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Sample records for high-cycle fatigue life

  1. Predicting random high-cycle fatigue life with finite elements

    Energy Technology Data Exchange (ETDEWEB)

    Preumont, A.; Piefort, V. (Universite Libre de Bruxelles, Brussels (Belgium))

    1994-04-01

    This paper extends the classical theory of random fatigue to multiaxial stress fields, using a quadratic criterion. An equivalent uniaxial random process is constructed by combining the power spectral densities of the normal and tangential stresses according to the von Mises criterion. This process, that we call the von Mises stress, is used to evaluate the damage with a uniaxial model of random fatigue. A finite element implementation is proposed. 17 refs.

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

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    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.

  3. 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.

  4. 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 an 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)

  5. Very high cycle fatigue of tool steels

    OpenAIRE

    Kazymyrovych, Vitaliy

    2010-01-01

    An increasing number of engineering components are expected to have fatigue life in the range of 107 - 1010 load cycles. Some examples of such components are found in airplanes, automobiles and high speed trains. For many materials fatigue failures have lately been reported to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicts the established concept of a fatigue limit, which postulates that having sustained around 107 load cycles th...

  6. 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.

  7. A two-parameter model to predict fatigue life of high-strength steels in a very high cycle fatigue regime

    Science.gov (United States)

    Sun, Chengqi; Liu, Xiaolong; Hong, Youshi

    2015-06-01

    In this paper, ultrasonic (20 kHz) fatigue tests were performed on specimens of a high-strength steel in very high cycle fatigue (VHCF) regime. Experimental results showed that for most tested specimens failed in a VHCF regime, a fatigue crack originated from the interior of specimen with a fish-eye pattern, which contained a fine granular area (FGA) centered by an inclusion as the crack origin. Then, a two-parameter model is proposed to predict the fatigue life of high-strength steels with fish-eye mode failure in a VHCF regime, which takes into account the inclusion size and the FGA size. The model was verified by the data of present experiments and those in the literature. Furthermore, an analytic formula was obtained for estimating the equivalent crack growth rate within the FGA. The results also indicated that the stress intensity factor range at the front of the FGA varies within a small range, which is irrespective of stress amplitude and fatigue life.

  8. Very high cycle fatigue of high performance steels

    OpenAIRE

    Kazymyrovych, Vitaliy

    2008-01-01

    Many engineering components reach a finite fatigue life well above 109 load cycles. Some examples of such components are found in airplanes, automobiles or high speed trains. For some materials the fatigue failures have lately been found to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicted the established concept of fatigue limit for these materials, which postulates that having sustained 107 load cycles the material is capable of ...

  9. Very high cycle fatigue of engineering materials : A literature review

    OpenAIRE

    Kazymyrovych, Vitaliy

    2009-01-01

    Many engineering components reach a finite fatigue life well above 109 load cycles. Some examples of such components are found in airplanes, automobiles or high speed trains. For some materials the fatigue failures have lately been found to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicted the established concept of fatigue limit for these materials, which postulates that having sustained 107 load cycles the material is capable of ...

  10. Physically short crack propagation in metals during high cycle fatigue

    OpenAIRE

    Taylor, David

    2009-01-01

    In metals, during high cycle fatigue on plain specimens, almost the entire fatigue life is spent as short crack initiation and propagation. The fatigue short crack life can be schematically divided into two subsequent phases: microstructurally short crack and physically short crack. Recently, Chapetti proposed a physically short crack threshold and propagation driving force model [1]. In his model the physically short crack behavior is obtained from the long crack propagation, just introducin...

  11. 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

  12. Effects of mean tensile stresses on high-cycle fatigue life and strain accumulation in some reactor materials

    International Nuclear Information System (INIS)

    An assessment has been made of the effects of mean tensile stresses on the high-cycle fatigue behavior of solution-treated Type 304 stainless steel, normalized and tempered 21/4Cr-1Mo steel, Incoloy-800H, and low-carbon Incoloy-800. Mean stresses are usually detrimental to fatigue strength, especially at high temperatures and stress levels, where significant creep can occur during fatigue cycling. Depending on the magnitudes of the alternating and mean stresses, failure may be creep or fatigue controlled. Strain accumulation is also affected by these stress levels and possibly, also, by the cyclic work-hardening characteristics of the material. It is shown that the Goodman Law for estimating mean stress effects is inadequate, since it does not account for time-dependent deformation. An alternative expression not having such a limitation was, therefore, derived and this relates the alternating and mean stresses to the time to failure. Based on limited metallographic observations of fatigue striations in the 21/4Cr-1Mo steel an estimate was made of the crack propagation rate. It was found that a crack of critical size could, under certain conditions, propagate through most of the specimen diameter in a matter of seconds. This presents a more significant safety problem than the case for a crack extending under low-cycle conditions since preventative measures probably could not be implemented before the crack had grown to a large size

  13. On high-cycle fatigue of 316L stents.

    Science.gov (United States)

    Barrera, Olga; Makradi, Ahmed; Abbadi, Mohammed; Azaouzi, Mohamed; Belouettar, Salim

    2014-01-01

    This paper deals with fatigue life prediction of 316L stainless steel cardiac stents. Stents are biomedical devices used to reopen narrowed vessels. Fatigue life is dominated by the cyclic loading due to the systolic and diastolic pressure and the design against premature mechanical failure is of extreme importance. Here, a life assessment approach based on the Dang Van high cycle fatigue criterion and on finite element analysis is applied to explore the fatigue reliability of 316L stents subjected to multiaxial fatigue loading. A finite element analysis of the stent vessel subjected to cyclic pressure is performed to carry out fluctuating stresses and strain at some critical elements of the stent where cracks or complete fracture may occur. The obtained results show that the loading path of the analysed stent subjected to a pulsatile load pressure is located in the safe region concerning infinite lifetime. PMID:22587434

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

    OpenAIRE

    Bayraktar, E.; 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...

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

    OpenAIRE

    Kolyshkin A.; Grigorescu A.; Kaufmann E.; Zimmermann M.; Christ H.-J.

    2014-01-01

    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 apply...

  16. 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.

  17. Specific features of high-cycle and ultra-high-cycle fatigue.

    Czech Academy of Sciences Publication Activity Database

    Lukáš, Petr; Kunz, Ludvík

    Vienna : BOKU, 2001 - (Stanzl-Tschegg, S.; Mayer, H.), s. 23-33 [International Conference on Fatigue in the Very High Cycle Regime. Vienna (AT), 02.06.2001-04.06.2001] R&D Projects: GA AV ?R IAA2041002; GA AV ?R KSK1010104 Institutional research plan: CEZ:AV0Z2041904 Keywords : ultra-high-cycle fatigue * fatigue mechanisms * cyclic plastic deformation Subject RIV: JL - Materials Fatigue, Friction Mechanics

  18. High cycle fatigue properties of stainless martensitic chromium steel springs

    OpenAIRE

    Pirouznia, Pouyan

    2012-01-01

    For many materials and components like in high speed trains and airplanes fatigue failures occur in the range of over 107 load cycles which is called the high cycle fatigue range. A modern version of the springs was invented which are applied in a certain application. Ultrasonic fatigue testing (20 kHz machine) was conducted for evaluating the steel of the springs. This research explores the fundamental understanding of high cycle fatigue testing of strip steel and assesses a stainless marten...

  19. 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

  20. Crack arrest in high cycle thermal fatigue crazing

    International Nuclear Information System (INIS)

    Thermal crazing in high cycle thermal fatigue due to thermal fluctuation in residual heat removal (RHR) system of some nuclear power plants is explained by crack arrest in the depth due to a decreasing stress intensity factor. This is related to high frequencies of thermal loading. An attempt has been made through a parametric study to acquire some knowledge about the loading, knowing the crack depth. For this purpose, analytical as well as finite element simulations of crack propagation in 2D- and 3D-semi-elliptical cracks have been performed. In periodic loading, bounds for the number of cycles to fatigue life are proposed. Moreover, it is shown that in the absence of mean stress, fatigue damage in RHR may be produced in the macroscopic elastic-plastic regime. Finally, it is shown by FE simulations that for a semi-elliptical crack, a small error on stress intensity factor may result in significant error on crack length at high number of cycles, due to error accumulation cycle by cycle. Moreover in this paper is given the reason as to why shielding effect has not been taken into account in the study of crack arrest in RHR.

  1. Investigation of very high cycle fatigue by thermographyc method

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    V. Crupi

    2014-10-01

    Full Text Available Nowadays, many components and structures are subjected to fatigue loading with a number of cycles higher than 107. In this scientific work, the behaviour of two kinds of tool steel was investigated in very high cycle fatigue regime. The fatigue tests were carried out at the frequency of 20 kHz and in fully reversed tensioncompression mode (R = -1 by means of an ultrasonic fatigue testing equipment. The radiometric surface temperature was detected during all the test by means of an IR camera in order to extend the Thermographic Method and the Energetic Approach in very high cycle fatigue regime. The failure mechanism of the investigated steels was evaluated by means of several experimental techniques (scanning electron microscopy, Energy Dispersive X-ray spectroscopy and Optical Microscopy.

  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. Very high cycle fatigue behavior of SAE52100 bearing steel by ultrasonic nanocrystalline surface modification.

    Science.gov (United States)

    Cho, In Shik; He, Yinsheng; Li, Kejian; Oh, Joo Yeon; Shin, Keesam; Lee, Chang Soon; Park, In Gyu

    2014-11-01

    In this paper, the SAE52100 bearing steel contained large quantities of cementite dispersed in ferrite matrix was subjected to the ultrasonic nanocrystalline surface modification (UNSM) treatment that aims for the extension of fatigue life. The microstructure and fatigue life of the untreated and treated specimens were studied by using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), and a developed ultra-high cycle fatigue test (UFT). After UNSM treatment, the coarse ferrite grains (- 10 ?m) were refined to nanosize (- 200 nm), therefore, nanostructured surface layers were fabricated. Meanwhile, in the deformed layer, the number density and area fraction of cementite were increased up to - 400% and - 550%, respectively, which increased with the decrease in depth from the topmost treated surface. The improvement of hardness (from 200 Hv to 280 Hv) and high cycles fatigue strength by - 10% were considered the contribution of the developed nanostructure in the UNSM treated specimen. PMID:25958512

  4. Plasticity-damage based micromechanical modelling in high cycle fatigue

    Science.gov (United States)

    Monchiet, Vincent; Charkaluk, Eric; Kondo, Djimedo

    2006-02-01

    A micro-macro approach of multiaxial fatigue in unlimited endurance is proposed. It allows one to take into account plasticity and damage mechanisms which occur at the scale of Persistent Slip Bands (PSB). The proposed macroscopic fatigue criterion, which corresponds to microcracks nucleation at the PSB-matrix interface, is derived for different homogenization schemes (Sachs, Lin-Taylor and Kröner). The role of a mean stress and of the hydrostatic pressure in high cycle fatigue is shown; in particular, in the case of Lin-Taylor scheme and linear isotropic hardening rule at microscale, one recovers the linear dependance in pressure postulated by K. Dang Van for the macroscopic fatigue criterion. This dependence is related here to the damage micro-mechanism. Finally, the particular case of affine loading is presented as an illustration. To cite this article: V. Monchiet et al., C. R. Mecanique 334 (2006).

  5. 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.

  6. Prevention of piping high cycle thermal fatigue at design stage

    International Nuclear Information System (INIS)

    High cycle thermal fatigue is one of the most difficult phenomena that maintenance people, who are in charge of maintaining the integrity of nuclear piping, encounter. Several efforts, such as temperature measurement and integrity evaluation, or non-destructive examination, have been implemented for avoiding the crack or leakage occurrence. However, because of the complication of the phenomena itself, those efforts have not been fundamental, nor effective answers. Mitsubishi Heavy Industries (MHI) has been involved in collecting information about field experiences on high cycle thermal fatigue on PWR piping domestically and abroad, and studying the radical measures which should be applied at the design stage of construction or remodeling of existing plants. The concept and the outline of those countermeasures are introduced in this paper. (authors)

  7. 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

  8. 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)

  9. Characterization of high cycle fatigue behavior of a new generation aluminum lithium alloy

    International Nuclear Information System (INIS)

    Highlights: ? Effect of microstructure on fatigue fracture of an advanced Al-Li alloy was studied in detail. ? Preferential crack propagation in T3 state at specific orientations was analyzed. ? Fatigue crack propagation difference between T3 and T8 tempers and friction stir welded condition was rationalized. ? The effect of grain size on fatigue life for T3 and T8 tempers was justified based on current theories. ? Delamination in T3 and T8 tempers was rationalized using microstructural analysis and FEA simulation. - Abstract: The high cycle fatigue life characteristics of an Al-Li alloy were studied as a function of microstructure. While for the parent microstructure fatigue life decreased as grain size increased, no such effect was noted at high stresses. This decrease in fatigue life was correlated with lower crack initiation life due to small crack effect. Under multiaxial stress conditions, the alloy exhibited intergranular cracking. The cross-linking of intergranular cracks (in the T8 condition) caused a further deterioration in fatigue life. Additionally, planar slip movements (in the T3 condition) in stage I crack propagation were observed. Slip planarity depended on both the sample texture and the nature of the precipitates. Fractographic and textural evidence is presented.

  10. High cycle fatigue of Type 422 stainless steel

    International Nuclear Information System (INIS)

    High cycle fatigue testing has been carried out on Type 422 stainless steel to determine the performance of cyclically stressed disks and blades in the main and auxiliary HTGR helium circulators. Tests were performed at 316, 482, and 5380C (600, 900, and 10000F) in air for the fully reversible and mean load conditions. Goodman's analysis is shown to be valid in predicting failure at 3160C (6000F), marginally valid at 4820C (9000F), and probably invalid at 5380C (10000F). Metallographic analyses were conducted to characterize the nature of failure for the temperatures and loading conditions investigated

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

    Directory of Open Access Journals (Sweden)

    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.

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

    International Nuclear Information System (INIS)

    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 106 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.

  13. 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.

  14. 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)

  15. Fatigue behavior of ultrafine-grain copper in very high cycle fatigue regime.

    Czech Academy of Sciences Publication Activity Database

    Lukáš, Petr; Kunz, Ludvík; Svoboda, Milan; Bok?vka, O.

    Warrendale, Pennsylvania : TMS , 2007 - (Allison, J.; Jones, J.; Larsen, J.; Ritchie, R.), s. 265-270 ISBN 978-0-87339-704-9. [VHCF-4. International Conference on Very High Cycle Fatigue /4./. Ann Arbor, MI (US), 19.08.2007-22.08.2007] Institutional research plan: CEZ:AV0Z20410507 Keywords : Fatigue strength * Ultrasonic frequency Subject RIV: BM - Solid Matter Physics ; Magnetism

  16. High cycle fatigue property of Ti-600 alloy at ambient temperature

    International Nuclear Information System (INIS)

    Research highlights: Ti-600, developed by Northwest Institute for Nonferrous Metal Research (NIN) in China, is a near alpha titanium alloy designed for components used in turbine engines up to 600 deg. C. Mechanical behavior of the alloy at ambient temperature and its service temperature has widely been studied, the fatigue property for the alloy has never been systematically discussed. Smooth axial fatigue tests were taken for solutioned plus aged alloy, and the fractographies were observed. In order to get the damage mechanism, OM and TEM microstructures were also investigated. - Abstract: Smooth axial fatigue tests were carried out at ambient temperature on one kind of near alpha titanium alloy named after Ti-600 at a frequency of 120-130 Hz and with two kinds of load ratios. The high cycle fatigue (HCF) strength for the solutioned and aged alloy is found to be 475 MPa fatigued with a load ratio R of 0.1, and which is 315 MPa with a load ratio R of -1. The observed high HCF strength for the samples fatigued with a load ratio R of 0.1 is attributed to its overlapping fine and thin plate like ? + ? phase microstructure. During the crack propagation region, at the same stress of 600 MPa, the sample with a fatigue life of 1.78 x 106 cycles has a better fatigue resistance than that of the sample with a fatigue life of 8.61 x 105 cycles, because of its smaller striation distance, its well-developed secondary cracks, more wider and coarsened ? lat cracks, more wider and coarsened ? lathes precipitated at grain boundaries, and the heavily arranged interlacing transformed ? microsructures. The average grain size of rare earth phases varies from several micrometers to 0.2 ?m, no cracks corresponding to rare earth particles can be initiated.

  17. 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)

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

    International Nuclear Information System (INIS)

    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)

  19. Characterization of the temperature evolution during high-cycle fatigue of the ULTIMET superalloy: Experiment and theoretical modeling

    Science.gov (United States)

    Jiang, L.; Wang, H.; Liaw, P. K.; Brooks, C. R.; Klarstrom, D. L.

    2001-09-01

    High-speed, high-resolution infrared thermography, as a noncontact, full-field, and nondestructive technique, was used to study the temperature variations of a cobalt-based ULTIMET alloy subjected to high-cycle fatigue. During each fatigue cycle, the temperature oscillations, which were due to the thermal-elastic-plastic effects, were observed and related to stress-strain analyses. A constitutive model was developed for predicting the thermal and mechanical responses of the ULTIMET alloy subjected to cyclic deformation. The model was constructed in light of internal-state variables, which were developed to characterize the inelastic strain of the material during cyclic loading. The predicted stress-strain and temperature responses were found to be in good agreement with the experimental results. In addition, the change of temperature during fatigue was employed to reveal the accumulation of fatigue damage, and the measured temperature was utilized as an index for fatigue-life prediction.

  20. A very high cycle fatigue thermal dissipation investigation for titanium alloy TC4

    International Nuclear Information System (INIS)

    Titanium alloy TC4 is widely used in aeronautics applications where it is subjected to high frequency fatigue loads. Tests are performed to investigate the alloy fatigue behavior sustaining ultrasonic fatigue load in Very High Cycle Fatigue (VHCF) regime. Thermal dissipation for the alloy in 20 kHz frequency is studied and a model is proposed to describe the temperature increment in the framework of thermodynamics by estimation of the anelastic and inelastic thermal dissipation at microscopic active sites in the reference element volume. The failure probability prediction method is used to evaluate the VHCF dispersion based on the two scale model and fatigue thermal dissipation analysis

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

    Czech Academy of Sciences Publication Activity Database

    Major, Št?pán; Hubálovský, Š.; Kocour, Vladimír; Valach, Jaroslav

    Vol. 732. Zürich : 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./. Mariánské Lázn? (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

  2. 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

  3. 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

  4. 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.

  5. Non-local high cycle fatigue criterion for metallic materials with corrosion defects

    Directory of Open Access Journals (Sweden)

    May Mohamed El

    2014-06-01

    Full Text Available Designing structures against corrosion fatigue has become a key problem for many engineering structures evolving in complex environmental conditions of humidity (aeronautics, civil engineering …. In this study, we investigate the effect of corrosion defects on the high cycle fatigue (HCF strength of a martensitic stainless steel with high specific mechanical strength, used in aeronautic applications. A volumetric approach based on Crossland equivalent stress is proposed. This can be applied to any real defects.

  6. 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

  7. Infrared temperature mapping of ULTIMET alloy during high-cycle fatigue tests

    International Nuclear Information System (INIS)

    Fatigue analysis is an important aspect of understanding mechanical properties of metals and alloys. It is well known that the temperature of a specimen during cyclic fatigue testing increases as a result of internal friction. The temperature changes of a specimen are usually obtained using a thermocouple, but such measurements only provide temperature readings at a specific location. On the other hand, a detailed temperature distribution map of the specimen obtained during fatigue tests could be used as a new dynamic method of monitoring crack initiation and propagation behavior. Temperature changes during fatigue tests are expected to be local and in the form of thermal transients. Capturing thermal signatures associated with fatigue cracks requires a high-speed, high-sensitivity infrared imaging system. Relevant studies using a scanning infrared camera (IR) with temperature resolution of 0.1 K at 293 K can be found in the literature. In the present study, a state-of-the-art IR camera was employed to monitor temperature changes of ULTIMET* alloy during high-cycle fatigue tests. Using the snap-shot and the sequence modes of the IR camera, temperature distribution maps of the specimen as a function of time (cycles) have been obtained. This work reports temperature changes during high-cycle fatigue tests and infrared imaging of fatigue cracks as a heat source before the final failure

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

    Czech Academy of Sciences Publication Activity Database

    Šmíd, Miroslav; Kunz, Ludvík; Huta?, Pavel; Hrbá?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 MŠk(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

  9. On the high cycle fatigue behavior of a type 304L stainless steel at room temperature

    International Nuclear Information System (INIS)

    An extensive study of the uniaxial cyclic material behavior of an AISI 304L austenitic stainless steel is proposed in the high cycle regime and in constant amplitude loadings. More particularly, the effect on the material behavior and lifetime of a mean axial stress is evaluated imposing either a stress or a strain amplitude. Almost no effect is observed on the stress fatigue curve while a reduction of about 30% is obtained on the strain fatigue curve in the endurance regime. It appears that a stress amplitude fatigue parameter or a Smith-Watson-Topper parameter predict accurately such differences based on the material behavior at maximum cyclic softening. (authors)

  10. 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)

  11. 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

  12. Influence of defects on the very high cycle fatigue behaviour of forged aeronautic titanium alloy

    Directory of Open Access Journals (Sweden)

    Nikitin Alexander

    2014-06-01

    Full Text Available This paper is focused on fatigue failure of forged aeronautic titanium alloy Ti-6Al-4Mo under VHCF loading. Continuous fatigue tests were carried out in gigacycle fatigue regime (up to on 1010 cycles on specimens machined from real aircraft compressor disk produced by forging. It has been shown, that crack initiation site shifts from surface to subsurface location with stress amplitude decreasing and fatigue life increasing. Microstructural inhomogeneities so that “hard” alpha particles, borders of large alpha lamella clusters and TiN particles are the cause of fatigue crack nucleation in forged Ti-6Al-4Mo titanium alloy under VHCF loading.

  13. Durability patch: application of passive damping to high-cycle fatigue cracking on aircraft

    Science.gov (United States)

    Rogers, Lynn C.; Searle, Ian R.; Ikegami, Roy; Gordon, Robert W.; Conley, Dave

    1997-05-01

    Although high-cycle fatigue cracks in secondary structure are often termed 'nuisance cracks,' they are costly to repair. Often the repairs do not last long because the repaired part still responds in a resonant fashion to the environment. Although the use of visco-elastic materials for passive dampening applications is well understood, there have been few applications to high-cycle fatigue problems because the design information: temperature, resonant response frequency, and strain levels are difficult to determine. The damage dosimeter, and the durability patch are an effort to resolve these problems with the application of compact, off-the-shelf electronics, and a damped bonded repair patch. This paper presents the electronics, and patch design concepts as well as damping performance test data from a laboratory patch demonstration experiment.

  14. 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

  15. 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

  16. Study and perspectives on high cycle thermal fatigue in nuclear power plants

    International Nuclear Information System (INIS)

    Various kinds of thermal fatigue failure modes exist in nuclear power plant components. Main causes of thermal loads are structural responses to fluid temperature changes. These phenomena have complex mechanisms and so many patterns, that their problems still occur even though well-known issues. Among them, this paper treats high cycle thermal fatigue of branch pipes as the typical mode. Firstly, experimental and analytical researches are explained for thermal load evaluation. Through them, both numerical and kinematic methods were developed. Next chapter describes thermal fatigue strength studies on both crack initiations and propagations. They revealed the similarities of thermal crack initiations with mechanical ones and frequency characteristics of crack propagation. Finally, current status and future challenges are discussed for evaluation of actual plants. (author)

  17. The role of the microstructure and defects on crack initiation in 316L stainless steel under multiaxial high cycle fatigue

    OpenAIRE

    GUERCHAIS, Raphaël; Morel, Franck; Saintier, Nicolas

    2014-01-01

    The aim of this study is to analyse the influence of both the microstructure and defects on the high cycle fatigue behaviour of the 316L austenitic stainless steel, using finite element simulations of polycrystalline aggregates. High cycle fatigue tests have been conducted on this steel under uniaxial (push-pull) and multiaxial (combined in-phase tension and torsion) loading conditions, with both smooth specimens and specimens containing artificial semi-spherical surface defects. 2D numerical...

  18. High cycle fatigue test and regression methods of S-N curve

    International Nuclear Information System (INIS)

    The fatigue design curve in the ASME Boiler and Pressure Vessel Code Section III are based on the assumption that fatigue life is infinite after 106 cycles. This is because standard fatigue testing equipment prior to the past decades was limited in speed to less than 200 cycles per second. Traditional servo-hydraulic machines work at frequency of 50 Hz. Servo-hydraulic machines working at 1000 Hz have been developed after 1997. This machines allow high frequency and displacement of up to ±0.1 mm and dynamic load of ±20 kN are guaranteed. The frequency of resonant fatigue test machine is 50-250 Hz. Various forced vibration-based system works at 500 Hz or 1.8 kHz. Rotating bending machines allow testing frequency at 0.1-200 Hz. The main advantage of ultrasonic fatigue testing at 20 kHz is performing Although S-N curve is determined by experiment, the fatigue strength corresponding to a given fatigue life should be determined by statistical method considering the scatter of fatigue properties. In this report, the statistical methods for evaluation of fatigue test data is investigated

  19. 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.

  20. High cycle fatigue behavior of gas-carburized medium carbon Cr-Mo steel

    Science.gov (United States)

    Kim, Hyung-Jun; Kweon, Young-Gak

    1996-09-01

    High cycle fatigue properties of gas-carburized 4140 steel were assessed to compare with those of 8620 steel which is widely used as a carburizing steel. Fatigue limit was evaluated associated with microstructure, case depth, and distribution of retained austenite and compressive residual stress near the surface. Test results indicated that the reheat quenching method of 4140 and 8620 steels produced a reduction in grain size, retained austenite level, and compressive residual stress at the surface and an increase in fatigue limit. The fatigue limit of direct-quenched 4140 steel shows substantially lower value than that of direct-quenched 8620 steel due to larger grain size of direct-quenched 4140 steel. However, the fatigue limit of reheat-quenched 4140 steel is greatly improved and is comparable to the reheat-quenched 8620 steel. This is attributed to the larger reduction ratio in grain size and deeper case depth of reheat-quenched 4140 steel as compared to direct-quenched and reheat-quenched 8620 steels.

  1. 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...

  2. 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)

  3. 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.)

  4. Fatigue behavior of titanium alloy Ti-4Al-2V under high cycle loading at elevated temperature

    International Nuclear Information System (INIS)

    The high cycle fatigue behavior of titanium alloy Ti-4Al-2V rods with near a phase at elevated temperature (350 ?) was evaluated. The traditional high cycle fatigue (HCF) tests with group specimen as well as the up-and-down tests were performed under bending and rotating loadings at 350 ? in air atmosphere. The experimental data were analyzed and the theoretical S-N curve, the P-S-N curve and the S-N curve for nuclear design were processed, and the fracture morphology was analyzed by SEM. The results indicate that Ti-4Al-2V rods have good resistance to high cycle fatigue and the value is 339 MPa which is slightly higher than the calculated value from the corresponding equation, and elevated temperature accelerated the oxidation of the specimen which decreased the fatigue duration when compared with the result obtained at low temperature which is around 394 MPa. (authors)

  5. Influence of the microstructure and defects on the high cycle fatigue strength of 316L stainless steel under multiaxial loading

    OpenAIRE

    GUERCHAIS, Raphaël; Morel, Franck; Saintier, Nicolas; Robert, Camille

    2014-01-01

    In the present study, the effects of both the microstructure and defects on the high cycle fatigue behavior of the 316L austenitic stainless steel are investigated thanks to finite element simulations of polycrystalline aggregates. The numerical analysis relies on a metallurgical and mechanical characterization. To complete the experimental study, load-controlled fatigue tests are also carried out to determine the fatigue limits at 2.106 cycles under uniaxial and multiaxial loading conditions...

  6. Microstructure-sensitive weighted probability approach for modeling surface to bulk transition of high cycle fatigue failures dominated by primary inclusions

    Science.gov (United States)

    Salajegheh, Nima

    The mechanical alloying and casting processes used to make polycrystalline metallic materials often introduce undesirable non-metallic inclusions and pores. These are often the dominant sites of fatigue failure origination at the low stress amplitudes that correspond to the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regimes, in which the number of cycles to crack initiation is more than 106. HCF and VHCF experiments on some advanced metallic alloys, such as powder metallurgy Ni-base superalloys, titanium alloys, and high-strength steels have shown that the critical inclusions and pores can appear on the surface as well as in the bulk of the specimen. Fatigue lives have been much higher for specimens that fail from a bulk site. The relative number of bulk initiations increases as the stress amplitude decreases such that just below the traditional HCF limit, fatigue life data appears to be evenly scattered between two datasets corresponding to surface and bulk initiations. This is often referred to as surface to bulk transition in the VHCF regime. Below this transition stress, the likelihood of surface versus bulk initiation significantly impacts the low failure probability estimate of fatigue life. Under these circumstances, a large number of very costly experiments need to be conducted to obtain a statistically representative distribution of fatigue life and to predict the surface versus bulk initiation probability. In this thesis, we pursue a simulation-based approach whereby microstructure-sensitive finite element simulations are performed within a statistical construct to examine the VHCF life variability and assess the surface initiation probability. The methodology introduced in this thesis lends itself as a cost-effective platform for development of microstructure-property relations to support design of new or modified alloys, or to more efficiently predict the properties of existing alloys.

  7. Long life fatigue of type 304 stainless steel

    International Nuclear Information System (INIS)

    Fully reversed axial strain-controlled and load-controlled fatigue experiments have been conducted on type 304 stainless steel in air at 6000C and long-life or high cycle (more than 104 cycles to failure) fatigue properties have been obtained. Under strain-controlled conditions, the well-known Manson-Coffin relationship has not been observed. It was also found that softening occurred at the end of the primary hardening, followed by secondary hardening with further strain cycling. Under load-controlled conditions, fatigue life was shown to be significantly sensitive to the cyclic frequency. Strain-controlled fatigue life is compared with load-controlled fatigue life based on the strain range coverted from controlled stress range using the cyclic stress-strain relations. (orig.)

  8. 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 (30°C) and with heating (300°C) of the building platform and in diff...

  9. 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.

  10. 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.

  11. 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.

  12. Influence of HVOF sprayed WC/Co coatings on the high-cycle fatigue strength of mild steel

    International Nuclear Information System (INIS)

    HVOF thermally sprayed WC/Co coatings are applied onto components which are exposed to wear caused by abrasion, erosion, fretting and sliding. Beside wear attacks and static stresses in lots of cases alternating mechanical stresses caused by dynamic loads occur additionally. Therefore, the fatigue resistance of WC/Co 88/12 and WC/Co 83/17 coated specimens was investigated by high-cycle fatigue tests (HCF). The results of the fatigue tests were documented in statistically ascertained Woehler-diagrams (S-N-curves). Furthermore, the mechanisms of failure are discussed

  13. Experiment investigation of laser shock peening on TC6 titanium alloy to improve high cycle fatigue performance

    International Nuclear Information System (INIS)

    Laser shock peening (LSP) is an innovative surface treatment technique, and can significantly improve the fatigue performance of metallic components. In this paper, the objective of this work was to improve the fatigue resistance of TC6 titanium alloy by laser shock peening. Firstly, the effects on the microstructure and mechanical properties with different LSP impacts were investigated, which were observed and measured by X-ray diffraction (XRD), transmission electron microscope (TEM), residual stress tester and microhardness tester. Specially, nanostructure was detected in the laser-peened surface layer with multiple LSP impacts. Whereafter, a better parameter was chosen to be applied on the standard vibration fatigue specimens. Via the high-cycle vibration fatigue tests, the high cycle fatigue limits of the specimens without and with LSP were obtained and compared. The fatigue results demonstrate that LSP can effectively improve the fatigue limit of TC6 titanium alloy. The strengthening mechanism was indicated by analyzing the effects on the microstructure and mechanical properties comprehensively

  14. 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.

  15. 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)

  16. Effect of low temperature gas nitriding and low temperature gas carburizing on high cycle fatigue property in SUS316L

    International Nuclear Information System (INIS)

    It is known that nitrogen and carbon S phases are formed in the diffusion layer on the surface of austenitic stainless steels if nitriding or carburizing is performed at the temperature of 500degC or less. In order to investigate the effect of the nitrogen and carbon S phases on high cycle fatigue properties of type316L austenitic stainless steel, rotating bending fatigue tests were carried out for four specimens with different treatments: One was gas carburized at 470degC. The other three were gas nitrided at 420degC, 460degC and 570degC, respectively. The former three specimens had the carbon or the nitrogen S phase and the last one had no S phase in the diffusion layer, depending on the temperature. As the fatigue tests result, the S phase is effective to enhance the fatigue properties. The effect of fatigue properties improvement of the nitrogen S phase is greater than that of the carbon S phase. The fatigue strength increases with an increase in the thickness of the diffusion layer in the nitrided specimens. External observation suggests that the fatigue crack initiated from the chipped part on the surface due to fatigue loading. Although the chipping behavior depended on the diffusion species, the propagation behavior of fatigue cracks did not depend on them. (author)

  17. 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 compósitos sob fadiga de altos ciclos. O modelo constitutivo proposto relaciona a evolução da variável de dano, d, com a velocidade de crescimento da delaminagem, da/dN. O modelo coesivo é implementado no código de eleme [...] ntos finitos ABAQUS e é utilizado na simulação de provetes fabricados em carbono-epoxy carregados ciclicamente em modo I, modo II e modo misto I e II. O modelo é validado comparando as suas previsões 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.

  18. 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

  19. 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

  20. 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)

  1. 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

  2. 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 estimati 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)

  3. High-cycle fatigue tests as a method for rapid determination of materials endurance

    International Nuclear Information System (INIS)

    It is suggested, that high-frequency cyclic loading should be used for accelerated determination of the metal fatigue characteristics. Data on the dependence of the endurance limit of some materials (1Kh2M, I5 steel, VT22M, VT20Y alloys) on the frequency of symmetric extension-compression within 10-20000 Hz range are presented. Perspectiveness of high-frequency cyclic loading methods is noted for comparative fatigue tests with minimum expenditures of time and facilities

  4. Optimal Reliability in Design for Fatigue Life

    OpenAIRE

    Gottschalk, Hanno; Schmitz, Sebastian

    2012-01-01

    The failure of a component often is the result of a degradation process that originates with the formation of a crack. Fatigue describes the crack formation in the material under cyclic loading. Activation and deactivation operations of technical units are important examples in engineering where fatigue and especially low-cycle fatigue (LCF) play an essential role. A significant scatter in fatigue life for many materials results in the necessity of advanced probabilistic mod...

  5. Nitinol Fatigue Life for Variable Strain Amplitude Fatigue

    Science.gov (United States)

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

    2012-12-01

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

  6. 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

  7. 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)

  8. High Cycle Fatigue of Al and Cu Thin Films by a Novel High-Throughput Method

    OpenAIRE

    Burger, Sofie

    2013-01-01

    In the last two decades, the reliability of small electronic devices used in automotive or consumer electronics gained researchers attention. Thus, there is the need to understand the fatigue properties and damage mechanisms of thin films. In this thesis a novel high-throughput testing method for thin films on Si substrate is presented. The specialty of this method is to test one sample at different strain amplitudes at the same time and measure an entire lifetime curve with only one experiment.

  9. Calculation estimate of damage for metal construction elements with stress concentrators during high-cycle fatigue

    Directory of Open Access Journals (Sweden)

    Vitaly Sergeevich Evgrafov

    2014-04-01

    Full Text Available This article is about the one of the main questions of ensuring the fatigue strength of steel elements. Questions of this kind are extremely important and usually considered at the designing calculations stage. Modified ? - damage assessment model is based on energy criteria using experimental data on laboratory samples with different types of concentrators. Results are based on the maximum stress gradients values in the concentrator areas.

  10. Mechanism of fatigue crack initiation and propagation in the very high cycle fatigue regime of high-strength steels

    International Nuclear Information System (INIS)

    Fatigue fracture surfaces of high-strength steels generated by a very high number of cycles to failure show so-called fine granular areas, for which the crack initiation and propagation mechanism is not fully understood. To clarify this mechanism of crack growth, scanning electron/ion microscopy, focused ion beam and transmission electron microscopy investigations were carried out at fracture surfaces showing this special crack part. On the basis of the results a mechanism for the formation of this area is proposed.

  11. 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)

  12. 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)

  13. 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.

  14. 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.

  15. 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.

  16. Biaxial High Cycle Fatigue of a Type 304L Stainless Steel: Cyclic Strains and Crack Initiation Detection by Digital Image Correlation

    OpenAIRE

    Poncelet, M.; Barbier, G.; Raka, B.; Courtin, S.; Desmorat, R.; Le-roux, J. C.; Vincent, L.

    2010-01-01

    Abstract A series of biaxial High Cycle Fatigue tests at room temperature is performed to build up an extensive and well-documented database. The testing specimen is a maltese cross thinned in its centre with non homogeneous strain/stress fields. The experimental protocol uses exclusively full-field strain measurements. The strains (cyclic and residual) as well as the crack initiation detection are obtained by use of Digital Image Correlation (DIC) techniques combined with a multis...

  17. Fatigue life and backface strain predictions in adhesively bonded joints

    OpenAIRE

    Solana, AG; Crocombe, AD; Ashcroft, IA

    2010-01-01

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

  18. 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

  19. 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...

  20. 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.

  1. Fatigue crack threshold depending on loading history

    International Nuclear Information System (INIS)

    Effect of loading history on the high cycle fatigue crack propagation behavior was experimentally studied in SUS 316 stainless steel, paying a special attention to an interaction between low-cycle thermo-mechanical fatigue loading and high cycle fatigue one in the fatigue crack propagation rates. The experimental results clearly demonstrated that the interaction was significant. If was shown that the stress ratio which was built-up under an influence of previous loading history made a major contribution there. Based on these findings, a new remaining life estimation method and model has been proposed to prevent the fatigue failures under the combined low/high cycle fatigue loadings. (author)

  2. Effect of Corrosion on the High Cycle Fatigue Strength of Martensitic Stainless Steel X12CrNiMoV12-3

    OpenAIRE

    EL MAY, Mohamed; PALIN-LUC, Thierry; Saintier, Nicolas; Devos, Olivier

    2012-01-01

    This paper addresses the effects of corrosion on the high cycle fatigue (HCF) strength of a high mechanical strength martensitic stainless steel (X12CrNiMoV12-3) that is used in aeronautic applications. HCF tests (between 105 and 107 cycles) were carried out in two environments: (i) in air and (ii) in an aqueous solution (pH = 6) of 0.1 M NaCl + 0.044 M Na2SO4 at a loading frequency of 120 Hz. Surface crack initiation is observed in air, whereas in solution, the crack initiated at corrosion d...

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

    Science.gov (United States)

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

    2003-09-01

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

  4. 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)

  5. Certain characteristics of the development of fatigue and creep in heat-resistant alloys under asymmetric high-cycle loading

    Energy Technology Data Exchange (ETDEWEB)

    Golub, V.P.

    1984-08-01

    The high-temperature fatigue and creep behavior of nickel superalloys is examined from the standpoint of thermal activation. An analysis is made of experimental data on the activation energies of fracture of nickel-base superalloys, EI867, EP109, and VZhU12U, for stress ratios from zero to infinity. It is found that a discontinuous change in the activation energy of fracture occurs in the stress region corresponding to the transition from fatigue to creep. 17 references.

  6. 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 2·109). 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.

  7. Experimental study on prevention of high cycle thermal fatigue in a compact reactor vessel of advanced sodium cooled reactor. Thermal striping phenomena at bottom of upper internal structure

    International Nuclear Information System (INIS)

    Japan sodium-cooled fast reactor, JSFR, has been investigated in the frame work of Fast Reactor Cycle Technology Development Project (FaCT). As the temperature difference between the control rod channels and the core fuel subassemblies is around 100degC, temperature fluctuation due to the fluid mixing at the core outlet may cause high cycle thermal fatigue at the bottom of Upper Internal Structure (UIS). Then, a water experiment was conducted using a 1/3 scale 60 degree sector model. Temperature and its fluctuation intensity distributions around the control rod were measured and an effect of the improved structure against the thermal fatigue was examined. The objectives of the experiment are as follows; (1) to grasp the flow pattern around the control rod(CR) channel outlet, (2) to grasp the amplitude and the frequency characteristics of the temperature fluctuation, (3) to confirm the effect of a countermeasure for the high cycle thermal fatigue. As a result, thermal striping phenomena in the region between the fuel subassembly outlet and the bottom of the UIS were grasped. The geometry of the UIS bottom and the handling head of the primary CR channel was modified so as to suppress the cold jets exiting from the CR channels. The comparison of measured temperature fluctuations around the CR channels revealed that the modified geometry was effective to decrease the temperature fluctuation intensity and amplitude in the sensitive frequency band to the stress in the structures. Temperature fluctuation intensity distributions at the boundary between blanket subassemblies and core fuel subassemblies were also grasped. (author)

  8. Enhanced Prediction of Gear Tooth Surface Fatigue Life Project

    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...

  9. 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 ...

  10. Effect of inclusion size on the high cycle fatigue strength and failure mode of a high V alloyed powder metallurgy tool steel

    Science.gov (United States)

    Yao, Jun; Qu, Xuan-hui; He, Xin-bo; Zhang, Lin

    2012-07-01

    The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was shown that brittle inclusions with large sizes above 30 ?m prompted the occurrence of subsurface crack initiation and the reduction in fatigue strength. The fracture toughness and the stress amplitude both exerted a significant influence on the fish-eye size. A larger fish-eye area would form in the sample with a higher fracture toughness subjected to a lower stress amplitude. The stress intensity factor of the inclusion was found to lie above a typical value of the threshold stress intensity factor of 4 MPa·m1/2. The fracture toughness of the sample with a hardness above HRC 56 could be estimated by the mean value of the stress intensity factor of the fish-eye. According to fractographic evaluation, the critical inclusion size can be calculated by linear fracture mechanics.

  11. Biaxial High Cycle Fatigue of a type 304L stainless steel: Cyclic strains and crack initiation detection by digital image correlation

    Energy Technology Data Exchange (ETDEWEB)

    Poncelet, M.; Vincent, L. [CEA Saclay, DEN/SRMA, 91 - Gif-sur-Yvette (France); Barbier, G.; Raka, B.; Desmorat, R. [LMT Cachan, ENS Cachan/CNRS/UPMC/PRES Univ. Sud Paris, 94 - Cachan (France); Courtin, S. [AREVA NP SAS, Tour AREVA, 92 - Paris La Defense (France); Barbier, G.; Le-Roux, J.C. [EDF e R and D, Departement Materiaux et Mecanique des Composants, 77 - Moret Sur Loing Cedex, (France)

    2010-09-15

    A series of biaxial High Cycle Fatigue tests at room temperature is performed to build up an extensive and well-documented database. The testing specimen is a maltese cross thinned in its centre with non-homogeneous strain/stress fields. The experimental protocol uses exclusively full-field strain measurements. The strains (cyclic and residual) as well as the crack initiation detection are obtained by use of Digital Image Correlation (DIC) techniques combined with a multi-scale stroboscopic image acquisition in-situ set-up. Nine cruciform specimens made of type 304L austenitic stainless steel are loaded by a multiaxial testing machine. Two kinds of loading paths are presented: equi-biaxial with a load ratio of 0.1, non-proportional with a cyclic load in one direction and a constant load in the other. The experimental results are given (strain amplitude, residual strain, number of cycles to crack initiation) for each loading path. The time history of local strain amplitudes and residual strains are recorded and plotted. Total strain vs. number of cycles fatigue curves show the different trends associated with each loading path. For instance, non-proportional loadings are found very damaging and leading to strong ratchetting effects. The tested material is briefly introduced, followed by an in-depth description of the experimental set-up. The fatigue test campaign results are then presented, with a final discussion. (authors)

  12. Fatigue Life Investigation of PZT Ceramics by MSP Method

    Directory of Open Access Journals (Sweden)

    DENG Qi-Huang, WANG Lian-Jun, XU Hong-Jie, WANG Hong-Zhi, JIANG Wan

    2012-10-01

    Full Text Available The cycle fatigue of PZT ceramic under different stress was investigated by modified small punch (MSP tests. The research results show that residual strength and piezoelectric constant decrease with increasing cycle stress, which is attributed to crack propagation during cyclic stress process. The value of fatigue crack propagation (n is calculated to be 395 according to the relationship between maximum stress and fatigue life. The fatigue life under series cycle maximum stress can be induce by fatigue crack propagation. Below the maximum strength of 79.1 MPa, the PZT ceramics can be used over 5 years.

  13. 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.

  14. 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.

  15. 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.

  16. Development of a procedure for estimating the high cycle fatigue strength of some high temperature structural alloys

    International Nuclear Information System (INIS)

    The generation of strain controlled fatigue data, for the standard strain rate of 4 x 10-3 sec-1, presents a problem when the cycles to failure exceed 105 because of the prohibitively long test times involved. In an attempt to circumvent this difficulty an evaluation has been made of a test procedure involving a fast cycling rate (40 Hz) and load controlled conditions. The validity of this procedure for extending current fatigue curves from 105 to 108 cycles and beyond, hinges upon the selection of an appropriate effective strain value, since the strain usually changes rapidly during the early stage of fatigue. Results from annealed 2 1/4 Cr-1 Mo, type 304 stainless steel, Incoloy 800H and Hastelloy X, tested over a wide range of temperatures, show that the strain measured N/sub f/2 is a reasonable estimate since it gives an excellent correlation between the strain and load controlled tests in the 105 cycle range where the data overlap. It seems clear that the differences in cycling rate and early stress-strain history for the two tests do not significantly affect the correlation. It may, therefore, be concluded that such load control test procedures may be used as a valid fast way for extending currently available fatigue curves from 105 to 108 cycles, and beyond

  17. 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.

  18. 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

  19. Effect of ratcheting deformation on fatigue and creep-fatigue life of 316FR stainless steel

    International Nuclear Information System (INIS)

    Components of fast breeder reactor (FBR) plants will be subjected to large thermal load, and progressive deformation with loading cycles (ratcheting) and creep-fatigue damage should be considered in their design. To clarify the effect of ratcheting on fatigue and creep-fatigue life, a series of fatigue and creep-fatigue tests coupled with strain progress were carried out for 316FR stainless steel. It was found that tensile ratcheting decreases the failure life to a large extent at small strain range, while compressive ratcheting does not decrease the failure life. Measurement of striation intervals on fracture surface showed small influence of strain increment on the crack propagation rate, suggesting that the main cause of the life reduction is the decrease in the crack initiation life. It was also found that failure life in various conditions is correlated well with a product of strain range and tensile peak stress

  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 ?m 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. A Question of Location - Life with Fatigue after Stroke

    DEFF Research Database (Denmark)

    Andersen, Michael

    2014-01-01

    This thesis treats the experiences of fatigue after stroke. Based on a qualitative fieldwork conducted among people who have had a stroke, it explores how they experience fatigue. This is done by way of an ethnological examination of how the informants locate fatigue in their everyday lives. By approaching their location as both place and practice, it is illustrated how a stroke may dislocate and relocate the experience of fatigue and how a new location of fatigue calls for new meaningful contexts in everyday life.

  2. Analysis of fatigue properties and failure mechanisms of Ti6Al4V in the very high cycle fatigue regime using ultrasonic technology and 3D laser scanning vibrometry.

    Science.gov (United States)

    Heinz, Stefan; Balle, Frank; Wagner, Guntram; Eifler, Dietmar

    2013-12-01

    Accelerated fatigue tests with Ti6Al4V were carried out using a 20kHz ultrasonic testing facility to investigate the cyclic deformation behavior in the Very High Cycle Fatigue (VHCF) regime in detail. Beside parameters like the ultrasonic generator power and the displacement of the specimen, a 3D laser scanning vibrometer was used to characterize the oscillation and fatigue behavior of the Ti-alloy. The course of the S-N(f) curve at the stress ratio R=-1 shows a significant decrease of the bearable stress amplitude and a change from surface to subsurface failures in the VHCF regime for more than 10? cycles. Microscopic investigations of the distribution of the ?- and ?-phase of Ti6Al4V indicate that inhomogeneities in the phase distribution are reasons for the internal crack initiation. High resolution vibrometry was used to visualize the eigenmode of the designed VHCF-specimen at 20 kHz in the initial state and to indicate local changes in the eigenmodes as a result of progressing fatigue damage. Non-contact strain measurements were realized and used to determine the stress amplitude. The determined stress amplitudes were correlated with strain gauge measurements and finite element analysis. PMID:23545114

  3. Estimation of Fatigue Life of Laser Welded AISI304 Stainless Steel T-Joint Based on Experiments and Recommendations in Design Codes

    DEFF Research Database (Denmark)

    Lambertsen, SØren Heide; Damkilde, Lars

    2013-01-01

    In this paper the fatigue behavior of laser welded T-joints of stainless steel AISI304 is investigated experimentally. In the fatigue experiments 36 specimens with a sheet thickness of 1 mm are exposed to one-dimensional cyclic loading. Three different types of specimens are adopted. Three groups of specimens are used, two of these are non-welded and the third is welded with a transverse welding (T-Joint). The 13 laser welded specimens are cut out with a milling cutter. The non-welded specimens are divided in 13 specimens cut out with a milling cutter and 10 specimens cut out by a plasma cutter. The non-welded specimens are used to study the influence of heat and surface effects on the fatigue life. The fatigue life from the experiments is compared to fatigue life calculated from the guidelines in the standards DNV-RP-C203 and EUROCODE 3 EN-1993-1-9. Insignificant differences in fatigue life of the welded and non-welded specimens are observed in the experiments and the largest difference is found in the High Cycle Fatigue (HCF) area. The specimens show a lower fatigue life compared to DNV-RP-C203 and EUROCODE 3 EN-1993-1-9 when the spe-cimens are exposed to less than 4.0 1E06 cycles. Therefore, we conclude that the fatigue life assessment according to the mentioned standards is not satisfactory and reliable.

  4. Improving a bridge fatigue life prediction by monitoring

    OpenAIRE

    Leander, John

    2010-01-01

    For steel railway bridges, fatigue is the main reason for a limited service life. An initial prediction of the fatigue life is usually performed using loads and conservative assumptions stated in the governing standards. The result is used for decisions of further actions. Even if the result is an insufficient residual life, some bridges are not easy to strengthen or replace without causing large traffic disturbance. In this licentiate thesis, the real load effect is studied by monitoring a b...

  5. Prediction of residual fatigue life using nonlinear ultrasound

    International Nuclear Information System (INIS)

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

  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. Residual fatigue life estimation using a nonlinear ultrasound modulation method

    Science.gov (United States)

    Piero Malfense Fierro, Gian; Meo, Michele

    2015-02-01

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

  8. 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 layer’s much higher hardness than the substrate material’s, 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.

  9. 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)

  10. 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.

  11. Fatigue life estimation for internal threads in class 1 components

    International Nuclear Information System (INIS)

    7eat exchangers, steam generators and other pressure vessels in nuclear power plants are equipped with bolted closures for the purpose of in service inspection and maintenance. The ASME Boiler and Pressure Vessel Code specifies that all Class 1 components meet the fatigue life requirements for Level A and B Service Conditions. In the case of bolted closures, it is often found that the bolt/stud is the most critical part. In many situations, the bolts fail to meet the fatigue requirements for the design life of the equipment. In such cases, the bolts can be replaced after certain duration based upon their fatigue life. However, the mating threads in the flange (which is an integral part of the vessel) are still a concern. While the replacement of the bolts is relatively easy and inexpensive, the corrective action (e.g. replacement or repair) for the flange is usually difficult and expensive, or impossible. Hence, it is important to have a reasonable estimate of the fatigue life of internal threads to alleviate or minimize the concern. In this paper, a simplified approach is presented for this purpose. Considering various bolt sizes, commonly used thread series and typical Class 1 component materials, it is shown that the fatigue life of the internal threads is about three times the fatigue life of the bolt threads. This conclusion greatly reduces or eliminates the concern for in service replacement or repair of the components with internal threads. (orig.)ith internal threads. (orig.)

  12. Development of fatigue life evaluation method using small specimen

    International Nuclear Information System (INIS)

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

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

    Directory of Open Access Journals (Sweden)

    A.G.A. Rahman

    2012-12-01

    Full Text Available 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 stress fluctuations for fatigue simulations are considered with the road profile. The strain-life method is utilized to assess the fatigue life. The instantaneous stress distributions and maximum principal stress are used for fatigue life predictions. Mesh sensitivity analysis has been performed. The results show that the steering link in the knuckle is found to be the most susceptible region for fatigue failure. The number of times the knuckle can manage a road bump at 40 km/hr is determined to be approximately 371 times with a 50% certainty of survival. The proposed method of using the loading time history extracted from MBS simulation for fatigue life estimation is found to be very promising for the accurate evaluation of the performance of suspension system components.

  14. Fatigue life and microstructure of ODS steels.

    Czech Academy of Sciences Publication Activity Database

    Kub?na, Ivo; Kruml, Tomáš

    2013-01-01

    Ro?. 103, SI (2013), s. 39-47. ISSN 0013-7944 R&D Projects: GA MŠk(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. APPLICATION OF MULTIBODY SIMULATION FOR FATIGUE LIFE ESTIMATION

    Directory of Open Access Journals (Sweden)

    M. Kamal

    2013-06-01

    Full Text Available In automobile design, the safety of passengers is of prime concern to the manufacturers. Suspension is one of the safety-related automotive systems which is responsible for maintaining traction between the road and tires, and offers a comfortable ride experience to the passengers by absorbing disturbances. One of the critical components of the suspension system is the knuckle, which constantly faces cyclic loads subjecting it to fatigue failure. This paper presents an evaluation of the fatigue characteristics of a knuckle using a gravel road profile acquired using a data acquisition system and standard SAE profiles for the suspension (SAESUS, bracket (SAEBRAKT and transmission (SAETRN. The gravel road profile was applied as the input to a multi body simulation (MBS, and the load history for various mounting points of the knuckle is extracted. Fatigue life is predicted using the strain-life method. The instantaneous stress distributions and maximum principal stress are used for fatigue life predictions. From the results, the strut connection is found to be the critical region for fatigue failure. The fatigue life from loading extracted from gravel road MBS agreed well with the life prediction when standard SAE profiles were used. This close agreement shows the effectiveness of the load extraction technique from MBS. This method can also be effectively used for more complex loading conditions that occur during real driving environments.

  16. 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.

  17. Improved methods of creep-fatigue life assessment of components

    Energy Technology Data Exchange (ETDEWEB)

    Scholz, Alfred; Berger, Christina [Inst. fuer Werkstoffkunde (IfW), Technische Univ. Darmstadt (Germany)

    2009-07-01

    The improvement of life assessment methods contributes to a reduction of efforts at design and an effective long term operation of high temperature components, reduces technical risk and increases high economical advantages. Creep-fatigue at multi-stage loading, covering cold start, warm start and hot start cycles in typical loading sequences e.g. for medium loaded power plants, was investigated here. At hold times creep and stress relaxation, respectively, lead to an acceleration of crack initiation. Creep fatigue life time can be calculated by a modified damage accumulation rule, which considers the fatigue fraction rule for fatigue damage and the life fraction rule for creep damage. Mean stress effects, internal stress and interaction effects of creep and fatigue are considered. Along with the generation of advanced creep data, fatigue data and creep fatigue data as well scatter band analyses are necessary in order to generate design curves and lower bound properties inclusive. Besides, in order to improve lifing methods the enhancement of modelling activities for deformation and life time are important. For verification purposes, complex experiments at variable creep conditions as well as at creep fatigue interaction under multi-stage loading are of interest. Generally, the development of methods to transfer uniaxial material properties to multiaxial loading situations is a current challenge. For specific design purposes, a constitutive material model is introduced which is implemented as an user subroutine for Finite Element applications due to start-up and shut-down phases of components. Identification of material parameters have been performed by Neural Networks. (orig.)

  18. Fatigue life estimation by an indentation method for irradiated materials

    International Nuclear Information System (INIS)

    An indentation fatigue test method was developed to determine fatigue properties of irradiated materials. A hard steel ball or ceramic ball was used for cyclically loading the specimen, and an S-N curve was subsequently obtained. To represent true S-N relation by the curve, micro behavior in the specimen was compared with that in the axial fatigue test specimen. A hemisphere contact, it was observed that the persistent slip band accumulated near the surface as expected from the strain field desnity. S-N curves obtained the identification method compared well with that common fatigue test. Effect of the over load cycles in the reactor on the residual fatigue life was tested using non-irradiated material. (author). 4 refs., 7 figs

  19. X-43A Rudder Spindle Fatigue Life Estimate and Testing

    Science.gov (United States)

    Glaessgen, Edward H.; Dawicke, David S.; Johnston, William M.; James, Mark A.; Simonsen, Micah; Mason, Brian H.

    2005-01-01

    Fatigue life analyses were performed using a standard strain-life approach and a linear cumulative damage parameter to assess the effect of a single accidental overload on the fatigue life of the Haynes 230 nickel-base superalloy X-43A rudder spindle. Because of a limited amount of information available about the Haynes 230 material, a series of tests were conducted to replicate the overload and in-service conditions for the spindle and corroborate the analysis. Both the analytical and experimental results suggest that the spindle will survive the anticipated flight loads.

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

    OpenAIRE

    Abikchi, Meriem; Billot, Thomas; Cre?pin, Je?rome; Longuet, Arnaud; Mary, Caroline; Morgeneyer, Thilo F.; Pineau, Andre?

    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 450°C. Grain size distributions and phase distributions were characterized in the specimens and related to fatigue failure initiation modes. Fatigue cr...

  1. Bayesian inference model for fatigue life of laminated composites

    DEFF Research Database (Denmark)

    Dimitrov, Nikolay Krasimirov; Kiureghian, Armen Der

    2015-01-01

    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.

  2. 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)

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

    OpenAIRE

    K.C.Goes; G.F. Batalha; M.V. Pereira; A.F. Camarao

    2011-01-01

    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 loadi...

  4. 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)

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

    DEFF Research Database (Denmark)

    Petersen, Rasmus Ingomar; Agerskov, Henning

    1996-01-01

    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 from Ø 324-610 mm tubes, and the joints were loaded in in-plane bending. Both fatigue tests under constant amplitude loading and tests with a stochastic loading that is realistic in relation to offshore structures, are included in the investigation.A comparison between constant amplitude and variable 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 corresponding tests on joints in conventional offshore structural steel.

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

    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...

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

    OpenAIRE

    Yasir, Ali S.

    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...

  8. 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)

  9. 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 evaluate a fatigue life function formulated in terms of the load parameters. The concept of a shape operator introduced by Weibull for probability distributions, is employed to correlate fatigue lives under different power spectral shapes. Good correlations in the test results are obtained.

  10. Plastic strai-controlled short crack growth and fatigue life.

    Czech Academy of Sciences Publication Activity Database

    Polák, Jaroslav

    27 2005, 10-12 (2005), s. 1192-1201. ISSN 0142-1123 R&D Projects: GA AV ?R(CZ) IAA2041201; GA ?R(CZ) GA106/02/0584 Institutional research plan: CEZ:AV0Z20410507 Keywords : Sort crack * Plastic strain * Fatigue life Subject RIV: JG - Metallurgy Impact factor: 1.180, year: 2005

  11. 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.

  12. 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)

  13. 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)

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

    Science.gov (United States)

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

    2010-05-01

    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.

  15. 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.

  16. 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.

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

    OpenAIRE

    Qasim Bader; Emad Kadum

    2014-01-01

    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 wi...

  18. Fatigue life prediction in wheel design

    Energy Technology Data Exchange (ETDEWEB)

    Finzi, A.; Piazza, L. [GIANETTI RUOTE S.p.A., Ceriano Laghetto (Italy)

    2000-07-01

    In the fatigue components design is getting more and more consideration in the different design hypothesis of the whole load spectrum. As far as the commercial vehicles are concerned, in order to represent the load spectrum around 53 loading conditions, coupled to the relevant frequency are sufficient. Such a kind of load spectrum is usually used also in the project validation step, through 'Biaxial Machines' which indefinitely repeat the load program representing the mission profile. The design procedure developed is able not only to obtain the results relevant to the different loading conditions starting from the 3 main load cases, but also to synthesize the result in one scalar only, and namely the damage. (orig.)

  19. 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.

  20. 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).

  1. 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

  2. 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

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

    Czech Academy of Sciences Publication Activity Database

    Kunz, Ludvík; Lukáš, Petr; Kone?ná, R.; Fintová, S.

    2012-01-01

    Ro?. 41, AUG (2012), s. 47-51. ISSN 0142-1123 R&D Projects: GA MPO(CZ) FR-TI3/055; GA MŠk(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

  4. 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...

  5. A strategy for the estimation of the fatigue life of notched components under random multiaxial fatigue

    OpenAIRE

    Cailletaud, Georges; Herbland, Thibault; Melnikov, B.; Musienko, Andrei; Quilici, Stéphane

    2010-01-01

    This paper describes three new models that can be used (1) to determine the stress-strain response in stress concentration zones for components submitted to complex multiaxial loading paths, (2) to extract relevant cycle sequences from a general threedimensional loadin path, (3) to find the hypersphere enclosing any type of cyclic load history. These three models can be combined to post-process an elastic Finite Element Analysis, and provide a fast estimation of the fatigue life of the compon...

  6. 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.

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

    Czech Academy of Sciences Publication Activity Database

    Ková?ík, O.; Haušild, P.; Siegl, J.; Mat?jí?ek, Ji?í; 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#

  8. Bending Fatigue Initiation Life Estimation of Disposable Spur Gears

    Directory of Open Access Journals (Sweden)

    Yuefeng Li

    2013-07-01

    Full Text Available A method to estimate the bending fatigue initiation life of disposable gears is proposed in this study. Disposable gears used in disposable aeronautics and space equipment undertake much higher loads than general gears. The main damage type for disposable gears is low-cycle bending fatigue failure. In the study, the finite element method is used to analyze the stress-strain state of disposable gears. The moving load model is established to simulate the real load acting on the teeth. For the purpose of analyzing the multi-axial stress state of teeth roots, the crack initiation life is calculated based on the critical plane theory. As the basis parameter of the critical plane theory, the orientation of critical plane is determined by using maximum variance method. The comparison of the simulation results and the experiment data shows that it is security to predict the bending fatigue crack initiation life of disposable gears using the method provided in the study.

  9. 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)

  10. 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

  11. Geometrical size effect in high cycle fatigue strength of heavy-walled Ductile Cast Iron GJS400: Weakest link vs. defect-based approach

    Directory of Open Access Journals (Sweden)

    Cova Matteo

    2014-06-01

    Full Text Available Fatigue strength is known to decrease with increasing dimension of the component. This is due to a technological size effect, related to the production process, and to a geometrical size effect, due to a higher probability of finding a large defect. To investigate the latter, an heavy-walled component made of Ductile Cast Iron (DCI has been trepanned and a fatigue test plan has been carried out using 4 different specimen geometries. An attempt has been made to relate the resulting fatigue strength using a weakest-link approach based on the effective volumes and surfaces. This approach seems to work well only in cases of different specimen's lengths. Some of the fracture surfaces were analyzed by means of SEM and the initiating defects were identified and measured. An approach in which the defects population can be randomly distributed in the specimen has been tried. Virtual fatigue tests have been carried out by considering pure propagation of the worst defect. The resulting fatigue curves showed that this approach is promising but needs further description of the initiation phase.

  12. Constrained fatigue life optimization of a NASVYTIS multiroller traction drive

    Science.gov (United States)

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

    1980-01-01

    A contact fatigue life analysis method for multiroller traction drives is presented. The method is based on the Lundberg-Palmgren analysis method for rolling element bearing life prediction, and also uses life adjustment factors for materials, processing, lubrication, and effect of traction. The analysis method is applied in an optimization study to the multiroller traction drive, consisting of a single-stage planetary configuration with two rows of stepped planet rollers of five rollers per row. The drive was approximately 25 centimeters in diameter by 11 centimeters long, having a nominal ratio of 15:1. The theoretically predicted drive life was 2510 hours at a nominal continuous power and speed of 74.6 kW (100 hp) and 75,000 rpm.

  13. Fatigue life evaluation of 42CrMo4 nitrided steel by local approach: Equivalent strain-life-time

    International Nuclear Information System (INIS)

    Highlights: ? Ion nitriding treatment of 42CrMo4 steel improves their fatigue strength by 32% as compared with the untreated state. ? This improvement is the result of the beneficial effects of the superficial work- hardening and of the stabilized compressive residual stress. ? The notch region is found to be the fatigue crack nucleation site resulting from a stress concentration (Kt = 1.6). ? The local equivalent strain-fatigue life method was found to be an interesting predictive fatigue life method for nitrided parts. -- Abstract: In this paper, the fatigue resistance of 42CrMo4 steel in his untreated and nitrided state was evaluated, using both experimental and numerical approaches. The experimental assessment was conducted using three points fatigue flexion tests on notched specimens at R = 0.1. Microstructure analysis, micro-Vickers hardness test, and scanning electron microscope observation were carried out for evaluating experiments. In results, the fatigue cracks of nitrided specimens were initiated at the surface. The fatigue life of nitrided specimens was prolonged compared to that of the untreated. The numerical method used in this study to predict the nucleation fatigue life was developed on the basis of a local approach, which took into account the applied stresses and stabilized residual stresses during the cyclic loading and the low cyclic fatigue characteristics. The propagation fatigue life was calculated using fracture mechanics concepts. It was found that the numerical results were well correlated with the experimental ones.

  14. Fatigue in cold-forging dies: Tool life analysis

    DEFF Research Database (Denmark)

    Skov-Hansen, P.; Bay, Niels

    1999-01-01

    In the present investigation it is shown how the tool life of heavily loaded cold-forging dies can be predicted. Low-cycle fatigue and fatigue crack growth testing of the tool materials are used in combination with finite element modelling to obtain predictions of tool lives. In the models the number of forming cycles is calculated first to crack initiation and then during crack growth to fatal failure. An investigation of a critical die insert in an industrial cold-forging tool as regards the influence of notch radius, the amount and method of pre-stressing and the selected tool material is reported. (C) 1999 Elsevier Science S.A. All rights reserved.

  15. 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 2·109). 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.

  16. 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 ampli...

  17. Estimating the Fatigue Life of Wire Rope with a Stochastic Approach

    Science.gov (United States)

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

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

  18. 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; Abdullah, S; 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 ...

  19. A critical investigation of techniques for stress determination and equivalent static analysis in fatigue life estimation

    OpenAIRE

    A. P. Grove; Van Tonder, F.; Heyns, P. Stephan

    2007-01-01

    This study entails the fatigue analysis of a complex plate-like structure subjected to random loading. The stress and fatigue life assessment is performed by means of experimental strain gauge measurements, finite element analysis and a quasi-static fatigue assessment procedure known as the fatigue equivalent static load (FESL) methodology. Firstly, the integrity of shell elements for accurately capturing the stiffness properties and stress distribution in the vicinity of welds is investigate...

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

    OpenAIRE

    So, Winnie K. W.; 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...

  1. Theoretical modeling and experimental study on fatigue initiation life of 16MnR notched components

    International Nuclear Information System (INIS)

    In order to investigate the effects of notch geometry and loading conditions on the fatigue initiation life and fatigue fracture life of 16MnR material, fatigue experiments were conducted for both smooth rod specimens and notched rod specimens. The detailed elastic-plastic stress and strain responses were computed by the finite element software (ABAQUS) incorporating a robust cyclic plasticity model via a user subroutine UMAT. The obtained stresses and strains were applied to the multiaxial fatigue damage criterion to compute the fatigue damage induced by a loading cycle on the critical material plane. The fatigue initiation life was then obtained by the proposed theoretical model. The well agreement between the predicted results and the experiment data indicated that the fatigue initiation of notched components in the multiaxial stress state related to all the nonzero stress and strain quantities. (authors)

  2. High cycle thermal crazing: a phenomena related to the structure

    International Nuclear Information System (INIS)

    The aim of this paper is to give an explanation of crazing observed in some areas of residual heat removal systems (RHR) in French PWR plants. High cycle thermal crazing is explained through the arrest of cracks initiated at surface, in the thickness of the component due to high stress gradient related to high frequencies of thermal load. The conclusion is that there is no difference between high cycle thermal and mechanical fatigue in term of metal behaviour. A parametric study is realised which gives in the case of a thermal periodic loading some bounds for load frequency in function of crack arrest depth. On some RHR the crack network configuration is explained through the sign of weld residual stress in relation with strain control. Far from the weld the presence of crack network under high compressive stress for stainless steels is explained by detrimental effect of pre-hardening on fatigue life in strain control in opposition with stress control. We conclude that shot peening may be detrimental in thermal fatigue. (authors)

  3. Determination of Turboprop Reduction Gearbox System Fatigue Life and Reliability

    Science.gov (United States)

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

    2007-01-01

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

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

    DEFF Research Database (Denmark)

    IbsØ, 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.

  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 elastic–plastic fracture toughness of the welded joint at the tower base. These material strength characteristics are used to estimate (i) the critical crack size for structural integrity on the basis of fracture toughness tests, elastoplastic finite element analyses and loading spectra under extreme wind conditions, (ii) the residual life before structural collapse, applying a frequency-domain method to typical in-service wind actions and wind directionality. (paper)

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

    Science.gov (United States)

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

    2013-04-01

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

  7. 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.

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

    OpenAIRE

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

    2008-01-01

    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 ...

  9. Fatigue

    Science.gov (United States)

    ... to help you find out what's causing your fatigue and recommend ways to relieve it. Fatigue itself is not a disease. Medical problems, treatments, and personal habits can add to fatigue. These include Taking certain medicines, such as antidepressants, ...

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

    Science.gov (United States)

    Woo, Chang Su; Kim, Wan Doo

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

  11. 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.

  12. 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.

  13. 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.

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

    Science.gov (United States)

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

    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.

  15. 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)

  16. 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)

  17. 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.

  18. 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 consideredl 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)

  19. Effect of hardening induced by cold expansion on damage fatigue accumulation and life assessment of Aluminum alloy 6082 T6

    OpenAIRE

    Bendouba Mostefa; Aid Abdelkrim; Benhamena Ali; Benguediab Mohamed

    2012-01-01

    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 dam...

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

    OpenAIRE

    Huang, I-chan; Anderson, Mary; Gandhi, Pranav; Tuli, Sanjeev; Krull, Kevin; Lai, Jin-shei; Nackashi, John; Shenkman, Elizabeth

    2013-01-01

    Objective?To examine the relationships among pediatric fatigue, health-related quality of life (HRQOL), and family impact among children with special health care needs (CSHCNs), specifically whether HRQOL mediates the influence of fatigue on family impact.?Methods?266 caregivers of CSHCNs were studied. The Pediatric Quality of Life Inventory Multidimensional Fatigue Scale, Pediatric Quality of Life Inventory Generic Scale, and Impact on Family Scale were used to measure fatigue, HRQOL, ...

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

    OpenAIRE

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

    2008-01-01

    Despite the fact that fatigue is a common and debilitating symptom among HIV-infected persons, we know little about the predictors of fatigue in this population. The goal of this cross-sectional study was to examine the effects of early childhood trauma, recent stressful life events and depression on intensity and impairment of fatigue in HIV, over and above demographic factors and clinical characteristics. We studied 128 HIV-infected men and women from one southern state. The median number o...

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

    OpenAIRE

    Barman A; Chatterjee A; Km, Das; Pk, Mandal; 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...

  3. 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.

  4. 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.

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

    International Nuclear Information System (INIS)

    The existing fatigue strain vs life (S-N) data, foreign and domestic, for carbon and low-alloy steels used in the construction of nuclear power plant components have been compiled and categorized according to material, loading, and environmental conditions. A statistical model has been developed for estimating the effects of the various test conditions on fatigue life. The results of a rigorous statistical analysis have been used to estimate the probability of initiating a fatigue crack. Data in the literature were reviewed to evaluate the effects of size, geometry, and surface finish of a component on its fatigue life. The fatigue S-N curves for components have been determined by applying design margins for size, geometry, and surface finish to crack initiation curves estimated from the model

  6. Study on creep-fatigue life of irradiated austenitic stainless steel

    International Nuclear Information System (INIS)

    The low cycle creep-fatigue test with tensile strain hold of the austenitic stainless steel irradiated to 2 dpa was carried out at 823K in vacuum. The applicability of creep-fatigue life prediction methods to the irradiated specimen was examined. The fatigue life on the irradiated specimen without tensile strain hold time was reduced by a factor of 2-5 in comparison with the unirradiated specimen. The decline in fatigue life of the irradiated specimen with tensile strain hold was almost equal to that of the unirradiated specimen. The creep damage of both unirradiated and irradiated specimens was underestimated by the time fraction rule or the ductility exhaustion rule. The creep damage calculated by the time fraction rule or the ductility exhaustion rule increased by the irradiation. The predictions derived from the linear damage rule are unsafe as compared with the experimental fatigue lives. (author)

  7. 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.

  8. Cyclic plastic response and fatigue life in symmetric and asymmetric cyclic loading.

    Czech Academy of Sciences Publication Activity Database

    Polák, Jaroslav; Petrenec, Martin; Kruml, Tomáš; Chlupová, Alice

    10 2011, - (2011), 568–577. ISSN 1877-7058. [11th International Conference on the Mechanical Behavior of Materials. Lake Como, 06.06.2001-09.06.2011] R&D Projects: GA ?R GAP108/10/2371 Institutional research plan: CEZ:AV0Z20410507 Keywords : hysteresis loop * mean stress * fatigue life Subject RIV: JL - Materials Fatigue, Friction Mechanics

  9. Effect of surface layer depth on fatigue life of carburized steel and analysis of fracture proces.

    Czech Academy of Sciences Publication Activity Database

    Major, Št?pán; Jakl, L.

    Kazan : Foliant Kazan, 2012 - (Shlyannikov, V.; Goldstein, R.; Makhutov, N.), s. 224-231 ISBN 978-5-905576-18-8. [European conference on fracture /19./. Kazan (RU), 26.08.2012-31.08.2012] Institutional support: RVO:68378297 Keywords : carburization * fatigue life * surface layer Subject RIV: JL - Materials Fatigue, Friction Mechanics

  10. Cyclic plastic response and fatigue life in superduplex 2507 stainless steel.

    Czech Academy of Sciences Publication Activity Database

    Polák, Jaroslav; Petrenec, Martin; Kruml, Tomáš

    2010-01-01

    Ro?. 32, ?. 2 (2010), s. 279-287. ISSN 0142-1123 R&D Projects: GA AV ?R IAA100480704; GA ?R GA101/07/1500 Institutional research plan: CEZ:AV0Z20410507 Keywords : Cyclic plasticity * Hysteresis loop * Fatigue life * Superduplex steel Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.799, year: 2010

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

    Science.gov (United States)

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

    2014-10-01

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

  12. 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.

  13. 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 estias 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)

  14. Effects of LWR environments on fatigue life of carbon and low-alloy steels

    International Nuclear Information System (INIS)

    SME Boiler and Pressure Vessel Code provides construction of nuclear power plant components. Figure I-90 Appendix I to Section III of the Code specifies fatigue design curves for structural materials. While effects of environments are not explicitly addressed by the design curves, test data suggest that the Code fatigue curves may not always be adequate in coolant environments. This paper reports the results of recent fatigue tests that examine the effects of steel type, strain rate, dissolved oxygen level, strain range, loading waveform, and surface morphology on the fatigue life of A 106-Gr B carbon steel and A533-Gr B low-alloy steel in water

  15. 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(Pearson’s 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.

  16. 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.

  17. Application of plateau value to predict fatigue life

    OpenAIRE

    Pais, Jorge; Pereira, Paulo; Minhoto, Manuel; Fontes, Liseane; Kumar, D. S. N. V. A.; Silva, B.T.A.

    2009-01-01

    Fatigue resistance of asphalt mixtures represents an important parameter for pavement design. This fatigue resistance is calculated through laboratory tests which require some time depending on the strain level applied to the specimen. For very low strain levels, identical to the one installed in the pavement, one test may last more than one week depending on the testing frequency. The time needed for the development of the fatigue law may last long-er. Recent developments introduced an energ...

  18. 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...

  19. 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.

  20. 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.

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

    Science.gov (United States)

    Pisarski, Anne; Barbour, Jennifer P

    2014-05-01

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

  2. Reliability analysis for fatigue crack growth life of high temperature turbine wheel

    International Nuclear Information System (INIS)

    The fatigue fracture which occurs under repeated loads is a major concern in mechanical component design. Recently, fatigue life evaluation is getting important to guarantee reliability and safety of a product. In the fatigue analysis and design, uncertainties are caused by the variances of geometry data and applied loads, and the scatter of material properties. It makes the deterministic methods less useful. In this reason, reliability analysis concept should be incorporated to ensure fatigue safety in more sophisticated way. In this paper, fatigue crack growth life of turbine wheel which exposed to severe environments subject to high temperature and centrifugal forces is evaluated by fracture mechanics. Also the reliability analysis is accessed by the fist order second moment method and Monte Carlo simulation.

  3. Prediction of Fatigue Life of Boom Nose End Casting Using Linear Elastic Fracture Mechanics

    Directory of Open Access Journals (Sweden)

    Nitin D.Ghongade

    2014-08-01

    Full Text Available The main objective of this study is to get the life estimation of Boom nose end casting using theoretical approach and compaired it with finite element method. Therefore, this study consists of three major sections : (1 dynamic load analysis (2 FEM and stress analysis (3 prediction of fatigue life for Boom nose end casting. In this study a dynamic loads were obtained from cyclic loading at different time. Finite element analysis was performed to obtain the variation of stress magnitude at the crack locations. This loads and boundary condition were applied to the FE model in ANSYS. The analysis was carried out for different crack length on the surface area of circle of Boom Nose End Casting. As a result, fatigue life for different crack length on the Boom Nose End Casting is obtained. The main objective of this study is to investigate the fatigue life of Boom Nose End Casting under complex loading conditions. Due to the repeated bending and tensile loading acting, Boom Nose End Casting fails, as cracks forms in surface area of circle. Hence, fatigue plays an important role in Boom Nose End Casting development. Accurate prediction of fatigue life is very important to insure safety of components and its reliability. The Linear Elastic Fracture Mechanics approach is used to predict the fatigue life of Boom Nose End Casting.

  4. Nanosize Carbides Formation and Fatigue Life Increase of Stainless Steel by Electron Beam Treatment

    Directory of Open Access Journals (Sweden)

    Gromov V.E.

    2012-08-01

    Full Text Available Electron – beam treatment with 20 J/cm2 energy density of Fe-0.20C-23Cr-18Ni stainless steel increases fatigue life up to 2.1 times. Fracture surface investigations have been carried out by the methods of scanning and transmission diffraction electron microscopy and layer-by-layer analysis of structural phase states and defect substructure of steel subjected to the multicyclic fatigue tests, has been made as well. Nanosize (Cr,Fe23C6 carbides formation and physical reasons of steel fatigue life increase by electron – beam treatment have been found out.

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

    OpenAIRE

    V.K.Aher; R.A.Gujar; Wagh, J. P.; P.M.Sonawane

    2012-01-01

    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). Th...

  6. Fatigue life prediction under variable amplitude axial–torsion 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 axial–torsion 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 Miner–Palmgren 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

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

    Science.gov (United States)

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

    2015-01-01

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

  8. 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

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

    DEFF Research Database (Denmark)

    SØrensen, Eigil V.

    2011-01-01

    The cementitious material in grouted connections of offshore monopile wind turbine structures is subjected to very high oscillating service stresses. The fatigue capacity of the grout therefore becomes essential to the performance and service life of the grouted connection. In the present work the 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.

  10. Formulation of tearing energy for fatigue life evaluation of rubber material

    International Nuclear Information System (INIS)

    Fatigue life of metal material can be predicted by the use of fracture theory and experimental database. Although prediction of fatigue life of rubber material uses the same way as metal, there are many reasons to make it almost impossible. One of the reasons is that there is not currently used fracture criteria for rubber material because of non-standardization, various way of composition process of rubber and so on. Tearing energy is one of the fracture criteria which can be applied to a rubber. Even if tearing energy relaxes the restriction of rubber composition, it is also not currently used because of complication to apply in. Research material about failure process of rubber and tearing energy was reviewed to define the process of fatigue failure and the applicability of tearing energy in estimation of fatigue life for rubber. Also, finite element formulation of tearing energy which can be used in FE analysis was developed

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

    DEFF Research Database (Denmark)

    Rafsanjani, Hesam Mirzaei; SØrensen, 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.

  12. 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

  13. 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.

  14. Determination of the fatigue life under cyclic loading of fuel can tubes made of relieved zircaloy-4

    International Nuclear Information System (INIS)

    Fatigue, fatigue-holding time and internal pressure creep tests have been carried out on clad tubes made of relieved zircaloy-4. 1 Hz fatigue test results show a reduction of the fatigue life when temperature rises from 350 C to 380 C, but identical behaviours at high stresses for both temperatures; at 20 C, results show a fatigue life decrease compared to other temperatures, and a behaviour that could be more representative of the one that is observed at 350 C on irradiated tubes. It is also shown that a relatively precise prediction of the fatigue life, in terms of fracture, for fatigue-holding time tests, is possible. Fracture deformations and fracture patterns appear to be notably different with respect to the stress mode (fatigue, creep)

  15. Remaining fatigue life estimates for riveted railway bridges

    OpenAIRE

    Imam, B.; Righiniotis, Td; Chryssanthopoulos, Mk

    2005-01-01

    A large number of metallic railway bridges currently in use in the UK are of riveted construction and are close to 100 years old. A fatigue assessment methodology is needed for such bridges since these may be close to the end of their fatigue lives. Part of such a methodology is the global analysis of the bridge in order to identify the most fatigue critical details. The aim of this paper is to present results, in terms of Miner’s damage at the riveted connections of a typical riveted UK ra...

  16. Damage study of an austenitic stainless steel in high cycle multiaxial fatigue regime;Etude de l'endommagement d'un acier inoxydable austenitique par fatigue multiaxiale a grand nombre de cycles

    Energy Technology Data Exchange (ETDEWEB)

    Poncelet, M. [CEA Saclay, DEN, SRMA, 91 - Gif-sur-Yvette (France); Barbier, G.; Raka, B.; Vincent, L.; Desmorat, R. [LMT Cachan, ENS Cachan/CNRS/UPMC/PRES Univ. Sud Paris, 94 - Cachan (France); Barbier, G. [EDF R and D / LaMSID, 92 - Clamart (France)

    2010-02-15

    Biaxial fatigue tests are performed up to 1 000 000 cycles at room temperature. Cross specimens of 304L steel thinned in their centre to initiate crack, are loaded by a biaxial testing machine. The strain at the centre of the sample is measured during loading using a stroboscopic Digital Image Correlation (DIC) technique, and crack initiation on the whole gauge zone is early detected by a second DIC-based measurement. A special optical assembly is designed to allow for simultaneous measurements. Three types of loadings are performed: equi-biaxial with a loading ratio R = 0.1, equi-biaxial with loading ratio R = -1, pseudo uniaxial (cyclic loading at R 0.1 in one direction and constant loading in the other). First results are commented. (authors)

  17. Design characteristics that improve the fatigue life of threaded pipe connections

    Directory of Open Access Journals (Sweden)

    De Baets, Patrick

    2011-10-01

    Full Text Available Threaded pipe connections are commonly used to connect risers, tendons, drill pipes and well casing strings. In these applications fatigue resistance plays an important role. A large variety of patented design features exist, all claiming to improve the connection’s fatigue life. However, patent documents only contain claims and numerical or experimental data about these connection’s performance is generally not published. This makes it hard to make a quantitative comparison between different designs. In this study anoverview is given of fatigue resistant threaded connections. Two major methods to improve the fatigue life of a connection were identified. First of all, local stress concentrations can be reduced by optimizing the geometry of the threads. Second the global shape of the connection can be optimized to obtain a more uniform load distribution.Using a parametric finite element model, different designs were compared. The connections were modelled by a 2D axisymmetric geometry with non-linear material properties and elaborate contact conditions.Selected designs have been subjected to experimental tests in a four-point bending fatigue setup. The experimental tests serve as a validation for the results of the numerical simulations. It was found that the multiaxial stress distribution at the thread roots is the defining factor for the fatigue life of the connection. Nevertheless, these stresses can be changed by the global geometry of the connection. It can be concluded that the fatigue life of threaded connections is determined by a combination of global and local aspects which should both be analysed for fatigue life calculations.

  18. 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 ...

  19. Crack initiation life prediction method of thermal creep-fatigue

    International Nuclear Information System (INIS)

    Experimental and analytical results are presented of different surface roughness SUS304 tapered cylinders subjected to thermal creep-fatigue in liquid sodium. An experimental formula was developed to determine crack initiation cycles and subsequent propagation behaviors under repeated temperature gradient loads in a wall. A failure criterion of 'unity in creep-fatigue damage' roughly agreed with the occurrance of experimental 1 mm deep cracks. Surface roughness had no effect on crack initiation cycles and subsequent propagation behavior. (orig.)

  20. APPLICATION OF MULTIBODY SIMULATION FOR FATIGUE LIFE ESTIMATION

    OpenAIRE

    Kamal, M.; Rahman, M. M.; Sani, M. S. M.

    2013-01-01

    In automobile design, the safety of passengers is of prime concern to the manufacturers. Suspension is one of the safety-related automotive systems which is responsible for maintaining traction between the road and tires, and offers a comfortable ride experience to the passengers by absorbing disturbances. One of the critical components of the suspension system is the knuckle, which constantly faces cyclic loads subjecting it to fatigue failure. This paper presents an evaluation of the fatigu...

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

    OpenAIRE

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

    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...

  2. Ratcheting and low cycle fatigue behavior of SA333 steel and their life prediction

    International Nuclear Information System (INIS)

    Ratcheting and low cycle fatigue (LCF) experiments have been conducted at 25 oC temperature in laboratory environment under different loading conditions. SA333 steel exhibits cyclic hardening throughout its life during LCF. It is found that ratcheting strain increases with both increasing mean stress and stress amplitude. It has also been noticed that plastic strain amplitude and plastic strain energy decrease with increase in mean stress at constant stress amplitude. Ratcheting and LCF life in the range of 102-105 cycles have been predicted with the help of a mean stress-based fatigue lifing equation.

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

    Science.gov (United States)

    Hooke, F. H.

    1972-01-01

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

  4. FATIGUE LIFE PREDICTION OF COMMERCIALLY PURE TITANIUM AFTER NITROGEN ION IMPLANTATION

    Directory of Open Access Journals (Sweden)

    Nurdin Ali

    2013-06-01

    Full Text Available Prediction of fatigue life has become an interesting issue in biomaterial engineering and design for reliability and quality purposes, particularly for biometallic material with modified surfaces. Commercially pure titanium (Cp-Ti implanted with nitrogen ions is a potential metallic biomaterial of the future. The effect of nitrogen ion implantation on fatigue behavior of Cp-Ti was investigated by means of axial loading conditions. The as-received and nitrogen-ion implanted specimens with the energy of 100 keV and dose of 2 × 1017 ions cm-2, were used to determine the fatigue properties and to predict the life cycle of the specimens. The effect of nitrogen ion implantation indicated revealed improved the tensile strength due to the formation of nitride phases, TiN and Ti2N. The fatigue strength of Cp-Ti and Nii-Ti was 250 and 260 MPa, respectively. The analytical results show good agreement with experimental results.

  5. An approach for determining an appropriate assumed distribution of fatigue life under limited data

    International Nuclear Information System (INIS)

    The case of limited data implies that some unknown uncertainties may be involved in fatigue reliability analysis. For the sake of statistical convenience, for consistency with the relevant physical arguments and, most importantly, to ensure the safety in design evaluation, an approach is developed to determine an appropriate distribution, from four possible assumed distributions--three-parameter Weibull, two-parameter Weibull, lognormal and extreme maximum-value distributions. The approach makes allowance for consistency with the fatigue physics and checking tail fit effects. An application to nine groups of fatigue life data of 16Mn steel (Chinese steel) welded plate specimens shows that the lognormal distribution and the extreme maximum-value distribution may be the appropriate distributions of the fatigue life under limited data

  6. Self-reported fatigue and physical function in late mid-life

    DEFF Research Database (Denmark)

    Boter, Han; Mänty, Minna

    2014-01-01

    Objective: To determine the association between the 5 subscales of the Multidimensional Fatigue Inventory (MFI-20) and physical function in late mid-life. Design: Cross-sectional study. Subjects: A population-based sample of adults who participated in the Copenhagen Aging and Midlife Biobank population cohort (n?=?4,964; age 49-63 years). Methods: Self-reported fatigue was measured using the MFI-20 comprising: general fatigue, physical fatigue, reduced activity, reduced motivation, and mental fatigue. Handgrip strength and chair rise tests were used as measures of physical function. Multiple logistic regression analyses were used to determine the associations between handgrip strength and the chair rise test with the MFI-20 subscales, adjusted for potential confounders. Results: After adjustments for potential confounders, handgrip strength was associated with physical fatigue (adjusted odds ratio (OR) 0.75 (95% confidence interval (CI) 0.66-0.86); p???0.001) and reduced motivation (adjusted OR 0.85 (95% CI 0.75-0.96); p???0.05), but not with the other subscales. After these adjustments, the chair rise test was associated with physical fatigue (adjusted OR 0.61 (0.53-0.69); p???0.001), general fatigue (adjusted OR 0.72 (0.62-0.84); p???0.001), reduced activity (adjusted OR 0.79 (0.70-0.90); p???0.001) and reduced motivation (adjusted OR 0.84 (0.74-0.95); p???0.01), but not with mental fatigue. Subgroup analyses for sex did not show statistically significant different associations between physical function and fatigue. Conclusion: The present study supports the physiological basis of 4 subscales of the MFI-20. The association between fatigue and function was independent of gender.

  7. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zangenberg Hansen, J.

    2013-09-15

    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. (Author)

  9. 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.

  10. Fatigue

    Science.gov (United States)

    ... tips may help you avoid excessive fatigue during pregnancy: Take naps and breaks. Rest when you can during the day, during your ... second trimester, some women feel tired throughout their pregnancy. Talk to your ... go away with adequate rest Severely fatigued a few weeks into your second ...

  11. 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.

  12. Fatigue life prediction of ZE41A magnesium alloy using Weibull distribution

    International Nuclear Information System (INIS)

    In this investigation, the fatigue life prediction of ZE41A magnesium alloy has been statistically analyzed by Weibull distribution. The mechanical fatigue tests are conducted under R = 0.1 axial tension condition on specimen machined at as cast and welded materials. The micro structural investigations performed shows strong influence of precipitation on the fatigue failure of material. The curve for maximum stress and cycles to failure has been constructed for above stated materials. Using Weibull, the probability distribution according to which the material will fail is obtained. The fracture surface of the specimens is studied using scanning electron microscope

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

    DEFF Research Database (Denmark)

    SØrensen, Eigil V.; Westhof, Luc

    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 shorter when tested in water than when tested in air.

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

    Czech Academy of Sciences Publication Activity Database

    Pokorný, Pavel; Náhlík, Luboš; Šev?ík, 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 MŠk(CZ) EE2.3.20.0214 Grant ostatní: 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

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

    OpenAIRE

    Helmerich, Rosemarie; Ku?hn, 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...

  16. FATIGUE LIFE PREDICTION OF COMMERCIALLY PURE TITANIUM AFTER NITROGEN ION IMPLANTATION

    OpenAIRE

    Nurdin Ali; M.S. Mustapa; M.I. Ghazali; T. Sujitno; M. Ridha

    2013-01-01

    Prediction of fatigue life has become an interesting issue in biomaterial engineering and design for reliability and quality purposes, particularly for biometallic material with modified surfaces. Commercially pure titanium (Cp-Ti) implanted with nitrogen ions is a potential metallic biomaterial of the future. The effect of nitrogen ion implantation on fatigue behavior of Cp-Ti was investigated by means of axial loading conditions. The as-received and nitrogen-ion implanted specimens with the...

  17. Fatigue Life Analysis of Fixed Structure of Posterior Thoracolumbar Pedicle Screw

    OpenAIRE

    Tong Yang; Kai Chen; Yonggui Lv

    2013-01-01

    In order to analyze the fatigue life of the posterior thoracolumbar fixed structure, a loading model was established in accordance with the anti-fatigue test requirements specified by ASTM Standard F1717-04. Two three-dimensional Models of the fixed structure with two bars and four bars were built by 3D software (UG), and imported into ANSYS software for static analysis. The maximum and minimum stresses of risk nodes under different loads and moments were obtained. The ...

  18. 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 .

  19. 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.

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

    International Nuclear Information System (INIS)

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

  1. Fatigue life law for smooth specimens at elevated temperatures derived from fracture mechanics law of crack propagation

    Energy Technology Data Exchange (ETDEWEB)

    Ohtani, R.; Kitamura, T.

    1985-07-01

    The fatigue life of smooth specimens was modeled through integration of the crack propagation model for cycle and time dependent fatigue. The lifetime was thereby a function of the creep strain range, the stress range, the maximum stress, and the elastic strain range. High temperature fatigue data were gathered with 2.5 Cr-1 MO steel, 30 stainless steel, and Inconel 18 specimens and compared, with the model predictions showing good agreement for both time- and cycle-dependent fatigue. 22 references.

  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. 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.

  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. On fatigue life prediction of composites in automotive engineering; Zur Lebensdauerberechnung faserverstaerkter Kunststoffe im Automobilbau

    Energy Technology Data Exchange (ETDEWEB)

    Oppermann, Helge [BMW AG, Muenchen (Germany). Forschungszentrum

    2012-07-01

    Fibre reinforced composites are a major aspect in terms of lightweight design, sustainability and costs. Therefore they are currently in the focus of all major automobile manufacturers. Methodological approaches already exist for individual facets of fatigue life prediction of such material systems. However in most cases these are insufficiently validated or the application corridor is very narrow. Therefore such methodologies are not integrable into the development process of automotive engineering. Due to the complexity of influencing factors (interlaminar stresses, viscoelasticity, ageing etc.) and the lack of comprehensive material models, high expenditures are to be expected for the fatigue life calculation of composites. It is essential to take into account this aspect during development of methods for fatigue life calculation i.e. the experimental expenditure for the determination of material data for the calculation shall not be exceed an acceptable level. (orig.)

  6. Fatigue-life prediction for a copper alloy degraded by multiple flaws

    International Nuclear Information System (INIS)

    A study to establish fatigue life prediction for alloy 155 copper degraded by multiple flaws is described. Twelve specimens with natural flaws were radiographically characterized and fatigue tested to failure in a manner which minimized data scatter. Disposition of defective alloy 155 copper plate stock and Doublet III B-coil machined center post components was based on radiographically determined flaw size. Along with the macroscopic vertical internal flaws detected by radiography, undetectable microscopic alloy segregations were present in the microstructure. Data scatter, including microscopic flaw distribution, was related to radiographically detectable flaw size, and the reliability of the radiographic method was evaluated. B-coil fatigue lives for various load conditions were predicted. B-coil life expended to date and useful life remaining are discussed

  7. Fatigue-life prediction for a copper alloy degraded by multiple flaws

    Energy Technology Data Exchange (ETDEWEB)

    Sweig, R.A.

    1981-07-01

    A study to establish fatigue life prediction for alloy 155 copper degraded by multiple flaws is described. Twelve specimens with natural flaws were radiographically characterized and fatigue tested to failure in a manner which minimized data scatter. Disposition of defective alloy 155 copper plate stock and Doublet III B-coil machined center post components was based on radiographically determined flaw size. Along with the macroscopic vertical internal flaws detected by radiography, undetectable microscopic alloy segregations were present in the microstructure. Data scatter, including microscopic flaw distribution, was related to radiographically detectable flaw size, and the reliability of the radiographic method was evaluated. B-coil fatigue lives for various load conditions were predicted. B-coil life expended to date and useful life remaining are discussed.

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

    DEFF Research Database (Denmark)

    Rafsanjani, Hesam Mirzaei; SØrensen, 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. 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.

  10. Life prediction methods for the combined creep-fatigue endurance

    International Nuclear Information System (INIS)

    The basis and current status of development of the various approaches to the prediction of the combined creep-fatigue endurance are reviewed. It is concluded that an inadequate materials data base makes it difficult to draw sensible conclusions about the prediction capabilities of each of the available methods. Correlation with data for stainless steel 304 and 316 is presented. (U.K.)

  11. Shape optimization for prolonging fatigue life of a structure

    International Nuclear Information System (INIS)

    Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization for two types of specimens, which are very typical ones in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. Also shape optimization for a cantilever beam in mixed mode was carried out by the same techniques. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was found that shapes of two types of specimens and a cantilever beam optimized by the growth-strain method prolong their fatigue lives significantly. Therefore, it was verified that the growth-strain method is an appropriate technique for shape optimization of a structure having a crack

  12. Life-prediction methods for combined creep-fatigue endurance

    International Nuclear Information System (INIS)

    The basis and current status of development of the various approaches to the prediction of the combined creep-fatigue endurance are reviewed. It is concluded that an inadequate materials data base makes it difficult to draw sensible conclusions about the prediction capabilities of each of the available methods. (author)

  13. Creep, fatigue and creep-fatigue damage evaluation and estimation of remaining life of SUS 304 austenitic stainless steel at high temperature

    International Nuclear Information System (INIS)

    Experimental study was made on the damage evaluation and estimation of remaining life of SUS 304 stainless steel in creep, low-cycle fatigue and creep-fatigue at 873 K in air. Creep, fatigue and creep-fatigue damage curves were drawn by the method proposed by D.A. Woodford and the relations between these damages and non-destructive parameters, i.e., microvickers hardness and quantities obtained from X-ray diffraction, were discussed. From these tests, the following conclusions were obtained. (1) Constant damage lines in the diagram of remaining lives in creep and fatigue could be drawn by changing load levels during the tests. Constant damage lines in creep-fatigue were also made by a linear damage rule using both static creep and fatigue damage curves, which agree well with the experimental data in creep-fatigue. (2) Microvickers hardness and half-value breadth in X-ray diffraction are appropriate parameters to evaluate creep damage but are not proper to evaluate fatigue damage. Particle size and microstrain obtained by X-ray profile analysis are good parameters to evaluate both creep and fatigue damages. (author)

  14. 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.

  15. Predicting the Fatigue Life in Steel and Glass Fiber Reinforced Plastics Using Damage Models

    Directory of Open Access Journals (Sweden)

    Roselita Fragoudakis

    2011-06-01

    Full Text Available Three cumulative damage models are examined for the case of cyclic loading of AISI 6150 steel, S2 glass fibre/epoxy and E glass fibre/epoxy composites. The Palmgren-Miner, Broutman-Sahu and Hashin-Rotem models are compared to determine which of the three gives the most accurate estimation of the fatigue life of the materials tested. In addition, comparison of the fatigue life of the materials shows the superiority of AISI 6150 steel and S2 glass fibre/epoxy at lower mean stresses, and that of steel to the composites at higher mean stresses.

  16. Predicting the Fatigue Life in Steel and Glass Fiber Reinforced Plastics Using Damage Models

    OpenAIRE

    Roselita Fragoudakis; Anil Saigal

    2011-01-01

    Three cumulative damage models are examined for the case of cyclic loading of AISI 6150 steel, S2 glass fibre/epoxy and E glass fibre/epoxy composites. The Palmgren-Miner, Broutman-Sahu and Hashin-Rotem models are compared to determine which of the three gives the most accurate estimation of the fatigue life of the materials tested. In addition, comparison of the fatigue life of the materials shows the superiority of AISI 6150 steel and S2 glass fibre/epoxy at lower mean stresses, and that of...

  17. 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...

  18. 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.)

  19. 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

  20. The impact of disability, fatigue and sleep quality on the quality of life in multiple sclerosis

    OpenAIRE

    Ghaem Haleh; Haghighi Afshin

    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 refe...

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

    Science.gov (United States)

    Alam, Mohammad Shah

    2005-11-01

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

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2013-01-01

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

  5. 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)

  6. Effects of cellular growth on fatigue life of directionally solidified hypoeutectic Al-Fe Alloys

    Scientific Electronic Library Online (English)

    Pryscilla Liberato, Ribeiro; Bismarck Luiz, Silva; Wanderson Santana da, Silva; José E, Spinelli.

    2014-06-01

    Full Text Available Al-Fe hypoeutectic alloys are a family of casting alloys characterized by cell growth, low cost and appreciable formability. It is well known that fatigue strength is a requirement of prime importance considering the nature of load typically observed during operations involving the risers used in oi [...] l extraction. The aim of this study is to examine the influence of cell size and its intercellular phase distribution on the fatigue life (Nf) of the directionally solidified Al-0.5, 1.0 and 1.5wt% Fe alloys. A water-cooled vertical upward unidirectional solidification system was used to provide the castings. Microscopy light and SEM microscopy were used. It was found that fatigue life decreases as cell spacing (? c) increases. Smaller cell spacing allows a homogeneous distribution of Al-Fe fibers to happen within the intercellular regions, which tends to improve the mentioned fatigue property. Hall-Petch type correlations [Nf= Nf0+A(?c -1/2)-B(?c -1); where A and B are constants] seems to be able to encompass the fatigue life variation along the Al-Fe alloys.

  7. 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.

  8. 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.)

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

    Science.gov (United States)

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

    2015-02-01

    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.

  10. 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.

  11. 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.

  12. Evaluation of extrapolation for creep-fatigue life by hysteresis energy

    International Nuclear Information System (INIS)

    The creep-fatigue life has been evaluated by the hysteresis energy in 316FR stainless steel with low carbon and medium nitrogen, which is a candidate for structural material in Fast Breeder Reactor (FBR) plant with the design life of 60 years. The creep-fatigue is a main damage mode to prevent. The hysteresis energy rate is considered as the parameter to predict the life time. It is clear that the relationship between this parameter and the time to failure can be approximately expressed by the power-law function. The function depends on the ratio of plastic strain to total strain. Total fracture energy for creep-fatigue loading intends to be independent of the ratio of plastic strain to total strain in long-term test condition. The value is related to grain boundary strength for creep-fatigue loading because fracture mode in long-term test condition is intergranular fracture. The life could be predicted by the function in the case of no significant change of fracture energy. Coarse precipitation, for example sigma phase, might be considered as a factor to change the fracture energy. It is important to predict the precipitation formation. The result of life prediction by the hysteresis energy rate is compared with that of the time fraction rule based on 'Demonstration Reactor Design Standard (Draft)'. The predicted lives by both methods for long-term region are comparable and independent of the ratio of plastic strain to total strain. (author)strain. (author)

  13. Fatigue life prediction of a stainless steel plate-fin structure using equivalent-homogeneous-solid method

    International Nuclear Information System (INIS)

    Highlights: ? A fatigue life prediction method is established for 304 stainless steel plate-fin structure. ? The fatigue cracks initiate at the fillet and then propagate to the base metal of fin. ? The fatigue fracture in the filler metal shows brittle character. ? Typical dimple and striation are shown in the base metal. -- Abstract: Stainless steel plate-fin heat exchangers are key components in nuclear power stations and hydrogen production systems using High Temperature Gas-cooled Reactors (HTGR). Fatigue is the most failure mode for plate-fin structures because they operate under cyclic high pressures and high temperatures. This paper establishes a life prediction method of fatigue based on equivalent-homogeneous-solid method for a 304 stainless steel plate-fin structure. A finite element analysis (FEA) program of fatigue life has been developed, which has been verified by fatigue experiments. By using this method, both the local stress concentration and the fatigue life for the whole plate-fin structure can be predicted. The results show that the fatigue cracks initiate at the fillet and then propagate to the interface and eventually the base metal of fin. The fatigue fracture in the filler metal shows brittle character, while typical dimple and striation are shown in the base metal.

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

    Science.gov (United States)

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

    1992-01-01

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

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

    International Nuclear Information System (INIS)

    A nonlinear acoustic measurement is studied for fatigue damage monitoring. An electromagnetic acoustic transducer (EMAT) magnetostrictively couples to a surface-shear-wave resonance along the circumference of a rod specimen during rotating bending fatigue of carbon steels. Excitation of the EMAT at half of the resonance frequency caused the standing wave to contain only the second-harmonic component, which was received by the same EMAT to determine the second-harmonic amplitude. Thus measured surface-wave nonlinearity always showed two distinct peaks at 60% and 85% of the total life. We attribute the earlier peak to crack nucleation and growth, and the later peak to an increase of free dislocations associated with crack extension in the final stage. This noncontact resonance-EMAT measurement can monitor the evolution of the surface-shear-wave nonlinearity throughout the metal's fatigue life and detect the pertinent precursors of the eventual failure. [copyright] 2001 American Institute of Physics

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

    Science.gov (United States)

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

    2011-03-01

    The aim of this study was to investigate the fatigue life of laser welded joints in a commercially available cast cobalt-chromium alloy. Twenty rod shaped specimens (40 mm x 1.5 mm) were cast and sand blasted. Ten specimens were used as controls and the remaining ten were sectioned and repaired using a pulsed Nd: YAG laser welder. All specimens were subjected to fatigue testing (30N - 2Hz) in a controlled environment. A statistically significant difference in median fatigue life was found between as-cast and laser welded specimens (p repairing cobalt chromium clasps on removable partial dentures. Scanning electron microscopy indicated the presence of cracks, pores and constriction of the outer surface in the welded specimens despite 70% penetration of the weld. PMID:21528682

  17. Fatigue life prediction of Ni-base thermal solar receiver tubes

    Energy Technology Data Exchange (ETDEWEB)

    Hartrott, Philipp von; Schlesinger, Michael [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany); Uhlig, Ralf; Jedamski, Jens [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Stuttgart (Germany)

    2010-07-01

    Solar receivers for tower type Solar Thermal Power Plants are subjected to complex thermo-mechanical loads including fast and severe thermo-mechanical cycles. The material temperatures can reach more than 800 C and fall to room temperature very quickly. In order to predict the fatigue life of a receiver design, receiver tubes made of Alloy 625 with a wall thickness of 0.5 mm were tested in isothermal and thermo-cyclic experiments. The number of cycles to failure was in the range of 100 to 100,000. A thermo-mechanical fatigue life prediction model was set up. The model is based on the cyclic deformation of the material and the damage caused by the growth of fatigue micro cracks. The model reasonably predicts the experimental results. (orig.)

  18. Evaluation of accuracy of fatigue-creep life preciction based on inelastic analysis

    International Nuclear Information System (INIS)

    In our institute, the research on the improvement of solution accuracy of inelastic analysis is under way for the purpose of contribution to the rationalization in design of fast breeder reactors. In this research, the prediction accuracy of inelastic constitutive equations and creep-fatigue life estimation laws is evaluated based on a number of test results. In this report, we conduct the stress-strain analyses by elastic-plastic-creep equations and the failure life estimation by linear damage fraction rule. The results of them are compared with the experimental results. The following two types of tests, both of which are conducted at 550 deg C, are analyzed: (i) strain-hold type low-cycle fatigue tests (ii) slow strain-rate type low-cycle fatigue tests. The predicted failure lives for type (i) tests are smaller than the experimental values, whereas those for type (ii) tests tend to be larger than the test results. (author)

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

    Science.gov (United States)

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

    2014-01-01

    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.

  20. 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

  1. 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

  2. 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.

  3. Fatigue

    International Nuclear Information System (INIS)

    The phenomenon of materal fatigue, i.e. fracture caused by alternating load with stresses being below ultimate strength is considered. Formation of a complex dislocation structure during fatigue tests as well as formation of stable bands of slip (SBS) which are a symptom of deformation localization are described. Dislocation models for formation of surface topography in SBS are presented. Theory of crack formation as a resut of disordering slip inside SBS is discussed. The mechanism of crack propagation is considered in the framework of fracture mechanisms. Environment influence on this process is marked

  4. 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,…

  5. Fatigue life of carburized steel specimens under push-pull loading.

    Czech Academy of Sciences Publication Activity Database

    Major, Št?pán; Hubálovský, Š.; Šedivý, J.; Bryscejn, Jan

    2014-01-01

    Ro?. 1, ?. 1 (2014), s. 99-104. ISSN 2313-0555 Institutional support: RVO:68378297 Keywords : carburizing * fatigue life * sub-surface crack * highstrength steel * push-pull loading Subject RIV: JM - Building Engineering http://www.naun.org/cms.action?id=7631

  6. Improvement of fatigue life of steel orthotropic desks with carbon fibre reinforcement composites.

    Czech Academy of Sciences Publication Activity Database

    Urushadze, Shota; Frýba, Ladislav; Pirner, Miroš

    Brno : Czech society for mechanics, 2011 - (Návrat, 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

  7. 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.

  8. A study on fretting fatigue life in elevated temperature for Inconel 600 alloy

    International Nuclear Information System (INIS)

    The safety needs in the operation of nuclear power plant facilities have been increased due to the high temperature and pressure operation conditions within these facilities. Several reports exist on the fretting occurring in the materials of steam generator tubes used in nuclear power plants, which leads to a lower service life. The Inconel 600 alloy, used in steam generator tubes, is a type of nickel-chromium based heat resistant alloy. However, it is necessary to establish a systematic database to guarantee its integrity because there are few data indicating fretting fatigue behaviors at both room and high temperature conditions for the Inconel 600 alloy. Thus, this study analyzed the change in the fatigue characteristics of the Inconel 600 alloy under fretting fatigue by applying plain and fretting fatigue tests at 320 .deg. C, which is the room and actual operating temperature applied to the materials of steam generator tubes. In addition, this study measured the change in the friction force for repetitive cycles in fretting fatigue tests and analyzed the mechanism of fretting fatigue by observing the fracture surfaces.

  9. ARRANGING THICKNESSES AND SPANS OF ORTHOTROPIC DECK FOR DESIRED FATIGUE LIFE AND DESIGN CATEGORY

    Directory of Open Access Journals (Sweden)

    Abdullah Fettahoglu

    2013-09-01

    Full Text Available Orthotropic steel highway bridges are subject to variable traffic loads, which differ in type and magnitude. Most of these bridges were built in 1960’s under design traffic load, which reflects the traffic conditions of those times. However, the number and weight of vehicles in traffic have increased since then too much in comparison to today. As a result these bridges are loaded more than their designed traffic loads and hence bridges' fatigue lives are shorten. As a remedy for this issue, thicknesses of fatigue sensitive structural parts of bridge shall be determined under today' s valid wheel loads and design category for desired fatigue life. In the scope of this study the traditional steel orthotropic highway bridge is analyzed using a FE- model, which encompasses bridge' s entire geometry. The traffic load is selected so conservatively, that it is composed of static wheel loads and wheel load area, which comply with the wheels of vehicles used today in traffic. Subsequently, fatigue lives of four fatigue sensitive structural parts of bridge are calculated. These are critical section in web of cross girder due to cut outs, weld connecting deck plate to trapezoidal rib, continuous longitudinal stringer and deck plate. Finally, required thicknesses and spans of these structural parts depending on their fatigue lives and design categories are given.

  10. Prediction of Fatigue Life of Boom Nose End Casting Using Linear Elastic Fracture Mechanics

    OpenAIRE

    Nitin D.Ghongade; Rajesh.M. Metkar

    2014-01-01

    The main objective of this study is to get the life estimation of Boom nose end casting using theoretical approach and compaired it with finite element method. Therefore, this study consists of three major sections : (1) dynamic load analysis (2) FEM and stress analysis (3) prediction of fatigue life for Boom nose end casting. In this study a dynamic loads were obtained from cyclic loading at different time. Finite element analysis was performed to obtain the variation of stress...

  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 S–Ncurves 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.

  12. Multiaxial creep-fatigue life analysis using strainrange partitioning

    International Nuclear Information System (INIS)

    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

  13. 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.

  14. 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 ??tot for the fatigue damage ?f; b) long-term strength relation for the time to creep rupture t? dependent on numerical average stress ?¯ during dwell ?t for the creep damage ?cr; c) non-linear creep-fatigue interaction diagram for the total damage. Numerically estimated N? for different ?t and ??tot shows good quantitative agreement with experiments. A parametric study of different dwell times ?t is used to formulate the functions for N? and residual life L? dependent on ?t 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

  15. 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.

  16. Robust design and thermal fatigue life prediction of anisotropic conductive film flip chip package

    International Nuclear Information System (INIS)

    The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF(Anisotropic Conductive Film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue life of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear bi-thermal analysis was conducted and the result was compared with Moire interferometer experiment. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. DOE (Design Of Experiment) technique was used to find important design factors. The results show that PCB CTE (Coefficient of Thermal Expansion) and elastic modulus of ACF material are important material parameters. And as important design parameters, chip width, bump pitch and bump width were chose. 2nd DOE was conducted to obtain RSM equation for the choose 3 design parameter. The coefficient of determination (R2) for the calculated RSM equation is 0.99934. Optimum design is conducted using the RSM equation. MMFD is conducted using the RSM equation. MMFD (Modified Method for Feasible Direction) algorithm is used to optimum design. The optimum value for chip width, bump pitch and bump width were 7.87mm, 430?m, and 78?m, respectively. Approximately, 1400 cycles have been expected under optimum conditions. Reliability analysis was conducted to find out guideline for control range of design parameter. Sigma value was calculated with changing standard deviation of design variable. To acquire 6 sigma level thermal fatigue reliability, the Std. Deviation of design parameter should be controlled within 3% of average value

  17. Fatigue-ratcheting interaction

    International Nuclear Information System (INIS)

    An experimental investigation of fatigue Life and ratcheting strain has been carried out on 304 L steel tubes. They are loaded by a constant tensile primary stress and cyclic torsional strain. Under this type of loading, which can be estimated as severe for ratchet strain enhancement if we consider the shake down diagram drawn with an elastic perfectly plastic materially, The 3 Sm rule has been shown to be over conservative to limit the cumulative strain, especially when the primary mean stress is at low Level. The ratcheting strain at failure ?R can be assessed by using the RCC-MR efficiency diagram and the ratcheting strain at N cycle can be assessed as ?(N) = ?R (Log N/Log NR). No interaction between ratcheting strain and fatigue life reduction has been brought in the light if these tests but a of strong effect of the primary constant stress on the endurance limit of the material reduces the high cycle fatigue life even when the 3 Sm rule is complied with. This effect can be taken into account by use of an effective strain defined as ??eff ?? + B P/SY where B is the endurance limit and Sy the conventional yield strength. This effective strength is to be applied with the fatigue curve in order to determine the allowable number of cycles. (author)

  18. Evaluation of creep–fatigue life based on fracture energy for modified 9Cr–1Mo steel

    International Nuclear Information System (INIS)

    Preventing creep–fatigue damage is a major consideration in nuclear power plants, which operate at high temperatures. Energy absorbed during creep–fatigue loading is focused on for predicting long-term creep–fatigue life for modified 9Cr–1Mo 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 creep–fatigue and low strain-rate fatigue. The creep–fatigue 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.

  19. Numerical Estimation of Fatigue Life of Wind Turbines due to Shadow Effect

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle; Pedersen, Ronnie

    2009-01-01

    The influence of tower design on damage accumulation in up-wind turbine blades during tower passage is discussed. The fatigue life of a blade is estimated for a tripod tower configuration and a standard mono-tower. The blade stresses are determined from a dynamic mechanical model with a delay effect included in the normal coefficient used to compute the transverse load. Furthermore, the rotational effect of the turbulence spectrum is included in the model. The proposed tripod configuration of the tower limits the damage accumulation in the turbine blades significantly when compared to the fatigue of a blade from a monotower wind turbine.

  20. Thermal fatigue life prediction based on crack propagation behaviors in high-temperature materials for power plant components

    International Nuclear Information System (INIS)

    For reducing an electric power supply cost, it is desired to extend the life of thermal power plant being still supplying the greater part of electric power in Japan. It is, therefore, becoming more and more important for the remaining life control of long-operated thermal power plants to exactly estimate the thermal fatigue damage accumulating in high temperature components. In this report, a discussion was made on thermal fatigue life laws derived from the crack propagation laws. As a result, the life laws were found to be effective for the evaluation of thermal fatigue life as well as isothermal fatigue life. Based on the concept of the life laws, the thermal and isothermal fatigue lives were also predicted as a propagation period of a crack with initial length equal to grain size from the characteristics of high temperature fatigue crack propagation. In addition to them, the rapid straining method was found to be required for more accurate estimation of creep strain in in-phase thermal fatigue. (author)

  1. Low cycle fatigue behaviors of type 316LN austenitic stainless steel in 310 deg. C deaerated water-fatigue life and dislocation structure development

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Hyunchul [Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701 (Korea, Republic of); Kim, Byoung Koo [Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701 (Korea, Republic of); Corporate R and D Institute, Doosan Heavy Industries and Construction Co. Ltd., 555 Gwigok-dong, Changweon, Gyeongnam 641-792 (Korea, Republic of); Kim, In Sup [Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701 (Korea, Republic of); Jang, Changheui [Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701 (Korea, Republic of)], E-mail: chjang@kaist.ac.kr

    2008-03-15

    The low cycle fatigue tests for type 316LN stainless steel were performed in 310 deg. C deaerated water at various strain amplitudes and strain rates. The primary hardening was observed in all test conditions. It was found that the increase of bulk dislocation density and the interaction between mobile dislocations and atoms, which occur under the dynamic strain aging condition, were responsible for the primary hardening. On the other hand, the secondary hardening occurred distinctly for 0.4%/s and 0.4%. For that specific condition, the corduroy contrast resulted from pinned dislocations was observed at the crack tip. The secondary hardening may be associated with the corduroy contrast. The dislocation structure and fatigue surface revealed the characteristic feature of the hydrogen-induced cracking. Thus, we concluded the hydrogen-induced cracking contributed to the reduction in fatigue life and the enhancement of decreasing fatigue life with a decreasing strain rate in 310 deg. C deaerated water.

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

    Science.gov (United States)

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

    2006-04-01

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

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

    Science.gov (United States)

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

    2007-08-01

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

  4. Influence of Subgrade and Unbound Granular Layers Stiffness on Fatigue Life of Hot Mix Asphalts - HMA

    Directory of Open Access Journals (Sweden)

    Hugo A. Rondón-Quintana

    2013-11-01

    Full Text Available The mainly factors studied to predict fatigue life of hot mix asphalt-HMA in flexible pavements are the loading effect, type of test, compaction methods, design parameters of HMA (e.g., particle size and size distribution curve, fine content, type of bitumen and the variables associated with the environment (mainly moisture, temperature, aging. This study evaluated through a computer simulation, the influence of the granular layers and subgrade on the fatigue life of asphalt layers in flexible pavement structures. Mechanics parameters of granular layers of subgrade, base and subbase were obtained using the mathematical equations currently used for this purpose in the world. The emphasis of the study was the city of Bogotá, where the average annual temperature is 14°C and soils predominantly clay, generally experience CBR magnitudes between 1% and 4%. General conclusion: stiffness of the granular layers and subgrade significantly affect the fatigue resistance of HMA mixtures. Likewise, the use of different equations reported in reference literature in order to characterize granular layers may vary the fatigue life between 4.6 and 48.5 times, varying the thickness of the pavement layers in the design.

  5. The Prevalence of Fatigue Following Deep Brain Stimulation Surgery in Parkinson's Disease and Association with Quality of Life

    OpenAIRE

    Dawn Bowers; Skoblar, Barry M.; Amanda Fogel; Fernandez, Hubert H.; Rodriguez, Ramon L.; Garvan, Cynthia W.; Charles Jacobson; Veronica Parra; Kluger, Benzi M.; Okun, Michael S.

    2012-01-01

    Fatigue is a common and disabling nonmotor symptom seen in Parkinson's disease (PD). While deep brain stimulation surgery (DBS) improves motor symptoms, it has also been associated with non-motor side effects. To date no study has utilized standardized instruments to evaluate fatigue following DBS surgery. Our objective was to determine the prevalence of fatigue following DBS surgery in PD its impact on quality of life and explore predictive factors. We recruited 44 PD subjects. At least one ...

  6. Seismic fatigue life evaluation of mechanical structures using energy balance equation

    International Nuclear Information System (INIS)

    Evaluation of seismic resistant performance for severe earthquakes is required, because of occurrence of earthquakes which exceed the design criteria. Additionally, quantitative evaluation of cumulative damage by earthquake is also required. In this study, the energy balance equation is applied to the evaluation. The energy balance equation expresses integral information of response, so that the energy balance equation is adequate for the evaluation of the influence of cumulative load such as seismic response. At first, vibration experiment that leads experimental model to fatigue failure by continuous vibration disturbance is conducted. As a result of the experiment, relation between fatigue failure and energy balance equation is confirmed. Then the relation is proved from the viewpoint of hysteresis energy, and consistency between energy balance equation and hysteresis energy is confirmed. Finally, we adopted cumulative damage rule to energy balance equation in order to expect the fatigue life under random waves that have various input acceleration. (author)

  7. 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)

  8. 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.

  9. Creep-fatigue life property of FBR high-temperature structural materials under tension-torsion loading and life evaluation method

    International Nuclear Information System (INIS)

    Creep-fatigue damage in high temperature structural components in a FBR progress under multiaxial stress condition depending on their operating conditions and configuration. Therefore, multiaxial stress effects on creep-fatigue damage evolution must be clarified to make precise creep-fatigue damage evaluation of these components. In this study, creep-fatigue tests in FBR high temperature materials such as SUS304, 316FR stainless steels and a modified 9Cr steel were conducted under biaxial stress subjecting tension-compression and torsion loading, in order to examine biaxial stress effects on failure mechanism and life property, and to discuss creep-fatigue life evaluation methods under biaxial stress. Main results obtained in this study are summarized as follows: 1. The main cracks under cyclic torsion loading propagated by shear mode in three materials. But intergranular failure was occurred in SUS304 and 316FR, and transgranular failure was observed in Mod.9Cr steel. 2. Nonlinear damage accumulation model proposed based on uniaxial creep-fatigue test results was extended to apply for creep-fatigue damage evaluation under biaxial stress state by considering the biaxial stress effects on fatigue and creep damage evolution. 3. It was confirmed that creep-fatigue life under biaxial stress could be predicted by the extended evaluation method with higher accuracy than existing methods. (author)

  10. 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

  11. 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.

  12. 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 Young’s 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.

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

    DEFF Research Database (Denmark)

    Blasques, José Pedro Albergaria Amaral; Natarajan, Anand

    2013-01-01

    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. The fatigue damage is analysed in terms of the lifetime fatigue damage equivalent bending moment. Three different mean value correction techniques are considered, namely, Goodman, Walker, and mean sensitivity factor. An increase in the lifetime fatigue damage equivalent bending moment between 6% (mean sensitivity factor) and 33% (Goodman) is observed when mean load corrections are considered. The lifetime damage equivalent bending moment is further increased by approximately 7% when considering sea current forces. The results indicate that mean load correction techniques should be employed in the analysis 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.

  14. Effects of specimen configuration and test frequency on fatigue strength

    International Nuclear Information System (INIS)

    For the fatigue design of pressure vessels, low cycle fatigue design if often applied, such as earthquakes and the thermal stress due to start and stop of actual plants. As the standards stipulating the fatigue design method for reactor pressure vessels, there is ASME Boiler and Pressure Vessel Code, Section 3, Division 1, and for ordinary pressure vessels, Section 8, Division 2. Recently, the high cycle fatigue with low stress amplitude has also been taken in consideration, but the data on long life side for the structural materials of pressure vessels are few. In this study, the effect of test conditions on fatigue strength was examined on the high cycle fatigue of welded joints in which fatigue fracture is apt to occur. As the test materials, the rolled steels for welded structures, SM 50B, SM 58Q and HT 80QT were used, and the plate thickness was 9, 20 and 40 mm. The forms of joints were butt joint and cross type fillet welding joint. Ordinary arc welding with coated electrodes was performed. The results of the fatigue test, the variation of fatigue strength, and the effects of plate thickness, loading frequency, plate width and materials are reported. (Kako, I.)

  15. Evaluation of vibration and vibration fatigue life for small bore pipe in nuclear power plants

    International Nuclear Information System (INIS)

    The assessment method of the steady state vibration and vibration fatigue life of the small bore pipe in the supporting system of the nuclear power plants is proposed according to the ASME-OM3 and EDF evaluation methods. The GGR supporting pipe system vibration is evaluated with this method. The evaluation process includes the filtration of inborn sensitivity, visual inspection, vibration tests, allowable vibration effective velocity calculation and vibration stress calculation. With the allowable vibration effective velocity calculated and the vibration velocity calculated according to the acceleration data tested, the filtrations are performed. The vibration stress at the welding coat is calculated with the spectrum method and compared with the allowable value. The response of the stress is calculated with the transient dynamic method, with which the fatigue life is evaluated with the Miners linear accumulation model. The vibration stress calculated with the spectrum method exceeds the allowable value, while the fatigue life calculated from the transient dynamic method is larger than the designed life with a big safety margin. (authors)

  16. Optimal Shot Peening Treatments to Maximize the Fatigue Life of Quenched and Tempered Steels

    Science.gov (United States)

    Llaneza, V.; Belzunce, F. J.

    2015-05-01

    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.

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

    International Nuclear Information System (INIS)

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

  18. Comments on Linear Summation Hypothesis of Fatigue Failures

    Directory of Open Access Journals (Sweden)

    Szala Grzegorz

    2014-10-01

    Full Text Available This paper presents a comparative analysis of results of fatigue life calculations with the u se of the linear summation hypothesis of fatigue failures (LHSUZ, confronted with experimental test results. Te calculations and fatigue tests were performed for variable amplitude(VA, two-step and ten-step loading conditions, both in the low-cycle fatigue (LCF and high-cycle fatigue (HCF range, for the case of C45 steel as an example. Experimental verification of the hypothesis LHSUZ did not revealed any significant influence of load level and form of load spectrum on conformity of results of the calculation by using the LHSUZ, to results of fatigue tests on C45 steel. However, it enabled to assess magnitude of a correction factor which appears in the considered linear hypothesis.

  19. 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.

  20. 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)

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

    Science.gov (United States)

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

    2014-12-01

    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.

  2. 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.

  3. 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

  4. 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.

  5. 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...

  6. Effect of carburizing on fatigue life of highstrength steel specimen under push-pull loading.

    Czech Academy of Sciences Publication Activity Database

    Major, Št?pán; Jakl, V.; Hubálovský, Š.

    Santorini : WSEAS Press, 2014 - (Pshikhopov, V.; Foti, D.), s. 143-146 ISBN 978-1-61804-241-5. [International conference on materials: MATERIALS 2014. Santorini (GR), 17.07. 2014-21.07.2014] Institutional support: RVO:68378297 Keywords : carburizing * fatigue life * sub-surface crack * highstrength steel * push-pull * bending-torsion Subject RIV: JM - Building Engineering http://www.europment.org/library/2014/santorini/bypaper/MECHANICS/MECHANICS-00.pdf

  7. 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 25–65 yr) living in Queensland, Australia was conducted. Physical activity level, depression, fatigue and quality of life were assessed using the International Physical Activity Questio...

  8. Fatigue life estimation of different welding zones of oxy acetylene welded aluminum alloy (AA 5052-H32)

    International Nuclear Information System (INIS)

    Fatigue life of aluminum alloys are reviewed mainly on the basis of experimental results. Fatigue strength and failure history of the representative AA5052- H32 are summarized with respect to surface temperature effects during the welding process. In oxy acetylene welding three different zones named as welded zone (WZ), heat affected zone (HAZ) and base metal (BM) are formed having totally varying properties depending on their specific grain structure. Fatigue life and hardness of these different zones are determined in three successive phases of experiments. It is viewed that the grains are shifted from large rough round to elongated oval shaped from WZ to HAZ and relatively small and fine in BM respectively. Depending on grain configuration the fatigue strength increases from WZ to BM due to concentration of grain boundaries, a hindrance in fatigue crack propagation. (author)

  9. A proposal of parameter determination method in the residual strength degradation model for the prediction of fatigue life (I)

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sang Tae [Yeungnam Univ., Gyeongsan (Korea, Republic of); Jang, Seong Soo [Cheju College of Technology, Cheju (Korea, Republic of)

    2001-05-01

    The static and fatigue tests have been carried out to verify the validity of a generalized residual strength degradation model. And a new method of parameter determination in the model is verified experimentally to account for the effect of tension-compression fatigue loading of spheroidal graphite cast iron. It is shown that the correlation between the experimental results and the theoretical prediction on the statistical distribution of fatigue life by using the proposed method is very reasonable. Furthermore, it is found that the correlation between the theoretical prediction and the experimental results of fatigue life in case of tension-tension fatigue data in composite material appears to be reasonable. Therefore, the proposed method is more adjustable in the determination of the parameter than maximum likelihood method and minimization technique.

  10. A proposal of parameter determination method in the residual strength degradation model for the prediction of fatigue life (I)

    International Nuclear Information System (INIS)

    The static and fatigue tests have been carried out to verify the validity of a generalized residual strength degradation model. And a new method of parameter determination in the model is verified experimentally to account for the effect of tension-compression fatigue loading of spheroidal graphite cast iron. It is shown that the correlation between the experimental results and the theoretical prediction on the statistical distribution of fatigue life by using the proposed method is very reasonable. Furthermore, it is found that the correlation between the theoretical prediction and the experimental results of fatigue life in case of tension-tension fatigue data in composite material appears to be reasonable. Therefore, the proposed method is more adjustable in the determination of the parameter than maximum likelihood method and minimization technique

  11. 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 initialelation 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.

  12. ??????????????????????????? Investigation of Fatigue Life of Solder Bumps in a Thermally Enhanced FC-PBGA Assembly

    Directory of Open Access Journals (Sweden)

    ???

    2012-01-01

    Full Text Available ??????????ANSYS??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????,????????????????????????????????????????????Von-Mise?????????Coffin-Manson????????????????????????????????????????????????????,??????????????????????????????In this paper, three-dimensional finite element analysis using the commercial ANSYS software is performed to study solder bump fatigue life for a thermally enhanced FC-PBGA (Flip-Chip Plastic Ball Grid Array assembly subjected to temperature cycling. The thermally enhanced FC-PBGA assembly is a basic FC-PBGA package that is overmolded with molding compound, after which an aluminum heat spreader is adhered to the top of the molding compound and subsequently mounted on a PCB (Printed Circuit Board. In the simulation, all the solder bumps and the solder balls are modeled with nonlinear viscoplastic time and temperature dependent material properties based on Anand’s constitutive equation. Solder bump fatigue life is estimated by the widely accepted modified Coffin-Manson equation. The thermo-mechanical behavior of the solder bumps is presented. Solder bump fatigue life is analyzed by considering various design parameters of the polymer-based materials and the thermal enhancement components.

  13. 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 32.6±9.6 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.

  14. 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 25–65 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 sessions·wk-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.

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

    Science.gov (United States)

    Hatamleh, Omar; Lyons, Jed; Forman, Royce

    2006-01-01

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

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

    DEFF Research Database (Denmark)

    Li, M.; Singh, B.N.

    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 regime (i.e., at low strain amplitudes) than those of materials tested under the same conditions without hold times. The influence of hold times on fatigue life in the low cycle fatigue, short life regime (i.e., at high strain amplitudes) was minimal. When hold time effects were observed, fatigue lives were reduced with hold times as short as two seconds. Appreciable stress relaxation was observed during 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 the CuCrZr alloy.

  17. 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.

  18. 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

    2014-07-01

    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.

  19. Thermomechanical fatigue of 1.4849 cast steel. Experiments and life prediction using a fracture mechanics approach

    Energy Technology Data Exchange (ETDEWEB)

    Seifert, Thomas; Schweizer, Christoph; Schlesinger, Michael; Moeser, Martin [Fraunhofer Inst. for Mechanics of Materials IWM, Freiburg (Germany); Eibl, Martin [BMW Group, Munich (Germany)

    2010-08-15

    In this paper the thermomechanical fatigue properties of 1.4849 cast steel, which is used for exhaust manifolds and turbochargers, are investigated and a fracture mechanics based approach is used for fatigue life prediction. Isothermal low-cycle fatigue tests and thermomechanical fatigue tests are conducted in the temperature range from room temperature up to 1000 C. Fractographic investigations show that fracture occurs predominantly intergranularly at 600 C, whereas mixed transgranular and intergranular crack growth is found otherwise. The methodology for fatigue life prediction is based on a time and temperature dependent cyclic plasticity model, which describes the transient stresses and strains, and on a law for time and temperature dependent microcrack growth. The crack growth law assumes that the increment in crack length in each cycle, da/dN, is correlated with the cyclic crack-tip opening displacement, {delta}CTOD. An analytical fracture mechanics based estimate of {delta}CTOD is used, which is derived for non-isothermal loadings. The fatigue lives of the low-cycle and the thermomechanical fatigue tests are predicted well with the model. Only predictions for the low-cycle fatigue tests at 600 C, where integranular fracture is predominant, are non-conservative. (orig.)

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

    Science.gov (United States)

    Zaretsky, Erwin V.

    1992-01-01

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

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

    Science.gov (United States)

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

    2015-02-01

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

  3. A generalized fitting technique for the LIFE2 fatigue analysis code

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-08-01

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

  4. 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.

  5. Fatigue damage in 20% cold-worked type 316L stainless steel under deuteron irradiation

    International Nuclear Information System (INIS)

    Type 316L stainless steel samples in 20% cold-worked conditions were exposed to fully reversed fatigue cycling in torsion at 400 C during an irradiation with 19 MeV deuterons. Fatigue tests were performed in the high cycle fatigue (HCF) range under continuous cycling and in the low cycle fatigue (LCF) range by imposing a hold-time at the minimum strain value. In comparison with tests under thermal conditions, an increase in the number of cycles to failure Nf by a factor of 6 is observed for the HCF tests and a decrease in Nf, by more than an order of magnitude, for the LCF tests. The data are analyzed using a fatigue damage model: a fatigue damage parameter is defined and the change in this parameter caused by the different irradiation or loading conditions shows directly the effect of changed experimental conditions on the fatigue life. ((orig.))

  6. 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.

  7. Factors affecting the corrosion fatigue life in nickel based superalloys for disc applications

    Directory of Open Access Journals (Sweden)

    Rosier Hollie

    2014-01-01

    Full Text Available The nickel based superalloy 720Li is employed in the gas turbine due to its mechanical performance at elevated temperature. A comprehensive assessment of the materials behaviour under representative service conditions is reported to address the drive for ever increasing temperatures and more arduous environmental exposure. Fatigue experiments have been performed in an air and air/SOx environment at 700??C containing a mixed salt as a contaminant. There is an intimate relationship between local salt level (flux, stress level and stress state, i.e. static or cyclic. The interaction with these variables with the work hardened layer present on the surface of all tested specimens as a result of the shot peening process directly affects the crack initiation process. If specific conditions of environment and stress are achieved, a significant reduction in fatigue life is observed.

  8. 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)

  9. 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.

  10. 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

  11. The Comparative Study of Fatigue Crack Propagation Experiment and Computer Simulation on the Component Materials for the Crane Life Remained

    OpenAIRE

    Hanshik Chung; Seongsoo Kim; Myeongkwan Park; Hyungsub Bae; Sangyeol Kim; Heekyu Choi

    2011-01-01

    This study presents fatigue crack propagation experiments and the simulation used to estimate the life remaining in a crane that is currently in use at a port. The fatigue crack propagation experiments were performed by an Instron 8516 fatigue testing machine and the simulation was performed using the AFGROW software. The simulation results indicated that the critical size of the crack in the upper flange surface of the main jib was 107.4 mm and that it would take 818,000 cycles to reach that...

  12. Fatigue life determination by damage measuring in SAE 8620 specimens steel subjected to multiaxial experiments in neutral and corrosive environment

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Luiz L. da; Filho, Nelson do N.A.; Gomes, Paulo de T.V.; Rabello, Emerson G.; Mansur, Tanius R., E-mail: silvall@cdtn.br, E-mail: nnaf@cdtn.br, E-mail: ptvg@cdtn.br, E-mail: egr@cdtn.br, E-mail: tanius@cdtn.br [Centro de Desenvolvimento da Tencologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)

    2013-07-01

    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)

  13. Assessment of Surface Treatment on Fatigue Life of Cylinder Block for Linear Engine using Frequency Response Approach

    OpenAIRE

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

  14. Comparative Study of Fatigue Damage Models Using Different Number of Classes Combined with the Rainflow Method

    Directory of Open Access Journals (Sweden)

    S. Zengah

    2013-06-01

    Full Text Available Fatigue damage increases with applied load cycles in a cumulative manner. Fatigue damage models play a key role in life prediction of components and structures subjected to random loading. The aim of this paper is the examination of the performance of the “Damaged Stress Model”, proposed and validated, against other fatigue models under random loading before and after reconstruction of the load histories. To achieve this objective, some linear and nonlinear models proposed for fatigue life estimation and a batch of specimens made of 6082T6 aluminum alloy is subjected to random loading. The damage was cumulated by Miner’s rule, Damaged Stress Model (DSM, Henry model and Unified Theory (UT and random cycles were counted with a rain-flow algorithm. Experimental data on high-cycle fatigue by complex loading histories with different mean and amplitude stress values are analyzed for life calculation and model predictions are compared.

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

    Science.gov (United States)

    Sung, In-Kyung

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

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

    Science.gov (United States)

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

    1993-01-01

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

  17. 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.

  18. Fatigue analysis and life prediction of composite highway bridge decks under traffic loading

    Scientific Electronic Library Online (English)

    Fernando N., Leitão; José Guilherme S. da, Silva; Sebastião 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.

  19. Fracture mechanics and residual fatigue life analysis for complex stress fields. Technical report

    International Nuclear Information System (INIS)

    This report reviews the development and application of an influence function method for calculating stress intensity factors and residual fatigue life for two- and three-dimensional structures with complex stress fields and geometries. Through elastic superposition, the method properly accounts for redistribution of stress as the crack grows through the structure. The analytical methods used and the computer programs necessary for computation and application of load independent influence functions are presented. A new exact solution is obtained for the buried elliptical crack, under an arbitrary Mode I stress field, for stress intensity factors at four positions around the crack front. The IF method is then applied to two fracture mechanics problems with complex stress fields and geometries. These problems are of current interest to the electric power generating industry and include (1) the fatigue analysis of a crack in a pipe weld under nominal and residual stresses and (2) fatigue analysis of a reactor pressure vessel nozzle corner crack under a complex bivariate stress field

  20. Experimental research into operating strength and fatigue life of bodywork of buses and trolleybuses

    International Nuclear Information System (INIS)

    Operational strength and fatigue life reliability of trolleybus and bus bodies are usually assessed by computational methods in combination with selected tests. The latter include test runs of vehicles on real routes or on specially designed tracks, tests on complete vehicles under model test conditions and laboratory tests on selected materials, parts and subassemblies. This paper describes a method of experimental investigation of operational strength and reliability developed and applied at the Central Research Institute Skoda for public-transport road vehicles made in Czechoslovakia. (orig.)

  1. 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

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

    International Nuclear Information System (INIS)

    Pressurized tube specimens have been exposed to simultaneous multi-energy surface ion bombardment, fast neutron irradiation and stress and temperature cycling, in a simulation of a possible fusion reactor first wall environment. After ion bombardments equivalent to months-years of reactor operation and up to 30,000 cycles, no detrimental effects on post-irradiation fatigue life were found. The ion damage is found to enhance surface cracking, but this effect is limited to the several micron surface layer in which the ions are implanted

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

    Science.gov (United States)

    Nelson, Richard S.; Schoendorf, John F.

    1986-01-01

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

  4. 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 effet predicting the relative effects of the different peening treatments. Possible reasons for this are explored.

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

    International Nuclear Information System (INIS)

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

  6. Thermal fatigue life prediction. Verification of Coffin-Mansons's law in the phase transformation range of ferrite matrix ductile cast iron

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi Morihito

    2004-07-01

    For clarifying the behavior of thermal fatigue and verifying the role of Coffin-Manson's law in thermal fatigue, out-of-phase type thermal fatigue tests were carried out on ferritic ductile cast iron. As a result of the tests, the dependence of thermal fatigue life and the plastic strain produced in each cycle on cyclic peak temperature and the dependence of thermal fatigue life on cyclic plastic strain were made clear. Particularly, the exponent and the coefficient in the latter relationship, i.e. Coffin-Manson's law, are kept constant over all ranges, including the phase transformation range. And it shows that the thermal fatigue life can be predicted by the tensile the properties of specimens at room temperature. By the way, the microstructure and the fracture surface of failed specimens were observed and the mechanism of thermal fatigue is discussed here. (orig.)

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

    Science.gov (United States)

    Guo, Runhua

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

  8. 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.

  9. 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

  10. 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)

  11. Voltage sag influence on fatigue life of the drivetrain of fixed speed wind turbines

    DEFF Research Database (Denmark)

    Veluri, Badrinath; Santos-Martin, David

    2011-01-01

    Occurrence of voltage sags due to electrical grid faults and other network disturbances generate transients of the generator electromagnetic torque which result in significant high stresses and noticeable vibrations for the wind turbine mechanical system and may also have a detrimental effect on the fatigue life of important drivetrain components. The high penetration of wind energy in the electrical grids demands new requirements for the operation of wind energy conversion systems. Although fixed speed wind turbine technology is nowadays replaced by variable speed wind turbines. In some countries (Spain and Germany) with high wind energy penetration it is mandatory or under bonus to retrofit these fixed speed wind turbines and provide ride through capability. An electro-mechanical model is built to simulate the grid disturbances that easily excite the asynchronous generators poorly damped by the stator flux oscillations which cause high transients of the generator electromagnetic torque. This paper focuses in estimating the resulting significant stresses transients due to the electromagnetic torque transients, which transmits to the wind turbine mechanical system that may have a detrimental effect on the fatigue life of drivetrain components. The capability to simulate these phenomena is a novel aspect in the present effort.

  12. Voltage sag influence on fatigue life of the drivetrain of fixed speed wind turbines

    Directory of Open Access Journals (Sweden)

    Badrinath Veluri

    2011-03-01

    Full Text Available Occurrence of voltage sags due to electrical grid faults and other network disturbances generate transients of the generator electromagnetic torque which result in significant high stresses and noticeable vibrations for the wind turbine mechanical system and may also have a detrimental effect on the fatigue life of important drivetrain components. The high penetration of wind energy in the electrical grids demands new requirements for the operation of wind energy conversion systems. Although fixed speed wind turbine technology is nowadays replaced by variable speed wind turbines. In some countries (Spain and Germany with high wind energy penetration it is mandatory or under bonus to retrofit these fixed speed wind turbines and provide ride through capability. An electro-mechanical model is built to simulate the grid disturbances that easily excite the asynchronous generators poorly damped by the stator flux oscillations which cause high transients of the generator electromagnetic torque. This paper focuses in estimating the resulting significant stresses transients due to the electromagnetic torque transients, which transmits to the wind turbine mechanical system that may have a detrimental effect on the fatigue life of drivetrain components. The capability to simulate these phenomena is a novel aspect in the present effort.

  13. 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.

  14. 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.

  15. 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.

  16. Effect of substrate surface roughening and cold spray coating on the fatigue life of AA2024 specimens

    International Nuclear Information System (INIS)

    Highlights: • Investigated effect of CP-Al coatings cold sprayed onto roughened Al2024 substrate. • CP-Al coating improved rotating-bend fatigue strength up to 50% on average. • CP-Al coating diminished stress raisers caused by the surface roughening. • Glass-bead blasting plus coating offered most significant fatigue life improvement. - Abstract: The effects of cold spray coating and substrate surface preparation on crack initiation under cyclic loading have been studied on Al2024 alloy specimens. Commercially pure (CP) aluminum feedstock powder has been deposited on Al2024-T351 samples using a cold-spray coating technique known as high velocity particle consolidation. Substrate specimens were prepared by surface grit blasting or shot peening prior to coating. The fatigue behavior of both coated and uncoated specimens was then tested under rotating bend conditions at two stress levels, 180 MPa and 210 MPa. Scanning electron microscopy was used to analyze failure surfaces and identify failure mechanisms. The results indicate that the fatigue strength was significantly improved on average, up to 50% at 180 MPa and up to 38% at 210 MPa, by the deposition of the cold-sprayed CP-Al coatings. Coated specimens first prepared by glass bead grit blasting experienced the largest average increase in fatigue life over bare specimens. The results display a strong dependency of the fatigue strength on the surface preparation and cold spray parameters

  17. 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 studyest results in this study

  18. An effective continuum damage mechanics model for creep-fatigue life assessment of a steam turbine rotor

    International Nuclear Information System (INIS)

    A nonlinear Continuum Damage Mechanics model is proposed to assess the creep-fatigue life of a steam turbine rotor, in which the effects of complex multiaxial stress and the coupling of fatigue and creep are taken into account. The nonlinear evolution of damage is also considered. The model is applied to a 600 MW steam turbine under a practical start-stop operation. The results are compared with those from the linear accumulation theory that is dominant in life assessment of steam turbine rotors at present. The comparison show that the nonlinear continuum damage mechanics model describes the accumulation and development of damage better than the linear accumulation theory

  19. 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.)

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

    Science.gov (United States)

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

    1983-01-01

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

  1. The mediating effect of coping on the association between fatigue and quality of life in patients with multiple sclerosis.

    Science.gov (United States)

    Mikula, Pavol; Nagyova, Iveta; Krokavcova, Martina; Vitkova, Marianna; Rosenberger, Jaroslav; Szilasiova, Jarmila; Gdovinova, Zuzana; Groothoff, Johan W; van Dijk, Jitse P

    2015-09-01

    Fatigue, as one of the most frequent symptoms in patients with multiple sclerosis (MS), has various adverse effects on the physical and mental health-related quality of life (PCS, MCS) of patients. The aim of this study was to explore whether coping mediates the relationship between fatigue and PCS and MCS. We collected data from 154 consecutive MS patients (76.0% women; mean age 40.0 ± 9.9). Patients completed the Short-Form Health Survey (SF-36), the multidimensional fatigue inventory (MFI-20) and the coping self-efficacy scale. The mediating effect of coping was analysed using linear regressions and the Sobel z-test. In PCS significant mediation was found in some of the fatigue dimensions (general, physical and reduced Motivation), while in MCS, it was significant in all dimensions. These results can be implemented into educational programmes for patients, their caregivers or physicians, and can also be helpful in the treatment process. PMID:25879302

  2. Fatigue Life Prediction of Carbon Fiber-Reinforced Ceramic-Matrix Composites at Room and Elevated Temperatures. Part I: Experimental Analysis

    Science.gov (United States)

    Longbiao, Li

    2015-05-01

    This paper presents an experimental analysis on the fatigue behavior in C/SiC ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply and 2.5D woven, at room and elevated temperatures in air atmosphere. The experimental fatigue life S - N curves of C/SiC composites corresponding to different stress levels and test conditions have been obtained. The damage evolution processes under fatigue loading have been analyzed using fatigue hysteresis modulus and fatigue hysteresis loss energy. By comparing the experimental fatigue hysteresis loss energy with theoretical computational values, the interface shear stress corresponding to different peak stress, fiber preforms and test conditions have been estimated. It was found that the degradation of interface shear stress and fibres strength caused by oxidation markedly decreases the fatigue life of C/SiC composites at elevated temperature.

  3. Thermal fatigue loading for a type 304-L stainless steel used for pressure water reactor: investigations on the effect of a nearly perfect biaxial loading, and on the cumulative fatigue life

    International Nuclear Information System (INIS)

    Fatigue-life curves are used in order to estimate crack-initiation, and also to prevent water leakage on Pressure Water Reactor pipes. Such curves are built exclusively from push-pull tests performed under constant and uniaxial strain or stress-amplitude. However, thermal fatigue corresponds to a nearly perfect biaxial stress state and severe loading fluctuations are observed in operating conditions. In this frame, these two aspects have been successively investigated in this paper: In order to investigate on potential difference between thermal fatigue and mechanical fatigue, tests have been carried out at CEA using thermal fatigue devices. They show that for an identical level of strain-amplitude, the number of cycles required to achieve crack-initiation is significantly lower under thermal fatigue. This enhanced damage results probably from a perfect biaxial state under thermal fatigue. In this frame, application of the multiaxial Zamrik's criterion seems to be very promising. In order to investigate on cumulative damage effect in fatigue, multi-level strain controlled fatigue tests have been performed. Experimental results show that linear Miner's rule is not verified. A loading sequence effect is clearly evidenced. The double linear damage rule ('DLDR') improves significantly predictions of fatigue-life. (authors)

  4. 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.

  5. 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.

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

    International Nuclear Information System (INIS)

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

  7. 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.

  8. Pre-crack fatigue life assessment of relevant aircraft materials using fractal analysis of eddy current test data

    Science.gov (United States)

    Schreiber, Jürgen; Cikalova, Ulana; Hillmann, Susanne; Meyendorf, Norbert; Hoffmann, Jochen

    2013-01-01

    Successful determination of residual fatigue life requires a comprehensive understanding of the fatigue related material deformation mechanism. Neither macroscopic continuum mechanics nor micromechanic observations provide sufficient data to explain subsequent deformation structures occurring during the fatigue life of a metallic structure. Instead mesomechanic deformation on different scaling levels can be studied by applying fractal analysis of various means of nondestructive inspection measurements. The resulting fractal dimension data can be correlated to the actual material damage states, providing an estimation of the remaining residual fatigue life before macroscopic fracture develops. Recent efforts were aimed to apply the fractal concept to aerospace relevant materials AA7075-T6 and Ti-6Al-4V. Proven and newly developed fractal analysis methods were applied to eddy current (EC) measurements of fatigued specimens, with the potential to transition this approach to an aircraft for an in-situ nondestructive inspection. The occurrence of mesomechanic deformation at the material surface of both AA7075-T6 and Ti-6Al-4V specimens could be established via topography images using confocal microscopy (CM). Furthermore, a pulsed eddy current (PEC) approach was developed, combined with a sophisticated new fractal analysis algorithm based on short pulse excitation and evaluation of EC relaxation behavior. This paper presents concept, experimental realization, fractal analysis procedures, and results of this effort.

  9. A Study on Fatigue Fracture Mechanism of Cr-Mo Steel SCM435 in Super Long Life Range

    Science.gov (United States)

    Murakami, Ri Ichi; Yonekura, Daisuke; Murayama, Taishi

    For high strength steels, a characteristic fatigue behavior, which S-N curve comes down again in the long life region of N > 107 cycles, was reported by many researchers. Specifically, for high strength steel, the fatigue limit is temporal value because of the fish-eye fracture in the long life region over about N = 107 cycles. However, fish eye fracture does not appear for medium strength steel in super long life range. In this paper, cantilever-type rotational bending fatigue tests were carried out for quenched and tempered Cr-Mo steel (JIS: SCM435) up to 109 cycles at room temperature in air. The S-N curve showed a horizontal part in long life region over 107 cycles. In addition, fish- eye fracture was not observed and for all specimens, the crack initiation occurred from the specimen surface. The fatigue fracture behavior of SCM435 in super long life was discussed based on optical microscopy observation and scanning electron microscopy observation.

  10. Influence of grain orientation on evolution of surface features in fatigued polycrystalline copper: a comparison of thermal and uniaxial mechanical fatigue results

    CERN Document Server

    Aicheler, M

    2010-01-01

    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 2x10(11). 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 fatigu...

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

    Science.gov (United States)

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

    2015-01-01

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

  12. The Effects of Shot and Laser Peening on Fatigue Life and Crack Growth in 2024 Aluminum Alloy and 4340 Steel

    Science.gov (United States)

    Everett, R. A., Jr.; Matthews, W. T.; Prabhakaran, R.; Newman, J. C., Jr.; Dubberly, M. J.

    2001-01-01

    Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life.

  13. Standard practice for statistical analysis of linear or linearized stress-life (S-N) and strain-life (?-N) fatigue data

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2010-01-01

    1.1 This practice covers only S-N and ?-N relationships that may be reasonably approximated by a straight line (on appropriate coordinates) for a specific interval of stress or strain. It presents elementary procedures that presently reflect good practice in modeling and analysis. However, because the actual S-N or ?-N relationship is approximated by a straight line only within a specific interval of stress or strain, and because the actual fatigue life distribution is unknown, it is not recommended that (a) the S-N or ?-N curve be extrapolated outside the interval of testing, or (b) the fatigue life at a specific stress or strain amplitude be estimated below approximately the fifth percentile (P ? 0.05). As alternative fatigue models and statistical analyses are continually being developed, later revisions of this practice may subsequently present analyses that permit more complete interpretation of S-N and ?-N data.

  14. Stress analysis and life prediction of gas turbine blade

    Science.gov (United States)

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

    1988-01-01

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

  15. Effect of twinning, slip, and inclusions on the fatigue anisotropy of extrusion-textured AZ61 magnesium alloy

    Energy Technology Data Exchange (ETDEWEB)

    Jordon, J.B., E-mail: bjordon@eng.ua.edu [Department of Mechanical Engineering, University of Alabama, Tuscaloosa, AL 35487 (United States); Gibson, J.B. [Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Mississippi State, MS 39762 (United States); Horstemeyer, M.F.; Kadiri, H. El [Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Mississippi State, MS 39762 (United States); Department of Mechanical Engineering, Mississippi State University, Mississippi State, MS 39762 (United States); Baird, J.C. [Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Mississippi State, MS 39762 (United States); Luo, A.A. [General Motors Research and Development Center, Warren, MI 48090 (United States)

    2011-08-25

    Highlights: {yields} Twinning and detwinning was observed in the hysteresis loops of the AZ61 mg alloy. {yields} Fatigue cracks incubated from fractured intermetallic particles in the AZ61 mg alloy. {yields} Inclusions were more important in determining fatigue life than microstructure. {yields} The model predicted the different fatigue lives in the two orientations tested. - Abstract: In this study, experiments were conducted to quantify structure-property relations with respect to fatigue of an extruded AZ61 magnesium alloy using a MultiStage Fatigue (MSF) model. Experiments were conducted in the extruded and transverse directions under low and high cycle strain control fatigue conditions. The cyclic behavior of this alloy displayed varying degrees of twinning and slip depending on the strain amplitude as observed in the hysteresis loops of both directions. Under low cyclic conditions, asymmetrical stress strain response was observed for both orientations. However, systematic stabilization of the hysteresis occurred by half-life due to subsequent twinning and detwinning mechanisms. In addition, under high cycle fatigue, pseudo-elasticity was observed at the first and at half-life cycles. Structure-property relations were quantified by examining the fracture surfaces of the fatigued specimens using a scanning electron microscope. In terms of crack incubation, fatigue cracks were found to initiate from intermetallic particles (inclusions) that were typically larger than the mean size. Quantified sources of fatigue crack incubation, microstructurally small cracks, and cyclic stress-strain behavior were correlated to the MSF model. Based on the specific material parameters, the MSF model was able to predict the difference in the strain-life results of the AZ61 magnesium alloy in the extruded and extruded transverse directions including the scatter of the experimental results. Finally, the MSF model revealed that the inclusion size was more important in determining the fatigue life than the anisotropic effects from the texture, yield, and work hardening.

  16. 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.

  17. Stochastic Analysis of the Influence of Tower Shadow on Fatigue Life of Wind Turbine Blade

    DEFF Research Database (Denmark)

    Pedersen, Ronnie; Nielsen, SØren 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.

  18. Laser shock processing: an emerging technique for the improvement of fatigue life and surface properties of high reliability metallic components

    OpenAIRE

    Ocaña Moreno, Jose Luis; Porro González, Juan Antonio; Morales Furió, Miguel; Iordachescu, Danut; Diaz Muñoz, Marcos; Ruiz de Lara de Luis, Leonardo; Correa Guinea, Carlos

    2012-01-01

    •Introduction •Process Experimental Setup •Experimental Procedure •Experimental Results for Al2024 - T351, Ti6Al4V and AISI 316L - Surface Roughness and Compactation - Residual stresses - Tensile Strength - Fatigue Life •Discussion and Outlook - Prospects for technological applications of LSP

  19. Fatigue evaluation of socket welded piping in nuclear power plant

    International Nuclear Information System (INIS)

    Fatigue failures in piping systems occur, almost without exception, at the welded connections. In nuclear power plant systems, such failures occur predominantly at the socket welds of small diameter piping ad fillet attachment welds under high-cycle vibratory conditions. Nearly all socket weld fatigue failures are identified by leaks which, though not high in volume, generally are costly due to attendant radiological contamination. Such fatigue cracking was recently identified in the 3/4 in. diameter recirculation and relief piping socket welds from the reactor coolant system (RCS) charging pumps at a nuclear power plant. Consequently, a fatigue evaluation was performed to determine the cause of cracking and provide an acceptable repair. Socket weld fatigue life was evaluated using S-N type fatigue life curves for welded structures developed by AASHTO and the assessment of an effective cyclic stress range adjacent to each socket weld. Based on the calculated effective tress ranges and assignment of the socket weld details to the appropriate AASHTO S-N curves, the socket weld fatigue lives were calculated and found to be in excellent agreement with the accumulated cyclic life to-date

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

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

    International Nuclear Information System (INIS)

    The objective of the present study is to understand the fatigue crack growth behavior in austenitic stainless steel pipes and pipe welds by carrying out analysis/predictions and experiments. The Paris law has been used for the prediction of fatigue crack growth life. To carry out the analysis, Paris constants have been determined for pipe (base) and pipe weld materials by using Compact Tension (CT) specimens machined from the actual pipe/pipe weld. Analyses have been carried out to predict the fatigue crack growth life of the austenitic stainless steel pipes/pipes welds having part through cracks on the outer surface. In the analyses, Stress Intensity Factors (K) have been evaluated through two different schemes. The first scheme considers the 'K' evaluations at two points of the crack front i.e. maximum crack depth and crack tip at the outer surface. The second scheme accounts for the area averaged root mean square stress intensity factor (KRMS) at deepest and surface points. Crack growth and the crack shape with loading cycles have been evaluated. In order to validate the analytical procedure/results, experiments have been carried out on full scale pipe and pipe welds with part through circumferential crack. Fatigue crack growth life evaluated using both schemes have been compared with experimental results. Use of stress intensity factor (KRMS) evaluated using second scheme gives better fatigue crack growth life prediction compared to that of fowth life prediction compared to that of first scheme. Fatigue crack growth in pipe weld (Gas Tungsten Arc Welding) can be predicted well using Paris constants of base material but prediction is non-conservative for pipe weld (Shielded Metal Arc Welding). Further, predictions using fatigue crack growth rate curve of ASME produces conservative results for pipe and GTAW pipe welds and comparable results for SMAW pipe welds. - Highlights: ? Predicting fatigue crack growth of Austenitic Stainless Steel pipes and pipe welds. ? Use of RMS-SIF and local SIF at maximum depth and tip end in Paris law. ? Prediction using RMS-SIF compare well with test results.

  2. Experimental observations on uniaxial whole-life transformation ratchetting and low-cycle stress fatigue of super-elastic NiTi shape memory alloy micro-tubes

    Science.gov (United States)

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2015-07-01

    In this work, the low-cycle fatigue failure of super-elastic NiTi shape memory alloy micro-tubes with a wall thickness of 150 ?m is investigated by uniaxial stress-controlled cyclic tests at human body temperature 310 K. The effects of mean stress, peak stress, and stress amplitude on the uniaxial whole-life transformation ratchetting and fatigue failure of the NiTi alloy are observed. It is concluded that the fatigue life depends significantly on the stress levels, and the extent of martensite transformation and its reverse play an important role in determining the fatigue life. High peak stress or complete martensite transformation shortens the fatigue life.

  3. Prediction of residual life of low-cycle fatigue in austenitic stainless steel based on indentation test

    International Nuclear Information System (INIS)

    In this study, a method to predict residual life of low-cycle fatigue in austenitic stainless steel (SUS316NG) was proposed based on indentation test. Low-cycle fatigue tests for SUS316NG were first conducted based on uniaxial tensile-compressive loading under the control of true strain range. Applied strain ranges were varied from about 3 to 12%. Their hysteresis loops of stress and strain were monitored during the fatigue tests. Plastic deformation range in hysteresis loop at each cycle could be roughly expressed by bi-linear hardening rule, whose plastic properties involve yield stress and work-hardening coefficient. The cyclic plastic properties were found to be dependent on the number of cycles and applied strain range, due to work-hardening. We experimentally investigated the empirical relationship between the plastic properties and number of cycles for each applied strain range. It is found that the relationship quantitatively predicts the applied strain range and number of cycles, when the plastic properties, or yield stress and work-hardening coefficient were known. Indentation tests were applied to the samples subjected to low cycle fatigue test, in order to quantitatively determine the plastic properties. The estimated properties were assigned to the proposed relationship, yielding the applied strain range and the cycle numbers. The proposed method was applied to the several stainless steel samples subjected to low cycle fatigue tests, suggesting that theircycle fatigue tests, suggesting that their residual lives could be reasonably predicted. Our method is thus useful for predicting the residual life of low-cycle fatigue in austenitic stainless steel. (author)

  4. Reliability approach to rotating-component design. [fatigue life and stress concentration

    Science.gov (United States)

    Kececioglu, D. B.; Lalli, V. R.

    1975-01-01

    A probabilistic methodology for designing rotating mechanical components using reliability to relate stress to strength is explained. The experimental test machines and data obtained for steel to verify this methodology are described. A sample mechanical rotating component design problem is solved by comparing a deterministic design method with the new design-by reliability approach. The new method shows that a smaller size and weight can be obtained for specified rotating shaft life and reliability, and uses the statistical distortion-energy theory with statistical fatigue diagrams for optimum shaft design. Statistical methods are presented for (1) determining strength distributions for steel experimentally, (2) determining a failure theory for stress variations in a rotating shaft subjected to reversed bending and steady torque, and (3) relating strength to stress by reliability.

  5. Fatigue life analysis on multi-stacked film under thermal and residual stresses

    International Nuclear Information System (INIS)

    Reliability problem in inkjet printhead, one of MEMS devices, is also very important. To eject an ink drop, the temperature of heater must be high so that ink contacting with surface reaches above 280 .deg. C on the instant. Its heater is embedded in the thin multi-layer in which several materials are deposited. MEMS processes are the main sources of residual stresses development. Residual stress is one of the factors reducing the reliability of MEMS devices. We measured residual stresses of single layers that consist of multilayer. FE analysis is performed using Design Of experiment(DOE). Transient analysis for heat transfer is performed to get a temperature distribution. And then static analysis is performed with the temperature distribution obtained by heat transfer analysis and the measured residual stresses to get a stress distribution in the structure. Although the residual stress is bigger than thermal stress, thermal stress is more influential on fatigue life

  6. Standard test method for ambient temperature fatigue life of metallic bonded resistance strain gages

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2003-01-01

    1.1 This test method covers a uniform procedure for the determination of strain gage fatigue life at ambient temperature. A suggested testing equipment design is included. 1.2 This test method does not apply to force transducers or extensometers that use bonded resistance strain gages as sensing elements. 1.3 Strain gages are part of a complex system that includes structure, adhesive, gage, leadwires, instrumentation, and (often) environmental protection. As a result, many things affect the performance of strain gages, including user technique. A further complication is that strain gages, once installed, normally cannot be reinstalled in another location. Therefore, it is not possible to calibrate individual strain gages; performance characteristics are normally presented on a statistical basis. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices ...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-10-01

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

  8. Effect of laser shock peening on residual stress and fatigue life of clad 2024 aluminium sheet containing scribe defects

    Energy Technology Data Exchange (ETDEWEB)

    Dorman, M. [Department of Aerospace Engineering, Cranfield University, Cranfield, Beds, MK43 0AL (United Kingdom); Toparli, M.B. [Materials Engineering, The Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom); Smyth, N.; Cini, A. [Department of Materials, Cranfield University, Cranfield, Beds, MK43 0AL (United Kingdom); Fitzpatrick, M.E. [Materials Engineering, The Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom); Irving, P.E., E-mail: p.e.irving@cranfield.ac.uk [Department of Materials, Cranfield University, Cranfield, Beds, MK43 0AL (United Kingdom)

    2012-06-30

    Highlights: Black-Right-Pointing-Pointer Effect of laser peen intensity on local residual stress fields in 2024 aluminium. Black-Right-Pointing-Pointer Peening induces significant changes in surface topography and local hardness. Black-Right-Pointing-Pointer Residual stress at peen spot centre in tension, spot overlap in compression. Black-Right-Pointing-Pointer Notched fatigue lives increased; crack morphology correlated to residual stress field. Black-Right-Pointing-Pointer 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 {mu}m deep scribes, and slight improvement for samples with 150 {mu}m scribes. Use of the residual stress intensity K{sub resid} 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.

  9. Self-regulatory Fatigue in Hematologic Malignancies: Impact on Quality of Life, Coping, and Adherence to Medical Recommendations

    Science.gov (United States)

    Ehlers, Shawna L.; Patten, Christi A.; Gastineau, Dennis A.

    2015-01-01

    Background Hematopoietic stem cell transplantation (HSCT) is an intensive cancer therapy entailing numerous physical, emotional, cognitive, and practical challenges. Patients' ability to adjust and cope with such challenges may depend on their ability to exert control over cognitive, emotional, and behavioral processes, that is, ability to self-regulate. Self-regulatory capacity is a limited resource that can be depleted or fatigued (i.e., “self-regulatory fatigue”), particularly in the context of stressful life events such as cancer diagnosis and treatment. Purpose This is one of the first studies to examine self-regulatory fatigue in a cancer population. The current study aimed to (1) extract items for a specific scale of self-regulatory capacity and (2) examine the impact of such capacity on adaptation in patients with hematologic malignancies preparing for HSCT. Methods Factor analysis of four existing scales gauging psychological adjustment and well-being in 314 patients preparing for HSCT (63% male and 89% Caucasian) identified 23 items (?=0.85) related to self-regulatory control or fatigue. This measure was then examined using existing clinical data obtained from 178 patients (57% male and 91% Caucasian) undergoing treatment for hematologic malignancies in relationship to quality of life, coping, and self-reported adherence to physicians' recommendations. Results Controlling for pain severity, physical fatigue, and depression, self-regulatory fatigue scores were incrementally associated with decreased quality of life, use of avoidance coping strategies, and decreased adherence to physicians' recommendations. Conclusion These results emphasize the potential role of self-regulatory capacity in coping with and adjusting to hematologic cancers and future research is warranted. PMID:21928059

  10. Experimental Study of Crack Growth Behavior and Fatigue Life of Spot Weld Tensile-Shear Specimens

    OpenAIRE

    M. Shariati; M.J. Maghrebi

    2009-01-01

    In this study, the experimental behaviors of the fatigue crack growth are studied and the fatigue lives of tensile-shear (TS) specimens are determined. To achieve this, many TS specimens are prepared by the welding mild steel sheets of 1 and 1.5 mm thickness and then tested under constant amplitude loading using a servo-hydraulic fatigue testing machine (INSTRON 8802). The fatigue crack growth and the crack length are measured simultaneously by an optical microscope with 100X magnificat...

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

    Science.gov (United States)

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

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

  12. A study on creep-fatigue life analysis using a unified constitutive equation and a continuous damage law

    International Nuclear Information System (INIS)

    A newly developed type of life analysis is introduced using a unified constitutive equation and a continuous damage law on 2 1/4Cr - 1Mo steel at 600 deg C. the viscoplasticity theory based on total strain and overstress used for the rate effect at room temperature is extended for application to the inelastic analysis at elevated temperature, and the extended uniaxial model is shown to reproduce the inelastic stress and strain behavior with a strain rate change observed in the experiment. The incremental life prediction law is employed and its coupling with the viscoplasticity model produces both an inelastic stress-strain response and the damage accumulation, simultaneously and continuously. The life prediction for creep, fatigue and creep-fatigue loading shows good correspondence with the experimental data. (author)

  13. Multi-scale analysis of behavior and fatigue life of 304L stainless under cyclic loading with pre-hardening

    International Nuclear Information System (INIS)

    This study investigates the effects of loading history on the cyclic stress-strain curve and fatigue behavior of 304L stainless steel at room temperature. Tension-compression tests were performed on the same specimen under controlled strain, using several loading sequences of increasing or decreasing amplitude. The results showed that fatigue life is significantly reduced by the previous loading history. A previously developed method for determining the effect of prehardening was evaluated. Microstructural analyses were also performed; the microstructures after pre-loading and their evolution during the fatigue cycles were characterized by TEM. The results of these analyses improve our understanding of the macroscopic properties of 304L stainless steel and can help us identify the causes of failure and lifetime reduction. (author)

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

    International Nuclear Information System (INIS)

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

  15. Influence of long-term strain hold on creep-fatigue life of Mod.9Cr-1Mo steel

    International Nuclear Information System (INIS)

    Modified 9Cr-1Mo steel is the principal candidate material of a steam generator in a fast breeder reactor because of its superior high-temperature property. In this study, the influence of long-term strain hold on the failure life of Mod.9Cr-1Mo steel was investigated and the applicability of existing creep-fatigue life evaluation methods was discussed based on the experimental results. Creep-fatigue tests with hold time up to 10 hours per cycle at either tension or compression maximum strain were conducted under strain control of 0.5% and 1.0% at 550degC. Although failure life reduction occurred by introducing short hold period in the compression hold tests, the degree of reduction became smaller with increasing hold period. On the other hand, the failure life reduction became larger with increasing hold period in the tension hold tests. It was found that the failure life reduction in the compression hold tests was mainly due to the accumulation of tensile strain at the center of a specimen and that in the tension hold tests it was caused by intergranular damage in terms of creep cavity nucleation and growth from observation of the failure specimens. The time fraction rule adopted in a design code gave longer life compared to the experimental life, especially at low strain level. The failure life was well predicted by the ductility exhaustion method and the nonlinear damage accumulation model. (author)

  16. A STUDY OF FATIGUE LIFE OF ASPHALT CONCRETE BASED ON SHUNGITE MINERAL POWDER

    Directory of Open Access Journals (Sweden)

    D. I. Chernousov

    2011-11-01

    Full Text Available Problem statement. Shortage of mineral powder stimulates seeking of new materials and technologiesby which traditional ones can be replaced without deterioration of their operating properties. Thatis why a study of mineral powder from shungite and development of new technologies of arrangementof high quality and durable asphalt concrete pavement based on shungite is an actual problem.Results. Bearing capacity and service life of asphalt concrete pavement is most completely characterizedby modulus of elasticity and tensile bending strength. To forecast operating properties ofasphalt concrete, 4×4×16 cm beams were tested on vibrostand ?? 70/100, which enables one toobtain frequency and amplitude of oscillations continuously adjustable during operation. The techniqueuses analytical relationships which allow one to determine durability of operating period undersimulation of axis load of 6 and 10 tons. Comparison of the relationships obtained shows thatmodulus of elasticity, bending and comparison strength of involved asphalt concrete mixes markedlydecrease. However, this decrease is more pronounced with reference asphalt concretes.Conclusions. The use of shungite mineral powder provides for increasing fatigue life of asphaltconcrete, which can be related to higher adhesion activity of shungite powder compared with limestonepowder.

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

    International Nuclear Information System (INIS)

    This study proposes a structural design for developing a medium scale composite wind turbine blade made of E-glass/epoxy for a 750 kW class horizontal axis wind turbine system. The design loads were determined from various load cases specified at the IEC61400-1 international specification and GL regulations for the wind energy conversion system. A specific composite structure configuration, which can effectively endure various loads such as aerodynamic loads and loads due to accumulation of ice, hygro-thermal and mechanical loads, was proposed. To evaluate the proposed composite wind turbine blade, structural analysis was performed by using the finite element method. Parametric studies were carried out to determine an acceptable blade structural design, and the most dominant design parameters were confirmed. In this study, the proposed blade structure was confirmed to be safe and stable under various load conditions, including the extreme load conditions. Moreover, the blade adapted a new blade root joint with insert bolts, and its safety was verified at design loads including fatigue loads. The fatigue life of a blade that has to endure for more than 20 years was estimated by using the well-known S-N linear damage theory, the service load spectrum, and the Spera's empirical equations. With the results obtained from all the structural design and analysis, prototype composite blades were manufactured. A specific construction process including the lay-up molding method ocess including the lay-up molding method was applied to manufacturing blades. Full-scale static structural test was performed with the simulated aerodynamic loads. From the experimental results, it was found that the designed blade had structural integrity. In addition, the measured results of deflections, strains, mass, and radial center of gravity agreed well with the analytical results. The prototype blade was successfully certified by an international certification institute, GL (Germanisher Lloyd) in Germany

  18. Improvement of Fatigue Life of Welded Structural Components of a Large Two-Stroke Diesel Engine by Grinding

    DEFF Research Database (Denmark)

    Agerskov, Henning; Hansen, Anders V.

    2004-01-01

    The crankshaft housings of large two-stroke diesel engines are welded structures subjected to constant amplitude loading and designed for infinite life at full design load. A new design of the so-called frame box has been introduced in the engine using butt weld joints of thick plates, welded from one side only, with no access to the root side. Various investigations on the fatigue life of the structural components of this new design have been carried out. The present investigation concentrates on the improvement in fatigue life which may be obtained by grinding of the weld toes. The tests performed showed a significant increase in fatigue life due to the grinding, ranging from a factor of approx. 2.8 to infinity, depending on the load level. Although the number of tests was limited, the results indicate a favourable change of slope of the S-N curve, from m=3 for the test series without grinding to m=6 for the test series with grinding. In one of the test series, it was observed that in most cases crack initiation moved from the weld toe to the non-ground surface between the ground areas at the weld toes. Tests were made on steel S 275, on centrally and eccentrically loaded test specimens.

  19. Effect of surface integrity of hard turned AISI 52100 steel on fatigue performance

    International Nuclear Information System (INIS)

    This paper addresses the relationship between surface integrity and fatigue life of hard turned AISI 52100 steel (60-62 HRC), with grinding as a benchmark. The impact of superfinishing on the fatigue performance of hard turned and ground surfaces is also discussed. Specifically, the surface integrity and fatigue life of the following five distinct surface conditions are examined: hard turned with continuous white layer, hard turned with no white layer, ground, and superfinished hard turned and ground specimens. Surface integrity of the specimens is characterized via surface topography measurement, metallography, residual stress measurements, transmission electron microscopy (TEM), and nano-indentation tests. High cycle tension-tension fatigue tests show that the presence of white layer does not adversely affect fatigue life and that, on average, the hard turned surface performs as well or better than the ground surface. The effect of superfinishing is to exaggerate these differences in performance. The results obtained from this study suggest that the effect of residual stress on fatigue life is more significant than the effect of white layer. For the hard turned surfaces, the fatigue life is found to be directly proportional to both the surface compressive residual stress and the maximum compressive residual stress. Possible explanations for the observed effects are discussed

  20. Fatigue characterization of flowformed A356-T6

    Directory of Open Access Journals (Sweden)

    Roy Matthew J.

    2014-06-01

    Full Text Available Flowforming is an incremental rotary forming technology consisting of deforming a cylindrical workpiece through contact between a roller and a rotating mandrel. This process delivers significant local compressive plastic strain to the workpiece. The effects on fatigue resilience of a common aluminum foundry alloy (A356 processed in this manner at an elevated temperature has been shown to improve post heat treatment. Fatigue properties of material processed with a standard heat treatment following casting is compared to material which has been cast and flowformed to varying degrees and then heat treated. Flowformed material with varying degrees of rotary deformation have been tested. Endurance limits have been found to be generally governed by porosity and maximum principal stress for high cycle fatigue on undeformed material. Fatigue properties have been quantified employing stress-life relationships derived from uniaxial fatigue tests. A 30% increase in the high-cycle endurance limits of flowformed compared to non-deformed material has been observed and is linked to the extent of deformation. Fractographic examination shows that this increase in endurance limit can be attributed primarily to the mitigation of porosity. Microstructural changes due to processing appear to be a secondary factor.

  1. Use of Neuber's rule to estimate the fatigue life of notched specimens of ASME SA 106-B steel piping in 2880C air

    International Nuclear Information System (INIS)

    Fatigue strain-life tests were conducted on notched specimens of ADMESA 106-B piping steel at PWR operating temperatures (2880C (5500F)), under completely reversed loading. Fatigue limits at 107 cycles were estimated for smooth specimens to be 185 M Pa (26.8 ksi) at 240C and 232 MPa (33.7 ksi) at 2880C. The higher fatigue strength observed at the PWR temperature is postulated to be caused by dynamic strain aging processes. However, a reduction in fatigue strength in the low cycle fatigue regime was observed in 2880C air environment tests, which may indicate that the current ASME Section III design curve for carbon steels is nonconservative in its positioning. Notch strain histories were estimated for the notched specimen tests using various interpretations of Neuber's rule. It was concluded that the use of the fatigue notch concentration factor (Kf) in the Neuber relation in conjunction with the uniaxial cyclic stress-strain curve provided the best correlation of notched specimen fatigue data with results obtained from smooth specimen tests. The notched specimen strain-life results derived from the application of Neuber's rule alone proved to be conservative when compared with smooth specimen test results to such an extent that Neuber-generated notch stresses and strain amplitudes cannot accurately be compared with the mean data curves derived from the ASME Section III fatigue curves for carbe ASME Section III fatigue curves for carbon steels which are based on net section stress measurements. (author)

  2. Service life prediction. Development of models for predicting the service life of power plant components subject to thermomechanical creep fatigue; Lebensdauervorhersage. Entwicklung von Modellen zur Lebensdauervorhersage von Kraftwerksbauteilen unter thermisch-mechanischer Kriechermuedungsbeanspruchung. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Cui, L.; Scholz, A. [Technische Univ. Darmstadt (Germany). Institut fuer Werkstoffkunde; Hartrott, P. von; Schlesinger, M. [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany)

    2009-07-01

    Extensive use is made of massive components of heat resistant and highly heat resistant materials in installations of the power and heating industry. These components are exposed to varying thermomechanical stress as a result of ramping-up and down processes. In this research project two computer-assisted methods of predicting service life until crack initiation were extended to include cases of thermomechanical multi-axis stress conducive to creep fatigue and of superposition of high-cycle stress on power plant components. Investigations were limited to rotor steel of type X12CrMoWVNbN10-1-1. Complex thermomechanical multi-axis experiments were performed on round, notched and cruciform test specimens of close-to-life dimensions in order to demonstrate by experiment the validity of these models. The results of these calculations showed an acceptable degree of agreement between experiment and simulation for both models. Calculations on earlier TMF experiments performed at IfW on hollow specimens of 1%CrMoNiV showed good predictability for both the SARA and the ThoMat programme. Calculations on experiments performed at MPA Stuttgart on model bodies consisting of the same 1%CrMoNiV showed a predictability of acceptable variability considering the complexity of the stresses involved. A further outcome of this project is that the use of SARA appears universally suitable for the construction of new plants and in the service area, while the use of ThoMat appears suited for detail optimisation in the development process.

  3. Life prediction and mechanisms for the initiation and growth of short cracks under fretting fatigue loading

    OpenAIRE

    Cadario, Alessandro

    2006-01-01

    Fretting fatigue is a damage process that may arise in engineering applications where small cyclic relative displacements develop inside contacts leading to detrimental effects on the material fatigue properties. Fretting is located in regions not easily accessible, which makes it a dangerous phenomenon. It is therefore important to be able to make reliable predictions of the fretting fatigue lives. The work presented in this thesis has its focus on different aspects related to fretting fatig...

  4. Life-time reliability based assessment of structures submitted to thermal fatigue

    OpenAIRE

    Guede, Zakoua; Suldret, B; Lemaire, M.

    2007-01-01

    A probabilistic approach of the current thermal fatigue design of nuclear components is set up. It aims at incorporating all kinds of uncertainties that affect the thermal fatigue behaviour. This approach is based on the theory of structural reliability. Two dual approaches of reliability analysis for the thermal fatigue are defined, respectively, in the time domain and in the frequency domain. Beside the probability of failure calculation, the sensitivity of the reliability index to each ran...

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

    OpenAIRE

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

    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 weigh...

  6. Analysis of the variation in the fatigue life through four-point bending tests

    OpenAIRE

    Pais, Jorge; Pereira, Paulo; Minhoto, Manuel; Fontes, Liseane; Kumar, D. S. N. V. A.; Silva, B.T.A.

    2009-01-01

    The fatigue resistance of asphalt mixtures is calculated through laboratory tests which require some time depending on the strain level applied to the specimen. For very low strain levels, identical to the one installed in the pavement of this study, one test may last more than one week depending on the testing frequency. The time needed for the development of the fatigue law may last longer. The number of specimens used to calculate the fatigue resistance of an asphalt mixture plays an impor...

  7. Prediction of fatigue life of reinforced concrete bridges using Fracture Mechanics

    OpenAIRE

    Biondini, Fabio; Frangopol, Dan; Rocha, Marina; Brühwiler, Eugen

    2012-01-01

    With the occurrence of higher and more frequent axle loads, bridges are more solicited by fatigue loading. Bridge elements like deck slabs are subjected to a high number of stress cycles at relatively small stress magnitudes. The application of Fracture Mechanics as a useful tool for the analysis of fatigue crack growth in steel elements was demonstrated by Paris et al. in the early 1960s. With respect to reinforced concrete, the fatigue strength of the steel reinforcement is determinant. The...

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

    Science.gov (United States)

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

    2013-01-01

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

  9. The effect of allergic rhinitis on the degree of stress, fatigue and quality of life in OSA patients.

    Science.gov (United States)

    Park, Cheol Eon; Shin, Seung Youp; Lee, Kun Hee; Cho, Joong Saeng; Kim, Sung Wan

    2012-09-01

    Both allergic rhinitis (AR) and obstructive sleep apnea (OSA) are known to increase stress and fatigue, but the result of their coexistence has not been studied. The objective of this study was to evaluate the amount of stress and fatigue when AR is combined with OSA. One hundred and twelve patients diagnosed with OSA by polysomnography were enrolled. Among them, 37 patients were diagnosed with AR by a skin prick test and symptoms (OSA-AR group) and 75 patients were classified into the OSA group since they tested negative for allergies. We evaluated the Epworth sleepiness scale (ESS), stress score, fatigue score, ability to cope with stress, and rhinosinusitis quality of life questionnaire (RQLQ) with questionnaires and statistically compared the scores of both groups. There were no significant differences in BMI and sleep parameters such as LSAT, AHI, and RERA between the two groups. However, the OSA-AR group showed a significantly higher ESS score compared to the OSA group (13.7 ± 4.7 vs. 9.3 ± 4.8). Fatigue scores were also significantly higher in the OSA-AR group than in the OSA group (39.8 ± 11.0 vs. 30.6 ± 5.4). The OSA-AR group had a significantly higher stress score (60.4 ± 18.6 vs. 51.2 ± 10.4). The ability to cope with stress was higher in the OSA group, although this difference was not statistically significant. RQLQ scores were higher in the OSA-AR group (60.2 ± 16.7 compared to 25.1 ± 13.9). In conclusion, management of allergic rhinitis is very important in treating OSA patients in order to eliminate stress and fatigue and to minimize daytime sleepiness and quality of life. PMID:22207526

  10. Estimation of Fatigue-life of Electronic Packages Subjected to Random Vibration Load

    Directory of Open Access Journals (Sweden)

    M.I. Sakri

    2009-01-01

    Full Text Available Random vibration is being specified for acceptance tests, screening tests, and qualification tests by manufacturers of electronic equipment meant for military applications, because it has been shown that random vibration more closely represents the true environment in which the electronic equipment must operate. In this paper, the methodology of testing an electronic package subjected to random vibration load is illustrated using Joint Electronic Device Engineering Council’s (JEDEC JESD22-B103B standard. The electronic package mounted at the centre of the printed circuit board was subjected to vibration, variable frequency condition ‘D’ of JEDEC standard for 30 min. After 30 min of random vibration test, the component lead-wires, solderjoints, and PCB were thoroughly inspected for failure. From the observations, it was found that no failure occurred during the test period. The fatigue life of the component, estimated using analytical method, was found to be 96.48 hours.Defence Science Journal, 2009, 59(1, pp.58-62, DOI:http://dx.doi.org/10.14429/dsj.59.1486

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

    Science.gov (United States)

    Frantziskonis, George N.

    2013-04-01

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

  12. The effect of microstructure and geometry on the fatigue behaviour of bundle assembly welds

    International Nuclear Information System (INIS)

    Cracking of end plates, in the Darlington NGS, was attributed to high-cycle fatigue resulting from flow-induced vibrations. Because the cracks were predominantly associated with the bundle assembly welds and with certain element positions, a program was initiated to study whether the microstructure and geometry of the weld zone affected the fatigue behaviour of the assembly welds. Assembly weld samples were subjected to different heat treatments, resulting in different microstructures of the weld zone. Results of fatigue testing suggest that heat treatment of the welds (i.e., microstructure) had little effect on the fatigue life. Assembly welds were also produced with different weld notch geometries, and compared with samples having notches produced by machining (instead of welding). The results of these tests showed that geometry of the weld had a significant effect on fatigue life. However, the geometry of the weld notch required to significantly improve fatigue life is not achievable using the current assembly welding process. A small improvement in fatigue life of welded samples appears possible by increasing the weld diameter. (author)

  13. Unified approach for estimating the probabilistic design S-N curves of three commonly used fatigue stress-life models

    International Nuclear Information System (INIS)

    A unified approach, referred to as general maximum likelihood method, is presented for estimating probabilistic design S-N curves and their confidence bounds of the three commonly used fatigue stress-life models, namely three parameter, Langer and Basquin. The curves are described by a general form of mean and standard deviation S-N curves of the logarithm of fatigue life. Different from existent methods, i.e., the conventional method and the classical maximum likelihood method,present approach considers the statistical characteristics of whole test data. The parameters of the mean curve is firstly estimated by least square method and then, the parameters of the standard deviation curve is evaluated by mathematical programming method to be agreement with the maximum likelihood principle. Fit effects of the curves are assessed by fitted relation coefficient, total fitted standard error and the confidence bounds. Application to the virtual stress amplitude-crack initiation life data of a nuclear engineering material, Chinese 1Cr18Ni9Ti stainless steel pipe-weld metal, has indicated the validity of the approach to the S-N data where both S and N show the character of random variable. Practices to the two states of S-N data of Chinese 45 carbon steel notched specimens (kt = 2.0) have indicated the validity of present approach to the test results obtained respectively from group fatigue test and from maximum likelihood fatigue test. At the practices, it was reveatigue test. At the practices, it was revealed that in general the fit is best for the three-parameter model,slightly inferior for the Langer relation and poor for the Basquin equation. Relative to the existent methods, present approach has better fit. In addition, the possible non-conservative predictions of the existent methods, which are resulted from the influence of local statistical characteristics of the data, are also overcome by present approach

  14. Effect of salt-water fog on fatigue crack nucleation of Al and Al-Li alloys

    Scientific Electronic Library Online (English)

    O. C., Gamboni; J. A., Moreto; L. H. C., Bonazzi; C. O. F. T., Ruchert; W. W., Bose Filho.

    2014-02-01

    Full Text Available Fatigue and corrosion-fatigue tests were performed to quantify the fatigue properties of AA2524-T3 and AA2198-T851 Al alloys. High cycle axial fatigue tests were carried out under air and salt-water fog conditions. In air, the specimens were fatigue tested at a frequency of 50 Hz, using specimens wi [...] th and without preconditioning in a salt spray chamber, and for the corrosion fatigue condition, the tests took place at a frequency of 30 Hz in a salt-water fog condition. In all cases it was used a sinusoidal waveform and a stress ratio (R) of 0.1. The results indicate that the saline environment had a deleterious effect on the fatigue life of the two aluminum alloys. AA2524-T3 exhibited a better fatigue strength than AA2198-T851 when fatigue tested in air. However, considering the corrosion fatigue test in a saline fog environment an inverse behavior was observed with the AA2198-T851 exhibiting higher fatigue strength.

  15. Fatigue Life Prediction of Carbon Fiber-Reinforced Ceramic-Matrix Composites at Room and Elevated Temperatures. Part II: Experimental Comparisons

    Science.gov (United States)

    Longbiao, Li

    2015-05-01

    This paper follows on from the earlier study (Part I) which investigated the fatigue behavior of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures. In this paper, a micromechanics approach to predict the fatigue life S-N curves of fiber-reinforced CMCs has been developed considering the fatigue damage mechanism of interface wear or interface oxidation. Upon first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. The two-parameter Weibull model is used to describe fibers strength distribution. The stress carried by broken and intact fibres on the matrix crack plane under fatigue loading is determined based on the Global Load Sharing (GLS) criterion. The fibres failure probabilities under fatigue loading considering the degradation of interface shear stress and fibres strength have been obtained. When the broken fibres fraction approaches critical value, the composite would fatigue fail. The fatigue life S-N curves of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures have been predicted. The predicted results agreed with experimental data.

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

    Science.gov (United States)

    Foltz, John W., IV

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

  17. Fatigue behavior of high-Mn TWIP steels

    International Nuclear Information System (INIS)

    Fatigue behavior of three high-Mn TWIP steels with the grain sizes between 4.5 and 55 ?m were investigated in reversed plane bending in the high-cycle regime. Crack initiation and propagation stages were examined by optical, scanning electron and atom force microscopy. It was found that the fatigue limit, which is the stress amplitude leading to fatigue life beyond 2 x 106 cycles, is quite high, about 400 MPa, for these steels. This value is between 0.42 and 0.48 of the tensile strengths, similarly as for austenitic stainless steels. Refining the grain size still increases the fatigue resistance. Neither martensite is formed nor mechanical twinning takes place in the course of cycling, but intense slip bands are created with extrusions and intrusions. Fatigue cracks tend to nucleate at an early stage of fatigue life, and preferentially on grain and twin boundaries, especially in the intersection sites of slip bands and boundaries, besides slip bands. However, the crack propagation takes place mainly transgranularly creating ductile striations and protrusions on fracture surfaces.

  18. Fatigue behavior of high-Mn TWIP steels

    Energy Technology Data Exchange (ETDEWEB)

    Hamada, A.S. [Materials Engineering Laboratory, Box 4200, University of Oulu, 90014 Oulu (Finland); Karjalainen, L.P., E-mail: pentti.karjalainen@oulu.fi [Materials Engineering Laboratory, Box 4200, University of Oulu, 90014 Oulu (Finland); Puustinen, J. [Microelectronics and Physics Laboratories, Box 4500, University of Oulu, 90014 Oulu (Finland)

    2009-08-20

    Fatigue behavior of three high-Mn TWIP steels with the grain sizes between 4.5 and 55 {mu}m were investigated in reversed plane bending in the high-cycle regime. Crack initiation and propagation stages were examined by optical, scanning electron and atom force microscopy. It was found that the fatigue limit, which is the stress amplitude leading to fatigue life beyond 2 x 10{sup 6} cycles, is quite high, about 400 MPa, for these steels. This value is between 0.42 and 0.48 of the tensile strengths, similarly as for austenitic stainless steels. Refining the grain size still increases the fatigue resistance. Neither martensite is formed nor mechanical twinning takes place in the course of cycling, but intense slip bands are created with extrusions and intrusions. Fatigue cracks tend to nucleate at an early stage of fatigue life, and preferentially on grain and twin boundaries, especially in the intersection sites of slip bands and boundaries, besides slip bands. However, the crack propagation takes place mainly transgranularly creating ductile striations and protrusions on fracture surfaces.

  19. On-line fatigue monitoring and service-life analysis performed in a recuperative exchanger in the primary circuit

    International Nuclear Information System (INIS)

    A recuperative heat exchanger is taken to exemplify on-line service-life monitoring used as a practical means to safeguard systems against fatigue damage. The authors demonstrate configuration, geometry, operation modes, i.e. transient operating conditions and discuss the use of additional transducers for temperature measurements as a supplement to on-line instrumentation. Measured data post-processing allows outer-wall temperatures to be converted to fluid temperatures. This, in turn, allows the thermal inertia of transducers to be quantified in order to evaluate previously recorded transients. A FE analysis of the pipe plate area showed the measured temperature distributions to agree well with calculated ones. Comparisons are discussed using temperature/time graphs. Determination of stresses and fatigue is demonstrated. (orig./DG)

  20. Lamb wave-based damage quantification and probability of detection modeling for fatigue life assessment of riveted lap joint

    Science.gov (United States)

    He, Jingjing; Wang, Dengjiang; Zhang, Weifang

    2015-03-01

    This study presents an experimental and modeling study for damage detection and quantification in riveted lap joints. Embedded lead zirconate titanate piezoelectric (PZT) ceramic wafer-type sensors are employed to perform in-situ non-destructive testing during fatigue cyclical loading. A multi-feature integration method is developed to quantify the crack size using signal features of correlation coefficient, amplitude change, and phase change. In addition, probability of detection (POD) model is constructed to quantify the reliability of the developed sizing method. Using the developed crack size quantification method and the resulting POD curve, probabilistic fatigue life prediction can be performed to provide comprehensive information for decision-making. The effectiveness of the overall methodology is demonstrated and validated using several aircraft lap joint specimens from different manufactures and under different loading conditions.

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

    Science.gov (United States)

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

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

  2. Fatigue behaviour and crack growth rate of cryorolled Al 7075 alloy

    International Nuclear Information System (INIS)

    Highlights: ? High cycle fatigue of cryorolled Al 7075 alloy has been investigated. ? Cryorolled Al alloy showed significant enhancement in fatigue strength. ? FCGR resistance of the ufg Al alloy is higher at higher values of applied stress. - Abstract: The effects of cryorolling (CR) on high cycle fatigue (HCF) and fatigue crack growth rate behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its tensile strength, fatigue life, and fatigue crack growth mechanism were studied by using tensile testing, constant amplitude stress controlled fatigue testing, and fatigue crack growth rate testing using load shedding (decreasing ?K) technique. The microstructural characterization of the alloy was carried out by using Field emission scanning electron microscopy (FESEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain (ufg) structure as observed from its FESEM micrographs. The cryorolled Al 7075 alloys showed improved mechanical properties (Y.S, U.T.S, Impact energy and Fracture toughness are 430 Mpa, 530 Mpa, 21 J, 24 Mpa m1/2 for 40CR alloy) as compared to the bulk 7075 Al alloy. It is due to suppression of dynamic recovery and accumulation of higher dislocations density in the cryorolled Al alloys. The cryorolled Al alloy investigated under HCF regime of intermediate to low plastic ste of intermediate to low plastic strain amplitudes has shown the significant enhancement in fatigue strength as compared to the coarse grained (CG) bulk alloy due to effective grain refinement. Fatigue crack growth (FCGR) resistance of the ufg Al alloy has been found be higher, especially at higher values of applied stress intensity factor ?K The reasons behind such crack growth retardation is due to diffused crack branching mechanism, interaction between a propagating crack and the increased amount of grain boundaries (GB), and steps developed on the crack plane during crack-precipitate interaction at the GB due to ultrafine grain formation.

  3. Fatigue life of creep resisting steels under conditions of cyclic mechanical and thermal interactions

    OpenAIRE

    Marek, A.; Junak, G.; Okrajni, J.

    2009-01-01

    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 T...

  4. Fatigue life prediction for broad-band multiaxial loading with various PSD curve shapes.

    Czech Academy of Sciences Publication Activity Database

    Nieslony, A.; R?ži?ka, M.; Papuga, J.; Hodr, A.; Balda, Miroslav; Svoboda, Jaroslav

    2012-01-01

    Ro?. 44, NOV 2012 (2012), s. 74-88. ISSN 0142-1123 R&D Projects: GA ?R(CZ) GA101/09/0904 Institutional research plan: CEZ:AV0Z20760514 Keywords : random loading * spectral method * power spectral density * fatigue damage Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.976, year: 2012 http://www.sciencedirect.com/science/article/pii/S0142112312001971#

  5. Damage mechanics and Paris regime in fatigue life assessment of metals

    International Nuclear Information System (INIS)

    The fatigue assessment of structural components under uniaxial or multiaxial stress histories can be performed by employing damage mechanics concepts and a physics-based approach. A model for fatigue damage evaluation for an arbitrary loading (uniaxial or multiaxial, cyclic or random) has recently been proposed by the authors using an endurance function which quantifies the damage accumulation in the material up to the final failure. On the other hand, the approach based on the Paris law interprets fatigue failure as the result of the crack propagation inside the material up to the final collapse. In the context of damage mechanics, the structure collapse is assumed to occur when a scalar damage parameter (evaluated by using a proper damage accumulation law depending on the material parameters) is equal to the unity, whereas the final failure according to the Paris law is assumed to occur when the growing crack reaches the ‘critical size’ which depends on the mechanical properties of the material. In the present paper, these two fatigue assessment methods (damage model and Paris approach) are compared in order to determine both a damage value according to the Paris law and the crack length corresponding to a given damage. Such two methods are shown to be different formulations of the same physics-based approach to fatigue. -- Highlights: ? Both damage mechanics and the Paris law can be used to analyse fatigue problems. ? The proposed damage model examines the fatigue effects through damage increments. ? The damage approach is compared with the Paris approach. ? The two methods are shown to be different formulations of the fatigue problem. ? Applications to uniaxial cyclic and variable amplitude loading are presented

  6. Cyclic response and fatigue life of TiAl alloys at high temperatures.

    Czech Academy of Sciences Publication Activity Database

    Kruml, Tomáš; Obrtlík, Karel; Petrenec, Martin; Polák, Jaroslav

    2010-01-01

    Ro?. 417 - 418, - (2010), s. 585-588. ISSN 1013-9826. [8th International Conference on Fracture and Damage Mechanics. St. Georges Bay, 08.09.2009-10.09.2010] R&D Projects: GA ?R GA106/07/0762; GA ?R GA106/08/1631 Institutional research plan: CEZ:AV0Z20410507 Keywords : TiAl * lamellar microstructure * low cycle fatigue * transmission electron microscopy Subject RIV: JL - Materials Fatigue , Friction Mechanics

  7. Fatigue life of drawn filled niti-ag wires for medical applications.

    Czech Academy of Sciences Publication Activity Database

    Major, Št?pán; Hubalovský, Š.; Šedivý, J.; Hanuš, J.

    Sliema : WSEAS Press, 2012 - (Marques, V.; Dmitriev, A.; Pop, E.; Barbu, C.), s. 249-253 ISBN 978-1-61804-118-0. [International conference WSEAS /5./. Sliema (MT), 07.09.2012-09.09.2012] Institutional support: RVO:68378297 Keywords : nitinol * fatigue crack growth * drawn filled wires * fatigue crack initiation. Subject RIV: JI - Composite Materials http://www.wseas.us/e-library/conferences/2012/sliema/dnmat/dnmat-00.pdf

  8. DETERMINATION OF VEHICLE COMPONENTS FATIGUE LIFE BASED ON FEA METHOD AND EXPERIMENTAL ANALYSIS

    Directory of Open Access Journals (Sweden)

    Arif Senol SENER

    2012-01-01

    Full Text Available In this study, construction and standardization of a track for performing fatigue and reliability test of light commercial vehicles is described. For the design and process verification of the company’s vehicles one test track is defined. A questionnaire was used to determine the average usage of light commercial vehicles in Turkey. Fatigue characteristics of Turkish roads were determined by analyzing fifty different roads and this article focuses on defining the load spectrum and equivalent fatigue damage of the leaf spring resulting from the accelerated test route. Fatigue analysis and estimated lifespan of the part were calculated using Finite Element Analyses and verified by the Palmgren-Miner rule. When the customer profile is taken into consideration; Turkish customer automotive usage profile, the aim of usage of this kind of vehicle (LCV, fatigue characteristics of Turkish roads for this vehicle were determined and around Bursa one accelerated test tracks were formed for the reliability and fatigue test for the related company, linear analysis executed on the FEA of the spring was more convenient were obtained.

  9. Applications of a new magnetic monitoring technique to in situ evaluation of fatigue damage in ferrous components

    International Nuclear Information System (INIS)

    This project consisted of research into the use of magnetic inspection methods for the estimation of fatigue life of nuclear pressure vessel steel. Estimating the mechanical and magnetic properties of ferromagnetic materials are closely interrelated, therefore, measurements of magnetic properties could be used to monitor the evolution of fatigue damage in specimens subjected to cyclic loading. Results have shown that is possible to monitor the fatigue damage nondestructively by magnetic techniques. For example, in load-controlled high-cycle fatigue tests, it has been found that the plastic strain and coercivity accumulate logarithmically during the fatigue process. Thus a quantitative relationship between coercivity and the number of fatigue cycles could be established based on two empirical coefficients, which can be determined from the test conditions and material properties. Also it was found that prediction of the onset of fatigue failure in steels was possible under certain conditions. In strain-controlled low cycle fatigue, critical changes in Barkhausen emissions, coercivity and hysteresis loss occurred in the last ten to twenty percent of fatigue life

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

    Science.gov (United States)

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

    1986-01-01

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

  11. Retraction: Psychometric characteristics of the ankylosing spondylitis quality of life questionnaire, short form 36 health survey, and functional assessment of chronic illness therapy-fatigue subscale

    OpenAIRE

    Wong Robert L; Luo Michelle P; Rentz Anne M; Revicki Dennis A; Doward Lynda C; McKenna Stephen P

    2009-01-01

    Abstract Retraction of Revicki DA, Rentz AM, Luo MP, Wong RL, Doward LC, McKenna SP: Psychometric characteristics of the ankylosing spondylitis quality of life questionnaire, short form 36 health survey, and functional assessment of chronic illness therapy-fatigue subscale. Health and Quality of Life Outcomes 2009, 7: 6.

  12. Effect of rare earth Ce on the fatigue life of SnAgCu solder joints in WLCSP device using FEM and experiments

    International Nuclear Information System (INIS)

    With the addition of 0.03 wt% rare earth Ce, in our previous works, the properties of SnAgCu solder were enhanced obviously. Based on the Garofalo–Arrhenius creep constitutive model, finite element method was used to simulate the stress–strain response during thermal cycle loading, and combined with the fatigue life prediction models, the fatigue life of SnAgCu/SnAgCuCe solder joints was calculated respectively, which can demonstrate the effect of the rare earth Ce on the fatigue life of SnAgCu solder joints. The results indicated that the maximum stress–strain can be found on the top surface of the corner solder joint, and the warpage of the PCB substrate occurred during thermal cycle loading. The trends obtained from modeling results have a good agreement with the experimental data reported in the literature for WLCSP devices. In addition, the stress–strain of SnAgCuCe solder joints is lower than that of SnAgCu solder joints. The thermal fatigue lives of solder joints calculated based on the creep model and creep strain energy density model show that the fatigue life of SnAgCuCe solder joints is higher than the SnAgCu solder joints. The fatigue life of SnAgCuCe solder joints can be enhanced significantly with the addition of Ce, is 30.2% higher than that of SnAgCu solder joints, which can be attributed to the CeSn3 particles formed resisting the motion of dislocation; moreover, the refinement of microstructure and the IMC sizes alancement of fatigue life, which elucidates that SnAgCuCe solder can be utilized in electronic industry with high reliability replacing the SnAgCu solder

  13. Influence of phosphorus content and quenching/tempering temperatures on fracture toughness and fatigue life of SAE 5160 steel

    Scientific Electronic Library Online (English)

    Danilo Borges Villarino de, Castro; Jaime Milan, Ventura; Cassius Olivio Figueiredo Terra, Ruckert; Dirceu, Spinelli; Waldek Wladimir, Bose Filho.

    2010-12-01

    Full Text Available This study investigates the influence of quenching/tempering temperatures on the fracture toughness and fatigue life of SAE 5160 steel, considering different phosphorus contents. Quenching and tempering treatments were applied to samples removed from different bars of commercial SAE 5160 steel with [...] different P content. Three different austenitizing temperatures for quenching: 850, 900 and 1000 ºC and a constant holding time of 15 minutes were used. The oil temperature for quenching was kept at 66 ºC and the tempering conditions were 470, 500 and 530 ºC with the necessary time for a final hardness of 45 ± 3 HRC. Therefore, the heat treatments cycles were applied to specimens containing low (0.012 wt. (%)), medium (0.017 wt. (%)) and high (above 0.025 wt. (%)) phosphorus contents, in order to observe the effects of this element on the susceptibility of these steels to enhance quench and tempering embrittlements. The Charpy tests results showed that the phosphorus content analyzed in this work has caused embrittlement, even in the bars with the lowest P content, leading to intergranular fracture. However, if the nucleation life is taken into consideration, this embrittlement has no effect on the nucleation fatigue life of the component.

  14. Bending fatigue strength of austenitic stainless steel SUS316 in mercury

    International Nuclear Information System (INIS)

    Liquid mercury target system for spallation neutron source is installed at Materials and Life Science Experimental Facility in Japan Proton Accelerator Research Complex (J-PARC), which will promote innovative science. Austenitic stainless steel SUS316 for a structural material of the target vessel is contact with mercury, and imposed by cyclic pressure that is induced by pulsed proton beam injection at 25Hz. Therefore, it is important from the viewpoint of the structural integrity to investigate the effect of mercury on fatigue behavior of the structural material. Bending fatigue tests in mercury and air were performed to evaluate the effect of mercury on fatigue behavior. FRActure Surface Topography Analyses (FRASTA) were carried out to evaluate the change in fracture morphology with mercury. It was confirmed that the fatigue strength was decreased by mercury immersion in low cycle region less than 105 cycles and intergranular fracture surface was observed, while in high cycle region the mercury immersion effect was hardly recognized. (author)

  15. Approach to a Method of Integrated Evaluation of Thermal Fatigue and its Validation Using SPECTRA

    Science.gov (United States)

    Oumaya, Toru; Nakamura, Akira; Takenaka, Nobuyuki

    Thermal fatigue may initiate at a T-junction or a branched off line where high and low temperature fluids mix. These are common piping elements in nuclear power plants. To ensure structural integrity against thermal fatigue during the design phase, it is important to estimate thermal load from such design specifications as flow rate, temperature difference, pipe diameter, etc. IMAT-F, an evaluation method integrating thermal hydraulic and structural analysis, was developed in this study to precisely determine thermal load excluding safety margins or conservative engineering judgment. The method was validated by numerical flow simulations of high-cycle thermal fatigue experiment SPECTRA, conducted by Japan Atomic Energy Agency. Results confirmed that IMAT-F can accurately simulate fluid and pipe wall temperature fluctuation using fluid-structure coupled analysis. Thermal stress fluctuation resulting from distribution of temperature fluctuation in the pipe wall was then calculated. Fluctuation fatigue life was also estimated for comparison with the experimental results.

  16. The influence function method for fracture mechanics and residual fatigue life analysis of cracked components under complex stress fields

    International Nuclear Information System (INIS)

    This paper reviews the development and application of an influence function method for calculating stress intensity factors and residual fatigue life for two- and three-dimensional structures with complex stress fields and geometries. Through elastic superposition the method properly accounts for redistribution of stress as the crack grows through the structure. The analytical methods utilized and the computer programs necessary for computation and application of load independent influence functions are presented. A new exact solution is obtained for the buried elliptical crack, under an arbitrary Mode I stress field, for stress intensity factors at four positions around the crack front. The IF method is then applied to two fracture mechanics problems with complex stress fields and geometries. These problems are of current interest to the electric power generating industry and include (1) the fatigue analysis of a crack in a pipe weld under nomial and residual stresses and (2) fatigue analysis of a reactor pressure vessel nozzle corner crack under a complex bivariate stress field. (Auth.)

  17. Effects from fully nonlinear irregular wave forcing on the fatigue life of an offshore wind turbine and its monopile foundation

    DEFF Research Database (Denmark)

    SchlØer, Signe; Bredmose, Henrik

    2013-01-01

    The effect from fully nonlinear irregular wave forcing on the fatigue life of the foundation and tower of an offshore wind turbine is investigated through aeroelastic calculations. Five representative sea states with increasing significant wave height are considered in a water depth of 40 m. The waves are both linear and fully nonlinear irregular 2D waves. The wind turbine is the NREL 5-MW reference wind turbine. Fatigue analysis is performed in relation to analysis of the sectional forces in the tower and monopile. Impulsive excitation of the sectional force at the bottom of the tower is seen when the waves are large and nonlinear and most notably for small wind speeds. In case of strong velocities and turbulent wind, the excitation is damped out. In the monopile no excitation of the force is seen, but even for turbulent strong wind the wave affects the forces in the pile significantly. The analysis indicates that the nonlinearity of the waves can change the fatigue damage level significantly in particular when the wave and wind direction is misaligned.

  18. FATIGUE LIFE PREDICTION BASED ON MACROSCOPIC PLASTIC ZONE ON FRACTURE SURFACE OF AISI-SAE 1018 STEEL

    Directory of Open Access Journals (Sweden)

    G.M. Domínguez Almaraz

    2010-06-01

    Full Text Available This paper deals with rotating bending fatigue tests at high speed (150 Hz carried out on AISI-SAE 1018 steel with a high content of impurities (non metallic inclusions, for which the high experimental stress inside the specimen is close to the elastic limit of the material. Simulations of rotating loading are obtained by Visual NASTRAN software in order to determine the numerical stresse and strain distributions inside a hypothetical homogeneous specimen; later, this information is used for the experimental set up. A general description of experimental test machine and experimental conditions are developed and then, the experimental results are presented and discussed according the observed failure origin related to the non metallic inclusions and the associated high stress zones. Finally, a simple model is proposed to predict the fatigue life for this non homogeneous steel under high speed rotating bending fatigue tests close to the elastic limit, based on the rate between the visual macro-plastic deformation zone at fracture surface and the total fracture surface, together with the crack initiation inclusion (or inclusions located at this zone.

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  1. Lap shear strength and fatigue life of friction stir spot welded AZ31 magnesium and 5754 aluminum alloys

    International Nuclear Information System (INIS)

    Lightweighting is today considered as one of the key strategies in reducing fuel consumption and anthropogenic greenhouse gas emissions. The structural applications of lightweight magnesium and aluminum alloys in the transportation industry inevitably involve welding and joining while guaranteeing the safety and reliability of motor vehicles. This study was aimed at evaluating lap shear strength and fatigue properties of friction stir spot welded (FSSWed) AZ31B-H24 Mg and 5754-O Al alloys in three combinations, i.e., similar Mg-to-Mg, Al-to-Al, and dissimilar Al-to-Mg joints. The Mg/Mg similar weld had a nugget-shaped stir zone (SZ) around the keyhole where fine recrytallized equiaxed grains were observed. While the hardness profile of the Mg/Mg similar weld exhibited a W-shaped appearance, the lower hardness values appeared in the TMAZ and HAZ of both Mg/Mg and Al/Al similar welds. In the Al/Mg dissimilar weld, a characteristic interfacial layer consisting of intermetallic compounds (IMC) Al12Mg17 and Al3Mg2 was observed. Both Mg/Mg and Al/Al similar welds had significantly higher lap shear strength, failure energy and fatigue life than the Al/Mg dissimilar weld. While the Al/Al weld displayed a slightly lower lap shear strength than the Mg/Mg weld, the Al/Al weld had higher failure energy and fatigue life. Three types of failure modes were observed. In the Mg/Mg and Al/Al similar welds, at higher cyclic loads nugget pullouelds, at higher cyclic loads nugget pullout failure occurred due to fatigue crack propagation circumferentially around the nugget, while at lower cyclic loads fatigue failure occurred perpendicular to the loading direction caused by the opening of keyhole through crack initiation in the TMAZ and HAZ. In the Al/Mg dissimilar weld nugget debonding failure mode was observed because of the presence of an interfacial IMC layer.

  2. Lap shear strength and fatigue life of friction stir spot welded AZ31 magnesium and 5754 aluminum alloys

    Energy Technology Data Exchange (ETDEWEB)

    Chowdhury, S.H. [Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario, Canada M5B 2K3 (Canada); Chen, D.L., E-mail: dchen@ryerson.ca [Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario, Canada M5B 2K3 (Canada); Bhole, S.D. [Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario, Canada M5B 2K3 (Canada); Cao, X.; Wanjara, P. [Aerospace Manufacturing Technology Centre, National Research Council Canada, 5145 Decelles Avenue, Montreal, Quebec, Canada H3T 2B2 (Canada)

    2012-10-30

    Lightweighting is today considered as one of the key strategies in reducing fuel consumption and anthropogenic greenhouse gas emissions. The structural applications of lightweight magnesium and aluminum alloys in the transportation industry inevitably involve welding and joining while guaranteeing the safety and reliability of motor vehicles. This study was aimed at evaluating lap shear strength and fatigue properties of friction stir spot welded (FSSWed) AZ31B-H24 Mg and 5754-O Al alloys in three combinations, i.e., similar Mg-to-Mg, Al-to-Al, and dissimilar Al-to-Mg joints. The Mg/Mg similar weld had a nugget-shaped stir zone (SZ) around the keyhole where fine recrytallized equiaxed grains were observed. While the hardness profile of the Mg/Mg similar weld exhibited a W-shaped appearance, the lower hardness values appeared in the TMAZ and HAZ of both Mg/Mg and Al/Al similar welds. In the Al/Mg dissimilar weld, a characteristic interfacial layer consisting of intermetallic compounds (IMC) Al{sub 12}Mg{sub 17} and Al{sub 3}Mg{sub 2} was observed. Both Mg/Mg and Al/Al similar welds had significantly higher lap shear strength, failure energy and fatigue life than the Al/Mg dissimilar weld. While the Al/Al weld displayed a slightly lower lap shear strength than the Mg/Mg weld, the Al/Al weld had higher failure energy and fatigue life. Three types of failure modes were observed. In the Mg/Mg and Al/Al similar welds, at higher cyclic loads nugget pullout failure occurred due to fatigue crack propagation circumferentially around the nugget, while at lower cyclic loads fatigue failure occurred perpendicular to the loading direction caused by the opening of keyhole through crack initiation in the TMAZ and HAZ. In the Al/Mg dissimilar weld nugget debonding failure mode was observed because of the presence of an interfacial IMC layer.

  3. Long-term creep-fatigue life property of Mod.9Cr-1Mo steel for steam generator material in FBR

    International Nuclear Information System (INIS)

    Extensive research is being executed to establish creep-fatigue life evaluation methodology for Mod.9Cr-1Mo steel which is the principal candidate material of steam generators in Demonstration Fast Breeder Reactor. Previous studies showed that the features of the creep-fatigue life property of the steel are small life reduction by tensile strain hold and significant reduction in compressive hold tests due to oxidation effect. Most of the experiments, however, were conducted under relatively short-term hold conditions and the failure life properties under long-term hold conditions have not yet been clarified. In order to investigate the oxidation and long-term strain hold effects on the creep-fatigue life property, the crack propagation tests in vacuum and air conditions, and the long-term creep-fatigue tests, up to 10 hours hold time per cycle, were performed. As a result, it was found that the significant life reduction occurred by introducing the tensile strain hold longer than 1 hour because of increase of the grain boundary damage due to cavity nucleation, and that the life reduction in compressive hold was caused by acceleration of the crack propagation rate due to accumulation of the tensile strain in center of the specimen. (author)

  4. Comparison of crack initiation life estimation procedures under creep-fatigue conditions

    International Nuclear Information System (INIS)

    This paper describes the application of 'high temperature structural integrity assessment procedures' developed in the UK and Japan to creep-fatigue crack initiation in welded Type 316 features tests. The components were subjected to both fatigue and creep-fatigue loading at 630 deg C. The loadings are representative of those on the upper seal gimbal joint in an advanced gas cooled reactor (AGR), except that the tests were isothermal and the imposed dwell times were reduced. It is demonstrated that application of the procedures gives accurate predictions of the observed crack initiation in the weldment, based on two different advanced inelastic constitutive models (BE and CRIEPI models) and best estimate materials data. Application of simplified assessment methods based on elastic analysis is shown to be conservative. Where appropriate, contrasts between the UK and the Japanese assessment procedures and inelastic modelling techniques have been highlighted

  5. A study on fretting fatigue life for the Inconel alloy 600 at high temperature

    International Nuclear Information System (INIS)

    Fatigue tests of the Inconel 600, a type of nickel-chromium based heat resistant alloy used for steam generator tubes in nuclear power plants, were carried out. Temperature increase to 320 oC did not change the fatigue strength much, but the fretting condition caused a significant reduction in the fatigue strength. The reduction at 107 cycles was about 70% for both of room and the high temperatures. An apparatus to realize the fretting condition has been developed and instrumented to measure the normal and friction forces. The bridge type of contact pad was fabricated of SUS 409 stainless steel. Fracture surfaces and wear scars were observed by electron microscope and the profiles of wear scar were measured by non-contact 3D-profiler.

  6. Fatigue life evaluation of TIG-weld of reduced activation ferritic/martensitic steel F82H by small specimen test technique

    International Nuclear Information System (INIS)

    Evaluation of the low cycle fatigue life by the small specimen test technique (SSTT) and some other properties (metallographical structure and Vickers hardness) for the TIG (tungsten inert gas) weld of F82H IEA-heat were carried out. The TIG-weld was distinguished into seven regions with different metallographical structure and hardness, which were the base metal (BM) region (region with almost no thermal history in the weld), three regions of the heat affected zone (HAZ), and the three regions of the weld metal. There seemed to be no significant correlation between Vickers hardness and average prior austenitic grain size of the individual regions of the TIG-weld. The region with larger prior austenitic grain than the base metal showed similar fatigue life to the BM and the raw material (material used for the TIG-weld). While, the region with relatively small prior austenitic grain showed longer fatigue life than it. (author)

  7. Neurobiological studies of fatigue

    OpenAIRE

    Harrington, Mary E.

    2012-01-01

    Fatigue is a symptom associated with many disorders, is especially common in women and in older adults, and can have a huge negative influence on quality of life. Although most past research on fatigue uses human subjects instead of animal models, the use of appropriate animal models has recently begun to advance our understanding of the neurobiology of fatigue. In this review, results from animal models using immunological, developmental, or physical approaches to study fatigue are described...

  8. Estimation of low cycle fatigue life of elbows considering bi-axial stress effect

    International Nuclear Information System (INIS)

    Elbow pipes are commonly used in the piping systems of power plants and chemical plants. The stress states at elbow part are complex and quite different from those of the straight pipes. It is well known that the fatigue lives of metals under simple push-pull conditions were successfully predicted by the Manson's universal slope method. However, it have been pointed out by the several researchers that the low cycle fatigue lives of elbows under combined cyclic bending and inner pressure could not be predicted by the Manson's universal slope method. However, the reasons for this are not made clear. In this work, the low cycle fatigue tests and the finite element analysis of elbows under cyclic bending and inner pressures were carried out. It was found that the bi-axial stress ratio, which is a ratio of hoop stress and axial stress, at elbows are quite high. Considering the bi-axial stress ratio, the revised Manson's universal slope method was proposed in this paper. It was shown that the low cycle fatigue lives of elbows under combined cyclic bending and inner pressure were predicted conservatively by the proposed method. (author)

  9. Testing station for fatigue life examinations with superposed mechanical and thermal cyclide loads

    International Nuclear Information System (INIS)

    A testing station concept is presented by means of which fatigue live examinations under complex loads can be carried out on hollow samples which are simultaneously exposed to mechanical and thermal cyclic loads. Because of the required statistical validation of the test results the testing station has been designed as multiple sample testing station. (orig.)

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

    Science.gov (United States)

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

    2007-02-01

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

  11. Effects on fatigue life of gate valves due to higher torque switch settings during operability testing

    International Nuclear Information System (INIS)

    Some motor operated valves now have higher torque switch settings due to regulatory requirements to ensure valve operability with appropriate margins at design basis conditions. Verifying operability with these settings imposes higher stem loads during periodic inservice testing. These higher test loads increase stresses in the various valve internal parts which may in turn increase the fatigue usage factors. This increased fatigue is judged to be a concern primarily in the valve disks, seats, yokes, stems, and stem nuts. Although the motor operators may also have significantly increased loading, they are being evaluated by the manufacturers and are beyond the scope of this study. Two gate valves representative of both relatively weak and strong valves commonly used in commercial nuclear applications were selected for fatigue analyses. Detailed dimensional and test data were available for both valves from previous studies at the Idaho National Engineering Laboratory. Finite element models were developed to estimate maximum stresses in the internal parts of the valves and to identity the critical areas within the valves where fatigue may be a concern. Loads were estimated using industry standard equations for calculating torque switch settings prior and subsequent to the testing requirements of USNRC Generic Letter 89--10. Test data were used to determine both; (1) the overshoot load between torque switch trip and final seating of the disk during valve closing and (2) the stem thrust required to open the valves. The ranges of peak stresses thus determined were then used to estimate the increase in the fatigue usage factors due to the higher stem thrust loads. The usages that would be accumulated by 100 base cycles plus one or eight test cycles per year over 40 and 60 years of operation were calculated

  12. Impurity levels and fatigue lives of pseudoelastic NiTi shape memory alloys

    International Nuclear Information System (INIS)

    In the present work we show how different oxygen (O) and carbon (C) levels affect fatigue lives of pseudoelastic NiTi shape memory alloys. We compare three alloys, one with an ultrahigh purity and two which contain the maximum accepted levels of C and O. We use bending rotation fatigue (up to cycle numbers >108) and scanning electron microscopy (for investigating microstructural details of crack initiation and growth) to study fatigue behavior. High cycle fatigue (HCF) life is governed by the number of cycles required for crack initiation. In the low cycle fatigue (LCF) regime, the high-purity alloy outperforms the materials with higher number densities of carbides and oxides. In the HCF regime, on the other hand, the high-purity and C-containing alloys show higher fatigue lives than the alloy with oxide particles. There is high experimental scatter in the HCF regime where fatigue cracks preferentially nucleate at particle/void assemblies (PVAs) which form during processing. Cyclic crack growth follows the Paris law and does not depend on impurity levels. The results presented in the present work contribute to a better understanding of structural fatigue of pseudoelastic NiTi shape memory alloys

  13. Multimodal intervention improves fatigue and quality of life in subjects with progressive multiple sclerosis: a pilot study

    Directory of Open Access Journals (Sweden)

    Bisht B

    2015-02-01

    Full Text Available Babita Bisht,1 Warren G Darling,2 E Torage Shivapour,3 Susan K Lutgendorf,4–6 Linda G Snetselaar,7 Catherine A Chenard,1 Terry L Wahls1,8 1Department of Internal Medicine, Carver College of Medicine, University of Iowa, 2Department of Health and Human Physiology, College of Liberal Arts and Sciences, University of Iowa, 3Department of Neurology, Carver College of Medicine, University of Iowa, 4Department of Psychology, College of Liberal Arts and Sciences, University of Iowa, 5Department of Obstetrics and Gynecology, Carver College of Medicine, University of Iowa, 6Department of Urology, Carver College of Medicine, University of Iowa, 7Department of Epidemiology, College of Public Health, University of Iowa, 8Department of Internal Medicine, VA Medical Center, Iowa City, IA, USA Background: Fatigue is a disabling symptom of multiple sclerosis (MS and reduces quality of life. The aim of this study was to investigate the effects of a multimodal intervention, including a modified Paleolithic diet, nutritional supplements, stretching, strengthening exercises with electrical stimulation of trunk and lower limb muscles, and stress management on perceived fatigue and quality of life of persons with progressive MS. Methods: Twenty subjects with progressive MS and average Expanded Disability Status Scale (EDSS score of 6.2 (range: 3.5–8.0 participated in the 12-month phase of the study. Assessments were completed at baseline and at 3 months, 6 months, 9 months, and 12 months. Safety analyses were based on monthly side effects questionnaires and blood analyses at 1 month, 3 months, 6 months, 9 months, and 12 months. Results: Subjects showed good adherence (assessed from subjects' daily logs with this intervention and did not report any serious side effects. Fatigue Severity Scale (FSS and Performance Scales-fatigue subscale scores decreased in 12 months (P<0.0005. Average FSS scores of eleven subjects showed clinically significant reduction (more than two points, high response at 3 months, and this improvement was sustained until 12 months. Remaining subjects (n=9, low responders either showed inconsistent or less than one point decrease in average FSS scores in the 12 months. Energy and general health scores of RAND 36-item Health Survey (Short Form-36 increased during the study (P<0.05. Decrease in FSS scores during the 12 months was associated with shorter disease duration (r=0.511, P=0.011, and lower baseline Patient Determined Disease Steps score (rs=0.563, P=0.005 and EDSS scores (rs=0.501, P=0.012. Compared to low responders, high responders had lower level of physical disability (P<0.05 and lower intake of gluten, dairy products, and eggs (P=0.036 at baseline. High responders undertook longer duration of massage and stretches per muscle (P<0.05 in 12 months. Conclusion: A multimodal intervention may reduce fatigue and improve quality of life of subjects with progressive MS. Larger randomized controlled trials with blinded raters are needed to prove efficacy of this intervention on MS-related fatigue. Keywords: modified Paleolithic diet, exercise, neuromuscular electrical stimulation, stress management, lifestyle changes, vitamins, supplements

  14. Fatigue Criterion for System Design

    Science.gov (United States)

    Zeretsky, E. V.

    1986-01-01

    Report discusses principles of structural-life prediction. Generalized methodology developed for structural life prediction, design, and reliability, based upon fatigue criterion. Approach incorporates computed life of elemental stress volumes of complex machine elements to predict system life. Results of coupon fatigue testing incorporated into analysis, allowing for life prediction and component or structural renewal rates, with reasonable statistical certainty.

  15. Prediction of creep-fatigue life based on the damage mechanism of grain boundary cavitation and improvement of life by the modification of carbide characteristics in austenitic stainless steels

    International Nuclear Information System (INIS)

    IT is understood that grain boundary cavitation is one of the detrimental processes for the degradation of austenitic stainless steels that reduces the creep-fatigue life at high temperatures. A new damage function based on a model for the creep-fatigue life prediction in terms of nucleation and growth of grain boundary cavities is proposed for austenitic stainless steel. This damage function is a combination of the fatigue and creep terms related to the cavitational damage (cavity nucleation and growth) in the life prediction equation and is found to be generally applicable to all the materials in which failure is controlled by the grain boundary cavitational damage. The cavity nucleation factor, P', which is introduced in the creep-fatigue life model, is found to be closely related with the characteristics of grain boundary carbides acting as cavity nucleation sites. The modification of carbide characteristics through grain boundary serration is successfully made by the special heat treatment so that the modified carbides are favorable for cavitation resistance, resulting in a lowered P' value of material. It is observed that the creep-fatigue life is remarkably improved by the modification of carbide characteristics through grain boundary serration

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

    Science.gov (United States)

    Rangaswamy, Partha; Terutung, Hendra; Jeelani, Shaik

    1989-01-01

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

  17. Fatigue life and crack growth mechanisms of the type 316LN austenitic stainless steel in 310degC deoxygenated water

    International Nuclear Information System (INIS)

    The low cycle fatigue tests of the type 316LN stainless steel were conducted to investigate the cracking mechanisms in high-temperature water. The fatigue lives of the specimens tested in 310degC deoxygenated water were considerably shorter than those tested in air. For the specimens tested in 310degC deoxygenated water, the evidences for the metal dissolution such as the stream downed feature, the blunt crack shape, and the wider crack opening were observed but rather weakly. In the same specimens, the evidences for the hydrogen-induced cracking such as the coalescence of microvoids and the decrease of the dislocation spacing at the crack tip were observed rather clearly. Therefore, it is thought that the hydrogen-induced cracking is mainly responsible for the reduction in the fatigue life of the type 316LN stainless steel in 310degC deoxygenated water while the effect of metal dissolution is less significant. The hydrogen-induced cracking is more pronounced in the slower strain rates. This behavior is in accordance with the larger reduction in the fatigue life at the slower strain rates. Furthermore, the fatigue life and the dislocation spacing show the minimum value in the strain rate range from 0.008 to 0.04%/s, which indicates the existence of the critical strain rate. (author)

  18. The effect of group mindfulness - based stress reduction program and conscious yoga on the fatigue severity and global and specific life quality in women with breast cancer

    Science.gov (United States)

    Rahmani, Soheila; Talepasand, Siavash

    2015-01-01

    Background: Cancer is not merely an event with a certain end, but it is a permanent and vague situation that is determined by delayed effects due to the disease, its treatment and its related psychological issues. The aim of this study was to examine the effectiveness of the mindfulness-based stress reduction program and conscious yoga on the mental fatigue severity and life quality of women with breast cancer. Methods: This was a quasi-experimental study with a pre-test, post-test and control group. In this study, 24 patients with the diagnosis of breast cancer were selected among the patients who referred to the Division of Oncology and Radiotherapy of Imam Hossein hospital in Tehran using available sampling method, and were randomly assigned into the experimental and control groups. All the participants completed the Fatigue Severity Scale, Global Life Quality of Cancer Patient and Specific Life Quality of Cancer Patient questionnaires. Data were analyzed by multivariate repeated measurement variance analysis model. Results: Findings revealed that the mindfulness-based stress reduction treatment significantly improved the overall quality of life, role, cognitive, emotion, social functions and pain and fatigue symptoms in global life quality in the experimental group. It also significantly improved the body image, future functions and therapy side effects in specific life quality of the experimental group compared to the control group. In addition, fatigue severity caused by cancer was reduced significantly. Conclusion: The results showed that the mindfulness - based stress reduction treatment can be effective in improving global and specific life quality and fatigue severity in women with breast cancer.

  19. Creep-fatigue life estimation scheme based on stress redistribution locus concept

    International Nuclear Information System (INIS)

    High temperature components are operated under cyclic thermal transient. In the design of these components, creep-fatigue is the most dominant failure mode. To evaluate creep-fatigue damage, methodology to estimate inelastic strain concentration should be presented in a design standard. This paper presents new technique to estimate inelastic strain behavior based on Stress Redistribution Locus (SRL) method. An applicability of SRL concept is discussed with a help of FEM results for representative components of pressure vessel under various analytical conditions. It is confirmed that SRL does not depend on constitutive equations, thermal load range or plasticity/creep under monotonic loading condition. Including some differences under cyclic loading condition or other, whole results is conservatively represented by proposed design SRL curve. (author)

  20. ARRANGING THICKNESSES AND SPANS OF ORTHOTROPIC DECK FOR DESIRED FATIGUE LIFE AND DESIGN CATEGORY

    OpenAIRE

    Abdullah Fettahoglu

    2013-01-01

    Orthotropic steel highway bridges are subject to variable traffic loads, which differ in type and magnitude. Most of these bridges were built in 1960’s under design traffic load, which reflects the traffic conditions of those times. However, the number and weight of vehicles in traffic have increased since then too much in comparison to today. As a result these bridges are loaded more than their designed traffic loads and hence bridges' fatigue lives are shorten. As a remedy for this issue,...