of life in patients with multiple sclerosis

    Directory of Open Access Journals (Sweden)

    Jessie M. Huisinga, PhD

    2011-08-01

    Full Text Available Fatigue, reduced quality of life (QOL, and lower physical activity levels are commonly reported in patients with multiple sclerosis (MS. This study evaluated the effects of elliptical exercise on fatigue and QOL reports in patients with MS. Patients with MS (n = 26 completed the Fatigue Severity Scale (FSS, the Modified Fatigue Impact Scale (MFIS, and the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36 before and after completing 15 elliptical exercise training sessions. Changes in fatigue and QOL were assessed based on any changes in the fatigue and SF-36 questionnaires, and correlations between changes in each of the scales were made to determine whether a relationship was present between the fatigue and QOL measures. Results showed significant improvement in FSS, MFIS, and five SF-36 subscales as a result of elliptical exercise. The change in FSS correlated with change in two of the SF-36 subscales. Elliptical exercise for patients with MS results in significant improvements in both fatigue and QOL. These findings indicate that regular elliptical exercise could be a part of inpatient and outpatient MS rehabilitation programs.

  5. Fatigue life prediction in composites using progressive damage modelling under block and spectrum loading

    DEFF Research Database (Denmark)

    Passipoularidis, Vaggelis; Philippidis, T.P.

    2010-01-01

    A progressive damage fatigue simulator for variable amplitude loads named FADAS is discussed in this work. Fatigue Damage Simulator (FADAS) performs ply by ply stress analysis using classical lamination theory and implements adequate stiffness discount tactics based on the failure criterion of Puck, to model the degradation caused by failure events in ply level. Residual strength is incorporated as fatigue damage accumulation metric. Once the typical fatigue and static properties of the constitutive ply are determined, the performance of an arbitrary lay-up under uniaxial and/or multi-axial load time series can be simulated. The predictions are validated against fatigue life data both from repeated block tests at a single stress ratio as well as against spectral fatigue using the WISPER, WISPERX and NEW WISPER load sequences on a Glass/Epoxy multidirectional laminate typical of a Wind Turbine Rotor Blade construction. Two versions of the algorithm, the one using single-step and the other using incremental application of each load cycle (in case of ply failure) are implemented and compared. Simulation results confirm the ability of the algorithm to take into account load sequence effects. In general, FADAS performs well in predicting life under both spectral and block loading fatigue.

  6. The fatigue life and fatigue crack through thickness behavior of a surface cracked plate, 2

    International Nuclear Information System (INIS)

    Most structures have a region where stresses concentrate, and the probability of fatigue crack initiation may be higher than in other parts. Therefore, to improve the reliability of an LBB design, it is necessary to evaluate the growth and through thickness behavior of fatigue cracks in the stress concentration part. In this paper, a fatigue crack growth test at a stress concentration region has been made on 3 % NiCrMo and HT 80 steel. Stress concentration is caused by a fillet on the plate. The main results obtained are as follows : (1) Before cracking through the plate thickness, stress concentration has a remarkable effect on the fatigue crack growth behavior and it flatens the shape of a surface crack. The crack growth behavior can be explained quantatively by using the Newman-Raju equation and the stress resolving method proposed by ASME B and P Code SecXI. (2) The da/dN-?K relation obtained in a stress concentration specimen shows good agreement with that obtained in a surface cracked smooth specimen. (3) It is shown that stress concentration caused by a fillet has little effect on the crack growth rate after cracking through the plate thickness. (4) By using the K value based on eq. (1), (2), particular crack growth behavior and the change in crack shape after cracking through thickness can be explained quantatively. (author)

  7. Fatigue failure by in-line flow-induced vibration and fatigue life evaluation

    International Nuclear Information System (INIS)

    The phenomenon of fatigue failure by the In-line flow-induced vibration was studied. A newly water-flow-induced vibration system was made and used to reproduce fatigue failure by flow-induced vibration. A medium carbon steel specimen was fixed to the experimental equipment. A small artificial hole was introduced onto the specimen surface. Fatigue crack initiated from the artificial hole. A small portable strain histogram recorder (Mini Rainflow Corder, MRC) developed in another project of the authors' team was used to acquire the service strain hisogram at a critical point of the specimen and to measure the variation of natural frequency. Cumulative fatigue damage D defined by the Modified Miner Rule was calculated by using the strain histogram at the initial stage of test. The value of D was almost unity in the case of In-line vibration, while the values of D in the case of the Cross-flow vibration ranged from 0.2 to 0.8. (author)

  8. Effects of variable loading on residual fatigue life of the railway wheelset.

    Czech Academy of Sciences Publication Activity Database

    Pokorn, Pavel; Nhlk, Lubo; ev?k, Martin; Huta?, Pavel

    Zurich : Trans Tech Publications, 2014 - (Milazzo, A.; Aliabadi, M.), s. 121-124 ISBN 978-3-03785-830-1. ISSN 1013-9826. - (Key Engineering Materials. 577-578). [FDM 2013 - International Conference on Fracture and Damage Mechanics /12./. Sardinia (IT), 17.09.2013-19.09.2013] R&D Projects: GA Mk(CZ) EE2.3.20.0214 Grant ostatn: VUT(CZ) FSIJ- 13-2046 Institutional support: RVO:68081723 Keywords : variable amplitude loading * residual fatigue life * generalized Willenborg model * fatigue crack * railway wheelset Subject RIV: JL - Materials Fatigue, Friction Mechanics

  9. Probabilistic Modelling of Fatigue Life of Composite Laminates Using Bayesian Inference

    DEFF Research Database (Denmark)

    Dimitrov, Nikolay Krasimirov; Kiureghian, Armen Der

    2014-01-01

    A probabilistic model for estimating the fatigue life of laminated composite plates subjected to constant-amplitude or variable-amplitude loading is developed. The model is based on lamina-level input data, making it possible to predict fatigue properties for a wide range of laminate configurations. Model parameters are estimated by Bayesian inference. The reference data used consists of constant-amplitude fatigue test results for a multi-directional laminate subjected to seven different load ratios. The paper describes the modelling techniques and the parameter estimation procedure, supported by an illustrative application and result assessment.

  10. Fatigue Life of High Performance Grout for Wind Turbine Grouted Connection in Wet or Dry Environment

    DEFF Research Database (Denmark)

    Srensen, Eigil V.; Westhof, Luc; Yde, Elo; Serednicki, Andrzej

    Grouted connections of monopile supported offshore wind turbine structures are subjected to loads leading to very high oscillating service stresses in the grout material. The fatigue capacity of a high performance cement based grout was tested by dynamic compressive loading of cylindrical specimens...... at varying levels of cyclic frequency and load. The fatigue tests were performed in two series: one with the specimens in air and one with the specimens submerged in water during the test. The fatigue life of the grout, in terms of the number of cycles to failure, was found to be significantly...

  11. Evaluation of Fatigue Life of Semiconductor Power Device by Power Cycle Test and Thermal Cycle Test Using Finite Element Analysis

    OpenAIRE

    Kazunori Shinohara; Qiang Yu

    2010-01-01

    To accurately predict the fatigue life of a power device, a fatigue life evaluation method that is based on the power cycle is presented in terms of an algorithm based on a combination of electrical analysis, heat analysis, and stress analysis. In literature, the fatigue life of power devices has been evaluated on the basis of the thermal cycle. This cycle is alternately repeated within a range from a high temperature to a low temperature. In an actual operating environment, however, a power ...

  12. Mean load effects on the fatigue life of offshore wind turbine monopile foundations

    DEFF Research Database (Denmark)

    Blasques, Jos Pedro Albergaria Amaral; Natarajan, Anand

    This paper discusses the importance of mean load effects on the estimation of the fatigue damage in offshore wind turbine monopile foundations. The mud line bending moment time series are generated using a fully coupled aero-hydro-elastic model accounting for non-linear water waves and sea current...... of the fatigue life of offshore wind turbine monopile foundations. Moreover, it is shown that a nonlinear hydrodynamic model is required in order to correctly account for the effect of the current....

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

    OpenAIRE

    Helmerich, Rosemarie; Khn, Bertram; Nussbaumer, Alain

    2007-01-01

    In many countries and regions, traffic infrastructure projects suffer from low funding. The budget is tight for new infrastructure building and, thus, the importance of inspection, maintenance and assessment of the existing traffic infrastructure increases. A new fatigue assessment guideline for the estimation of the remaining fatigue life of steel bridges has been written by technical committee 6 from ECCS. It will be a useful tool for the complementation of bridge management systems, used c...

  14. Effect of V Notch Shape on Fatigue Life in Steel Beam Made of AISI 1037

    Directory of Open Access Journals (Sweden)

    Qasim Bader

    2014-04-01

    Full Text Available The present work encompasses effect of V notch shape with various geometries and dimensions on fatigue life behavior in steel beam made of Medium Carbon Steel AISI 1037 which has a wide application in industry. Fatigue life of notched specimens is calculated using the fatigue life obtained from the experiments for smooth specimens (reference and by use Numerical method (FEA.The fatigue experiments were carried out at room temperature, applying a fully reversed cyclic load with the frequency of (50Hz and mean stress equal to zero (R= -1, on a cantilever rotating-bending fatigue testing machine. The stress ratio was kept constant throughout the experiment. Different instruments have been used in this investigation like Chemical composition analyzer type (Spectromax ,Tensile universal testing machine type (WDW-100E ,Hardness tester type (HSV- 1000 , Fatigue testing machine model Gunt WP 140, Optical Light Microscope (OLM and Scanning Electron Microscope (SEM were employed to examine the fracture features . The results show that there is acceptable error between experimental and numerical works .

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

    Directory of Open Access Journals (Sweden)

    Esmaeili F.

    2010-06-01

    Full Text Available 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.

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

    Science.gov (United States)

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

    2010-06-01

    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.

  17. Improvement of fatigue life of an aluminum alloy by overstressing

    Science.gov (United States)

    STRICKLEY G W

    1942-01-01

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

  18. Fatigue life prediction of fiber reinforced concrete under flexural load

    DEFF Research Database (Denmark)

    Zhang, Jun; Stang, Henrik; Li, Victor

    1999-01-01

    This paper presents a semi-analytical method to predict fatigue behavior in flexure of fiber reinforced concrete (FRC) based on the equilibrium of force in the critical cracked section. The model relies on the cyclic bridging law, the so-called stress-crack width relationship under cyclic tensile...... load as the fundamental consitutive relationship in tension....

  19. Load Identification of Offshore Platform for Fatigue Life Estimation

    DEFF Research Database (Denmark)

    Perisic, Nevena; Kirkegaard, Poul Henning; Tygesen, Ulf T.

    The lifetime of an offshore platform is typically governed by accumulated fatigue damage. Thus, the load time history is an essential parameter for prediction of the lifetime of the structure and its components. Consequently, monitoring of structural loads is of special importance in relation to re...

  20. Fatigue life prediction of fiber reinforced concrete under flexural load

    DEFF Research Database (Denmark)

    Zhang, Jun; Stang, Henrik; Li, Victor

    1999-01-01

    This paper presents a semi-analytical method to predict fatigue behavior in flexure of fiber reinforced concrete (FRC) based on the equilibrium of force in the critical cracked section. The model relies on the cyclic bridging law, the so-called stress-crack width relationship under cyclic tensile load as the fundamental consitutive relationship in tension.

  1. The impact of hysteresis shape on failure mechanisms and the endurance fatigue life of ductile materials subject to high-temperature fatigue stressing

    International Nuclear Information System (INIS)

    The paper discusses the various effects of load cycle shape and load cycle duration on the fatigue damage and thus on the endurance fatigue life of a material. The author illustrates his point by explaining experiments with two high-temperature alloys 800H and 617, which cannot be age-hardened or only slightly. (orig.)

  2. Application of the strain energy for fatigue life prediction (LCF) of metals by the energy-based criterion

    International Nuclear Information System (INIS)

    Full text: In this study, the plastic strain energy under multiaxial fatigue condition has been calculated in the cyclic plasticity models by the stress-strain hysteresis loops. Then, using the results of these models, the fatigue lives in energy-based fatigue model is predicted and compared to experimental data. Moreover, a weighting factor on shear plastic work is presented to decrease the life factors in the model fatigue. (author)

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

    Science.gov (United States)

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

    2002-01-01

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

  4. Fatigue and Quality of Life of Women Undergoing Chemotherapy or Radiotherapy for Breast Cancer

    Directory of Open Access Journals (Sweden)

    Winnie K.W.So

    2009-06-01

    Full Text Available OBJECTIVE To examine fatigue and quality of life (QOL in breast cancer patients undergoing chemotherapy or radiotherapy.METHODS A self-report survey derived from the Chinese version of Brief Fatigue Inventory, the Functional Assessment of Chronic Illness Therapy for Breast Cancer, and the Medical Outcomes Study Social Support Survey. Descriptive statistics was used to examine the intensity of fatigue and the prevalence of severe fatigue. Multivariate analysis of variance was used to determine factors that a ff ect the fi ve domains of QOL among the participants.RESULTS The majority of the participants ( n = 261 perceived a mild level of fatigue, but 35.6% of them suff ered severe fatigue. Fatigue had a significantly negative association with all domains of QOL except social/family wellbeing. The participants who were receiving chemotherapy, undergoing curative treatment and having inadequate social support were more likely to have poorer QOL in all five domains (after adjustment for age. CONCLUSION Although the majority of the participants experienced a mild level of fatigue, there was a substantial group of breast cancer patients who perceived their fatigue as severe. The findings of this study showed that fatigue had a detrimental effect on the various aspects of the participants QOL. Demographic and clinical characteristics of breast cancer patients who were at risk of getting poorer QOL were identified. The results of the study demonstrate that we should enhance healthcare professionals awareness of the importance of symptom assessment, and provide them with information for planning effective symptom-management strategies among this study population.

  5. Prevalence of fatigue in patients with multiple sclerosis and its effect on the quality of life

    Science.gov (United States)

    Nagaraj, Karthik; Taly, Arun B.; Gupta, Anupam; Prasad, Chandrajit; Christopher, Rita

    2013-01-01

    Objective: This prospective study was carried out to observe the prevalence of fatigue in patients with multiple sclerosis (MS) and its effect on quality-of-life (QoL). Study Design and Setting: Prospective observational study in a University Tertiary Research Hospital in India. Patients and Methods: A total of 31 patients (25 females) with definite MS according to McDonald's criteria presented in out-patient/admitted in the Department of Neurology (between February 2010 and December 2011) were included in the study. Disease severity was evaluated using the Kurtzke's expanded disability status scale (EDSS). Fatigue was assessed using Krupp's fatigue severity scale (FSS). QoL was assessed by the World Health Organization QoL-BREF questionnaire. Results: The mean age of patients was 30.1 9.1 years. The mean age at first symptom was 25.23 6.4 years. The mean number of relapses was 4.7 3.6 in the patients. The mean duration of illness was 4.9 4.4 years. The mean EDSS score was 3.5 2.2. Mean fatigue score was 38.7 18.5 (cut-off value 36 in FSS). The prevalence of fatigue in patients with MS was 58.1% (18/31). MS patients with fatigue were significantly more impaired (P < 0.05) on all QoL domains (i.e., physical, psychosocial, social, and environment) than MS patients without fatigue. Conclusion: Prevalence of fatigue was found to be high in the MS patients in the study. All four domains of QoL were significantly more impaired in the group with fatigue than in those without fatigue. PMID:24250159

  6. Prevalence of fatigue in patients with multiple sclerosis and its effect on the quality of life

    Directory of Open Access Journals (Sweden)

    Karthik Nagaraj

    2013-01-01

    Full Text Available Objective: This prospective study was carried out to observe the prevalence of fatigue in patients with multiple sclerosis (MS and its effect on quality-of-life (QoL. Study Design and Setting: Prospective observational study in a University Tertiary Research Hospital in India. Patients and Methods: A total of 31 patients (25 females with definite MS according to McDonald?s criteria presented in out-patient/admitted in the Department of Neurology (between February 2010 and December 2011 were included in the study. Disease severity was evaluated using the Kurtzke?s expanded disability status scale (EDSS. Fatigue was assessed using Krupp?s fatigue severity scale (FSS. QoL was assessed by the World Health Organization QoL-BREF questionnaire. Results: The mean age of patients was 30.1 9.1 years. The mean age at first symptom was 25.23 6.4 years. The mean number of relapses was 4.7 3.6 in the patients. The mean duration of illness was 4.9 4.4 years. The mean EDSS score was 3.5 2.2. Mean fatigue score was 38.7 18.5 (cut-off value 36 in FSS. The prevalence of fatigue in patients with MS was 58.1% (18/31. MS patients with fatigue were significantly more impaired (P < 0.05 on all QoL domains (i.e., physical, psychosocial, social, and environment than MS patients without fatigue. Conclusion: Prevalence of fatigue was found to be high in the MS patients in the study. All four domains of QoL were significantly more impaired in the group with fatigue than in those without fatigue.

  7. Practical methodology to evaluate the fatigue life of seam welded joints

    Directory of Open Access Journals (Sweden)

    K.C.Goes

    2011-11-01

    Full Text Available Purpose: of this paper is to present a practical and robust methodology developed to evaluate the fatigue life of seam welded joints under combined cyclic loading.Design/methodology/approach: Fatigue analysis was conducted in virtual environment. The finite element stress results from each loading were imported to fatigue code FE-Fatigue and combined to perform the fatigue life prediction using the S x N (stress x life method. A tube-to-plate specimen was submitted to a combined cyclic loading (bending and torsion with constant amplitude. The virtual durability analysis result was calibrated based on these laboratory tests and design codes such as BS7608 and Eurocode 3. The feasibility and application of the proposed numerical-experimental methodology and contributions for the technical development are discussed. Major challenges associated with this modelling and improvement proposals are finally presented.Findings: The finite element model was validated due to laboratory results. The analytical stress result presented upper value due to the approach used that considered the fillet weld supported all work. The model presented a good representation of failure and load correlation.Research limitations/implications: The measurement or modelling of the residual stresses resulting from the welding process was not included in this work. However, the thermal and metallurgical effects, such as distortions and residual stresses, were considered indirectly with regard to the corrections performed in the fatigue curves obtained from the investigated samples.Practical implications: Integrating fatigue analysis and finite elements, it is possible to analyse several welded joint configurations in the design phase, providing development time and cost reduction, increasing the project reliability.Originality/value: This methodology will permit, in further studies, the modelling of both stresses, in-service and residual stresses, acting together, which seem like an advantage to engineers and researchers who work in design and evaluation of structural components against fatigue failures.

  8. Statistical analysis of manufacturing defects on fatigue life of wind turbine casted Component

    DEFF Research Database (Denmark)

    Rafsanjani, Hesam Mirzaei; Srensen, John Dalsgaard

    2014-01-01

    Wind turbine components experience heavily variable loads during its lifetime and fatigue failure is a main failure mode of casted components during their design working life. The fatigue life is highly dependent on the microstructure (grain size and graphite form and size), number, type, location and size of defects in the casted components and is therefore rather uncertain and needs to be described by stochastic models. Uncertainties related to such defects influence prediction of the fatigue strengths and are therefore important in modelling and assessment of the reliability of wind turbine components. The defect distribution is usually affected by the manufacturing process. In this paper, two methods of casting, sand casting and chill casting are considered. These are compared in statistical analyses of a large number of representative test samples using two basic stochastic models for the fatigue life, namely LogNormal and Weibull distributions. The statistical analyses are performed using the Maximum Likelihood Method and the statistical uncertainty is estimated. Further, stochastic models for the fatigue life obtained from the statistical analyses are used for illustration to assess the reliability of a representative component in an offshore wind turbine.

  9. SOURCES OF DIFFERENCES IN CALCULATIONS AND EXPERIMENTAL TEST RESULTS OF FATIGUE LIFE OF STRUCTURAL ELEMENTS

    Directory of Open Access Journals (Sweden)

    Jzef SZALA

    2014-06-01

    Full Text Available Calculation results are the base for evaluation of fatigue life of structural elements during machine design processes. It results from the fact that there are no material objects in the phase of existence of a product. Reliability of tests results is an essential element in the calculation fatigue life evaluation method and it can be evaluated by comparison of the results with experimental ones. In the paper there was performed an analysis of the chosen factors essentially influencing conformity of calculation results and experimental test ones connected with basic elements of a calculation algorithm including: - elaboration and analysis of service loadings of a structural element, - determination and analysis of cyclic properties of structural elements, - selection of fatigue damage accumulation hypothesis being a description of fatigue life processes. The mentioned analysis was illustrated with examples of fatigue life tests performed in the Machine Design Department of the University of Technology and Agriculture within the research grant no. 2221/B/T02/2010/39 financed by The Ministry of Science and Higher Education and National Science Centre.

  10. Reduction factors for creep strength and fatigue life of modified 9 Cr-1 Mo steel weldments

    International Nuclear Information System (INIS)

    The provisions of ASME B ampersand PV Code Case N-47 currently include reduction factors for creep strength and fatigue life of weldments. To provide experimental confirmation of such factors for modified 9 Cr-1 Mo steel, tests of tubular specimens were conducted at 538 degree C (1000 degree F). Three creep-rupture specimens with longitudinal welds were tested in tension; and, of three with circumferential welds, two were tested in tension and one in torsion. In each specimen with a circumferential weld, a nonuniform axial distribution of strain was easily visible. The test results were compared to an existing empirical model of creep-rupture life. For the torsion test, the comparison was based on a definition of equivalent normal stress recently adopted in Code Case N-47. Some 27 fatigue specimens, with longitudinal, circumferential, or no welds, were tested under axial or torsional strain control. In specimens with welds, fatigue cracking initiated at fusion lines. In axial tests cracks grew in the circumferential direction, and in torsional tests cracks grew along fusion lines. The test results were compared to empirical models of fatigue life based on two definition of equivalent normal strain range. The results have provided some needed confirmation of the reduction factors for creep strength and fatigue life of modified 9 Cr-1 Mo steel weldments currently under consideration by ASME Code committees. 8 refs., 5 figs

  11. Effects of High Temperature Exposures on Fatigue Life of Disk Superalloys

    Science.gov (United States)

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

    2004-01-01

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

  12. Fatigue and depression in multiple sclerosis: Correlation with quality of life

    Directory of Open Access Journals (Sweden)

    Mileti? Svetlana

    2011-01-01

    Full Text Available The aim of this work was to examine the relationship between fatigue and depression, common features of multiple sclerosis (MS, and the quality of life (QOL. The study was comprised of 120 patients with clinical manifestations of definite MS. Relapsing-remitting MS was present in 76.7% patients and secondary progressive MS was present in 23.3% patients. Mean disease duration was 8.1 5.6 years and the mean Expanded Disability Status Score (EDSS was 3.5 1.8 (range 1-8. Fatigue was measured with the Fatigue Severity Scale (FSS, depression was measured by the Beck Depression Inventory (BDI and QOL was assessed using the health-related quality of life questionnaire SF-36. We observed that the global FSS score was 4.6 1.8 (range 1-7 and BDI was 10.7 10.3 (range 0-39. The FSS significantly and positively correlated with the BDI scores (r = 0.572; p = 0.000. The severity of fatigue had a significant impact on the quality of life (r = -0.743; p = 0.000, in particular on mental health (r = -0.749; p = 0.000. We observed a significant correlation between the severity of depression and impaired quality of life (r = -0.684; p = 0.000. This study shows that fatigue and depression are associated with impaired QOL in MS.

  13. Effects of sodium tartrate anodizing on fatigue life of TA15 titanium alloy

    Directory of Open Access Journals (Sweden)

    Fu Chunjuan

    2015-08-01

    Full Text Available Anodizing is always used as an effective surface modification method to improve the corrosion resistance and wear resistance of titanium alloy. The sodium tartrate anodizing is a new kind of environmental anodizing method. In this work, the effects of sodium tartrate anodizing on mechanical property were studied. The oxide film was performed on the TA15 titanium alloy using sodium tartrate as the film former. The effects of this anodizing and the traditional acid anodizing on the fatigue life of TA15 alloy were compared. The results show that the sodium tartrate anodizing just caused a slight increase of hydrogen content in the alloy, and had a slight effect on the fatigue life. While, the traditional acid anodizing caused a significant increase of hydrogen content in the substrate and reduced the fatigue life of the alloy significantly.

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

    Science.gov (United States)

    Hudson, C. M.

    1972-01-01

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

  15. Fatigue, mood and quality of life improve in MS patients after progressive resistance training

    DEFF Research Database (Denmark)

    Dalgas, U; Stenager, E

    2010-01-01

    Fatigue occurs in the majority of multiple sclerosis patients and therapeutic possibilities are few. Fatigue, mood and quality of life were studied in patients with multiple sclerosis following progressive resistance training leading to improvement of muscular strength and functional capacity. Fatigue (Fatigue Severity Scale, FSS), mood (Major Depression Inventory, MDI) and quality of life (physical and mental component scores, PCS and MCS, of SF36) were scored at start, end and follow-up of a randomized controlled clinical trial of 12 weeks of progressive resistance training in moderately disabled (Expanded Disability Status Scale, EDSS: 3-5.5) multiple sclerosis patients including a Control group (n = 15) and an Exercise group (n = 16). Fatigue (FSS > 4) was present in all patients. Scores of FSS, MDI, PCS-SF36 and MCS-SF36 were comparable at start of study in the two groups. Fatigue improved during exercise by -0.6 (95% confidence interval (CI) -1.4 to 0.4) a.u. vs. 0.1 (95% CI -0.4 to 0.6) a.u. in controls (p = 0.04), mood improved by -2.4 (95% CI -4.1 to 0.7) a.u. vs. 1.1 (-1.2 to 3.4) a.u. in controls (p = 0.01) and quality of life (PCS-SF36) improved by 3.5 (95% CI 1.4-5.7) a.u. vs. -1.0 (95% CI -3.4-1.4) a.u. in controls (p = 0.01). The beneficial effect of progressive resistance training on all scores was maintained at follow-up after further 12 weeks. Fatigue, mood and quality of life all improved following progressive resistance training, the beneficial effect being maintained for at least 12 weeks after end of intervention.

  16. Fatigue Life of Extended Hollobolt Connection in Concrete Filled Tube

    OpenAIRE

    Norashidah Abd Rahman; Walid Tizani

    2013-01-01

    Studies on the performance of blind bolt connections have been carried out by many researchers. A number of recent studies of new blind bolted connection system have been proposed. The system uses the so called Extended Hollobolt fastener to connect the concrete filled tubular columns. The strength performance of this system has been investigated under both monotonic and cyclic loading. However, the performance of such connections under fatigue loading is still unknown. Therefore, a stu...

  17. Fatigue life assessment of components damaged by pitting corrosion.

    Czech Academy of Sciences Publication Activity Database

    Gajdo, Lubomr; perl, Martin

    Zagreb : Studio HRG Zagreb, 2004 - (Jeci?, S.; Semenski, D.), s. 282-283 ISBN 953-96243-6-3. [DANUBIA-ADRIA Symposium on Experimental Methods in Solid Mechanics /21./. Brijuni - Pula (HR), 29.09.2004-02.10.2004] R&D Projects: GA AV ?R IAA2811201 Institutional research plan: CEZ:AV0Z2071913 Keywords : pipeline * fatigue * corrosion Subject RIV: JM - Building Engineering

  18. Cancer-related fatigue: impact on patient quality of life and management approaches

    Directory of Open Access Journals (Sweden)

    Yeo TP

    2015-07-01

    Full Text Available Theresa Pluth Yeo,1,2 Shawnna Cannaday1 1Thomas Jefferson University Hospital, Department of Surgery Thomas Jefferson University, 2Jefferson College of Nursing, Philadelphia, PA, USA Abstract: Cancer-related fatigue is a common and distressing symptom that is present in the majority of cancer patients at some point during the disease course. Cancer-related fatigue has a profound influence on patients, affecting functional performance, mood, and one's overall quality of life. The etiology of cancer-related fatigue is multifactorial, involving a complex interplay of biological and body system factors. All cancer patients should be screened for fatigue, as it often coexists with other symptoms and its side effects may be underdiagnosed. Treatment modalities for cancer-related fatigue are still evolving. Current recommendations for management from national and international cancer experts and societies focus on patient and family education regarding cancer-related fatigue, exercise and physical activity, and psychosocial interventions. Pharmacologic interventions are less effective but may be helpful in a selected subset of affected individuals. Keywords: evidence based practice, CRF, disease management, quality of life, exercise

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

    Science.gov (United States)

    Jeelani, S.; Collins, M. R.

    1988-01-01

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

  20. Using artificial neural networks to predict the fatigue life of carbon and low-alloy steels

    International Nuclear Information System (INIS)

    The ASME boiler and pressure vessel code contains rules for the construction of nuclear power plant components. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify 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 life 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. (orig.)

  1. Fatigue life of the plasma-facing components in PULSAR

    International Nuclear Information System (INIS)

    The PULSAR project is a multi-institutional effort to determine the advantages that can be gained by building a tokamak without current drive. This machine would reduce the capital and operating costs of the machine by avoiding the need for complex current drive hardware but it must compensate for this with an energy storage scheme and with increased structural requirements due to cyclic fatigue. This paper presents the results of the fatigue analysis for the plasma-facing components of PULSAR. The structural analysis is carried out using two-dimensional finite element models and a variety of boundary conditions to account for the third dimension. In some cases the temperature distribution is modified to simulate behaviors which cannot normally be modeled with two-dimensional finite element models. PULSAR features two major engineering designs: a liquid metal-cooled vanadium design and a helium-cooled SiC/SiC design. Results are given for each. It is shown that the superior thermal and strength properties of the vanadium alloy simplify the component design process significantly. The SiC composite properties cause significantly more difficulty for the designer and, in particular, no credible design is found for a divertor fabricated solely from the SiC composite. This conclusion is based on current data for the thermophysical properties and fatigue strength of SiC fiber composites, so developments in these areas could allow the fabrication of a SiC/SiC divertor for a pulsed tokamak

  2. Establishment of fatigue life evaluation and management system for district heating pipes according to temperature variation

    International Nuclear Information System (INIS)

    District Heating(DH) plant is one of major facility can be used to reduce environmental pollution. The DH pipes transmit the heat and prevent heat loss during transportation, which consists of supply and return pipes, and each pipe is operated under different temperature fluctuation condition. The objectives of this paper are to systematize data processing of transition temperature and investigate its effects on fatigue life of DH pipes. As a result, reliable fatigue life evaluation procedures as well as a relational database management system were established and successfully applied to Korean DH pipes

  3. Fatigue life analysis of weld ends : Comparison between testing and FEM-calculations

    OpenAIRE

    Göransson, Andréas

    2014-01-01

    The thesis examines the fatigue life of weld ends, where very little usable research previously has been conducted, and often the weld ends are the critical parts of the weld. It is essential knowing the fatigue life of welds to be able to use them most efficiently.The report is divided into two parts; in the first the different calculation methods used today at Toyota Material Handling are examined and compared. Based on the results from the analysis and what is used mostly today, the effect...

  4. Quantitative description of the fatigue life with the four-parameter Weibull distribution

    International Nuclear Information System (INIS)

    Frequently, statistical distributions of service life which are observed with ageing and fatigue processes do not obey to Weibull's distribution function. In those cases, the introduction of a third parameter into the distribution function permits to restore, quite phenomenologically, the straight line in the service life network that is advantageous for the evaluation. The article briefly discusses basic doubts about this approach. A procedure is described which avoids grave drawbacks of the three-parameter approach and is suitable for being used on a PC. The basic idea of this procedure is in unisson with recent results from research concerning the fatigue of metals. (orig.)

  5. Accelerated ultrasonic fatigue testing applications and research trends

    International Nuclear Information System (INIS)

    Very high cycle fatigue (VHCF) behavior of aerospace components has emerged much attention due to their long service life. In this study, a piezoelectric ultrasonic fatigue testing (UFT) system has been developed by Mbrosiatec Co., Ltd. to study the high cycle fatigue (HCF) strength of Ti 6Al 4V alloy. Hourglass shaped specimens have been investigated in the range from 10'6' to 10'9' cycles at room temperature under completely reversed R=-1 loading conditions, Scanning electron microscopy (SEM) analysis revealed that failures occurred in the entire range up to the gigacycle regime, and the fractures have been found to be initiated from the surface, unlike in steels. However, it was found from the SEM microgprahs that microcracks transformed into intergranular fractures. Thus, it can be concluded from according to the results that this test method can be applicable to commercialized automotive and railroad parts that require high cycle fatigue strength

  6. Accelerated ultrasonic fatigue testing applications and research trends

    Energy Technology Data Exchange (ETDEWEB)

    Cho, In Sik; Shin, Choongshig; Kim, Jong Yup; Jeon, Yongho [Ajou Univ., Gyeonggi (Somalia)

    2012-06-15

    Very high cycle fatigue (VHCF) behavior of aerospace components has emerged much attention due to their long service life. In this study, a piezoelectric ultrasonic fatigue testing (UFT) system has been developed by Mbrosiatec Co., Ltd. to study the high cycle fatigue (HCF) strength of Ti 6Al 4V alloy. Hourglass shaped specimens have been investigated in the range from 10'6' to 10'9' cycles at room temperature under completely reversed R=-1 loading conditions, Scanning electron microscopy (SEM) analysis revealed that failures occurred in the entire range up to the gigacycle regime, and the fractures have been found to be initiated from the surface, unlike in steels. However, it was found from the SEM microgprahs that microcracks transformed into intergranular fractures. Thus, it can be concluded from according to the results that this test method can be applicable to commercialized automotive and railroad parts that require high cycle fatigue strength.

  7. Proposal of life prediction method based on long-term creep-fatigue test results of 304 stainless steel

    International Nuclear Information System (INIS)

    Failure induced by creep-fatigue damage during operation, is an important failure mode to be avoided in high temperature structural components of thermal and nuclear power plants. Prediction of failure mechanism under creep-fatigue conditions in actual plants, and evaluation of the validity of creep-fatigue life prediction methods need to be done on the basis of long-term creep-fatigue test results. In this study, long-term creep-fatigue tests with up to 10 hours strain peak dwell were conducted using 304 stainless steel and the subsequent failure mechanism and creep-fatigue life prediction method were discussed. From the detailed observations of the failure specimens using a scanning electron microscope, many creep cavities and microcracks at grain boundaries were observed inside specimens. It was indicated that the main crack initiated on the specimen surface and propagated favorably on the cavitated grain boundaries under long-term creep-fatigue conditions with a tension hold period of over 30 min. A creep-fatigue life evaluation method was proposed considering the interaction between fatigue and creep damage based on the failure observation. The experimental data of long-term creep-fatigue life in this study and existing literatures were compared with the predicted life by the proposed method and it showed good agreement. (author)

  8. Life estimation of low-cycle fatigue of pipe elbows. Proposed criteria of low-cycle fatigue life under the multi-axial stress field

    International Nuclear Information System (INIS)

    Pipe elbows were important parts frequently used in the pipelines of nuclear power, thermal power and chemical plants, and their integrity needed to be assured under seismic loads and thermal stresses considering local wall thinning or complex stress distribution due to special configuration different from straight pipe. This article investigated in details elastic-plastic stress-strain state of pipe elbow using finite element analysis and clarified there existed high bi-axial stress field at side inner surface of pipe elbow axial cracks initiated. Bi-axial stress factor was around 0.6 for sound elbow and up to 0.95 for local wall thinning at crown. Fracture strain of 1.15 was reduced to around 0.15 for bi-axial stress factor from 0.6 to 0.9. Normalized fatigue life for bi-axial stress field (0.6 - 0.8) was largely reduced to around 15, 19 and 10% of fatigue life of uni-axial state dependent on material strength level. Proposed revised universal slopes taking account of multi-axial stress factor could explain qualitatively effects of strain range, internal pressure and ratchet strain (pre-strain) on low-cycle fatigue life of pipe elbow. (T. Tanaka)

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

    Science.gov (United States)

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

    2003-01-01

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

  10. Early Life Stress and Inflammatory Mechanisms of Fatigue in the Coronary Artery Risk Development in Young Adults (CARDIA) Study

    OpenAIRE

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

    2012-01-01

    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-re...

  11. Statistical analysis of the effect of machining parameters on fatigue life of aerospace grade aluminum alloy (Al 6082T6)

    OpenAIRE

    Jamshaid, Muhammad; Jaffery, Husain; Ali, Liaqat; Khan, Mushtaq; Alam, Khurshid; Ahmed, Riaz; Rehman, Masood

    2013-01-01

    In this research work, aerospace grade aluminium alloy (Al 6082-T6) was analysed for the effect of cutting parameters on the fatigue life of the machined samples and optimization of cutting parameters for response factor. Different combinations of machining parameters were selected according to the ISO 3685 for sample preparation. Fatigue life of the samples was the response variable under investigation. Specimens for the rotating bending fatigue test were prepared according to the BS ISO 114...

  12. Perkiraan Fatigue Life pada Bracket Kapal Tanker Berdasarkan Common Structural Rules

    Directory of Open Access Journals (Sweden)

    Dita septiana

    2012-09-01

    Full Text Available Umur kelelahan (fatigue life dari struktur kapal dianalisis dengan menggunakan standar pada Common Structural Rules for Double Hull Oil Tanker. Kapal tanker single hull direncanakan akan dikonversi menjadi FPSO sehingga perlu diketahui sisa fatigue life konstruksinya. Dalam penelitian ini, fokus analisis dilakukan pada konstruksi bracket karena bracket sebagai salah satu penopang yang esensial pada kapal ini. Oleh karena itu, perlu diketahui letak bracket dengan tegangan paling besar dan besar fatigue lifenya. Kapal tersebut dimodelkan menggunakan softwareMSC Pastran sebagai pre-processor dan MSC Nastran sebagai processor. Bagian kapal yang dimodelkan adalah 3 ruang muat pada midship. Ruang muat pada bagian tengah dari ketiga ruang muat tersebut adalah ruang muat yang paling besar. Fatigue life yang dianalisa merupakan pengaruh dari beban lingkungan (beban gelombang air laut dan beban internal (beban tangki. Kondisi pembebanan yang dilakukan ada 6 macam load cases sesuai dengan ketentuan CSR. Tegangan pada bracket yang didapat dari pemodelan diambil tegangan yang paling besar untuk dianalisa fatigue lifenya. Hasil perhitungan menunjukkan bahwa bracket dengan tegangan paling besar terjadi pada web frame 7 pada ruang muat tengah dan pada kondisi pembebanan A2 didapat umur kapal yang paling rendah yaitu sebesar 26 tahun.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhuang, W., E-mail: wyman.zhuang@dsto.defence.gov.au [Aerospace Division, Defence Science and Technology Organisation, 506 Lorimer Street, Fishermans Bend, Victoria 3207 (Australia); Liu, Q.; Djugum, R.; Sharp, P.K. [Aerospace Division, Defence Science and Technology Organisation, 506 Lorimer Street, Fishermans Bend, Victoria 3207 (Australia); Paradowska, A. [Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2232 (Australia)

    2014-11-30

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

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

    Science.gov (United States)

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

    2015-03-01

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

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

    Science.gov (United States)

    Koh, Seung K.; Stephens, Ralph I.

    1992-01-01

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

  16. Fatigue life evaluation for spot weldment of dissimilar materials using PDM

    International Nuclear Information System (INIS)

    The fatigue crack initiation lives are studied on spot weldments of cold rolled carbon steel(SPC X SPC), galvanized steel(GA X GA) and dissimilar joining steel(SPC X GA) sheets by using DC potential drop method(DCPDM). Through the various test results, it can be known that the fatigue crack initiation behavior in all type of specimens can be definitely detected by DCPDM. With the exception of SPC X GA weldment, the fatigue crack initiation life of spot weldment increased as the welding current increased in SPC X SPC and GA X GA specimens. At the welding current 10kA, it is found that the SPC X GA weldment shows the shortest fatigue life in all specimens due to the distortion and/or ununiformity of the spot weldment. Moreover, the fatigue life of SPC X SPC weldment decreased than that of GA X GA weldment due to a large indentation and a thinned weldment occurred by high welding current density.

  17. A computational approach for thermomechanical fatigue life prediction of dissimilarly welded superheater tubes

    Energy Technology Data Exchange (ETDEWEB)

    Krishnasamy, Ram-Kumar; Seifert, Thomas; Siegele, Dieter [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany)

    2010-07-01

    In this paper a computational approach for fatigue life prediction of dissimilarly welded superheater tubes is presented and applied to a dissimilar weld between tubes made of the nickel base alloy Alloy617 tube and the 12% chromium steel VM12. The approach comprises the calculation of the residual stresses in the welded tubes with a multi-pass dissimilar welding simulation, the relaxation of the residual stresses in a post weld heat treatment (PWHT) simulation and the fatigue life prediction using the remaining residual stresses as initial condition. A cyclic fiscoplasticity model is used to calculate the transient stresses and strains under thermocyclic service loadings. The fatigue life is predicted with a damage parameter which is based on fracture mechanics. The adjustable parameters of the model are determined based on LCF and TMF experiments. The simulations show, that the residual stresses that remain after PWHT further relax in the first loading cycles. The predicted fatigue lives depend on the residual stresses and, thus, on the choice of the loading cycle in which the damage parameter is evaluated. It the first loading cycle, where residual stresses are still present, is considered, lower fatigue lives are predicted compared to predictions considering loading cycles with relaxed residual stresses. (orig.)

  18. Fatigue Life Prediction of Multi Leaf Spring used in the Suspension System of Light Commercial Vehicle

    Directory of Open Access Journals (Sweden)

    V.K.Aher

    2012-06-01

    Full Text Available The Leaf spring is widely used in automobiles and one of the components of suspension system. It needs to have high fatigue life. As a general rule, the leaf spring is regarded as a safety component as failure could lead to severe accidents. The purpose of this paper is to predict the fatigue life of steel leaf spring along with analytical stress and deflection calculations. This present work describes static and fatigue analysis of a steel leaf spring of a light commercial vehicle (LCV. The dimensions of the leaf spring of a LCV are taken and are verified by design calculations. The non-linear static analysis of 2D model of the leaf spring is performed using NASTRAN solver and compared with analytical results. The preprocessing of the model is done by using HYPERMESH software. The stiffness of the leaf spring is studied by plotting load versus deflection curve for various load applications. The simulation results are compared with analytical results. The fatigue life of the leaf spring is predicted using MSC Fatigue software.

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

    International Nuclear Information System (INIS)

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

  20. Influence of the non-singular stress on the crack extension and fatigue life

    International Nuclear Information System (INIS)

    Highlights: ? BEM is combined by characteristic analysis to calculate the singular stress field. ? A new method is proposed to evaluate the full stress field at crack tip region. ? Effect of non-singular stress on the propagation direction of the fatigue crack is analyzed. ? The influence of non-singular stress on the fatigue crack life is evaluated. - Abstract: The complete elasticity stress field at a crack tip region can be presented by the sum of the singular stress and several non-singular stress terms according to the Williams asymptotic expansion theory. The non-singular stress has a non-negligible influence on the prediction of the crack extension direction and crack growth rate under the fatigue loading. A novel method combining the boundary element method and the singularity characteristic analysis is proposed here to evaluate the complete stress field at a crack tip region. In this new method, any non-singular stress term in the Williams series expansion can be evaluated according to the computational accuracy requirement. Then, a modified Paris law is introduced to predict the crack propagation under the mixed-mode loading for exploring the influence of the non-singular stress on the fatigue life duration. By comparing with the existed experimental results, the predicted crack fatigue life when the non-singular stress is taken into consideration is more accurate than the predicted ones only considering the singular stress.

  1. Natalizumab treatment reduces fatigue in multiple sclerosis. Results from the TYNERGY trial; a study in the real life setting

    DEFF Research Database (Denmark)

    Svenningsson, Anders; Falk, Eva

    2013-01-01

    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

  2. Low Cycle Fatigue Life Prediction of Notched Specimens Under Proportional and Non-proportional Multiaxial Loadings

    Science.gov (United States)

    Itoh, Takamoto; Ozaki, Tomohiko

    This study discusses multiaxial low cycle fatigue life of notched specimens under proportional and non-proportional loadings at room temperature. Strain controlled multiaxial low cycle fatigue tests were carried out using smooth and circumferentially notched round-bar specimens of two types of steels, SUS316 and SGV410. Two kinds of shallow notched specimens were employed of which elastic stress concentration factors, Kt, are 1.5 and 2.5. The strain paths include proportional and non-proportional loadings. The former employed a push-pull straining or a reversed torsion straining. The latter was achieved by strain path where axial and shear strains had 90 degree phase difference but their amplitudes were the same based on von Mises' criterion. The notch dependency of multiaxial low cycle fatigue life and the life predictability were discussed. The lives for both steels depend on both Kt and strain path. The data correlations also showed the different trend between the steels. The strain parameter for the life prediction was discussed with the non-proportional strain parameter proposed by one of the authors with introducing Kt. The proposed parameter gave a satisfactory correlation with multiaxial low cycle fatigue life of notched specimens for two steels under proportional and non-proportional loadings.

  3. Multiaxial creep-fatigue life analysis using strainrange partitioning

    Energy Technology Data Exchange (ETDEWEB)

    Manson, S.S.; Halford, G.R.

    1976-01-01

    Strain-Range Partitioning is a recently developed method for treating creep-fatigue interaction at elevated temperature. Most of the work to date has been on uniaxially loaded specimens, whereas practical applications often involve load multiaxiality. This paper shows how the method can be extended to treat multiaxiality through a set of rules for combining the strain components in the three principal directions. Closed hysteresis loops, as well as plastic and creep strain ratcheting, are included. An application to hold-time tests in torsion is used to illustrate the approach.

  4. Natalizumab treatment reduces fatigue in multiple sclerosis. Results from the TYNERGY trial; a study in the real life setting

    DEFF Research Database (Denmark)

    Svenningsson, Anders; Falk, Eva; Celius, Elisabeth G; Fuchs, Siegrid; Schreiber, Karen; Berk, Sara; Sun, Jennifer; Penner, Iris-Katharina

    2013-01-01

    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...

  5. Implementation of on-line fatigue monitoring methodology in Heavy Water Plant, Kota for remnant life assessment programme

    International Nuclear Information System (INIS)

    Fatigue, creep and creep-fatigue interaction phenomena are important in the design and operation of components used in nuclear industry, thermal power plant and chemical process plant. Extension of life of the existing plants is a major concern to plant management. Recently, a methodology has been developed to predict the aging degradation of various components subjected to severe fluctuating loading conditions. This methodology converts the plant transients to responses on the structure using Green's function technique. The stresses on the structure due to combined thermal and mechanical loading is transformed into stress frequency spectrum using Rainflow cycle counting algorithm. Using material fatigue data, fatigue usage factor is computed. There is a proposal to implement this on-line fatigue life monitoring system to estimate the fatigue degradation of components at Heavy Water Plant, Kota. This present paper describes the implementation of this methodology for remnant life assessment of components. (author). 3 refs., 3 figs

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

    Energy Technology Data Exchange (ETDEWEB)

    Wong, F.M.G.

    1990-06-01

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

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

    International Nuclear Information System (INIS)

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

  8. Study on creep-fatigue life improvement and life evaluation of 316FR stainless steels

    International Nuclear Information System (INIS)

    Creep rupture and creep-fatigue interaction tests were conducted at 550deg C for modified 316FR austenitic stainless steels in order to improve the creep-fatigue lives. Reducing the carbon contents from 0.01% to 0.002 or 0.003% and finning the grain size were effective for increasing the creep-fatigue lives and the creep rupture ductilities. From these results, an estimation method of the creep-fatigue lives by using the creep rupture ductilities in the modified 316FR steels was proposed. (author)

  9. Thermomechanical fatigue – Damage mechanisms and mechanism-based life prediction methods

    Indian Academy of Sciences (India)

    H-J Christ; A Jung; H J Maier; R Teteruk

    2003-02-01

    An existing extensive database on the isothermal and thermomechanical fatigue behaviour of high-temperature titanium alloy IMI 834 and dispersoidstrengthened aluminum alloy X8019 in SiC particle-reinforced as well as unreinforced conditions was used to evaluate both the adaptability of fracture mechanics approaches to TMF and the resulting predictive capabilities of determining material life by crack propagation consideration. Selection of the correct microstructural concepts was emphasised and these concepts were, then adjusted by using data from independent experiments in order to avoid any sort of fitting. It is shown that the cyclic -integral ($\\Delta J_{\\text{eff}}$ concept) is suitable to predict the cyclic lifetime for conditions where the total crack propagation rate is approximately identical to pure fatigue crack growth velocity. In the case that crack propagation is strongly affected by creep, the creep–fatigue damage parameter $\\Delta_{C\\ F}$ introduced by Riedel can be successfully applied. If environmental effects are very pronounced, the accelerating influence of corrosion on fatigue crack propagation can no longer implicitly be taken into account in the fatigue crack growth law. Instead, a linear combination of the crack growth rate contributions from plain fatigue (determined in vacuum) and from environmental attack is assumed and found to yield a satisfactory prediction, if the relevant corrosion process is taken into account.

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

    International Nuclear Information System (INIS)

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

  11. Crack mode and life of Ti-6Al-4V under multiaxial low cycle fatigue

    Directory of Open Access Journals (Sweden)

    Takamoto Itoh

    2015-10-01

    Full Text Available This paper studies multiaxial low cycle fatigue crack mode and failure life of Ti-6Al-4V. Stress controlled fatigue tests were carried out using a hollow cylinder specimen under multiaxial loadings of ?=0, 0.4, 0.5 and 1 of which stress ratio R=0 at room temperature. ? is a principal stress ratio and is defined as ?=?II/?I, where ?I and ?II are principal stresses of which absolute values take the largest and middle ones, respectively. Here, the test at ?=0 is a uniaxial loading test and that at ?=1 an equi-biaxial loading test. A testing machine employed is a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loadings with inner pressure onto the hollow cylinder specimen. Based on the obtained results, this study discusses evaluation of the biaxial low cycle fatigue life and crack mode. Failure life is reduced with increasing ? induced by cyclic ratcheting. The crack mode is affected by the surface condition of cut-machining and the failure life depends on the crack mode in the multiaxial loading largely.

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

    OpenAIRE

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

    2012-01-01

    Background: Qi (? q) refers to the vital energy of the body in Traditional Chinese medicines (TCM). Qi deficiency (?? q x?) is the most common symptom in cancer patients according to the concept of TCM. We hypothesized that cancer patients with Qi deficiency suffer from poor quality of life (QOL) and fatigue.

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

    Science.gov (United States)

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

    2011-01-01

    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,

  14. Improvement of fatigue life of steel orthotropic desks with carbon fibre reinforcement composites.

    Czech Academy of Sciences Publication Activity Database

    Urushadze, Shota; Frba, Ladislav; Pirner, Miro

    Brno : Czech society for mechanics, 2011 - (Nvrat, T.; Fuis, V.; Houfek, L.; Vlk, M.), s. 403-410 ISBN 978-80-214-4275-7. [EAN 2011. Znojmo (CZ), 06.06.2011-09.06.2011] Institutional research plan: CEZ:AV0Z20710524 Keywords : orthotropic deck * fatigue * prolonged life Subject RIV: JM - Building Engineering

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

    Science.gov (United States)

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

    2005-01-01

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

  16. Probabilistic fatigue life of balsa cored sandwich composites subjected to transverse shear

    DEFF Research Database (Denmark)

    Dimitrov, Nikolay Krasimirov; Berggreen, Christian

    2015-01-01

    A probabilistic fatigue life model for end-grain balsa cored sandwich composites subjectedto transverse shear is proposed. The model is calibrated to measured three-pointbending constant-amplitude fatigue test data using the maximum likelihood method. Some possible applications of the probabilistic model are obtaining characteristic SNcurves corresponding to a given survival probability, and calibrating partial safety factorsfor material fatigue. The latter is demonstrated by a calibration performed using reliability analysis with the first-order reliability method. The measured variance in balsa shearproperties, for both static strength and fatigue failure, is higher than the variance normallyobserved in the properties for fiber-reinforced polymer composite laminates. This could be attributed to the fact that end-grain balsa wood is the product of a naturally occurringgrowth process, which cannot be controlled to the same extent as an industrial manufacturing processes. The large variance in the probabilistic model for fatigue life is reflected in the corresponding calibrated partial safety factors, which are higher thanthe factors usually associated with synthetic materials such as fiber-reinforced laminates.

  17. Fatigue life assessment of cast nodular iron disc brakes for railway vehicles

    Energy Technology Data Exchange (ETDEWEB)

    Sonsino, C.M.; Hanselka, H. [Fraunhofer-Institut fuer Betriebsfestigkeit (LBF), Darmstadt (Germany); Technical Univ. Darmstadt (Germany)

    2008-07-01

    Disc brakes, not only for railway applications but generally in all vehicle applications count as safety components. Therefore, their reliability during service is essential. A disc brake is submitted to different loadings: braking, including emergency braking; horizontal and vertical wheel forces and forces on driving over switches; mass forces acting in the attachment of the disc brakes to the wheels due to relative displacements and centrifugal forces during rolling of the wheel at higher speeds. In the present work, only the influence of thermal strains/stresses caused by braking on the fatigue life will be discussed. For the disc brake of the cast nodular iron EN-GJS-400-15 considered in this study, the other loadings were proved to be not critical. Because of the continuous distortions of a disc brake after each brake operation due to heating, calculated local strains had to be verified experimentally by strain and temperature measurements. The experiments were carried out in a special test rig of the manufacturer where a spectrum of braking operations from the speeds 200, 160 and 90 km/h were investigated. With the preliminary design, the required fatigue life could not be achieved but the fatigue critical areas were recognized. After the redesign of the discs, fatigue failures were prevented. This study is a re-evaluation of a former analysis on the fatigue behaviour of railway disc brakes. (orig.)

  18. Complex System Models used in the Automobile Clutch Release Bearing Fatigue Life Studies

    Directory of Open Access Journals (Sweden)

    Guoliang Chen

    2013-01-01

    Full Text Available According to the system engineering point of view, any kind of technical product, regardless of the size and complexity of its structure are how a system should achieve the intended technical process and in this process relies on the input and output into contact with the outside world. Any mechanical system\\should be achieved economically task book the required technical capabilities and maintain the safety of people and the environment as part of its general goal to pursue. Regardless of economic feasibility, technical capabilities alone to achieve the target will lose mechanical practical value. In the automotive power transmission process, the role of the clutch release bearing by means of the axial displacement of the bearing to connect or disconnect the power transmission between the transmission and the engine, thus completing the smooth start the car, suspended and transform operations such gear. Automobile clutch release bearings are vital parts clutch parts of the merits of its performance, the car's handling performance vehicle has great influence. Release bearing fatigue life analysis is based on the bearing rings or rolling fatigue spalling began to appear, a phenomenon with exposure to cyclic stress related. Rolling elastic contact between components belong, the contact stress analysis methods used in the past experience or simple analytical method. In this study, bearing materials, lubricants, sealing structure, fatigue life test and simulate working conditions failure data processing methods have raised new research content, by establishing a new release bearing fatigue life model for complex systems, the introduction of the smelting process, the surface defect, roughness, residual stress, EHL oil film, environmental cleanliness, temperature, variable load characteristics And other factors that affect the fatigue life. The results showed that: release bearing new life prediction model is closer to the actual condition clutch for further study a new generation of high- speed heavy automobile clutch release bearings provide a theoretical support.

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

    Energy Technology Data Exchange (ETDEWEB)

    Backer, F. de; Schoss, V.; Maussner, G. E-mail: gerd.maussner@erl19.siemens.de

    2001-06-01

    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 loads, which were not taken into account in the design e.g. temperature cycling arising from unforeseen stratification flow conditions. Therefore lifetime calculations should be supported by non-destructive measurements on the components during the operation life to guarantee their integrity, by monitoring of the changes in the microstructure, and the related mechanical and physical material properties, which are due to fatigue damage. Those changes of the microstructure appear in a period before crack initiation, which covers a considerable part of the fatigue life. To gain information on the changes in the microstructure during fatigue loading, samples of the stainless steel materials 1.4541 and 1.4550, which are the representative materials for the majority of auxiliary and safety systems, were strained under static and dynamic conditions at different temperature between RT and 300 deg. C in order to correlate the fatigue loading conditions and residual lifetime with the microstructural phenomena. In particular the formation of deformation induced martensite was analysed, which is accompanied by pronounced changes in the magnetic properties. Non-destructive testing methods (NDT), based on eddy current techniques, are of use to detect these changes in the magnetic properties. The results lead to an assessment scheme for the evaluation of the residual lifetime of components.

  20. Fatigue Life of Cast Titanium Alloys Under Simulated Denture Framework Displacements

    Science.gov (United States)

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

    2013-02-01

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

  1. Deterioration of fatigue life of 316L stainless steel due to TEXTOR exposure

    International Nuclear Information System (INIS)

    Fatigue tests in vacuum and air were carried out on solution-annealed 316L stainless steel specimens (NET reference material) in push-pull type, load-controlled experiments at 20, 150 and 425deg C. Reference specimens were compared to specimens which had been exposed to the plasma of the TEXTOR tokamak prior to testing. It is found that the surface modifications caused by the TEXTOR exposure lead to fatigue life deterioration by factors between 2 (at 20deg C) and 6 (at 425deg C). Possible reasons for this degradation are discussed. (orig.)

  2. Cancer Related Fatigue and Quality of Life in Patients with Advanced Prostate Cancer Undergoing Chemotherapy

    OpenAIRE

    CHARALAMBOUS, ANDREAS; Kouta, Christiana

    2016-01-01

    Cancer related fatigue (CRF) is a common and debilitating symptom that can influence quality of life (QoL) in cancer patients. The increase in survival times stresses for a better understanding of how CRF affects patients QoL. This was a cross-sectional descriptive study with 148 randomly recruited prostate cancer patients aiming to explore CRF and its impact on QoL. Assessments included the Cancer Fatigue Scale, EORTC QLQ-C30, and EORTC QLQ-PR25. Additionally, 15 in-depth structured intervi...

  3. Effect of Defects Distribution on Fatigue Life of Wind Turbine Components

    DEFF Research Database (Denmark)

    Rafsanjani, Hesam Mirzaei; Srensen, John Dalsgaard

    2015-01-01

    by a Poisson process / field where the defects form clusters that consist of a parent defect and related defects around the parent defect. The fatigue life is dependent on the number, type, location and size of the defects in the component and is therefore quite uncertain and needs to be described by...... stochastic models. In this paper, the Poisson distribution for modeling of defects of component are considered and the surface and sub-surface defects categorized. Furthermore, a model to estimate the probability of failure by fatigue due to the defects is proposed. Moreover, the relation between defect...

  4. ITER-FEAT central solenoid structural analysis and fatigue life assessment

    International Nuclear Information System (INIS)

    In this paper, we report about the fatigue life assessment of the ITER central-solenoid (CS) together with the related stress analyses. Two design options for integrating the structural support into the conductor have been considered. Various sources of fatigue crack growth rate (FCGR) data (including the CS model coil) have been taken into account. R and D is still needed to confirm the various assumptions made about the material quality and inspection procedures that have not yet been justified by any trial production

  5. Mechanisms of fatigue-crack initiation and their impact on fatigue life of AlSi7 die-cast components

    Directory of Open Access Journals (Sweden)

    Redik Sabine

    2014-06-01

    Full Text Available In the course of the present study, in-situ observations of crack initiation and crack growth of naturally induced cracks in cyclically loaded specimens along with conventional fatigue tests and fracture surface analyses were performed. The specimens used were taken from different sampling positions of standard and HIPed aluminum-die-cast engine blocks, with different cooling conditions. In one sampling position within the standard engine block microporosity was able to form, acting as a source for fatigue-crack initiation. While in the absence of microporosity, as observed in specimens taken from HIPed components, crack initiation occured via slip band mechanism. If material defects such as pores were present, premature crack initiation reduced the fatigue life yielding a lower fatigue life and fatigue strength than specimens where cracks formed by slip band mechanism. For cracks formed at pores, the pore size is the determining factor for fatigue behavior. While for cracks initiated via slip band mechanism fatigue strength is a function of the local material strength.

  6. Influence of shrinkage porosity on fatigue performance of iron castings and life estimation method

    Directory of Open Access Journals (Sweden)

    Wei Liu

    2016-01-01

    Full Text Available Shrinkage porosity exists more or less in heavy castings, and it plays an important role in the fatigue behavior of cast materials. In this study, fatigue tests were carried out on the QT400-18 cast iron specimens containing random degrees of shrinkage porosity defect. Experimental results showed that the order of magnitude of life scattered from 103 to 106 cycles when the shrinkage percentage ranged from 0.67% to 5.91%. SEM analyses were carried out on the shrinkage porosity region. The inter-granular discontinuous, micro cracks and inclusions interfered with the fatigue sliding or hindering process. The slip in shrinkage porosity region was not as orderly as the ordinary continuous medium. The shrinkage porosity area on fracture surface (SPAFS and alternating stress intensity factor (ASIF were applied to evaluate the tendency of residual life distribution; their relationship was fitted by negative exponent functions. Based on the intermediate variable of ASIF, a fatigue life prediction model of nodular cast iron containing shrinkage porosity defects was established. The modeling prediction was in agreement with the experimental results.

  7. Fatigue life prediction of a cable harness in an industrial robot using dynamic simulation

    International Nuclear Information System (INIS)

    The cable which transfers the signal and power in an industrial robot has a problem of fatigue fracture like steel components. Since the cable is very flexible compared to other components of the system, it is difficult to estimate its motion numerically. Some studies have been done on a large deformation problem, especially in a cable, and a few attempts have been made to apply the absolute nodal coordinate formulation (ANCF), which can simulate a large deformation. Only researches about the fatigue life of structural cables or comparative studies of FEM and ANCF simulations can be found. This paper presents a method to simulate the behavior of the cable harness using the ANCF and to predict the fatigue life while computing the strain time history of the point of interest. Rigid body dynamics is applied for the robot system, while ANCF is used for the cable harness. The simulation is performed by using the dynamic analysis process. The material property of the cable is obtained by a test. A simplified model is prepared. With these data, the behavior of the cable is simulated and the fatigue life is predicted

  8. Fatigue life prediction of a cable harness in an industrial robot using dynamic simulation

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Ji Won; Park, Tae Won [Ajou University, Suwon (Korea, Republic of); Yim, Hong Jae [Kookmin University, Seoul (Korea, Republic of)

    2008-03-15

    The cable which transfers the signal and power in an industrial robot has a problem of fatigue fracture like steel components. Since the cable is very flexible compared to other components of the system, it is difficult to estimate its motion numerically. Some studies have been done on a large deformation problem, especially in a cable, and a few attempts have been made to apply the absolute nodal coordinate formulation (ANCF), which can simulate a large deformation. Only researches about the fatigue life of structural cables or comparative studies of FEM and ANCF simulations can be found. This paper presents a method to simulate the behavior of the cable harness using the ANCF and to predict the fatigue life while computing the strain time history of the point of interest. Rigid body dynamics is applied for the robot system, while ANCF is used for the cable harness. The simulation is performed by using the dynamic analysis process. The material property of the cable is obtained by a test. A simplified model is prepared. With these data, the behavior of the cable is simulated and the fatigue life is predicted

  9. Prediction of Fatigue Life of Gear Subjected to Varying Loads

    Directory of Open Access Journals (Sweden)

    D. Hanumanna

    1998-07-01

    Full Text Available Structural members and components of a vehicle during service are subjected to varying loads which are random in nature. For structural members subjected to loads of constant amplitude, it is possible to describe the load with explicit mathematical relationship, and thereby, the life span can be estimated. Whereas, for structural members subjected to varying loads with time, there is no satisfactory method to estimate their life span. This paper describes a method for the estimation of life span of a gear in the gear box of a fighting vehicle subjected to fluctuating loads. For this purpose, it is assumed that the load spectrum corresponds to Gaussian (normal distribution, and the life has been worked out by applying linear cumulative damage theory.

  10. Evaluation of creepfatigue life based on fracture energy for modified 9Cr1Mo steel

    International Nuclear Information System (INIS)

    Preventing creepfatigue damage is a major consideration in nuclear power plants, which operate at high temperatures. Energy absorbed during creepfatigue loading is focused on for predicting long-term creepfatigue life for modified 9Cr1Mo steel. Fracture energy decreases with time owing to creep deformation localization. Change in fracture energy is described by a power law function of hysteresis energy density rate and time to fracture. Hysteresis energy density is approximately expressed as a function of the total strain range. Then, hysteresis energy density rate is determined by dividing hysteresis energy density by time per cycle. The function gives a good fit of data for creepfatigue and low strain-rate fatigue. The creepfatigue life can be predicted using the power law function. According to microstructure observation, change in fracture energy is due to annihilation of block and packet boundary.

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

    Energy Technology Data Exchange (ETDEWEB)

    Kim, In-Tae [Department of Civil Engineering, Nagoya University, Furo-cho, Chikusa-Ku, Nagoya 464-8603 (Japan)]. E-mail: itkim@civil.nagoya-u.ac.jp; Kainuma, Shigenobu [Department of Civil Engineering, Kyushu University, 6-10-1 Kakozaki, Higashi-Ku, Fukuoka 812-8581 (Japan)

    2005-11-01

    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 deg. to the normal direction of the uniaxial cyclic loading. Fatigue cracks propagated perpendicularly to the stress direction, and formed a flat plane or multiple propagation planes according to the inclination angles. The fatigue crack propagation rate may be estimated by only the mode I stress intensity factor of an inclined through crack assumed in this study. The fatigue life can be evaluated by the stress range at the weld throat in the normal direction to the inclined crack propagation, irrespective of difference in the inclination angle.

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

    International Nuclear Information System (INIS)

    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 deg. to the normal direction of the uniaxial cyclic loading. Fatigue cracks propagated perpendicularly to the stress direction, and formed a flat plane or multiple propagation planes according to the inclination angles. The fatigue crack propagation rate may be estimated by only the mode I stress intensity factor of an inclined through crack assumed in this study. The fatigue life can be evaluated by the stress range at the weld throat in the normal direction to the inclined crack propagation, irrespective of difference in the inclination angle

  13. Relation Between Residual and Hoop Stresses and Rolling Bearing Fatigue Life

    Science.gov (United States)

    Oswald, Fred B.; Zaretsky, Erwin V.; Poplawski, Joseph V.

    2015-01-01

    Rolling-element bearings operated at high speed or high vibration may require a tight interference fit between the bore of the bearing and shaft to prevent rotation of the bearing bore around the shaft and fretting damage at the interfaces. Previous work showed that the hoop stresses resulting from tight interference fits can reduce bearing lives by as much as 65 percent. Where tight interference fits are required, case-carburized steel such as AISI 9310 or M50 NiL is often used because the compressive residual stresses inhibit subsurface crack formation and the ductile core inhibits inner-ring fracture. The presence of compressive residual stress and its combination with hoop stress also modifies the Hertz stress-life relation. This paper analyzes the beneficial effect of residual stresses on rolling-element bearing fatigue life in the presence of high hoop stresses for three bearing steels. These additional stresses were superimposed on Hertzian principal stresses to calculate the inner-race maximum shearing stress and the resulting fatigue life of the bearing. The load-life exponent p and Hertz stress-life exponent n increase in the presence of compressive residual stress, which yields increased life, particularly at lower stress levels. The Zaretsky life equation is described and is shown to predict longer bearing lives and greater load- and stress-life exponents, which better predicts observed life of bearings made from vacuum-processed steel.

  14. Estimation of fatigue life for aluminium welded joints with the application of artificial neural networks

    Energy Technology Data Exchange (ETDEWEB)

    Karakas, Oe.

    2011-10-15

    The aim of this investigation was determining the fatigue behaviour of welded aluminium joints and so the appertaining SN-lines by application of Artificial Neural Network (ANN) architectures. For this, fatigue data obtained with aluminium welded joints subjected to constant amplitude loading were used. The main benefit of ANN is the good description of the effects of different factors on fatigue life. The results determined by the ANN method for four aluminium alloys are displayed in scatter bands of SN-lines. It is observed that the trained results are in good agreement with the tested data and enable the estimation of SN-lines. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Influences of cyclic deformation on creep property and creep-fatigue life prediction considering them

    International Nuclear Information System (INIS)

    Evaluation of creep-fatigue is essential in design and life management of high-temperature components in power generation plants. Cyclic deformation may alter creep property of the materials and its consideration may improve predictability of creep-fatigue failure life. To understand them, creep tests were conducted for the materials subjected to cyclic loading and their creep rupture and deformation behaviors were compared with those of as-received materials. Both 316FR and modified 9Cr-1Mo steel were tested. (1) Creep rupture time and elongation generally tend to decrease with cyclic loading in both materials, and especially elongation of 316FR drastically decreases by being cyclically deformed. (2) Amount of primary creep deformation decreases by cyclic loading and the ways to improve its predictability were developed. (3) Use of creep rupture ductility after cyclic deformation, instead of that of as-received material, brought about clear improvement of life prediction in a modified ductility exhaustion approach. (author)

  16. Load Identification of Offshore Platform for Fatigue Life Estimation

    DEFF Research Database (Denmark)

    Perisic, Nevena; Kirkegaard, Poul Henning

    2014-01-01

    The lifetime of an offshore platform is typically governed by accumulated fatigue damage. Thus, the load time history is an essential parameter for prediction of the lifetime of the structure and its components. Consequently, monitoring of structural loads is of special importance in relation to re-assessment of offshore platforms. Structural monitoring systems (SMSs) on offshore structures typically consist of a set of sensors such as strain gauges, accelerometers, wave radars and GPSs, however direct measuring of the actual loading is usually not feasible. One approach is to measure the loads indirectly by monitoring of the available dynamic responses of the structure. This work investigates the possibility for using an economically beneficial, model-based load estimation algorithm for indirect measuring of the loading forces acting on the offshore structure. The algorithm is based on the reduced order model of the structure and the discrete Kalman filter which recursively estimates unknown states of the system in real time. As a test-case, the algorithm is designed to estimate the equivalent total loading forces of the structure. The loads are estimated from noised displacement measurements of a single location on the topside of the offshore structure. The method is validated using simulated data for two wave loading cases: regular and irregular wave loadings.

  17. Evaluation for probabilistic distributions of fatigue life of marine propeller materials by using a Monte Carlo simulation

    International Nuclear Information System (INIS)

    Engineering materials have been studied and developed remarkably for a long time. But, few reports about marine propeller materials are presented. Recently, some researchers have studied the material strength of marine propellers. However, studies on parametric sensitivity and probabilistic distribution of fatigue life of propeller materials have not been made yet. In this study, a method to predict the probabilistic distributions of fatigue life of propeller materials is presented, and the influence of several parameters on the life distribution is discussed

  18. Fatigue, Sleep Quality, and Disability in Relation to Quality of Life in Multiple Sclerosis

    Science.gov (United States)

    Radfar, Moloud

    2015-01-01

    Background: Quality of life (QOL) is impaired in multiple sclerosis (MS) in part due to physical disability. MS-associated fatigue and poor sleep are common and treatable features of MS that affect QOL. We assessed the association between fatigue, sleep quality, and QOL in people with MS. Methods: Cross-sectional data were collected from 217 patients with MS. Health-related QOL (MS Quality of Life-54), fatigue (Fatigue Severity Scale [FSS]), and sleep quality (Pittsburgh Sleep Quality Inventory [PSQI]) were assessed. Expanded Disability Status Scale scores were also provided by a qualified neurologist. Results: The mean SD age of the 217 patients was 32.6 8.6 years, and 79% were female. One hundred fifty-two patients (70.0%) were classified as poor sleepers based on PSQI scores; 122 (56.2%) had significant fatigue based on FSS results. The mean SE physical (PCS) and mental (MCS) health composite scores of the MSQOL-54 were 40.12 1.27 and 43.81 1.61, respectively. There was a strong statistically significant positive correlation between PCS scores and MCS (r = 0.58), FSS (r = 0.49), and PSQI (r = 0.52) scores. MCS scores were strongly correlated with FSS (r = 0.53) and PSQI (r = 0.35) scores. Age exhibited statistically significant negative correlations with PCS (r = ?0.21) and MCS (r = ?0.58) scores, and was statistically significantly correlated with FSS (r = 0.23) and PSQI (r = 0.21) scores. Expanded Disability Status Scale scores were strongly correlated with FSS scores. Conclusions: These findings support screening of fatigue severity and sleep quality and their effects on QOL. PMID:26664332

  19. Fatigue in Children With Sickle Cell Disease: Association With Neurocognitive and Social-Emotional Functioning and Quality of Life.

    Science.gov (United States)

    Anderson, Lindsay M; Allen, Taryn M; Thornburg, Courtney D; Bonner, Melanie J

    2015-11-01

    Children with sickle cell disease (SCD) report fatigue in addition to acute and chronic pain, which can decrease overall health-related quality of life (HRQL). The primary objective of the current study was to investigate the relationship between fatigue and HRQL. Given limited prior research, secondary objectives included investigation of associations between fatigue and functional outcomes, including child neurocognitive and social-emotional functioning. Children aged 8 to 16 years (N=32) and a caregiver completed measures of fatigue, HRQL, pain, and neurocognitive and social-emotional functioning. Controlling for pain and number of SCD-related hospitalizations, hierarchical linear regression models were used to determine the impact of child-reported and parent-reported fatigue on child HRQL. Correlational analyses were used to explore the relationship between fatigue and additional child outcomes. Data indicated that children with SCD experience clinically relevant levels of fatigue, which independently predicts lower HRQL. Fatigue was also associated with lower working memory, executive functioning, and higher levels of internalizing symptoms. Given its observed impact on HRQL and relationship to functional outcomes, fatigue may be an important target of clinical, home, or school interventions. This practice may attenuate the burden of fatigue in these patients, and in turn, help improve the quality of life of children living with SCD. PMID:26479993

  20. Thermal fatigue. Materials modelling

    International Nuclear Information System (INIS)

    In the framework of the ongoing joint research project 'Thermal Fatigue - Basics of the system-, outflow- and material-characteristics of piping under thermal fatigue' funded by the German Federal Ministry of Education and Research (BMBF) fundamental numerical and experimental investigations on the material behavior under transient thermal-mechanical stress conditions (high cycle fatigue V HCF and low cycle fatigue - LCF) are carried out. The primary objective of the research is the further development of simulation methods applied in safety evaluations of nuclear power plant components. In this context the modeling of crack initiation and growth inside the material structure induced by varying thermal loads are of particular interest. Therefore, three scientific working groups organized in three sub-projects of the joint research project are dealing with numerical modeling and simulation at different levels ranging from atomistic to micromechanics and continuum mechanics, and in addition corresponding experimental data for the validation of the numerical results and identification of the parameters of the associated material models are provided. The present contribution is focused on the development and experimental validation of material models and methods to characterize the damage evolution and the life cycle assessment as a result of thermal cyclic loading. The individual purposes of the subprojects are as following: - Material characterization, Influence of temperature and surface roughness on fatigue endurances, biaxial thermo-mechanical behavior, experiments on structural behavior of cruciform specimens and scatter band analysis (IfW Darmstadt) - Life cycle assessment with micromechanical material models (MPA Stuttgart) - Life cycle assessment with atomistic and damage-mechanical material models associated with material tests under thermal fatigue (Fraunhofer IWM, Freiburg) - Simulation of fatigue crack growth, opening and closure of a short crack under thermal cyclic loading conditions, developing methods for the damage assessment based on the cyclic J-integral (IFSW Darmstadt, AREVA) - Further development of plasticity models (IFSW Darmstadt, AREVA) Within this paper the various investigations and the main results are presented.

  1. Inclusions Size-based Fatigue Life Prediction Model of NiTi Alloy for Biomedical Applications

    Science.gov (United States)

    Urbano, Marco Fabrizio; Cadelli, Andrea; Sczerzenie, Frank; Luccarelli, Pietro; Beretta, Stefano; Coda, Alberto

    2015-06-01

    Current standards consider the size and distribution of inclusions in semi-finished material, but do not place requirements on final biomedical devices made of NiTi shape memory alloys. In this paper, we analyze this by comparing the fatigue performances of NiTi superelastic wires obtained by different processes through a simple bilinear model of fatigue response in terms of strain life. The fracture surfaces of failed wires are analyzed through SEM microscopy and data regarding the presence of particles, and their morphology is recorded and analyzed using Type-I extreme value distribution. The results show a strong correlation between the fatigue limit of wires (in terms of strain) and the predicted extreme values of inclusions at fracture origin. Then, following the concept of treating the inclusions as `small cracks,' a simple relationship between fatigue limit strain range and inclusion size is proposed based on ?Kth data from the literature. The model is compared with the fatigue data obtained from the tested wires.

  2. Creep-fatigue life prediction for modified 9Cr-1Mo steel

    International Nuclear Information System (INIS)

    A research committee has studied the applicability of Modified 9Cr-1Mo steel to the steam generators in the Demonstration FBR plant in Japan. A series of creep-rupture, fatigue, and creep-fatigue tests has been conducted on Modified 9Cr-1Mo steel in support of creep-fatigue damage rules. From the data obtained, it has been shown that the conventional time fraction rule isn't applicable to Modified 9Cr-1Mo steel because creep damage accumulated until failure is estimated as nearly zero in the all cases. The calculated creep damage per cycle drastically decreases with increasing cycle number because of cyclic softening. The time fraction rule modified by creep rupture time after cyclic softening and the ductility exhaustion method have been found to be promising candidates for creep-damage assessment. Furthermore, by introducing appropriate creep and fatigue reduction factors for weldments, the creep-fatigue life of weldment can be estimated using the linear damage rule

  3. Influence of Graphite Nodules Geometrical Features on Fatigue Life of High-Strength Nodular Cast Iron

    Science.gov (United States)

    Costa, Nuno; Machado, Nuno; Silva, Filipe Samuel

    2008-06-01

    This paper is concerned with the evaluation of different fatigue strength theories to predict the fatigue life of high-strength nodular cast iron. There have been some studies on the effects of the shape and size of graphite nodules, and of microstructure, on the fatigue strength of nodular cast iron. However, there is not a consensus on how to correlate the fatigue limit with material intrinsic properties or with external features such as considering graphite nodules as defects. Some researchers found good correlations between fatigue strength, ?w0, and the geometrical aspects of the graphite nodules, considering it as internal material defects. It will be shown in this study that geometrical features such as shape, size, and relative position seem to be adequate to be included in those predictions. In this article, a high-strength cast iron, with rupture strength of about 1300 MPa and Youngs modulus of about 160 GPa, has been used. Correlations both with intrinsic properties as well as with other geometrical effects have been made. A comparison of different theories has also been carried out.

  4. Influence of cyclic prestressing or additional hardening on the fatigue life of various steels under stress or strain control

    International Nuclear Information System (INIS)

    Tests performed on various steels (A42 mild steel, 304 and 316 L stainless steels) show that a new overload cycles have a favorable effect on the fatigue life in push-pull, in stress control, but a detrimental effect in strain-control, and that biaxial non-proportional loadings (90 deg out-of-phase tension and torsion) also enhance the fatigue life in stress control but reduce it in strain control. A method to estimate the influence of cyclic overloading and non-proportional loadings yields conservative predictions of the fatigue life. (authors)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-10-09

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

  6. Fatigue, mood and quality of life improve in MS patients after progressive resistance training

    DEFF Research Database (Denmark)

    Dalgas, U; Stenager, E; Petersen, T; Hansen, Hans Jacob; Knudsen, C; Overgaard, K; Ingemann-Hansen, T; Jakobsen, Johannes Klitgaard

    2010-01-01

    . Fatigue (Fatigue Severity Scale, FSS), mood (Major Depression Inventory, MDI) and quality of life (physical and mental component scores, PCS and MCS, of SF36) were scored at start, end and follow-up of a randomized controlled clinical trial of 12 weeks of progressive resistance training in moderately...... disabled (Expanded Disability Status Scale, EDSS: 3-5.5) multiple sclerosis patients including a Control group (n = 15) and an Exercise group (n = 16). Fatigue (FSS > 4) was present in all patients. Scores of FSS, MDI, PCS-SF36 and MCS-SF36 were comparable at start of study in the two groups. Fatigue...... improved during exercise by -0.6 (95% confidence interval (CI) -1.4 to 0.4) a.u. vs. 0.1 (95% CI -0.4 to 0.6) a.u. in controls (p = 0.04), mood improved by -2.4 (95% CI -4.1 to 0.7) a.u. vs. 1.1 (-1.2 to 3.4) a.u. in controls (p = 0.01) and quality of life (PCS-SF36) improved by 3.5 (95% CI 1.4-5.7) a...

  7. Optimal Shot Peening Treatments to Maximize the Fatigue Life of Quenched and Tempered Steels

    Science.gov (United States)

    Llaneza, V.; Belzunce, F. J.

    2015-07-01

    The search for the optimal Almen intensity to use in shot peening treatments to maximize the fatigue life of industrial steel components involves many different variables and physical phenomena. In this paper, the optimal peening intensity of different steel grades obtained from an AISI 4340 steel through heat treatments has been determined. Six different steel grades were subjected to shot peening treatments, which were performed under full coverage, but employing diverse Almen intensities, shot sizes and air pressures. The role of the mechanical properties of the treated steel and the applied Almen intensity on the shot peening effects were studied to understand the results obtained by means of rotating bending fatigue tests. Each steel has a specific Almen intensity value able to optimize its fatigue life, thereby allowing an optimal balance between the positive and negative effects induced by shot peening. This value, or range of values, is dependent on the mechanical properties of the treated steel, increasing with increasing steel properties up to a certain point and then decreasing for stronger steels. In these cases, over peening treatments produce sufficiently large surface defects to induce relaxation of the surface residual stress and facilitate the initiation of surface fatigue cracks.

  8. Fatigue, mood and quality of life improve in MS patients after progressive resistance training

    DEFF Research Database (Denmark)

    Dalgas, U; Stenager, E; Petersen, T; Hansen, Hans Jacob; Knudsen, C; Overgaard, K; Ingemann-Hansen, T; Jakobsen, Johannes Klitgaard

    2010-01-01

    disabled (Expanded Disability Status Scale, EDSS: 3-5.5) multiple sclerosis patients including a Control group (n = 15) and an Exercise group (n = 16). Fatigue (FSS > 4) was present in all patients. Scores of FSS, MDI, PCS-SF36 and MCS-SF36 were comparable at start of study in the two groups. Fatigue......Fatigue occurs in the majority of multiple sclerosis patients and therapeutic possibilities are few. Fatigue, mood and quality of life were studied in patients with multiple sclerosis following progressive resistance training leading to improvement of muscular strength and functional capacity...... improved during exercise by -0.6 (95% confidence interval (CI) -1.4 to 0.4) a.u. vs. 0.1 (95% CI -0.4 to 0.6) a.u. in controls (p = 0.04), mood improved by -2.4 (95% CI -4.1 to 0.7) a.u. vs. 1.1 (-1.2 to 3.4) a.u. in controls (p = 0.01) and quality of life (PCS-SF36) improved by 3.5 (95% CI 1.4-5.7) a...

  9. Assessment of Surface Treatment on Fatigue Life of Cylinder Block for Linear Engine using Frequency Response Approach

    Directory of Open Access Journals (Sweden)

    M. M. Rahman

    2009-01-01

    Full Text Available Objectives: This study was focused on the finite element techniques to investigate the effect of surface treatment on the fatigue life of the vibrating cylinder block for new two-stroke free piston engine using random loading conditions. Motivation: An understanding of the effects related to the random loading is necessary to improve the ability of designers to accurately predict the fatigue behavior of the components in service. An internal combustion engine cylinder block is a high volume production component subjected to random loading. Problem statement: Proper optimization of this component that is critical to the engine fuel efficiency and more robustly pursued by the automotive industry in recent years. A detailed understanding of the applied loads and resulting stresses under in-service conditions is demanded. Approach: The finite element modeling and analysis were performed utilizing the computer aided design and finite element analysis codes respectively. In addition, the fatigue life prediction was carried out using finite element based fatigue analysis code. Aluminum alloys were considered as typical materials in this study. Results: The frequency response approach was applied to predict the fatigue life of cylinder block using different load histories. Based on the finite element results, it was observed that the fatigue life was significantly influenced for the nitriding treatment. The obtained results were indicated that the nitrided treatment produces longest life for all loading conditions. Conclusion: The nitriding process is one of the promising surface treatments to increase the fatigue life for aluminum alloys linear engine cylinder block.

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

    Science.gov (United States)

    Voothaluru, Rohit

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

  11. Effect of mean stress on short crack growth and fatigue life in austenitic-ferritic duplex steel.

    Czech Academy of Sciences Publication Activity Database

    Polk, Jaroslav; Obrtlk, Karel; Petrenec, Martin

    Ottawa : NRCan - CANMET, 2009, s. 1-10. ISBN N. [International Conference on Fracture /12./. Ottawa (CA), 12.07.2009-17.07.2009] R&D Projects: GA ?R GA101/07/1500 Institutional research plan: CEZ:AV0Z20410507 Keywords : short crack * mean stress * fatigue life Subject RIV: JL - Materials Fatigue, Friction Mechanics

  12. Influence of specimen type and reinforcement on measured tension-tension fatigue life of unidirectional GFRP laminates

    DEFF Research Database (Denmark)

    Korkiakoski, Samuli; Brndsted, Povl; Sarlin, Essi; Saarela, Olli

    2016-01-01

    It is well known that standardised tension-tension fatigue test specimens of unidirectional (UD) glass-fibre-reinforced plastics (GFRP) laminates tend to fail at end tabs. The true fatigue life is then underestimated. The first objective of this study was to find for UD GFRP laminates a test spec...

  13. A Nonlinear Reduced Order Method for Prediction of Acoustic Fatigue

    Science.gov (United States)

    Przekop, Adam; Rizzi, Stephen A.

    2006-01-01

    The goal of this investigation is to assess the quality of high-cycle-fatigue life estimation via a reduced order method, for structures undergoing geometrically nonlinear random vibrations. Modal reduction is performed with several different suites of basis functions. After numerically solving the reduced order system equations of motion, the physical displacement time history is obtained by an inverse transformation and stresses are recovered. Stress ranges obtained through the rainflow counting procedure are used in a linear damage accumulation method to yield fatigue estimates. Fatigue life estimates obtained using various basis functions in the reduced order method are compared with those obtained from numerical simulation in physical degrees-of-freedom.

  14. Fatigue life improvement factors obtained by weld reinforcement and toe grinding

    Energy Technology Data Exchange (ETDEWEB)

    Mullen, C.L.; Merwin, J.E.

    1982-01-01

    The potential of weld reinforcement and toe grinding techniques for improving the fatigue life of welded joints protected from seawater corrosion is quantified based on tests performed in air on welded plate specimens. Results are presented in terms of median fatigue life improvement factors and prediction intervals obtained by linear regression analysis. The significant improvements possible with weld reinforcement are shown to be caused partly by a slight alleviation of the stress concentration imposed by sharp angles at the weld toe. Variable improvements observed for toe ground welds are shown to be associated with the variable surface modifications which different tools impose on weld toes. Load and weld geometry are shown to be particulary important when bending stresses are applied to the weld toe, since reinforcement affects the bending moment at the toe section and toe grinding affects the conditions at the highly stressed outer fibers. 14 references.

  15. On the fatigue life of M50 NiL rolling bearings

    Science.gov (United States)

    Harris, T. A.; Skiller, John; Spitzer, Ronald F.

    1992-10-01

    The fatigue life of rolling bearings made of M50 NiL (a nickel-low carbon variant of M50 tool steel) was investigated using data from a battery of 15 R2 endurance test rigs specially modified to accommodate the aircraft application test conditions. Results indicate that bearings manufactured from case-hardened M50 NiL steel can provide significantly greater rolling contact fatigue life than bearings made from through-hardened M50 steel. In addition, it was found that M50 NiL bearings endurance-tested under conditions of heavy tensile hoop stresses showed no tendency toward raceway spalling or cracking through, unlike M50 bearings, which exhibited both tendencies.

  16. Random thermal stress oscillations and fatigue life estimation for steam generator tubes

    International Nuclear Information System (INIS)

    A one-dimensional computation model was used to determine the temperature and stress fields under conditions corresponding to those found in once-through steam generator tubes. The random oscillatory nature of the water/steam convective boundary conditions in the transition boiling zone was simulated by postulating random variations in heat transfer coefficients for flow temperatures. Statistical parameters describing the tube temperatures and thermal stress oscillatory history are determined allowing appropriate fatigue life estimations to be made. The results indicate that the tube wall temperature oscillation parameter provides a strong influence on thermal stress and the predicted fatigue life. In contrast, Biot number variations provide only a relatively small effect. An improved method of determining the allowable thermal stress limitations due to certain wall temperature oscillations is proposed

  17. The effects of ageing and environment on the fatigue life of adhesive joints

    Science.gov (United States)

    Su, Ning; Mackie, R. I.; Harvey, W. J.

    1992-04-01

    This paper presents the results of a durability program designed to study the effects of aging and environment on the fatigue life of adhesive joints. The adhesives were typical of those which might be used in civil engineering applications. Specimens were kept under a variety of loading and environmental conditions for eight years. It was observed that some adhesives showed excellent durability properties, and that the fatigue life of some specimens actually improved with age. Other adhesives were adversely affected by the environment, particularly high humidity or exposure to the natural environment. It was found that good performance in a laboratory high humidity environment does not guarantee good performance when exposed to the natural environment. The durability performance of the adhesives bore a close relation to the effects of moisture uptake in the adhesives.

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

    International Nuclear Information System (INIS)

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

  19. Prediction of fatigue crack initiation life of circumferentially notched steel bars under cyclic torsion

    International Nuclear Information System (INIS)

    Torsional fatigue tests were conducted for smooth solid bars, smooth hollow cylinders, and circumferentially notched bars of carbon steel (JIS SGV410) and austenitic stainless steel (JIS SUS316L) under completely reversed cyclic torsion. The cyclic stress strain relation was first determined for two steels. The yield stress and the flow stress were higher for SUS316L than for SGV410. The torsional fatigue life of smooth solid bars was longer than that of hollow cylinders when compared at the same nominal stress amplitude. The true strain amplitude on the surface of solid bars under torsion was calculated by the elastic-plastic analysis by the finite element method (FEM). The relation between the strain amplitude on the specimen surface calculated by FEM and the fatigue life was nearly equal to the relation obtained for hollow cylinders. The crack initiation life for notched specimens was determined by the direct electrical potential method. When compared at the same nominal stress amplitude, the crack initiation life got shorter as the notches became sharper. The distribution of the amplitude of equivalent strain near the root of circumferential notches under torsion was calculated by the elastic-plastic analysis of FEM. The crack initiation life got slightly longer for sharper notches when the life was correlated to the strain amplitude at the notch root. The relation between the crack initiation life and the strain amplitude at 0.1 mm distant from the notch root was nearly unique independent of the notch shapes and was equivalent to the relation obtained for smooth specimens. (author)

  20. Technique for Exterior Expansion Measurement During Autofrettaging for Constant Fatigue Life

    Directory of Open Access Journals (Sweden)

    Rajeev M. Bhatnagar

    2014-07-01

    Full Text Available In an autofrettage process a given thick cylinder is subjected to such a pressure which gives a specified depth of elasto-plastic boundary. The outside diameter expansion during autofrettage process is a function of depth of autofrettage. To obtain a specified depth of elastic-plastic interface, the applied autofrettage pressure increases in direct proportion to the proof stress of the pressure vessel material. Although this increases the load bearing capacity of the barrel, resulting in enhanced factor of safety, this increases the maintenance cost of a hydraulic autofrettage plant. To assure quality, product safety and manufacturing economy, an optimal autofrettage pressure is defined. The paper proposes that the minimum autoftrettage pressure is the pressure at which the pressure exterior expansion curve intersects line of constant factor of safety. At higher values of 0.2 per cent proof stress of tube material autofrettaging based on line of constant factor of safety will result in a reduction in fatigue life. The point of intersection of exterior expansion curve with line of constant fatigue life has been defined as the optimal pressure because the specifications of factor of safety and fatigue life are simultaneously achieved. The proposed process design based on above concept has been validated using finite element simulation and empirical post-autofrettage measurements. The verification of the shakedown condition for reverse yielding due to the Bauschinger effect (Huangs model and fatigue life has also been satisfied.Defence Science Journal, Vol. 64, No. 4, July 2014, pp. 385-392, DOI:http://dx.doi.org/10.14429/dsj.64.3886

  1. Prevalence of fatigue in patients with multiple sclerosis and its effect on the quality of life

    OpenAIRE

    Karthik Nagaraj; Arun B Taly; Anupam Gupta; Chandrajit Prasad; Rita Christopher

    2013-01-01

    Objective: This prospective study was carried out to observe the prevalence of fatigue in patients with multiple sclerosis (MS) and its effect on quality-of-life (QoL). Study Design and Setting: Prospective observational study in a University Tertiary Research Hospital in India. Patients and Methods: A total of 31 patients (25 females) with definite MS according to McDonald?s criteria presented in out-patient/admitted in the Department of Neurology (between February 2010 and December 2011) we...

  2. Fatigue life evaluation of A356 aluminum alloy used for engine cylinder head

    OpenAIRE

    Angeloni, Mauricio

    2011-01-01

    The studied material is an A356 Al alloy, used to produce engine cylinder heads for the automotive industry by die casting process. The material displays a quite coarse dendritic microstructure in a eutectic matrix, with a mean grains size of 25 microns, intemetallic precipitates and porosities. The tensile properties are strongly affected by testing temperature, with a quite sensitive drop of the Young's modulus, the Yield stress as the temperature was raised. The isothermal fatigue life dro...

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

    Science.gov (United States)

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

    1979-01-01

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

  4. Space Shuttle Rudder Speed Brake Actuator-A Case Study Probabilistic Fatigue Life and Reliability Analysis

    Science.gov (United States)

    Oswald, Fred B.; Savage, Michael; Zaretsky, Erwin V.

    2015-01-01

    The U.S. Space Shuttle fleet was originally intended to have a life of 100 flights for each vehicle, lasting over a 10-year period, with minimal scheduled maintenance or inspection. The first space shuttle flight was that of the Space Shuttle Columbia (OV-102), launched April 12, 1981. The disaster that destroyed Columbia occurred on its 28th flight, February 1, 2003, nearly 22 years after its first launch. In order to minimize risk of losing another Space Shuttle, a probabilistic life and reliability analysis was conducted for the Space Shuttle rudder/speed brake actuators to determine the number of flights the actuators could sustain. A life and reliability assessment of the actuator gears was performed in two stages: a contact stress fatigue model and a gear tooth bending fatigue model. For the contact stress analysis, the Lundberg-Palmgren bearing life theory was expanded to include gear-surface pitting for the actuator as a system. The mission spectrum of the Space Shuttle rudder/speed brake actuator was combined into equivalent effective hinge moment loads including an actuator input preload for the contact stress fatigue and tooth bending fatigue models. Gear system reliabilities are reported for both models and their combination. Reliability of the actuator bearings was analyzed separately, based on data provided by the actuator manufacturer. As a result of the analysis, the reliability of one half of a single actuator was calculated to be 98.6 percent for 12 flights. Accordingly, each actuator was subsequently limited to 12 flights before removal from service in the Space Shuttle.

  5. The impact of disability, fatigue and sleep quality on the quality of life in multiple sclerosis

    Directory of Open Access Journals (Sweden)

    Ghaem Haleh

    2008-01-01

    Full Text Available Background: Only few papers have investigated the impact of multiple sclerosis (MS, especially MS-related fatigue and the impact of the quality of sleep on the quality of life (QoL in MS patients. Objective: The objective of this study was to measure the quality of life in MS patients and the impact of disability, fatigue and sleep quality, using statistical modeling. Materials and Methods: A cross-sectional study was conducted and data was collected from 141 MS patients, who were referred to the Mottahari Clinic, Shiraz, Iran, in 2005. Data on health-related quality of life (MSQoL-54, fatigue severity scale (FSS, and Pittsburgh sleep quality Index (PSQI were obtained in the case of all the patients. Epidemiology data concerning MS type, MS functional system score, expanded disability status scale (EDSS etc. were also provided by a qualified neurologist. Spearman a coefficient, Mann-Whitney U test, and linear regression model were used to analyze the data. Results : The mean SD age of 141 MS patients was 32.69.6 year. Thirty five (24.8% of them were male and the others were female. Eighty two (58.1% of the patients had EDSS score of ? 2, 36 (25.5% between 2.5 and 4.5, and 23 (16.3% ? 5. As per PSQI scores, two (1.4% of the patients had good sleep, 16 (11.3% had moderate sleep and 123 (87.2% had poor sleep. There was a significant high positive correlation between the quality of mental and physical health composite scores (r = 0.791, P < 0.001. There was a significant negative correlation between the quality of physical score and age (r = -0.88, P < 0.001, fatigue score (r = -0.640, P < 0.001, EDSS score (r = -0.476, P < 0.001 and PSQI (sleep quality r = -0.514, P < 0.000. Linear regression analysis showed that PSQI score, EDSS, and fatigue score were predictors in the model between the quality of physical score and covariates ( P < 0.001. Linear regression model showed that fatigue score and PSQI were predictors in the model between the quality of mental score and covariates ( P < 0.001. Discussion and Conclusion: In conclusion, it may be said that MS patients had poor and moderate quality of mental and physical health. The quality of life was impaired as seen by PSQI, EDSS, and FSS. It is our suggestion that these patients require the attention of health care professionals, to be observed for the need of possible psychological support.

  6. The impact of disability, fatigue and sleep quality on the quality of life in multiple sclerosis

    Science.gov (United States)

    Ghaem, Haleh; Haghighi, Afshin Borhani

    2008-01-01

    Background: Only few papers have investigated the impact of multiple sclerosis (MS), especially MS-related fatigue and the impact of the quality of sleep on the quality of life (QoL) in MS patients. Objective: The objective of this study was to measure the quality of life in MS patients and the impact of disability, fatigue and sleep quality, using statistical modeling. Materials and Methods: A cross-sectional study was conducted and data was collected from 141 MS patients, who were referred to the Mottahari Clinic, Shiraz, Iran, in 2005. Data on health-related quality of life (MSQoL-54), fatigue severity scale (FSS), and Pittsburgh sleep quality Index (PSQI) were obtained in the case of all the patients. Epidemiology data concerning MS type, MS functional system score, expanded disability status scale (EDSS) etc. were also provided by a qualified neurologist. Spearman ? coefficient, Mann-Whitney U test, and linear regression model were used to analyze the data. Results: The mean SD age of 141 MS patients was 32.69.6 year. Thirty five (24.8%) of them were male and the others were female. Eighty two (58.1%) of the patients had EDSS score of ? 2, 36 (25.5%) between 2.5 and 4.5, and 23 (16.3%) ? 5. As per PSQI scores, two (1.4%) of the patients had good sleep, 16 (11.3%) had moderate sleep and 123 (87.2%) had poor sleep. There was a significant high positive correlation between the quality of mental and physical health composite scores (r = 0.791, P<0.001). There was a significant negative correlation between the quality of physical score and age (r = -0.88, P<0.001), fatigue score (r = -0.640, P<0.001), EDSS score (r = -0.476, P<0.001) and PSQI (sleep quality r = -0.514, P<0.000). Linear regression analysis showed that PSQI score, EDSS, and fatigue score were predictors in the model between the quality of physical score and covariates (P<0.001). Linear regression model showed that fatigue score and PSQI were predictors in the model between the quality of mental score and covariates (P<0.001). Discussion and Conclusion: In conclusion, it may be said that MS patients had poor and moderate quality of mental and physical health. The quality of life was impaired as seen by PSQI, EDSS, and FSS. It is our suggestion that these patients require the attention of health care professionals, to be observed for the need of possible psychological support. PMID:19893680

  7. Statistical property of initiation and growth life distributions of surface fatigue cracks in spheroidal graphite cast iron

    International Nuclear Information System (INIS)

    Rotating bending fatigue tests were carried out smooth specimens of ferrite-base and mainly pearlite-base spheroidal graphite cast iron (FDI and PDI, respectively) at room temperature. The statistical properties of initiation and propagation lives of surface cracks and fatigue life were discussed in detail from results of successive observations of specimen surface. The distribution of the initiation life Ni, the propagation process life Np1, Np2 and the fracture life Nf, determined in this study, were well represented by a three-parameter Weibull distribution. The coefficient of variation ? of those distributions decreased with increasing crack length 2a during the fatigue process. The correlation coefficient in order Z of Ni, Np for Nf increased with increasing 2a, and in the lower stress level the Z reached about 1.0 in the early stage of fatigue (2a=700?m). (author)

  8. Prediction of creep-fatigue life by use of creep rupture ductility

    International Nuclear Information System (INIS)

    It was clarified that tension strain hold reduced creep-fatigue life of many engineering materials in different degrees depending on material, temperature and test duration. However the reduction in the life due to holding for various durations could be correlated to the fraction of intergranular facets on fracture surfaces which was considered to be an index of the damage introduced during strain hold. This fraction of intergranular facets by creep-fatigue failure exhibited a direct relation to the creep rupture ductility of the material tested at the same temperature and for the same creep-fatigue life-time. From these results an empirical equation has been derived as follow; (? sub(epsilonsub(i)))/Dsub(c).(N sub(h sup(?))) = C, where ? sub(epsilonsub(i)) is inelastic strain range, Dsub(c) is the creep rupture ductility for the same duration as creep-fatigue life time, Nsub(h) is the creep-fatigue life under tension strain hold conditions, and ? and C are constants depending on the material and testing temperature. From the equation the life prediction is possible for a given inelastic strain range ? sub(epsilonsub(i)) if the constants ? and C, and Dsub(c) are known. The value of ? was found to be 0.62 and 0.74 for various austenitic stainless steels and NCF800 at 600 0C and 700 0C, respectively, and 0.69 for 1 1/4Cr-1/2Mo steel at 600 0C. The value of C was found to be 0.50 and 0.59 for various austenitic stainless steels and NCF800 at 600 0C and 700 0C, respectively, and 0.49 for 1 1/4Cr-1/2Mo steel at 600 0C. The creep rupture ductility Dsub(c) is available in the NRIM Creep Data Sheets up to 105 h for multi-heats of many kinds of heat resistant alloys. (author)

  9. Short-Time Procedure for the Determination of Woehler and Fatigue Life Curves Using Mechanical, Thermal and Electrical Data

    Science.gov (United States)

    Walther, Frank; Eifler, Dietmar

    Mechanical stress-strain hysteresis, temperature and electrical resistance measurements were performed to characterize the fatigue behavior and to calculate the lifetime of metals under constant amplitude loading and random loading. Constant amplitude sequences were periodically inserted in random load tests to measure the plastic strain amplitude as well as the deformation-induced changes in specimen temperature and electrical resistance. These data are plotted versus the number of cycles for the fatigue assessment under random loading, similar as commonly practiced under constant amplitude loading. On the basis of Morrow and Basquin equations in generalized formulations, to be applicable for mechanical, thermal and electrical measurement techniques, a physically based fatigue life calculation method PHYBAL was developed. This new short-time procedure requires data of only three fatigue tests for a rapid and nevertheless precise determination of Woehler curves for constant amplitude loading or fatigue life curves for random loading.

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

    Science.gov (United States)

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

    1976-01-01

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

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

    OpenAIRE

    Minahan Clare L; Stroud Nicole M

    2009-01-01

    Abstract 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 2565 yr) living in Queensland, Australia was conducted. Physical activity level, depression, fatigue and quality of life were assessed using the International Physical Activity Questionn...

  12. A work-life perspective on sleep and fatigue-looking beyond shift workers.

    Science.gov (United States)

    Skinner, Natalie; Dorrian, Jill

    2015-10-01

    This study examines sleep and fatigue through a work-life lens. Whilst most often thought of as an issue for shift workers, this study observed that self-reported insufficient sleep and fatigue were prevalent for workers on standard daytime schedules. Using a representative sample of 573 daytime workers (51.3% men; 70.7% aged 25-54?yr) from one Australian state, it was observed that 26.4% of daytime workers never or rarely get the seven hours of sleep a night that is recommended for good health. Those with parenting responsibilites (29.4%) or working long (45+) hours (37.4%) were most likely to report insufficient sleep. Whereas mothers in full-time work were most likely to report frequent fatigue (42.5%). This study highlights the common experience of insufficient sleep and fatigue in a daytime workforce, with significant implications for health and safety at work and outside of work. Stronger and more effective legislation addressing safe and 'decent' working time is clearly needed, along with greater awareness and acceptance within workplace cultures of the need to support reasonable workloads and working hours. PMID:26027709

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

    Science.gov (United States)

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

    2015-06-01

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

  14. Room temperature creep-fatigue response of selected copper alloys for high heat flux applications

    DEFF Research Database (Denmark)

    Li, M.; Singh, B.N.; Stubbins, J.F.

    Two copper alloys, dispersion-strengthened CuAl25 and precipitation-hardened CuCrZr, were examined under fatigue and fatigue with hold time loading conditions. Tests were carried out at room temperature and hold times were imposed at maximum tensile and maximum compressive strains. It was found...... that hold times could be damaging even at room temperature, well below temperatures typically associated with creep. Hold times resulted in shorter fatigue lives in the high cycle fatigue, long life regime (i.e., at low strain amplitudes) than those of materials tested under the same conditions without...... the hold period at all applied strain levels in both tension and compression. In all cases, stresses relaxed quickly within the first few seconds of the hold period and much more gradually thereafter. The CuAl25 alloy showed a larger effect of hold time on reduction of high cycle fatigue life than did...

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

    Science.gov (United States)

    Stroud, Nicole M; Minahan, Clare L

    2009-01-01

    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 2565 yr) living in Queensland, Australia was conducted. Physical activity level, depression, fatigue and quality of life were assessed using the International Physical Activity Questionnaire, Health Status Questionnaire Short Form 36, Becks Depression Inventory and Modified Fatigue Impact Scale. Results 52 participants performed at least two 30-min exercise sessionswk-1 (Exercisers) and 69 did not participate in regular physical activity (Non-exercisers). Exercisers reported favourable fatigue, depression and quality of life scores when compared to Non-exercisers. Significant weak correlations were found between both leisure-time and overall reported physical activity levels and some subscales of the quality of life and fatigue questionnaires. Additionally, some quality of life subscale scores indicated that regular physical activity had a greater benefit in subjects with moderate MS. Conclusion Favourable fatigue, depression and quality of life scores were reported by persons with MS who regularly participated in physical activity, when compared to persons with MS who were classified as Non-exercisers. PMID:19619337

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

    Directory of Open Access Journals (Sweden)

    Minahan Clare L

    2009-07-01

    Full Text Available Abstract 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 2565 yr living in Queensland, Australia was conducted. Physical activity level, depression, fatigue and quality of life were assessed using the International Physical Activity Questionnaire, Health Status Questionnaire Short Form 36, Becks Depression Inventory and Modified Fatigue Impact Scale. Results 52 participants performed at least two 30-min exercise sessionswk-1 (Exercisers and 69 did not participate in regular physical activity (Non-exercisers. Exercisers reported favourable fatigue, depression and quality of life scores when compared to Non-exercisers. Significant weak correlations were found between both leisure-time and overall reported physical activity levels and some subscales of the quality of life and fatigue questionnaires. Additionally, some quality of life subscale scores indicated that regular physical activity had a greater benefit in subjects with moderate MS. Conclusion Favourable fatigue, depression and quality of life scores were reported by persons with MS who regularly participated in physical activity, when compared to persons with MS who were classified as Non-exercisers.

  17. Creep-fatigue life assessment of cruciform weldments using the linear matching method

    International Nuclear Information System (INIS)

    This paper presents a creep-fatigue life assessment of a cruciform weldment made of the steel AISI type 316N(L) and subjected to reversed bending and cyclic dwells at 550 °C using the Linear Matching Method (LMM) and considering different weld zones. The design limits are estimated by the shakedown analysis using the LMM and elastic-perfectly-plastic material model. The creep-fatigue analysis is implemented using the following material models: 1) Ramberg–Osgood model for plastic strains under saturated cyclic conditions; 2) power-law model in “time hardening” form for creep strains during primary creep stage. The number of cycles to failure N⋆ under creep-fatigue interaction is defined by: a) relation for cycles to fatigue failure N∗ dependent on numerical total strain range Δεtot for the fatigue damage ωf; b) long-term strength relation for the time to creep rupture t∗ dependent on numerical average stress σ¯ during dwell Δt for the creep damage ωcr; c) non-linear creep-fatigue interaction diagram for the total damage. Numerically estimated N⋆ for different Δt and Δεtot shows good quantitative agreement with experiments. A parametric study of different dwell times Δt is used to formulate the functions for N⋆ and residual life L⋆ dependent on Δt and normalised bending moment M-tilde , and the corresponding contour plot intended for design applications is created. -- Highlights: ► Ramberg–Osgood model is used for plastic strains under saturated cyclic conditions. ► Power-law model in time-hardening form is used for creep strains during dwells. ► Life assessment procedure is based on time fraction rule to evaluate creep damage. ► Function for cycles to failure is dependent on dwell period and normalised moment. ► Function for FSRF dependent on dwell period takes into account the effect of creep

  18. Influence of grain orientation on evolution of surface features in fatigued polycrystalline copper: A comparison of thermal and uniaxial mechanical fatigue results

    International Nuclear Information System (INIS)

    Surface state plays a major role in the crack nucleation process of pure metals in the High-Cycle-Fatigue (HCF) as well as in the Ultra-High-Cycle-Fatigue (UHCF) regime. Therefore, in studies dealing with HCF or UHCF, special attention is paid to the evolution of surface degradation during fatigue life. The accelerating structures of the future Compact Linear Collider (CLIC) under study at CERN will be submitted to a high number of thermal-mechanical fatigue cycles, arising from Radio Frequency (RF) induced eddy currents, causing local superficial cyclic heating. The number of cycles during the foreseen lifetime of CLIC reaches 2x1011. Fatigue may limit the lifetime of CLIC structures. In order to assess the effects of superficial fatigue, specific tests are defined and performed on polycrystalline Oxygen Free Electronic (OFE) grade Copper, a candidate material for the structures. Surface degradation depends on the orientation of near-surface grains. Copper samples thermally fatigued in two different fatigue experiments, pulsed laser and pulsed RF-heating, underwent postmortem Electron Backscattered Diffraction measurements. Samples fatigued by pulsed laser show the same trend in the orientation-fatigue damage behavior as samples fatigued by pulsed RF-heating. It is clearly observed that surface grains, oriented [1 1 1] with respect to the surface, show significantly more damage than surface grains oriented [1 0 0]. Results arising from a third fatigue experiment, the ultrasound (US) swinger, are compared to the results of the mentioned experiments. The US swinger is an uniaxial mechanical fatigue test enabling to apply within several days a total number of cycles representative of the life of the CLIC structures, thanks to a high repetition rate of 24 kHz. For comparison, laser fatigue experiments have much lower repetition rates. The dependence of surface degradation on grain orientation of samples tested by the US swinger was monitored during the fatigue life. Results are presented and compared to the ones arising from the two other test methods.

  19. Assessment of Cancer-Related Fatigue, Pain, and Quality of Life in Cancer Patients at Palliative Care Team Referral: A Multicenter Observational Study (JORTC PAL-09)

    OpenAIRE

    Iwase, Satoru; Kawaguchi, Takashi; Tokoro, Akihiro; YAMADA, KIMITO; Kanai, Yoshiaki; Matsuda, Yoshinobu; Kashiwaya, Yuko; OKUMA, KAE; Inada, Shuji; Ariyoshi, Keisuke; Miyaji, Tempei; Azuma, Kanako; Ishiki, Hiroto; Unezaki, Sakae; Yamaguchi, Takuhiro

    2015-01-01

    Introduction Cancer-related fatigue greatly influences quality of life in cancer patients; however, no specific treatments have been established for cancer-related fatigue, and at present, no medication has been approved in Japan. Systematic research using patient-reported outcome to examine symptoms, particularly fatigue, has not been conducted in palliative care settings in Japan. The objective was to evaluate fatigue, pain, and quality of life in cancer patients at the point of interventio...

  20. Method and data analysis example of fatigue tests

    International Nuclear Information System (INIS)

    In the design and operation of a nuclear fusion reactor, it is important to accurately assess the fatigue life. Fatigue life is evaluated by preparing a database on the relationship between the added stress / strain amplitude and the number of cycles to failure based on the fatigue tests on standard specimens, and by comparing this relationship with the generated stress / strain of the actual constructions. This paper mainly chooses low-cycle fatigue as an object, and explains standard test methods, fatigue limit, life prediction formula and the like. Using reduced-activation ferrite steel F82H as a material, strain controlled low-cycle fatigue test was performed under room temperature atmosphere. From these results, the relationship between strain and the number of cycles to failure was analyzed. It was found that the relationship is asymptotic to the formula of Coffin-Manson Law under high-strain (low-cycle condition), and asymptotic to the formula of Basquin Law under low-strain (high-cycle condition). For F82H to be used for the blanket of a nuclear fusion prototype reactor, the arrangement of fatigue life data up to about 700°C and the establishment of optimal fatigue design curves are urgent tasks. As for fusion reactor structural materials, the evaluation of neutron irradiation effect on fatigue damage behavior and life is indispensable. For this purpose, it is necessary to establish standardized testing techniques when applied to small specimens. (A.O.)

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

    Science.gov (United States)

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

    2014-11-01

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

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

    Science.gov (United States)

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

    2002-01-01

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

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

    Science.gov (United States)

    Statecny, Jiri; Drexler, Jan; Janak, Antonin

    Besides the conventional SL (Safe Life) philosophy for disk cyclic life predictions, the DT (Damage Tolerance) philosophy starts to be used in connection with the RFC (Retirement for Cause) strategy. The present paper is aimed especially at the certification demonstrations proofs. The use of advanced life prediction approaches is quite dependent on a reliable NDIT (Nondestructive Inspection Technique). Therefore the reliability of the information gained by NDI macrographic findings during the LCF (Low Cycle Fatigue) tests must be verified by micrographic analysis of the failed components. The approach used in ARTI and some experience from tests are presented. Several models have been developed in ARTI in recent years as a means for life prediction on a probabilistic basis. A new one is presented which may be useful for disks with critical circumferentially shaped concentrators.

  4. Service Life Of Main Piping Component Due To Low Thermal Stresses.Fatigue

    International Nuclear Information System (INIS)

    The paper deals with estimating the service life of the power station Main piping component and describing the repair process for extending of its service life. After a long period of service, several circular fatigue cracks have been discovered at the bottom of the Main piping component chamber. Finite element analyses of transient thermal stresses, caused by power station startup, are carried out in the paper. The calculation results show good agreement between the theoretical locations of the maximum stresses and the actual locations of the cracks. There is a good agreement between theoretical evaluation and actual service life, as well. The possibility of machining out the cracks in order to prevent their growing is examined here. The machining enables us to extend the power station component's life service

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

    International Nuclear Information System (INIS)

    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.

  6. Fatigue life of creep resisting steels under conditions of cyclic mechanical and thermal interactions

    Directory of Open Access Journals (Sweden)

    A. Marek

    2009-11-01

    Full Text Available urpose: This study sets out to determine the characteristics of high-temperature creep resisting steels under conditions of thermo-mechanical fatigue with the use of a method proposed in the Code-of-Practice under the EU TMF-Standard project.Design/methodology/approach: The thermo-mechanical fatigue (TMF tests were carried out in the conditions where the value of complete strain and the temperature were under control. Two methods of investigating samples in TMF tests were applied: OP (out-of-phase and IP (in-phase.Findings: Based on the tests, the characteristics of TMF life was determined and it was found that X20CrMoV12.1 steel shows lower life in comparison with new steels: X10CrMoVNb9-1 (T/P91 and X10CrWMoVNb9-2 (T/P92. The results of the OP tests made for X10CrMoVNb9-1 (T/P91 steel are an exception here. Tests of thermo-mechanical fatigue have shown that in a majority of cases in fatigue tests, the X20CrM0V12.1 steel has lower TMF life when compared to X10CrMoVNb9-1 (T/P91 and X10CrWMoVNb9-2 (T/P92 steels, despite its better strength properties, as a measure of which, the range of stress was adopted.Research limitations/implications: At the present stage of the research, two types of tests (IP and PO were performed. Due to a limited number of experiments connected with the application of selected types of tests and their number, the conclusions resulting from the research may, at the present stage, serve as guidelines for its continuation only.Practical implications: The test results may also be used to compare the properties of creep resisting steels used in the power engineering industry and represent a contribution to widening the knowledge of the behaviour of materials under thermo-mechanical fatigue conditions.Originality/value: This study is one of the first attempts to determine the TMF life characteristics of the steels used in the Polish power engineering industry.

  7. Effect of Buckling Modes on the Fatigue Life and Damage Tolerance of Stiffened Structures

    Science.gov (United States)

    Davila, Carlos G.; Bisagni, Chiara; Rose, Cheryl A.

    2015-01-01

    The postbuckling response and the collapse of composite specimens with a co-cured hat stringer are investigated experimentally and numerically. These specimens are designed to evaluate the postbuckling response and the effect of an embedded defect on the collapse load and the mode of failure. Tests performed using controlled conditions and detailed instrumentation demonstrate that the damage tolerance, fatigue life, and collapse loads are closely tied with the mode of the postbuckling deformation, which can be different between two nominally identical specimens. Modes that tend to open skin/stringer defects are the most damaging to the structure. However, skin/stringer bond defects can also propagate under shearing modes. In the proposed paper, the effects of initial shape imperfections on the postbuckling modes and the interaction between different postbuckling deformations and the propagation of skin/stringer bond defects under quasi-static or fatigue loads will be examined.

  8. A combined approach to buffet response analyses and fatigue life prediction

    Science.gov (United States)

    Jacobs, J. H.; Perez, R.

    1994-03-01

    Experimental measurement and neural network based prediction of wind tunnel model empennage random pressures are discussed. Artificially generated neural network power spectral densities of surface pressures are used to augment existing data and then load an elastic finite element model to obtain response spectra. Details on the use of actual response spectra from flight test data are also discussed. A random spectra fatigue method is described which effectively combines buffet and maneuver loads into a time series based on aircraft usage data. A peak-valley damage analysis procedure is employed to compute the aggregate fatigue life of the structure based on five combined load time series information. Applications of the method as a continual learning tool for buffet response spectra is elaborated.

  9. Fatigue life of silumin irradiated by high intensity pulsed electron beam

    Science.gov (United States)

    Konovalov, S. V.; Alsaraeva, K. V.; Gromov, V. E.; Ivanov, Yu F.

    2015-09-01

    The electron-beam processing of silumin, leading to the evolution of structure-phase state of its surface is carried out. It has been shown that this alloy is a multiphase material and contains, except an aluminum-based phase, the particles of intermetallic compounds of Al-Si- Fe-Mn. It is shown that electron beam treatment of the eutectic silumin surface increases the fatigue service life more than in 3.5 times. The analysis of structure-phase states modification of silumin subjected to electron beam treatment with the following fatigue loading up to the failure is carried out by methods of optical and scanning electron diffraction microscopy. Analysis of the surface layer structure revealed the sources of nucleation of submicrocracks. It is revealed that the large silicon plates located on the surface and in the subsurface layer are the most dangerous stress concentrators.

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

    International Nuclear Information System (INIS)

    Specimens of 20%-cold-worked AISI type 316 stainless steel were irradiated in the High Flux Isotope Reactor (HFIR) at 5500C 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 5500C. No significant effect of the irradiation on low-cycle fatigue life was observed; however, the strain range of the 107 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 ?epsilon/sub T/ = 0.02N/sub f/-012 + N/sub f/-06 for N/sub f/ 7 cycles

  11. Fatigue Behavior of Inconel 718 TIG Welds

    Science.gov (United States)

    Alexopoulos, Nikolaos D.; Argyriou, Nikolaos; Stergiou, Vasillis; Kourkoulis, Stavros K.

    2014-08-01

    Mechanical behavior of reference and TIG-welded Inconel 718 specimens was examined in the present work. Tensile, constant amplitude fatigue, and fracture toughness tests were performed in ambient temperature for both, reference and welded specimens. Microstructure revealed the presence of coarse and fine-grained heat-affected zones. It has been shown that without any post-weld heat treatment, welded specimens maintained their tensile strength properties while their ductility decreased by more than 40%. It was found that the welded specimens had lower fatigue life and this decrease was a function of the applied fatigue maximum stress. A 30% fatigue life decrease was noticed in the high cycle fatigue regime for the welded specimens while this decrease exceeded 50% in the low cycle fatigue regime. Cyclic stress-strain curves showed that Inconel 718 experiences a short period of hardening followed by softening for all fatigue lives. Cyclic fatigue response of welded specimens' exhibited cyclically stable behavior. Finally, a marginal decrease was noticed in the Mode I fracture toughness of the welded specimens.

  12. Prediction of fatigue life under service loading using the relative method

    International Nuclear Information System (INIS)

    Fatigue life estimates obtained with the local strain approach (LSA) and with the conventional nominal stress approach (NSA) were compared with experimental results obtained on notched AlCuMg2 aircraft material specimens with flight simulation random tensile loading. The effect of change of the reference stress, of the loading program and of some changes in the loading frequency distribution, on the ratio Nsub(exp)/Nsub(pred) was investigated. A material strain-life curve, a cyclic stress-strain curve. The Neuber-Topper rule Ksub(sigma) x Ksub(epsilon) = K2 = const. and a K value estimated with an exact two-parameter notch factor formula for the case R = 0, N = 107 were used for life predictions. (orig./RW)

  13. A model for life predictions of nickel-base superalloys in high-temperature low cycle fatigue

    Science.gov (United States)

    Romanoski, Glenn R.; Pelloux, Regis M.; Antolovich, Stephen D.

    1988-01-01

    Extensive characterization of low-cycle fatigue damage mechanisms was performed on polycrystalline Rene 80 and IN100 tested in the temperature range from 871 to 1000 C. Low-cycle fatigue life was found to be dominated by propagation of microcracks to a critical size governed by the maximum tensile stress. A model was developed which incorporates a threshold stress for crack extension, a stress-based crack growth expression, and a failure criterion. The mathematical equivalence between this mechanistically based model and the strain-life low-cycle fatigue law was demonstrated using cyclic stress-strain relationships. The model was shown to correlate the high-temperature low-cycle fatigue data of the different nickel-base superalloys considered in this study.

  14. Fatigue life determination by damage measuring in SAE 8620 specimens steel subjected to multiaxial experiments in neutral and corrosive environment

    International Nuclear Information System (INIS)

    Fatigue is the fail phenomenon of a material subjected to cyclic loads. This phenomenon affects any component under loads (forces, temperatures, etc.) that changes in time. When there is a combined load, originating multiaxial fatigue, which is the most of the real loads, worst is the situation. Before the component fail, the fatigue phenomenon produces damages to its material and this is a cumulative process that could not be reduced. In the continuum mechanic context, material damage is defined as a parameter that reduces the component resistance and this could cause its fail. The process of damage measuring by changes in electrical resistance is used in this work, and from experimental results of SAE 8620 steel specimens subjected to multiaxial fatigue in corrosive and neutral environment, the remaining specimen time life could be determined. Each specimen has its initial electrical resistance measured and after a certain number of fatigue cycles stopping points, its electrical resistance was measured again. In order to study multiaxial fatigue in specimens, a machine that induces simultaneously bending and torsional loads in the specimen was developed. Air at the temperature range of 18 deg C and 20 deg C was considered neutral environment. The corrosive environment was a NaCl solution with a concentration of 3,5% in weigh. The experimental results showed that the measuring fatigue damage using the changes in electrical resistance is efficient and that is possible to estimate the effect of a corrosive environment in the fatigue damage. (author)

  15. Fatigue analysis and life prediction of composite highway bridge decks under traffic loading

    Scientific Electronic Library Online (English)

    Fernando N., Leito; Jos Guilherme S. da, Silva; Sebastio A. L. de, Andrade.

    2013-05-01

    Full Text Available Steel and composite (steel-concrete) highway bridges are currently subjected to dynamic actions of variable magnitude due to convoy of vehicles crossing on the deck pavement. These dynamic actions can generate the nucleation of fractures or even their propagation on the bridge deck structure. Proper [...] consideration of all of the aspects mentioned pointed our team to develop an analysis methodology with emphasis to evaluate the stresses through a dynamic analysis of highway bridge decks including the action of vehicles. The design codes recommend the application of the curves S-N associated to the Miner's damage rule to evaluate the fatigue and service life of steel and composite (steel-concrete) bridges. In this work, the developed computational model adopted the usual mesh refinement techniques present in finite element method simulations implemented in the ANSYS program. The investigated highway bridge is constituted by four longitudinal composite girders and a concrete deck, spanning 40.0m by 13.5m. The analysis methodology and procedures presented in the design codes were applied to evaluate the fatigue of the bridge determining the service life of the structure. The main conclusions of this investigation focused on alerting structural engineers to the possible distortions, associated to the steel and composite bridge's service life when subjected to vehicle's dynamic actions.

  16. Strength and fatigue life evaluation of composite laminate with embedded sensors

    Science.gov (United States)

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

    2014-04-01

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

  17. Evaluation of corrosion fatigue life of steam turbine (Monte Carlo simulation of pitting initiation and crack propagation)

    International Nuclear Information System (INIS)

    For simulating corrosion fatigue fracture of blades and rotors in wet steam environment at the low-pressure stages of steam turbines, Monte Carlo method is developed. The corrosion fatigue, which seriously affects the life of low-temperature sections of steam turbine units, is an extremely complex phenomenon, and involves many factors that can not be predicted by deterministic analysis. Paying attention to the fact that the process of corrosion fatigue is a stochastic (random) process, this study enabled such complex phenomenon to be analyzed by visual simulation

  18. Class I review of LOFT steam generator stress and fatigue life analysis report

    International Nuclear Information System (INIS)

    Review of the LOFT steam generator stress and fatigue life analysis report is presented. Deficiencies were found which will require evaluation and in some areas reanalysis. The effects of these deficiencies upon the steam generator will include: to further reduce the allowable ?P across the tubesheet for the abnormal design case of pressure on primary; and to reduce the allowable number of LOCE transients at some locations of the steam generator from the numbers listed in the stress report and to increase them at other locations

  19. Long-life fatigue test results for two nickel-base structural alloys

    International Nuclear Information System (INIS)

    The results are reported of fatigue tests on two nickel--base alloys, hot-cold-worked and stress-relieved nickel--chrome--iron Alloy 600 and mill-annealed nickel--chrome--moly--iron Alloy 625 in which S-N data were obtained in the life range of 106 to 1010 cycles. The tests were conducted in air at 6000F, in the reversed membrane loading mode, at a frequency of approx. 1850 Hz. An electromagnetic, closed loop servo-controlled machine was built to perform the tests. A description of the machine is given

  20. Machine for use in monitoring fatigue life for a plurality of elastomeric specimens

    Science.gov (United States)

    Fitzer, G. E. (inventor)

    1977-01-01

    An improved machine is described for use in determining the fatigue life for elastomeric specimens. The machine is characterized by a plurality of juxtaposed test stations, specimen support means located at each of the test stations for supporting a plurality of specimens of elastomeric material, and means for subjecting the specimens at each of said stations to sinusoidal strain at a strain rate unique with respect to the strain rate at which the specimens at each of the other stations is subjected to sinusoidal strain.

  1. Assessment of Surface Treatment on Fatigue Life of Cylinder Block for Linear Engine using Frequency Response Approach

    OpenAIRE

    M.M.Rahman; A.K.Ariffin; S. Abdullah; Noor, M. M.; Rosli A. Bakar; Maleque, M.A.

    2009-01-01

    Objectives: This study was focused on the finite element techniques to investigate the effect of surface treatment on the fatigue life of the vibrating cylinder block for new two-stroke free piston engine using random loading conditions. Motivation: An understanding of the effects related to the random loading is necessary to improve the ability of designers to accurately predict the fatigue behavior of the components in service. An internal combustion engine cylinder block is a high volume p...

  2. Influence of Hold Times on Fatigue Life and Fracture Behavior of Cast Superalloy INCONEL 713LC at 700C.

    Czech Academy of Sciences Publication Activity Database

    Obrtlk, Karel; Man, Ji?; Petrenec, Martin; Polk, Jaroslav; Podrbsk, T.

    Ottawa : NRCan - CANMET, 2009, s. 1-9. ISBN N. [International Conference on Fracture /12./. Ottawa (CA), 12.07.2009-17.07.2009] R&D Projects: GA AV ?R 1QS200410502; GA ?R GA106/08/1631; GA ?R GA106/07/1507 Institutional research plan: CEZ:AV0Z20410507 Keywords : Fatigue life * Hold times * High temperature * Inconel 713LC Subject RIV: JL - Materials Fatigue, Friction Mechanics http://www.icf12.org/

  3. Effect of laser shock peening on residual stress and fatigue life of clad 2024 aluminium sheet containing scribe defects

    International Nuclear Information System (INIS)

    Highlights: ? Effect of laser peen intensity on local residual stress fields in 2024 aluminium. ? Peening induces significant changes in surface topography and local hardness. ? Residual stress at peen spot centre in tension, spot overlap in compression. ? Notched fatigue lives increased; crack morphology correlated to residual stress field. ? Large peening power densities can cause fatigue life reduction in notched samples. - Abstract: Laser peening at a range of power densities has been applied to 2 mm-thick sheets of 2024 T351 aluminium. The induced residual stress field was measured using incremental hole drilling and synchrotron X-ray diffraction techniques. Fatigue samples were subjected to identical laser peening treatments followed by scribing at the peen location to introduce stress concentrations, after which they were fatigue tested. The residual stresses were found to be non-biaxial: orthogonal to the peen line they were tensile at the surface, moving into the desired compression with increased depth. Regions of peen spot overlap were associated with large compression strains; the centre of the peen spot remaining tensile. Fatigue lives showed moderate improvement over the life of unpeened samples for 50 ?m deep scribes, and slight improvement for samples with 150 ?m scribes. Use of the residual stress intensity Kresid approach to calculate fatigue life improvement arising from peening was unsuccessful at predicting the relative effects of the different peening treatments. Possible reasons for this are explored.

  4. Independent effect of fatigue on health-related quality of life in patients with idiopathic Parkinson's disease.

    Science.gov (United States)

    Dogan, Vasfiye Burcu; Koksal, Ayhan; Dirican, Ayten; Baybas, Sevim; Dirican, Ahmet; Dogan, Gulsum Buse

    2015-12-01

    Nonmotor symptoms (NMS) of idiopathic Parkinson's disease (IPD), specifically fatigue, depression and sleep disturbances, are important contributors for worse quality of life and poor patient outcomes. The aim of this research is to determine the relationship between fatigue and other NMS and the independent effect of fatigue on health-related quality of life (HRQoL) in patients with IPD. 86 IPD patients and 85 healthy individuals were included in our study. Participants were evaluated by their answers to the Beck Depression Inventory, Fatigue Severity Scale, Epworth Sleepiness Scale and Parkinson's Disease Questionnaire-39. Hoehn-Yahr stage, disease duration, medications and demographical characteristics were also noted. ROC analysis was used to determine the cutoff point for HRQoL. Nonparametric Spearman correlation analysis was used for determining the relationship between variables. Independent factors which affect HRQoL were detected by multiple forward stepwise logistic regression analysis. NMS were associated with each other and with HRQoL when they act concomitantly (psleep disturbances did not (p>0.05). The stage of IPD and levodopa-entacapone treatment had independent effects on HRQoL too (p<0.05). Fatigue was found as the most important factor which affects HRQoL among all investigated NMS. So, it is important to ask about fatigue in routine controls of IPD patients and try to treat it for improving life quality. PMID:26198763

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

    International Nuclear Information System (INIS)

    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 a fatigue crack. Data in the literature were reviewed to evaluate the effects of the size, geometry and surface finish of a component on its fatigue life. Fatigue S-N curves for components have been determined by adjusting the probability distribution curves of smooth test specimens for the effect of mean stress and then applying design margins to account for the uncertainties that arise because of component size, geometry and surface finish. The significance of the effect of the environment on the current code design curve and on the proposed interim design curves published in NUREG/CR-5999 is discussed. Estimations of the probability of fatigue cracking in sample components from boiling water reactors and pressurized water reactors are presented. (orig.)

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

    Science.gov (United States)

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

    2014-10-01

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

  7. Ti6Al4V welded joints via electron beam welding: Microstructure, fatigue properties, and fracture behavior

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Xiaoguang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Co-Innovation Center for Advanced Aero-Engine, Beijing 100191 (China); Li, Shaolin [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Qi, Hongyu, E-mail: qhy@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Co-Innovation Center for Advanced Aero-Engine, Beijing 100191 (China)

    2014-03-01

    The effect of microstructural characteristics on the fatigue properties of electron beam-welded joints of forged Ti6Al4V and its fracture behavior were investigated. Tensile tests and fatigue tests were conducted at room temperature in air atmosphere. The test data were analyzed in relation to microstructure, high-cycle fatigue properties, low-cycle fatigue properties, and fatigue crack propagation properties. The high-cycle fatigue test results indicated that the fatigue strength of the joint welded via electron beam welding was higher than that of the base metal because the former had a high yield strength and all high-cycle fatigue specimens were fractured in the base metal. Although the joint specimens had a lower low-cycle fatigue life than the base metal, they mainly ruptured at the fusion zone of the joint specimen and their crack initiation mechanism is load-dependent. The fatigue crack propagation test results show that the joint had a slower crack propagation rate than the base metal, which can be attributed to the larger grain in the fusion zone.

  8. Ti–6Al–4V welded joints via electron beam welding: Microstructure, fatigue properties, and fracture behavior

    International Nuclear Information System (INIS)

    The effect of microstructural characteristics on the fatigue properties of electron beam-welded joints of forged Ti–6Al–4V and its fracture behavior were investigated. Tensile tests and fatigue tests were conducted at room temperature in air atmosphere. The test data were analyzed in relation to microstructure, high-cycle fatigue properties, low-cycle fatigue properties, and fatigue crack propagation properties. The high-cycle fatigue test results indicated that the fatigue strength of the joint welded via electron beam welding was higher than that of the base metal because the former had a high yield strength and all high-cycle fatigue specimens were fractured in the base metal. Although the joint specimens had a lower low-cycle fatigue life than the base metal, they mainly ruptured at the fusion zone of the joint specimen and their crack initiation mechanism is load-dependent. The fatigue crack propagation test results show that the joint had a slower crack propagation rate than the base metal, which can be attributed to the larger grain in the fusion zone

  9. Fatigue life of the casting-magnesium alloy AZ91; Ermuedungslebensdauer der Magnesium-Gusslegierung AZ91

    Energy Technology Data Exchange (ETDEWEB)

    Eisenmeier, G.; Mughrabi, H.; Holzwarth, B.; Hoeppel, H.W.; Ding, H.Z. [Erlangen-Nuernberg Univ., Erlangen (Germany). Inst. fuer Werkstoffwissenschaften

    2000-07-01

    The cyclic deformation behaviour of the die-casting magnesium alloy AZ91 was investigated at constant total strain amplitudes between 1.4 x 10{sup -3} and 2 x 10{sup -2} at room temperature (20 C) and at 130 C. At low total strain amplitudes, a weak cyclic softening at the beginning of the fatigue tests is followed by cyclic hardening, whereas at high total strain amplitudes a strong cyclic hardening occurs throughout. The fatigue lives at 130 C are slightly longer at high strain amplitudes but shorter at low strain amplitudes than at room temperature. The fatigue life data for both temperatures can be described well by the laws of Manson-Coffin and Basquin. The microstructural investigations performed show the strong influence of several microstructural features on the initiation and propagation of fatigue cracks. In order to understand the fatigue crack propagation behaviour, fatigue tests were interrupted at certain numbers of cycles in order to make replicas of the surface of the samples. It could be verified that crack propagation occurs mainly by the coalescence of smaller cracks. Furthermore, unloading tests, performed within a closed cycle, were carried out in order to capture the changes of stiffness (compliance) during a closed cycle with the aim to ascertain the damage evolution occurring during the fatigue tests and to determine the stresses at which the cracks open and close. Finally, two-step fatigue tests were carried out with the objective to quantify deviations from the linear damage rule (LDR) of Palmgren and Miner. The results obtained in this study will be used to formulate a microstructurally based life-prediction concept for single-step as well as for two-step fatigue loading. (orig.)

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

    Science.gov (United States)

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

    2012-01-01

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

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

    Science.gov (United States)

    Mcgaw, Michael A.

    1989-01-01

    Constitutive and life prediction models are developed and verified for materials typically used in hot gas path components of reusable space propulsion systems over the range of relevant operating environments. The efforts were centered on the development of crack initiation life prediction methods, while the efforts of a counterpart group were centered on the development of cyclic crack propagation life prediction methods. The complexion of the active tasks are presented. A significant new task started this year will incorporate the various material constitutive and life prediction models developed in this program into a comprehensive creep-fatigue damage analysis and life assessment computer code. The program will function as a postprocessor to general structural analysis programs (such as finite element or boundary element codes) using the output of such analyses (stress, strain, and temperature fields as functions of time) as the input to the damage analysis and life assessment code. The code will be designed to execute on engineering/scientific workstations and will feature a windowing, mouse-driven user interface. Current plans call for the code to be finished and made available for use in mid 1991.

  12. Uncertainties in fatigue life prediction and a rational definition of safety factors

    International Nuclear Information System (INIS)

    To cope with uncertainties in mechanical and structural design, engineers exercise their judgement through the use of safety factors based on service experience and laboratory data on relevant design parameters. Using the problem of fatigue life prediction as a vehicle, the relationship between the size of a safety factor and the associated risk and cost-benefit estimates of the engineering judgement based on new technical information, is demonstrated. The subtle influence of the choice of a distribution function for a given set of data is exhibited by comparing the gaussian with the three-parameter Weibull fits of a set of fatigue life data on 6061-T6 aluminium. A system of ranking the importance of different sources of uncertainties based on an analysis of service data is proposed along with an example to ''refine'' the system using up-to-date laboratory and field measurements. The concept of a rational definition of safety factors as a tool for engineers who design under uncertainty is discussed. (Auth.)

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

    Science.gov (United States)

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

    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 80C and 125C as well as the room temperature.

  14. Fatigue behavior of reactor pressure vessel steels

    International Nuclear Information System (INIS)

    High-cycle fatigue tests have been conducted on reactor pressure vessel steels, SA533-B1, with four levels of sulfur contents at room temperature. The applied stress versus fatigue life cycle (S-N) curves were developed at load ratios, R, of 0.2 and 0.8. At a load ratio of 0.2, the fatigue limit for SA533-B1 steels with sulfur contents less than 0.015 wt % is around 650 MPa, which is slightly higher than that with sulfur contents higher than 0.027 wt %. At a load ratio of 0.8, there were no fatigue indications on the fracture surface. In some fatigue-tested specimens, specifically those with higher sulfur content levels, fatigue cracks were observed to initiate around the inclusions. A digital video camera was used to record the entire fatigue process, and the results demonstrated that the crack initiation period dominated more than 80% of the total fatigue life. The fatigue-tested specimen surface had been thoroughly examined using optical and scanning electron microscopy. Apparent distinctions were observed between the neighborhood of the crack initiation site and the rest of the specimen surface. A great number of precipitates were found distributed along the sub-grain boundary using transmission electron microscopy. There is no or little change of the morphology of precipitates before and after fatigue tests. The mis-orientation between two neighboring sub-grains ranges from 1 to 5degree. The effects of the applied maximum stress, precipitate distribution, and fatigue cycle on the mis-orientation of the sub-grain boundary will be discussed in this paper

  15. Fatigue Life Assessment of Structures Using Electro-Mechanical Impedance Technique

    International Nuclear Information System (INIS)

    This paper describes a new experimental approach for fatigue life assessment of structures based on the equivalent stiffness determined by surface bonded piezo-impedance transducers through the electro-mechanical impedance (EMI) technique. The remaining life of the component (in terms of the cycles of loading that can be sustained) is non-dimensionally correlated with the equivalent identified stiffness. The proposed approach circumvents the determination of the absolute stiffness of the joint and employs the admittance signature of the surface-bonded piezo-transducers directly. The second part of the paper briefly describes the recent advances made in the field of impedance based structural health monitoring (SHM) in terms of low-cost hardware system and improved damage diagnosis through the integration of global dynamic and EMI techniques using the same set of piezo-sensors. Other recent applications such as bio-sensors and traffic sensors pioneered at the Smart Structures and Dynamics Laboratory (SSDL) are also briefly covered.

  16. Fatigue Life Assessment of Structures Using Electro-Mechanical Impedance Technique

    Science.gov (United States)

    Bhalla, S.

    2012-05-01

    This paper describes a new experimental approach for fatigue life assessment of structures based on the equivalent stiffness determined by surface bonded piezo-impedance transducers through the electro-mechanical impedance (EMI) technique. The remaining life of the component (in terms of the cycles of loading that can be sustained) is non-dimensionally correlated with the equivalent identified stiffness. The proposed approach circumvents the determination of the absolute stiffness of the joint and employs the admittance signature of the surface-bonded piezo-transducers directly. The second part of the paper briefly describes the recent advances made in the field of impedance based structural health monitoring (SHM) in terms of low-cost hardware system and improved damage diagnosis through the integration of global dynamic and EMI techniques using the same set of piezo-sensors. Other recent applications such as bio-sensors and traffic sensors pioneered at the Smart Structures and Dynamics Laboratory (SSDL) are also briefly covered.

  17. Influence of Working Environment on Fatigue Life Time Duration for Runner Blades of Kaplan Turbines

    Directory of Open Access Journals (Sweden)

    Ana-Maria Budai

    2010-10-01

    Full Text Available The paper present an analytical analyzes refer to influence of working environment on life time duration in service of runner blades of Kaplan turbines. The study are made using only analytical method, the entry dates being obtained from measurements made in situ for a Kaplan turbine. To calculate the maximum number of stress cycles whereupon the runner blades work without any damage it was used an analytical relation known in specialized literatures under the name of Morrow’s relation. To estimate fatigue life time duration will be used a formula obtained from one of most common cumulative damage methodology taking in consideration the real exploitation conditions of a specified Kaplan turbine.

  18. Investigation of Bearing Fatigue Damage Life Prediction Using Oil Debris Monitoring

    Science.gov (United States)

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

    2011-01-01

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

  19. Effect of vanadium addition of the fatigue life of aluminum grain refined by titanium or titanium plus boron

    International Nuclear Information System (INIS)

    Aluminum and aluminum alloys are industrially grain refined by either titanium (Ti), or titanium plus boron, (Ti+B), to enhance their surface quality and improve their mechanical behavior. Vanadium is also used as a grain refiner alone or in addition to Ti or Ti+B. The effect of addition of vanadium on the mechanical behavior and machinability of commercially pure aluminum grain refined by titanium and boron has been previously investigated and reported by the first author. Examination of the available literature reveals that the effect of addition of vanadium on the fatigue life of aluminum has not been previously reported. In this paper, the effect of vanadium addition at a concentration rate of 0.1%, which corresponds to the peritictic limit on the Aluminum-Titanium phase diagram, on the fatigue life and strength of commercially pure aluminum grain refined by Ti or Ti+B, at different stress levels is investigated. Fatigue S-N curves at different stress levels were obtained and discussed. It was found that grain refining of commercially pure aluminum by Ti, Ti+B or V resulted in enhancement of its fatigue life at all stress levels. It was also found that the addition of vanadium to commercially pure aluminum, at a concentration rate of 0.1%, resulted in better fatigue life in the case of Al grain refined by Ti than in the case of Al grain refined by Ti+B, at all stress levels. (author)

  20. Establishment of fatigue life evaluation and management system for district heating pipes considering operating temperature transition data

    International Nuclear Information System (INIS)

    A District Heating(DH) system supplies environmentally-friend heat and is appropriate for reduction of energy consumption and/or air pollutions. The DH transmission pipe, composed of supply and return pipes, has been used to transmit the heat and prevent heat loss during transportation. The two types of pipes are operated at a temperature of 75?115 .deg. C and 40?65 .deg. C, respectively, with an operating pressure of less than 1.568MPa. The objectives of this paper are to systematize data processing of transition temperature and investigate its effects on fatigue life of DH pipes. For the sake of this, about 5 millions temperature data were measured during one year at ten locations, and then available fatigue life estimation schemes were examined and applied to quantify the specific thermal fatigue life of each pipe. As a result, a relational database management system as well as reliable fatigue life evaluation procedures is established for Korean DH pipes. Also, since the prototypal evaluation results satisfied both cycle-based and stress-based fatigue criteria, those can be used as useful information in the future for optimal design, operation and energy saving via setting of efficient condition and stabilization of water temperature

  1. Effects of exercise on angiogenesis and apoptosis-related molecules, quality of life, fatigue and depression in breast cancer patients.

    Science.gov (United States)

    Ergun, M; Eyigor, S; Karaca, B; Kisim, A; Uslu, R

    2013-09-01

    The aim of this study was to explore the effects of exercise on angiogenesis and apoptosis-related molecules, quality of life, fatigue and depression in patients who completed breast cancer treatment. Sixty breast cancer patients were randomised into three groups, as supervised exercise group, home exercise group and education group. Angiogenesis and apoptosis-related cytokine levels and quality of life (EORTC QOL-C30: European Organisation for Research and Treatment of Cancer Quality of Life C30), fatigue (Brief Fatigue Inventory) and depression (BDI: Beck Depression Inventory) scores were compared before and after a 12-week exercise programme. After the exercise programme, statistically significant decreases were found in interleukin-8 and neutrophil activating protein-78 levels in the home exercise group (P depression in breast cancer patients whose treatments are complete. PMID:23731173

  2. Evaluation of creep-fatigue life prediction methods for low-carbon nitrogen-added 316 stainless steel

    International Nuclear Information System (INIS)

    Low-carbon, medium-nitrogen 316 stainless steel is a principal candidate for a main structural material of a demonstration fast breeder reactor plant in Japan. A number of long-term creep tests and creep-fatigue tests have been conducting for two heats of the steel. Two representative creep-fatigue life prediction methods, i.e., time fraction rule and ductility exhaustion method were applied. An introduction of a simple viscous strain term improved the description of stress relaxation behavior and only the conventional (primary plus secondary) creep strain was assumed to contribute to creep damage in the ductility exhaustion method. The present ductility exhaustion approach was found to have very good accuracy in creep-fatigue life prediction, while the time fraction rule overpredicted failure life as large as a factor of 30

  3. Equivalent configurations for notch and fretting fatigue

    Directory of Open Access Journals (Sweden)

    J. A. Arajo

    2015-07-01

    Full Text Available Under the typical partial slip conditions under which fretting fatigue takes place, the amount of superficial damage is small. Therefore, the substantial reduction in fatigue life caused by fretting, when compared to plain fatigue, may well be more associated with the stress concentration and the stress gradient phenomena generated by the contact problem than to the superficial loss of material. In this setting, notch stress-based methodologies could, in principle, be applied to fretting in the medium/high cycle fatigue regime. The aim of this work was to investigate whether it is possible to design fretting and notch fatigue configurations, which are nominally identical in terms of damage measured by a multiaxial fatigue model. The methodology adopted to carry out this search considered a cylindrical on flat contact and a V-notch. Load and geometry dimensions of both configurations were adjusted in order to try to obtain the same decay of the Multiaxial Fatigue Index from the hot spot up to a critical distance. Positive results of such simulations can lead us to design an experimental program that can bring more firm conclusions on the use of pure stress-based approaches, which do not include the wear damage, in the modeling of fretting fatigue.

  4. Statistical analysis of bending fatigue life data using Weibull distribution in glass-fiber reinforced polyester composites

    International Nuclear Information System (INIS)

    The bending fatigue behaviors were investigated in glass fiber-reinforced polyester composite plates, made from woven-roving with four different weights, 800, 500, 300, and 200 g/m2, random distributed glass-mat with two different weights 225, and 450 g/m2 and polyester resin. The plates which have fiber volume ratio Vf ? 44% and obtained by using resin transfer moulding (RTM) method were cut down in directions of [0/90 deg.] and [45 deg.]. Thus, eight different fiber-glass structures were obtained. These samples were tested in a computer aided fatigue apparatus which have fixed stress control and fatigue stress ratio [R = -1]. Two-parameter Weibull distribution function was used to analysis statistically the fatigue life results of composite samples. Weibull graphics were plotted for each sample using fatigue data. Then, S-N curves were drawn for different reliability levels (R = 0.99, R = 0.50, R = 0.368, R = 0.10) using these data. These S-N curves were introduced for the identification of the first failure time as reliability and safety limits for the benefit of designers. The probabilities of survival graphics were obtained for several stress and fatigue life levels. Besides, it was occurred that RTM conditions like fiber direction, resin permeability and full infiltration of fibers are very important when composites (GFRP) have been used for along time under dynamic loads by looking at test results in this study

  5. Comparison of fatigue life prediction based on local strains and nominal stresses respectively

    International Nuclear Information System (INIS)

    Fatigue life predictions based on local strains and nominal stresses respectively have been performed for notched cylindrical bending test specimens (Ksub(t)=1.4, 2.2, 3.3) made of steel 42 Cr Mo 4, Ck 45 and 49 Mn CS 3 under random loading. The results of calculation are compared with relevant test results. The accuracy of the life prediction based on local strains increases the more informations of the notched specimen (e. g. endurance limit, S-N-curve etc.) will be taken into consideration for the life calculation. In the main the accuracy of life prediction based on nominal stresses is dependent on the slope of the S-N-curve assumed to be valid below the endurance limit. By application of relative Miner's rule life prediction can be improved if relevant test results are available. The comparison of the two prediction methods investigated reveals no favour for one of them. Hence, the decision which method should be applied depends on the special problems to be solved. (orig.)

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

    Science.gov (United States)

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

    1989-01-01

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

  7. Analytical Method to Estimate Fatigue Life Time Duration in Service for Runner Blade Mechanism of Kaplan Turbines

    Directory of Open Access Journals (Sweden)

    Ana Maria Budai

    2010-10-01

    Full Text Available The paper present an analytical method that can be used to determianted fatigue life time duration in service for runner blade mechanism of Kaplan turbines. The study was made for lever button of runer blade mechanism using two analytical relation to calculate the maximum number of stress cycles whereupon the mechanism work without any damage. To estimate fatigue life time duration will be used a formula obtained from one of most comon cumulative damage methodology taking in consideration the real exploatation conditions of a specified Kapaln turbine.

  8. Microstructural Influence on Deformation and Fatigue Life of Composites Using the Generalized Method of Cells

    Science.gov (United States)

    Arnold, S. M.; Murthy, P.; Bednarcyk, B. A.; Pineda, E. J.

    2015-01-01

    A fully coupled deformation and damage approach to modeling the response of composite materials and composite laminates is presented. It is based on the semi--analytical generalized method of cells (GMC) micromechanics model as well as its higher fidelity counterpart, HFGMC, both of which provide closed-form constitutive equations for composite materials as well as the micro scale stress and strain fields in the composite phases. The provided constitutive equations allow GMC and HFGMC to function within a higher scale structural analysis (e.g., finite element analysis or lamination theory) to represent a composite material point, while the availability of the micro fields allow the incorporation of lower scale sub-models to represent local phenomena in the fiber and matrix. Further, GMC's formulation performs averaging when applying certain governing equations such that some degree of microscale field accuracy is surrendered in favor of extreme computational efficiency, rendering the method quite attractive as the centerpiece in a integrated computational material engineering (ICME) structural analysis; whereas HFGMC retains this microscale field accuracy, but at the price of significantly slower computational speed. Herein, the sensitivity of deformation and the fatigue life of graphite/epoxy PMC composites, with both ordered and disordered microstructures, has been investigated using this coupled deformation and damage micromechanics based approach. The local effects of fiber breakage and fatigue damage are included as sub-models that operate on the microscale for the individual composite phases. For analysis of laminates, classical lamination theory is employed as the global or structural scale model, while GMC/HFGMC is embedded to operate on the microscale to simulate the behavior of the composite material within each laminate layer. A key outcome of this study is the statistical influence of microstructure and micromechanics idealization (GMC or HFGMC) on the overall accuracy of unidirectional and laminated composite deformation and fatigue response.

  9. Small Crack Growth and Fatigue Life Predictions for High-Strength Aluminium Alloys. Part 1; Experimental and Fracture Mechanics Analysis

    Science.gov (United States)

    Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.

    1998-01-01

    The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.

  10. Effect of hardening induced by cold expansion on damage fatigue accumulation and life assessment of Aluminum alloy 6082 T6

    Directory of Open Access Journals (Sweden)

    Bendouba Mostefa

    2012-12-01

    Full Text Available Hole cold expansion (HCE is an effective method to extend the fatigue life of mechanical structures. During cold expansion process compressive residual stresses around the expanded hole are generated. The enhancement of fatigue life and the crack initiation and growth behavior of a holed specimen were investigated by using the 6082 Aluminum alloy. The present study suggests a simple technical method for enhancement of fatigue life by a cold expansion hole of pre-cracked specimen. Fatigue damage accumulation of cold expanded hole in aluminum alloy which is widely used in transportation and in aeronautics was analyzed. Experimental tests were carried out using pre-cracked SENT specimens. Tests were performed in two and four block loading under constant amplitude. These tests were performed by using two and four blocks under uniaxial constant amplitude loading. The increasing and decreasing loading were carried. The experimental results were compared to the damage calculated by the Miner's rule and a new simple fatigue damage indicator. This comparison shows that the 'damaged stress model', which takes into account the loading history, yields a good estimation according to the experimental results. Moreover, the error is minimized in comparison to the Miner's model.

  11. Effect of hardening induced by cold expansion on damage fatigue accumulation and life assessment of Aluminum alloy 6082 T6

    Scientific Electronic Library Online (English)

    Bendouba, Mostefa; Aid, Abdelkrim; Benhamena, Ali; Benguediab, Mohamed.

    2012-12-01

    Full Text Available Hole cold expansion (HCE) is an effective method to extend the fatigue life of mechanical structures. During cold expansion process compressive residual stresses around the expanded hole are generated. The enhancement of fatigue life and the crack initiation and growth behavior of a holed specimen w [...] ere investigated by using the 6082 Aluminum alloy. The present study suggests a simple technical method for enhancement of fatigue life by a cold expansion hole of pre-cracked specimen. Fatigue damage accumulation of cold expanded hole in aluminum alloy which is widely used in transportation and in aeronautics was analyzed. Experimental tests were carried out using pre-cracked SENT specimens. Tests were performed in two and four block loading under constant amplitude. These tests were performed by using two and four blocks under uniaxial constant amplitude loading. The increasing and decreasing loading were carried. The experimental results were compared to the damage calculated by the Miner's rule and a new simple fatigue damage indicator. This comparison shows that the 'damaged stress model', which takes into account the loading history, yields a good estimation according to the experimental results. Moreover, the error is minimized in comparison to the Miner's model.

  12. Creep-Fatigue Life Design with Various Stress and Temperature Conditions on the Basis of Lethargy Coefficient

    International Nuclear Information System (INIS)

    High temperature and stress are encounted in power plants and vehicle engines. Therefore, determination of the creep-fatigue life of a material is necessary prior to fabricating equipment. In this study, life design was determined on the basis of the lethargy coefficient for different temperatures, stress and rupture times. SP-Creep test data was compared with computed data. The SP-Creep test was performed to obtain the rupture time for X20CrMoV121 steel. The integration life equation was considered for three cases with various load, temperature and load-temperature. First, the lethargy coefficient was calculated by using the obtained rupture stress and the rupture time that were determined by carrying out the SP-Creep test. Next, life was predicted on the basis of the temperature condition. Finally, it was observed that life decreases considerably due to the coupling effect that results when fatigue and creep occur simultaneously

  13. Fatigue of metallic microdevices and the role of fatigue-induced surface oxides

    International Nuclear Information System (INIS)

    A new method for fatigue testing of metallic micro-electro-mechanical systems has been developed and applied to characterize the high-cycle fatigue behavior of nickel microspecimens formed by the LIGA process. Cantilever microbeams with a cross-section of 26 x 250 ?m were tested under fully reversed loading conditions at 20 Hz. The observed stress-life curve and fatigue limit was similar to what has typically been reported for conventional bulk nickel. SEM inspection of the fatigue surface revealed that failure initiated in zones of localized extrusions and intrusions associated with persistent slip bands (PSBs). Focused ion beam machining was used to extract a cross-sectional TEM foil from the deformation zone, revealing an unexpected thick (up to 400 nm) oxide on the surface of the PSBs. This PSB oxide thickening mechanism appears to be the source of crack initiation

  14. Fatigue life assessment of reactor coolant system components by using transfer functions of integrated FE model

    International Nuclear Information System (INIS)

    Recently, efficient operation and practical management of power plants have become important issues in the nuclear industry. In particular, typical aging parameters such as stress and cumulative usage factor should be determined accurately for continued operation of a nuclear power plant beyond design life. However, most of the major components have been designed via conservative codes based on a 2-D concept, which do not take into account exact boundary conditions and asymmetric geometries. The present paper aims to suggest an effective fatigue evaluation methodology that uses a prototype of the integrated model and its transfer functions. The validity of the integrated 3-D Finite Element (FE) model was proven by comparing the analysis results of individual FE models. Also, mechanical and thermal transfer functions, known as Green's functions, were developed for the integrated model with the standard step input. Finally, the stresses estimated from the transfer functions were compared with those obtained from detailed 3-D FE analyses results at critical locations of the major components. The usefulness of the proposed fatigue evaluation methodology can be maximized by combining it with an on-line monitoring system, and this combination, will enhance the continued operations of old nuclear power plants

  15. Literature Review on Design, Analysis and Fatigue Life of a Mechanical Spring

    Directory of Open Access Journals (Sweden)

    Supriya Burgul

    2014-07-01

    Full Text Available In this paper there is reviewed some papers on the design and analysis spring performance and fatigue life prediction of spring. There is also the analysis of failure in spring. The aim of this review paper is to represent a general study on the analysis of spring. Compression springs are commonly used in the I.C. Engine valves,2 wheeler horn & many more and are subjected to number of stress cycles leading to fatigue failure. A lot of research has been done for improving the performance of spring. Now the automobile industry has shown interest in the replacement of steel spring with composite spring. In general, it is found that fiberglass material has better strength characteristic and lighter in weight as compare to steel for spring. We can reduce product development cost and time while improving the safety, comfort, and durability of the vehicles produce. The CAE tool has where much of the design verification is now done using computer simulation rather than physical prototype testing.

  16. Stochastic Analysis of the Influence of Tower Shadow on Fatigue Life of Wind Turbine Blade

    DEFF Research Database (Denmark)

    Pedersen, Ronnie; Nielsen, Sren R.K.

    2012-01-01

    Fatigue damage accumulation in upwind turbine blades is primarily influenced by turbulence in the inflow. However, the stress reversals during blade passages through the stagnating and deflected mean wind field in front of the tower also contributes significantly. In the paper the lower order statistical moments of the fatigue life of a blade are estimated and compared for a turbine with a tripod tower and a standard mono-tower, respectively. The stagnation zones for each of the legs of the tripod are narrower than for the mono-tower, and hence the stress reversals will be comparable smaller. The blade stresses are calculated from a dynamic mechanical model based on a two dynamic degree of freedom with quasi-static correction for higher modes. The self-induced aero-elastic loading and the turbulence loading are modeled by means of a quasi-static model linearized around the operational point, ignoring any memory effects on the load coefficients. However, such memory effects are taken into consideration at the calculation of the aero-dynamic load during tower passage by the use of a rational approximation to the relevant indicial function. Based on Monte Carlo simulations it is demonstrated that the expected damage accumulation per unit of time in the turbine blades are reduced significantly for the tripod when compared to the damage in a comparable mono-tower design.

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

    Science.gov (United States)

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

    2012-06-01

    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.

  18. Improvements in the microstructure and fatigue behavior of pure copper using equal channel angular extrusion

    Science.gov (United States)

    Nemati, J.; Majzoobi, G. H.; Sulaiman, S.; Baharudin, B. T. H. T.; Azmah Hanim, M. A.

    2014-06-01

    In this study, annealed pure copper was extruded using equal channel angular extrusion (ECAE) for a maximum of eight passes. The fatigue resistance of extruded specimens was evaluated for different passes and applied stresses using fatigue tests, fractography, and metallography. The mechanical properties of the extruded material were obtained at a tensile test velocity of 0.5 mm/min. It was found that the maximum increase in strength occurred after the 2nd pass. The total increase in ultimate strength after eight passes was 94%. The results of fatigue tests indicated that a significant improvement in fatigue life occurred after the 2nd pass. In subsequent passes, the fatigue life continued to improve but at a considerably lower rate. The improved fatigue life was dependent on the number of passes and applied stresses. For low stresses (or high-cycle fatigue), a maximum increase in fatigue resistance of approximately 500% was observed for the extruded material after eight passes, whereas a maximum fatigue resistance of 5000% was obtained for high-applied stresses (or low-cycle fatigue). Optical microscopic examinations revealed grain refinements in the range of 32 to 4 ?m. A maximum increase in impact energy absorption of 100% was achieved after eight passes. Consistent results were obtained from fractography and metallography examinations of the extruded material during fatigue tests.

  19. Initial Assessment of the Effects of Nonmetallic Inclusions on Fatigue Life of Powder-Metallurgy-Processed Udimet(TM) 720

    Science.gov (United States)

    Gabb, T. P.; Telesman, J.; Kantzos, P. T.; Bonacuse, P. J.; Barrie, R. L.

    2002-01-01

    The fatigue lives of modern powder metallurgy (PM) disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary due to the different steps of materials/component processing and machining. One of these variables, the presence of nonmetallic inclusions, has been shown to significantly degrade low-cycle fatigue (LCF) life. Nonmetallic inclusions are inherent defects in powder alloys that are a by-product of powder-processing techniques. Contamination of the powder can occur in the melt, during powder atomization, or during any of the various handling processes through consolidation. In modern nickel disk powder processing facilities, the levels of inclusion contamination have been reduced to less than 1 part per million by weight. Despite the efforts of manufacturers to ensure the cleanliness of their powder production processes, the presence of inclusions remains a source of great concern for the designer. the objective of this study was to investigate the effects on fatigue life of these inclusions. Since natural inclusions occur so infrequently, elevated levels of inclusions were carefully introduced in a nickel-based disk superalloy, Udimet 720 (registered trademark of Special Metals Corporation), produced using PM processing. Multiple strain-controlled fatigue tests were then performed on this material at 650 C. Analyses were performed to compare the LCF lives and failure initiation sites as functions of inclusion content and fatigue conditions. A large majority of the failures in specimens with introduced inclusions occurred at cracks initiating from inclusions at the specimen surface. The inclusions could reduce fatigue life by up to 100 times. These effects were found to be dependent on strain range and strain ratio. Tests at lower strain ranges and higher strain ratios produced larger effects of inclusions on life.

  20. A Comparison of Fatigue Properties of Austempered Versus Quenched and Tempered 4340 Steel

    Science.gov (United States)

    Tartaglia, John M.; Hayrynen, Kathy L.

    2012-06-01

    This study was conducted to determine if austempered 4340 steel had different fatigue resistance compared to quench and tempered (Q&T) 4340 steel with an identical hardness of nominally 45 HRC and an identical yield strength of nominally 1340 MPa (194 ksi). Strain-life and stress-life fatigue testing was conducted at room temperature under identical test conditions. The standard array of strain-life and stress-life regression constants was obtained. The two heat treatments produced virtually identical total strain-life curves and fatigue limits at 5 million cycles. However, the two materials exhibited different trends in the elastic and plastic strain regimes. The austempered steel exhibited greater high cycle fatigue (finite) lives than the Q&T samples at comparable elastic strain amplitudes in strain-life fatigue testing and at comparable stress amplitudes in stress-life fatigue testing. However, the Q&T samples exhibited greater low cycle fatigue lives than the austempered samples at comparable plastic strain amplitudes in strain-life testing. Although both materials generally exhibited similar fatigue fracture characteristics, the overload regions of the Q&T samples were composed entirely of dimple rupture, whereas the austempered samples exhibited both dimple rupture and quasicleavage.