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1

Effect of low cycle fatigue on subsequent high cycle fatigue life of 316L stainless steel  

International Nuclear Information System (INIS)

The effect of low cycle fatigue (LCF) on the subsequent high cycle fatigue (HCF) life of a 316L steel was investigated. A spectacular increase of HCF life following a certain number of LCF cycles is reported. A further increase in the number of LCF cycles leads to a drop in HCF life. (orig.)

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

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

International Nuclear Information System (INIS)

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

4

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

5

High cycle thermal fatigue issues in PWR nuclear power plants, life time improvement of some austenitic stainless steel components  

International Nuclear Information System (INIS)

Examples of high cycle thermal fatigue (HCTF) damage cases on PWR austenitic stainless steel components are reported. High cycle thermal fatigue risk is primarily due to mixing of cold and hot water, unexpected leaks of cold water through check valves or to turbulent penetration of hot water running in a main pipe into a connected line. When such thermal fatigue issues are identified in PWR power plants, manufacturing improvement such as inner surface polishing of austenitic stainless steel parts can be performed to increase the fatigue resistance of the components. (authors)

6

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 e 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.)

7

Physically short crack propagation in metals during high cycle fatigue  

OpenAIRE

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

Taylor, David

2009-01-01

8

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

9

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

10

High cycle fatigue properties of inconel 690  

International Nuclear Information System (INIS)

Inconel 690 is presently used as sleeve material and a replacement alloy in degraded steam generators, as well as the material for new steam generators. But Inconel 690 has low thermal conductivity which are 3-8% less than that of Inconel 600 at operating temperature. For the same power output, conduction area must be increased. As a result, more fluid induced vibration can cause a fatigue damage of Inconel 690. High cycle fatigue ruptures occurred in the U-bend regions of North Anna Unit 1 and Mihama Unit 2 steam generators. At this study, the effect of temperature on fatigue crack growth rate in Inconel 690 steam generator tube was investigated at various temperature in air environment. With increasing temperature, fatigue crack growth rate increased and grain size effect decreased. Chromium carbides which have large size and semi-continuous distribution in the grain boundaries decreased fatigue crack growth rate

11

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.n detail.

12

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

International Nuclear Information System (INIS)

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

13

High cycle fatigue life of 70 series engine cast aluminum rotor housing. Final report on task 2. 1. 6 extended life studies  

Energy Technology Data Exchange (ETDEWEB)

Fatigue studies conducted to project the expected life and safety factors of the rotor housing of cast aluminum 2013R natural gas fueled rotary engines (NGREs) are documented. The rotor housing was selected because previous studies showed this major engine component to be the critical item in determining fatigue life. The report describes the sequential steps required for fatigue life calculations, including the heat transfer, thermal stress, pressure stress, fatigue life, and safety factor analyses. The fatigue analysis requires the determination of thermal and presure stresses. The former is viewed as providing the steady-state component, while the latter contributes both to the steady-state and the alternating components of the stresses in the fatigue analysis. Both of these stresses are a function of the engine peak combustion pressure at the rated condition, but are somewhat independent of speed. The rated speed enters only in the calculation of heat transfer coefficients, and when translating the projected cycles-to-failure into hours of operating life.

Bazaz, R.J.

1988-11-18

14

High Cycle Thermal Fatigue in French PWR  

International Nuclear Information System (INIS)

Different fatigue-related incidents which occurred in the world on the auxiliary lines of the reactor coolant system (SIS, RHR, CVC) have led EDF to search solutions in order to avoid or to limit consequences of thermodynamic phenomenal (Farley-Tihange, free convection loop and stratification, independent thermal cycling). Studies are performed on mock-up and compared with instrumentation on nuclear power stations. At the present time, studies allow EDF to carry out pipe modifications and to prepare specifications and recommendations for next generation of nuclear power plants. In 1998, a new phenomenal appeared on RHR system in Civaux. A crack was discovered in an area where hot and cold fluids (temperature difference of 140 deg. C) were mixed. Metallurgic studies concluded that this crack was caused by high cycle thermal fatigue. Since 1998, EDF is making an inventory of all mixing areas in French PWR on basis of criteria. For all identified areas, a method was developed to improve the first classifying and to keep back only potential damage pipes. Presently, studies are performing on the charging line nozzle connected to the reactor pressure vessel. In order to evaluate the load history, a mock-up has been developed and mechanical calculations are realised on this nozzle. The paper will make an overview of EDF conclusions on these different points: - dead legs and vortex in a no flow connected line; - stratification; - mixing tees with high ?T. (authors)ng tees with high ?T. (authors)

15

High cycle fatigue of austenitic stainless steels  

International Nuclear Information System (INIS)

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

16

High cycle fatigue of austenitic stainless steels under random loading  

International Nuclear Information System (INIS)

The effect of high cycle random loading at 330deg C and at 550deg C on the fatigue resistance of austenitic stainless steels Type 316NL has been investigated. The aim was to improve the predictions of the consequences of thermal fluctuations occurring in some reactor components. The experimental means used for this purpose was a minicomputer, which generated random stationary Gaussian load sequences in a Markov matrix, and several servo-hydraulic fatigue testing machines. This method has the advantage of taking into account the mean load for each cycle. The specimens tested were taken from two plates which were at two different heats, one 45 mm thick and slightly cold worked, the other 26.5 mm thick. Random fatigue tests were mainly performed in the endurance region of the fatigue curve, using the stair-case method to determine the scatter. The experimental data were analyzed in terms of the test temperature and the irregularity factor, with the aim of establishing design curves for reactor components. The results obtained have shown that the random loading is more damaging than the constant amplitude loading when compared on the basis of the mean square root conventional fatigue limit. They have also shown that the linear damage accumulation, according to the Miner's rule, yields conservative results at least when used in conjunction with the probability density function of peaks for a case when the irregularity factor is near 100%. Based on these observations a methr 100%. Based on these observations a method is proposed for predicting the fatigue life from the design curves, which includes random loading effects with the irregularity factor as the indexing parameter. (orig.)

17

Very high cycle fatigue behavior of nickel-based superalloy Rene 88 DT  

Science.gov (United States)

The fatigue behavior of the polycrystalline nickel-based superalloy Rene 88 DT has been investigated at 593°C up to the very high cycle fatigue regime using ultrasonic fatigue techniques. Conventional damage tolerant methods failed to predict the fatigue life nor the large fatigue life viability of two orders of magnitude observed in the very high cycle regime. Fatigue crack initiation rather than fatigue crack growth is the life determining process in this alloy in the very high cycle regime. At 593°C, all fatigue failures have subsurface origins. Most fatigue crack initiation sites consist of a large crystallographic facet or a cluster of several large crystallographic facets. By combining electron backscatter diffraction, metallographic serial sectioning and SEM-stereo-image-based quantitative fractographic analysis, critical microstructure features associated with subsurface crystallographic fatigue crack initiation were identified. Subsurface fatigue cracks formed by the localization of cyclic plastic deformation on {111} slip planes in the region close to and parallel to twin boundaries in favorably oriented large grains. The facet plane in the crack initiation grain is parallel to the slip plane with the highest resolved shear stresses. Analytical calculations show that twin boundary elastic incompatibility stresses contribute to the onset of cyclic plastic strain localization in the fatigue crack initiation grains. Favorably oriented neighbor grains also can assist with fatigue crack initiation and especially early small crack propagation. Environment may play an important role in the shift of fatigue crack initiation sites from surface to subsurface at elevated temperature. The fatigue behavior of Rene 88 DT was also investigated under fully reversed loading at room temperature using ultrasonic fatigue techniques. Cyclic plastic strain localization and microcrack formation on specimen surfaces were quantitatively studied by EBSD. All microcracks examined in detail initiated near Sigma3 twin boundaries, especially E3 twin boundaries which are parallel to slip planes with the highest Schmid factor within crack initiation grains.

Miao, Jiashi

18

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

19

High-cycle fatigue properties of FBR grade type 316ss at elevated temperatures  

International Nuclear Information System (INIS)

It is known that cyclic thermal stresses are caused by thermal striping at locations where coolant with different temperatures mixes in FBR plants, and the maximum number of cycles in the service life reaches to 108-109 cycles. So, it is important to understand experimentally the relationship between the mechanical strength and the damage mechanism in high cycle fatigue region. This report summarizes the results of the high cycle fatigue tests of FBR grade type 316 stainless steel (316FR) a candidate material for FBR structures. The major results are as follows: (1) Twenty data of high cycle fatigue tests were obtained under axial strain controlled conditions in the temperature range of 500 - 600degC. The maximum number of cycles was 109. (2) The fatigue lives were increased as total strain range decreased, and no fatigue limit was observed. (3) When the number of cycles to failure reached 106 or more, the fracture mode changed from 'the surface crack type' to 'the internal crack type'. However, the effect of the fracture mode on the fatigue lives was not observed. (4) It was confirmed that the high cycle fatigue curve established based on the low cycle fatigue lives data which was proposed in 1988 predicts the experimental data conservatively. (author)

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

Coupling Between Mesoplasticity and Damage in High-cycle Fatigue  

OpenAIRE

Abstract The multiaxial fatigue loading in the high-cycle regime leads to localized mesoscopic plastic strain that occurs in some preferential directions of individual grains for most metallic materials. Crack initiation modeling is difficult in this fatigue regime because the scale where the mechanisms operate is not the engineering scale (macroscopic scale), and local plasticity and damage act simultaneously. This article describes a damage model based on the interaction between ...

Flaceliere, Laurent; Morel, Franck; Dragon, Andre?

2007-01-01

22

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

Science.gov (United States)

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

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

2014-12-01

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

Energy balance properties of steels subjected to high cycle fatigue  

OpenAIRE

The paper presents an experimental protocol developed to locally estimate the different terms of the energy balance associated with the high cycle fatigue (HCF) of steels. Namely, the deformation and dissipated energy are respectively derived from displacement and temperature fields obtained using digital image correlation (DIC) techniques and quantitative infrared thermography (QIRT). The combined processing of visible and infrared images shows the precocious, gradual and heterogeneous devel...

Chrysochoos, Andre?; Blanche, Antoine; Berthel, Bruno; Wattrisse, Bertrand

2011-01-01

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

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

29

Overload influence on a ferritic-bainitic steel high-cycle-fatigue strenght under variable amplitude loading.  

OpenAIRE

Automotive frame components are designed against fatigue crack nucleation under variable amplitude service loadings. These so-called service loadings correspond to the High-Cycle-Fatigue (HCF) domain, however overloads corresponding to the Low-Cycle-Fatigue (LCF) domain may occur in the car life (pavement climbing at high speed). The investigation of the effects of overloads on the HCF strength (from 105 to 107 cycles) is the goal of this study. From an industrial point of view, the final obj...

Bidouard, Hadrien

2009-01-01

30

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

International Nuclear Information System (INIS)

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

31

Fatigue crack initiation life prediction of railroad  

Science.gov (United States)

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

Tehrani, P. Hosseini; Saket, M.

2009-08-01

32

Microstructural Influences on Very-High-Cycle Fatigue-Crack Initiation in Ti-6246  

Science.gov (United States)

The fatigue behavior of an alpha + beta titanium alloy, Ti-6Al-2Sn-4Zr-6Mo, has been characterized in the very-high-cycle fatigue (VHCF) regime using ultrasonic-fatigue (20 kHz) techniques. Stress levels ( ? max) of 40 to 60 pct of the yield strength of this alloy have been examined. Fatigue lifetimes in the range of 106 to 109 cycles are observed, and fatigue cracks initiate from both surface and subsurface sites. This study examines the mechanisms of fatigue-crack formation by quantifying critical microstructural features observed in the fatigue-crack initiation region. The fracture surface near the fatigue-crack-initiation site was crystallographic in nature. Facets, which result from the fracture of primary alpha ( ? p ) grains, are associated with the crack-initiation process. The ? p grains that form facets are typically larger in size than average. The spatial distribution of ? p grains relative to each other observed near the initiation site did not correlate with fatigue life. Furthermore, the spatial distribution of ? p grains did not provide a suitable means for discerning crack-initiation sites from randomly selected nominal areas. Stereofractography measurements have shown that the facets observed at or near the initiation sites are oriented for high shear stress; i.e., they are oriented close to 45 deg with respect to the loading axis. Furthermore, a large majority of the grains and laths near the site of crack initiation are preferentially oriented for either basal or prism slip, suggesting that regions where ? p grains and ? laths have similar crystallographic orientations favor crack initiation. Microtextured regions with favorable and similar orientations of ? p grains and the lath ? are believed to promote cyclic-strain accumulation by basal and prism slip. Orientation imaging microscopy (OIM) indicates that these facets form on the basal plane of ? p grains. The absence of a significant role of spatial clustering of ? p grains, coupled with the observation of regions of microtexture on the order of 300 to 500 ?m supports the idea that variability in fatigue life in the very-high-cycle fatigue regime results from the variability in the nature (intensity, coherence, and size) of these microtextured regions.

Szczepanski, C. J.; Jha, S. K.; Larsen, J. M.; Jones, J. W.

2008-12-01

33

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

International Nuclear Information System (INIS)

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

34

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

35

The significance of crack initiation stage in very high cycle fatigue of steels  

Energy Technology Data Exchange (ETDEWEB)

Different stages of the Very High Cycle Fatigue (VHCF) crack evolution in tool steels have been explored using a 20 kHz ultrasonic fatigue testing equipment. Extensive experimental data is presented describing VHCF behaviour, strength and crack initiating defects in an AISI H11 tool steel. Striation measurements are used to estimate fatigue crack growth rate, between 10{sup -8} and 10{sup -6} m/cycle, and the number of load cycles required for a crack to grow to critical dimensions. The growth of small fatigue cracks within the ''fish-eye'' is shown to be distinctively different from the crack propagation behaviour of larger cracks. More importantly, the crack initiation stage is shown to determine the total fatigue life, which emphasizes the inherent difficulty to detect VHCF cracks prior to failure. Several mechanisms for initiation and early crack growth are possible. Some of them are discussed here: crack development by local accumulation of fatigue damage at the inclusion - matrix interface, hydrogen assisted crack growth and crack initiation by decohesion of carbides from the matrix. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Bergstroem, J. [Department of Materials Engineering, Karlstad University (Sweden); Burman, C.; Kazymyrovych, V.

2010-04-15

36

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

37

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)

38

The effect of low cycle fatigue cracks and loading history on high cycle fatigue threshold  

OpenAIRE

High cycle fatigue (HCF) has been of great concern of late in light of the many HCF gas turbine engine failures experienced by the U.S. Air Force. Due to the high frequency, failures occur rapidly when components sustain damage from other sources. Low cycle fatigue (LCF) can initiate cracks that produce such damage. This study investigates the HCF threshold of Ti-6A1-4V when naturally initiated small surface cracks (2a = 25 ?m–600 ?m) are present. Small surface cracks are initiated in not...

Moshier, Monty Allen

2000-01-01

39

High cycle thermal fatigue issues in PWR nuclear power plants, life time improvement of some austenitic stainless steel components; Cas de fatigue thermique a grand nombre de cycles dans des generateurs PWR, allongement de la duree de vie de pieces en acier inoxydable  

Energy Technology Data Exchange (ETDEWEB)

Examples of high cycle thermal fatigue (HCTF) damage cases on PWR austenitic stainless steel components are reported. High cycle thermal fatigue risk is primarily due to mixing of cold and hot water, unexpected leaks of cold water through check valves or to turbulent penetration of hot water running in a main pipe into a connected line. When such thermal fatigue issues are identified in PWR power plants, manufacturing improvement such as inner surface polishing of austenitic stainless steel parts can be performed to increase the fatigue resistance of the components. (authors)

Le Duff, J.A.; Lefrancois, A.; Meyzaud, Y. [AREVA NP, Materials and Technology Dept., 92 - Paris La Defense (France); Vernot, J.Ph.; Martin, D. [AREVA NP, Fluids and Structural Mechanics Dept., 92 - Paris La Defense (France); Mendez, J.; Lehericy, Y. [Ecole Nationale Superieure de Mecanique et d' Aerotechnique (ENSMA), 86 - Poitiers (France)

2007-03-15

40

Orientation dependence of the high cycle fatigue properties in a hot-cross rolled Al-Li 8090 alloy plate  

OpenAIRE

High cycle fatigue properties were studied in different directions within the rolling plane and in the short transverse direction of a hot-cross rolled Al-Li 8090 alloy plate (45 mm thick). The fatigue tests were conducted at constant stress amplitudes ranging from 30% to 100% of the yield strength ay in the rolling direction, R = 0.1, a frequency of 20 Hz, room temperature in air using a self-aligning four-point bend rig. It was found that the fatigue life of a sample loaded in the rolling d...

Zhai, Tg; Wilkinson, Aj; Martin, Jw

2002-01-01

41

Effects of high mean stress on the high-cycle fatigue behavior of PWA 1480  

International Nuclear Information System (INIS)

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. This paper describes results obtained in an ongoing program to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material

42

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

Energy Technology Data Exchange (ETDEWEB)

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)

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

2001-07-01

43

Reliability high cycle fatigue design of gas turbine blading system using probabilistic goodman diagram  

Energy Technology Data Exchange (ETDEWEB)

A framework for the probabilistic analysis of high cycle fatigue is developed. The framework will be useful to U.S. Air Force and aeroengine manufacturers in the design of high cycle fatigue in disk or compressor components fabricated from Ti-6Al-4V under a range of loading conditions that might be encountered during service. The main idea of the framework is to characterize vibratory stresses from random input variables due to uncertainties such as crack location, loading, material properties, and manufacturing variability. The characteristics of such vibratory stresses are portrayed graphically as histograms, or probability density function (PDF). The outcome of the probability measures associated with all the values of a random variable exceeding the material capability is achieved by a failure function g(X) defined by the difference between the vibratory stress and Goodman line or surface such that the probability of HCF failure is P{sub f} =P(g(X<0)). Design can then be based on a go-no go criterion based on an assumed risk. The framework can be used to facilitate the development of design tools for the prediction of inspection schedules and reliability in aeroengine components. Such tools could lead ultimately to improved life extension schemes in aging aircraft, and more reliable methods for the design and inspection of critical components. (orig.)

Herman Shen, M.-H. [Ohio State Univ., Columbus, OH (United States). Dept. of Aerospace Engineering and Aviation; Nicholas, T. [MLLN, Wright-Patterson AFB, OH (United States). Air Force Research Lab.

2001-07-01

44

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

45

Effects of ?-ferrite and welding structure on high-cycle fatigue properties of austenitic stainless steels weld metals  

International Nuclear Information System (INIS)

We studied the effects of ?-ferrite and welding structure on high-cycle fatigue properties for austenitic stainless steel weld metals at cryogenic temperatures. SUS304L and SUS316L weld metals contained 0% ?-ferrite (0% material) and 10% ?-ferrite (10% material) were prepared. High-cycle fatigue tests were carried out at 293, 77 and 4 K. The S-N curves of those weld metals shifted towards higher stress levels, i.e., the longer life side, with decreasing test temperature. The ratios of 106-cycles fatigue strength (FS) to tensile strength (TS) of 0% material decreased from 0.8 to 0.45 and those of 10% material decreased between 0.35 to 0.65 with decreasing test temperature. Fatigue crack initiation sites of SUS304L 10% material were almost at blowholes, and those of SUS316L 10% material were at weld pass interface boundaries. On the other hand, those of 0% materials were considered to be due to the interface of the solidification structure. Although ?-ferrite reduces toughness at cryogenic temperatures in austenitic stainless steel weld metals, the effects of ?-ferrite on high-cycle fatigue properties are not significant

46

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

47

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.

48

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

Energy Technology Data Exchange (ETDEWEB)

This article investigates effects of adding rare earth elements (RE) into a magnesium–aluminum–zinc alloy (the AZ91 alloy) on its high cycle fatigue (HCF) behavior. For this purpose, AZ91 and AZ91+1% RE (AZE911) alloys were gravity casted in a metallic die. RE elements were added to the AZ91 alloy in the form of mischmetals. Microscopic evaluations with the scanning electron microscopy (SEM) and mechanical tests include tensile, hardness and HCF behaviors, were performed on prepared samples. Rotary bending fatigue tests were carried out at a stress ratio (R) of ?1 and a frequency of 125 Hz, at the room temperature, in the air. The microscopic investigation demonstrates that the addition of 1% RE elements leads to the formation of Al{sub 11}RE{sub 3} intermetallic particles which is associated to the reduction of ?-(Mg{sub 17}Al{sub 12}) phases. Results of mechanical experiments suggest a negligible effect of adding 1% RE elements on mechanical properties of the AZ91 alloy. Curves of stress-life (S–N) shows an increase in the fatigue strength at 10{sup 5} cycles, from 100±10 MPa to 135±10 MPa, when RE elements were added to the AZ91 alloy.

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

2013-12-10

49

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

50

On the formation of crack networks in high cycle fatigue  

International Nuclear Information System (INIS)

A probabilistic model based on an initial distribution of sites is proposed to describe different aspects of the formation, propagation and coalescence of crack networks in thermomechanical fatigue. This model aims at bridging 3 scales. First the micro-scale, which is related to stage 1 of the fatigue process, it depends upon the details of the microstructure. The cracks are considered as micro-structurally short (they will be referred to as micro-cracks). This scale ends when meso-cracks are initiated. The second scale corresponds to the propagation of meso-cracks that form the network, it is related to the stage 2 of fatigue. The cracks are considered as physically small. Last, the third scale is concerned with coalesced meso-cracks that form a long crack. The interaction between cracks is modeled by considering shielding effects

51

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

52

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

53

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

Energy Technology Data Exchange (ETDEWEB)

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.

Milesi, M., E-mail: marc.milesi@mines-paristech.fr [MINES ParisTech, Center for Materials Forming (CEMEF), UMR CNRS 7635, BP 207, 06904 Sophia-Antipolis Cedex (France); Chastel, Y.; Hachem, E.; Bernacki, M.; Loge, R.E.; Bouchard, P.O. [MINES ParisTech, Center for Materials Forming (CEMEF), UMR CNRS 7635, BP 207, 06904 Sophia-Antipolis Cedex (France)

2010-07-15

54

On the high cycle fatigue behavior of duplex stainless steels: Influence of thermal aging  

International Nuclear Information System (INIS)

In this investigation the high cycle fatigue (HCF) behavior of an austenite-ferrite duplex stainless steel (DSS) is studied as a function of aging at 475 C. It is found that the HCF strength and the fatigue sensitivity of DSS increase with aging. The fatigue strength improvement results from the higher cyclic yield stress of the spinodally-hardened ferrite which induces an increasing difficulty for early propagation, into and through the ferritic matrix, of microcracks nucleated within austenite. The fatigue sensitivity impairment is suggested to be correlated to an easier microcrack nucleation stage in the aged DSS as compared to the annealed or unaged one. (orig.)

55

High cycle fatigue properties of irradiated and unirradiated stainless steel DIN 1.4948 plate at 823 K  

International Nuclear Information System (INIS)

High cycle fatigue experiments have been carried out on stainless steel DIN X 6 CrNi 1811 (Werkst. 1.4948, similar to AISI 304) in irradiated and reference condition. Specimens were irradiated at 823 K up to a fast fluence (E > 0.1 MeV) of 5x1024n.m-2 and a thermal fluence of 1.6x1024n.m-2. The nominal test temperature was 823 K; deviations from this nominal value were kept smaller than 3 K by avoiding too high test frequencies. The results indicate a slight increase of the fatigue limit after irradiation from 152.5 MPa to 162.5 MPa. For both conditions the fatigue curve has a horizontal part for Nsub(f) > 8x104 cycles. Striation counts indicate that a major part of the fatigue life is consumed by initiation. As a consequence fatigue life and possibly the fatigue limit are dependent on factors which influence the initiation stage of fatigue, like surface roughness, residual stresses and defects

56

High-cycle fatigue strength of a pultruded composite material  

OpenAIRE

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 ...

Vergani, L.; Guagliano, M.; Colombo, C.

2009-01-01

57

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. These small-diameter pipe branches in particles are often damaged due to high-cycle fatigue. In order to ensure the reliability of a plant it is important to detect fatigue damages 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'', which measures the vibration of the pipe branch using a non-contact sensor. (author)

58

Role of microstructural heterogeneities in multiaxial high cycle fatigue : application to laser assisted machining  

OpenAIRE

The purpose of this work is to modelize the damage mechanisms in multiaxial high cycle fatigue (HCF). The role of microstructural heterogeneities, and in particular those introduced via the manufacturing process of Laser Assisted Machining (LAM), is given particular attention. Firstly, in order to take into account the dispersion observed in fatigue data, a critical plane approach and a two scale model are proposed. More precisely, a Weibull type probabilistic approach is introduced in order ...

Nguyen Thi Thu, Huyen

2008-01-01

59

Very high cycle fatigue of copper: Evolution, morphology and locations of surface slip markings  

OpenAIRE

The surfaces of commercially pure polycrystalline copper specimens subjected to interrupted 20 kHz fatigue tests in the very high cycle fatigue regime were investigated. The stress amplitude needed to form the early slip markings was found twice lower than the stress amplitude required to fracture which confirmed the results obtained by Stanzl-Tschegg et al. (2007). Three types of slip markings were classified according to their morphology and their location in the polycrystalline material. T...

Phung, Ngoc-lam; Favier, Ve?ronique; Ranc, Nicolas; Vales, Fre?deric; Murghrabi, Hae?l

2014-01-01

60

Study of the high cycle thermal fatigue of austenitic stainless steels components in PWR water environment  

International Nuclear Information System (INIS)

The new approaches that have been recently introduced to account for the potential effects of the PWR water environment on the high cycle thermal fatigue of austenitic stainless steel components have been experimentally assessed under conditions matching the actual in service loadings. (authors)

61

High cycle fatigue damage mechanisms in cast aluminium subject to complex loads  

OpenAIRE

This article is dedicated to the high cycle fatigue behaviour of cast hypo-eutectic Al-Si alloys. In particular, the AlSi7Cu05Mg03 alloy is investigated. It presents the results of a vast experimental campaign undertaken to investigate the fatigue behaviour, and more specifically the fatigue damage mechanisms observed under complex loading conditions: plane bending with different load ratios, fully reversed torsion and equibiaxial bending with a load ratio of R = 0.1. A specific test set-up h...

Koutiri, Imade; Bellett, Daniel; Morel, Franck; Augustins, Louis; Adrien, Je?ro?me

2013-01-01

62

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)

63

Orientation dependence of the high cycle fatigue properties in a hot-cross rolled Al-Li 8090 alloy plate  

Energy Technology Data Exchange (ETDEWEB)

High cycle fatigue properties were studied in different directions within the rolling plane and in the short transverse direction of a hot-cross rolled Al-Li 8090 alloy plate (45 mm thick). The fatigue tests were conducted at constant stress amplitudes ranging from 30% to 100% of the yield strength {sigma}{sub y} in the rolling direction, R = 0.1, a frequency of 20 Hz, room temperature in air using a self-aligning four-point bend rig. It was found that the fatigue life of a sample loaded in the rolling direction was about ten times longer than that of a sample loaded in the short transverse direction at the same stress amplitude. The fatigue limit for the short transverse samples was measured to be about 30% {sigma}{sub y}, while it was about 40% {sigma}{sub y} for the longitudinal samples. Growth of fatigue cracks in the short transverse samples was predominantly intergranular, whereas it was markedly crystallographic (along a 111 plane in each grain) in the samples cut from the plate center when loading axis was parallel to the rolling plane. The inferior high cycle fatigue property of the short transverse samples is believed to be due to the combination of planar grain boundaries (parallel to {l_brace}110{r_brace} plane) being perpendicular to the load axis and the existence of trace elements, Na and K, in the alloy. Within the rolling plane, the fatigue behavior was relatively isotropic in the surface region of the plate, while in the plate center it was significantly inferior in the direction of about 35 relative to the rolling direction. Strong texture (mainly {l_brace}110{r_brace} left angle 111 right angle and {l_brace}110{r_brace} left angle 112 right angle) in the center of this alloy was the main factor that contributed to the in-plane anisotropy. (orig.)

Zhai, T. [Dept. of Chemical and Materials Engineering, Univ. of Kentucky, Lexington, KY (United States); Wilkinson, A.J.; Martin, J.W. [Dept. of Materials, Univ. of Oxford, Oxford (United Kingdom)

2002-07-01

64

Effect of microstructure and temperature on high cycle fatigue of powder metallurgy astroloy  

Energy Technology Data Exchange (ETDEWEB)

Load-controlled high cycle fatigue tests were performed on a powder metallurgy superalloy, hot isostatically pressed Astroloy, with fine (0.08 {mu}m) or coarse (0.8-1.2 {mu}m) {gamma}' phase varied by heat treatment. Tests were carried out in vacuum or in air at 25, 550, 650 and 725degC. Fracture characteristics were examined by scanning electron microscopy and transmission electron microscopy. The fine-{gamma}' specimens displayed approximately the same fatigue strength as the coarse-{gamma}' specimens at all test temperatures, even though they possess greatly different tensile properties. Therefore the coarse-{gamma}' specimens show higher normalized fatigue resistance than the fine-{gamma}' specimens. The fatigue ratio of the coarse-{gamma}' specimens increased gradually with increasing temperature to 725degC while the fatigue ratio of the fine-{gamma}' specimens increased sharply between 550 and 725degC. Both the fine- and the coarse-{gamma}' specimens exhibited stage I crack initiation at the surface and transgranular crack propagation when tested under vacuum. At high stress amplitudes, more extensive stage I cracking occurred in the fine-{gamma}' specimens. At low stress amplitudes, the fatigue lives for specimens with both {gamma}' sizes, tested in air, were extended compared with those under vacuum. No contribution of creep damage to the high cycle fatigue behavior was found for either microstructure. (orig.).

Isomoto, T.; Stoloff, N.S. (Materials Engineering Dept., Rensselaer Polytechnic Inst., Troy, NY (USA))

1990-04-20

65

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

66

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.

67

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,he 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.

68

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

OpenAIRE

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,...

Nikitin Alexander; Palin-Luc Thierry; Shanyavskiy Andrey; Bathias Claude

2014-01-01

69

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)

70

Effects of Laser Peening Treatment on High Cycle Fatigue and Crack Propagation Behaviors in Austenitic Stainless Steel  

Science.gov (United States)

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.

Masaki, Kiyotaka; Ochi, Yasuo; Matsumura, Takashi; Ikarashi, Takaaki; Sano, Yuji

71

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

Energy Technology Data Exchange (ETDEWEB)

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)

Poncelet, M.; Hild, F. [Univ Paris 11, PRES, Univ Paris 06, LMT Cachan, ENS Cachan, CNRS, F-94235 Cachan (France); Doudard, C.; Calloch, S. [Univ Brest, ENIB, ENSIETA, LBMS EA 4325, F-29806 Brest, (France); Weber, B. [ArcelorMittal Maizieres Res Voie Romaine, F-57283 Maizieres Les Metz (France)

2010-07-01

72

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

Science.gov (United States)

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 multiaxiality at a microscopic scale, whereas the second one relies on a probabilistic modelling of microplasticity 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.

Poncelet, M.; Doudard, C.; Calloch, S.; Weber, B.; Hild, F.

2010-04-01

73

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)

74

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

International Nuclear Information System (INIS)

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

75

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

76

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

Science.gov (United States)

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

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

1997-05-01

77

Real-time monitoring of acoustic linear and nonlinear behavior of titanium alloys during low-cycle fatigue and high-cycle fatigue  

Science.gov (United States)

An in-situ technique to measure sound velocity, ultrasonic attenuation and acoustic nonlinear property has been developed for characterization and early detection of fatigue damage in aerospace materials. For this purpose we have developed a computer software and measurement technique including hardware for the automation of the measurement. New transducer holder and special grips are designed. The automation has allowed us to test the long-term stability of the electronics over a period of time and so proof of the linearity of the system. Real-time monitoring of the material nonlinearity has been performed on dog-bone specimens from zero fatigue all the way to the final fracture under low-cycle fatigue test condition (LCF) and high-cycle test condition (HCF). Real-time health monitoring of the material can greatly contribute to the understanding of material behavior under cyclic loading. Interpretation of the results show that correlation exist between the slope of the curve described by the material nonlinearity and the life of the component. This new methodology was developed with an objective to predict the initiation of fatigue microcracks, and to detect, in-situ fatigue crack initiation as well as to quantify early stages of fatigue damage.

Frouin, Jerome; Sathish, Shamachary; Na, Jeong K.

2000-05-01

78

Effects of In-Situ Proton-Irradiation and Thermal-Pulse on the High-Cycle Fatigue Properties of Low Carbon 316 Stainless Steels  

OpenAIRE

For the modifîed 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, i...

Mizubayashi, H.; Tateishi, K.; Tanimoto, H.; Nakata, K.

1996-01-01

79

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

80

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

81

Nonlinear Ultrasonic to Assess Localized Plastic Deformation during High Cycle Fatigue  

Science.gov (United States)

Nonlinear ultrasonic is the new approach for the effective evaluation of material degradation in the area of non-destructive evaluation (NDE). Fatigue damage of a material produces a substantial distortion of ultrasonic waves propagating through the degraded material. The wave distortion is quantified by means of a material nonlinearity parameter ? that is defined as the ratio of the amplitude of the 2nd; harmonic to the square of the amplitude of the fundamental. This nonlinear parameter changes when, for instance, a distribution of microcracks appears inside the material. This feature has recently been found as a new potential application in the characterization of fatigued and degraded materials. In this present work, an attempt has been made to assess the localized plastic deformation during high cycle fatigue to locate the position of crack initiation much before the failure along the gage length of hourglass type specimen in polycrystalline copper by nonlinear ultrasonic technique.

Sagar, S. Palit; Metya, Avijit; Parida, N.; Ghosh, R. N.

2008-02-01

82

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

83

Effective Fatigue Stress and Criterion for High-Cycle Multi-axial Fatigue  

Science.gov (United States)

Multi-axial fatigue criterion corresponding to the limiting condition of complicated multi-axial stress state is very important in application. Stresses and deformations are usually elastic if cyclic loadings are near to the limiting condition. A definition of effective fatigue stress has been proposed. Adopting the effective fatigue stress, a multi-axial fatigue criterion has been proposed by considering the equivalence of multi-axial stresses to a uni-axial problem. To clarify the fatigue criterion for a uni-axial problem with arbitrary mean stress, a quantitative relationship between fatigue limit and mean stress has also been proposed and examined. To verify the multi-axial fatigue criterion, examinations have been carried out for the cases of pure shear, shear and axial, and two-axial fatigue by experimental results. It is found that the criterion agrees well with experimental results, even for the cases with various multi-axial mean stresses and phase differences. It is also found that the shear fatigue limit is not an independent material property in common metals.

Cai, Xiaojing; Xu, Jinquan

2015-01-01

84

Effective Fatigue Stress and Criterion for High-Cycle Multi-axial Fatigue  

Science.gov (United States)

Multi-axial fatigue criterion corresponding to the limiting condition of complicated multi-axial stress state is very important in application. Stresses and deformations are usually elastic if cyclic loadings are near to the limiting condition. A definition of effective fatigue stress has been proposed. Adopting the effective fatigue stress, a multi-axial fatigue criterion has been proposed by considering the equivalence of multi-axial stresses to a uni-axial problem. To clarify the fatigue criterion for a uni-axial problem with arbitrary mean stress, a quantitative relationship between fatigue limit and mean stress has also been proposed and examined. To verify the multi-axial fatigue criterion, examinations have been carried out for the cases of pure shear, shear and axial, and two-axial fatigue by experimental results. It is found that the criterion agrees well with experimental results, even for the cases with various multi-axial mean stresses and phase differences. It is also found that the shear fatigue limit is not an independent material property in common metals.

Cai, Xiaojing; Xu, Jinquan

2014-11-01

85

The interactive role of inclusions and SiC reinforcement on the high-cycle fatigue resistance of particle reinforced metal matrix composites  

Science.gov (United States)

The effect of intermetallic inclusions on the fatigue crack initiation and growth in 2080 Al alloy and 2080/SiC p composites was investigated. Using surface replication, it was determined that, in the high-cycle fatigue region, life is dominated by the initiation process. It was also determined that the majority of initiation sites were associated with intermetallic inclusions. While 2080/SiC/20 p showed a definitive relationship between inclusion size and fatigue life, i.e., a higher inclusion size resulted in lower fatigue life, there was no correlation in 2080/SiC/30 p . This was attributed to more of the load being shared by the higher volume fraction of SiC particles and smaller average inclusion sizes in the latter composite. A conceptual model is proposed that accounts for these observations and qualitatively shows the effect of reinforcement on stress enhancement in near-surface inclusions.

Chawla, N.; Andres, C.; Davis, L. C.; Jones, J. W.; Allison, J. E.

2000-03-01

86

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

87

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

88

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

International Nuclear Information System (INIS)

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

89

High cycle fatigue behavior of commercial purity zirconium under cyclic reversed bend loading  

International Nuclear Information System (INIS)

High cycle fatigue behavior of commercial-purity zirconium cast and annealed at 900 degree C x 6 h conditions under cyclic reversed bend loading is investigated. The testing results show that the cyclic deformation behavior of zirconium is characterized with three stages, i.e. hardening, softening and saturation with their relative proportions depending on the heat treatment conditions and cyclic ranges. On the basis of SEM examination it can be confirmed that the HCF failure process is developed by coalescence of several microcracks nucleating along the persistent slip bands, twin/matrix boundaries and grain boundaries. TEM analysis exhibits that the predominant dislocation configuration of HCF specimens is parallel dislocation walls. {l1 2-bar 1}, {l0 1-bar 2} and {l1 2-bar 2}-types twins are an important plastic deformation modes in hexagonal metals. The fatigue deformation mechanism of zirconium is discussed finally

90

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)

91

High cycle fatigue of a die cast AZ91E-T4 magnesium alloy  

International Nuclear Information System (INIS)

This study reveals the micro-mechanisms of fatigue crack nucleation and growth in a commercial high-pressure die cast automotive AZ91E-T4 Mg component. Mechanical fatigue tests were conducted under R=-1 conditions on specimens machined at different locations in the casting at total strain amplitudes ranging from 0.02% to 0.5%. Fracture surfaces of specimens that failed in the high cycle fatigue regime with lives spanning two orders of magnitude were examined using a scanning electron microscope. The difference in lives for the Mg specimens was primarily attributed to a drastic difference in nucleation site sizes, which ranged from several hundred ?m's to several mm's. A secondary effect may include the influence of average secondary dendrite arm spacing and average grain size. At low crack tip driving forces (Kmaxmax>3.5 MPa ? m fractured particles and boundary decohesion created weak paths for fatigue crack propagation, and consequently the cracks followed the interdendritic regions, leaving serrated markings as the crack progressed through this heterogeneous region. The ramifications of the results on future modeling efforts are discussed in detail discussed in detail

92

Investigation of thermal high cycle and low cycle fatigue mechanisms of thick thermal barrier coatings  

Energy Technology Data Exchange (ETDEWEB)

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 this paper, the mechanisms of fatigue crack initiation and propagation in a ZrO{sub 2}-8wt%Y{sub 2}O{sub 3} thermal barrier coating, under simulated engine thermal LCF and HCF conditions, are investigated using a high power CO{sub 2} laser. Experiments showed that the combined LCF-HCF tests induced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. Lateral crack branching and the ceramic/bond coat interface delaminations were also facilitated by HCF thermal loads, even in the absence of severe interfacial oxidation. Fatigue damage at crack wake surfaces, due to such phenomena as asperity/debris contact induced cracking and splat pull-out bending during cycling, were observed especially for the combined LCF-HCF tests. It is found that 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. The failure associated with HCF process, however, is mainly associated with a surface wedging mechanism. The interaction between the LCF, HCF and ceramic coating creep, and the relative importance of LCF and HCF in crack propagation are also discussed based on the experimental evidence. (orig.) 19 refs.

Zhu Dongming; Miller, R.A. [National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center

1998-05-01

93

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)

94

Influence of microstructure on high-cycle fatigue of Ti-6Al-4V: Bimodal vs. lamellar structures  

Science.gov (United States)

The high-cycle fatigue (HCF) of titanium alloy turbine engine components remains a principal cause of failures in military aircraft engines. A recent initiative sponsored by the United States Air Force has focused on the major drivers for such failures in Ti-6Al-4V, a commonly used turbine blade alloy, specifically for fan and compressor blades. However, as most of this research has been directed toward a single processing/heat-treated condition, the bimodal (solution-treated and overaged (STOA)) microstructure, there have been few studies to examine the role of microstructure. Accordingly, the present work examines how the overall resistance to high-cycle fatigue in Ti-6Al-4V compares between the bimodal microstructure and a coarser lamellar ( ?-annealed) microstructure. Several aspects of the HCF problem are examined. These include the question of fatigue thresholds for through-thickness large and short cracks; microstructurally small, semi-elliptical surface cracks; and cracks subjected to pure tensile (mode I) and mixed-mode (mode I+II) loading over a range of load ratios (ratio of minimum to maximum load) from 0.1 to 0.98, together with the role of prior damage due to sub-ballistic impacts (foreign-object damage (FOD)). Although differences are not large, it appears that the coarse lamellar microstructure has improved smooth-bar stress-life (S-N) properties in the HCF regime and superior resistance to fatigue-crack propagation (in pure mode I loading) in the presence of cracks that are large compared to the scale of the microstructure; however, this increased resistance to crack growth compared to the bimodal structure is eliminated at extremely high load ratios. Similarly, under mixed-mode loading, the lamellar microstructure is generally superior. In contrast, in the presence of microstructurally small cracks, there is little difference in the HCF properties of the two microstructures. Similarly, resistance to HCF failure following FOD is comparable in the two microstructures, although a higher proportion of FOD-induced microcracks are formed in the lamellar structure following high-velocity impact damage.

Nalla, R. K.; Ritchie, R. O.; Boyce, B. L.; Campbell, J. P.; Peters, J. O.

2002-03-01

95

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 ir 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)

96

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

97

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

Science.gov (United States)

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

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

2001-01-01

98

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

99

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 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)

100

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

Energy Technology Data Exchange (ETDEWEB)

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

Nie, Xiangfan, E-mail: skingkgd@163.com; He, Weifeng; Zhou, Liucheng; Li, Qipeng; Wang, Xuede

2014-01-31

101

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

International Nuclear Information System (INIS)

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

102

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

1995-11-01

103

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)

104

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)

105

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 brittle phase,in spite of the increase in layer depth. (author)

106

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

107

High cycle fatigue behavior of Incoloy 800H in a simulated high-temperature gas-cooled reactor helium environment  

Energy Technology Data Exchange (ETDEWEB)

The current study was an attempt to evaluate the high cycle fatigue strength of Incoloy 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 corrosion in the helium test gas. Results from in-helium tests were compared to those from a standard air environment. It was found that the mechanisms of fatigue failure were very complex and involved recovery/recrystallization of the surface ground layer on the specimens, sensitization, hardness changes, oxide scale integrity, and oxidation at the tips of propagation cracks. For certain situations a corrosion-fatigue process seems to be controlling. However, for the helium environment studied, there was usually no aging or test condition for which air gave a higher fatigue strength.

Soo, P.; Sabatini, R.L.; Epel, L.G.; Hare, J.R. Sr.

1980-01-01

108

Low-to-high cycle fatigue behavior of wood-concrete composite beams with notched interlayer connections  

OpenAIRE

In a wood-concrete composite structural member the wood layer overlapped by the concrete layer are interconnected to prevent the relative slip. In this research notched shear-key interlayer connections were used. A problem with using these novel composite members in bridges is that the fatigue behavior of the composite member is not well known. This paper presents an S-N curve for fatigue verification of notched wood-concrete connections based on static and low-to-high-cycle repeated loading ...

Balogh, Jeno; Fragiacomo, Massimo; Gutkowski, Richard M.; Atadero, Rebecca; Ivanyi, Peter

2013-01-01

109

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

International Nuclear Information System (INIS)

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

110

Effect of retained austenite on high cycle fatigue behaviour of carburized 14NiCr11 steel  

Science.gov (United States)

Two vacuum carburizing treatments were applied to ductile steel 14NiCr11 to obtain equivalent hardened layers with retained austenite contents of 25% and 41%. The properties of the carburized surfaces were examined and characterized before fatigue tests and during cyclic loading. Transformation of retained austenite into martensite during loading, was evaluated by dispersive X-ray diffraction method. The effects of this transformation on the residual stresses have been measured by X ray diffraction in martensite and in retained austenite structures. It was shown that the cyclic retained austenite transformation caused a redistribution of the compressive residual stresses and an increased surface hardness that stabilized after a small number of cycles. The dependence of fatigue behaviour on surface properties was determined, and a relationship between the stabilized state and the fatigue limit is suggested. A phenomenological approach is proposed to correlate the influence of surface hardening and the stabilized residual stresses on fatigue limit of carburized specimens. The Crossland, Dang Van and Findley-Matake, multiaxial high cycle fatigue criteria were used in this approach and results have shown a good agreement with experimental data.

Jeddi, D.; Sidhom, H.; Lieurade, H.-P.

2008-11-01

111

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

International Nuclear Information System (INIS)

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

112

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

OpenAIRE

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 t...

Turon Travesa, Albert; Costa I Balanzat, Josep; Camanho, Pedro P.; Da?vila, Carlos G.

2006-01-01

113

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

114

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.

115

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

116

Life prediction techniques for combined creep and fatigue  

International Nuclear Information System (INIS)

The techniques that are currently available for predicting the life of metallic materials when they fail at high temperatures under the combined action of creep and fatigue are reviewed. The work concentrates on those theories that are relevant to engineering design without specifically employing fracture mechanics concepts. As a consequence this generally limits the prerequisite data to that of low cycle fatigue under high rate strain cycling conditions and monotonic creep at a given temperature. Some techniques require additional or alternative data on tensile ductility, high cycle fatigue, cyclic plasticity and creep. Each technique is appraised from the results of laboratory experiments. It is shown that life may be predicted quite reliably in one instance but not in another. Some attempt is made to provide explanations and recommendations where these anomalies occur. The range of application is also clarified. Many approaches are limited to strain controlled cycling under uniaxial stress conditions. Only a limited number may further be applied to predict life for cycles in which ratcheting occurs. At present it appears that very few techniques are available to predict the creep-fatigue life of materials under high temperature multiaxial stress states. (author)

117

Simulation of damage evolution in a uni-directional titanium matrix composite subjected to high cycle fatigue  

Energy Technology Data Exchange (ETDEWEB)

Among the advanced material systems under consideration for use in gas turbine engines special consideration is given to the family of metal matrix composites especially the Titanium matrix composites. This is attributed mainly to the superior stiffness to weight ratio as compared to other conventional materials. The lack of appropriate material models capable of simulating the material behavior realistically is a major drawback in the success of this material system. In the current research the results of numerical simulations for the damage evolution in a unidirectional Titanium matrix composite subjected to high cycle fatigue loading are presented. The employed micro-mechanical fatigue damage model has been developed previously by the authors. Results obtained from the numerical simulations include those from parametric studies on the influence of various model parameters as well as those for damage evolution in the constituents during the material lifetime. Comparison of the final results for the number of cycles to failure for room temperature fatigue with those obtained from experimental investigations show good agreement. (author)

Echle, R. [HILTI Servicegesellschaft GbR, Kaufering (Germany); Voyiadjis, G.Z. [Louisiana State University, Baton Rouge, LA (United States). Dept. of Civil and Environmental Engineering

1999-10-01

118

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 (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

119

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

120

High cycle fatigue behavior of as-cast Mg{sub 96.34}Gd{sub 2.5}Zn{sub 1}Zr{sub 0.16} alloy fabricated by semi-continuous casting  

Energy Technology Data Exchange (ETDEWEB)

This article presents the tension–compression high cycle fatigue behavior of as-cast Mg{sub 96.34}Gd{sub 2.5}Zn{sub 1}Zr{sub 0.16} alloy produced by semi-continuous casting at ambient temperature. The relationship between stress amplitude and cycles to failure is established, which indicates that fatigue strength of this alloy is approximately 105±8 MPa. Fracture surface of specimens were examined using a scanning electron microscope, indicating that the fatigue cracks all initiate from the oxides located at the surface. Different from other cast Mg alloys, there exist two kinds of unique fatigue morphologies at the fatigue propagation region, which consists of fine steps. Meanwhile, there is a fatigue life gap between 10{sup 5} and 10{sup 7} cycles on the S–N curve, which probably demonstrates that the growth rate of the fatigue cracks of as-cast Mg{sub 96.34}Gd{sub 2.5}Zn{sub 1}Zr{sub 0.16} alloy is relatively large, and once the fatigue cracks form, the samples could fails in less than 10{sup 5} cycles.

He, Zongling; Fu, Penghuai, E-mail: fph112sjtu@sjtu.edu.cn; Wu, Yujuan; Peng, Liming; Zhang, Yu; Li, Zhenming

2013-12-10

121

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

International Nuclear Information System (INIS)

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

122

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

123

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

124

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.

125

Damage study of an austenitic stainless steel in high cycle multiaxial fatigue regime  

International Nuclear Information System (INIS)

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

126

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 ithermal 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)

127

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

128

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

129

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)

130

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

131

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.

132

High-cycle fatigue of 10M Ni–Mn–Ga magnetic shape memory alloy in reversed mechanical loading  

International Nuclear Information System (INIS)

Application of Ni–Mn–Ga magnetic shape memory alloys in magnetic-field-induced actuation relies on their performance in long-term high-cycle fatigue. In this paper the performance and changes in the microstructure of a Ni–Mn–Ga 10M martensite single crystal material are reported in a long-term mechanically induced shape change cycling. The longest test was run for 2 × 109 cycles at a frequency of 250 Hz and a strain amplitude of ± 1%. After the test a clear increase of the dynamic stiffness of the material was detected. Three specimens out of ten were cycled until fracture occurred and their fracture mechanism was studied. It was observed that the macroscopic crack growth took place roughly at a 45° angle with respect to the loading direction that was along the (100) crystallographic direction of the sample. The macroscopic fracture plane seemed to correspond roughly to the {111} crystal planes. On a microscopic scale the fracture propagated in a step-like manner at least partly along crystallographic planes. The steps at the fracture plane correspond to the {101} twin planes, with the height of steps along the (101) direction. The final fracture of the samples occurred in a brittle manner after the critical stress was exceeded

133

High-cycle fatigue of 10M Ni-Mn-Ga magnetic shape memory alloy in reversed mechanical loading  

Science.gov (United States)

Application of Ni-Mn-Ga magnetic shape memory alloys in magnetic-field-induced actuation relies on their performance in long-term high-cycle fatigue. In this paper the performance and changes in the microstructure of a Ni-Mn-Ga 10M martensite single crystal material are reported in a long-term mechanically induced shape change cycling. The longest test was run for 2 × 109 cycles at a frequency of 250 Hz and a strain amplitude of ± 1%. After the test a clear increase of the dynamic stiffness of the material was detected. Three specimens out of ten were cycled until fracture occurred and their fracture mechanism was studied. It was observed that the macroscopic crack growth took place roughly at a 45° angle with respect to the loading direction that was along the lang100rang crystallographic direction of the sample. The macroscopic fracture plane seemed to correspond roughly to the {111} crystal planes. On a microscopic scale the fracture propagated in a step-like manner at least partly along crystallographic planes. The steps at the fracture plane correspond to the {101} twin planes, with the height of steps along the lang101rang direction. The final fracture of the samples occurred in a brittle manner after the critical stress was exceeded.

Aaltio, I.; Soroka, A.; Ge, Y.; Söderberg, O.; Hannula, S.-P.

2010-07-01

134

Advanced creep-fatigue life prediction model  

International Nuclear Information System (INIS)

A study has been made to extend the mechanistic model for creep-fatigue damage assessment which has initially been developed to describe creep-fatigue damage of Modified 9Cr-1Mo steel by taking into account a retardation in initiation of creep damage. This extension is necessary to apply the mechanistic model to 316FR stainless steel. Experimental verification showed that the extended model gives an excellent prediction of creep-fatigue life of Modified 9Cr-1Mo and 316FR steel. (orig.)

135

Considerations concerning fatigue life of metal matrix composites  

Science.gov (United States)

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

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

1993-05-01

136

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)

137

Life prediction technique for ratcheting fatigue  

International Nuclear Information System (INIS)

A push-pull strain controlled low cycle fatigue test was made under uniaxial stress at room temperature with 304 stainless steel in which a completely reversed strain was superposed upon a stepwisely increasing mean strain in every n? strain cycle (SMSI Test), in order to study a fatigue life reduction due to a development of accumulated strain due to ratcheting. The results of the SMSI Test was compared with the results by the cyclic tension test conducted with a 304 steel at room temperature in order to examine a similarity of the SMSI Test. The SMSI Test shows also a development of a mean axial stress which is affected with an increment of the mean strain and cyclic strain range as it was in the cyclic tension test. A dominant reduction of a fatigue life was observed also in the SMSI Test. This life reduction is very similar to that observed in the cyclic tension test and is lower than what predicted by a linear damage interaction between a fatigue damage and a ductility damage. Suggested is to take into account the effect of progressive ratcheting strain on a very low cycle fatigue life in which a primary plus secondary stress exceeds the shake down limit

138

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

OpenAIRE

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

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

2010-01-01

139

Study of the high cycle thermal fatigue of austenitic stainless steels components in PWR water environment; Etude du comportement en fatigue oligocyclique des aciers inoxydables austenitiques en milieu eau primaire REP  

Energy Technology Data Exchange (ETDEWEB)

The new approaches that have been recently introduced to account for the potential effects of the PWR water environment on the high cycle thermal fatigue of austenitic stainless steel components have been experimentally assessed under conditions matching the actual in service loadings. (authors)

Le Duff, J.A.; Lefrancois, A.; Vernot, J.Ph.; Martin, D.; Calonne, O. [AREVA, 75 - Paris (France)

2007-11-15

140

Fatigue life and backface strain predictions in adhesively bonded joints  

OpenAIRE

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

Solana, Ag; Crocombe, Ad; Ashcroft, Ia

2010-01-01

141

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)

142

Predicting fatigue life of metal bellows  

Science.gov (United States)

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

Daniels, C. M.

1968-01-01

143

Predicting the Fatigue life of Structures  

Science.gov (United States)

Report reviews fracture-mechanics technology for predicting life expectancy of structural components subjected to cyclic loads. Report covers analytical tools for modeling and forecasting subcritical fatigue-crack growth in structures. It emphasizes use of tools in practical, day-to-day problems of engineering design, development, and decisionmaking.

Besuner, P. M.; Harris, D. O.; Thomas, J. M.; Allison, D. E.; Bannantine, J. M.; Brown, S. B.; Davis, C. S.; Derbalian, G. A.; Eischen, J. W.; Fowler, G. F.; Osteraas, J. D.; Robinson, J. N.; Sire, R. A.; Vroman, G. A.

1985-01-01

144

Fatigue maps and multistage life prediction methods  

International Nuclear Information System (INIS)

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

145

Fatigue maps and multistage life prediction methods  

Energy Technology Data Exchange (ETDEWEB)

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

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

1992-04-01

146

The relationship between observed fatigue damage and life estimation models  

Science.gov (United States)

Observations of the surface of laboratory specimens subjected to axial and torsional fatigue loadings has resulted in the identification of three damage fatigue phenomena: crack nucleation, shear crack growth, and tensile crack growth. Material, microstructure, state of stress/strain, and loading amplitude all influence which of the three types of fatigue damage occurs during a dominant fatigue life fraction. Fatigue damage maps are employed to summarize the experimental observations. Appropriate bulk stress/strain damage parameters are suggested to model fatigue damage for the dominant fatigue life fraction. Extension of the damage map concept to more complex loadings is presented.

Kurath, Peter; Socie, Darrell F.

1988-01-01

147

High-Strength Bolt Corrosion Fatigue Life Model and Application  

OpenAIRE

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

Wang Hui-li; Qin Si-feng

2014-01-01

148

Fatigue life prediction of bonded primary joints  

Science.gov (United States)

The validation of a proposed fatigue life prediction methodology was sought through the use of aluminum butt and scarf joint and graphite/epoxy butt joint specimens in a constant amplitude fatigue environment. The structural properties of the HYSOL 9313 adhesive system were obtained by mechanical test of molded heat adhesive specimens. Aluminum contoured double cantilever beam specimens were used to generate crack velocity versus stress intensity factor data. The specific objectives were: (1) to ascertain the feasibility of predicting fatigue failure of an adhesive in a primary bonded composite structure by incorporating linear elastic crack growth behavior; and (2) to ascertain if acoustic emission and/or compliance measurement techniques can be used to detect flaws.

Knauss, J. F.

1979-01-01

149

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)

150

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

151

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)

152

Fatigue Life Investigation of PZT Ceramics by MSP Method  

OpenAIRE

The cycle fatigue of PZT ceramic under different stress was investigated by modified small punch (MSP) tests. The research results show that residual strength and piezoelectric constant decrease with increasing cycle stress, which is attributed to crack propagation during cyclic stress process. The value of fatigue crack propagation (n) is calculated to be 395 according to the relationship between maximum stress and fatigue life. The fatigue life under series cycle maximum stress can be induc...

Deng Qi-huang, Wang Lian-jun

2012-01-01

153

A predictive fatigue life model for anodized 7050 aluminium alloy  

OpenAIRE

The objective of this study is to predict fatigue life of anodized 7050 aluminum alloy specimens. In the case of anodized 7050-T7451 alloy, fractographic observations of fatigue tested specimens showed that pickling pits were the predominant sites for crack nucleation and subsequent failure. It has been shown that fatigue failure was favored by the presence of multiple cracks. From these experimental results, a fatigue life predictive model has been developed including multi-site crack consid...

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

2013-01-01

154

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

Science.gov (United States)

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

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

2003-09-01

155

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)

156

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

157

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

Energy Technology Data Exchange (ETDEWEB)

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.

Soo, P.; Sabatini, R.L.

1984-08-01

158

High cycle fatigue behavior of a nanostructured composite produced via extrusion of amorphous Al{sub 89}Gd{sub 7}Ni{sub 3}Fe{sub 1} alloy powders  

Energy Technology Data Exchange (ETDEWEB)

A nanostructured composite Al{sub 89}Gd{sub 7}Ni{sub 3}Fe{sub 1} alloy was created by extruding atomized amorphous Al{sub 89}Gd{sub 7}Ni{sub 3}Fe{sub 1} 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.

El-Shabasy, Adel B., E-mail: ashabasy@hotmail.com [Dept. of Design and Prod. Eng., Faculty of Eng., Ain Shams University, Cairo 11517 (Egypt); Dept. of Mat. Sci. and Eng., Case Western Reserve University, Cleveland, OH 44106 (United States); Hassan, Hala A. [Dept. of Design and Prod. Eng., Faculty of Eng., Ain Shams University, Cairo 11517 (Egypt); Dept. of Mat. Sci. and Eng., Case Western Reserve University, Cleveland, OH 44106 (United States); Liu Yi [Dept. of Chemistry, Wayne State University, Detroit, MI 48202 (United States); Dept. of Mat. Sci. and Eng., Case Western Reserve University, Cleveland, OH 44106 (United States); Li Dingqiang; Lewandowski, John J. [Dept. of Mat. Sci. and Eng., Case Western Reserve University, Cleveland, OH 44106 (United States)

2009-07-15

159

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

International Nuclear Information System (INIS)

Low-pressure steam turbine blades are usually made of martensitic steels with Cr contents between 9 and 12%, which combine good corrosion resistance, high mechanical strength and sufficient ductility. The inhomogeneous flow field behind the vanes generates high-frequency oscillations above 1 kHz. In addition, the blades with lengths up to 1.5 m are operated at rotational speeds up to 3000 rpm, resulting in large centrifugal forces leading to the superposition of extremely high mean stresses. Also resonance oscillations during start-up and shutdown cannot be completely excluded. Currently, the components are designed using high safety factors against S-N curves with an assumed asymptotic fatigue limit above 107 load cycles. Nevertheless, fatigue cracks are observed even at high number of cycles, starting from the blade root without pre-damage by erosion or steam droplet impingement. While fatigue failure usually occurs at the surface, fatigue cracks at very high number of cycles (> 108) initiate at oxides or intermetallic inclusions below the surface. This transition between both failure mechanisms in the Very High-Cycle Fatigue (VHCF) regime is in the focus of numerous current research activities, because numbers of cycles above 108 can be attained in a viable period of time using the recently developed high-frequency testing techniques operated at 20 kHz. Also for wind turbines, gas turbines, bearings, springs, etc. VHCF issues become increasingly important. Within this work, the fatigue life and damage behavior of a martensitic Cr-steel during fatigue loading with and without high mean stresses at number of cycles to failure above 108 was analyzed. On the one hand, the studies gave insights into the relation between fatigue life and fatigue damage evolution of the investigated group of high-strength steels in the very high cycle fatigue regime (up to 2·109). In particular, the influence of high mean stresses on the VHCF behavior (fracture origin, crack growth, fatigue life) which was not investigated in detail before is studied and the crack initiation and propagation mechanisms are analyzed by electron microscopy (SEM, TEM / FIB). With this, the work contributes to the reliable design of future low-pressure steam turbines. The results show that in particular non-metallic inclusions in the steel cause fracture by fatigue cracks initiated in the volume under very high cycle fatigue conditions. This fatigue behavior can be described very well by means of fracture mechanics approaches over a wide range of load ratios.

160

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

161

Effects of conventional machining on high cycle fatigue behavior of the intermetallic alloy Ti-47Al-2Nb-2Cr (at.%)  

Energy Technology Data Exchange (ETDEWEB)

The TiAl based alloy, Ti-47Al-2Nb-2Cr (at.%), was used as a model system to explore effects of machining-induced surface deformation on fatigue behavior of an intermetallic alloy with limited ductility. Conventional machining processes, such as grinding and turning, harden TiAl to depths ranging from 40 to 180 {mu}m. Turning doubled the hardness to approximately 500 VHN in the outer 20 {mu}m, and hardness increased at least 50 VHN to a depth of 180 {mu}m. The deformed layer formed during machining recrystallized after 1 h at 760 C. Axial fatigue tests were performed by step loading every 10{sup 6} cycles through a fixed set of stress levels until failure. At room temperature, mean fatigue strength was not affected by surface condition. The outer 20 {mu}m of the electropolished surface hardened to the same level as the turned samples during the fatigue test. After hardening, these two surfaces would have similar crack initiation resistance and, therefore, similar fatigue strengths. At 760 C, turning improved the average fatigue strength by 5%, and the average life at the final stress level by about 1.5 orders of magnitude. Fatigue resistance of the turned samples was improved by formation of a continuous, crack initiation resistant, recrystallized layer in the outer 30-50 {mu}m during the test. (orig.) 27 refs.

Jones, P. [GM Powertrain, Saginaw, MI (United States); Eylon, D.

1999-05-15

162

Fatigue Life Investigation of PZT Ceramics by MSP Method  

Directory of Open Access Journals (Sweden)

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

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

2012-10-01

163

Fatigue life of automotive rubber jounce bumper  

International Nuclear Information System (INIS)

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

164

Fatigue life of automotive rubber jounce bumper  

Science.gov (United States)

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

Sidhu, R. S.; Ali, Aidy

2010-05-01

165

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-09-15

166

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

Energy Technology Data Exchange (ETDEWEB)

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-O{sub 2} alloy that is marketed under the trade name ATI 425{sup TM}. 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 (N{sub f}) 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.

Srivatsan, T.S., E-mail: tsrivatsan@uakron.edu [Division of Materials Science and Engineering, Department of Mechanical Engineering, University of Akron, Akron, OH 44325-3903 (United States); Kuruvilla, Mithun [Division of Materials Science and Engineering, Department of Mechanical Engineering, University of Akron, Akron, OH 44325-3903 (United States); Park, Lisa [Department of Geology, University of Akron, Akron, OH 44325, United States of America (United States)

2010-01-15

167

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.

168

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

International Nuclear Information System (INIS)

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

169

Conductor fatigue-life research. Final report  

Energy Technology Data Exchange (ETDEWEB)

This is the final report of Research Project RP 1278-1 sponsored by the Electric Power Research Institute and carried out at the Civil Engineering Department of Auburn University (Auburn, Alabama). The objective of this study was to evaluate the effects of reducing vibration amplitudes of ACSR conductors which had been minimally damaged by aeolian vibration. The aeolian vibration was simulated by mechanical means in a controlled laboratory situation and the reduction in vibration amplitudes was a simulation of the addition of amplitude limiting devices (dampers). Conductors were vibrated at high amplitudes until a predetermined number of strand breaks occurred, after which the vibration was continued at reduced amplitudes. Three different ACSB conductors were tested: 795 KCM 26/7, 795 KCM 45/7, and 397.5 KCM 26/7. These conductors were chosen to establish the effects of conductor size and stranding on the amplitude reduction tests. Two different amplitude reductions were used to establish a threshold value for a maximum reduced amplitude. Previous preliminary research by others indicated that amplitude reductions extended the working life of conductors. This research expanded the amplitude reduction values and conductor sizes and strandings tested. For each set of parameters, four duplicative tests were performed to give statistical credence to the data. The results of the investigation indicated that amplitude reductions arrested fatigue strand breakage in each case. Electric utilities can utilize the results of this EPRI project in assessing the fatigue life of minimally damaged transmisson lines and in evaluating techniques for mitigating fatigue damage.

Ramey, G.E.

1981-07-01

170

Rolling-element fatigue life of AMS 5900 balls  

Science.gov (United States)

The rolling-element fatigue life of AMS 5900 12.7-mm (1/2-in.) dia was determined in five-ball fatigue testers. The 10% life with the warm headed AMS 5900 balls was equivalent to that of AMS 5749 and over eight times that of AISI M-50. The AMS balls fabricated by cold heading had small surface cracks which initiated fatigue spalls where these cracks were crossed by running tracks. The cold-headed AMS 5900 balls had a 10% fatigue life an order of magnitude less than that of the warm headed balls even when failures on the cold headed balls at visible surface cracks were omitted.

Parker, R. J.

1983-01-01

171

Effect of surface irregularities on bellows fatigue life  

Science.gov (United States)

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

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

1968-01-01

172

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

International Nuclear Information System (INIS)

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

173

Fatigue life of metals under cyclic loading in vacuum  

Science.gov (United States)

The effect of vacuum on the cyclic strength of metals is examined. Experimental data are presented of studies to clarify the mechanism of vacuum influence on fatigue failure. The dependence of copper and armco-iron fatigue life on vacuum level is studied. It is found that the presence of saturation on the curve of fatigue life versus vacuum level is common for the materials studied. The effect of vacuum on fatigue fracture of copper is studied over a wide range of deformations. It is shown that fatigue life increase under vacuum conditions and the observed characteristics of the fatigue fracture itself in vacuum are associated with homogenization of the plastic deformation under these conditions.

Verkin, B. I.; Lyubarskiy, I. M.; Boychuk, V. M.; Grinberg, N. M.; Alekseyev, A. I.

1974-01-01

174

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

175

Fatigue life prediction for carbon-epoxy composite design  

Science.gov (United States)

A simple design method for the prediction of fatigue life for long fiber carbon-epoxy composites with multi-angular lay-ups is presented. The approach, based in part on the traditional metallic method of fatigue life prediction, can be applied to fully tensile, fully compressive or part-tensile part-compressive loading of either constant or variable amplitude. Predictions produced by the method are compared with extensive data from fatigue tests on XAS/914C material for both relatively fatigue-sensitive and -insensitive lay-ups.

Wright, B. D.

176

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)

177

Fatigue life characterization for piezoelectric macrofiber composites  

International Nuclear Information System (INIS)

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

178

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

OpenAIRE

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

Zhang, Xiang; Wang, Z.

2003-01-01

179

Prediction of residual fatigue life using nonlinear ultrasound  

Science.gov (United States)

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.

Amura, Mikael; Meo, Michele

2012-04-01

180

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)

181

Residual fatigue life estimation using a nonlinear ultrasound modulation method  

Science.gov (United States)

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

Piero Malfense Fierro, Gian; Meo, Michele

2015-02-01

182

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.))

183

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

184

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

185

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

186

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

2014-11-01

187

An investigation on fatigue life of borided AISI 1010 steel  

Directory of Open Access Journals (Sweden)

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

O.N. Celik

2009-01-01

188

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

Science.gov (United States)

The nickel-hydrogen secondary battery system is now the one of choice for use in GEO satellites. It offers superior energy density to that of nickel-cadmium, with a lifetime that is at least comparable in terms of both cycle life and overall operating life. While the number of deep cycles required for GEO use is small, LEO satellites with long lifetimes (5 to 10 years) will require secondary battery systems allowing 30,000 to 60,000 useful cycles which are characterized by an approximately 2C charge rate and C average discharge rate. Recent work has shown that birnessite MnO2 doped with bismuth oxide can be cycled at very high rates (6C) over a very large number of cycles (thousands) at depths-of-discharge in the 85 to 90 percent range, based on two electrons, which discharge at the same potential in a flat plateau. The potential is about 0.7 V vs. hydrogen, with a cut-off at 0.6 V. At first sight, this low voltage would seem to be a disadvantage, since the theoretical energy density will be low. However, it permits the use of lightweight materials that are immune from corrosion at the positive. The high utilization and low equivalent weight of the active material, together with the use of teflon-bonded graphite for current collection, result in very light positives, especially when these are compared with those in a derated nickel-hydrogen system. In addition, the weight of the pressure vessel falls somewhat, since the dead volume is lower. Calculations show that a total system will have 2.5 times the Ah capacity of a derated nickel-hydrogen LEO battery, so that the energy density, based on 1.2 V for nickel-hydrogen and 0.7 V for MnO2-hydrogen, will be 45 percent higher for comparable cycling performance.

Appleby, A. John; Dhar, Y. J.; Murphy, O. J.; Srinivasan, Supramaniam

1989-12-01

189

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

190

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

Energy Technology Data Exchange (ETDEWEB)

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.

Bantounas, Ioannis [Department of Materials, Imperial College, South Kensington, London SW7 2AZ (United Kingdom); Dye, David, E-mail: david.dye@imperial.ac.uk [Department of Materials, Imperial College, South Kensington, London SW7 2AZ (United Kingdom); Lindley, Trevor C [Department of Materials, Imperial College, South Kensington, London SW7 2AZ (United Kingdom)

2010-06-15

191

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

192

Prestraining and its influence on subsequent fatigue life  

Energy Technology Data Exchange (ETDEWEB)

An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid uniform gage section were fatigued to failure under fully-reversed strain-control. Additional specimens were prestrained to 2 percent, 5 percent, and 10 percent (engineering strains) in the tensile direction and to 2 percent (engineering strain) in the compressive direction under stroke-control, and were subsequently fatigued to failure under fully-reversed strain-control. Experimental results are compared with estimates of remaining fatigue lives (after prestraining) using three life prediction approaches: (1) the Linear Damage Rule; (2) the Linear Strain and Life Fraction Rule; and (3) the nonlinear Damage Curve Approach. The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, best remaining fatigue life predictions were obtained with the nonlinear Damage Curve Approach.

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

1995-03-01

193

Prestraining and its influence on subsequent fatigue life  

Energy Technology Data Exchange (ETDEWEB)

An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid uniform gage section were fatigued to failure under fully reversed strain control. Additional specimens were prestrained to 2, 5, and 10% (engineering strains) in the tensile direction and to 2% (engineering strain) in the compressive direction under stroke control and were subsequently fatigued to failure under fully reversed strain control. Experimental results are compared with estimates of remaining fatigue lives (after prestraining) using three life prediction approaches: (1) the linear damage rule (LDR), (2) the linear strain and life fraction rule (LSLFR), and (3) the nonlinear damage curve approach (DCA). The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, the best remaining fatigue life predictions were obtained with the nonlinear damage curve approach.

Kalluri, S. [NYMA, Inc., Cleveland, OH (United States). NASA Lewis Research Center; Halford, G.R.; McGaw, M.A. [NASA Lewis Research Center, Cleveland, OH (United States)

1996-12-31

194

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

195

Prestraining and Its Influence on Subsequent Fatigue Life  

Science.gov (United States)

An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid uniform gage section were fatigued to failure under fully-reversed strain-control. Additional specimens were prestrained to 2 percent, 5 percent, and 10 percent (engineering strains) in the tensile direction and to 2 percent (engineering strain) in the compressive direction under stroke-control, and were subsequently fatigued to failure under fully-reversed strain-control. Experimental results are compared with estimates of remaining fatigue lives (after prestraining) using three life prediction approaches: (1) the Linear Damage Rule; (2) the Linear Strain and Life Fraction Rule; and (3) the nonlinear Damage Curve Approach. The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, best remaining fatigue life predictions were obtained with the nonlinear Damage Curve Approach.

Halford, Gary R.; Mcgaw, Michael A.; Kalluri, Sreeramesh

1995-01-01

196

Fatigue life and strain hardening behavior of JLF-1 steel  

Energy Technology Data Exchange (ETDEWEB)

Low cycle fatigue (LCF) properties of JLF-1 steel were studied from room temperature (RT) to 873 K in a vacuum condition using engineering size cylinder specimens with 8 mm in diameter. When the fatigue life was plotted against the plastic strain range, the fatigue life curves at RT, 673 K and 873 K were on different lines, which is not in agreement with the Coffin's model. The TEM images showed that dislocation rearrangements forming cell structure and keeping high density at room temperature. But dislocation cell structure was not observed at 873 K, dislocation density decrease to low level. Loss of dislocation pile up will result in reduction of strain hardening at high temperature. So, the loss of strain hardening will be responsible for the increase of fatigue life at high temperature when plotted against the plastic strain range.

Li Huailin [China Institute of Atomic Energy, P.O. Box 275-51, Beijing 102413 (China)], E-mail: lihuailin2003@yahoo.com.cn; Nishimura, Arata; Muroga, Takeo; Nagasaka, Takuya [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan)

2009-04-30

197

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

198

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 100> 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

199

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

200

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

201

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

202

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

203

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)

204

Multiaxial fatigue models for short glass fibre reinforced polyamide. Part II: Fatigue life estimation  

OpenAIRE

Components made of short fibre reinforced thermoplastics are increasingly used in the automotive industry, and more frequently subjected to fatigue loadings during their service life. The determination of a predictive fatigue criterion is therefore a serious issue for the designers, and requires the knowledge of the local mechanical response. As the cyclic behaviour of polymeric material is reckoned to be highly nonlinear, even at room temperature, an accurate constitutive model is a prelimin...

Launay, Antoine; Maitournam, M. H.; Marco, Yann; Raoult, Ida

2013-01-01

205

a Study on the Fretting Fatigue Life of Zircaloy Alloys  

Science.gov (United States)

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

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

206

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

207

Fatigue life prediction modeling for turbine hot section materials  

Science.gov (United States)

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

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

1989-01-01

208

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

209

Fatigue life of the casting-magnesium alloy AZ91  

International Nuclear Information System (INIS)

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

210

Fatigue Crack Propagation and Fatigue Life Evaluation of High-Performance Steel using Modified Forman Model  

International Nuclear Information System (INIS)

Fatigue crack propagation behavior and the fatigue life in-high performance steel were investigated by means of fatigue crack propagation tests under constant loading conditions of 'R=0.1 and f=0.1 Hz', 'R=0.3 and f=0.3 Hz', and 'R=0.5 and f=0.5 Hz' for the load ratio and frequency, respectively. A modified Forman model was developed to describe the fatigue crack propagation behavior for the conditions. The modified Forman model is applicable to all fatigue crack propagation regions I, II, and III by implementing the threshold stress intensity factor range and the effective stress intensity factor range caused by crack closure. The results show that predicted fatigue lives of Forman and modified Forman models were 8,814 and 12,292 cycles, respectively when the crack propagated approximately 5.0 mm and the load ratio and frequency were both 0.1. Comparison of the test results indicates that the modified Forman model showed much more effective fatigue crack propagation behavior in high-performance steel

211

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)

212

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.

Petersen, Rasmus Ingomar; Agerskov, Henning

1996-01-01

213

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)

214

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

215

Prediction of fatigue life using extreme statistics analysis  

International Nuclear Information System (INIS)

Fatigue fracture in machine components is produced by surface micro-crack from stress concentration area such as notch and material defect. It is difficult to predict the remaining fatigue life of mechanical components because the surface micro-crack on critical area initiates and grows with statistical distribution. Plane bending fatigue tests were carried out on the plain specimen of Al 2024-T3 and the initiation and growth behavior of surface micro cracks were observed. The statistical distribution of surface length of multiple micro cracks and their maximum length were investigated. The maximum surface crack length distributions were analyzed on the basis of the statistics of extremes in order to examine the prediction of remaining life

216

Prediction of fatigue life using extreme statistics analysis  

Energy Technology Data Exchange (ETDEWEB)

Fatigue fracture in machine components is produced by surface micro-crack from stress concentration area such as notch and material defect. It is difficult to predict the remaining fatigue life of mechanical components because the surface micro-crack on critical area initiates and grows with statistical distribution. Plane bending fatigue tests were carried out on the plain specimen of Al 2024-T3 and the initiation and growth behavior of surface micro cracks were observed. The statistical distribution of surface length of multiple micro cracks and their maximum length were investigated. The maximum surface crack length distributions were analyzed on the basis of the statistics of extremes in order to examine the prediction of remaining life.

Lee, Dong Woo; Joo, Won Sik; Hong, Soon Hyeok [Donga Univ., Busan (Korea, Republic of); Cho, Seok Swoo [Samcheok National Univ., Samcheok (Korea, Republic of)

2002-09-01

217

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

218

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

OpenAIRE

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 und...

Yates, John R.; Choi Jae-Chil; Shahrum Abdullah; Giacomin, Joseph A.

2008-01-01

219

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

220

Evolution of creep-fatigue life prediction models  

Science.gov (United States)

The evolution of high-temperature, creep-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940s. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches have been identified as being combinations of fourteen different classifications. This review is intended to aid both developers and users of high-temperature fatigue life prediction methods by providing a background from which choices can be made.

Halford, Gary R.

1991-01-01

221

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

222

Ductility normalized-strain-range partitioning life relations for creep-fatigue life predictions  

Science.gov (United States)

Techniques utilizing strainrange partitioning may be used to estimate the effects of the environment on the high-temperature, low-cycle, creep-fatigue resistance of alloys. Three levels of ductility-normalized strainrange-partitioning life relations are discussed: (1) strainrange partitioning relations from ductility data, (2) strainrange partitioning relations scaled by ductility ratios, and (3) strainrange partitioning life relations with measured PP lines. The procedures have demonstrated good agreement with available creep-fatigue data.

Halford, G. R.; Saltsman, J. F.; Hirschberg, M. H.

1978-01-01

223

Fatigue Life and Strain Hardening Behavior of JLF-1 Steel  

Energy Technology Data Exchange (ETDEWEB)

Full text of publication follows: Development of reactor materials and blankets is a critical issue for early realization of fusion energy. A reduced activation ferritic/martensitic steel, JLF-I, is considered as one of the candidate alloys for the first wall application of fusion reactor. In this paper, the low cycle fatigue (LCF) properties of JLF-1 steel were studied from room temperature (RT) to 873 K in a vacuum condition using engineering size cylinder specimens with 8 mm in diameter. The fatigue life at elevated temperature was almost as same as that at RT when the life was plotted against the total strain range. But when the life was plotted against the plastic strain range, the fatigue life curves for RT, 673 K and 873 K of JLF-1 were on different lines, which is not in agreement with the Coffin's model. The TEM images showed that dislocation structure is dependent on temperature. At RT, dislocation rearrangements forming cell structure and keeping high density. At 673 K, dislocation decrease to medium level, dislocation cell was observed at 10. cycle. However the cell structure did not remain during the following fatigue and were not observed at the TEM images at 500. cycle and the final failure at 673 K. At 873 K, the cell structure was not observed, dislocation density decrease to low level. Loss of dislocation pile up will result in reduction of strain hardening at high temperature. So, the loss of strain hardening will be responsible for the increase of fatigue life at high temperature when plotted against the plastic strain range. (authors)

Li, H. [China Institute of Atomic Energy, China Institute of Atomic Energy, 275-51 Box, 102413 Bejing (China); Nishimura, A.; Muroga, T.; Nagasaka, T. [National Institute for Fusion Science - NIPS, 322-6 Oroshi, 509-5292 Toki, Gifu (Japan)

2007-07-01

224

Fatigue Life Assessment of Selected Engineering Materials Based on Modified Low-Cycle Fatigue Test  

Directory of Open Access Journals (Sweden)

Full Text Available In this study, the mechanical tests were carried out on ductile iron of EN-GJS-600-3 grade and on grey cast iron of EN-GJL-250 grade.The fatigue life was evaluated in a modified low-cycle fatigue test (MLCF, which enables the determination of parameters resulting fromthe Manson-Coffin-Morrow relationship.The qualitative and quantitative metallographic studies conducted by light microscopy on selected samples of ductile iron with spheroidalgraphite and grey cast iron with lamellar graphite (showing only small variations in mechanical properties, confirmed also smallvariations in the geometrical parameters of graphite related with its content and morphological features.

M. Maj

2013-01-01

225

Fatigue Life Assessment of Selected Engineering Materials Based on Modified Low-Cycle Fatigue Test  

OpenAIRE

In this study, the mechanical tests were carried out on ductile iron of EN-GJS-600-3 grade and on grey cast iron of EN-GJL-250 grade.The fatigue life was evaluated in a modified low-cycle fatigue test (MLCF), which enables the determination of parameters resulting fromthe Manson-Coffin-Morrow relationship.The qualitative and quantitative metallographic studies conducted by light microscopy on selected samples of ductile iron with spheroidalgraphite and grey cast iron with lamellar graphite (s...

Maj, M.

2013-01-01

226

Cumulative fatigue damage behavior of MAR M-247  

Science.gov (United States)

The objective was to examine the room temperature fatigue and nonlinear cumulative fatigue damage behavior of the cast nickel-based superalloy, MAR M-247. The fatigue test matrix consisted of single-level, fully reversed fatigue experiments. Two series of tests were performed: one of the two baseline fatigue LCF (Low-Cycle Fatigue) life levels was used in the first loading block, and the HCF (High-Cycle Fatigue) baseline loading level was used in the second block in each series. For each series, duplicate tests were performed at each applied LCF life fraction.

Mcgaw, Michael A.; Halford, Gary R.; Kalluri, Sreeramesh

1991-01-01

227

Simulation work of fatigue life prediction of rubber automotive components  

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-05-15

228

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.

229

Bending Fatigue Initiation Life Estimation of Disposable Spur Gears  

OpenAIRE

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 p...

Yuefeng Li; Xudong Pan; Guanglin Wang

2013-01-01

230

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)

231

In Situ Imaging of High Cycle Fatigue Crack Growth in Single Crystal Nickel-Base Superalloys by Synchrotron X-Radiation  

Energy Technology Data Exchange (ETDEWEB)

A novel X-ray synchrotron radiation approach is described for real-time imaging of the initiation and growth of fatigue cracks during ultrasonic fatigue (f=20 kHz). We report here on new insights on single crystal nickel-base superalloys gained with this approach. A portable ultrasonic fatigue instrument has been designed that can be installed at a high-brilliance X-ray beamline. With a load line and fatigue specimen configuration, this instrument produces stable fatigue crack propagation for specimens as thin as 150 {mu}m. The in situ cyclic loading/imaging system has been used initially to image real-time crystallographic fatigue and crack growth under positive mean axial stress in the turbine blade alloy CMSX-4.

Liu, Liu; Husseini, Naji S.; Torbet, Christopher J.; Kumah, Divine P.; Clarke, Roy; Pollock, Tresa M.; Jones, J.Wayne (Michigan)

2008-05-01

232

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

233

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

234

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

235

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

236

Analysis of effect of design transients and fatigue damage on RPV design life  

International Nuclear Information System (INIS)

This paper presents the effect of design transient and fatigue damage on RPV design life by using the results of fatigue analysis, fatigue crack propagation analysis and fast fracture mechanics analysis. The result shows that 60-year design life of RPV satisfies the RCCM code criteria. (authors)

237

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

OpenAIRE

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

Yan Yifei; Shao Bing; Liu Jinkun; Cheng Lufeng

2013-01-01

238

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

Science.gov (United States)

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

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

2015-01-01

239

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

Science.gov (United States)

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

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

2014-11-01

240

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

241

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

Directory of Open Access Journals (Sweden)

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

Bogdan LIGAJ

2014-12-01

242

Evaluation of fatigue life characteristic of a real waterwork pipe using the probability density function  

International Nuclear Information System (INIS)

The fatigue characteristics of a material or a structure are generally derived from fatigue tests of standard specimens. However, test results of standard specimens are different from those of real structures or components. Therefore, to calculate more accurate fatigue life, the geometrical effect and surface condition must be considered by comparing test results of standard specimens with those of real structures or components. Thus the object of this paper is to evaluate the fatigue characteristics of a real waterwork pipe. Also, to evaluate fatigue characteristic based on life distribution, the statistical fatigue characteristics were analyzed by the normal distribution and related data of P-S-N curve

243

A comparison of two total fatigue life prediction methods  

Energy Technology Data Exchange (ETDEWEB)

A 2-D analytical model which is termed the PICC-RICC model combines the effects of plasticity-induced crack closure (PICC) and roughness-induced crack closure (RICC). The PICC-RICC model handles naturally the gradual transition from RICC to PICC dominated crack growth. In this study, the PICC-RICC model is combined with a crack nucleation model to predict the total fatigue life of a notched component. This modified PICC-RICC model will be used to examine several controversial aspects of an earlier, computationally simpler total-life model known as the IP model.

Chen, N.; Lawrence, F.V.

1999-07-01

244

Corrosion fatigue behavior and life prediction method under changing temperature condition  

International Nuclear Information System (INIS)

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

245

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

246

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

247

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

248

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.

249

A review of creep-fatigue life prediction methods  

International Nuclear Information System (INIS)

A review of ten creep-fatigue life prediction methods is made. An application to continuous fatigue and cyclic relaxation data on an austenitic stainless steel is shown, then the models are used to evaluate the number of cycles to failure in hypothetical tests involving very long hold times (until 105 mn). Such an exercise allows to point out the similarities (and the differences) between the different methods, to discuss their general trends and finally to characterize two main classes of models, the one taking the plastic strain, the other the integrated actual stress as the critical variable to represent hold time influence: this opposite choice may lead to opposite responses if very long hold times are considered. (orig.)

250

Fatigue in cold-forging dies: Tool life analysis  

DEFF Research Database (Denmark)

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

Skov-Hansen, P.; Bay, Niels

1999-01-01

251

The Effect of Geometry on Fatigue Life for Bellows  

Science.gov (United States)

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

Kim, Jinbong

252

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)

253

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

Science.gov (United States)

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

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

1993-01-01

254

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

Science.gov (United States)

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

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

1993-07-01

255

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

256

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

Energy Technology Data Exchange (ETDEWEB)

Low-pressure steam turbine blades are usually made of martensitic steels with Cr contents between 9 and 12%, which combine good corrosion resistance, high mechanical strength and sufficient ductility. The inhomogeneous flow field behind the vanes generates high-frequency oscillations above 1 kHz. In addition, the blades with lengths up to 1.5 m are operated at rotational speeds up to 3000 rpm, resulting in large centrifugal forces leading to the superposition of extremely high mean stresses. Also resonance oscillations during start-up and shutdown cannot be completely excluded. Currently, the components are designed using high safety factors against S-N curves with an assumed asymptotic fatigue limit above 107 load cycles. Nevertheless, fatigue cracks are observed even at high number of cycles, starting from the blade root without pre-damage by erosion or steam droplet impingement. While fatigue failure usually occurs at the surface, fatigue cracks at very high number of cycles (> 108) initiate at oxides or intermetallic inclusions below the surface. This transition between both failure mechanisms in the Very High-Cycle Fatigue (VHCF) regime is in the focus of numerous current research activities, because numbers of cycles above 108 can be attained in a viable period of time using the recently developed high-frequency testing techniques operated at 20 kHz. Also for wind turbines, gas turbines, bearings, springs, etc. VHCF issues become increasingly important. Within this work, the fatigue life and damage behavior of a martensitic Cr-steel during fatigue loading with and without high mean stresses at number of cycles to failure above 108 was analyzed. On the one hand, the studies gave insights into the relation between fatigue life and fatigue damage evolution of the investigated group of high-strength steels in the very high cycle fatigue regime (up to 2·109). In particular, the influence of high mean stresses on the VHCF behavior (fracture origin, crack growth, fatigue life) which was not investigated in detail before is studied and the crack initiation and propagation mechanisms are analyzed by electron microscopy (SEM, TEM / FIB). With this, the work contributes to the reliable design of future low-pressure steam turbines. The results show that in particular non-metallic inclusions in the steel cause fracture by fatigue cracks initiated in the volume under very high cycle fatigue conditions. This fatigue behavior can be described very well by means of fracture mechanics approaches over a wide range of load ratios.

Kovacs, Stephan

2014-07-01

257

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

258

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

OpenAIRE

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

259

Development of a Generic Creep-Fatigue Life Prediction Model  

Science.gov (United States)

The objective of this research proposal is to further compile creep-fatigue data of steel alloys and superalloys used in military aircraft engines and/or rocket engines and to develop a statistical multivariate equation. The newly derived model will be a probabilistic fit to all the data compiled from various sources. Attempts will be made to procure the creep-fatigue data from NASA Glenn Research Center and other sources to further develop life prediction models for specific alloy groups. In a previous effort [1-3], a bank of creep-fatigue data has been compiled and tabulated under a range of known test parameters. These test parameters are called independent variables, namely; total strain range, strain rate, hold time, and temperature. The present research attempts to use these variables to develop a multivariate equation, which will be a probabilistic equation fitting a large database. The data predicted by the new model will be analyzed using the normal distribution fits, the closer the predicted lives are with the experimental lives (normal line 1 to 1 fit) the better the prediction. This will be evaluated in terms of a coefficient of correlation, R 2 as well. A multivariate equation developed earlier [3] has the following form, where S, R, T, and H have specific meaning discussed later.

Goswami, Tarun

2002-01-01

260

Fatigue Life Analysis of Thrust Ball Bearing Using ANSYS  

OpenAIRE

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. ...

Prabhat Singh*1; , Prof Upendra Kumar Joshi2

2014-01-01

261

Continuum Fatigue Damage Modeling for Use in Life Extending Control  

Science.gov (United States)

This paper develops a simplified continuum (continuous wrp to time, stress, etc.) fatigue damage model for use in Life Extending Controls (LEC) studies. The work is based on zero mean stress local strain cyclic damage modeling. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modeling. Stress based continuum models are derived. Extension to plastic strain-strain rate models are also presented. Application of these models to LEC applications is considered. Progress toward a nonzero mean stress based continuum model is presented. Also, new nonlinear explicit equation forms in terms of stress amplitude are also derived for this case.

Lorenzo, Carl F.

1994-01-01

262

Role of defects in fatigue damage mechanisms of cast polycrystalline superalloy MAR-M 247  

OpenAIRE

High-cycle fatigue life of nickel-based superalloy MAR-M 247 was experimentally determined for as-cast material and material processed by hot isostatic pressing (HIP). Fatigue testing was conducted at temperatures 650, 800, 900??C in laboratory air. HIP was done at the following conditions: 1200??C/100?MPa/240?min. It has been found that HIP significantly improves the fatigue life. Obtained results indicate that main factors which determine the fatigue strength of material in both...

Šmíd Miroslav; Fintová Stanislava; Kunz Ludvík; Huta? Pavel

2014-01-01

263

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

OpenAIRE

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

So, Winnie K. W.; Gene Marsh; Ling, W. M.

2009-01-01

264

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

International Nuclear Information System (INIS)

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

265

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

Directory of Open Access Journals (Sweden)

Full Text Available The aim of the fatigue experiment study is to solve the fatigue fracture problem of X70 submarine tubing when it is under the scouring effect of offshore current. The multilevel fatigue experiments are carried out following the internation (GB4337-84 recommended method. The standard round bar fatigue specimen was made by the material of submarine pipeline steel. The fatigue life of submarine pipeline steel in different survival probability and P-S-N curve were achieved. According to reliability numerical analysis method, the reliability fatigue life of pipeline steel in different stress level is got. The results show that the fatigue life of X70 submarine pipeline steel obeys the normal distribution. The detection of submarine pipeline scouring condation should be enhanced and the pipeline zone which was scoured seriously should be repaired and controlled effectively in order to reduce the scouring effect of ocean current.

Yan Yifei

2013-02-01

266

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

Science.gov (United States)

Fighter/trainer empennages and STOL (Short Take-Off and Landing) aircraft flap systems are subjected to severe acoustic pressure levels as high as 150-170 dB. As a result, acoustic fatigue has become one of the major factors in design. Empennages and flap systems are also subject to high temperatures and thus the influence of thermal buckling on fatigue life must be taken into consideration. To estimate the sonic fatigue life of skin structures, combined use is made of the Monte Carlo method of non-linear panel response analysis and local stress-strain simulations with rheological models. Calculations were conducted and comparison of the results with experimental data shows that the method estimates the sonic fatigue life accurately when adequate values of fatigue notch factors are chosen. Example calculations with thermal as well as static pressure effects were also carried out and the effect of thermal buckling on sonic fatigue life is clarified.

Maekawa, S.

1982-01-01

267

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)

268

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

269

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

DEFF Research Database (Denmark)

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

IbsØ, Jan Behrend; Agerskov, Henning

1996-01-01

270

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

OpenAIRE

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

271

Development and testing of a high cycle life 30 A-h sealed AgO-Zn battery  

Science.gov (United States)

A two-phase program was initiated to investigate design parameters and technology to develop an improved AgO-Zn battery. The basic performance goal was 100 charge/discharge cycles (22 h/2 h) at 50 percent depth of discharge following a six-month period of charged stand at room temperature. Phase 1, cell evaluation, involved testing 70 cells in five-cell groups. The major design variables were active material ratios, electrolyte concentrations, separator systems, and negative plate shape. Phase 1 testing showed that cycle life could be improved 10 percent to 20 percent by using greater ratios of zinc to silver oxide and higher electrolyte concentrations. Wedge-shaped negatives increased cycle life by nearly 100 percent. Phase 2 battery evaluation, which was initiated before the Phase 1 results were known completely, involved evaluation of six designs as 19-cell batteries. Only one battery exceeded 100 cycles following nine months charged stand.

Bogner, R. S.

1972-01-01

272

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

273

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

International Nuclear Information System (INIS)

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

274

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

275

Fatigue damage interaction behavior of PWA 1480  

Science.gov (United States)

The fatigue damage interaction behavior of PWA 1480 single crystal alloy has been experimentally established for the two-level loading case in which a block of low-cycle fatigue loading is followed by high-cycle fatigue loading to failure. A relative life ratio N1/N2 (where N1 and N2 are the low- and high-cycle fatigue baseline lives, respectively) of approximately 0.002 was explored to assess the interaction behavior. The experimental results thus far show evidence of a loading order interaction effect to a similar degree of detriment as has been observed in polycrystalline materials. Current generation single crystal alloys in general, and PWA 1480 in particular, contain pores; indeed, it was observed in all cases that specimen failure initiated from pores connected with or immediately below the surface. Detailed fractographic and metallographic studies are currently being made to assess the nature of the porosity in terms of its effect on fatigue life.

Mcgaw, Michael A.

1987-01-01

276

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

277

Creep-Fatigue Life Assessment for Sn-3.0Ag-0.5Cu Solder  

Science.gov (United States)

This paper describes the creep-fatigue life assessment of Sn-3.0Ag-0.5Cu solder under pull-push loading using fast-fast, fast-slow, slow-fast and strain-hold strain waveforms. Strain controlled creep-fatigue tests were carried out using solid bar specimen, and the effect of strain waveform on the creep-fatigue life was discussed. Creep-fatigue damage was evaluated by the linear damage rule, the frequency modified fatigue life, the ductility exhaustion model, the strain range partitioning method and the grain boundary sliding model. The strain range partitioning method and the grain boundary sliding model only predicted the creep-fatigue lives within a small scatter.

Zhang, Shengde; Ogawa, Shinsuke; Sakane, Masao

278

The fatigue life prediction of aluminium alloy using genetic algorithm and neural network  

Science.gov (United States)

The behavior of the fatigue life of the industrial materials is very important. In many cases, the material with experiencing fatigue life cannot be avoided, however, there are many ways to control their behavior. Many investigations of the fatigue life phenomena of alloys have been done, but it is high cost and times consuming computation. This paper report the modeling and simulation approaches to predict the fatigue life behavior of Aluminum Alloys and resolves some problems of computation. First, the simulation using genetic algorithm was utilized to optimize the load to obtain the stress values. These results can be used to provide N-cycle fatigue life of the material. Furthermore, the experimental data was applied as input data in the neural network learning, while the samples data were applied for testing of the training data. Finally, the multilayer perceptron algorithm is applied to predict whether the given data sets in accordance with the fatigue life of the alloy. To achieve rapid convergence, the Levenberg-Marquardt algorithm was also employed. The simulations results shows that the fatigue behaviors of aluminum under pressure can be predicted. In addition, implementation of neural networks successfully identified a model for material fatigue life.

Susmikanti, Mike

2013-09-01

279

Effect of a submicroscopic structure on the fatigue life of precipitation-hardening nickel-chromium alloys  

Science.gov (United States)

The effect of the submicroscopic-structure parameters of typical precipitation-hardening Ni-Cr alloys on their resistance to fatigue failure is studied. The presence of hardening ?'-phase (Ni3(Al,Ti)) particles in the alloys is found to retard the nucleation kinetics of fatigue microcracks and to increase the fatigue lives of the alloys in the range of low cyclic-deformation amplitudes (high-cycle fatigue). At high cyclic-deformation amplitudes (low-cycle fatigue), the precipitated particles and the fields of elastic interfacial strains hinder plastic deformation in the mouths of cracks, which increases the rate of their propagation and decreases the fatigue lives of the alloys. The precipitation of the particles that are under hydrostatic tension during aging of the alloys substantially decreases their resistance to fatigue failure due to facilitated nucleation of fatigue microcracks at interphase boundaries and their further rapid propagation.

Kukareko, V. A.

2009-01-01

280

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

281

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.

282

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

Science.gov (United States)

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

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

1992-01-01

283

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, ...

284

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

285

Evaluation of Creep-Fatigue Life by Fraction of Cavity Area  

Science.gov (United States)

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

Kim, Bumjoon; Lim, Byeongsoo

286

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

Energy Technology Data Exchange (ETDEWEB)

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.

Park, Joong Cheul; Lyu, Geun Jun; Kwon, Jeong Rock [Korea Gas Safety Corporation, Siheung (Korea, Republic of); Kwon, Jae Do [Yeungnam Univ., Gyeongsan (Korea, Republic of)

2005-07-01

287

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

288

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

Energy Technology Data Exchange (ETDEWEB)

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.

Park, Joong Cheul [Yeungnam Univ., Gyeongsan (Korea, Republic of); Kwon, Jae Do [KAERI, Daejeon (Korea, Republic of)

2005-06-01

289

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

290

Fatigue life of aluminum wires in all aluminum and ACSR (aluminum conductor steel-reinforced) conductors  

Energy Technology Data Exchange (ETDEWEB)

A project was initiated to describe the mechanisms of fatigue of aluminum conductor steel-reinforced (ACSR) electrical conductors, based on conductor fatigue tests, aluminum fatigue and fretting-fatigue tests and bending stress calculations derived from a linear cable analysis model. The results of the study would lead to recommendations aimed at increasing fatigue life of overhead conductors. A total of 101 aluminum wire fatigue tests, among which 38 fretting-fatigue tests, and 30 complete conductor fatigue tests were performed. In all tests, the specimens were fatigued in cyclic bending mode under a constant axial stress. Fatigue lives ranged from 5 x 10{sup 4} cycles to 2 x 10{sup 8} cycles and beyond. From linear cable analysis, conductor bending stress can be estimated for a given bending amplitude. Aluminum fatigue diagrams can be used afterwards to estimate conductor safe bending amplitude. Conductor fatigue test results allow to confirm some predictions of the model and make apparent some limitations in its applications. Maximum safe bending amplitude estimations can then be extended to other ACSRs. 52 refs., 62 figs., 28 tabs.

Lanteigne, J.; Cloutier, L.; Cardou, A.

1986-07-01

291

Transverse Tension Fatigue Life Characterization Through Flexure Testing of Composite Materials  

Science.gov (United States)

The transverse tension fatigue life of S2/8552 glass-epoxy and IM7/8552 carbon-epoxy was characterized using flexure tests of 90-degree laminates loaded in 3-point and 4-point bending. The influence of specimen polishing and specimen configuration on transverse tension fatigue life was examined using the glass-epoxy laminates. Results showed that 90-degree bend specimens with polished machined edges and polished tension-side surfaces, where bending failures where observed, had lower fatigue lives than unpolished specimens when cyclically loaded at equal stress levels. The influence of specimen thickness and the utility of a Weibull scaling law was examined using the carbon-epoxy laminates. The influence of test frequency on fatigue results was also documented for the 4-point bending configuration. A Weibull scaling law was used to predict the 4-point bending fatigue lives from the 3-point bending curve fit and vice-versa. Scaling was performed based on maximum cyclic stress level as well as fatigue life. The scaling laws based on stress level shifted the curve fit S-N characterizations in the desired direction, however, the magnitude of the shift was not adequate to accurately predict the fatigue lives. Furthermore, the scaling law based on fatigue life shifted the curve fit S-N characterizations in the opposite direction from measured values. Therefore, these scaling laws were not adequate for obtaining accurate predictions of the transverse tension fatigue lives.

OBrien, T. Kevin; Chawan, Arun D.; Krueger, Ronald; Paris, Isabelle

2001-01-01

292

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

293

Impact of depression, fatigue and disability on quality of life in Chinese patients with multiple sclerosis.  

Science.gov (United States)

The aim of this work is to investigate and analyze the main factors that influence the quality of life (QOL) of multiple sclerosis (MS) patients. The QOL (multiple sclerosis impact scale), disability (expanded disability status scale), fatigue (modified fatigue impact scale) and depression (Beck Depression Inventory) were assessed in 100 MS patients. Correlation analysis shows that QOL is positively correlated with disability status, fatigue and depression, i.e., the more severe the disability, fatigue and depression, the worse the QOL. Multiple linear regression analysis indicated that Expanded Disability Status Scale grade and fatigue have important predictive value on the somatic QOL of MS patients. On the other hand, depression and fatigue have important predictive value on the mental QOL of MS patients. The QOL of MS patients is influenced by various factors, nursing care that focuses on patient disability, fatigue and depression should be strengthened. PMID:22566371

Chen, Kelong; Fan, Yongping; Hu, Rui; Yang, Tao; Li, Kangning

2013-04-01

294

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.

295

Effect of carbide distribution on rolling-element fatigue life of AMS 5749  

Science.gov (United States)

Endurance tests with ball bearings made of corrosion resistant bearing steel which resulted in fatigue lives much lower than were predicted are discussed. Metallurgical analysis revealed an undesirable carbide distribution in the races. It was shown in accelerated fatigue tests in the RC rig that large, banded carbides can reduce rolling element fatigue life by a factor of approximately four. The early spalling failures on the bearing raceways are attributed to the large carbide size and banded distribution.

Parker, R. J.; Bamberger, E. N.

1983-01-01

296

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

OpenAIRE

Background: Fatigue is one of the most common and disabling symptoms of multiple sclerosis (MS) disease. Since fatigue can cause a great deal of problems it create can cause a variety of psychological symptoms particularly depression, anxiety and stress as well, that quality of daily lives, endanger. Thus, the objective of this study was to determine the relation between fatigue severity and psychological symptoms and quality of life in patients with MS.Materials and Methods: In this descript...

Ghasem Salehpoor; Mousa Kafi, S.; Sajjad Rezaei; Mozaffar Hosseininezhad; Iraj Salehi

2012-01-01

297

Fatigue Life Prediction under Random Loading Conditions in 7475-T7351 Aluminum Alloy using the RMS Model  

OpenAIRE

Abstract This article is concerned with the fatigue life prediction in specimens of 7475-T7351 high strength aluminum alloy subjected to random fatigue loading. Fatigue life predictions are made using the root mean square model. This model is chosen because it has been defined as the most simple and effective one for fatigue life prediction in the components subjected to random loading by the authors of thi...

Kim, Sang Tae; Tadjiev, Damir; Yang, Hyun Tae

2006-01-01

298

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.

299

Creep-fatigue life prediction: What about initiation  

International Nuclear Information System (INIS)

Metallographical observations permit the nature of creep and fatigue damage to be exhibited and give some information on the creep-fatigue interaction. The macroscopic models can make qualitative use of these data. A Damage Mechanics model is proposed, which takes into account the initiation and propagation stages during the fatigue process. The implementation of new creep-fatigue rules leads to a good modelization of any creep-fatigue sequence tests or LCF tests. A unique set of material dependent coefficients is needed for both in-air and in-vacuum tests. (orig.)

300

Effect of cyclic plastic pre-strain on low cycle fatigue life  

International Nuclear Information System (INIS)

In order to evaluate structural integrity of nuclear components subjected large seismic load which produce locally plastic strain, low cycle fatigue life was examined using cyclic plastic pre-strained materials of austenitic steel (SUS316, SUS316L, SUS304TP: JIS (Japanese Industrial Standards)) and ferritic steel (SFVQ1A, STS480, STPT410, SFVC2B, SS400: JIS). It was not found that cyclic plastic pre-strain up to range of 16%, 2.5 times affected on low cycle fatigue life. The validity of existing procedure of fatigue life estimation based on usage factor was confirmed when large seismic load brought nuclear materials cyclic plastic strain. (author)

301

A non-linear creep-fatigue life prediction model and application to some commercial steels  

International Nuclear Information System (INIS)

In this present paper, a non-linear damage model for creep-fatigue life evaluation in high vacuum environment was applied to three commercial steels: 9Cr-1Mo-V-Nb steel, 316FR stainless steel, and 2(1/4)Cr-Mo Steel. The model considered that fatigue damage process consists of initiation and growth of fatigue crack, creep damage process consists of nucleation of creep voids and taken into account of interaction process as fatigue crack propagation from creep voids. This unified approach of creep-fatigue interaction problem was verified by performing a life prediction under complex waveform, and complex strain history in all types of steel. Life prediction results in most cases showed a good correlation with experimental data within a factor of 2 range. (orig.)

302

Study on creep-fatigue life of irradiated austenitic stainless steel  

International Nuclear Information System (INIS)

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

303

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

304

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

305

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

306

Effect of notch dimension on the fatigue life of V-notched structure  

International Nuclear Information System (INIS)

Highlights: ? A novel method is proposed to calculate the SIFs of crack at notch tip. ? Effect of notch opening angle on the crack extension and propagation is studied. ? Influence of notch depth on the crack extension and propagation is analyzed. ? The fatigue life of a welded joint is analyzed by the present method. - Abstract: The stress singularity degree associated to a V-notch has a great influence on the fatigue life of V-notched structure. The growth rate of the crack initiated at the tip of a V-notch depends on the stress singularity of the V-notch. The fatigue life accompanying with this small crack will represent a large amount of the total fatigue life. In this work, boundary element method (BEM) is used to study the propagation of the crack emanating from a V-notch tip under fatigue loading. A comparison of the fatigue life between the crack initiated from V-notch tip and a lateral crack is done by a crack propagation law until these two cracks have the same stress intensity factors (SIFs). The effect of initial crack length, notch opening angle and notch depth on the crack extension and propagation is analyzed. As an example of engineering application, the fatigue life of a welded joint is investigated by the present method. The influence of weld toe angle and initial crack length on the fatigue life of the welded structure is studied. Some suggestions are given as an attempt to improve the fatigue life of welded structures at the end. structures at the end.

307

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

Directory of Open Access Journals (Sweden)

Full Text Available Background: Fatigue is one of the most common and disabling symptoms of multiple sclerosis (MS disease. Since fatigue can cause a great deal of problems it create can cause a variety of psychological symptoms particularly depression, anxiety and stress as well, that quality of daily lives, endanger. Thus, the objective of this study was to determine the relation between fatigue severity and psychological symptoms and quality of life in patients with MS.Materials and Methods: In this descriptive-correlational study, 76 patients with MS with a mean age of 34.02±9.42 (16-58 year, a member of Guilan province MS association, were selected consecutively. At first, all patients completed the questionnaire of demographic information, and then they were evaluated by the Fatigue Severity Scale (Fatigue Severity Scale, depression, anxiety, Stress Scale (depression, anxiety, stress scale-21 and Quality of Life questionnaire (Short Form-36. Results: Correlational analyses indicated a significant association between fatigue severity and patient's age, depression, anxiety and stress (p<0.05 and quality of life (p<0.01, While there were no significant relations between fatigue severity and duration of MS. The results of multiple stepwise regression analysis showed that only the factor of quality of life as a selected variable in final model could explain 27% of the shared variance of fatigue severity results (p=0.002.Conclusion: The findings showed that regardless of other variables, the levels of quality of life are predictor of fatigue severity in patients with MS. Therefore it is suggested in these patients psychotherapy based on improvement of quality of life for decrease of the levels of fatigue be set as the central aim of psychological interventions.

Ghasem Salehpoor

2012-09-01

308

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

309

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

Science.gov (United States)

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

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

2014-10-01

310

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

International Nuclear Information System (INIS)

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

311

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

International Nuclear Information System (INIS)

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

312

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

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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

313

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

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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

314

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

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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

315

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

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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

316

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

317

Fatigue life evaluation of pressure housing of SMART CEDM  

International Nuclear Information System (INIS)

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

318

Component fatigue life evaluation using fragmentary load histories  

Energy Technology Data Exchange (ETDEWEB)

On-line data acquisition for fatigue monitoring was not begun in numerous nuclear power plants until many operating years had already passed. Now, with a complete load history recorded over several years time, the current fatigue status of those components particularly susceptible to fatigue is determined. An example of automated fatigue calculations is discussed. Particular attention is given to the problem of inadequate load data from the time before implementation of on-line data acquisition. This report shows how it is possible to use the detailed analysis of the complete database in evaluating the load history for the time for which the load data are incomplete. (author). 6 refs., 6 figs.

Golembiewski, H.J. [Siemens AG, Erlangen (Germany); Tulke, K. [Kernkraftwerk Philippsburg GmbH (Germany); Maersch, S. [Bayernwerk AG, Muenchen (Germany); Baumann, F. [Kernkraftwerk Grafenrheinfeld (Germany)

1995-12-31

319

Component fatigue life evaluation using fragmentary load histories  

International Nuclear Information System (INIS)

On-line data acquisition for fatigue monitoring was not begun in numerous nuclear power plants until many operating years had already passed. Now, with a complete load history recorded over several years time, the current fatigue status of those components particularly susceptible to fatigue is determined. An example of automated fatigue calculations is discussed. Particular attention is given to the problem of inadequate load data from the time before implementation of on-line data acquisition. This report shows how it is possible to use the detailed analysis of the complete database in evaluating the load history for the time for which the load data are incomplete. (author). 6 refs., 6 figs

320

Fatigue life of ZhS6U alloy with protective coatings under thermal cycling loading  

Energy Technology Data Exchange (ETDEWEB)

Empirical equations are obtained which relate the fatigue life of ZhS6U, a turbine blade alloy, to the parameters of the thermal and stress-strain states. The equations obtained here provide a way to predict the thermal cycling fatigue life of ZhS6U alloy with different coatings under conditions of inhomogeneous stressed state in the temperature range 1040-1100 C and thermal stress range 220-470 MPa. 6 refs.

Buiskikh, K.P.; Barilo, V.G. (Institut Problem Prochnosti, Kiev (Ukrainian SSR))

1989-08-01

321

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

322

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

323

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

324

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

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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

325

Ductility normalized-strainrange partitioning life relations for creep-fatigue life predictions  

Science.gov (United States)

Procedures based on Strainrange Partitioning (SRP) are presented for estimating the effects of environment and other influences on the high temperature, low cycle, creep fatigue resistance of alloys. It is proposed that the plastic and creep, ductilities determined from conventional tensile and creep rupture tests conducted in the environment of interest be used in a set of ductility normalized equations for making a first order approximation of the four SRP inelastic strainrange life relations. Different levels of sophistication in the application of the procedures are presented by means of illustrative examples with several high temperature alloys. Predictions of cyclic lives generally agree with observed lives within factors of three.

Halford, G. R.; Saltsman, J. F.; Hirschberg, M. H.

1977-01-01

326

Simplified inelastic analysis and creep-fatigue life of perforated plates in elevated temperature  

International Nuclear Information System (INIS)

Prediction methods of macroscopic deformation and local stress-strain behavior of perforated plates in plastic and creep regime are proposed in this paper. Predicted results for macroscopic behavior are compared with the experimental results for cyclic stress strain behavior and relaxation behavior. Creep-fatigue lives at around a hole of perforated plates are predicted by using the local stress-strain behavior and are compared with experimentally observed lives. Furthermore, the proposed methods are applied to the inelastic analysis and creep-fatigue life prediction of perforated cylinder subjected to cyclic thermal stress. The characteristics of damage and creep fatigue life correspond well with prediction based on the analysis

327

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

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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

328

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

329

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

Science.gov (United States)

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

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

2015-01-01

330

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

331

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

332

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

Science.gov (United States)

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

James, Brad A; Sire, Robert A

2010-01-01

333

Thermal fatigue life and failure mode in high-temperature component materials for power plant  

Energy Technology Data Exchange (ETDEWEB)

The thermal fatigue life characteristics of various materials is described for high-temperature components in power plants, including low-alloy steels, austenitic stainless steels and superalloys, were summarized. As a result, the characteristics were found to be basically classified into four types associated with a difference in failure mode. A discussion was also made on thermal fatigue life prediction methods based on other mechanical properties such as tensile and isothermal failure properties. It was found that the good or safe prediction, excepting a case showing the great effect of creep-fatique interaction, could be made by applying the total-strain-range-based relations, particularly the total strain range vs. life relation in isothermal fatigue at the maximum temperature in thermal fatigue.

Nitta, Akihito; Kuwabara, Kazuo; Kitamura, Takayuki; Ogata, Takashi (Central Research Inst. of Electric Power Industry, Tokyo (Japan))

1984-02-01

334

Study on durability of welded bellows. Fatigue life of bellows with crack in welded bead  

International Nuclear Information System (INIS)

Reports of study for welded bellows with cracks have apparently not been published to date. The purpose of this investigation is to understand the relationship between the state of stress of welded bellows with micro cracks and the fatigue life. Stresses of welded bellows with cracks were calculated for several different crack lengths by finite element method (FEM), and lives of bellows with cracks were examined by fatigue test. The fatigue life, i.e. the number of cycles to failure was arranged against the remaining wall thickness measured after test instead of the crack length. As a result, it was found that there is a regular relationship between the stress amplitude of peak stress calculated by FEM and the fatigue life of bellows. And then, it was shown that the life of bellows becomes longer than the life estimated using a theoretical S-N curve calculated by Manson's method. Stress intensity factor range (?K) and crack propagation rate (da/dN) were also calculated using the results of stress analysis by FEM and fatigue test. The relationship between ?K and da/dN obtained was almost coincident with the earlier result of fatigue crack growth test of Inconel 718 in the region of da/dN > 1.5x10-6 mm/cycle, and the propriety of the present results was confirmed. (author)

335

Influence of initial heat treatment on the fatigue life of austenitic Fe–Ni alloy  

Directory of Open Access Journals (Sweden)

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

K.J. Ducki

2008-02-01

336

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

Energy Technology Data Exchange (ETDEWEB)

A systematic experimental and analytical study has been carried out to investigate the effect of vibration loading on the fatigue life of the piping components. Three Point bend (TPB) specimens machined from the actual pipe have been used for the evaluation of Paris constants by carrying out the experiments under vibration + cyclic and cyclic loading as per the ASTM Standard E647. These constants have been used for the prediction of the fatigue life of the pipe having part-through notch of a/t = 0.25 and aspect ratio (2c/a) of 10. Predicted results have shown the reduction in fatigue life of the notched pipe subjected to vibration + cyclic loading by 50% compared to that of cyclic loading. Predicted results have been validated by carrying out the full-scale pipe (with part-through notch) tests. Notched pipes were subjected to loading conditions such that the initial stress-intensity factor remains same as that of TPB specimen. Experimental results of the full-scale pipe tests under vibration + cyclic loading has shown the reduction in fatigue life by 70% compared to that of cyclic loading. Fractographic examination of the fracture surface of the tested specimens subjected to vibration + cyclic loading have shown higher presence of brittle phases such as martensite (in the form of isolated planar facets) and secondary micro cracks. This could be the reason for the reduction of fatigue life in pipe subjected to vibration + cyclic loading. - Highlights: > Vibration loading affects fatigue crack growth rate. > Crack initiation life depends on crack tip radius. > Crack initiation life depends on the characteristic distance. > Characteristic distance depends on the loading conditions. > Vibration + cyclic load gives lower fatigue life.

Mittal, Rahul [Nuclear Power Corporation of India Limited, Mumbai (India); Singh, P.K., E-mail: singh_pawank@yahoo.com [Bhabha Atomic Research Centre, Mumbai (India); Pukazhendi, D.M. [Structural Engineering research Centre, Chennai (India); Bhasin, V.; Vaze, K.K.; Ghosh, A.K. [Bhabha Atomic Research Centre, Mumbai (India)

2011-10-15

337

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

Science.gov (United States)

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

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

2009-05-01

338

Multiaxial Fatigue Life Prediction for Steels Based on Some Simple Approximations  

Science.gov (United States)

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

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

2015-01-01

339

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

340

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

341

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

342

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

343

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

344

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

345

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

Science.gov (United States)

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

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

2015-01-01

346

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

347

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

348

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

349

Crack initiation life prediction method of thermal creep-fatigue  

International Nuclear Information System (INIS)

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

350

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-02-15

351

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)

352

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 reasonably predict 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 the ambient air at a 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)

353

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

International Nuclear Information System (INIS)

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

354

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

Energy Technology Data Exchange (ETDEWEB)

Ratcheting and low cycle fatigue (LCF) experiments have been conducted at 25 {sup o}C temperature in laboratory environment under different loading conditions. SA333 steel exhibits cyclic hardening throughout its life during LCF. It is found that ratcheting strain increases with both increasing mean stress and stress amplitude. It has also been noticed that plastic strain amplitude and plastic strain energy decrease with increase in mean stress at constant stress amplitude. Ratcheting and LCF life in the range of 10{sup 2}-10{sup 5} cycles have been predicted with the help of a mean stress-based fatigue lifing equation.

Paul, Surajit Kumar, E-mail: paulsurajit@yahoo.co.i [Materials Science and Technology Division, National Metallurgical Laboratory (Council of Scientific and Industrial Research), Jamshedpur 831 007 (India); Sivaprasad, S. [Materials Science and Technology Division, National Metallurgical Laboratory (Council of Scientific and Industrial Research), Jamshedpur 831 007 (India); Dhar, S. [Department of Mechanical Engineering, Jadavpur University, Kolkata 700 032 (India); Tarafder, S. [Materials Science and Technology Division, National Metallurgical Laboratory (Council of Scientific and Industrial Research), Jamshedpur 831 007 (India)

2010-06-15

355

Fatigue life prediction of an intermetallic matrix composite at elevated temperatures  

Science.gov (United States)

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

Bartolotta, P. A.

1991-01-01

356

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

357

Improvement of high cycle fatigue strength of P/M Ti-6Al-2Sn-4Zr-2Mo/TiB particulate composites by the modification of matrix microstructure; Ryushi kyokagata P/M Ti-6Al-2Sn-4Zr-2Mo/TiB fukugo zairyo no kishitsu no kinzoku soshiki seigyo ni yoru ko cycle hiro kyodo no kojo  

Energy Technology Data Exchange (ETDEWEB)

Further performance improvement was attempted on high cycle fatigue characteristics of Ti-6Al-2Sn-4Zr-2Mo/TiB particulate composites by finely controlling metallic structure of a matrix. A Ti alloy matrix was strengthened by dispersing in it ceramic TiB particles. The metallic structure of a composite when it is manufactured depends on cooling rate from vacuum sintering temperature. In case of a high cooling rate (10 k/sec for example), the structure was a colonial structure in which each thin {alpha} phase can be identified clearly. In case of a low cooling rate (0.03 k/sec, for example), the thin {alpha} phases are integrated presenting a massive colonial structure. When the composite is quenched from a single {beta} phase region at an elevated temperature to make the matrix metal into a martensite structure, and then retained in the {alpha}-{beta}2 phase region, the material was transformed into a micro needle shape, largely increasing the high cycle fatigue strength. Contributions of the major factors to the high cycle fatigue strength were found as micronization of the metallic structure in the matrix, increase in the tensile strength, and increase in the Young`s modulus, which were 43%, 18% and 39%, respectively. 14 refs., 9 figs., 1 tab.

Hagiwara, M.; Emura, S.; Kawabe, Y. [National Research Institute for Metals, Tsukuba (Japan); Kim, S.

1998-09-01

358

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; Philippidis, T.P.

2010-01-01

359

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

360

Fatigue life prediction of ZE41A magnesium alloy using Weibull distribution  

International Nuclear Information System (INIS)

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

361

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

362

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

363

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

364

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

365

Design characteristics that improve the fatigue life of threaded pipe connections  

OpenAIRE

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

366

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

OpenAIRE

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

367

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 required to predict the fatigue life of notched specimens, so Ansys finite element code has been used and non-linear analyses have been performed to obtain the stress and strain distributions around the notches. The plastic deformations of the material have been simulated using multi-linear kinematic hardening and cyclic stress-strain relation. The work here shows that the volumetric approach does a very good job for predicting the fatigue life of the notched specimens.

Esmaeili F.

2010-06-01

368

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

369

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

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

Qasim Bader

2014-06-01

370

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

International Nuclear Information System (INIS)

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

371

Multiaxial fatigue life prediction of duplex stainless steels with thermal aging at 430 C under axial-torsional load  

Energy Technology Data Exchange (ETDEWEB)

Multiaxial low cycle fatigue tests with degradation were performed on duplex stainless steels(CF8M). The fatigue properties of CF8M to predict multiaxial fatigue life are obtained from the pure axial and torsional low cycle fatigue. CF8M is used in pipes and valves in a nuclear reactor coolant system. The specimens to be used at the experiment are virgin and degraded of CF8M. The degraded material was aged at 430 C for 3600 hrs. In the present study, von Mises equivalent strain and a critical plane method proposed by Fatemi-Socie(FS) and Smith-Watson-Topper(SWT) are used to calculate fatigue damage. The predicted result by von Mises equivalent strain and FS parameter show good agreement with experimental results. In conclusion, fatigue life by material degradation is decreased and multiaxial fatigue life prediction which was used FS parameter is not conservative but the best result. (orig.)

Kwon, J.D. [Dept. of Mechanical Engineering, Yeungnam Univ., Gyeongbuk (Korea); Park, J.C. [Korea Atomic Energy Research Inst., Daejeon (Korea)

2004-07-01

372

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

Science.gov (United States)

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

Colin, Julie

373

Practical methodology to evaluate the fatigue life of seam welded joints  

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

K.C.Goes

2011-11-01

374

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

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

Winnie K.W.So

2009-06-01

375

Dynamic loads in Francis runners and their impact on fatigue life  

Science.gov (United States)

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

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

2014-12-01

376

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-07-01

377

Fatigue damage assessment using X-ray diffraction and life prediction methodology  

International Nuclear Information System (INIS)

X-ray diffraction line broadening was used to monitor surface damage due to deformation (distortion) that was induced by low-cycle fatigue. The integral breadth of selected diffraction peaks was identified as a useful parameter with which to evaluate cumulative fatigue damage. Torsional fatigue tests were conducted on nickel-based Waspaloy material which exhibited planar slip at 1200deg F (649deg C). X-ray diffraction measurements were taken at 22, 41, 60, and 90% of the life. The data disclosed an increase in breadth with each increment of cycling. The results obtained from line broadening analysis were carefully correlated with observations made on the specimen surface using scanning electron microscopy which showed the progressive distortion occurring in the cycled specimen. The integral breadth, ?, was successfully correlated with the applied shear strain to predict the expended fraction of life and hence the remaining cyclic life. (orig.)

378

Fatigue life estimation of cruciform welded joint considering multiple collinear surface cracks  

International Nuclear Information System (INIS)

Fatigue life of welded joints is governed by the propagation of multiple collinear surface cracks distributed randomly along weld toe. These cracks propagate under the mechanisms of mutual interaction and coalescence of the adjacent two cracks. To estimate the fatigue life, its influences on the above two mechanisms should be taken into account, which appear through the stress intensity factors disturbed mutually. However, it is difficult to calculate the stress intensity factors of the multiple surface cracks located in vicinity of weld toe due to its geometrical complexity. They are calculated normally by using the Mk-factors, but such Mk-factors are very rare in literature. In this study, the Mk-factors were obtained from a parametric study on crack length and depth, for which a finite element method is used. A fatigue test for a cruciform welded joint was conducted and the fatigue life of the tested specimen was estimated using the present method with the information obtained from the test, such as the number, size, and locations of the cracks. The estimated and measured fatigue life showed a good agreement

379

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

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

Mileti? Svetlana

2011-01-01

380

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

International Nuclear Information System (INIS)

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

381

A hybrid model for fatigue life estimation of polymer matrix composites  

Science.gov (United States)

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

Uleck, Kevin R.

382

Sterilization by gamma radiation impairs the tensile fatigue life of cortical bone by two orders of magnitude.  

Science.gov (United States)

Cortical bone grafts are utilized frequently for skeletal reconstruction, spinal fusion and tumor surgery. Due to its efficacy and convenience terminal sterilization by gamma radiation is often essential to minimize disease transmission and infection. However, the impairment in the material properties of bone tissue secondary to gamma radiation sterilization is a concern since the mechanical functionality of a bone graft is of primary importance. While the extent of this impairment is well investigated for monotonic loading conditions, there does not seem to exist any information on the effects of gamma radiation sterilization on cortical bone's fatigue properties, the physiologically relevant mode of loading. In this study we investigated the degradation in the high-cycle and low-cycle tensile fatigue lives of cortical bone tissue secondary to gamma radiation sterilization at a dose of 36.4 kGy which approximately falls in the higher end of the standard dose range used in tissue banking. The high-cycle and the low-cycle fatigue tests were conducted under load control at initial strain levels of 0.2% and 0.4%, respectively. Monotonic tensile tests were also conducted to compare the impairment of fatigue properties with the impairment of monotonic properties. Results demonstrated that the impairment in both the high-cycle and the low-cycle fatigue lives were two orders of magnitude following sterilization, a change much more pronounced than that observed for monotonic loading. In conclusion, the results suggest that the impairment of the mechanical function of gamma radiation sterilized allografts is even worse in fatigue than monotonically. Therefore, grafts should be designed to minimize functional strains and avoid stress raisers to prevent premature fatigue failures. PMID:16140190

Akkus, Ozan; Belaney, Ryan M

2005-09-01

383

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

International Nuclear Information System (INIS)

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

384

Life prediction methods for the combined creep-fatigue endurance  

International Nuclear Information System (INIS)

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

385

Life-prediction methods for combined creep-fatigue endurance  

International Nuclear Information System (INIS)

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

386

Improvement of fatigue life of an aluminum alloy by overstressing  

Science.gov (United States)

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

STRICKLEY G W

1942-01-01

387

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

Science.gov (United States)

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

Jeelani, S.; Collins, M. R.

1988-01-01

388

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

International Nuclear Information System (INIS)

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

389

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

International Nuclear Information System (INIS)

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

390

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

Directory of Open Access Journals (Sweden)

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

Roselita Fragoudakis

2011-06-01

391

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

International Nuclear Information System (INIS)

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

392

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

Science.gov (United States)

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

Alam, Mohammad Shah

2005-11-01

393

Fatigue  

Science.gov (United States)

... diseases) and mitochondrial diseases. But fatigue also can creep into the lives of those with many of ... To determine your sleep hygiene take a short test from Discovery.com. Visit http://discoveryhealth.queendom.com/ ...

394

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

Science.gov (United States)

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

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

2013-01-01

395

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

International Nuclear Information System (INIS)

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

396

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

International Nuclear Information System (INIS)

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

397

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

Scientific Electronic Library Online (English)

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

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

2014-06-01

398

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-07-01

399

Fatigue life evaluation for spot weldment of dissimilar materials using PDM  

International Nuclear Information System (INIS)

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

400

Influence of cyclic thermal loading on residual fatigue life of materials damaged by simulated plasma disruption  

International Nuclear Information System (INIS)

Surface damage of type 304 stainless steel, which is one of the candidates for the first-wall structural material in a fusion reactor, at cyclic plasma disruption loadings is simulated by a high heat flux Neutron Beam Injection. Influences of the cyclic thermal loads on the residual fatigue life are studied. The results obtained are summarized as follows. (1) The maximum tensile residual stresses near the damaged surface increased with increasing thermal loading cycles from 1 to 5. (2) The fatigue strength and the fatigue limit of the specimen subjected to 5 cycles of thermal loading and those for 1 cycle are the same. (3) A critical crack length, 2be to vanish from sight caused by thermal loading is important for the evaluation of the residual fatigue life. If the defect length, 2be, residual life after the second thermal loading and that before thermal loading are the same. If 2b>2be, fatigue crack growth occurs due to the cyclic thermal load. (author)

401

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

Science.gov (United States)

This study discusses multiaxial low cycle fatigue life of notched specimens under proportional and non-proportional loadings at room temperature. Strain controlled multiaxial low cycle fatigue tests were carried out using smooth and circumf