WorldWideScience
 
 
1

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

Directory of Open Access Journals (Sweden)

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.

M. Malnati

2014-04-01

2

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

Science.gov (United States)

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

Kihm, Frederic; Rizzi, Stephen A.

2014-01-01

3

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

Directory of Open Access Journals (Sweden)

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.

Guian Qian

2013-07-01

4

High-cycle and long-life fatigue of 25CrMo4 under multiaxial load conditions by three alternating stresses  

International Nuclear Information System (INIS)

Statistically verified experimental results from high-cycle and long-life fatigue tests (HCF and LLF) with altogether 537 unnotched solid cylindrical and thin-walled hollow specimen are demonstrating the fatigue behaviour (S-N-characteritics, scatterband) of 25CrMo4 under uniaxial loading with superimposed static stresses (consideration of the mean stress effect) and under biaxial loadings in variation of phase differences between the three combined normal and torsional stresses ?x, ?y, ?xy. The fatigue strength is commonly decreasing with life time in the high-cycle regime until reaching the fatigue endurance limit in the transition range to infinite life. The 'ductility level' ?W/?W and the 'mean stress sensibility' p=p (?W, ?zSch, Rm) are relatively independent of the intensity by stress amplitudes and fatigue life to failure. In comparison with the specific case of biaxial combined loading with synchroneous amplitudes, the fatigue resistance characteristics are detrimentally influenced by out-of-phase normal stresses ?x, ?y; a phase difference of 180deg between the normal stress amplitudes is the most critical state of combination, especially in the lower cycle regime caused by a greater slope coefficient (probability of survival Ps=50%). On the contrary is there in the high-cycle regime as well as in the long-life range no significant influence to the fatigue strength by biaxial load conditions of simultaneously normal stresses with out-of-phase torsional stress ?xy. (orig.)

5

A comparison of high cycle fatigue methodologies  

Science.gov (United States)

To evaluate alternate turbopump development (ATD) high cycle fatigue (HCF) methodology, a comparison was made with the space shuttle main engine (SSME) methodology. This report documents the comparison and evaluates ATD's HCF system.

Herda, D. A.

1992-01-01

6

Fatigue characteristics of bearing steel in very high cycle fatigue  

International Nuclear Information System (INIS)

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

7

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

8

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

International Nuclear Information System (INIS)

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

9

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

Directory of Open Access Journals (Sweden)

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.

Kolyshkin A.

2014-06-01

10

High-Cycle Fatigue Behavior of a Nicalon(tm)/Si-N-C Composite  

Science.gov (United States)

Elevated temperature, high-cycle fatigue behavior of a woven SiC/Si-N-C ceramic matrix composite system was investigated at 910 C. High frequency (100 Hz) fatigue tests were conducted in air on specimens machined from the composite system, A power-law type fatigue life relationship adequately characterized the high-cycle fatigue data generated in the study. Post failure fractographic and metallographic studies were performed to document the fatigue crack initiation regions and damage mechanisms in the composite system. Fatigue cracks initiated primarily from the corners of the specimens and propagated along the 90 degree fiber tows.

Verrilli, Michael J.; Kalluri, Sreeramesh; Kantzos, Peter T.

1999-01-01

11

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

Science.gov (United States)

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

Majumdar, S.; Kwasny, R.

1985-01-01

12

High cycle fatigue of metastable austenitic stainless steels  

International Nuclear Information System (INIS)

Metastable austenitic stainless steels are currently used in applications where severe forming operations are required, such as automotive bodies, due to its excellent ductility. They are also gaining interest for its combination of high strength and formability after forming. The biggest disadvantage is the difficulty to predict the mechanical response, which depends heavily on the amount of martensite formed. The martensitic transformation in metastable stainless steels can be induced by plastic deformation at room temperature. In this research, the martensitic transformation was provoked by means of torsion testing. Several torsion angles were selected to achieve different percentages of martensite at the surface of the specimens. The next step was to evaluate their effect on the fatigue life of the steel. Fatigue testing in the high cycle regime was done at different levels of mean stress. As a conclusion, the presence of martensite in the surface of the specimen led to an increase of the fatigue life when high mean stress was imposed. By contrast, at lower values of mean stress, martensitic transformation has no positive effect on the fatigue life.

13

On the Use of Equivalent Linearization for High-Cycle Fatigue Analysis of Geometrically Nonlinear Structures  

Science.gov (United States)

The use of stress predictions from equivalent linearization analyses in the computation of high-cycle fatigue life is examined. Stresses so obtained differ in behavior from the fully nonlinear analysis in both spectral shape and amplitude. Consequently, fatigue life predictions made using this data will be affected. Comparisons of fatigue life predictions based upon the stress response obtained from equivalent linear and numerical simulation analyses are made to determine the range over which the equivalent linear analysis is applicable.

Rizzi, Stephen A.

2003-01-01

14

High cycle fatigue behaviour of extruded Magnesium alloys containing Neodymium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Nascimento Silva Ferri, Ligia

2014-01-01

15

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.

16

Surface finish effects on the high-cycle fatigue of Alloy 718  

International Nuclear Information System (INIS)

Load control high-cycle fatigue tests at 427 and 6490C were conducted on Alloy 718 specimens given various surface finishes. The standard surface preparation for fatigue specimens involves a low-stress grind to minimize the residual surface stresses. A low-stress grind surface was used for generating baseline data; various other surfaces that could be considered feasible for large components fabricated in commercial shops were produced on test specimens, and the high-cycle fatigue strength of each was compared. Surface finishes produced by belt sanding, grit blasting, fine machining, and electropolishing were examined. Surface roughness measurements were taken on typical specimens with each surface finish, and residual stress profiles were measured on three of the surface types. Results show little or no difference in fatigue life for the various surfaces and indicate that residual stress profile and grain size are more important factors than surface roughness in determining high-cycle fatigue strength. 12 figures, 5 tables

17

Investigation of very high cycle fatigue by thermographyc method  

Directory of Open Access Journals (Sweden)

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.

V. Crupi

2014-11-01

18

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

Directory of Open Access Journals (Sweden)

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

Mirco D. Chapetti

2002-06-01

19

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

Scientific Electronic Library Online (English)

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

Mirco D., Chapetti.

20

Fatigue behavior of Alloy 690 and Alloy 800 SG tubing at temperatures up to 330oC in very high cycle fatigue regime  

International Nuclear Information System (INIS)

During the service in nuclear power plants, steam generator (SG) tubing will suffer from a vibration with a frequency from 30-40 Hz. This means that SG tubing will undergo a very high cycle fatigue process during the design life time (25 years=about 3x1010cycles). The material degradation and the very high cycle fatigue life of SG tubing materials due to the vibration are therefore of concern. In this investigation, the fatigue properties of Alloy 690 and Alloy 800 SG tubing in the very high cycle fatigue regime (higher than 107 cycles) and strain controlled fatigue at temperatures up to 330oC have been investigated. The fatigue properties of SG tubing of Alloy 690 are comparable to that of wrought material. The strain controlled fatigue properties of Alloy 690 and Alloy 800 are slightly better at 288oC than at room temperature (RT). At the stress near the fatigue endurance, the influence of temperature on the high cycle fatigue properties of Alloy 690 is small. The fatigue properties of Alloy 800 are comparable to that of Alloy 690. The strain controlled fatigue properties of Alloy 690 and Alloy 800 are higher than the Argonne design curve and the ASME design curve. The high cycle fatigue properties in the very high cycle fatigue regime are comparable to that of Alloy 600. (author)

 
 
 
 
21

High-cycle fatigue behavior of type 316 stainless steel at 5930C  

International Nuclear Information System (INIS)

The available low- and high-cycle fatigue data on Type 316 stainless steel at 593 to 6000C have been combined and analyzed to provide a preliminary strain-life correlation. This correlation was then reduced by the appropriate safety factors to a design curve and compared with the ASME T-1420-1B curve. The comparison indicates that significant increases in allowable fatigue cycles should be realized when the present study is concluded

22

High-cycle fatigue behavior of type 316 stainless steel at 593/sup 0/C  

Energy Technology Data Exchange (ETDEWEB)

The available low- and high-cycle fatigue data on Type 316 stainless steel at 593 to 600/sup 0/C have been combined and analyzed to provide a preliminary strain-life correlation. This correlation was then reduced by the appropriate safety factors to a design curve and compared with the ASME T-1420-1B curve. The comparison indicates that significant increases in allowable fatigue cycles should be realized when the present study is concluded.

Raske, D.T.

1980-01-01

23

High-cycle fatigue strength of a pultruded composite material  

Directory of Open Access Journals (Sweden)

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.

L. Vergani

2009-01-01

24

Plasticity-damage based micromechanical modelling in high cycle fatigue  

Science.gov (United States)

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).

Monchiet, Vincent; Charkaluk, Eric; Kondo, Djimedo

2006-02-01

25

Evaluation of high-cycle fatigue behavior of 316FR at high temperature  

International Nuclear Information System (INIS)

High-cycle fatigue data which are necessary in evaluating integrity of upper sore structures of FBR plants were collected for 316FR steel. Fatigue data up to 10 million cycles were obtained and the following observations were made: (1) Influence of loading frequency on deformation and failure life was small. (2) Forging material showed lower life than plate material at low strain range. (3) Best-fit fatigue strength equation can be applied to forging material but modification was proposed for plate material to correct nonconservative tendency at low strain ranges. (author)

26

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

27

Development of high-cycle fatigue design curves for a cast aluminum alloy  

Science.gov (United States)

Life prediction curves for rocket engine pump parts were developed from the results of high-cycle fatigue tests run on cast-aluminum specimens. Notched and smooth specimens were cyclically tested at different mean stress levels at -320 F (78 K). The notch size and mean stress enveloped the design operating conditions. Local stress computed in the groove of the notched specimen was used to represent its fatigue strength. The von Mises criterion was used to determine effective cyclic stresses. The Goodman rule was applied to determine equivalent reversed alternating stresses. The procedure permitted the notched and smooth data sets to each be described by a single curve. High-cycle fatigue life curves were provided for the stress state, mean stress, and stress concentration spanned by the data.

Cooper, R. A.

1979-01-01

28

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.

29

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

Energy Technology Data Exchange (ETDEWEB)

Highlights: {yields} Effect of microstructure on fatigue fracture of an advanced Al-Li alloy was studied in detail. {yields} Preferential crack propagation in T3 state at specific orientations was analyzed. {yields} Fatigue crack propagation difference between T3 and T8 tempers and friction stir welded condition was rationalized. {yields} The effect of grain size on fatigue life for T3 and T8 tempers was justified based on current theories. {yields} 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.

De, P.S. [Center for Friction Stir Processing, Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO 65409 (United States); Mishra, R.S., E-mail: rsmishra@mst.edu [Center for Friction Stir Processing, Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO 65409 (United States); Baumann, J.A. [Boeing Company, St. Louis, MO 631666 (United States)

2011-09-15

30

A multi-temporal scale approach to high cycle fatigue simulation  

Science.gov (United States)

High cycle fatigue (HCF) is a failure mechanism that dominates the life of many engineering components and structures. Time scale associated with HCF loading is a main challenge for developing a simulation based life prediction framework using conventional FEM approach. Motivated by these challenges, the extended space-time method (XTFEM) based on the time discontinuous Galerkin formulation is proposed. For HCF life prediction, XTFEM is coupled with a two-scale continuum damage mechanics model for evaluating the fatigue damage accumulation. Direct numerical simulations of HCF are performed using the proposed methodology on a notched specimen of AISI 304L steel. It is shown the total fatigue life can be accurately predicted using the proposed simulation approach based on XTFEM. The presented computational framework can be extended for predicting the service and the residual life of structural components.

Bhamare, Sagar; Eason, Thomas; Spottswood, Stephen; Mannava, Seetha R.; Vasudevan, Vijay K.; Qian, Dong

2014-02-01

31

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

32

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. (author)

33

High-cycle fatigue properties of small-bore socket-welded pipe joint  

International Nuclear Information System (INIS)

Piping and equipment in nuclear power plants are structures including many welded joints. Reliability of welded joints is one of high-priority issues to improve the safety of nuclear power plants. However, occurrence of fatigue failures in small-bore socket-welded pipe joints by high-cycle vibrations is still reported. In this study, fatigue experiments on a socket-welded joint of austenitic stainless steel pipe was conducted under excitation conditions similar to those in actual plants to investigate vibration characteristics and fatigue strength. It was found that the natural frequency of pipe with socket-welded joint gradually decreased as fatigue damage developed, according to the Miner rule for fatigue life evaluation. The results indicate that the fatigue life of the welded pipe joint could be estimated by monitoring the decreasing ratio of the natural frequency of the pipe. The evaluation of decreasing ratio of the natural frequency in addition to fatigue damage evaluation by the Miner rule could enhance the accuracy of fatigue life evaluation. (author)

34

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

Directory of Open Access Journals (Sweden)

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.

E. Bayraktar

2010-06-01

35

High Cycle Fatigue Behavior of Shot-Peened Steels  

Science.gov (United States)

The uniaxial fully reversed (R = -1) long life fatigue behavior of four shot-peened engineering steels with approximately the same hardness was investigated. Shot-peening, air-cooled forged AISI 1141 and crackable AISI 1070 steels had little effect on their fatigue limits (+2.5 and -2.0 pct, respectively). In the case of a powder forged 0.5 pct C steel, an increase in the fatigue limit of 10.4 pct was observed, albeit with a large standard deviation. Shot-peening quench and tempered AISI 1151 steel decreased its fatigue limit 12.0 pct, as a result of cyclic softening. In general, the beneficial effects of shot-peening these smooth specimens were relatively small. Neither cyclic softening nor hardening occurred in the non-shot-peened steels cycled under the same conditions.

Mirzazadeh, M. M.; Plumtree, A.

2012-08-01

36

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.

37

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

38

Probabilistic high cycle fatigue failure analysis with application to liquid propellant rocket engines  

Science.gov (United States)

A probabilistic high cycle fatigue (HCF) failure analysis of a welded duct in a rocket engine of the Space Shuttle main engine class is described. A state-of-the-art HCF failure prediction method was used in a Monte Carlo simulation to generate a distribution of failure lives. A stochastic stress/life model is used for material characterization, and a composite stress history is generated for accurately deriving the stress cycles for the fatigue-damage calculations. The HCF failure model expresses fatigue life as a function of stochastic parameters including environment, loads, material properties, geometry, and model specification errors. A series of HCF failure life analyses were performed to study the impact of a fixed parameter and to assess the importance of each stochastic input parameter through marginal analyses.

Sutharshana, S.; Newlin, L.; Ebbeler, D.; Moore, N.; O'Hara, K.

1990-01-01

39

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 ? 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.

40

Fatigue crack initiation life prediction of railroad  

Energy Technology Data Exchange (ETDEWEB)

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

Tehrani, P Hosseini; Saket, M, E-mail: hosseini_t@iust.ac.i, E-mail: M_Saket@rail.iust.ac.i [Department of Railway Engineering, Iran University of Science and Technology, Narmak, 16846, Tehran (Iran, Islamic Republic of)

2009-08-01

 
 
 
 
41

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)

42

High-Cycle Fatigue Behavior of Microarc Oxidation Coatings Deposited on a 6061-T6 Al Alloy  

Science.gov (United States)

The objective of this article is to evaluate the influence of microarc oxidation (MAO) coatings on the high-cycle rotating bending fatigue behavior of the 6061-T6 aluminum alloy. Toward this purpose, the influence of the MAO coating process parameter (current density) and coating thickness on the fatigue life of the 6061-T6 Al alloy has been evaluated in the present study. In addition, the influence of the coating roughness on the fatigue life of the MAO-coated 6061-T6 Al-alloy sample has also been investigated. The results indicate that the high-cycle fatigue life of the 6061-T6 Al alloy is substantially degraded due to the presence of MAO coatings, especially at lower alternating stress values and for thicker coatings. Surface roughness, altered by polishing, does not have any effect on fatigue life. An examination of coated samples interrupted at various fractions of fatigue life leads to the conclusion that the crack propagates from the coating surface to the coating-substrate interface very rapidly and thus fatigue life is largely controlled by the propagation of the crack into the substrate.

Wasekar, Nitin P.; Ravi, N.; Suresh Babu, P.; Rama Krishna, L.; Sundararajan, G.

2010-01-01

43

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

Science.gov (United States)

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

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

2014-01-01

44

High-cycle fatigue tests of modified 316 stainless steels under 20 MeV proton irradiation and thermal pulses  

International Nuclear Information System (INIS)

In situ radiation damage and thermal pulses considerably modify the high cycle fatigue property of solution treated specimens of the modified 316L stainless steels, where the observed effects show a characteristic relationship with the chemical composition of the specimens. For the specimens which show a low work-hardening exponent, the fatigue life elongates under irradiation. In contrast, the fatigue life of the specimens which show a high work-hardening exponent is shortened under irradiation. A probable dislocation-defect interaction responsible for these effects is discussed. (orig.)

45

High cycle fatigue tests of low carbon 316 stainless steels under 20 MeV proton irradiation and thermal pulse  

International Nuclear Information System (INIS)

The effects of in situ 20 MeV proton pulse-irradiation and thermal-pulse on the high-cycle fatigue properties of low carbon 316 stainless steels were investigated at 333-573 K with variations of carbon content, 0.001, 0.002 and 0.005 mass%C, and were compared with those reported for 316 stainless steels with 0.038 mass%C and 316(ST-1) with 0.077 mass%C. The fatigue hardening associated with the fatigue induced precipitation decreased with decreasing carbon content. For the case of high C content, the fatigue induced precipitation played the major role in the whole fatigue process, where the fatigue life Nf could considerably be modified by in situ thermal-pulse and radiation damage through their effects on the fatigue induced precipitation. In contrast, for the case of low C content, the fatigue hardening was associated with both the fatigue induced precipitation and the usual work hardening, where the different effects of radiation damage and thermal-pulse were found on the fatigue hardening and the fatigue life Nf: At 333 K, radiation damage caused enhancement of the fatigue hardening and a decrease in Nf, and thermal-pulse caused suppression of the fatigue hardening and an increase in Nf. We surmised that under radiation damage as well as thermal-pulse, Nf was modified mainly through some changes in the usual work hardening process and on the other hand, the fatigue hardening preferentially reflected the changes in the fatigue induced precipitation. For both 316PSI and 316P, suppression of the fatigue hardening due to radiation damage was observed, suggesting that even in 316PSI and 316P the fatigue induced precipitation occurred but the precipitates (or carbon-solute complexes) were too fine to stand against irradiation dispersion. (author)

46

Interaction of High-cycle and Low-cycle Fatigue of Haynes 188 Alloy at 1400 F Deg  

Science.gov (United States)

The interaction of low-cycle fatigue (LCF) and high-cycle fatigue (HCF) was evaluated at the NASA Lewis Research Center on Haynes 188 alloy at 1400 F. Completely reversed, axial-load, strain-controlled fatigue tests were performed to determine the baseline data for this study. Additional specimens for interaction tests were cycled first at a high strain range for various small portions of expected LCF life followed by a step change to a low strain range to failure in HCF. Failure was defined as complete specimen separation. The resultant lives varied between 10 and 5000 cycles for the low-cycle fatigue tests and between 4500 and 3 million for the high-cycle fatigue tests. For the interaction tests the low-cycle-life portion ranged from 30 and 1000 applied cycles while the high-frequency life ranged from 300 and 300,000 cycles to failure. The step change results showed a significant nonlinear interaction in expected life. Application of a small part of the LCF life drastically decreased the available HCF life as compared with what would have been expected by the classical linear damage rule (LDR).

Bizon, P. T.; Thoma, D. J.; Halford, G. R.

1985-01-01

47

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)

48

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

International Nuclear Information System (INIS)

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

49

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-07-01

50

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

Science.gov (United States)

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

Knobbe, H.; Köster, P.; Krupp, U.; Christ, H.-J.; Fritzen, C.-P.

2010-07-01

51

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

International Nuclear Information System (INIS)

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

52

High cycle fatigue properties of type 316 stainless steel  

International Nuclear Information System (INIS)

Strain-controlled fatigue tests using a flexural resonant vibration were performed on miniature specimens of the solution treated 316 stainless steel with the total strain amplitude ?t ? 12 x 10-4 at temperatures between 293 K and 573 K. From the investigations of in situ changes in the resonant period, P, and in the drive force, DF, applied to the specimens during the fatigue tests, the following results were obtained. (1) Overlapped on general changes in P and DF, small and step-like changes in P and DF were observed for ?t larger than the fatigue limit and were considered to be associated with the proceeding of fatigue damages. (2) General changes of P at the middle stage during the fatigue tests were a slight increase (softening) at T = 333 K but a strong decrease (hardening) at T = 573 K. From the detailed study of the above mentioned phenomena, it was concluded that the fatigue test with ?t above the fatigue limit induced an age hardening at T = 573 K. The age hardening became to be revealed above T = 473 K and increased in magnitude with increasing ?t. (author)

53

High cycle fatigue properties of type 316 stainless steel  

International Nuclear Information System (INIS)

Strain-controlled fatigue tests using a flexural resonant vibration were performed on the miniature specimens of the solution treated 316 stainless steel up to 12 x 10-4 in the total strain amplitude, ?t, between 293 K and 573 K. From the investigations of in situ changes in the resonant period, P, and in the drive force, DF, applied to the specimens during the fatigue tests, the following are obtained. (1) Overlapped on general changes in P and DF, small and step-like changes in P and DF were observed for ?t above the fatigue limit and were considered to be associated with a proceeding of fatigue damages. (2) The general change of P observed in the middle stage during the fatigue tests showed a tendency of stableness or increase (softening) at T = 333 K but a strong decrease (hardening) at T = 573 K. From the detailed investigation into the above mentioned phenomena, it was concluded that the fatigue test with ?t above the fatigue limit itself induced an age hardening at T = 573 K but not at T = 333 K. The age hardening became to be revealed above T = 473 K and increased in magnitude with increasing ?t. (author)

54

Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl  

Science.gov (United States)

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

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

2002-01-01

55

Very high cycle fatigue crack initiation in electroplated Ni films under extreme stress gradients  

International Nuclear Information System (INIS)

A characterization technique based on kilohertz micro-resonators is presented to investigate the very high cycle fatigue behavior of 20 ?m thick electroplated Ni films with a columnar microstructure (grain diameter less than 2 ?m). The films exhibit superior fatigue resistance due to the extreme stress gradients at the surface. The effects of stress amplitude and environment on the formation of fatigue extrusions and micro-cracks are discussed based on scanning electron microscopy and the tracking of the specimens’ resonant frequency.

56

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

57

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

Science.gov (United States)

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

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

2011-01-01

58

A multi-scale approach for high cycle anisotropic fatigue resistance: Application to forged components  

International Nuclear Information System (INIS)

Forged components exhibit good mechanical strength, particularly in terms of high cycle fatigue properties. This is due to the specific microstructure resulting from large plastic deformation as in a forging process. The goal of this study is to account for critical phenomena such as the anisotropy of the fatigue resistance in order to perform high cycle fatigue simulations on industrial forged components. Standard high cycle fatigue criteria usually give good results for isotropic behaviors but are not suitable for components with anisotropic features. The aim is to represent explicitly this anisotropy at a lower scale compared to the process scale and determined local coefficients needed to simulate a real case. We developed a multi-scale approach by considering the statistical morphology and mechanical characteristics of the microstructure to represent explicitly each element. From stochastic experimental data, realistic microstructures were reconstructed in order to perform high cycle fatigue simulations on it with different orientations. The meshing was improved by a local refinement of each interface and simulations were performed on each representative elementary volume. The local mechanical anisotropy is taken into account through the distribution of particles. Fatigue parameters identified at the microscale can then be used at the macroscale on the forged component. The linkage of these data and the process scale is the fiber vector and the deformation state, used to calculate global mechanical anisotropy. Numerical results reveal an expected behavior compared to experimental tendencies. We proved numerically the dependence of the anisotropy direction and the deformation state on the endurance limit evolution.

59

The influence of growth rate and temperature on high cycle fatigue of Al-Al3Ni  

Science.gov (United States)

High-cycle fatigue tests have been conducted on specimens of an Al-Al3Ni eutectic alloy, unidirectionally solidified at selected rates from 0.000139 to 0.3 cm/sec. Tests were conducted in air at 298, 458 and 683 K. Room temperature fatigue lives were independent of growth rate at low solidification rates but were markedly improved in samples grown at 0.3 cm/sec. Materials grown at 0.00833 cm/sec exhibited fatigue lives similar to those of the lower growth rates, despite gross misalignment due to cellular growth. The dependence of fatigue life on growth rate at elevated temperatures appears to be due primarily to differences in cyclic creep rates as a result of varying interfiber spacings. Crack initiation and propagation mechanisms were established by metallographic and fractographic examination. Dislocation substructure-fiber interactions were studied by transmission electron microscopy.

Maurer, G. E.; Duquette, D. J.; Stoloff, N. S.

1976-01-01

60

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

Energy Technology Data Exchange (ETDEWEB)

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

Zay, K., E-mail: zay.khaung@tu-clausthal.de [Clausthal University of Technology, Institute of Materials Science and Engineering, Clausthal-Zellerfeld D-38678 (Germany); Maawad, E. [Clausthal University of Technology, Institute of Materials Science and Engineering, Clausthal-Zellerfeld D-38678 (Germany); Brokmeier, H.-G. [Clausthal University of Technology, Institute of Materials Science and Engineering, Clausthal-Zellerfeld D-38678 (Germany); GKSS Research Center, Geesthacht D-21502 (Germany); Wagner, L. [Clausthal University of Technology, Institute of Materials Science and Engineering, Clausthal-Zellerfeld D-38678 (Germany); Genzel, Ch. [Helmholtz-Zentrum Berlin (BESSY-II), Berlin (Germany)

2011-03-15

 
 
 
 
61

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

International Nuclear Information System (INIS)

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

62

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.

63

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

Directory of Open Access Journals (Sweden)

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.

May Mohamed El

2014-06-01

64

Analysis of methods for determining high cycle fatigue strength of a material with investigation of titanium-aluminum-vanadium gigacycle fatigue behavior  

Science.gov (United States)

Today, aerospace engineers still grapple with the qualitative and quantitative understanding of fatigue behavior in the design and testing of turbine-driven jet engines. The Department of Defense has taken a very active role in addressing this problem with the formation of the National High Cycle Fatigue Science & Technology Program in 1994. The primary goal of this program is to further the understanding of high cycle fatigue (HCF) behavior and develop methods in order to mitigate the negative impact of HCF on aerospace operations. This research supports this program by addressing the fatigue strength testing guidance currently provided by the DoD to engine manufacturers, with the primary goal to investigate current methods and recommend a test strategy to characterize the fatigue strength of a material at a specified number of cycles, such as the 109 design goal specified by MIL-HDBK-1783B, or range of cycles. The research utilized the benefits of numerical simulation to initially investigate the staircase method for use in fatigue strength testing. The staircase method is a commonly used fatigue strength test, but its ability to characterize fatigue strength variability is extremely suspect. A modified staircase approach was developed and shown to significantly reduce bias and scatter in estimates for fatigue strength variance. Experimental validation of this proposed test strategy was accomplished using a dual-phase Ti-6Al-4V alloy. The HCF behavior of a second material with a very different microstructure (beta annealed Ti-6Al-4V) was also investigated. The random fatigue limit (RFL) model, a recently developed analysis tool, was investigated to characterize stress-life behavior but found to have difficulty representing fatigue life curves with sharp transitions. Two alternative models (bilinear and hyperbolic) were developed based on maximum likelihood methods to better characterize the Ti-6Al-4V fatigue life behavior. These models provided a good fit to the experimental data for the dual-phase Ti-6Al-4V and were applied to the beta annealed variant in order to estimate stress-life behavior using a small-sample approach. Based on this research, designers should be better able to make reliable estimates of fatigue strength parameters using small-sample testing.

Pollak, Randall D.

65

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

66

High cycle fatigue of squeeze cast AL/SiC{sub w} composites  

Energy Technology Data Exchange (ETDEWEB)

The high cycle fatigue behavior of squeeze cast SiC whisker-reinforced aluminum composites based on either A356 Al or A390 Al matrices has been studied. Squeeze cast Al/SiC{sub w} specimens, which contain roughly 17 vol.% whiskers from two different sources, have been examined for their high cycle fatigue strength under fully reversed test conditions using a staircase method to determine the mean fatigue strength at 10{sup 7} cycles. The results show 30-40% increases in the fatigue strength of the A356 Al-based composites when compared to the unreinforced matrix alloy, but much less fatigue strengthening in the A390 Al-based composites. A fractographic analysis indicates that about 80% of the composite specimens fail as a result of crack initiation within regions which are characterized by low volume fractions of the SiC whiskers. These reinforcement-free regions assume two forms: continuous 'veins', which are the more deleterious to fatigue, and discontinuous 'unreinforced areas,' which are deleterious only in certain shapes and sizes. Both finite element analysis and an Eshelby-based analysis indicate that the localized stresses within the unreinforced regions appear to be high enough to initiate fatigue cracks, especially if unreinforced areas are elongated and their major axis is aligned to the stress axis. The fractographic analysis also identifies the importance of primary Si particles in limiting the fatigue strength of the A390 Al-based composites. (orig.)

Kim, S.-B.; Koss, D.A. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering; Gerard, D.A. [G.M. Powertrain, 1629 Washington Avenue, Saginaw, MI (United States)

2000-01-31

67

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)

68

Influence of anodizing process on fatigue life of a machined aluminium alloy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In order to investigate the coupled effects of machining and anodizing processes on fatigue life of alloy 7010-T7451, a series of rotating bending fatigue tests were conducted at 60Hz. In the as machined condition, test results showed that fatigue life is surface roughness dependent and that fatigue life decreases with an increase in surface roughness and this effect is found to be more pronounced in high cycle fatigue where major portion of fatigue life is consumed in nucleating the cracks. ...

Shahzad, Majid; Chaussumier, Michel; Chieragatti, Re?my; Mabru, Catherine; Rezai?-aria, Farhad

2010-01-01

69

Robust high-cycle fatigue stress threshold optimization under uncertain loadings  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english This paper proposes a strategy to achieve robust optimization of structures against high-cycle fatigue when a potentially large number of uncertain load cases are considered. The strategy is heavily based on a convexity property of some of the most commonly used high-cycle design criteria. The conve [...] xity property is rigorously proven for the Crossland fatigue criterion. The proof uses a perturbation technique and involves the principal stress components and analytical expressions for the applicable fatigue criteria. The multiplicity of load cases is treated using load ratios which are bounded but are otherwise free to vary within certain limits. The strategy is applied to a notched plate subject to traditional normal and shear loadings that possess uncertain or unspecified components.

Alfredo R. de, Faria; Roberto T. C., Frota Jr..

70

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

71

Effects of load ratio, R, and test temperature on high cycle fatigue behavior of nano-structured Al-4Y-4Ni-X alloy composites  

Energy Technology Data Exchange (ETDEWEB)

Nanostructured Al-4Y-4Ni-X composites created by extruding atomized amorphous powders at different extrusion ratios were tested under high cycle bending fatigue at load ratios, R=0.1, 0.33 and -1 at room temperature, 149 Degree-Sign C and 260 Degree-Sign C. Increasing the extrusion ratio generally improved the fatigue life and the fatigue limits were well in excess of that obtained on conventional aluminum alloys at all temperatures tested. The fatigue limits obtained in this work were also compared to previously reported values for a nanostructured composite Al-Gd-Ni-Fe alloy produced via similar means.

El-Shabasy, Adel B., E-mail: ashabasy@hotmail.com [Department of Design and Production Engineering, Faculty of Engineering, Ain Shams University, Cairo 11517 (Egypt); Hassan, Hala A. [Department of Design and Production Engineering, Faculty of Engineering, Ain Shams University, Cairo 11517 (Egypt); Lewandowski, John J. [Department of Material' s Science and Engineering, Case Western Reserve University, Cleveland, OH 44106 (United States)

2012-12-15

72

Effects of in-situ proton-irradiation and thermal-pulse on the high-cycle fatigue properties of low carbon 316 stainless steels  

International Nuclear Information System (INIS)

For the modified 316L stainless steel in which the dislocation interaction governs the fatigue hardening process, the high-cycle fatigue tests were carried out between 300 and 403 K. The in situ irradiation tests and the in situ thermal-pulse tests indicate that dislocation rearrangements due to thermal-pulse give rise to an increase in the areal density of persistent slip bands (PSBs), resulting in elongation of the fatigue life Nf, and an introduction of obstacles to dislocation motions, irradiation induced lattice defects or the fatigue induced precipitates, brings about a decrease in the areal density of PSBs, giving shortening of Nf. (orig.)

73

Effects of load ratio, R, and test temperature on high cycle fatigue behavior of nano-structured Al–4Y–4Ni–X alloy composites  

International Nuclear Information System (INIS)

Nanostructured Al–4Y–4Ni–X composites created by extruding atomized amorphous powders at different extrusion ratios were tested under high cycle bending fatigue at load ratios, R=0.1, 0.33 and ?1 at room temperature, 149 °C and 260 °C. Increasing the extrusion ratio generally improved the fatigue life and the fatigue limits were well in excess of that obtained on conventional aluminum alloys at all temperatures tested. The fatigue limits obtained in this work were also compared to previously reported values for a nanostructured composite Al–Gd–Ni–Fe alloy produced via similar means.

74

Cyclic fatigue analysis of rocket thrust chambers. Volume 2: Attitude control thruster high cycle fatigue  

Science.gov (United States)

A finite element stress analysis was performed for the film cooled throat section of an attitude control thruster. The anlaysis employed the RETSCP finite element computer program. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the thruster operating cycle. The configuration and operating conditions considered, correspond to a flightweight integrated thruster assembly which was thrust pulse tested. The computed strain range was used in conjuction with Haynes 188 Universal Slopes minimum life data to predict throat section fatigue life. The computed number of cycles to failure was greater than the number of pulses to which the thruster was experimentally subjected without failure.

Miller, R. W.

1974-01-01

75

Probabilistic multi-scale models and measurements of self-heating under multiaxial high cycle fatigue  

International Nuclear Information System (INIS)

Different approaches have been proposed to link high cycle fatigue properties to thermal measurements under cyclic loadings, usually referred to as 'self-heating tests'. This paper focuses on two models whose parameters are tuned by resorting to self-heating tests and then used to predict high cycle fatigue properties. The first model is based upon a yield surface approach to account for stress multi-axiality at a microscopic scale, whereas the second one relies on a probabilistic modelling of micro-plasticity at the scale of slip-planes. Both model identifications are cost effective, relying mainly on quickly obtained temperature data in self-heating tests. They both describe the influence of the stress heterogeneity, the volume effect and the hydrostatic stress on fatigue limits. The thermal effects and mean fatigue limit predictions are in good agreement with experimental results for in and out-of phase tension-torsion loadings. In the case of fatigue under non-proportional loading paths, the mean fatigue limit prediction error of the critical shear stress approach is three times less than with the yield surface approach. (authors)

76

Effects of laser peening treatment on high cycle fatigue and crack propagation behaviors in austenitic stainless steel  

International Nuclear Information System (INIS)

Laser peening without protective coating (LPwC) treatment is one of surface enhancement techniques using an impact wave of high pressure plasma induced by laser pulse irradiation. High compressive residual stress was induced by the LPwC treatment on the surface of low-carbon type austenitic stainless steel SUS316L. The affected depth reached about 1mm from the surface. High cycle fatigue tests with four-points rotating bending loading were carried out to confirm the effects of the LPwC treatment on fatigue strength and surface fatigue crack propagation behaviors. The fatigue strength was remarkably improved by the LPwC treatment over the whole regime of fatigue life up to 108 cycles. Specimens with a pre-crack from a small artificial hole due to fatigue loading were used for the quantitative study on the effect of the LPwC treatment. The fracture mechanics investigation on the pre-cracked specimens showed that the LPwC treatment restrained the further propagation of the pre-crack if the stress intensity factor range ?K on the crack tip was less than 7.6 MPa?m. Surface cracks preferentially propagated into the depth direction as predicted through ?K analysis on the crack by taking account of the compressive residual stresses due to the LPwC treatment. (author)

77

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

International Nuclear Information System (INIS)

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

78

Interaction of high cycle fatigue and creep in 9%Cr-1%Mo steel at elevated temperature  

International Nuclear Information System (INIS)

High-cycle-fatigue/creep experiments were performed on a 9%Cr-1%Mo tempered martensite ferritic steel at 873 K in air. The stress ratio R = ?min/?max ranged from -1 (''pure'' fatigue) to 1 (''pure'' creep). The maximum stress ?max was kept constant at 240 MPa.The lifetime depends on the stress ratio R in a non-monotonic way. In the stress ratio interval 0.6 mean of the stress cycle. In the stress ratio interval -1 a. The fatigue/creep interaction occurs in between these intervals. The fatigue/creep loading induces transformation of the tempered martensite ferritic structure into an equiaxed subgrain structure. The resulting subgrain size depends strongly on the stress ratio. (author)

79

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

Directory of Open Access Journals (Sweden)

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.

Nikitin Alexander

2014-06-01

80

Effect of Fatigue Behavior on Microstructural Features in a Cast Al-12Si-CuNiMg Alloy Under High Cycle Fatigue Loading  

Science.gov (United States)

High cycle fatigue tests of a cast Al-12Si-CuNiMg alloy are carried out under different stress amplitudes at room temperature. The scanning and transmission electron microscopy observations are used to examine the fracture surfaces and dislocation structures of the tested material, respectively. The results show that the fatigue damage originates from the microstructural defects, and the fracture surface morphology is typical quasi-cleavage fracture. With the increasing strain amplitude, the material fatigue life obviously decreases; however, the dislocation density increases significantly, which leads to the formation of the dislocation walls and cells. Under the cycle loading, the eutectic Si phase and the secondary particles undergo fracture. The pinning effect of the precipitates on the dislocations becomes obvious, indicating that the Al-12Si-CuNiMg alloy has the cyclic hardening characteristic.

Liu, Jinxiang; Zhang, Qing; Zuo, Zhengxing; Xiong, Yi

2013-12-01

 
 
 
 
81

Study of crack initiation or damage in very high cycle fatigue using ultrasonic fatigue test and microstructure analysis.  

Science.gov (United States)

Fatigue damage behaviors of four metal materials in the very high cycle fatigue (VHCF) regime have been studied using ultrasonic fatigue test and microstructure analysis. The results show that the fatigue crack initiation in VHCF regime could occur at subsurface non-defect fatigue crack origin (SNDFCO), where the accumulated cyclic strains or damage in the specimens were highly localized, especially in the materials with some softer phase, where the local maximum strain can be eight times higher than the average strain value in the specimen. This high strain localization can cause a local plasticity exhaustion that leads to a stress concentration and consequently fatigue crack initiation, and finally the formation of SNDFCO. For pure single phase austenitic material, strain localization can also occur due to dislocation accumulation at or near grain boundaries, which can become fatigue crack initiation origin in the VHCF regime. The results in this study show that fatigue damage and crack initiation mechanisms in the VHCF regime can be different in different metals due to the mechanisms for local plasticity exhaustion. PMID:23850182

Chai, Guocai; Zhou, Nian

2013-12-01

82

Effects of High Mean Stress on High-cycle Fatigue Behavior of PWA 1480  

Science.gov (United States)

PWA 1480 is a potential candidate material for use in the high-pressure fuel turbine blade of the space shuttle main engine. As an engine material it will be subjected to high-cycle fatigue loading superimposed on a high mean stress due to combined centrifugal and thermal loadings. The present paper describes the results obtained in an ongoing program at the Argonne National Laboratory, sponsored by NASA Lewis, to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material. Straight-gauge high-cycle fatigue specimens, 0.2 inch in diameter and with the specimen axis in the 001 direction, were supplied by NASA Lewis. The nominal room temperature yield and ultimate strength of the material were 146 and 154 ksi, respectively. Each specimen was polished with 1-micron diamond paste prior to testing. However, the surface of each specimen contained many pores, some of which were as large as 50 micron. In the initial tests, specimens were subjected to axial-strain-controlled cycles. However, very little cyclic plasticity was observed.

Majumdar, S.; Antolovich, S. D.; Milligan, W. W.

1985-01-01

83

Variations of Fatigue Damage Growth in Cross-Ply and Quasi-Isotropic laminates Under High-Cycle Fatigue Loading  

Science.gov (United States)

The behavior of transverse crack growth and delamination growth under high-cycle fatigue loadings was investigated with cross-ply CFRP laminates, [0/902]s and [0/906]s, and quasi-isotropic CFRP laminates, [45/0/-45/90]s. As a result, it was observed that the behavior of damage growth was different depending on the applied stress level. The growth of local or edge delamination was exacerbated under the test conditions of a low applied stress level and high-cycle loadings, because the areas of stress concentration were applied with high-cyclic loadings. On the other hand, when the fatigue tests were conducted under the applied stress level of 40% of the transverse crack initiation, the growth of transverse cracks was hardly observed until 108 cycles with [0/902]s, [0/906]s and [45/0/-45/90]s laminates.

Hosoi, Atsushi; Shi, Jiadi; Sato, Narumichi; Kawada, Hiroyuki

84

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

85

Surface-finish effects on the high-cycle fatigue of Alloy 718  

International Nuclear Information System (INIS)

Alloy 718 us a precipitation-hardening nickel-base superalloy that is being specified for various components for liquid-meal fast breeder reactors (LMFBRs). This alloy maintains high strength at elevated temperatures making it a desirable structural material. But the property that justifies most LMFBR applications is the alloy's resistance to thermal striping damage due to its high fatigue endurance strength. Thermal striping is a high-cycle fatigue phenomenon caused by thermal stresses from the fluctuating mixing action of sodium streams of differing temperatures impinging on the metal surfaces. Most of the design data is generated from laboratory fatigue specimens with carefully controlled surface finishes prepared with a low-stress grind and buffed to a surface finish 8--12 in. Since Alloy 718 has been shown to be quite notch sensitive under cyclic loading, the detrimental effect on the high-cycle fatigue properties caused by shop surface finishes of actual components has been questioned. This report examines some of the surface finishes that could be produced in a commercial shop on an actual component

86

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)

87

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

88

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

Energy Technology Data Exchange (ETDEWEB)

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.

Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio; Demura, Masahiko [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Matsuoka, Saburo [Kyushu University, 744, Motooka, Nishi-ku, Fukuoka, Fukuoka 819-0395 (Japan); Sunakawa, Hideo [Japan Aerospace Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505 (Japan)

2014-01-27

89

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

Science.gov (United States)

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.

Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio; Demura, Masahiko; Matsuoka, Saburo; Sunakawa, Hideo

2014-01-01

90

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

Science.gov (United States)

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

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

2007-01-01

91

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

92

A mechanism of sub-surface crack growth in very high cycle fatigue  

International Nuclear Information System (INIS)

This study carried out uniaxial tension fatigue tests of Ti-6Al-4V focusing on sub-surface fractures in very high cycle regime. Crack growth properties in high vacuum were also investigated to simulate sub-surface crack propagation, which is kept away from atmosphere in principle. Fracture surfaces were closely compared between the sub-surface crack and the crack propagated in vacuum. As a result, it was clarified that crack growth rate in vacuum was much lower than that in air, which corresponded to longer fatigue lives of sub-surface fractures. Fracture surfaces between the sub-surface crack and the crack propagated in vacuum were quite similar showing a unique granular feature with fine concave convexo pattern. The granular fracture surface was never observed in surface-originating cracks; therefore, it was considered a key process of sub-surface crack growth. The granular features also resembled so-called ODA region of sub-surface fractures in high strength steel. Based on this observation, a common mechanism of sub-surface crack growth regardless of materials was discussed for very high cycle fatigue phenomena. (author)

93

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

CERN Document Server

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...

Heikkinen, Samuli; Wuensch, Walter

2010-01-01

94

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

Science.gov (United States)

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

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

2006-01-01

95

Shot-Peening Effect on High Cycling Fatigue of Al-Cu Alloy  

Science.gov (United States)

The present work was aimed at evaluating the effects of shot-peening on the high cycle fatigue performance of the age-hardening aircraft alloy Al 2024 at different almen intensities. Shot-peening to full coverage (100 pct) was performed using spherically conditioned cut wire (SCCW 14) with an average shot size of 0.36 mm and at almen intensities of 0.1, 0.2, and 0.3 mmA. After applying the various mechanical surface treatments, the changes in the surface and near-surface layer properties such as microhardness, residual stress-depth profiles, and surface roughness were determined. The microhardness, surface roughness, and the residual stresses increased proportionally with the almen intensity. Electropolitically polished conditions were used as reference in the mechanically surface treated specimens. A significant improvement was seen in the fatigue performance of the 0.1 mmA.

Fouad, Yasser; Metwally, Mostafa El

2013-12-01

96

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1982-11-01

97

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.)

98

Piezoelectric driven testing facilities to research the very high cycle fatigue regime  

Energy Technology Data Exchange (ETDEWEB)

Cyclic low amplitude loading and a huge number of cycles characterizes the Very High Cycle Fatigue (VHCF) regime. The challenge in research of the Very High Cycle Fatigue regime is to apply this large number of cycles to fracture in an acceptable time frame. For this reason, it is essential to use a machine, which is able to operate at high frequencies of cycles. Two testing machine concepts with piezo actuators are presented in this study. In the first concept, a high performance piezo stack actuator is presented, in which the specimen and the load cell are mechanically assembled in series. This set-up applies forces up to 10 kN and testing frequencies up to 1000 Hz. The second testing facility is a hybrid testing system, which consists of an inertial mass actuator and a servo hydraulic actuator connected in parallel. Both systems are capable of testing normal specimen dimensions and provide the possibility to work with variable as well as constant amplitude loading. (orig.)

Fischer, Christian [Technische Univ. Darmstadt (Germany). Inst. of System Reliability and Machine Acoustics; Wagener, Rainer; Friedmann, Andreas; Matthias, Michael; Melz, Tobias; Kaufmann, Heinz [Fraunhofer-Institut fuer Betriebsfestigkeit (LBF), Darmstadt (Germany); Axt, Christoph [ISYS Adaptive Solutions GmbH, Darmstadt (Germany)

2012-07-01

99

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

Science.gov (United States)

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

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

2000-01-01

100

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)

 
 
 
 
101

High-cycle fatigue properties of low carbon 316 stainless steel under 20 MeV proton irradiation and thermal-pulse  

International Nuclear Information System (INIS)

The high-cycle fatigue properties of low carbon 316 stainless steels, 316F with 0.038 %C(mass%), 316PSI with 0.001 %C and 316P with 0.002 %C, and effects of in situ 20 MeV proton irradiation and thermal-pulse on them were investigated in between 333 and 573K, and compared with the results reported on 316 (ST-1) with 0.77 %C. the fatigue hardening reported on 316 (ST-1) was again observed in 316F, 316PSI and 316P but decreased with decreasing C-content. The fact suggests that the fatigue hardening was mainly associated with fatigue induced carbides or some carbon-solute complexes. Thermal-pulse always suppressed the fatigue hardening, suggesting a shortening of the fatigue life under thermal-pulses. The results for the fatigue life of 316F at 333K under thermal-pulses appeared to confirm this prediction. The effects of in situ irradiation were variable: The fatigue hardening was always enhanced in 316(ST-1). In contrast, in 316PSI and 316P the fatigue hardening was suppressed at early elapsed cycles, where it was surmised that effects of irradiation dispersion of fatigue induced precipitates were larger than other effects of irradiation. The effects of irradiation in 316F were intermediate between those in 316 (ST-1) and in 316PSI and 316P. The fatigue life of 316F at 333K became shorter for the tests with small Nf of ? 105 cycle and longer for those with large Nf of ? 106 cycle under irradiation, where Nf denotes the elapsed cycles to failure. The present results demonstrate the significant effects of in situ irradiation and thermal-pulse on the fatigue properties. (author)

102

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

DEFF Research Database (Denmark)

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

BrØndsted, P.

2002-01-01

103

Hydrogen induced surface cracking in an 8090 Al-Li alloy during high cycle fatigue  

Energy Technology Data Exchange (ETDEWEB)

In recent years, there has been an increasing interest in understanding the effects of aggressive or moist environments on the properties of Al-Li alloys. However, most of the existing work has been focused on their stress corrosion cracking resistance. Consequently, only a few reports are available on the environmental fatigue strength of these alloys. Upon exposure to aggressive environments, the fatigue crack propagation resistance can be detrimentally affected. R. Piascik and R. Gangloff found enhanced cyclic crack growth rates in an Al-Li-Cu alloy when a critical water vapor pressure was exceeded. Thermodynamically, at atmospheric pressures, strong interactions between hydrogen and lithium are expected to give rise to stable lithium hydrides. Evidence for the development of hydride phases in Al-Li alloys exposed to hydrogen environments has been reported by various workers. Thus, it is likely that HE via hydride formation can be the relevant mechanisms in Al-Li alloys that have been in contact with hydrogen. Since lithium hydrides are stable up to temperatures of 773 K, previous hydrogen exposure can lead to an irreversible mode of embrittlement. Thus, it was the objective of the present work to investigate the effects of hydrogen during aging on the ensuing high cycle fatigue (HCF) performance of an 8090 Al-Li alloy.

Laffin, C.; Raghunath, C.R.; Lopez, H.F. (Univ. of Wisconsin, Milwaukee, WI (United States). Materials Dept.)

1993-10-01

104

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

Science.gov (United States)

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.

Salajegheh, Nima

105

Study of the influence of microstructure on fatigue crack propagation in the high cycle fatigue regime in 316L steel  

International Nuclear Information System (INIS)

Full text of publication follows: In the High cycle fatigue regime, about 80 percent of the fatigue live of austenitic stainless steel specimens consists in the propagation of short cracks whose length is comparable to the size of few grains. This high sensitivity of crack propagation to microstructure can explain partly the dispersion that is observed in this regime. At very low load level close to the fatigue limit, this dispersion can reach a factor 100 which complicates predictions of fatigue lives of large structures in service. As a consequence, to assess and predict this dispersion, it is necessary to understand better how microstructure influences locally crack propagation, i.e., the development of cyclic plasticity at the crack tip. In this aim, we propose to describe the influence of crystallographic orientation on the cyclic behavior of the grains of 316L stainless steel using crystal plasticity theory. In a first step, the stress strain response of the 316L grains is simulated using elastic-plastic constitutive equations that have been implemented in the three dimensional finite element code Cast3m of the CEA. The evolution of the resolved shear stress on each slip system is described with a non linear kinematics hardening law. This law is identified using cyclic stress strain curves obtained on austenitic stainless steel monocrystal. In a second step, the crack tip opening displacement (CTOD) will be calculated for different crystallographic orientation in order to quantify the influence of the crystallographic orientation of the grain at the crack tip on crack propagation. A statistic treatment of the CTOD values obtained from the finite element simulations performed at the local scale of the grain can help to understand the dispersion observed at the macroscopic scale. (authors)

106

The Effect of Casting Conditions on the High-Cycle Fatigue Properties of the Single-Crystal Nickel-Base Superalloy PWA 1483  

Science.gov (United States)

Different solidification conditions are employed to produce sets of single-crystal samples with different primary dendrite arm spacings, i.e., 600 ?m, 400 ?m, and 250 ?m. The material with the smaller dendrite arm spacing is shown to possess considerably increased high-cycle fatigue life. Fatigue cracks are found to originate from shrinkage porosity rather than from carbides, in which the size of the largest pores in the samples scales with the primary dendrite arm spacing. Fatigue life can be rationalized using a fracture mechanics approach based on a Kitagawa Takahashi plot. The impact of the results with respect to the development of new commercial casting processes that produce higher temperature gradients and cooling rates will be discussed.

Lamm, M.; Singer, R. F.

2007-06-01

107

The Effect of a Non-Gaussian Random Loading on High-Cycle Fatigue of a Thermally Post-Buckled Structure  

Science.gov (United States)

High-cycle fatigue of an elastic-plastic beam structure under the combined action of thermal and high-intensity non-Gaussian acoustic loadings is considered. Such loadings can be highly damaging when snap-through motion occurs between thermally post-buckled equilibria. The simulated non-Gaussian loadings investigated have a range of skewness and kurtosis typical of turbulent boundary layer pressure fluctuations in the vicinity of forward facing steps. Further, the duration and steadiness of high excursion peaks is comparable to that found in such turbulent boundary layer data. Response and fatigue life estimates are found to be insensitive to the loading distribution, with the minor exception of cases involving plastic deformation. In contrast, the fatigue life estimate was found to be highly affected by a different type of non-Gaussian loading having bursts of high excursion peaks.

Rizzi, Stephen A.; Behnke, marlana N.; Przekop, Adam

2010-01-01

108

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

Science.gov (United States)

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.

Zhang, YangYang; Duan, Zheng; Shi, HuiJi

2013-03-01

109

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

Science.gov (United States)

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.

Shanyavskiy, A. A.

2014-01-01

110

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

2012-01-01

111

Investigation of Thermal High Cycle and Low Cycle Fatigue Mechanisms of Thick Thermal Barrier Coatings  

Science.gov (United States)

Ceramic thermal barrier coatings have attracted increased attention for diesel engine applications. The advantages of using the ceramic coatings include a potential increase in efficiency and power density and a decrease in maintenance cost. Zirconia-based ceramics are the most important coating materials for such applications because of their low thermal conductivity, relatively high thermal expansivity and excellent mechanical properties. However, durability of thick thermal barrier coatings (TBCS) under severe temperature cycling encountered in engine conditions, remains a major question. The thermal transients associated with the start/stop and no-load/full-load engine cycle, and with the in-cylinder combustion process, generate thermal low cycle fatigue (LCF) and thermal high cycle fatigue (HCF) in the coating system. Therefore, the failure mechanisms of thick TBCs are expected to be quite different from those of thin TBCs under these temperature transients. The coating failure is related not only to thermal expansion mismatch and oxidation of the bond coats and substrates, but also to the steep thermal stress gradients induced in the coating systems. Although it has been reported that stresses generated by thermal transients can initiate surface and interface cracks in a coating system, the mechanisms of the crack propagation and of coating failure under the complex LCF and HCF conditions are still not understood. In this paper, the thermal fatigue behavior of an yttria partially stabilized zirconia coating system under simulated LCF and HCF engine conditions is investigated. The effects of LCF and HCF on surface crack initiation and propagation are also discussed.

Zhu, Dong-Ming; Miller, Robert A.

1998-01-01

112

Influence of High Cycle Thermal Loads on Thermal Fatigue Behavior of Thick Thermal Barrier Coatings  

Science.gov (United States)

Thick thermal barrier coating systems in a diesel engine experience severe thermal Low Cycle Fatigue (LCF) and High Cycle Fatigue (HCF) during engine operation. In the present study, the mechanisms of fatigue crack initiation and propagation, as well as of coating failure, under thermal loads which simulate engine conditions, are investigated using a high power CO2 laser. In general, surface vertical cracks initiate early and grow continuously under LCF and HCF cyclic stresses. It is found that in the absence of interfacial oxidation, the failure associated with LCF is closely related to coating sintering and creep at high temperatures, which induce tensile stresses in the coating after cooling. Experiments show that the HCF cycles are very damaging to the coating systems. The combined LCF and HCF tests produced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. It is suggested that the HCF component cannot only accelerate the surface crack initiation, but also interact with the LCF by contributing to the crack growth at high temperatures. The increased LCF stress intensity at the crack tip due to the HCF component enhances the subsequent LCF crack growth. Conversely, since a faster HCF crack growth rate will be expected with lower effective compressive stresses in the coating, the LCF cycles also facilitate the HCF crack growth at high temperatures by stress relaxation process. A surface wedging model has been proposed to account for the HCF crack growth in the coating system. This mechanism predicts that HCF damage effect increases with increasing temperature swing, the thermal expansion coefficient and the elastic modulus of the ceramic coating, as well as the HCF interacting depth. A good agreement has been found between the analysis and experimental evidence.

Zhu, Dongming; Miller, Robert A.

1997-01-01

113

A High cycle fatigue behavior of squeeze cast A356 Al/SiC{sub w} and A390 Al/SiC{sub w} MMCs  

Energy Technology Data Exchange (ETDEWEB)

Specimens of A356 Al/SiC{sub w} and A390 Al/SiC{sub w} metal matrix composites (MMCs) were produced by squeeze casting and tested under fully reversed high cycle fatigue conditions at room temperature. A staircase method was employed to determine the mean fatigue strength at 10{sup 7} cycles. The presence of 17 vol. % SiC whiskers in the A356 Al alloy increases the fatigue strength by 29%. In contrast, the A390 Al/SiC{sub w} composite, containing identical whisker reinforcements, showed very little improvement of fatigue strength when compared to the matrix alloy. An analysis of the fracture surfaces of both composites shows that fatigue cracks initiated primarily at pre-existing regions within the preforms which are characterized by the absence of the SiC whiskers. The reinforcement-free regions take two forms: continuous veins, which are very deleterious to fatigue, and discontinuous unreinforced regions, which are deleterious only in certain geometries. An analysis is presented to rationalize the geometry effect. Finally, the authors also identify the importance of large primary Si particles in limiting fatigue life of the A390 Al materials.

Kim, S.B.; Koss, D.A. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering; Gerard, D.A. [GM Powertrain, Saginaw, MI (United States)

1997-12-31

114

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

115

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)

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.

Bast, Callie C.; Boyce, Lola

1995-01-01

116

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Portugal | Language: English Abstract in portuguese 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.

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

2008-01-01

117

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Portugal | Language: English Abstract in portuguese 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.

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

118

The Effect of Nitriding Treatment Variables on the Fatigue Limit of Alloy Steel (34crnimo6) Under High Cycle Fatigue  

International Nuclear Information System (INIS)

The aim of this research is to improve the fatigue limit for alloy steel (34CrNiMo6) by salt bath nitriding process. This property is more effective to increase the fatigue life for parts which are used in continuous cyclic loading. All the fatigue tests were implemented before and after nitriding process under rotating bending. Constant and variable capacity stresses were applied before and after nitriding processes. The nitriding process were implemented in salt bath component at three different times (1, 2, 3) hr when temperature was constant at (555 degree centigrade). The depth of the nitride layer reached (0.24, 0.37, 0.5) mm. The nitriding process repeated of another specimens at the same times but the temperature was (600 degree centigrade), the layer depth reached (0.28, 0.41, 0.55) mm. The formation of a high nitrogen iron phases were detected with a layer of the hard chrome nitrides on the surface. The nitriding process is forming the barriers on the surface that resist the initiation and propagation of cracks, as well as generating the compressive residual stresses which delay the progress of fatigue crack. This research deduced that the nitriding processes increased the fatigue limit and this limit is proportional to the time of the nitriding process. When the time increased, the depth of nitride layer is increased, but decreased when the temperature increased to (600 degree centigrade) because of the formation of brittle phase,in spite of the increase in layer depth. (author)

119

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)

120

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)

 
 
 
 
121

Methodologies for predicting fatigue life  

Science.gov (United States)

This article reviews the basic techniques employed in fatigue life prediction. The stress-life, local-strain, and fracture-mechanics methods as applied to life prediction under constant amplitude loading and variable amplitude loading are discussed. Life prediction methodology under variable maplitude loading is also discussed, with particular emphasis on the linear-damage accumulation approach, or Miner's rule. Finally, a discussion of various cycle-counting techniques for variable amplitude loading is given.

Holman, R. K.; Liaw, P. K.

1997-07-01

122

Correlation of low-cycle and high-cycle fatigue data for solution-annealed Incoloy 800  

International Nuclear Information System (INIS)

It is shown that load-controlled high-cycle fatigue test data for Incoloy 800 may be correlated successfully with strain-controlled low-cycle results, provided stress-to-strain conversions and strain-to-stress conversions are made with the aid of cyclic stress-strain curves which must take into consideration steady state, or average, behavior during test. The differences in the initial stress-strain response for load- and strain-control procedures do not appear to significantly influence the correlation. In addition, the strain rate differences for the low- and high-cycle data given do not appear to be important. (Auth.)

123

Fatigue life prediction of stainless steel under variable loading. Damage factors determining fatigue life and damage evaluation for two-step test  

International Nuclear Information System (INIS)

To predict fatigue life under variable loading accurately, it is important to understand the damage factors determining fatigue life. In this study, the damage factors of high-cycle fatigue were investigated for Type 316 stainless steel and a procedure for predicting the fatigue life of two-step tests was discussed. Fully-reversed axial fatigue tests were performed in ambient air at room temperature. In order to evaluate applicability of the linear damage accumulation rule, two-step tests were performed. The crack initiation and propagation were investigated by replica observations. It was found that the linear damage accumulation rule did not always evaluate the fatigue life conservatively due to stress dependence of crack size against normalized fatigue life. Furthermore, the fatigue limit decreased in the two-step test. In order to evaluate the role of cracking on the fatigue life, the surface layer of specimens was removed after the first step of the two-step tests. The fatigue lives of the surface-removed specimens were almost equivalent to that of undamaged specimens, although the fatigue limit was less than that of the undamaged specimens. It was revealed that the fatigue limit of surface-removed specimens decreased due to cyclic softening caused by the cyclic loading in the first step. The fatigue lives correlated with the strain amplitude rather than the stress amplitude and fatigue limit was almost the same for the surface-removed, undamaged, and undamaged specimens subjected to constant strain tests. It was concluded that the fatigue life of Type 316 stainless steel should be predicted based on the strain amplitude even for the high-cycle regime. Accuracy of the fatigue life prediction could be improved by considering the stress dependency of the crack size in addition to the cyclic softening and hardening material behavior. (author)

124

Manifestations of ''high-cycle fatigue'' in the nickel based alloy Inconel 792; Erscheinungsformen von ''High-Cycle-Fatigue'' in der Nickel-Basis Legierung Inconel 792  

Energy Technology Data Exchange (ETDEWEB)

A cluster of turbine rotor blade breakages caused substantial damage to the APU generators used to generate electrical power for aircraft, eventually causing the APU to fail. The APU is located in the tail cone area of all large aircraft directly under the vertical tail. The examination of the damage to the turbine rotor blades revealed the unusual occurrence of the smooth facets which are typical of ''Stage I'' of a high-cycle fatigue fracture. The cracks had propagated from just under the surface of the strain-hardened marginal zone; the repair work being carried out made it difficult to detect the cracks. This presentation demonstrates the distinctive signs of high-cycle fatigue as well as pinpointing the problems associated with identifying these cracks in time during repair work. (orig.)

Wanzek, H.; Gartner, T.; Fruhner, A. [Lufthansa Technik, Hamburg (Germany)

2008-08-15

125

Effect of microstructure on high-cycle fatigue properties of Ti-6Al-4V alloy forging at cryogenic temperatures  

Science.gov (United States)

The effect of microstructure on the high-cycle fatigue properties of Ti-6Al-4V alloy forging at cryogenic temperature was investigated using four materials with different microstructure. One of them was ?+? annealed and has bimodal microstructure which consists of equiaxed-? and ?+? lamellar microstructure. Three other materials were water quenched (WQ), air cooled (AC) or furnace cooled (FC) after ?-annealing. The ?-annealed materials have lamellar microstructure and ? lamellar width increase in the order of WQ, AC and FC materials. The fatigue test was done with uni-axial load-controlled and a stress ratio of R = ?min/?max = 0.01 at 20 K (in gaseous helium), 77 K (in liquid nitrogen) and 293 K (in laboratory air). The 107-cycles fatigue strengths at 20 K decrease in the order of WQ, AC, FC and the ?+? annealed material. Namely, the ?-annealed Ti-6Al-4V alloys, which has lamellar ? microstructures shows higher fatigue strengths than bimodal microstructure.

Yuri, T.; Ono, Y.; Ogata, T.; Sunakawa, H.

2014-01-01

126

On the overall accuracy of the Modified Wöhler Curve Method in estimating high-cycle multiaxial fatigue strength  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of the present paper is to systematically investigate the accuracy of the so-called Modified Wöhler Curve Method (MWCM in estimating high-cycle fatigue strength of plain and notched engineering materials damaged by in-service multiaxial load histories. In more detail, the MWCM, which is a bi-parametrical critical plane approach, postulates that initiation and Stage I propagation of fatigue cracks occur on those material planes experiencing the maximum shear stress amplitude (this being assumed to be always trueindependently from the degree of multiaxiality of the applied loading path. Further, the fatigue damage extent is hypothesised to depend also on the maximum stress perpendicular to the critical plane, the mean normal stress being corrected through the so-called mean stress sensitivity index (i.e., a material constant capable of quantifying the sensitivity of the assessed material to the presence of superimposed static stresses. In the present investigation, the overall accuracy of the MWCM in estimating high-cycle fatigue strength was checked through 704 endurance limits taken from the literature and generated, under multiaxial fatigue loading, by testing both plain and notched samples made of 71 different materials. Such a massive validation exercise allowed us to prove that the MWCM is highly accurate, resulting in 95% of the estimates falling within an errorinterval equal to ±15%.

Luca Susmel

2011-04-01

127

A study on fatigue crack growth in the high cycle domain assuming sinusoidal thermal loading  

International Nuclear Information System (INIS)

The assessment of fatigue crack growth due to turbulent mixing of hot and cold coolants presents significant challenges, in particular to determine the thermal loading spectrum and the associated crack growth. The sinusoidal method is a simplified approach for addressing this problem, in which the entire spectrum is replaced by a sine-wave variation of the temperature at the inner pipe surface. The loading frequency is taken as that which gives the shortest crack initiation and growth life. Such estimates are intended to be conservative but not un-realistic. Several practical issues which arise with this approach have been studied using newly-developed analytical solutions for the temperature and stress fields in hollow cylinders, in particular the assumptions made concerning the crack orientation, dimensions and aspect ratio. The application of the proposed method is illustrated for the pipe geometry and loadings conditions reported for the Civaux 1 case where through wall thermal fatigue cracks developed in a short time, but the problem is relevant also for fast reactor components.

128

Very high-cycle fatigue failure in micron-scale polycrystalline silicon films: Effects of environment and surface oxide thickness  

Science.gov (United States)

Fatigue failure in micron-scale polycrystalline silicon structural films, a phenomenon that is not observed in bulk silicon, can severely impact the durability and reliability of microelectromechanical system devices. Despite several studies on the very high-cycle fatigue behavior of these films (up to 1012cycles), there is still an on-going debate on the precise mechanisms involved. We show here that for devices fabricated in the multiuser microelectromechanical system process (MUMPs) foundry and Sandia Ultra-planar, Multi-level MEMS Technology (SUMMiT V™) process and tested under equi-tension/compression loading at ˜40kHz in different environments, stress-lifetime data exhibit similar trends in fatigue behavior in ambient room air, shorter lifetimes in higher relative humidity environments, and no fatigue failure at all in high vacuum. The transmission electron microscopy of the surface oxides in the test samples shows a four- to sixfold thickening of the surface oxide at stress concentrations after fatigue failure, but no thickening after overload fracture in air or after fatigue cycling in vacuo. We find that such oxide thickening and premature fatigue failure (in air) occur in devices with initial oxide thicknesses of ˜4nm (SUMMiT V™) as well as in devices with much thicker initial oxides ˜20nm (MUMPs). Such results are interpreted and explained by a reaction-layer fatigue mechanism. Specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure of the entire device. The entirety of the evidence presented here strongly indicates that the reaction-layer fatigue mechanism is the governing mechanism for fatigue failure in micron-scale polycrystalline silicon thin films.

Alsem, D. H.; Timmerman, R.; Boyce, B. L.; Stach, E. A.; De Hosson, J. Th. M.; Ritchie, R. O.

2007-01-01

129

Surface crack nucleation and propagation in electrodeposited nanocrystalline Ni-P alloy during high cycle fatigue  

International Nuclear Information System (INIS)

The morphology of specimen surface after fatigue fracture was evaluated in connection with grain orientation distribution and grain boundary microstructure to reveal a mechanism of fatigue fracture in nanocrystalline materials. The electrodeposited and sharply {001} textured Ni -2.0 mass% P alloy with the average grain size of ca. 45 nm and high fractions of low-angle and ?3 boundaries showed 2 times higher fatigue limit than electrodeposited microcrystalline Ni polycrystal. The surface features of fatigued specimen were classified into two different types of morphologies characterized as brittle fracture at the central area and as ductile fracture at the surrounding area.

130

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

Science.gov (United States)

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

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

2000-01-01

131

High cycle thermal fatigue: benchmark at a Te junction piping system of the nuclear power plant Phenix  

International Nuclear Information System (INIS)

This paper presents the studies of the benchmark concerning a high cycle thermal fatigue problem. This benchmark is based on an industrial case, a Te junction piping system of the french FBR Phenix. The main objectives were the comparison of the different methods used by the participants and the analysis of the damage evaluation methods capacity compared to the observed phenomena. This study took place in an international framework with the United Kingdom, Italy, Japan, Korea, Russia, India and France. (A.L.B.)

132

Fatigue life of laser cut metals  

Science.gov (United States)

Fatigue tests were conducted to determine the actual reduction in fatigue life due to weight removal for balancing by: hand grinding, low power (20 watt) Nd:glass laser, and high power (400 watt) Nd:YAG laser.

Martin, M. R.

1986-01-01

133

Simulation of Delamination Propagation in Composites Under High-Cycle Fatigue by Means of Cohesive-Zone Models  

Science.gov (United States)

A damage model for the simulation of delamination propagation under high-cycle fatigue loading is proposed. The basis for the formulation is a cohesive law that links fracture and damage mechanics to establish the evolution of the damage variable in terms of the crack growth rate dA/dN. The damage state is obtained as a function of the loading conditions as well as the experimentally-determined coefficients of the Paris Law crack propagation rates for the material. It is shown that by using the constitutive fatigue damage model in a structural analysis, experimental results can be reproduced without the need of additional model-specific curve-fitting parameters.

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

2006-01-01

134

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

135

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

136

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

International Nuclear Information System (INIS)

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

137

Thermal mixing in T-junction piping system related to high-cycle thermal fatigue in structure  

International Nuclear Information System (INIS)

The numerical simulation code 'MUGTHES' has been developed by the authors to investigate thermal striping phenomena caused by turbulence mixing of fluids at different temperatures and to utilize with an evaluation method for high-cycle thermal fatigue. MUGTHES employs the large eddy simulation (LES) approach to predict unsteady thermal mixing phenomena and the boundary fitted coordinate (BFC) system to fit complex boundary shapes in a reactor. In this paper, thermal striping phenomena in a T-junction piping system (T-pipe) are numerically simulated as a code validation study and the simulation results are used to investigate temperature fluctuation generation mechanism in the T-pipe. The boundary conditions for the simulation are chosen from the WATLON experiment which was a water experiment conducted at JAEA using the T-pipe. In the simulation, the standard Smagorinsky model is employed as a turbulence eddy viscosity model with the model coefficient of 0.14 (=Cs). Numerical results of MUGTHES are compared with experimental velocity and temperature profiles. Applicability of MUGTHES to the thermal striping phenomena is confirmed through the numerical simulation in the T-pipe and the characteristic large-scale vortex structure which dominates thermal mixing and may cause high-cycle thermal fatigue is revealed. (author)

138

High cycle fatigue properties and microstructure of zirconium and zircaloy-4 under reversal bending  

International Nuclear Information System (INIS)

Fatigue lifetime curves of a commercial-purity zirconium and zircaloy-4 were measured under reversal bending. Scanning electron microscopic examination on surfaces of fatigued specimens shows that zirconium displays planar slip, whereas zircaloy-4 displays wavy slip. Fracture surface analysis shows that many fatigue striations with a considerable number of micro-cracks are the primary characters in zirconium and zircaloy-4. Fatigue crack generally nucleates in persistent slip bands and twin-matrix interfaces. One set of stacking fault clusters was detected in zirconium. The stacking fault interface is the feeble barrier to dislocation motion. The typical fatigue dislocation configuration is the dislocation walls apparently parallel to the trace of the prismatic plane, which are separated by long straight screw dislocations perpendicular to walls in the commercial-purity zirconium, and also in zircaloy-4, whereas, zircaloy-4 is easier to cross-slip in comparison with zirconium. Several twins and their fine structures were detected in zirconium and zircaloy-4. The relations between twinning, cracking and slip are discussed. (orig.)

139

High cycle fatigue behavior of a nanostructured composite produced via extrusion of amorphous Al89Gd7Ni3Fe1 alloy powders  

International Nuclear Information System (INIS)

A nanostructured composite Al89Gd7Ni3Fe1 alloy was created by extruding atomized amorphous Al89Gd7Ni3Fe1 powders at different extrusion ratios (ER = 5:1, 10:1, 20:1). The microstructures and mechanical properties produced were examined with special attention given to the high cycle fatigue properties. High cycle fatigue tests were conducted at room temperature under three-point bending at a stress ratio R = 0.1. Increasing the extrusion ratio (ER) improved the hardness, bend strength, and fatigue behavior, with alloys extruded at higher ER exhibiting bend strengths exceeding 1000 MPa and high cycle fatigue behavior well in excess of conventional aluminum alloys. The results obtained are compared to conventional aluminum alloys and particulate reinforced composites.

140

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

Directory of Open Access Journals (Sweden)

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

D.S. Paolino,

2014-11-01

 
 
 
 
141

A parametric study of high cycle thermal fatigue caused by thermal striping  

International Nuclear Information System (INIS)

A numerical scheme is developed and evaluated for fatigue analysis due to thermal oscillation. This model uses calculated instantaneous coolant temperatures at a pipe surface, and then calculates the pipe wall temperature response, stress and stress intensity factor (SIF) separately. A crack propagation correlation is then applied to calculate the initial and final crack size. The model is a useful tool in identifying the relative importance of various parameters affecting fatigue crack failure. Effects of the heat transfer coefficient, the magnitude and frequency of temperature oscillations and the system pressure were evaluated. Results show that the heat transfer coefficient and the magnitude of temperature oscillations are correlated to each other and have a dominant effect on thermal fatigue failure. Also it is found that the frequency can be hazardous within a given range and the increase of system pressure has an adverse effect on the potential failure. (authors)

142

Some regularities of austenite steel structure phase state evolution at high-cycle fatigue  

International Nuclear Information System (INIS)

A study is made into the evolution of grain structure, structural and phase states and defect substructure of austenitic steel type 08Kh18N10T on fatigue testing at frequency of load alternations of 20 Hz and applied stress of 20 MPa. It is shown that under fatigue test conditions the transformation of dislocation structure occurs that is related not only with the process of material deformation but also with dynamic recrystallization. The latter results in the formation of gradient structure characterized by variations of mean longitudinal and lateral grain size, a coefficient of their anisotropy and a texture vector scattering angle as the distance to a fracture surface increases

143

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

International Nuclear Information System (INIS)

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

144

Study of high-cycle fatigue in materials under cantilever plane bending  

International Nuclear Information System (INIS)

UNV-machines intended to investigate a cyclic strength of structural materials in 293-4.2 K temperature range are presented. A technique is described for accelerated fatigue tests at cryogenic temperatures. Cyclic strength values obtained during conventional and accelerated tests of cryogenic materials are given

145

High cycle thermal fatigue crack initiation and growth behavior in the semi-infinite plate model  

International Nuclear Information System (INIS)

At a T-junction in piping systems, hot and cold water mixes in a whirl. The vibrating mixing boundary between the hot and cold water causes a temperature fluctuation on the inner surface of the pipe just after the connection point at T-junction, and this temperature fluctuation yields a cyclic thermal stress near the pipe surface, resulting in crack initiation. In this study the thermal stress distribution was analyzed for a semi-infinite plate model and the fatigue crack growth behavior was examined. The thermal fatigue cracks are arrested and the arrested crack depth is found to be in proportion to the reciprocal root of the frequency of temperature fluctuation

146

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

Directory of Open Access Journals (Sweden)

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.

Vitaly Sergeevich Evgrafov

2014-04-01

147

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-07-01

148

Nitinol Fatigue Life for Variable Strain Amplitude Fatigue  

Science.gov (United States)

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

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

2012-12-01

149

Establishment of a JSME code for the evaluation of high-cycle thermal fatigue in mixing tees  

International Nuclear Information System (INIS)

This paper describes a JSME code for high-cycle thermal fatigue evaluation by thermal striping in mixing tees with hot and cold water flows. The evaluation of thermal striping in a mixing tee has four steps to screen design parameters one-by-one according to the severity of the thermal load assessed from design conditions using several evaluation charts. In order to make these charts, visualization tests with acrylic pipes and temperature measurement tests with metal pipes were conducted. The influence of the configurations of mixing tees, flow velocity ratio, pipe diameter ratio and so on was examined from the results of the experiments. This paper makes a short mention of the process of providing these charts. (author)

150

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

International Nuclear Information System (INIS)

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

151

High cycle fatigue crack propagation under random and constant amplitude loadings  

International Nuclear Information System (INIS)

A summary is presented of work carried out during the period 1963-1973 into the constant and random amplitude fatigue crack propagation performance of a mild steel at ambient temperature. Conventional fracture mechanics parameters are shown to describe the process of propagation under a variety of mean stress intensity conditions. Calculations of random amplitude propagation using 'laws' determined from the constant amplitude data are shown to be in agreement with experimental results. This agreement of calculation and experiment gives confidence in the use of these calculation principles for reactor applications outside direct experimentation. (author)

152

Design and realization of a multisamples rotating high cycle fatigue machine  

Directory of Open Access Journals (Sweden)

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

Massimo Martorelli

2012-10-01

153

High cycle fatigue of bolted connections; Schwingfestigkeit von Schraube-Mutter-Verbindungen  

Energy Technology Data Exchange (ETDEWEB)

Extensive tests regarding the influences on the fatigue of bolt-nut-connections of preloading with torsion, of preloading with yielding, of loading with superimposed bending and of the tested lot are processed. These influences are not yet known according to VDI 2230. New testing devices were designed for these tests, which allow a far less expensive operation and may easily be used for bolts of diameters up to M100 and testing frequencies up to 1000 Hz. The validity of fatigue resistance according to VDI 2230 is specified with respect to the test results. The determined influence of the tested lots is unexpectedly high. The manufacturing process of bolts should be improved to minimize this influence. (Abstract Copyright [2007], Wiley Periodicals, Inc.) [German] Im vorliegenden Beitrag werden Erkenntnisse aus umfangreichen Versuchen zur Ueberlagerung von Zug- und Biegebeanspruchungen, des torsionsbehafteten sowie ueberelastischen Vorspannens und der Charge auf die Schwingfestigkeit von Schraube-Mutter-Verbindungen zusammengefasst, die in der VDI Richtlinie 2230 bislang nicht enthalten sind. Zur Durchfuehrung der Schwingversuche wurden voellig neuartige Resonanzpruefvorrichtungen entwickelt, die einen kostenguenstigeren Betrieb als die bislang eingesetzten Hochfrequenz- und Hydropulser ermoeglichen und die sich fuer Nenndurchmesser bis M100 und Prueffrequenzen bis 1000 Hz eignen. Der Geltungsbereich der Dauerfestigkeit nach VDI 2230 wird aufgrund der Ergebnisse spezifiziert. Der festgestellte ueberraschend hohe Chargeneinfluss gibt Anlass, den Fertigungsprozess von Schrauben zur Begrenzung dieses Einflusses zu praezisieren. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

Mertens, H. [TU Berlin (Germany). Fachgebiet Konstruktionslehre; Arz, U.; Berger, C. [TU Darmstadt (Germany). Institut fuer Werkstoffkunde; Blessing, L. [TU Berlin (Germany). Fachgebiet Konstruktionstechnik und Entwicklungsmethodik; Alt, A.

2007-05-15

154

Effect of stress ratio on high-cycle fatigue properties of Ti-6Al-4V ELI alloy forging at low temperature  

Science.gov (United States)

The effect of the stress ratio R (the ratio of minimum stress to maximum stress) on the high-cycle fatigue properties of Ti-6Al-4V extra-low interstitial (ELI) alloy forging was investigated at 293 and 77 K. At 293 K, the fatigue strength at 107 cycles exhibited deviations below the modified Goodman line in the R=0.01 and 0.5 tests. Moreover, at 77 K, larger deviations of the fatigue strength at 107 cycles below the modified Goodman line were confirmed in the same stress ratio conditions. The high-cycle fatigue strength of the present alloy forging exhibit an anomalous mean stress dependency at both temperatures and this dependency becomes remarkable at low temperature.

Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio; Matsuoka, Saburo; Sunakawa, Hideo

2014-01-01

155

Tensile and high cycle fatigue properties of Zirconium alloy at elevated temperature  

International Nuclear Information System (INIS)

Zirconium (Zr) alloys have been extensively used as cladding materials for fuel elements in nuclear reactor systems due to their low thermal neutron absorption cross-section, excellent corrosion resistance and good mechanical properties at high temperatures. Zirconium alloy containing 1.0 wt% Sn and small amounts of Fe and Cr is widely used as a spacer grid. In the present study, tensile tests were carried out for Zirconium alloy sheet-type specimens with different orientation and temperature conditions. In addition tention-tention fatigue test (stress ratio R=0.1) was studied at room temperature. The specimen surface was observed through scanning electron microscopy (SEM), and fracture mechanisms of the specimens were evaluated

156

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

International Nuclear Information System (INIS)

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

157

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.

158

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

International Nuclear Information System (INIS)

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

159

Coating pre-cracking effect on the LCF fatigue life of superalloys for gas turbine blades  

Energy Technology Data Exchange (ETDEWEB)

Low cycle fatigue (LCF) strain controlled experimental fatigue tests were conducted on the nickel superalloy MAR-M002 used in the construction of gas turbine blades. The aim of the study was to compare dwell times and high cycle fatigue (HCF) and LCF combined cycle fatigue test conditions. The study focused on investigating the potentially detrimental effect of coating cracking. A fatigue test system was equipped with an induction furnace and a high temperature extensometer. A procedure was developed to generate controlled cracking in the coating prior to fatigue testing. Loading modes used in the tests were representative of loads experienced by the superalloy turbine blades when in operation. HCF amplitudes were superimposed on major LCF cycles. It was concluded that coating cracks do not significantly impact the LCF fatigue life of aluminized investment casting nickel superalloy MAR-M002. 7 refs., 1 tab., 12 figs.

Filippini, M.; Foletti, S. [Politecnico di Milano, Milan (Italy); Pasquero, G. [AVIO SpA, Rivalta di Torino (Italy)

2009-07-01

160

High-cycle fatigue of micromachined single-crystal silicon measured using high-resolution patterned specimens  

International Nuclear Information System (INIS)

A single-crystal silicon fatigue test structure was fabricated using high-resolution lithography to improve smoothness and morphological uniformity. An on-chip test structure, including a notched test piece, a resonator, an electrostatic actuator and a deflection sensor, was fabricated using 0.6 µm resolution lithography. Fatigue tests were performed under different deflection amplitudes and humidity conditions. The lifetime scattering was limited nearly within 1 order at each condition, and this was a large improvement over other reported studies. Our test results indicated a clear tendency for the lifetime to lengthen when the strain amplitude or ambient humidity was decreased. Strain–life behaviors at two different humidity conditions were analyzed using Paris law and crack propagation exponents of 19.6 and 23.0 were obtained at 50%RH and 25%RH, respectively. A humidity dependence was clearly confirmed by the results of our low-scattering experiment. Moreover, for this measurement, a new parallel test system was built in which fatigue tests on up to 12 samples could be performed simultaneously. The drive circuit, which enables a deflection-controlled fatigue test, is described and its performance was demonstrated

 
 
 
 
161

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

Science.gov (United States)

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.

Forman, R. G.; Zanganeh, M.

2014-01-01

162

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)

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)

Lehericy, Y

2007-05-15

163

Multiscale Fatigue Life Prediction for Composite Panels  

Science.gov (United States)

Fatigue life prediction capabilities have been incorporated into the HyperSizer Composite Analysis and Structural Sizing Software. The fatigue damage model is introduced at the fiber/matrix constituent scale through HyperSizer s coupling with NASA s MAC/GMC micromechanics software. This enables prediction of the micro scale damage progression throughout stiffened and sandwich panels as a function of cycles leading ultimately to simulated panel failure. The fatigue model implementation uses a cycle jumping technique such that, rather than applying a specified number of additional cycles, a specified local damage increment is specified and the number of additional cycles to reach this damage increment is calculated. In this way, the effect of stress redistribution due to damage-induced stiffness change is captured, but the fatigue simulations remain computationally efficient. The model is compared to experimental fatigue life data for two composite facesheet/foam core sandwich panels, demonstrating very good agreement.

Bednarcyk, Brett A.; Yarrington, Phillip W.; Arnold, Steven M.

2012-01-01

164

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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.

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

165

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)

166

Influence of sodium on the low- and high-cycle fatigue behaviour of type 304 stainless steel  

International Nuclear Information System (INIS)

Strain controlled LCF-tests were performed on X 6 CrNi 18 11 steel (Type 304 ss) in air and flowing sodium in a non-isothermal sodium loop. The results measured at 550 0C in an upstream position of the sodium loop show an increase in fatigue life in the strain range from about 1.5 % to 0.4 % for the base material in the as-received condition while the welded joints remain unaffected by the environment. The LCF-behaviour of base material specimens tested at 500 0C in a downstream position after a prior pre-exposure to sodium (4058 h, 500 0C) is also improved in comparison to parallel specimens tested in air with comparable thermal aging. Load controlled HCF-tests performed on X 6 CrNi 18 11 steel at 550 0C show a significant increase in fatigue life in the low cycle region (Nsub(f) 6 cycles) and a higher endurance limit for the base material in sodium but no influence of the environment is indicated for the welded joints. (author)

167

Effect of different distribution condition of fatigue loads on fatigue life  

International Nuclear Information System (INIS)

In this article, 3 distribution styles, i.e, normal distribution, log-normal distribution and Gamma distribution, are used to simulate the variety of fatigue loads S. Same average value of fatigue loads variety S and different coefficient of variation C are adopted in every distribution style, and corresponding fatigue life Nrand and the average fatigue life Navg in the condition of S=S are calculated. By comparing the fatigue life Nrand and Navg, a rule can be found that when the average value of fatigue loads variety is small, the fatigue life will first increase and decrease later with the increasing of the coefficient of variation, and when the average value of the fatigue loads variety is large, the fatigue life will always decrease while the coefficient of variation increases. (authors)

168

High cycle fatigue behavior of implant Ti-6Al-4V in air and simulated body fluid.  

Science.gov (United States)

Ti-6Al-4V implants that function as artificial joints are usually subjected to long-term cyclic loading. To study long-term fatigue behaviors of implant Ti-6Al-4V in vitro and in vivo conditions exceeding 107 cycles, constant stress amplitude fatigue experiments were carried out at ultrasonic frequency (20 kHz) with two different surface conditions (ground and polished) in ambient air and in a simulated body fluid. The initiation mechanisms of fatigue cracks were investigated with scanning electron microscopy. Improvement of fatigue strength is pronounced for polished specimens below 106 cycles in ambient air since fatigue cracks are initiated from surfaces of specimens. While the cycles exceed 106, surface conditions have no effect on fatigue behaviors because the defects located within the specimens become favorable sites for crack initiation. The endurance limit at 108 cycles of polished Ti-6Al-4V specimens decreases by 7% if it is cycled in simulated body fluid instead of ambient air. Fracture surfaces show that fatigue failure is initiated from surfaces in simulated body fluid. Surface improvement has a beneficial effect on fatigue behaviors of Ti-6Al-4V at high stress amplitudes. The fatigue properties of Ti-6Al-4V deteriorate and the mean endurance limits decrease significantly in simulated body fluid. PMID:24211906

Liu, Yong-jie; Cui, Shi-ming; He, Chao; Li, Jiu-kai; Wang, Qing-yuan

2014-01-01

169

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

Science.gov (United States)

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

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

2000-01-01

170

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)

171

Aluminum/boron composite - fatigue life prediction  

International Nuclear Information System (INIS)

The fatigue behaviour of a 6061-0 aluminum alloy reinforce with 0.25 volume fraction undirectional boron fibres of 100 ?m diameter has been investigated. The specimens were tested under constant stress amplitude using a stress ratio (minimum/maximum stress) of 0.2 with the fibres oriented at an angle to the loading direction in order to study the matrix dominated fatigue behaviour. Two sets of data were obtained for unidirectional specimens tested with fibre to load axis angles of 200 and 450 A third set of data was obtained with V 45 angle-ply specimens. It is shown that a microstress/strain analysis in conjunction with a multiaxial fatigue parameter can be applied to successfully predict the fatigue lives of these boron reinforced aluminum alloy composites. The multiaxial parameter enables a generalized strain-life relationship to be determined using limited experimental data. Once this generalized relationship is known, the life of the composite cycled under different loads and load-fibre angles can be predicted. (author)

172

High-cycle fatigue behavior of Incoloy alloy 800H in a simulated HTGR helium environment containing high moisture levels  

International Nuclear Information System (INIS)

A study has been carried out to evaluate the highcycle fatigue strength of Incoloy alloy 800H in a high-temperature gas-cooled reactor helium environment containing significant quantities of moisture. As-heat-treated and thermally aged materials were tested to determine the effects of long-term oxidation in the helium test gas. Results from these tests were compared to those for a standard air environment. It was found that the mechanisms of fatigue failure were complex and involved recovery/recrystallization of the surface-ground layer on the specimens, sensitization, work hardening, oxide scale integrity, and oxidation at the tips of propagating cracks. For certain situations, a corrosion-fatigue process seems to be important. However, for the helium environment studied, the fatigue strength was nearly always higher than that for air

173

Fatigue Life of Superalloy Haynes 188 in Hydrogen  

Science.gov (United States)

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

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

2012-08-01

174

Experimental study on high cycle thermal fatigue in T-junction. Effect of local flow velocity on transfer of temperature fluctuation from fluid to structure  

International Nuclear Information System (INIS)

A quantitative evaluation on high cycle thermal fatigue due to temperature fluctuation in fluid is of importance for structural integrity in the reactor. It is necessary for the quantitative evaluation to investigate occurrence and propagation processes of temperature fluctuation, e.g., decay of fluctuation intensity near structures and transfer of temperature fluctuation from fluid to structures. The JSME published a guideline for evaluation of high-cycle thermal fatigue of a pipe as the JSME guideline in 2003. This JSME standard covers T-pipe junction used in LWRs operated in Japan. In the guideline, the effective heat transfer coefficients were obtained from temperature fluctuations in fluid and structure in experiments. In the previous studies, the effective heat transfer coefficients were 2 - 10 times larger than the heat transfer coefficients under steady state conditions in a straight tube. In this study, a water experiment of T-junction was performed to evaluate the transfer characteristics of temperature fluctuation from fluid to structure. In the experiment, temperatures in fluid and structure were measured simultaneously at 20 positions to obtain spatial distributions of the effective heat transfer coefficient. In addition, temperatures in structure and local velocities in fluid were measured simultaneously to evaluate the correlation between the temperature and velocity under the non-stationary fields. The large heat transfer coefficients were registered at the region where the local velocity was high. Furthermore it was found that the heat transfer coefficients were correlated with the time-averaged turbulent heat flux near the pipe wall. (author)

175

Fatigue life and crack growth prediction methodology  

Science.gov (United States)

This paper reviews the capabilities of a plasticity-induced crack-closure model and life-prediction code to predict fatigue crack growth and fatigue lives of metallic materials. Crack-tip constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (Delta K(sub eff)) under constant amplitude loading. Some modifications to the Delta K(sub eff)-rate relations were needed in the near threshold regime to fit small-crackgrowth rate behavior and endurance limits. The model was then used to calculate small- and large-crack growth rates, and in some cases total fatigue lives, for several aluminum and titanium alloys under constant-amplitude, variable-amplitude, and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks. Results from the tests and analyses agreed well.

Newman, J. C., Jr.; Phillips, E. P.; Everett, Richard A., Jr.

1994-03-01

176

Fatigue life prediction of shot peened components  

Scientific Electronic Library Online (English)

Full Text Available SciELO Portugal | Language: English Abstract in portuguese A grenalhagem é um dos tratamentos mais eficientes na prevenção da iniciação de fendas por fadiga e na fase inicial de propagação. Grande parte dos estudos sobre o feito da grenalhagem no comportamento à fadiga são experimentais. Praticamente não existem trabalhos publicados relativos ao estudo de p [...] revisão do comportamento da grenalhagem. Neste trabalho são usados modelos tradicionais, de determinação da vida à fadiga, em componentes grenalhados. O método dos elementos finitos é usado para determinar a tensão, extensão e energia de deformação de provetes grenalhados que foram testados experimentalmente. Estes resultados são usados em modelos de previsão da vida total à fadiga. É apresentada uma discussão sobre a capacidade dos modelos usados na previsão de vida à fadiga de provetes que foram testados experimentalmente. Abstract in english Shot peening is one of the most effective surface treatments in order to prevent crack initiation and early crack propagation. Part of the studies to determine the fatigue performance of shot peening are based on experimental tests. Almost no work is published related with the prediction of shot pee [...] ning behaviour. The present paper evaluates the ability of the current methodologies, used to predict fatigue life, on components treated with shot peening. The Finite Element Method was used to determine the stress, strain and strain energy due to shot peening of some specimens tested experimentally. These results were used to apply methods to predict the total fatigue life. A final discussion is presented about the ability of the methods used, to predict the fatigue life of the specimens tested experimentally.

R.A., Cláudio; J.M., Silva; C.M., Branco; J., Byrne.

177

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)

178

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

Directory of Open Access Journals (Sweden)

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.

Houria M. Iben

2014-06-01

179

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)

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.

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

2012-07-01

180

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

International Nuclear Information System (INIS)

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

 
 
 
 
181

Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations  

Science.gov (United States)

A methodology is presented for determining the fatigue life of bonded composite skin/stringer structures based on delamination fatigue characterization data and geometric nonlinear finite element analyses. Results were compared to fatigue tests on stringer flange/skin specimens to verify the approach.

Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin

2000-01-01

182

Towards a unified fatigue life prediction method for marine structures  

CERN Document Server

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 ...

Cui, Weicheng; Wang, Fang

2014-01-01

183

A new concept for high-cycle-life LEO: Rechargeable MnO2-hydrogen  

Science.gov (United States)

The nickel-hydrogen secondary battery system, developed in the early 1970s, has become the system of choice for geostationary earth orbit (GEO) applications. However, for low earth orbit (LEO) satellites with long expected lifetimes the nickel positive limits performance. This requires derating of the cell to achieve very long cycle life. A new system, rechargeable MnO2-Hydrogen, which does not require derating, is described here. For LEO applications, it promises to have longer cycle life, high rate capability, a higher effective energy density, and much lower self-discharge behavior than those of the nickel-hydrogen system.

Appleby, A. J.; Dhar, H. P.; Kim, Y. J.; Murphy, O. J.

1989-01-01

184

Effect of spectral shape on acoustic fatigue life estimates  

Science.gov (United States)

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

Miles, R. N.

1992-01-01

185

A Question of Location - Life with Fatigue after Stroke  

DEFF Research Database (Denmark)

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.

Andersen, Michael

2014-01-01

186

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)

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

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

2013-12-01

187

Life prediction of creep fatigue at very high temperatures  

International Nuclear Information System (INIS)

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

188

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)

189

How surface damage removal affects fatigue life  

Science.gov (United States)

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

Jeelani, S.; Scott, M. A.

1988-01-01

190

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)

191

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

International Nuclear Information System (INIS)

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

192

Influence of static magnetic field on fatigue life  

International Nuclear Information System (INIS)

The crack growth rate in a central notched carbon steel plate was not affected by static magnetic field under cyclic tension fatigue, but under reversed torsional fatigue some decrease of fatigue life was clearly observed in a static magnetic field for carbon steel bar. The decrease of fatigue life changed with specimen configuration, temperature, shear stress amplitude, specimen support condition. The additional tensile stress which gave almost same decrease of torsional fatigue life in the magnetic field was confirmed experimentally to be 20-50 MPa. The magnetostriction of tested steel was shrinkage in the longitudinal direction and elongation in the circumferential direction, and the volume magnetostriction was zero in this experimental condition. Some shift of fracture appearance to that of higher stress level were observed in a magnetic field: it would suggest a shear stress increase by the magnetic moment due to the Wertheim effect in which a circumferential magnetic field appears in a longitudinally magnetized bar when twisted. (author)

193

Fatigue life estimation of shot peened metal using accelerated life testing  

International Nuclear Information System (INIS)

Shot peening process is used as one of the various kinds of techniques to improve the fatigue properties. However, to obtain fatigue properties of metal materials, many efforts and time are needed. Because the fatigue life of shot peened metals increases highly. In this paper, fatigue properties of shot peened Al 7075-T6 are estimated using the fundamental of accelerated life test to reduce the experimental. Experimental results show that the estimated life data almost agree with actual rotary bending fatigue test data within 7% error

194

The effect of creep cavitation on the fatigue life under creep-fatigue interaction  

International Nuclear Information System (INIS)

Low cycle fatigue tests have been carried out with three different materials (1Cr-Mo-V steel, 12Cr-Mo-V steel and 304 stainless steel) for the investigation of the effect of surface roughness on the fatigue life. To see the effect systematically, we have chosen those materials which may or may not form grain boundary cavities.Test results show that the continuous fatigue life of 1Cr-Mo-V steel and aged 304 stainless steel with a rough surface is decreased compared with that of the specimens with a smooth surface. These two alloys are found to have no grain boundary cavities formed under creep-fatigue test conditions. On the contrary, the fatigue life of 12Cr-Mo-V steel and solutionized 304 stainless steel in which grain boundary cavities are formed under creep-fatigue test conditions is not influenced by the states of surface roughness.The characteristic test results strongly confirm that the fatigue life of the specimen under creep-fatigue interaction, during which creep cavities are forming, may be controlled by the cavity nucleation and growth processes rather than the process of surface crack initiation. ((orig.))

195

Application of strain-controlled fatigue concepts to the prediction of weldment fatigue life  

International Nuclear Information System (INIS)

The total fatigue life of weldments has been estimated for butt welds using strain controlled fatigue and fatigue crack propagation concepts. Key developments which facilitated these estimates were the assumption of Ksub(f max) conditions (the largest value of Ksub(f) possible for a given weld shape). The total fatigue life was estimated as the sum of a fatigue crack initiation period (cycles to obtain a 0.25 mm fatigue crack) and the fatigue crack propagation period. Mean stress relaxation effects and the fatigue properties of the actual weld zone materials were considered. Influence of welding residual stresses and material strength level were also investigated. The initiation life was found to be very sensitive to changes in Ksub(f) but not too sensitive to strength level. The importance of residual stresses and mean stress varied with material as did the fraction of total life devoted to crack initiation. Mild steels, quenched and tempered high strength low alloy steels, and aluminium alloy welds were considered. (orig.) 891 RW/orig. 892 RKD

196

Fatigue tests and life estimation of Incoloy alloy 908  

International Nuclear Information System (INIS)

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

197

Fatigue life estimation in welded joints under multiaxial loadings  

Directory of Open Access Journals (Sweden)

Full Text Available Welded joints are frequently locations for cracks initiation and propagation that may cause fatigue failure of engineering structures. Biaxial or triaxial stress-strain states are present in the vicinity of welded joints, due to local geometrical constraints, welding processes and/or multiaxial external loadings. Fatigue life evaluation of welded joints under multiaxial proportional (in-phase cyclic loading can be performed by using conventional hypotheses (e.g. see the von Mises criterion or the Tresca criterion on the basis of local approaches. On the contrary, the fatigue life predictions of welded joints under non-proportional (out-ofphase cyclic loading are generally unsafe if these conventional hypotheses are used. A criterion initially proposed by the authors for smooth and notched structural components has been extended to the fatigue assessment of welded joints. In more detail, fatigue life of welded joints under multiaxial stress states can be evaluated by considering a nonlinear combination of the shear stress amplitude (acting on the critical plane and the amplitude and the mean value of the normal stress (acting on the critical plane. In the present paper, fatigue lifetimes predicted through the proposed criterion are compared with experimental fatigue life data available in the literature, related to fatigue biaxial tests.

Sabrina Vantadori

2009-07-01

198

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

DEFF Research Database (Denmark)

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.

Lambertsen, SØren Heide; Damkilde, Lars

2013-01-01

199

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 specimens 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.

Søren Heide Lambertsen

2013-06-01

200

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

Science.gov (United States)

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.

Qi, Huan; Azer, Magdi; Deal, Andrew

2012-11-01

 
 
 
 
201

Experimental study on thermal hydraulics of high cycle thermal fatigue. Temperature fluctuation in mixing tee and parallel triple jets along wall  

International Nuclear Information System (INIS)

When temperature fluctuation in fluid is transferred to the structure, it induces thermal load via thermal expansion of the structure. If the fluid temperature fluctuation amplitude and then thermal stress are large, structural integrity might be lost due to high cycle thermal fatigue, i.e., thermal striping. Several incidents due to the thermal striping have occurred in nuclear power plants. Water experiments were carried out for thermal hydraulic aspects of the thermal striping. A mixing tee and a triple-parallel jet along wall were selected as the test geometry. Detailed temperature and velocity fields were measured by movable thermocouple trees and particle image velocimetry. The power spectrum density (PSD) of temperature fluctuation can be estimated by a representative curve, when the flow velocity ratio and then flow pattern was identical. Comparison of frequency characteristics between the temperature and velocity showed that the temperature fluctuation in the mixing tee was caused by flow structure like Karman vortex behind the jet exiting from the branch pipe in case of a wall jet condition. (author)

202

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

Science.gov (United States)

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

Zhao, Lihui; Zheng, Songlin; Feng, Jinzhi

2014-09-01

203

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

Science.gov (United States)

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

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

204

Probabilistic fatigue life prediction of metallic and composite materials  

Science.gov (United States)

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

Xiang, Yibing

205

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)

206

Development of fatigue life evaluation method using small specimen  

Energy Technology Data Exchange (ETDEWEB)

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

Nogami, Shuhei, E-mail: shuhei.nogami@qse.tohoku.ac.jp [Department of Quantum Science and Energy Engineering, Tohoku University, 6-6-01-2, Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8579 (Japan); Nishimura, Arata [National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292 (Japan); Wakai, Eichi [Japan Atomic Energy Agency, 2-4 Shirakata Shirane, Tokai, Naka, Ibaraki 319-1195 (Japan); Tanigawa, Hiroyasu [Japan Atomic Energy Agency, 2-166 Oaza-Obuchi-Aza-Omotedate, Rokkasho, Kamikita, Aomori 039-3212 (Japan); Itoh, Takamoto [Department of Mechanical Engineering, University of Fukui, 3-9-1, Bunkyo, Fukui 910-8507 (Japan); Hasegawa, Akira [Department of Quantum Science and Energy Engineering, Tohoku University, 6-6-01-2, Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8579 (Japan)

2013-10-15

207

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

208

Development of fatigue life evaluation method using small specimen  

Science.gov (United States)

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

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

2013-10-01

209

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.)

210

Light scattering diagnostics for metal fatigue detection and life estimation  

Science.gov (United States)

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

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

2005-08-01

211

FATIGUE LIFE EVALUATION OF SUSPENSION KNUCKLE USING MULTIBODY SIMULATION TECHNIQUE  

Directory of Open Access Journals (Sweden)

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.

A.G.A. Rahman

2012-12-01

212

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

International Nuclear Information System (INIS)

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

213

Thermomechanical fatigue life prediction of high temperature components  

Energy Technology Data Exchange (ETDEWEB)

The aim of the work described in this paper is to provide a computational method for fatigue life prediction of high temperature components, in which the time and temperature dependent fatigue crack growth is a relevant damage mechanism. The fatigue life prediction is based on a law for microcrack growth and a fracture mechanics estimate of the cyclic crack tip opening displacement. In addition, a powerful model for nonisothermal cyclic plasticity is employed, and an efficient laboratory test procedure is proposed for the determination of the model parameters. The models are efficiently implemented into finite element programs and are used to predict the fatigue life of a cast iron exhaust manifold and a notch in the perimeter of a turbine rotor made of a ferritic/martensitic 10%-chromium steel. (orig.)

Seifert, Thomas; Hartrott, Philipp von; Riedel, Hermann; Siegele, Dieter [Fraunhofer-Inst. fuer Werkstoffmechanik (IWM), Freiburg (Germany)

2009-07-01

214

APPLICATION OF MULTIBODY SIMULATION FOR FATIGUE LIFE ESTIMATION  

Directory of Open Access Journals (Sweden)

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.

M. Kamal

2013-06-01

215

A comparison of fatigue life prediction methodologies for rotorcraft  

Science.gov (United States)

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

Everett, R. A., Jr.

1990-01-01

216

Dramatic increase in fatigue life in hierarchical graphene composites.  

Science.gov (United States)

We report the synthesis and fatigue characterization of fiberglass/epoxy composites with various weight fractions of graphene platelets infiltrated into the epoxy resin as well as directly spray-coated on to the glass microfibers. Remarkably only ?0.2% (with respect to the epoxy resin weight and ?0.02% with respect to the entire laminate weight) of graphene additives enhanced the fatigue life of the composite in the flexural bending mode by up to 1200-fold. By contrast, under uniaxial tensile fatigue conditions, the graphene fillers resulted in ?3-5-fold increase in fatigue life. The fatigue life increase (in the flexural bending mode) with graphene additives was ?1-2 orders of magnitude superior to those obtained using carbon nanotubes. In situ ultrasound analysis of the nanocomposite during the cyclic fatigue test suggests that the graphene network toughens the fiberglass/epoxy-matrix interface and prevents the delamination/buckling of the glass microfibers under compressive stress. Such fatigue-resistant hierarchical materials show potential to improve the safety, reliability, and cost effectiveness of fiber-reinforced composites that are increasingly the material of choice in the aerospace, automotive, marine, sports, biomedical, and wind energy industries. PMID:20863061

Yavari, F; Rafiee, M A; Rafiee, J; Yu, Z-Z; Koratkar, N

2010-10-01

217

Improved methods of creep-fatigue life assessment of components  

Energy Technology Data Exchange (ETDEWEB)

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.)

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

2009-07-01

218

Surface fatigue life of high temperature gear materials  

Science.gov (United States)

Three high temperature gear materials were evaluated using spur gear surface fatigue tests. These materials were, VASCO max 350, VASCO matrix 2, and nitralloy N and were evaluated for possible use in high temperature gear applications. The fatigue life of the three high temperature gear materials were compared with the life of the standard AISI 9310 aircraft gear material. Surface fatigue tests were conducted at a lubricant inlet temperature of 321 K (120 F), a lubricant outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), a speed of 10,000 rpm, and with a synthetic paraffinic lubricant. The life of the nitralloy N was approximately the same as the AISI 9310, the life of the VASCO max 350 was much less than the AISI 9310 while the life of the VASCO matrix 2 was several times the life of the AISI 9310. The VASCO max 350 also showed very low fracture toughness with approximately half of the gears failed by tooth fracture through the fatigue spall. The VASCO matrix 2 had approximately 10-percent fracture failure through the fatigue spalls indicating moderate to good fracture toughness.

Townsend, Dennis P.

1994-04-01

219

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)

220

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 strength for sample that cooled by oil (medium cooling rate.The  fatigue test results show increasing in the fatigue life for samples that cooled by oil.

Ali S. Yasir

2013-07-01

 
 
 
 
221

Fatigue Life Prediction of Composite Under Two Block Loading  

Directory of Open Access Journals (Sweden)

Full Text Available The damage evolution mechanism is one of the important focuses of fatigue behaviour investigation of composite materials and also the foundation to predict fatigue life of composite structures for engineering applications. This paper is dedicated to damage investigation of composite materials under two block loading cycle fatigue conditions. The loading sequence effect and the influence of the cycle ratio of the first stage on the cumulative fatigue life are studied. Two loading sequences, i.e., high-to-low and low-to-high cases are considered. The proposed damage indicator is connected cycle by cycle to the S-N curve and the experimental results are in agreement with model expectations. Previous experimental research is employed for validation.

M. Bendouba

2014-02-01

222

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

Science.gov (United States)

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

Neu, R. W.; Sehitoglu, Huseyin

1989-09-01

223

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

Science.gov (United States)

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

Endo, T.; Sakon, T.

1983-05-01

224

X-43A Rudder Spindle Fatigue Life Estimate and Testing  

Science.gov (United States)

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.

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

2005-01-01

225

Fatigue life assessment under multiaxial variable amplitude loading  

International Nuclear Information System (INIS)

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

226

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

Science.gov (United States)

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

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

2012-11-01

227

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

2013-01-01

228

NASA GRC Fatigue Crack Initiation Life Prediction Models  

Science.gov (United States)

Metal fatigue has plagued structural components for centuries, and it remains a critical durability issue in today's aerospace hardware. This is true despite vastly improved and advanced materials, increased mechanistic understanding, and development of accurate structural analysis and advanced fatigue life prediction tools. Each advance is quickly taken advantage of to produce safer, more reliable, more cost effective, and better performing products. In other words, as the envelope is expanded, components are then designed to operate just as close to the newly expanded envelope as they were to the initial one. The problem is perennial. The economic importance of addressing structural durability issues early in the design process is emphasized. Tradeoffs with performance, cost, and legislated restrictions are pointed out. Several aspects of structural durability of advanced systems, advanced materials and advanced fatigue life prediction methods are presented. Specific items include the basic elements of durability analysis, conventional designs, barriers to be overcome for advanced systems, high-temperature life prediction for both creep-fatigue and thermomechanical fatigue, mean stress effects, multiaxial stress-strain states, and cumulative fatigue damage accumulation assessment.

Arya, Vinod K.; Halford, Gary R.

2002-01-01

229

A methodology to evaluate the fatigue life of flexible pipes  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-07-01

230

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

Science.gov (United States)

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

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

1985-01-01

231

Fatigue Life of High-Strength Steel Offshore Tubular Joints  

DEFF Research Database (Denmark)

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.

Agerskov, Henning

1996-01-01

232

Fracture Mechanics Prediction of Fatigue Life of Aluminium Highway Bridges  

DEFF Research Database (Denmark)

Fatigue damage accumulation in aluminium highway bridges under random loading is studied. The fatigue life of welded joints has been determined both from fracture mechanics analyses and from experimental investigations. The fatigue life of welded plate specimens has been investigated. The material that has been used has a 0.2% proof strength of 310 MPa and an ultimate tensile strength of 327 MPa. The fracture mechanics analyses and the fatigue tests have been carried out using load histories, which correspond to one week's traffic loading, determined by means of strain gauge measurements on the deck structure of the Farø Bridges in Denmark. The results obtained in the present investigation show a significant difference between constant amplitude and variable amplitude results. Both the fracture mechanics analyses and the fatigue test results indicate that Miner's rule, which is normally used in the design against fatigue in aluminium bridges, may give results which are unconservative. The validity of the results obtained from Miner's rule will depend on the distribution of the load history in tension and compression.

Agerskov, Henning

2012-01-01

233

Prediction of fatigue life of flawed pipe under vibration and fatigue loading  

International Nuclear Information System (INIS)

A systematic experimental and analytical study has been carried out to predict the fatigue life of a flawed pipe under vibration loading with cyclic loading. Three Point Bend (TPB) specimens machined from the actual pipe have been used for evaluation of Paris constants by carrying out experiments under vibration loading followed by cyclic loading and cyclic loading only as per ASTM standard E-647. These constants were used for predicting the fatigue life of the pipe having part through flaw of a/t=0.25 and aspect ratio (2c/a) of 10. Predicted results show that the life of the notched pipe subjected to vibration loading followed by cyclic loading has been reduced by 50% compared to that of cyclic loading only. Predicted results have been validated by carrying out full-scale pipe tests. Experimental results of fullscale pipe tests under vibration followed by cyclic loading showed the reduction in fatigue life by 70% compared to that of cyclic loading only. The analytical prediction for the crack initiation life and the crack growth behavior were carried out and the results were compared with that of experiments. Fatigue crack growth was confirmed by examine and measuring the striation spacing on fracture surface. ASME O and M design code calls for qualification of piping system subjected to the vibration. The deflection and velocity measurement have been taken on the pipe specimen and compared with the ASME criterion. (author)

234

Development of generic creep-fatigue life prediction models  

International Nuclear Information System (INIS)

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

235

On Fatigue Life Under Stationary Gaussian Random Loads (A)  

DEFF Research Database (Denmark)

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.

1973-01-01

236

Fatigue life of ablation-cast 6061-T6 components  

International Nuclear Information System (INIS)

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

237

Fatigue life of ablation-cast 6061-T6 components  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-01-01

238

Cyclic rate-dependent fatigue life in reactor water  

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-12-31

239

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)

240

Fatigue life assessment of free spanning pipelines containing corrosion defects  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-12-19

 
 
 
 
241

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

Directory of Open Access Journals (Sweden)

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.

Cheng Gang

2013-01-01

242

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.

243

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)

244

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)

245

Fatigue Life Analysis of Thrust Ball Bearing Using ANSYS  

Directory of Open Access Journals (Sweden)

Full Text Available This paper compares the total deformation of thrust ball bearing & contact stress b/w ball & raceways & its effect on fatigue life of thrust ball bearing. The 3-Dimensional Modeling has been done through modeling software Pro-e wildfire-5.0. The parts assembly is also done in Pro-e wildfire-5.0 & analysis has been done through ANSYS- 14. An analylitical method is good, less expensive and gives the best results. Analytical results give good agreement with the experimental data. The thrust ball bearings are subjected to various, thrust & dynamic loads, which simulated easily through Pro-E software & analysis because experimentally calculation is very complicated. The general theory used for calculating the Fatigue life of Bearing is basic life rating theory. The material taken for the Bearing is AISI8720H. In this study we have used various analysis codes and got a good result through these codes.

Prabhat Singh*1

2014-01-01

246

A frequency domain approach for estimating multiaxial random fatigue life  

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-10-15

247

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

Directory of Open Access Journals (Sweden)

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

Öztürk, A.

2005-01-01

248

Tension fatigue analysis and life prediction for composite laminates  

Science.gov (United States)

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

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

1988-01-01

249

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

Directory of Open Access Journals (Sweden)

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.

Angga Yustiawan

2013-04-01

250

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

251

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

252

Crack growth and high cycle fatigue behaviour of an aa6060 aluminium alloy after ecap combined with a subsequent heat treatment; Rissfortschritts- und Ermuedungsverhalten der Aluminiumlegierung EN AW-6060 nach ECAP und nachgelagerter Waermebehandlung  

Energy Technology Data Exchange (ETDEWEB)

Crack growth properties of the Al-Mg-Si alloy AA6060 as well as the high cycle fatigue behaviour have been investigated after equal-channel angular pressing (ECAP). In our study, experiments have been conducted on different stages of microstructural breakdown and strain hardening of the material as they were present after different numbers of ECAP passes. A bimodal condition, obtained after two pressings, and a homogeneously ultrafine-grained condition after eight repetitive pressings have been investigated. Furthermore, optimized conditions with an enhanced ductility, produced by ECAP processing combined with a following short-time aging treatment were included into the study. Crack growth experiments have been conducted in the near-threshold regime and the region of stable crack growth, covering a range of load ratios from R = 0.1 up to 0.7. It was found that the lowered fatigue threshold {delta}K{sub th} of the as-extruded material can be enhanced by the combination of ECAP and short-time aging, owing to the increased ductility and strain hardening capability of this material. By means of SEM investigations and tensile tests, the crack growth properties of the different conditions were related to microstructural and mechanical features. In fatigue tests, load reversals up to failure and the fatigue limit for an as-extruded condition and an optimized condition after two ECAP-passes have been compared to the coarse grained initial condition and a remarkable increase in fatigue strength was noted. (Abstract Copyright [2009], Wiley Periodicals, Inc.) [German] An der warmaushaertenden Aluminiumlegierung EN AW-6060 wurden Untersuchungen zum Rissfortschritt und zur Ermuedung nach hochgradig plastischer Verformung durch ECAP (Equal-Channel Angular Pressing) durchgefuehrt. Es wurden Zustaende in unterschiedlichen Stadien der Mikrostrukturfeinung und Verformungsverfestigung untersucht: ein bimodaler Zustand nach zwei sowie ein homogen ultrafeinkoerniger Zustand nach acht ECAP-Umformschritten. Zudem wurden zwei optimierte Zustaende mit verbesserter Duktilitaet, eingestellt durch eine Kombination aus ECAP mit einer nachfolgenden kurzen Auslagerungsbehandlung, in die Untersuchungen einbezogen. Rissfortschrittsversuche im Schwellwertbereich und dem stabilen Rissfortschrittsbereich bei Lastverhaeltnissen von R = 0,1 bis 0,7 ergaben fuer die optimierten Zustaende eine Verbesserung der Schwellwerte im Vergleich zu den ecapierten Zustaenden, was auf erhoehte Duktilitaet durch die Kombination von ECAP und einer Auslagerungsbehandlung zurueckgefuehrt wurde. Anhand von rasterelektronenmikroskopischen Analysen der Rissfortschrittsflaechen sowie den aus Zugversuchen ermittelten Festigkeits- und Zaehigkeitskennwerten konnte das Rissfortschrittsverhalten mit der Mikrostruktur und den mechanischen Eigenschaften in Verbindung gebracht werden. In Ermuedungsversuchen im Zeitfestigkeitsbereich (HCF ''high cycle fatigue'') wurden ein ecapierter sowie ein optimierter Zustand untersucht. Fuer beide Zustaende wurde eine deutliche Erhoehung der Ermuedungsfestigkeit im Vergleich zum Ausgangszustand festgestellt. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

Hockauf, K.; Meyer, L.W.; Halle, T.; Hockauf, M. [Lehrstuhl Werkstoffe des Maschinenbaus, TU Chemnitz, 09107 Chemnitz (Germany)

2009-07-15

253

Advances in fatigue life prediction methodology for metallic materials  

Science.gov (United States)

The capabilities of a plasticity-induced crack-closure model to predict small- and large-crack growth rates, and in some cases total fatigue life, for four aluminum alloys and three titanium alloys under constant-amplitude, variable-amplitude, and spectrum loading are described. Equations to calculate a cyclic-plastic-zone corrected effective stress-intensity factor range from a cyclic J-integral and crack-closure analysis of large cracks were reviewed. The effective stress-intensity factor range against crack growth rate relations were used in the closure model to predict small- and large-crack growth under variable-amplitude and spectrum loading. Using the closure model and microstructural features, a total fatigue life prediction method is demonstrated for three aluminum alloys under various load histories.

Newman, J. C., Jr.

1992-08-01

254

Fatigue life of catenary risers excited by vortex shedding  

Energy Technology Data Exchange (ETDEWEB)

A hybrid method is presented for predicting the fatigue life of catenary risers exposed to vortex shedding in steady ocean currents. The hybridization allows the user to separate the modelling of hydrodynamic excitation and damping from the detailed modelling of structural non-linearities. In the method described here the structural dynamic results in the form of natural frequencies, model shapes and modal curvatures are exported from a finite element model of the structure to a built-for-purpose vortex-induced vibration code known as SHEAR7. SHEAR7 uses the mode superposition method for response analysis. Since most FEM programs do not typically produce modal curvatures, particular attention is given to describing this aspect of the problem. An example fatigue life prediction is presented for a steel catenary riser. (author)

Vandiver, J. Kim [Massachusetts Inst. of Technology, Ocean Engineering Dept., Cambridge, MA (United States); Gonzalez, E.C. [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil)

1997-12-31

255

Fatigue life prediction for materials with hampered pore growth  

International Nuclear Information System (INIS)

The paper first summaries the current knowledge about the process of pore formation and nucleation in engineering materials. Then, the author discusses the reasons suggesting that pore growth follow the mechanism of hampered diffusion. Assuming this type of pore growth, the failure parameter ? and its role in the stress-strain rate law is derived, and its correlation with the Ac parameter is discussed. Finally, the application of the failure parameter ? to assessing the remaining fatigue life is explained. (orig./MM)

256

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

Science.gov (United States)

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

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

1987-08-01

257

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

Science.gov (United States)

The Hot Section Technology (HOST) program, creep fatigue life prediction for engine hot section materials (isotropic), is reviewed. The program is aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components. Significant results include: (1) cast B1900 and wrought IN 718 selected as the base and alternative materials respectively; (2) fatigue test specimens indicated that measurable surface cracks appear early in the specimen lives, i.e., 15% of total life at 871 C and 50% of life at 538 c; (3) observed crack initiation sites are all surface initiated and are associated with either grain boundary carbides or local porosity, transgrannular cracking is observed at the initiation site for all conditions tested; and (4) an initial evaluation of two life prediction models, representative of macroscopic (Coffin-Mason) and more microscopic (damage rate) approaches, was conducted using limited data generated at 871 C and 538 C. It is found that the microscopic approach provides a more accurate regression of the data used to determine crack initiation model constants, but overpredicts the effect of strain rate on crack initiation life for the conditions tested.

Moreno, V.

1983-01-01

258

Bending Fatigue Initiation Life Estimation of Disposable Spur Gears  

Directory of Open Access Journals (Sweden)

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.

Yuefeng Li

2013-07-01

259

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.

260

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)

 
 
 
 
261

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 degrea...

Shahzad, Majid; Chaussumier, Michel; Chieragatti, Re?my; Mabru, Catherine; Rezai?-aria, Farhad

2011-01-01

262

Fatigue life estimation of MD36 and MD523 bogies based on damage accumulation and random fatigue theory  

International Nuclear Information System (INIS)

Bogies are one of the multifunctional parts of trains which are extremely subjected to random loads. This type of oscillating and random excitation arises from irregularities of the track including rail surface vertical roughness, rail joints, variance in super-elevation, and also wheel imperfections like wheel flats and unbalancy. Since most of the prementioned sources have random nature, a random based theory should be applied for fatigue life estimation of the bogie frame. Two methods of fatigue life estimation are investigated in this paper. The first approach which is being implemented in time domain is based on the damage accumulation (DA) approach. Using Monte-Carlo simulation algorithm, the rail surface roughness is generated. Finite element (FE) model of the bogie is subjected to the generated random excitation in the first approach and the stress time histories are obtained, and consequently the fatigue life is estimated by using the rain-flow algorithm. In the second approach, the fatigue life is estimated in frequency domain. Power spectral density (PSD) of the stress is obtained by using the FE model of the bogie frame and the fatigue life is estimated using Rayleigh technique in random fatigue theory. A comprehensive parametric study is carried out and effects of different parameters like the train speeds and level of the rail surface vertical roughness on the estimated fatigue life are investigated

263

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

International Nuclear Information System (INIS)

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

264

Fatigue life of two steels under variable amplitude loading  

Science.gov (United States)

Smooth cylindrical specimens made from a very low carbon steel and a martensic cast steel were subjected to various loading histories arranged as a sequence of blocks with variable strain amplitudes. The number of blocks to failure were measured as a function of the maximum amplitude in a block. The effect of the ratio of number of lowest and highest amplitudes in a block is studied. The results show that fatigue lives depend strongly on both the maximum amplitude in a block and the relative frequency of the lowest and highest amplitudes in a block. Several fatigue life prediction methods were adopted. The best agreement with experiments is obtained using the methods based on the knowledge of the behavior of short cracks in the materials studied.

Vasek, Alois; Polak, Jaroslav

1992-07-01

265

Control technique of high-cycle thermal fatigue at a mixing tee with a 90-degree bend upstream by changing its location  

International Nuclear Information System (INIS)

o the inward side of the bended pipe. As a result, the temperature fluctuation intensity becomes lower and decays faster in the streamwise direction. This result means that the location of the mixing tee strongly affects the fluid mixing and the temperature fluctuation near the wall. Experimental results suggest that changing the location of the mixing tee closer to the 90-degree bend could be an effective control technique for the higher-cycle thermal fatigue. (author)

266

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.

267

Estimation of fatigue life of railway bridges under traffic loads  

Science.gov (United States)

Random modelling of railway bridge loading enables fatigue damage to be calculated on the basis of the cumulative damage theory of Palmgren-Miner and the classification of the stress-time history by means of the "rain-flow" counting method. The results of calculations are the mean value of the damage and the standard deviation of the stresses, and thus an estimation of the bridge fatigue life. Accordingly the bridge life is dependent on the number of stress cycles and their distribution, the standard deviation of stresses, and on the shape of the Wöhler curve. Bridge life increasing span and decreases with an increasing traffic load. Results are presented as obtained in a detailed study of the effects on the bridge life of different parameters (vehicle speed, damping of bridge vibrations, variability in length and time of the moving load and its magnitude, number of stress cycles and their distribution). The equivalent damage method (the ?T-method) in the integral form enables one to compare the effects of the traffic loads with those of the standard loading.

Frýba, L.

1980-06-01

268

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Nijssen, R. P. L.

2006-01-01

269

Fatigue life prediction for a cold worked T316 stainless steel  

International Nuclear Information System (INIS)

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

270

Evaluation of long term creep-fatigue life for type 304 stainless steel  

International Nuclear Information System (INIS)

The long term creep-fatigue life of type 304 stainless steel was evaluated by the creep-fatigue life prediction method based on a linear damage fraction rule. The displacement controlled creep-fatigue tests were carried out, and the time to failure of longer than 10000 hours was obtained. The creep damage of long term creep-fatigue was evaluated by taking into account the stress relaxation behavior with elastic follow-up during the hold period. The relationship between life reduction of creep-fatigue and fracture mode was provided by the creep cavity growth. The results of this study are summarized as follows; (1) The long term creep-fatigue data can be reasonably evaluated by the present method. The predicted lives were within a factor of 3 of the observed ones. (2) The present method provides the capability to predict the long term creep-fatigue life at lower temperatures as well as that at the creep dominant temperature. (3) The value of creep damage for the long term creep-fatigue data increased by elastic follow-up. The creep-fatigue damage diagram intercepted between 0.3 and 1 can represent the observed creep-fatigue damages. (4) The cavity growth depends on the hold time. The fracture of long term creep-fatigue is caused by the intergranular cavity growth. The intergranular fracture of creep-fatigue is initiated by the cavity growth and followed by the microcrack propagation along grain boundaries starting from creep cavities. (author)

271

Study on high-cycle fatigue evaluation for thermal striping in mixing tees with hot and cold water. 1. Type A: Characteristics of temperature fluctuations and heat transfer in collision-type mixing tees with same pipe diameters. 1  

International Nuclear Information System (INIS)

In order to establish the Japan Society of Mechanical Engineers (JSME) guidelines concerning high-cycle thermal fatigue of piping systems for thermal striping in mixing tees under Light Water Reactor (LWR), experimental studies of thermal striping with scale models of mixing tees with hot and cold water were performed for Type A of mixing tee in which water flows from both sides of a main pipe to a branch pipe. As a first step, visualization tests with acrylic pipes tests were performed in order to ascertain flow pattern characteristics and fluid temperature fluctuation. As a second step, temperature fluctuation measurement tests with metal pipes were performed to furnish data on temperature fluctuations of fluid and pipe wall. Unsteady heat transfer coefficients were also evaluated based on these results. (author)

272

Study on high-cycle fatigue evaluation for thermal striping in mixing tees with hot and cold water. 3. Type C; characteristics of temperature fluctuations and heat transfer in mixing tees with different pipe diameters  

International Nuclear Information System (INIS)

In order to establish the Japan Society of Mechanical Engineers (JSME) guidelines concerning high-cycle thermal fatigue of piping systems for thermal striping in the mixing tee, experimental studies of thermal striping with scale models of mixing tees with hot and cold water were planned. Mixing tees in Light Water Reactor (LWR) power plants are classified into three types based on actual plant investigations. This paper reports test results of Type C where the flow in the branch pipe with a smaller diameter than the main pipe joins at a right angle to the main flow. In visualization test, flow pattern and basic characteristics were examined. In temperature fluctuation test, mean and fluctuation temperature was measured and unsteady heat transfer coefficient was estimated. (author)

273

Life extension of components with high cumulative fatigue usage  

International Nuclear Information System (INIS)

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

274

An experimental study on fatigue life of interference-fit composite joint  

Science.gov (United States)

An experimental study on fatigue life of an interference-fit composite joint is presented. The experimental results show that suitable interference can increase fatigue life in comparison with the push-fit case. For the material and the laying studied, when the interference is 2 percent, the fatigue life is increased 2-3 times. An explanation for the result is given. In order to obtain the current result, some methods of processing and assembling are emphasized in the experiment. An explanation is given for the definition of fatigue life limitation and the choice of the best interference.

Liu, Ping; Zhang, Kaida

1991-12-01

275

Modeling fatigue crack growth for life-extending control  

Science.gov (United States)

This dissertation presents a nonlinear dynamic model of fatigue crack growth in the state-space setting under variable amplitude cyclic load. The model is especially suited to the needs of real-time decision-making for life-extending control. The state variables are crack length and crack opening stress. The model is capable of capturing the effects of a single-cycle overload, block loads, random loads, and irregular sequences through a fading memory algorithm. Model predictions are in good agreement with experimental data on 7075-T6 and 2024-T3 aluminum alloys. Compiled results also demonstrate that the proposed model compares well with one of the most comprehensive models, FASTRAN-II that is used by the aircraft industry. Specifically, the state-space model recursively computes the crack opening stress via a simple functional relationship based on the principle of fading memory and does not require the storage of the stress history for its execution. Therefore, savings in both computation time and memory requirements are significant. The need for a reliable damage model for life-extending control is addressed with reference to the colossal inaccuracies that could occur in controller synthesis for a reusable rocket engine if a simplistic damage model is used under variable-amplitude load conditions. The seemingly counter-intuitive notion of overload injection could be gainfully utilized for life-extending optimization. The proof of this concept is demonstrated on a laboratory test apparatus by life-extension of test specimens with intentionally injected overload pulses at specific intervals. A stochastic model of fatigue crack growth under variable-amplitude load is proposed using the framework of the state-space model. The stochastic model is validated with four sets of constant-amplitude load test data and a set under variable-amplitude load test. The crack growth process is observed to be nearly deterministic for a cyclic load applied to a given specimen, provided that its microstructure does not undergo any major change. Therefore, a reliable deterministic model is a prerequisite for a stochastic model of fatigue crack growth. The stochastic model of fatigue crack growth does not require expensive computations to obtain a solution to the stochastic difference equations.

Patankar, Ravindra Prakash

1999-12-01

276

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

Science.gov (United States)

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

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

2014-05-01

277

Fatigue Life Methodology for Tapered Composite Flexbeam Laminates  

Science.gov (United States)

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

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

1997-01-01

278

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

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

2008-01-01

279

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-06-01

280

Determination of Turboprop Reduction Gearbox System Fatigue Life and Reliability  

Science.gov (United States)

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

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

2007-01-01

 
 
 
 
281

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)

282

Estimate the thermomechanical fatigue life of two flip chip packages  

International Nuclear Information System (INIS)

The continuing demand towards high density and low profile integrated circuit packaging has accelerated the development of flip chip structures as used in direct chip attach (DCA) technology, ball grid array (BOA) and chip scale package (CSP). In such structures the most widely used flip chip interconnects are solder joints. The reliability of flip chip structures largely depends on the reliability of solder joints. In this work solder joint fatigue life prediction for two chip scale packages is carried out. Elasto-plastic deformation behavior of the solder was simulated using ANSYS. Two dimensional plain strain finite element models were developed for each package to numerically compute the stress and total strain of the solder joints under temperature cycling. These stress and strain values are then used to predict the solder joint lifetime through modified Coffin Manson equation. The effect of solder joint's distance from edge of silicon die on life of the package is explored. The solder joint fatigue response is modeled for a typical temperature cycling of -60 to 140 degree C. (author)

283

Blade fatigue life assessment with application to VAWTs  

Science.gov (United States)

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

Veers, P. S.

1982-05-01

284

NASALIFE - Component Fatigue and Creep Life Prediction Program  

Science.gov (United States)

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

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

2014-01-01

285

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)

286

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

Science.gov (United States)

The influences of both hole cold expansion and interference-fit fasteners for extending the fatigue life of multilayer aluminum alloy joint specimens under variable amplitude loading have been examined experimentally. Improvements in fatigue life were markedly dependent on the degree of load transfer in the specimen joint. The cold expansion of fastener holes enhanced fatigue life in low load transfer joints but not in 100% load transfer joints. The use of interference-fit fasteners, especially at high degrees of interference, was an effective means of life improvement irrespective of proportion of load transfer. Interfacial fretting limited the improvement in fatigue life of low load transfer joints to a factor of about six, and, although some fretting occurred in 100% load transfer joints, it was not determinative, and a 40-fold increase in fatigue life was obtained with a combination of hole cold expansion and interference-fit fastener.

Finney, J. M.

1993-10-01

287

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

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

2008-01-01

288

Estimation of fatigue strain-life curves for austenitic stainless steels in light water reactor environments.  

Energy Technology Data Exchange (ETDEWEB)

The ASME Boiler and Pressure Vessel Code design fatigue curves for structural materials do not explicitly address the effects of reactor coolant environments on fatigue life. Recent test data indicate a significant decrease in fatigue lives of austenitic stainless steels (SSs) in light water reactor (LWR) environments. Unlike those of carbon and low-alloy steels, environmental effects on fatigue lives of SSs are more pronounced in low-dissolved-oxygen (low-DO) water than in high-DO water, This paper summarizes available fatigue strain vs. life data on the effects of various material and loading variables such as steel type, DO level, strain range, and strain rate on the fatigue lives of wrought and cast austenitic SSs. Statistical models for estimating the fatigue lives of these steels in LWR environments have been updated with a larger data base. The significance of the effect of environment on the current Code design curve has been evaluated.

Chopra, O. K.; Smith, J. L.

1998-02-12

289

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-05-31

290

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

Science.gov (United States)

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

Hoshide, Toshihiko; Shimizu, Shohei; Tanaka, Motoki

2014-03-01

291

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

Directory of Open Access Journals (Sweden)

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

John R. Yates

2008-08-01

292

Fatigue Life Estimation of an Aircaft Engine Under Different Load Spectrums  

Science.gov (United States)

Aircraft engine components are subjected to variable amplitude load conditions usually they tend to experience fatigue damage. Many fatigue damage accumulation theories have been put forward to predict the fatigue lives of structure components. Under different load spectra, the aircraft engine has different working life. In this paper, based on the linear damage rule, the fatigue life of an aircraft engine was estimated by considering the load spectrum difference factor. According to one aircraft engine used for different load spectrums, the relationship between the load spectrum and the life is discussed. Moreover, the fatigue life of this engine used in A-type bomber is estimated based on the different load spectrum of the B-type bomber. A good agreement is found between the estimated results and real life data.

Huang, Hong-Zhong; Gong, Jie; Zuo, Ming J.; Zhu, Shun-Peng; Liao, Qiang

2012-12-01

293

Calculation of thermomechanical fatigue life based on isothermal behavior  

Science.gov (United States)

The isothermal and thermomechanical fatigue (TMF) crack initiation response of a hypothetical material was analyzed. Expected thermomechanical behavior was evaluated numerically based on simple, isothermal, cyclic stress-strain-time characteristics and on strainrange versus cyclic life relations that have been assigned to the material. The attempt was made to establish basic minimum requirements for the development of a physically accurate TMF life-prediction model. A worthy method must be able to deal with the simplest of conditions: that is, those for which thermal cycling, per se, introduces no damage mechanisms other than those found in isothermal behavior. Under these assumed conditions, the TMF life should be obtained uniquely from known isothermal behavior. The ramifications of making more complex assumptions will be dealt with in future studies. Although analyses are only in their early stages, considerable insight has been gained in understanding the characteristics of several existing high-temperature life-prediction methods. The present work indicates that the most viable damage parameter is based on the inelastic strainrange.

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

1987-01-01

294

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, ...

295

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

Energy Technology Data Exchange (ETDEWEB)

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

Kwak, Si Young; Kim, Hak Ku [Korea Institute of Industrial Technology, Cheonan (Korea, Republic of)

2011-10-15

296

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.

297

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.

298

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

Directory of Open Access Journals (Sweden)

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.

M.M. Rahman

2008-01-01

299

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

Science.gov (United States)

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

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

300

Cyclic plasticity and fatigue life of steel 15Kh2NMFA  

International Nuclear Information System (INIS)

15Kh2NMFA steel of Czechoslovak and Soviet make was ussed for the experiment which involved tests of low-cycle and high-cycle fatigue at temperatures of 20 degC and 350 degC. Cyclic deformation curves and lifetime curves were obtained in form of a Manson-Coffin dependence. It was found that fatigue properties of the two steels are very similar. The Soviet steel is more suitable for uses under conditions of controlled stress amplitude, the Czechoslovak type is more suitable for areas with limited lifetime. (E.S.)

 
 
 
 
301

Development of a Composite Delamination Fatigue Life Prediction Methodology  

Science.gov (United States)

Delamination is one of the most significant and unique failure modes in composite structures. Because of a lack of understanding of the consequences of delamination and the inability to predict delamination onset and growth, many composite parts are unnecessarily rejected upon inspection, both immediately after manufacture and while in service. NASA Langley is leading the efforts in the U.S. to develop a fatigue life prediction methodology for composite delamination using fracture mechanics. Research being performed to this end will be reviewed. Emphasis will be placed on the development of test standards for delamination characterization, incorporation of approaches for modeling delamination in commercial finite element codes, and efforts to mature the technology for use in design handbooks and certification documents.

OBrien, Thomas K.

2009-01-01

302

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)

303

A proposal of parameter to predict biaxial fatigue life for CF8M cast stainless steels  

International Nuclear Information System (INIS)

Biaxial low cycle fatigue test was carried out to predict fatigue life under combined axial-torsional loading condition which is that of in-phase and out-of-phase for CF8M cast stainless steels. Fatemi Socie(FS) parameter which is based on critical plane approach is not only one of methods but also the best method that can predict fatigue life under biaxial loading condition. But the result showed that, biaxial fatigue life prediction by using FS parameter with several different parameters for the CF8M cast stainless steels is not conservative but best results. So in this present research, we proposed new fatigue life prediction parameter considering effective shear stress instead of FS parameter which considers the maximum normal stress acting on maximum shear strain and its effectiveness was verified

304

A prediction of biaxial fatigue life of cast stainless steels(CF8M) by degradation  

International Nuclear Information System (INIS)

The multiaxial fatigue test under in-phase and out-of-phase load were performed to study what degradation phenomenon affects fatigue life with virgin and 3600 hrs degraded materials. The various kind of fatigue data for fatigue life prediction were acquired under pure axial and pure torsional load of fully reversal condition. The models which was investigated are: 1) the von Mises equivalent strain range, 2) the critical shear plane approach method of Fatemi-Socie(FS) parameter, 3) the modified Smith-Watson-Topper(SWT) parameter. The result showed that, fatigue life by material degradation are decreased and life prediction which was used the FS parameter is not conservative but the best result

305

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

International Nuclear Information System (INIS)

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

306

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

Science.gov (United States)

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

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

2012-01-01

307

Grain boundary oxidation and its effects on high temperature fatigue life  

Science.gov (United States)

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

Liu, H. W.; Oshida, Yoshiki

1986-01-01

308

Modeling size effects on fatigue life of a zirconium-based bulk metallic glass under bending  

International Nuclear Information System (INIS)

A size effect on the fatigue-life cycles of a Zr50Cu30Al10Ni10 (at.%) bulk metallic glass has been observed in the four-point-bending fatigue experiment. Under the same bending-stress condition, large-sized samples tend to exhibit longer fatigue lives than small-sized samples. This size effect on the fatigue life cannot be satisfactorily explained by the flaw-based Weibull theories. Based on the experimental results, this study explores possible approaches to modeling the size effects on the bending-fatigue life of bulk metallic glasses, and proposes two fatigue-life models based on the Weibull distribution. The first model assumes, empirically, log-linear effects of the sample thickness on the Weibull parameters. The second model incorporates the mechanistic knowledge of the fatigue behavior of metallic glasses, and assumes that the shear-band density, instead of the flaw density, has significant influence on the bending fatigue-life cycles. Promising predictive results provide evidence of the potential validity of the models and their assumptions.

309

Fatigue life predictions of welded specimens containing lack of penetration defects at ambient and elevated temperatures  

International Nuclear Information System (INIS)

Low cycle fatigue tests have been carried out on welded specimens containing buried lack of penetration defects. Tests were performed at ambient and elevated temperatures. Crack propagation data had been obtained previously at ambient and elevated temperatures for parent materials and weld metals. Using the crack propagation data, the defective specimens were analysed by fracture mechanics techniques to obtain fatigue predictions. It was found that, provided defect shape was taken into account, accurate fatigue life predictions could be made. (author)

310

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

International Nuclear Information System (INIS)

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

311

Study on high-cycle fatigue evaluation for thermal striping in mixing tees with hot and cold water. 2. Type B; characteristics of temperature fluctuations and heat transfer in mixing tees with same pipe diameters  

International Nuclear Information System (INIS)

Thermal striping tests were conducted in mixing tees with the same pipe diameters in order to construct databases for an evaluation method for high-cycle thermal fatigue of piping systems. Hot and cold water with a temperature difference of 40 K were supplied to the mixing tee. Temperature fluctuations of the fluid and pipe wall were measured as the velocity ratio of the flow in the branch pipe to that in the main pipe was varied from 0.1 to 5. The power spectrum method was used to evaluate the heat transfer coefficient. The fluid temperature fluctuation characteristics were dependent on the velocity ratio, rather than on the absolute value of the flow velocity. Large fluid temperature fluctuations of more than 90% of the incoming flow temperature difference occurred near the mixing tee, and the fluctuation frequency was random. The ratios of the measured heat transfer coefficient to that evaluated by Dittus-Boelter's empirical equation were independent of the velocity ratio and Reynolds number. The ratios were within about two. (author)

312

Aspects of fatigue life in thermal barrier coatings  

Energy Technology Data Exchange (ETDEWEB)

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.

Brodin, H.

2001-08-01

313

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.

314

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

Science.gov (United States)

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

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

1997-06-01

315

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

Science.gov (United States)

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

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

2014-01-01

316

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

Energy Technology Data Exchange (ETDEWEB)

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.

Keisler, J.; Chopra, O.K.

1995-03-01

317

Effects of stress concentrations on the fatigue life of a gamma based titanium aluminide  

International Nuclear Information System (INIS)

S-N curves for a gamma based titanium aluminide alloy of composition Ti-47.2Al-2.1Mn-1.9Nb(at.%)+2TiB2(wt.%) have been used to define fatigue life. Effects of residual stress, stressed volume, loading ratio, loading mode, elevated temperature and surface roughness have been considered. Residual tensile stresses and micro-cracking are introduced by Electro Discharge Machining and the fatigue life is reduced slightly compared with polished samples. Notched fatigue tests show a significant notch strengthening effect which increases with increasing stress concentration factor. The fracture surfaces of specimens tested at room temperature reveal fully brittle failure mechanisms and no evidence of stable crack growth is observed. The fatigue life appears, therefore, to be determined predominantly by the number of cycles to crack initiation. At the elevated temperature of 830 C, evidence for some stable fatigue crack growth has been found. Probable sites for crack initiation are addressed

318

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

319

Fracture mechanics and corrosion fatigue.  

Science.gov (United States)

Review of the current state-of-the-art in fracture mechanics, particularly in relation to the study of problems in environment-enhanced fatigue crack growth. The usefulness of this approach in developing understanding of the mechanisms for environmental embrittlement and its engineering utility are discussed. After a brief review of the evolution of the fracture mechanics approach and the study of environmental effects on the fatigue behavior of materials, a study is made of the response of materials to fatigue and corrosion fatigue, the modeling of the mechanisms of the fatigue process is considered, and the application of knowledge of fatigue crack growth to the prediction of the high cycle life of unnotched specimens is illustrated.

Mcevily, A. J.; Wei, R. P.

1972-01-01

320

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

Directory of Open Access Journals (Sweden)

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.

M.M. Rahman

2008-01-01

 
 
 
 
321

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

International Nuclear Information System (INIS)

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

322

Fatigue Life and Short Crack Behavior in Ti-6Al-4V Alloy; Interactions of Foreign Object Damage, Stress, and Temperature  

Science.gov (United States)

High-cycle fatigue (HCF) failures associated with foreign object damage (FOD) in turbine engines of military aircrafts have been of major concern for the aeronautic industry in recent years. The present work is focused on characterizing the effects of FOD on crack initiation and small crack growth of a Ti-6Al-4V alloy at ambient and also elevated temperatures. Results show that the preferred crack initiation site depends on applied stress and temperature as maximum fractions of cracks emanating from the simulated damage site, and naturally initiated cracks are observed at 25 °C under the maximum stress of 700 MPa and at 300 °C under the maximum stress of 300 MPa. The fatigue crack growth rate is influenced by increasing temperature, and the FCG rate at 300 °C is higher than that at room temperature under the same ? K, whereas this effect for FOD-site initiated cracks is not so remarkable. This observation seems to be due to the effect of stress relaxation at 300 °C. Results also indicate that fatigue crack initiation life ( N i ) and fatigue life ( N f ) are expressed by three-parameter Weibull distribution function.

Majidi, Behzad

2008-04-01

323

Fatigue life evaluation of pressure housing of SMART CEDM  

Energy Technology Data Exchange (ETDEWEB)

The pressure housing forming pressure boundary in SMART CEDM must be evaluated the structural stability for fatigue. The value obtained by fatigue analysis is compared with the standard of ASME, Sec. III and KEPIC MNB. Using the input data of PRDBE and SRDBE calculated by performing the safety analysis, the operation and stop of CEDM and the hydraulic test pressure, the fatigue analysis is performed. The analysis program is used to I-DEAS and ABAQUS. Because the usage factor obtained by the analysis is the value less than 1 with the limit, the stability of pressure housing is validated under fatigue.

Cho, D. H. [Halla Industry Co., Koyang (Korea, Republic of); Yoo, J. Y.; Kim, J. H.; Kim, J. I. [KAERI, Taejon (Korea, Republic of)

2002-05-01

324

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

Directory of Open Access Journals (Sweden)

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.

Barman A

2010-04-01

325

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

Directory of Open Access Journals (Sweden)

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.

Kholoud Abu Obead

2013-11-01

326

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 magnification. The experimental results indicate that the fatigue life of specimens decreases with any increase in load level. Also the crack initiation and propagation firstly occurs in plate with less thickness. According to the experimental observations when a high level loading is applied to the spot weld joints, the nugget suddenly pull-out and cannot withstand the fatigue loading.

M. Shariati

2009-01-01

327

Effect of the model’s geometry in fretting fatigue life prediction  

Directory of Open Access Journals (Sweden)

Full Text Available This paper analyses the influence that the type of geometry used to obtain the stress/strain fields in a cylindrical contact has on fretting fatigue life predictions. In addition, this work considers the effect that the fatigue crack shape assumed has on these fretting fatigue life predictions. The strain/stress fields are calculated using a series of finite elements models that consider the following three types of behaviour: plane stress, plane strain (2D geometries and 3D. Each of these models gives a different crack initiation life and a different evolution of the stress intensity factor (SIF, which are calculated using the weight function method. These models therefore provide different fretting fatigue life predictions. Finally, the lives obtained using the numerical models are compared with experimental lives.

J. Vázquez,

2014-10-01

328

The Recognition Of Fatigue : A qualitative study of life-stories from rehabilitation clients  

DEFF Research Database (Denmark)

Elsass P., Jensen B., Morup R., Thogersen M.H. (2007). The Recognition Of Fatigue: A qualitative study of life-stories from rehabilitation clients. International Journal of Psychosocial Rehabilitation. 11 (2), 75-87

Elsass, Peter; Jensen, Bodil

2007-01-01

329

Fatigue Life Analysis of Tapered Hybrid Composite Flexbeams  

Science.gov (United States)

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

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

2002-01-01

330

Fatigue Life Methodology for Tapered Hybrid Composite Flexbeams  

Science.gov (United States)

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

urri, Gretchen B.; Schaff, Jeffery R.

2006-01-01

331

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

DEFF Research Database (Denmark)

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

Birk-SØrensen, Martin

1996-01-01

332

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

Science.gov (United States)

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

Pisarski, Anne; Barbour, Jennifer P

2014-05-01

333

Modeling the effects of control systems of wind turbine fatigue life  

Energy Technology Data Exchange (ETDEWEB)

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.

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

1996-12-31

334

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

Science.gov (United States)

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

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

2011-01-01

335

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 pa...

2008-01-01

336

Biaxial fatigue of fiber-reinforced composites at cryogenic temperatures - 1. Fatigue fracture life and mechanisms  

International Nuclear Information System (INIS)

A study of biaxial fatigue of glass fiber-reinforced composites subjedted to in-phase, cyclic tensile and torsional loading at cryogenic temperatures is presented. Fatigue failure of the composite is investigated in terms of cyclic fracture, stiffness degradation, and energy dissipation. Fatigue fracture lives of the cryogenic composite are obtained for the cases of various combinations of cyclic tensile and torsional stresses. A power-law realtionship is established between the range of cyclic octahedral shear stress and the number of cycles to fracture. Influences of hydrostatic mean stress and stress biaxiality ratio on fatigue fracture of the fiber composite are determined. Fracture mechanisms in the material during the cryogenic biaxial fatigue are examined by using optical and scananing electron microscopes. 21 refs

337

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

Directory of Open Access Journals (Sweden)

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.

Gromov V.E.

2012-08-01

338

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

While investigating the fatigue strength of spot-welded joints, the effects of sheet spacing or gap amounts between sheet joints may be considered as one of the most important parameters on the fatigue life duration of the joints. The main goal of the present work is to study the influence of sheet spacing on the fatigue life of 5083-O aluminium alloy spot welded tensile-shear joints. The amounts of sheet spacing are the average values over three measurements of photograph observation o...

Esmaeili F.; Zehsaz M.; Hassanifard S.

2010-01-01

339

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

Directory of Open Access Journals (Sweden)

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.

Nitin D.Ghongade

2014-08-01

340

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

 
 
 
 
341

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

DEFF Research Database (Denmark)

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.

SØrensen, Eigil V.

2011-01-01

342

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

343

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

344

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

Science.gov (United States)

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

Everett, Richard A., Jr.

2004-01-01

345

An improved method for estimating fatigue life under combined stress  

Directory of Open Access Journals (Sweden)

Full Text Available The paper deals with a complicated problem of estimating fatigue lives of machine parts exposed to various kinds of dynamic loading. An origin of the presented method can be found 25 years ago when a simple algorithm of strain energy density cumulation was applied for evaluation of uniaxial harmonic and random fatigue tests. Recently, the method has been adopted for multiaxial loading. Unfortunately, results of its application have shown rather big variance. This paper presents the improved method, which yields much lower scattering of estimated fatigue lives compared with earlier approaches.

Svoboda J.

2007-10-01

346

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

Directory of Open Access Journals (Sweden)

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

Dong Zhang

2013-07-01

347

Microstructure-based fatigue life prediction methods for naval steel structures  

Science.gov (United States)

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

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

1994-09-01

348

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

International Nuclear Information System (INIS)

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

349

Study on giga-cycle fatigue characteristics at high temperature  

International Nuclear Information System (INIS)

Many tests and studies on fatigue have been carried out since German mining engineer, W.A.J. Albert tested metal fatigue in 1820's for the first time and much knowledge have been obtained. One of the important knowledge obtained through those tests and studies is that the S-N curve of many materials shows a plateau beyond the fatigue life of 105-106 cycles. However, it has been reported recently that the S-N curve of some high tensile strength steels and some surface modified steels re-drops in the fatigue life range over 107 cycles. This phenomenon means that there is a high risk of failure at an unexpected shorter life in the very high cycle fatigue estimated by the regular S-N curve obtained in the fatigue life range less than 107 cycles and requests the validation of the high cycle fatigue design. Therefore, this collaborative study 'Study on Giga-Cycle Fatigue Characteristics at High Temperature' was carried out as a program for 3 years from the 2002 financial year, in order to investigate giga-cycle fatigue characteristics of structural material in the fast breeder reactor (FBR). This report summarizes the results of 3 years' study on giga-cycle fatigue characteristics at high temperature. (author)

350

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

Science.gov (United States)

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

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

2011-07-01

351

Application of an Energy-Based Life Prediction Model to Bithermal and Thermomechanical Fatigue  

Science.gov (United States)

The inelastic hysteresis energy applied to the material in a cycle is used as the basis for predicting nonisothermal fatigue life of a wrought cobalt-base superalloy, Haynes 188, from isothermal fatigue data. Damage functions that account for hold-time effects and time-dependent environmental phenomena such as oxidation and hot corrosion are proposed in terms of the inelastic hysteresis energy per cycle. The proposed damage functions are used to predict the bithermal and thermomechanical fatigue lives of Haynes 188 between 316 and 760 C from isothermal fatigue data. Predicted fatigue lives of all but two of the nonisothermal tests are within a factor of 1.5 of the experimentally observed lives.

Radhakrishnan, V. M.; Kalluri, Sreeramesh; Halford, Gary R.

1994-01-01

352

A life evaluation under creep-fatigue-environment interaction of Ni-base wrought alloys  

International Nuclear Information System (INIS)

In order to determine a failure criteria under cyclic loading and affective environment for HTGR systems, a series of strain controlled low-cycle fatigue tests were carried out at HTGR maximum gas temperatures in air, in vacuum and in HTGR helium environments on two nickel-base wrought alloys, namely Inconel 617 and Hastelloy XR. This paper first describes the creep-fatigue-environment properties of these alloys followed by a proposal of an evaluation method of creep-fatigue-environment interaction based on the experimental data to define the more reasonable design criteria, which is a modification of the linear damage summation rule. Second, the creep-fatigue properties of Hastelloy XR at 900 deg C and the result evaluated by this proposed method are shown. This criterion is successfully applied to the life prediction at 900 deg C. In addition, the creep-fatigue properties of Hastelloy XR-II are discussed. (author)

353

Design characteristics that improve the fatigue life of threaded pipe connections  

Directory of Open Access Journals (Sweden)

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.

De Baets, Patrick

2011-10-01

354

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

International Nuclear Information System (INIS)

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

355

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

Science.gov (United States)

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

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

2013-07-01

356

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

International Nuclear Information System (INIS)

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

357

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

Directory of Open Access Journals (Sweden)

Full Text Available Introduction. The aim of the study was to assess the health related quality of life in patients suffering from multiple sclerosis (MS in association with clinical features, fatigue and depressive symptoms. Methods. The examined group consisted of 61 patients (45 women and 16 men in the mean age of 38.6±11.4. The mean duration of disease was 7.1±6.1 years. The control group consisted of 30 healthy volunteers. The following questionnaires were used: EuroQol (EQ5D with visual scale EuroQol-VAS, Modified Impact Fatigue Scale (MIFS and Beck Depression Inventory (BDI. Results. The quality of life in the examined group of MS patients was significantly lower in comparison to the control group. Results of EQ-5D and EQ-VAS were influenced by age, disease course, level of disability and carried treatment. Statistically significant association was also found between results of the questionnaires assessing quality of life and either fatigue or depressive symptoms. Conclusion. The used questionnaires confirmed that quality of life in patients with MS is significantly worse, especially in the older people with secondary progressive course of the disease, more disable and not treated. Presence of fatigue and depressive symptoms influenced the self-assessment of quality of life. Complex care of MS patient should consider diagnosis and treatment of fatigue and depression which could improve their quality of life.

?abuz-Roszak, Beata

2013-06-01

358

Damage due to low-cycle fatigue of type 316 stainless steel. Fatigue life under variable loading and influence of internal cracks  

International Nuclear Information System (INIS)

To obtain a reasonable prediction of fatigue life under variable loading, it is important to understand the damaging process. In this study, the damage process of low-cycle fatigue was investigated for Type 316 stainless steel. Fully-reversed axial fatigue tests were conducted in ambient air at room temperature by controlling strain amplitude, which was 6% at the maximum. Two-step strain tests were also conducted in order to assess the effect of loading history on fatigue life. The fatigue life was shown to be not always longer than that estimated using a linear damage accumulation rule. Furthermore, in order to evaluate the effect of initiation and growth of surface cracks on the fatigue life, the surface layer of specimens was removed after the first step. The fatigue life was extended by surface removal, although it was not recovered completely. Many internal cracks were observed on the fractured surface of the surface-removed specimens, and in some cases the specimens were fractured by these internal cracks. It was concluded that the low-cycle fatigue damage of Type 316 stainless steel consisted of three factors: surface cracking, internal cracking, and strain accumulation. (author)

359

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

DEFF Research Database (Denmark)

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.

Boter, Han; Mänty, Minna

2014-01-01

360

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-12-19

 
 
 
 
361

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

International Nuclear Information System (INIS)

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

362

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

Energy Technology Data Exchange (ETDEWEB)

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)

Zangenberg Hansen, J.

2013-09-15

363

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

DEFF Research Database (Denmark)

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.

Hansen, Jens Zangenberg

2013-01-01

364

Accelerated ultrasonic fatigue testing applications and research trends  

International Nuclear Information System (INIS)

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

365

Accelerated ultrasonic fatigue testing applications and research trends  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-06-15

366

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

DEFF Research Database (Denmark)

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.

Passipoularidis, Vaggelis; BrØndsted, Povl

2010-01-01

367

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

Directory of Open Access Journals (Sweden)

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

Jessie M. Huisinga, PhD

2011-08-01

368

A way of a life, fatigue and disease of students of pedagogical colleges  

Directory of Open Access Journals (Sweden)

Full Text Available The paper presents information about how the life, frequency of morbidity for the year and the nature of fatigue students teacher training colleges. The study used data questionnaire 1238 students' 1-4 courses three teacher training colleges. Found similar results in various colleges of the Western region of Ukraine. Bad habits in the student team of pedagogical higher education institutions are more widespread than technical. Nearly half of students at the end of the day feel considerable fatigue. Every third student revealed complains about the fatigue of general nature.

Romanchyshyn O.N.

2010-06-01

369

Probabilistic Modelling of Fatigue Life of Composite Laminates Using Bayesian Inference  

DEFF Research Database (Denmark)

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.

Dimitrov, Nikolay Krasimirov; Kiureghian, Armen Der

2014-01-01

370

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

DEFF Research Database (Denmark)

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.

SØrensen, Eigil V.; Westhof, Luc

371

Use of strainrange partitioning to predict high temperature low-cycle fatigue life. [of metallic materials  

Science.gov (United States)

The fundamental concepts of the strainrange partitioning approach to high temperature, low low-cycle fatigue are reviewed. Procedures are presented by which the partitioned strainrange versus life relationships for any material can be generated. Laboratory tests are suggested for further verifying the ability of the method of strainrange partitioning to predict life.

Hirschberg, M. H.; Halford, G. R.

1976-01-01

372

Design characteristics that improve the fatigue life of threaded pipe connections  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 diffe...

Baets, Patrick; Wittenberghe, Jeroen; Waele, Wim; Galle, Timothy; Bui, Tien Thanh; Roeck, Guido

2011-01-01

373

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Helmerich, Rosemarie; Ku?hn, Bertram; Nussbaumer, Alain

2007-01-01

374

Analysis of the Effects of Aggressive Shot Peening on Fatigue Life of 7075 ? T6 Aluminum Alloy  

Directory of Open Access Journals (Sweden)

Full Text Available For many years controlled shot peening was considered as a surface treatment. It is now clear that the performance of control shot peening in terms of fatigue depends on the balance between its beneficial (compressive residual stress and work hardening and beneficial effects (surface hardening.The overall aim of this paper is to study the effects of aggressive shot peening on fatigue life of 7075 ? T6 aluminum alloy. The fatigue life reduction factor (LRF due to the aggressive shot peening was established and empirical relations were proposed to describe the behavior of LRF, roughness and fatigue life. The benefits of shot peering in terms of fatigue life are dependent on the shot peening time (SPT. The higher SPT is the lower the benefit is. Higher roughness results in lower fatigue life.

Khairallah S. Jabur

2012-01-01

375

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

Science.gov (United States)

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

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

1991-01-01

376

Fatigue life assessment based on crack growth behavior in reduced activation ferritic/martensitic steel  

International Nuclear Information System (INIS)

Crack growth behavior under low cycle fatigue in reduced activation ferritic/martensitic steel, F82H IEA-heat (Fe-8Cr-2W-0.2V-0.02Ta), was investigated to improve the fatigue life assessment method of fusion reactor structural material. Low cycle fatigue test was carried out at room temperature in air at a total strain range of 0.4-1.5% using an hourglass-type miniature fatigue specimen. The relationship between the surface crack length and life fraction was described using one equation independent of the total strain range. Therefore, the fatigue life and residual life could be estimated using the surface crack length. Moreover, the microcrack initiation life could be estimated using the total strain range if there was a one-to-one correspondence between the total strain range and number of cycles to failure. The crack growth rate could be estimated using the total strain range and surface crack length by introducing the concept of the normalized crack growth rate. (author)

377

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

Science.gov (United States)

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

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

2013-12-01

378

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

379

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

Energy Technology Data Exchange (ETDEWEB)

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

Nogami, Shuhei, E-mail: shuhei.nogami@qse.tohoku.ac.jp [Department of Quantum Science and Energy Engineering, Tohoku University, 6-6-01-2, Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8579 (Japan); Takahashi, Manabu, E-mail: takahashi.manabu@jupiter.qse.tohoku.ac.jp [Department of Quantum Science and Energy Engineering, Tohoku University, 6-6-01-2, Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8579 (Japan); Hasegawa, Akira, E-mail: akira.hasegawa@qse.tohoku.ac.jp [Department of Quantum Science and Energy Engineering, Tohoku University, 6-6-01-2, Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8579 (Japan); Yamazaki, Masanori, E-mail: m-yamaza@imr.tohoku.ac.jp [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, 2145-2, Narita-cyo, Oarai, Ibaraki 311-1313 (Japan)

2013-11-15

380

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

Directory of Open Access Journals (Sweden)

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 re